Anatomy of the Orbit: Overall Aspects of the Peri- and Intra Orbital Soft Tissues

Gooris, Peter J. J.; Cornelius, Carl-Peter

doi:10.1007/978-3-031-40697-3_3

Peter J. J. Gooris^4,5,6 &
Carl-Peter Cornelius⁷

2796 Accesses

The original version of the chapter has been revised. A correction to this chapter can be found at https://doi.org/10.1007/978-3-031-40697-3_23

Abstract

Soft tissue systems in and around the orbit are presented in detail. The complexity of the soft tissue structures and its topographical location provides optimal environment for the delicate globe and supportive elements.

Anatomic aspects and the protective and physiological function of the eyelids are described. The secretory lacrimal system and the spread of aqueous fluid along the globe and final drainage will be discussed. Anatomical features of the globe and the accompanying extraocular musculature are highlighted. The involved musculature allows for a most efficient guarantee of function and protection. Participating fat compartments provide a cushion and play a gliding role. The control via the neuro-ophthalmologic pathways, motor-, sensory-, and autonomic innervation is the essential base for the function of the eye.

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Anatomy of the Orbit and Periorbital Region

Orbit

Orbital Anatomy

Keywords

FormalPara Learning Objectives

Appreciate anatomical aspects of soft tissue around the orbit including the eyelids and lacrimal system
Distinguish the different locations of adipose tissue in and around the orbit
Recall major anatomic topographic and functional details of the globe itself
Understand the extraocular musculature system
Apprehend the essentials of the neurovascular pathways involved in ophthalmic function

Introduction

The eye can be considered as a most important organ. It is the window of the human perception system: open your eyes and record the visible information; it offers personal detail: for your eyes only!

As it is such an essential and delicate organ, the globe needs adequate protection which is facilitated by the eyelid curtain system and ample humidification through the lacrimal system.

To provide a maximum of capability for the gathering of visual information, a highly effective intrinsic muscular system is attached to the globe which allows motility in all directions. Adipose tissue of the orbit facilitates physical motility of eye-related structures. The role of neurovascular supply is essential for vision and functional movement.

In view of the special task of this precious organ, this chapter will elaborate on anatomical aspects directly related to the globe. Anatomical soft tissue aspects of the apex of the orbit will be discussed.

The Protective Curtain System of the Ocular Globe

The Eyelids

The eyelids resemble to soft tissue plications, that form a mobile shutter to cover the anterior surface of the eyeball from above and below. The eyelids, are referred to as part of the facial soft tissue envelope, nonetheless they are indispensable for the orbit having functions such as mechanical protection and maintenance of the globe by the lacrimal system with lubrication, cleansing, and drainage of the region.

The aperture between upper and lower eyelid margins is called the palpebral fissure, which measures approximately 8–10 mm, widest at the midpoint when open. The upper eyelid just covers the upper aspect of the cornea for approximately 2 mm. The horizontal length is approximately 30 mm. Medially and laterally the eyelids meet at an angle of approximately 60^°.

When we follow the palpebral fissure sideways, the lateral canthal angle is positioned a little ±2 mm higher than the medial canthal angle.

Each eyelid can be divided into an external, anterior and internal, posterior lamella.

The outer or anterior lamella is coated with delicate skin on top of the orbicularis oculi muscle (OOM): myocutaneous lamella. In this anterior lamella, eyelashes are located.

The inner or posterior lamella is built up of the tarsal plates and covered by the palpebral conjunctiva, thus corresponding to a tarsoconjunctival lamella. This surface is in touch with the globe (Fig. 3.1).

A sagittal view diagram of the upper eyelid. From top to bottom labels read levator palpebrae superioris muscle, superior rectus muscle, superior tarsus, deep galea, orbital septum, and meibomian. — **Fig. 3.1**

The eyelid margin itself measures about 2 mm in thickness.

A line on the lid margins visible at the transition zone between the anterior and posterior lamellae is formed by the marginal projection of the pars ciliaris of Riolan’s muscle, called the Gray line (intermarginal sulcus) [1, 2]

The orifices of Meibomian glands open posterior to the Gray line and are positioned in the internal lamella.

Tarsal Plates

The superior and inferior tarsal cartilage plates give structural support to the eyelids. They are the central component within a fibrous framework of canthal tendons, fascial attachments, and suspension ligaments.

The tarsal plate itself consists of a dense fibrous connective tissue layer and supplies rigidity to the eyelid. The tarsi are ± 1–1.5 mm thick. Coursing medial and lateral, the tarsal plates’ height decreases. At their endings, they finally pass into the medial and lateral canthal ligament, fibrous connective tissue bands, acting as suspensory structures for the canthi. Meibomian sebaceous glands which produce meibum, an oily substance that prevents evaporation of the eye’s tear film are present in the upper and lower tarsal plate.

The tarsi are supported medially by the medial rectus, capsulopalpebral fascia, and Horner’s muscle.

Motor Innervation Eyelids

Motor innervation is dual: CN III, CN VII, and sympathetic nerve fibers.

CN III, a branch of its superior division is responsible for innervation of the main upper eyelid retractor, the levator palpebrae superior muscle. A branch of the inferior CN III division innervates the inferior rectus muscle which through the communication with the adjacent capsulopalpebral fascia is responsible for lower eyelid retraction during downward gaze.

CN VII supplies innervation to the orbicularis muscle (temporal and zygomatic divison CN VII—main eyelid protractor); the frontalis-, procerus- and corrugator supercilii musculature: brow depression and contribute—support to upper eyelid protraction.

Sympathetic fibers innervate the superior tarsal muscle, Müller’s muscle, which contributes to upper eyelid retraction and the inferior tarsal muscle, supportive for lower eyelid retraction.

The sensory innervation of the upper eyelid is multiple; terminal branches of the ophthalmic division (CN V1) are involved (frontal nerve), the supraorbital nerve, the supratrochlear nerve, the infratrochlear nerve and the lacrimal nerve [3]. The innervation will be described in more detail in subsequent subchapters.

Clinical Implications

The Gray line formed by the projecting pars ciliaris of Riolan’s muscle [2] separates the anterior from the posterior lamella; it indicates an avascular plane, which is a useful anatomic marker, for easy surgical access.

Surgical approaches to the orbit can have implications on the periorbital soft tissues.

Eyelid skin incisions can interfere with sensory innervation; approach to the orbital rim in case of orbital floor reconstruction, surgery through muscular planes should be carried out at different levels to minimize postoperative scar contractures. In case of a lateral canthotomy extension, too wide horizontal skin incisions can cause iatrogenic damage to the frontal branches of the CN VII.

Upper Eyelid

Musculature

Below the thin loosely attached dermis covering the eyelids, depending on the level we encounter the preseptal periocular striated OOM, the (aponeurosis) levator palpebrae superior and Müller’s superior tarsal muscle.

At a level in approximation to the lid margin, we encounter the pretarsal OOM, the muscle of Riolan and the tarsal plate. The inner aspect is covered by palpebral conjunctiva (Fig. 3.1).

Jean Riolan [2] first described a set of muscle fibers encircling the meibomian glands collectively known as the muscle of Riolan. In 2002, Lipham et al. [1] subsequently showed through histologic analysis that the muscle of Riolan is a component of the orbicularis muscle, relating eyelid blink to meibum secretion. In fact, the muscle of Riolan represents the pretarsal orbicularis muscle.

The OOM is a widespread array of muscle fibers that lies beneath the skin, over the orbital septum and the tarsoligamentous sling [4,5,6]. It is an integral part of the superficial musculoaponeurotic system (SMAS). The OOM is separated from the overlying dermis by a modest fibro-adipose tissue layer through which fibrous septa perforate merging with the underlying muscle layer (Fig. 3.2). It is a striated muscle that runs parallel to the eyelid margin and is innervated by multiple (zygomatic and frontotemporal) branches of CN VII, a plexus running deep to the OOM, arriving from lateral.

A photograph of the left eye of an individual presents the lateral half of the eyelids and the orbit. It presents a broad and dissected muscular patch on the eyelid that exposes the tissues and fatty pads in the lower eyelids. — **Fig. 3.2**

The OOM is divided into three major concentric or ring-shaped partitions, from peripheral to central, the orbital, preseptal, and pretarsal portions.

The orbital OOM arises medially from origins along the superior and inferior orbital rims as well as the medial canthal tendon and forms a wide loop around the lateral circumference of the orbital aperture. Superomedially, the orbital portion covers the corrugator supercilii muscle and the anterior temporoparietal fascia. In the inferior temporal and cheek area, the orbital orbicularis extends to the origin of the masseter and the zygomaticus minor muscle at the surface of the zygomatic body. Along the infraorbital rim and the maxillary frontal process, the origins of the upper lip and nasal ala elevators are surrounded by the OOM.

The preseptal and the pretarsal OOM portions overlie the orbital septum and the tarsal plates. At the medial canthal tendon and around the lacrimal canaliculi and lacrimal sac, both the portions divide into two components, anterior or superficial and posterior or deep heads. Both superficial heads connect to the medial canthal tendon and beyond to the anterior lacrimal crest as well as to the nasofrontal maxillary process. The deep head of the preseptal OOM portion, or Jones’ muscle, attaches latero-posteriorly to the fascia of the lacrimal sac (Fig. 3.3a, b). The deep pretarsal orbicularis head, known as Horner’s muscle, pars lacrimalis or tensor tarsi, passes posterior to the canaliculi and the lacrimal sac to attach to the posterior lacrimal crest (Fig. 3.3a–c) (see section “Canthal Ligaments”).

3 illustrations. 1. A diagram of the eye presents the lacrimal sac, Jone's muscle, and Horner's muscle. An inset focuses on an irregular incision near the eyeball. 2. A diagram of 4 orbicularis oculi muscles. 3. A photograph of the anterior medial wall of the orbit presents the Horner's muscle. — **Fig. 3.3**

Laterally, the preseptal orbicularis from the lower and upper eyelid inserts onto the horizontal lateral palpebral raphe which attaches to the zygoma.

The preseptal portion of the orbicularis muscle functions in voluntary and involuntary eyelid closure.

The pretarsal inferior and superior orbicularis portion join the lateral canthal ligament (LCL) at Whitnall’s tubercle.

The levator palpebrae superioris (LPSM) and Müller’s superior muscle retract or elevate the upper eyelid; they maintain the eyelid in position.

The LPSM is a striated muscle [7], which is separable from the underlying superior rectus muscle (Figs. 3.4 and 3.5) apart from the medial border, where both muscles are adherent to a common fascial sheat. The LPSM originates from the lesser wing of the sphenoid (LWS) above Zinn’s ring and extends forward where it blends with the fibers of the superior rectus muscle. About 1 cm behind the orbital septum, it fans out as a thin membranous sheet into the upper eyelid.

An intraoperative photograph of an eye. There is an incision in the upper eyelid, which is held with clamps. The superior rectus muscle is hooked up. — **Fig. 3.4**

An intraoperative photograph of an eye. It presents the right orbit after removal of lateral orbital wall exposing the ligaments, muscles, and nerves. Labels read S O N, S R M, L P S M, O R, T R O C, O P L G, W L, and I F N. — **Fig. 3.5**

At the level just behind the superior orbital rim and location of Whitnall’s ligament, the levator divides into two layers: a superior layer which continues into the aponeurosis and an inferior layer which blends forward into Müller’s muscle (Figs. 3.1 and 3.6). Interconnecting fibrous tissue between the covering sheaths of the levator and superior rectus muscle allows for corresponding movements during vertical gaze.

A photograph of an anatomic specimen. It exhibits a surgical scissor that is advanced inside the musculus tarsalis superior above the tarsal plate of the upper eyelid. — **Fig. 3.6**

Below the level of Whitnall’s ligament (WL) and before reaching the upper edge of the tarsal plate, the LPSM [8,9,10] is widening horizontally into a broad fibrous aponeurotic sheath, the levator aponeurosis, arching over the globe with two tendinous extremities, the lateral and medial horns.

The band-like lateral horn of the levator divides the lacrimal gland incompletely into the orbital and palpebral lobes before inserting on Whitnall’s lateral orbital tubercle as one of the components of the lateral retinaculum. The medial horn passes over the superior oblique muscle tendon, blends with the reflections of the medial canthal tendon, and joins the medial retinacular structures departing from the posterior lacrimal crest for osseous attachment. The cutaneous insertion of the aponeurosis is effected by terminal fibers traversing the orbicularis muscle and forming a distinct supratarsal fold. A subset of deeper fibers attaches to the anterior surface of the upper tarsus.

The innervation of the LPSM is by the superior CN III division.

The superior tarsal muscle of Müller’s (STM) is an involuntary smooth muscle innervated by postganglionic sympathetic fibers derived from the paravertebral chain—superior cervical ganglion; the fibers run with the carotid plexus to enter the orbit via the superior orbital fissure. The sympathetic branches run mainly along the infratrochlear and lacrimal branches of the ophthalmic nerve.

STM is incorporated in the undersurface of the levator palpebrae anterior to WL, is adherent to the palpebral conjunctiva posteriorly, and inserts into the superior tarsal border (Figs. 3.1 and 3.6). It measures 8–12 mm in length and is present across nearly the whole width of the tarsus. STM works in synergy with the LPSM to raise the upper eyelid. The ligament prevents the upper lid from pulling away from the globe during elevation by the LPSM. Additional smooth muscles fibers may arise from Tenon’s capsule.

The STM is separable from the LPM, whose aponeurosis continues on top of the tarsal plate (Fig. 3.6). Müller’s muscle is separated from the conjunctiva and the levator aponeurosis by a thin fibrovascular tissue layer. In fact, Müller’s muscle elevates the upper eyelid during sympathetic stimulation as in excitement.

The muscle of Riolan [2] consists of three subdivisions [1]. (1) The pars ciliaris/marginalis (striated muscle, the fibers of which are separate bundle from the pretarsal OOM running anterior to the tarsal plate and in parallel to the Gray line, (2) the pars subtarsalis, a smaller fibers bundle which is located posterior to the Meibomian orifices, and (3) the pars fascicularis. This third subdivision traverses the marginal surface of the tarsus and connects the former two muscle groupings.

Sensory innervation of the upper eyelid is provided by several branches of the CN V.

Clinical Implications

In patients presenting with Graves’ disease (Chap. 15 and 16), retraction of the upper eyelid >> lower eyelid retraction is a common sign, which results from excessive sympathetic activity within Müller’s muscle; to a lesser degree the LPSM may retract; inflammatory changes and fibrosis may also play a role in this process [11]. The involvement of the lateral horn of the LPSM in particular is supposed to be responsible for the typical aspect of the lateral flare (Fig. 3.7a–c).

3 photographs present front and lateral views of the eye of a patient. The tissues near the orbit of the affected eye present swelling. — **Fig. 3.7**

Whitnall’s Ligament

Whitnall’s superior suspensory ligament [8, 9] in the upper eyelid represents a portion of the globe suspensory system (Figs. 3.4 and 3.8).

Whitnall’s ligament in context with the LPSM, trochlea, and lacrimal gland. The capsulopalpebral fascia located anterior to the inferior oblique muscle in the inferior orbit forms Lockwood’s ligament (LL)—a kind of analogue to Whitnall’s ligament. Thus WL is a supportive fascia structure of the upper eyelid and in fact a condensation of the fascial sheath of the LPSM that thickens near the level where the levator muscle blends into the aponeurosis just behind the superior orbital rim approximately 18–20 mm above the superior border of the tarsus (Fig. 3.8). Whitnall’s ligament has a counterpart: the intermuscular transverse ligament underlying the LPSM on top of the superior rectus muscle. Both function as a sleeve supporting the LPSM and prevent the upper eyelid from pulling away from the globe during elevation. Medially the ligament attaches onto the periosteum of the medial orbital wall and the suspensory system of the trochlea, laterally the ligament blends with the capsule of the lacrimal gland and the lateral orbital wall superior to the gland.

WL serves multiple functions: it contributes to the suspension of the lacrimal gland as well as to LPSM, superior oblique muscle, and origin of Müller’s muscle.

Further contributing structures to the support system are fascial condensations, the medial and lateral check ligaments, Lockwood’s inferior ligament, lacrimal ligaments, and a complex network of multiple septa.

Lower Eyelid

Lid Retractors

The lower eyelid retractors consist of two principal layers, the capsulopalpebral fascia and Müller’s inferior tarsal muscle. The innervation to the sympathetic inferior tarsal muscle travels along with branches of the infraorbital nerve. The capsulopalpebral fascia is a supportive structure analogous to the LPSM.

Fibrous extensions originate from the sheath of the inferior rectus muscle to compose the head of the capsulopalpebral fascia. This head transforms into an envelope around the inferior oblique muscle. Anterior to the muscle the inferior and superior fascial portions conjoin to form Lockwood’s inferior suspensory ligament. The superior portion of the capsulopalpebral fascia then extends posteriorly into the inferior conjunctival fornix and converts into Tenon’s capsule.

The inferior portion fuses with the orbital septum anteriorly, connects through the orbicularis oculi muscle (OOM) to the skin, and inserts more upwardly on the inferior border of the lower tarsus. The dermal attachments are the basis of the lower eyelid crease. A limited depression of the lower eyelid margin occurs in downgaze to enable an unimpaired visual field. This movement is essentially a synergic effect of the inferior rectus muscle contraction which is translated by the capsulopalpebral head and the inferior fascial portion.

The sympathetic smooth inferior tarsal muscle is an accessory lower eyelid retractor. It originates and lies posterior to the capsulopalpebral fascia, extends upward distal from Lockwood’s ligament (LL), and inserts near and at the base of the inferior tarsus. LL is a band-like fascial sling, ± 45 mm in length and ± 6 mm wide. It is connected to the medial and lateral check ligaments.

It prevents downward and backward displacement of the globe and supports it as in a hammock. In its center, it is formed as a connective tissue thickening in the lower portion of Tenon’s caspule. Medially, Lockwood’s ligament blends with Horner’s muscle and the medial check ligament. These insert onto the posterior lacrimal crest. Part of its medial head joins the medial horn of the levator aponeurosis.

Laterally the LL spreads out two heads.

The anterior lateral LL head inserts onto the inferior border of the lateral canthal ligament. The posterior lateral LL head joins the lateral retinaculum at Whitnall’s tubercle together with the orbital septum, the lateral check ligament of the lateral rectus muscle, and the lateral horn of the levator aponeurosis.

Lockwood’s ligament extends as composed of two frontal layers: an anterior layer which interdigitates with the orbital septum and a posterior layer which fuses with the inferior border of the tarsal plate.

Lockwood’s ligament stabilizes spatial anatomy within the orbit during function.

The cutaneous innervation of the lower eyelid [12] is provided by the infraorbital nerve (ION) and the zygomaticofacial nerve (ZFN). The nerves run within and inferior to the epimysium of the orbicularis muscle and perforate the orbicularis muscle perpendicular to distribute to the overlying skin. Terminal branches of ION are mainly distributed medial to the lateral canthus. Most terminal branches of the ZFN are distributed lateral to the lateral canthus.

Clinical Implications

In Graves’ disease, traction on capsulopalpebral fascia of inferior rectus muscle contracture will result in retraction of the lower eyelid: if this results in inability to close the eyelids properly this may cause lagophthalmos, when the eyeball turns upwards while showing the white lower surface of the globe.

Several surgical approaches to the orbit, more specifically the orbital floor have been described.

All of them carry their own (dis)advantages [13,14,15] and vary in the extent of bony exposure.

The transconjunctival approach has fewest lower eyelid complications and reduces the prevalence of ectropion, however carries an increased risk of entropion when compared to the subciliary approach. Lacrimal system damage can occur.

The transcutaneous subciliary—and the subtarsal approach [16, 17] reduce the prevalence of entropion, the risk of ectropion increases including a higher risk of scleral show. The infraorbital approach includes the advantage not to directly interfere with the eyelid lamellae. Transcutaneous approaches however do leave a visible scar, though when applied in an available skin crease, scar visibility may be minimal. The trans (retro)caruncular approach [18,19,20,21,22,23,24,25,26,27,28] is a safe and effective method for decompression of the medial orbital wall in case of Graves’ exophthalmos or for reconstruction of the medial orbital wall in case of a fracture; a combined transcaruncular - transconjunctival approach may be indicated for reconstruction of large orbital wall defects involving both medial wall and orbital floor.

Canthal Ligaments

Medial Canthal Ligament (MCL)

The upper and lower tarsal plates convert into the superior and inferior crura, fibrous bands, and fuse to form the common medial ligament. Medial extensions of Whitnall’s ligament attach to the common ligament and the posterior lacrimal crest as do the medial extensions of Lockwood’s ligament (Fig. 3.8).

The crura are located between the OOM anteriorly and the conjunctiva posteriorly. Separate limbs originate from the common ligament and course to attach to the bone at the medial orbital rim and to the lacrimal sac. The anterior limb, approximately 10 mm in length and 4 mm in thickness inserts to the frontonasal process of the maxilla anterior and above the anterior lacrimal crest [15, 29]; as such it is the strongest component of the medial canthal tendon complex and provides the major support of the medial canthal angle. The thinner posterior limb, passing between the canaliculi, fans out and inserts to the posterior lacrimal crest. This limb provides a backward pull to maintain the eyelid in a posture tangential to the globe surface. The superior limb, connecting the anterior and posterior limb inserts onto the orbital process of the frontal bone.

The resultant vector of all the canthal limbs and attachments suggests that resuspension of the entire complex following disruption should be directed posteriorly and superiorly toward the posterior lacrimal crest.

Both the pretarsal and the preseptal OOM portions bifurcate into a separate rear (i.e. deep head) and forward-directed (i.e. superficial head) stripe just like the prongs of a pair of open scissors.

The posteriorly departing muscle pathways of the upper and lower OOM lid portions correspond to the deep head of the pretarsal (DHPT—Horner’s) muscle and the deep head of the preseptal (DHPS—Jones) muscle, respectively, both fanning out in a further medial course. The anterior or superficial stripes conform with the superficial head of the pretarsal (SHPT) muscle and the preseptal (SHPS) OOM portions (Fig. 3.3a,b).

The superficial heads of the upper and lower lid pretarsal OOM (SHPT) in conjunction with the superior and inferior muscles of Riolan extend over and interdigitate anteromedially with the crura of the medial canthal ligament. They invest both lacrimal canaliculi, cover the ampullae, and insert onto the anterior limb of the canthal tendon.

Reaching the level of the common canaliculus, the medial extensions of upper and lower lid DHPT fuse and compose a prominent flat muscular bulge with a vertical height of 6 mm and a thickness of 2.5 mm, referred to as Horner’s muscle. Horner’s muscle continues behind the posterior limb of the medial canthal ligament to insert at the posterior lacrimal crest (Fig. 3.3a,b): thus forming the deepest layer of the inner canthus tissues.

The DHPS or Jones’ muscle predominantly turns toward the lateral aspect of the lacrimal sac and creates a “second” layer which is somewhat overlapping the lateral part of the DHPT (Fig. 3.3a,b).

The SHPT and the SHPS remain foremost, run along the anterior surface of the lacrimal sac, and fuse with the medial canthal tendon to create a third most superficial tissue layer (Figs. 3.3b).

The posterior limb of the medial canthal ligament forming a frontal sheet to Horner’s muscle is adjoined by the medial horn of the levator aponeurosis, the posterior layer of the orbital septum, and the medial check ligament altogether composing the medial retinaculum. Horner’s muscle tone contributes to the apposition of the eyelid to the globe during eyelid closure.

The superior arm of the medial canthal ligament forms a kind of “roof” of the lacrimal sac/fossa and blends with the fascia of the lacrimal sac (Figs. 3.8, 3.9, and 3.10). The pulling actions of the DHPT and the DHPS are supposed to contribute to the induction of negative pressure in the tear sac supporting the lacrimal pump mechanism thereby.

A diagram of an eye. It presents the medial canthal ligament and a C-shaped muscular lacrimal sac on the left side of the eye. — **Fig. 3.9**

A photograph of an anatomical specimen. It focuses on the eye presenting the medial canthal ligament. — **Fig. 3.10**

Lateral Canthal Ligament (LCL)

The lateral canthal ligament has features of both a ligament and a tendon.

The lateral endings of the tarsal plates pass over into the crura of the lateral canthal ligament. The crura unite resulting in the common tendon with both superficial and deep components.

The superficial flat ligamentous layer is continuous with the overlying orbital septum and interdigitations of the pretarsal OOM [30]. It measures approximately 10 mm in length/width; this portion coalesces with the periosteal surface of the lateral orbital rim and the temporalis fascia (Fig. 3.11).

The deep LL components arise from the lateral aspect of the tarsal plate to develop a cable-like common tendon (Figs. 3.11, 3.12, and 3.13). This inserts onto the lateral orbital tubercle of Whitnall. This tubercle is a small roundly protuberance of about 2–3 mm diameter located on the inner orbital plate of the zygoma (OPZ), immediately (2–4 mm) in the marginal territory posterior to the lateral orbital rim and about 10 mm beneath the frontozygomatic suture (FZS)

A photograph of an anatomical specimen of an eye. It presents the superficial lateral canthal ligament and fat in the underlying regions. — **Fig. 3.11**

A photograph of the eye in an anatomical specimen. The eye presents a lateral canthal tendon attached to the Whitnall's tubercle. — **Fig. 3.12**

.

In summary, Whitnall’s lateral orbital tubercle is important as marking the point of attachment of the:

Lateral common canthal tendon (originally termed the “lateral palpebral ligament”)
Lateral check ligament—of the lateral rectus muscle (LRM)
Lateral horn of the LPSM aponeurosis
Lateral end of Lockwood’s inferior suspensory ligament of the eyeball

Somewhat paradoxically the eponymous superior transverse ligament of the eye, commonly addressed as Whitnall’s ligament is not listed having a specific attachment to the “tuberculum orbitale” in the original publications [8, 9]. Indeed Whitnall’s ligament inserts into the periorbita of the lacrimal fossa up to 10 mm above the lateral orbital tubercle by way of the fascia of the lacrimal gland.

The attachments of the lateral canthal tendon, the lateral LRM check ligament, and the lateral horn of the LPSM aponeurosis extend along the lateral orbital wall posterior to the tubercle in a successive order from the rim before they end. The LCL continues for about 5 mm, the check ligament for approximately 6.5 mm, and the lateral aponeurosis horn roughly for 8.5 mm.

The complex arrangement of the entire ligamentous and fascial lateral extensions is summarized as the lateral retinaculum.

The Periorbita and Orbital Septum

Periorbita

The periorbita is identical with the periosteal lining covering the internal orbit, that starts at the anterior bony aperture. While orbital fat is hold into place, the periosteal envelope serves as a covering membrane. In the anterior area, the periorbita is continuous with the orbital rim periosteum and the orbital septum. The fusion zone between periorbita and periosteum is thickened: arcus marginalis. This is the origin of the orbital septum, corresponding to the deep layer of the galea aponeurotica.

Posteriorly, in the orbital apex, the periorbita communicates with the dura mater of the middle cranial fossa and cavernous sinus through the optic canal and the SOF. Here, it also contributes to the Zinn’s ring. Infero-dorso-laterally, the periorbita extends into the inferior orbital fissure (IOF) and fuses with Müller’s orbital smooth muscle which covers the IOF. Inferior to the rear sinkhole of the IOF the periorbita transforms into the periosteal lining of the adjacent pterygopalatine and infratemporal fossa. At the lacrimal crest, the periorbita splits into a thin layer for the lacrimal fossa and a thick layer, the fascia lacrimalis which invests the lacrimal sac.

Orbital Septum

The orbital septum is a fibroelastic multilayer membrane. It defines the anterior boundary of the orbit as a barrier that separates facial from orbital structures.

The orbital septum originates from the arcus marginalis orbitae and consists of two layers. The outer superficial layer is formed by the deep layer of the galea (Fig. 3.1). The inner, deep layer is the anterior coursing fascia of the periorbita, which further separates into an upward layer superiorly covering the frontal bone and the inner layer becoming the orbital septum of the upper eyelid.

Within the eyelids, the orbital septum separates the anterior from the posterior lamella: the septum passes between the OOM and the fat pockets.

In the upper eyelid, the orbital septum inserts and fuses with the LSPM aponeurosis, several mm above the tarsal plate. Finally, the superficial layer of the septum continues further downward onto the anterior tarsal surface.

In the lower eyelid, the orbital septum fuses with the capsulopalpebral fascia inferior to the tarsus before they insert to the tarsal edge and the lower canthal crus together.

From the latter, as with Lockwood’s ligament, the orbital septum continues to insert onto the posterior lacrimal crest. An anterior septal layer inserts to the common medial canthal ligament and to the anterior lacrimal crest finally enclosing the lower part of the lacrimal sac anteriorly.

Another intermediate septal layer passes backward around the lacrimal sac in the upper and lower eyelid. Its insertions connect to the posterior limb of the canthal tendon and to the posterior lacrimal crest, frontal to Horner’s muscle. In the lower eyelid, the lower border of the layer fuses to the periorbita at the opening of the nasolacrimal duct. Laterally, the septum becomes intertwined with the superficial lateral canthal ligament and its circumferential borders insert onto the orbital margin of the zygomatic bone.

Lacrimal Functional Unit

The overall lacrimal functional unit [4, 31,32,33,34,35] is organized in three partitions: a glandular secretion system, a tear fluid distributional area (ocular surface, conjunctiva, cornea), and a drainage pathway, that collects, conveys, and empties the tear fluid into the lower meatus of the nasal cavity toward an orifice anteriorly underneath the inferior concha. The unit modulates lacrimation, protection of the ocular surface including immune responses from the anterior segment of the eye, and neurosensory perception (e.g., pain sensation).

Tear Producing Glands

Main and Accessory Aqueous Lacrimal Glands

The aqueous tear fluid production is effected by the main lacrimal gland [36,37,38] with contributions from numerous small accessory lacrimal glands. The accessory glands are located in the eyelid conjunctiva along the nonmarginal tarsal borders of the tarsi (Wolfring glands) and at the fornices—predominantly the superior fornix—(Krause glands) (Figs. 3.1 and 3.14).

A diagram of the orbit of an eye. It exhibits a muscle that partially covers the periphery of the orbit. — **Fig. 3.13**

The main lacrimal gland is a bilobed exocrine gland consisting of a larger superior orbital part and a smaller inferior palpebral part. The anterior horizontal lobe portions are sandwiched around the concave lateral horn of the LPSM aponeurosis, whereas the parenchyma of the gland is continuous around the posterior edge of the horn.

Both lobes are located posterior to the orbital septum. The orbital lobe is affixed to the lacrimal fossa in the anterolateral orbital roof. The fibrous periosteal attachments include Whitnall’s ligament. The palpebral lobe extends laterally into the superotemporal fornix of the upper lid, where it is adherent to the conjunctiva through which it becomes visible with lid eversion. Anteriorly the palpebral lobe spreads beyond the superior orbital margin, while the orbital lobe has a posterior orientation and conforms to the space between the orbital wall and the globe surface. The position and footprint area of the overall gland may vary considerably to behind the globe, over the superior rectus muscle (SRM) and the vertical midline of the globe as far as alongside the temporal aspect to the lower border of the lateral rectus muscle (LRM).

Excretory ducts from both lobes all empty at the superotemporal conjunctival fornix. Several interlobular ducts connect the orbital lobe to the ducts of the palpebral lobe. About 10–15 other ducts from the orbital lobe route independently through the palpebral lobe. Hence resection of the palpebral lobe ablates the lacrimal flow of the entire gland.

The arterial supply of the main gland derives from the lacrimal artery, a branch of the ophthalmic artery, with medial and lateral ramifications inside the lobes, subsequent branches supplying the palpebral marginal arcades, and a terminal conjunctival network. Venous drainage is via similar tributaries to the superior ophthalmic vein.

Sensory innervation is provided by the lacrimal nerve (¬CN V1). The aqueous secretion by the lacrimal gland is subject to parasympathetic and sympathetic stimulation via the VIIth CN parasympathetic pathway and via postganglionic axons from the superior cervical ganglion (SCG) (see autonomic innervation).

The accessory lacrimal glands of Wolfring and of Krause (Fig. 3.14) basically resemble the lobe structures and histologic characteristics of the main lacrimal gland. The nodule-shaped glands are individual organs with their own interstitial connective tissue coatings. They are located in the lamina propria of the conjunctiva and their ducts open onto the conjunctival surface. Wolfring’s glands are the larger type nodules found in numbers of 2–5 above or within the upper border of the superior tarsus near its midline and in a number of 2 within the lower border of the inferior tarsus. The total more numerous Krause’s glands lie in the upper fornix—about 20–40—below the palpebral lobe of the main lacrimal gland and in the lower fornix—about 6–8. Autonomic innervation in human accessory lacrimal glands has long been confirmed with parasympathetic prevailing over sympathetic formations.

Conjunctival Goblet Cell (CGC) Population

Goblet cells [39,40,41] of the conjunctiva are plump, rounded specialized cells that extend through the entire thickness of the stratified epithelium.

A diagram of orbital glands and 2 insets. In the former, the labels include lacrimal glands, accessory lacrimal glands, tear film, eyelids, and tarsal glands. In the insets, the release of proteins, ions, and H 2 O in tear film from accessory lacrimal glands is exhibited. — **Fig. 3.14**

They can occur individually or within clusters; the goblet cell population is distributed throughout the palpebral and bulbar conjunctiva with the greatest density in the medial canthus/lower fornix region and sparser dispersion over the superior and inferior bulbar regions. In regions with sparser numbers, single goblet cells exceed cell clusters.

Most importantly, conjunctival goblet cells secrete polymeric gel-forming and membrane-bound mucins onto the ocular surface. Based on their mucin secretion, several functions can be attributed to CGCs such as lubrication, maintenance of surface wetting and the tear film across the epithelium, prevention of corneal surface damage and infection.

Tarsal Glands

Processions of individual tarsal glands of Meibom (Meibomian Glands—MG) [42] are embedded in parallel arrangement perpendicular to the eyelid margins within connective tissue fibers of the tarsal plates (Figs. 3.1 and 3.14). MGs are a distinct variant of large sebaceous glands that are not associated with hair follicles.

The tarsi in the upper eyelids are fitted with between 20 and 40 MGs, the lower tarsi with between 20 and 30 MGs. The vertical measure of the meibomian glands follows the height of the tarsal plates and consequently differs according to the shape and dimensions of the upper and lower tarsi. A single MG is composed of multiple holocrine secretory acini, which are clustered in tiers around the long vertical axis of a central duct to which they link in oblique direction via short connecting ductuli. The open end of the central duct is lined by keratinized epidermal layers grown in from the free lid margin. This orifice is typically positioned at the posterior lid margin directly in front of the mucocutaneous junction and inner lid border. MGs produce a clear oily, lipid-rich secretion (i.e.,“Meibum”), that forms part of the tear film composition.

Ciliary Glands

There are two kinds of glands associated with the lashes on the eyelid margins (“eyelid cilia”), the modified apocrine sweat (sudor) glands of Moll, and the pilosebaceous glands of Zeis (Fig. 3.1).

Moll glands are tubules that form a long stretched spiral widening root in contrast to the coiled tubuloalveolar body of common sweat cells. They have a wide-lumen ampulla and open with a narrow duct into a ciliary follicle close to the surface or run into the duct of a sebaceous Zeis gland or directly onto the surface of the lid margin between the eyelashes—often with one orifice amid two lashes.

Moll glands are located anterior to the Meibomian glands and extend deep into the lid next to the tarsal plates. They are more numerous and more developed in the lower eyelid.

Zeis glands are larger than Moll glands and directly associated with each eyelash follicle. Usually two Zeiss glands exude their secretions through their excretory ducts surrounding the mid-length portion of the ciliary follicle. Each Zeis gland consists of clusters of several sac-shaped enlargements, the alveoli, which unite into a short wide duct.

Ocular Tear Film

The tear fluid is a complex solution [43,44,45]composed of water, enzymes, proteins, immunoglobulins, lipids, various metabolites, and exfoliated epithelial and polymorphonuclear cells. The classical concept of an interpalpebral, trilaminar, preocular tear film with a superficial lipid phase (from tarsal Meibomian glands) overlying an intermediate aqueous phase (from main and accessory lacrimal glands) and an innermost mucinous layer (from conjunctival goblet cell population) [46] is queried by novel research.

The three layered architecture is only applicable to the preocular fluid within the interpalpebral aperture, that is present in the interblink period. The modern reappraisal proposes a model that encompasses a coherent fluid extending over the whole “ocular surface (OS) system.” This integrates all conjunctival and corneal epithelia into a single three dimensional sack-like territory with the retropalpebral pouches up into the fornices. As a consequence thereof, the tear fluid is distributed in three continuous compartments, the fornix conjoined with the retrotarsal space (“cul de sac”), the tear menisci and the preocular area, all subject to the condition that the eyes are open. The preocular tear film is spread over the exposed bulbar conjunctiva and the contours of the cornea. Over the corneal region, this film is extraordinarily thin with a thickness of 2–5.5 μm.

The threefold junctional interface between the occlusal surface of the lid margin, the preocular tear film, and the atmosphere gives rise to the tear menisci. Thus they fill in and run along the corner profiles of the lower and upper lid margins with a concave front and a prismatic (or wedge-shaped) cross-sectional geometry. They act as a reservoir to supply the fluid which renovates the preocular tear film at each blink. The meniscus parameters (height, width, and radius of curvature) can be used to compute the meniscus volume which is supposed to correlate with the overall tear volume.

The tear film adhesion to the surface of the conjunctival and corneal epithelium is increased by large transmembrane mucins which, as part of the glycocalyx, attach to the microplicae of the cells and extend into the preocular tear film. The preocular tear fluid corresponds to a single layer of mucoaqueous gel with a decreasing mucous density toward the surface. It is still unclarified whether this is true for all OS compartments. The mucoaqueous gel makes up the bulk of the tear film and lies beneath a very thin lipid layer (at mean 42 nm). The lipid layer forms an ever present sealant closing off the mucoaqueous gel between the eyelid margins, where it is secreted from the Meibomian glands and spreads onto the tear film with each blink.

An intact lipid layer shielding is important in stabilizing the tear film and preventing excessive evaporation of the tear fluid. The preocular/precorneal tear film provides the primary refractive medium for light entering the visual system and provides a protective environment for all tissues involved in the OS.

Lacrimal Drainage Pathway—Nasolacrimal Sac/Duct

The meniscal stream carries the tear fluid along the upper and lower eyelid margins [46] toward the lacrimal puncta. Each punctum is a small or transversely oval-shaped orifice located on the peak of the papilla lacrimalis near the medial end of the lid margin next to the nasal canthal angle (Fig. 3.15). Both puncta face backward into the groove between the plica semilunaris and become only visible when the lids are everted. From the punctal outflow, the drainage continues sequentially via the upper and lower canaliculi into the lacrimal sac. Each canaliculus has a short vertical (2 mm) and then after a dilatation at right-angular turn (“ampulla”), a longer (8–10 mm) horizontal part. The horizontal canaliculi converge medially, the upper being shorter than the lower. Contraction of the lacrimal part of the orbicularis oculi muscle, i.e., Horner-Duverney’s muscle causes the tear fluid in the canaliculi to be transported toward the lacrimal sac.

A diagram of the eye presents the lacrimal drainage system. The lacrimal gland is magnified in an inset. The inset presents valve of Rosenmuller, valve of Krause, valve of Hasner, fundus of sac, body of sac, osseous nasolacrimal canal, and nasolacrimal duct. — **Fig. 3.15**

A histological scan of caruncle overlapped by plica semilunaris. It presents the epithelial surface, a hair follicle, and a sweat gland. — **Fig. 3.16**

The horizontal canaliculi enter the lacrimal sac on the posterolateral surface either united to a short (1–2 mm) common canaliculus piercing the lacrimal fascia or independently. An in-folding of the lacrimal sac mucosal lining is supposed to have a one-way valvular function at the internal canalicular entrance (valve of Rosenmüller) that might prevent a retrograde reflux eventually emerging at the puncta.

The lacrimal sac, a membranous conduit measuring approx. 0.2–0.5 cm in diameter and approx. 1.2–1.5 cm in length lies in the lacrimal fossa. Its upper end (fornix of lacrimal sac) is closed in a dome-shaped fashion, its lower part merges into the nasolacrimal duct configuring an isthmus at the entrance level into the bony canal.

The nasolacrimal duct is approx. 1.2–2.4 cm long. From the sac, it descends following the course of the intraosseous maxillary canal at an angulation of 15° to 30° degrees in a backward and of 5° in a lateral direction; the lower meatal duct portion with its terminal aperture (“lacrimal ostium”) is accommodated in the lateral wall of the inferior nasal passageway. The sagittal and vertical position as well as the shape of the ostium are most variable within limits of 2.0 –3.5 cm behind the anterior border of the nostril sill and 0.9–2.2 cm above the nasal floor in a round, punctiform, slit-like—linear, vertically or transversely oriented configuration, single or in a duplicated array.

Numerous mucosal folds in distinct places within the nasolacrimal duct have been described as valves and are still labeled with eponyms of anatomic celebrities but with no evidenced valvular function. The plica lacrimalis or valve of Hasner is the most constant variant situated on the side of inferior turbinate just prior the ostium.

The fluid dynamics within the lacrimal system are associated with pumping mechanics during eyelid closure and muscular contraction (e.g., preseptal and pretarsal OOM) involved therein.

The lower system comprises the lacrimal sac and the lacrimal duct. The lacrimal sac is anterior to the orbital septum, nestled in its own fascia in the lacrimal fossa. The lacrimal crest of the maxillary bone forms the anterior border of the lacrimal fossa.

The tendinous insertions of the OOM bind the lacrimal sac anteriorly and posteriorly, aiding in the movement of tears. Posterior to the sac, the deep heads of the pretarsal OOM insert. The deep heads of the preseptal OOM attach the lacrimal sac latero-posteriorly. Anterior to the sac, the superficial heads of the pretarsal and preseptal orbicularis muscles insert onto the anterior crest of the lacrimal fossa. Together, these insertions help squeeze the lacrimal sac to move tears forward through the system.

Plica Semilunaris

The plica semilunaris is a crescent-shaped conjunctival fold lateral to the caruncle conjoining to the bulbar conjunctiva and lacrimal portion of the eyelids. It surrounds the medial limbus from the superior to the inferior fornix. The plical fold functions in the distribution of the tear fluids, maintains the lacrimal lake, and keeps the lacrimal puncta in contact with the lake. Though the plica is not very prominent, it provides enough resiliency to the movements of the globe and the eyelids. It unfolds and flattens or is retracted on abduction or adduction, respectively, what allows the lacrimal puncta to hold up their position.

Lacrimal Caruncle

The lacrimal caruncle is a soft, pink bump with ovoid shape found in the tear lake at the inner canthus inferomedial to the plica semilunaris. It is oriented obliquely with an inferolateral angulation, while its superior border is at level with the inferior lid margin. The surface is lined with a nonkeratinizing epithelium giving it the look of conjunctival tissue. In fact, the caruncules feature skin appendages (pilosebaceous units, sweat gland, hair follicles, connective tissue, fat) (Fig. 3.16), since they derive from the lower eyelid margin developmentally. Equally the caruncles have direct connections to the lower lid retractors and to the MRM. Congenital supernumerary caruncles are extremely rare.

Clinical Implications

A trans- or preferably retrocaruncular approach [19, 20] provides direct and reliable adequate access to the medial aspect of the orbital floor and medial wall of the orbit posteriorly toward the orbital apex. It is a safe, rapid, and cosmetically pleasing surgical approach. The approach can be combined with a transconjunctival access and alateral canthotomy to gain overall access to the medial orbital wall, the orbital floor, and the lateral orbital wall. The retrocaruncular approach benefits the transcaruncular insofar that there is less risk of tarsus exposure and thus a decreased risk of lid complications. As the transcaruncular approach in fact consists of an inferior transconjunctival approach extending medially and superiorly, it divides the cutaneous-tissue caruncle. Horner’s muscle fixates the caruncle to the posterior lacrimal crest and helps to support the medial eyelid; as the retrocaruncular incison is performed lateral to the caruncle, the risk of damage to Horner’s muscle is minimized. Also some lower eyelid retractors attach to the caruncle, if division of the caruncle is performed, this may result in an inferolateral shift of the lateral aspect of the caruncle.

The Ocular Globe

The Globe—Gross Anatomical Outline/Overview

The ocular globe or eyeball has a volume of about 6–8 cm³, a vertical diameter of 23.5 mm, and an anterior to posterior diameter, called the eye/optical axis of 23 mm (Fig. 3.17).

3 diagrams of the orbits of an eye. 1. A slant line on both orbits denotes the axis of the orbit. A perpendicular line on the right orbit denotes the anteroposterior axis of the eyeball. 2 and 3. Anterior and posterior quadrants of the eyeball. — **Fig. 3.17**

The anatomic equator divides the globe topographically into two unequal halves: the anterior and the posterior hemispheres; it is a virtual line which corresponds to the greatest circumference of the eyeball (Fig. 3.17b, c). The cornea constitutes the anterior segment and occupies 1/6th of the surface area, the larger posterior segment is composed of the scleral shell and has a larger radius of curvature than the anterior segment.

The eyeball is surrounded by Tenon’s capsule a fascial bulbar sheath that runs from the optic nerve nearly to the corneal limbus or sclerocorneal junction, 2 mm dorsal to the corneal limbus. It is firmly adherent to the episclera. The white outer layer of the eyeball is called sclera, which is continuous with the transparent cornea at the front of the eye. The sclera is covered by the bulbar conjunctiva, the cornea lacks such conjunctival coverage. Both fibrous layers maintain the shape and size of the eyeball. The larger part, the firm sclera protects the inner contents of the globe; in addition, it provides attachment to the extra ocular muscles. As such, Tenon’s capsule, a dense elastic connective tissue membrane, is perforated to allow for adequate functional insertion of the EOM tendons.

The transparent cornea has a refractive power of 40–45 diopters and together with the lens (refractive power of 20–22 diopters) it assures that light beams are focused on the retina. The cornea has its thinnest aspect in the center. Its outer surface is covered by a multilayer and has an epithelium which is continuous with the adjacent bulbar conjunctiva, the structure that covers the anterior part of the globe, i.e., sclera and the backside of the eyelids.

For descriptive purposes, the conjunctiva may be divided into three subdivisions:

1.
Tarsal or palpebral lining the eyelids
2.
Forniceal, lining the upper and lower fornices
3.
Bulbar, overlying the sclera on the anterior portion of the globe (Fig. 3.1)

While the cornea is mostly avascular besides vascular supply at the region of the limbus, many sensory nerves derived from the ciliary nerves reach the cornea and make it a highly sensitive area. At the posterior pole of the globe, the sclera is perforated by fibers of the optic nerve at the lamina cribrosa.

The limbus is created by the sclerocorneal junction.

The canal of Schlemm, a vascular scleral venous sinus is located within the posterior part of the sclerocorneal junction. The canal collects the aqueous humor from the anterior chamber and drains into the veins of the eyeball thereby maintaining fluid homeostasis. The adjacent trabecular meshwork is a specialized tissue, draining aqueous humor from the anterior chamber and as such responsible for controlling the intraocular pressure.

There are in fact two fluid (aqueous humor)-filled chambers in the eye: an anterior chamber and posterior chamber. The anterior chamber including the trabecular meshwork is located between the cornea and the iris, the posterior chamber between the backside of the iris, the lens capsule, and the ciliary processes or corona ciliaris, which is part of the ciliary body (Fig. 3.18). The aqueous humor is produced by the ciliary body and flows into the anterior chamber through the narrow slit communication between the iris and the lens.

A cross-sectional diagram of the angle made by the anterior chamber. It presents ring of Schwalbe, anterior chamber, trabecular meshwork, iris process, iris, conjunctiva, scleral spur, and ciliary muscle. — **Fig. 3.18**

Centrally, behind the lens, the vitreous body (corpus vitreum) is located against the inner surface of the retina.

The uvea, or uveal tract is composed of three parts: iris, ciliary body, and choroid.

The iris, from anterior to posterior consists of an anterior border layer, a stroma including the sphincter pupillae muscle, an anterior pigment epithelium including the dilatator muscle and a posterior pigmented layer. The ciliary body, contiguous with the iris anteriorly and with the choroid posteriorly contains the ciliary muscle and the ciliary processes.

The largest part of the uvea is the choroid, the vascular layer of the eye ball, which extends from the ora serrata and is responsible for the nourishment of the outer half of the retina.

The iris, the diaphragm of the eye, a circular pigmented organ, the part of the uvea located anteriorly, conveys the pupil, a central hole looking black. This opening is regulated by the activity of the sphincter and dilatator pupillae muscle; the sphincter muscle being strongest.

The ciliary body also inhabits the smooth ciliary muscle and the ciliary processes which suspend the lens by the ciliary zonulae of Zinn: suspensory ligaments closely related to the ciliary processes and connecting the capsule of the lens to the ciliary body.

The lens itself, positioned behind the iris is situated on the anterior surface of the vitreous body. The ciliary muscle changes the curvature of the lens, necessary for accommodation, i.e., focusing of the eye. The central portion of the anterior lens is related to the pupil.

Contraction of ciliary muscle relieves tension upon the lens resulting in more convex form, which is made possible by the outermost layer of the lens, the highly elastic capsule. Increase of lens curvature resulting after contraction of ciliary muscle allows for near vision.

The choroid, supplied by the posterior ciliary arteries lies between the sclera and retina but is absent in the region of the lamina cribrosa to allow the optic fibers to exit to form the optic nerve. The choroid is built up of four layers: from outward, larger vessels inward containing smaller vessels up to capillaries and an inner layer, Bruch’s membrane, the lamina basalis or lamina vitrea.

The serrated junction between the retina and the ciliary body is called ora serrata: the termination of the retina which corresponds with the acute transition between the nonphotosensitive, nonfunctional area of the ciliary body and the complex multilayered photosensitive region of the retina. The inner surface of the choroid is covered by a pigmented single cell layer (stratum pigmenti) which continues around the whole inner surface of the eye.

The innermost layer, the so called neural tunic or retina consists of ten layers, from outward inwards the most fundamental being the layer of rods and cones (photoreceptors), the layer of bipolar cells, and a layer of ganglionic stratum of the retina. The innermost layer, the stratum internum borders the aqueous humor from the retina. External to the outer layer of rods and cones is the stratum pigmenti, which finally absorbs the light which has been transmitted to all the other inward directed layers. Located in the posterior retina is the macula lutea (central portion of vision) with the fovea centralis, measuring 1 mm². The fovea (centralis), a depression within the macula is located in a straight line behind the lens. Here the retina is markedly thin because of the absence of ganglionic cells; the rods (night vision) gradually disappear from the periphery to the center and are replaced by cones (day and color vision). The fovea centralis contains only cones.

During daylight, visual acuity is high including color vison, cones are stimulated more so at the fovea centralis. At night, mainly rods, which are present more abundantly in the macula than in the fovea centralis are activated and visual acuity is low. In the macula, around the fovea, the ganglionic cell layer of the optic nerve is thick. There is a point where to the nerve fibers converge to result in the optic disk: optic papilla. Here, no other layers are present: the disc is insensitive to light: the blind spot in the visual field. From the optic disc, the nerve fibers continue, after passing through the lamina cribrosa to form the myelinated optic nerve.

The retina is mainly supplied by the central retinal artery. A second (choroidal) circulation comes via the short and long posterior ciliary arteries. The central artery of the retina passes through the lamina cribrosa adjacent to the optic nerve at the location of the optic disk. The artery is accompanied by the central vein which drains in the cavernous sinus.

The globe is surrounded extensively by connective tissue septa including the extraocular muscles (EOM) connecting them all to the periorbita. It consists of a complicated network which maintains the spatial relationship and supports the coordinated globe position during ocular movement. It also serves as a protection system, especially in coadjuvancy with the abundant presence of orbital fat.

The optical axis extends from the anterior to the posterior pole of the eye and is defined by the straight line going through the geometrical center of the lens and the cornea.

The visual axis represents the direction of gaze; an axis from a fixation point toward the center of the pupillary entrance subsequently reaching the fovea.

As mentioned above the orbital axis is the line from the center of the optic foramen in the apex extending anteriorly, laterally, and inferiorly to the middle of the orbital aperture.

The optical axis and orbital axis do not align when looking straight forward (Fig. 3.17). The angle between the optical axis and the visual axis is called angle alpha.

Clinical Implications

An A-P diameter of 24 mm is seen in emmetropic (normal) eyes. An axis of > 24 mm is called myopia, of < 23 mm hypermetropia (Fig. 3.19).

An illustration eyes with normal emmetropia, hyperopia, and myopia. In hyperopia and myopia, the incident rays converge at the focal plane from the convex and concave lenses. — **Fig. 3.19**

Myopia (Nearsightedness)—difficulty focusing on faraway objects because of an abnormally elongated eyeball. Light rays come into focus before they reach the retina and begin to diverge again by the time they fall on it. Corrected with concave lenses, which cause light rays to diverge slightly before entering the eye.

Hyperopia (Farsightedness)—difficulty focusing on nearby objects because of an abnormally short eyeball. The retina lies in front of the focal point of the lens, and the light rays have not yet come into focus when they reach the retina. Corrected with convex lenses, which cause light rays to converge slightly before entering the eye.

Presbyopia—Declining ability to focus on nearby objects as one ages. An effect of declining elasticity of the aging lens, often first noticed around age 40–45. Results in difficulty in reading and doing close handwork. Corrected with reading glasses or bifocal lenses.

Astigmatism—Inability to simultaneously focus light rays that enter the eye on different planes. Focusing on vertical lines, such as the edge of a door, may cause horizontal lines, such as a tabletop, to go out of focus. Caused by a deviation in the shape of the cornea so that it is shaped like the back of a spoon rather than like part of a sphere. Corrected with “cylindrical” lenses, which refract light more in one plane than another.

Zinn’s Ring and Extraocular Muscle System

Zinn’s Ring

The common annular tendon is composed of fibrous tissue condensations from the periorbita within the orbital apex, the dura lining the SOF, and optic canal and the optic nerve sheath. The apical orbital area is located posteriorly in the orbit, exact definitions however vary (Chap. 2). The rectus extraocular muscles (EOM) originate from the ring, while the LPSM, the superior oblique muscle (SOM), and the inferior oblique muscle (IOM) outside the Zinn’s ring (Figs. 3.20, 3.21a, b, and 3.22). The rectus muscles diverge anteriorly to insert onto the sclera (Figs. 3.22 and 3.23).

A photograph and a diagram of the skull. 1. The photograph exhibits a deep groove, indicative of the orbit of an eye. 2. The diagram presents the common tendinous ring. Some labels read lacrimal nerve, frontal nerve, lateral rectus, medial rectus, and rim of the optic canal. — **Fig. 3.21**

A photograph of an anatomical specimen presents the rectus muscles. The markings expose the muscles, nerves, and a gland in the eye socket labeled L P S M, O N, M R M, L R M, and O P L G. — **Fig. 3.22**

A photograph of the dissected posterior orbit in an anatomical specimen. Some labels read Z N, I O N, T G G, O S, C N 2, 3, and 4, and S S. A metal probe is positioned near the optic strut. — **Fig. 3.23**

Zinn described the orbital fibrotendinous ring already in 1755 (J. G. Zinn 1727–1769 German Botanist and Anatomist Göttingen) (Fig. 3.24a–e). In the classic description, Zinn’s ring is the common origin of the rectus musculature (Figs. 3.20 and 3.24).

5 illustrations. 1. The cover page of a book reads, Descriptio Anatomica Ocvli Hvmani Iconibvs illvstrata. 2. A page has sketches of the orbit of the eye with muscles. 3, 4, and 5. 3 diagrams with different views of E O M and Zinn's ring. — **Fig. 3.24**

As the term apex already suggests, the orbital apical part is the narrowest compartment of all (Chap. 2). The bony boundaries of the apex consist of the lesser wing of the sphenoid: the roof, the ethmoidal sinus: the medial wall, the greater wing of the sphenoid: the lateral wall and the maxillary strut, the bony extension of the greater wing of the sphenoid connecting to the lesser wing: the floor of the apex. In fact once we cross the maxillary strut posteriorly, we enter the apex orbita [15, 17, 47] (Chap. 2).

Zinn’s ring begins at the orbital openings of the optic canal and SOF and is continuous with the dura mater, cavernous sinus, the optic canal, and the optic nerve sheath. It extends posteriorly along the optic strut coursing intracranially, originating from the lateral wall of the sphenoid body. The tissues are blended in a funnel, circular array structure extending backward rather than a ring, though for reasons of simplicity they are still portrayed as a cylindrical ring. The terminal posterior tip of the tendinous funnel inserts at the infraoptic tubercle or a canalicular depression which is located below and posterior to the optic strut.

The central SOF compartment or superolateral foramen, accommodates the oculomotor (CN III), and abducens (CN VI), and nasociliary nerves

(branch of CN V1) as well as the sensory and sympathetic roots of the ciliary ganglion. The CN III divides into its superior and inferior division before entering the ring. Since the superolateral foramen contains two of the optomotor nerves (CN III and CN VI), it is termed the oculomotor foramen (Figs. 3.20 and 3.21b).

The superior extra-annular compartment of the SOF transmits the frontal and lacrimal nerves (branches of CN V1), the trochlear nerve (CN IV), and the superior ophthalmic vein (Figs. 3.20 and 3.21b). The inferior extra-annular compartment contains the inferior ophthalmic vein and sympathetic fibers which accompany the internal carotid plexus eventually reaching the ciliary ganglion as well as the infraorbital and zygomatic nerves embedded in extraconal fat.

Summarizing, the annulus of Zinn surrounds the optic foramen and oculomotor foramen which encloses the central 1/3rd of the superior orbital fissure (Figs. 3.20 and 3.21a, b).

The extraocular muscle (EOM) system generates the coordinated voluntary ocular movements via six extraocular muscles, striated skeletal four rectus and two oblique muscles (Fig. 3.22).

A lateral diagram of the human eye. It exposes the muscles and a nerve posterior to the orbit. Some labels read L R M, M R M, L P S M, and I R M. — **Fig. 3.25**

The lateral, inferior, and medial rectus muscles (LRM, IRM, MRM) originate from the inferior tendon of Zinn’s ring, which is located inferior to the optic foramen; the superior rectus muscle (SRM) originates from the superior margin of the optic foramen and completes the upper aspect of the ring (Fig. 3.21b). Altogether, the rectus muscles arrange in a cone shape when they run anteriorly and form a “sleeve”-like structure surrounding and bounding a separate compartment behind the ocular globe (Fig. 3.22). This results in the differentiation into an intra- and extraconal space, the intraconal space located within a musculofascial cone with the base anterior, formed by the posterior half of the globe which converges posteriorly on the tendinous ring at the orbital apex where the rectus muscles insert (Figs. 3.22, 3.24, and 3.25)—see below chapter Topographic spaces of the orbit. Inferiorly, connective tissue extends from the annulus (Zinn’s ring) to blend with Müller’s orbital smooth muscle.

A lateral view photograph of the dissected eye in an anatomical specimen. Some labels posterior to the orbit are O R, C N 6, L R M, I O M, O S, T G G, S S, and O F. — **Fig. 3.26**

The LPSM arises from the periorbita outside Zinn’ ring over the lesser wing of the sphenoid just medial of the SRM. It runs in close contact just above and medially to the SRM until the muscles diverge at the level of the SRM scleral insertion.

The origin of the SOM is assigned to superomedial portion of the common annular tendon (Zinn’s ring) deriving from the periorbita covering the sphenoid body. The IOM does not originate from the annulus, but arises from the periosteum of the inferior orbital rim immediately lateral to the opening of the bony lacrimal duct.

As the CN IV emerges the annular tendon, it innervates the SOM from the extraconal surface, this is in contrast to the innervation on the intraconal (ocular) side for all other EOM.

Approximately 10 mm anterior to the optic strut, the EOM (LRM, IRM, MRM, SRM) and the SOM continue anteriorly as separate structures parallel to the orbital walls until they insert into the sclera anterior or posterior (SOM) to the equator of the globe (Fig. 3.23).

On their way, the MRM [48] and SRM show some origin from the adjacent dura covering the optic nerve. Lattice-like tissue septa separate the origin of the rectus muscles while radial septa connect the muscle to the adjacent orbital wall [49, 50]. These connective tissue septa are highly organized and form an accessory locomotor framework with structural organization and constant pattern; the soft tissue system, apart from connective tissue contains vessels, nerves, and smooth musculature. The relation of the eye musculature, the orbital walls, and the globe with these connective tissue structures allows for smooth normal eye movement [49, 50].

Before entering Zinn’s ring, the intracranial neurovascular structures run via the optic canal, pass the optic foramen to enter the orbital apex [47]: the optic nerve (ON), the ophthalmic artery (OA), and the postganglionic sympathetic nerves that accompany the carotid plexus.

Tenons capsule invests the anterior projection of the EOM. The muscle fibers are separated from each other by a surrounding endomysium. Halfway through forward, the muscle cone is centered within the orbit, ± 8 mm from the adjacent orbital walls. When the muscles enter Tenons capsule at the posterior surface of the globe, fascial strands from the muscle sheaths are interconnecting with Tenons capsule to contribute to the pulley—suspensory system.

A complex system of thin fibrous sheaths and fat tissue is present between the muscles and this functions together with connective tissue structures as a pulley through which the muscle moves and determines the direction of the muscle pull.

Once Tenons capsule is entered, the rectus muscles arc over the globe, flatten once across a model of orbital mechanics based the equator, and insert onto the sclera via a tendinous ligamentary band, approximately 10 mm in width (Fig. 3.26).

A fascial condensation from the sheath of the medial rectus muscle contributes to the medial check ligament and this, in conjunction with the medial horn of the LPSM, attaches behind the posterior lacrimal crest to the orbital septum and to the caruncle and plica semilunaris. The lateral check ligament is a fascial condensation from the lateral rectus sheath to Whitnall’s tubercle; additional attachments are present to the orbital septum and fornix of the conjunctiva.

The SOM runs forward and becomes invested by collagen with elastin fibers. It is intimately involved in the connective supportive system of the globe.

Unlike the rectus and IOM pulleys, the SOM has a rigid pulley in the superonasal orbit, the trochlea, that redirects the intermediate SOM tendon and consecutive muscle portion to the postero-supero-lateral globe quadrant.

The trochlea is a circular fibrocartilaginous structure, about 5 mm, firmly adherent to a bony fovea—occasionally to a spine of the frontal bone at the fovea trochlearis (Fig. 3.22); it consists of fibrocartilaginous elements making up an overall cylindrical shape with a characteristic posterolateral flange at the anterior end:

A biconcave cartilage “saddle” of limited size (ca. 4 × 4 × 5.5 mm—width/height)
An inner-tube fibrovascular or trabecular sheath providing the outer laminae for a fluid-filled bursa-like paratendinous space
An outermost layer of dense fibrous condensations with a bony securement folding

Presumptively, the SOM tendon moves within the trochlea by staggered interfiber sliding actions in concert with telescoping of the entire tendon bundle.

The SOM then finally inserts on the sclera on the posterotemporal globe surface, which explains its function: it will rotate the globe: infraduction (depression), incycloduction (internal rotation), and slight abduction.

The IOM is unique because of its origin far apart from Zinn’s ring.

It arises from the periosteum of the medially located orbital surface of the infraorbital rim, 1.5 mm lateral to the entrance of the nasolacrimal canal. Its course is posteriorly, lateralward and upward at an angulation of about 50^° to the medial orbital wall, bends around the lateral globe curvature toward its final insertion to the sclera at the postero-inferior-lateral aspect of the globe. Along its course, it passes inferior to the IRM where both enveloping sheaths of the IOM and IRM fuse. Here, thickening of Tenons capsule is present contributing to Lockwood’s ligament. Its function is extorsion (external rotation), elevation, and abduction: it rotates the eye and moves it upward and outward.

Clinical Implications

In case of Graves’ orbitopathy (Chaps. 15 and 16), enlargements of the EOM can be seen. They concern the muscle-bellies themseselves, not the tendons. Enlargement can reach 2–3 times the normal volume. Although all EOM can be involved, the inferior and medial rectus are involved most frequently.

The enlargement is caused by inflammatory changes including accumulation of glycoprotein, mucopolysaccharides as well as GlycosAminoGlycans (GAG) [11]. Enlargement can be massive causing apical compression.

The volume changes are responsible for the proptosis. In extreme volume increase of EOM, apical crowding can result which may lead to progressive pressure on the optic nerve: malignant Graves’ orbitopathy: urgent apical decompression is indicated in such cases (Fig. 3.27a–c).

3 C T scans of the orbit. They expose the darkly shaded muscles in both the orbits and apical crowding with unilateral Grave's orbitopathy. — **Fig. 3.27**

Eventually, inflammatory contracture will often result in motility disturbances and subsequently diplopia.

The anterior herniation of extraconal fat in patients with Graves’ disease affects the upper eyelid.

Traumatic rupture of the superior oblique tendon in approximation of the trochlea is a rare cause of acquired Brown’s syndrome: restricted elevation in adduction: upward gaze limitation.

Brown in 1949 [51,52,53] described a shortening of the tendon sheath of the superior oblique tendon. The origin of this entity however is still subject of debate.

Surgical reinsertion is highly favorable for the outcome and to prevent malfunction of the SOM.

As the trochlea is located very anteriorly and as such likely to be affected in medial orbital injury, direct trauma to the trochlea—pulley and/or superior oblique muscle tendon may result: acquired Brown’s syndrome.

In case of an orbital roof fracture (Chap. 11), also restriction of the superior oblique muscle tendon may occur [53]Acquired Brown’s syndrome [54] can be treated by superior oblique and trochlear luxation.

Once the connective tissue framework within the orbit is ruptured, motility disturbances of the globe may result [49, 50].

Topographic Spaces of the Orbit

The orbital cavity itself is divided into several spaces [14]: the subperiorbital or subperiosteal space, the extraconal and intraconal spaces, and the lacrimal space. The subperiorbital or subperiosteal space is a potential space. The cone-shaped array of the EOM and the connective septa system separate the extraconal from the intraconal space. Thus the extraconal space corresponds to the compartment outside the musculofascial cone. It is bounded by the periorbita externally and by the orbital septum anteriorly. The inner side of this space is formed by the fascial EOM envelopes.

The intraconal space is retrobulbar and lies within the musculofascial cone; so its anterior base is the posterior sphere of the globe while its sides are formed by the extraocular muscle contiguous to Zinn’s Ring within the orbital apex.

The intraconal space contains the CN II, the superior & inferior division CN III (including the parasympathetic motor root to the ciliary ganglion and the ganglion itself), nasociliary branches of CN V1 including the long and short ciliary nerves and CN V1, and branches of the ophthalmic artery including the central retinal artery.

The extraconal space contains the lacrimal and frontal and extraconal branches of the nasociliary branches: ethmoidal and infratrochlear nerve (CN V1), zygomatic and infraorbital branches (CN V2), CN IV, branches of the ophthalmic artery and vein, and the lacrimal gland.

Both compartments contain abundant intraconal and extraconal fat which protects and facilitates motility. The lacrimal gland fossa can be regarded as a distinct compartment accommodating the orbital lobe of the lacrimal gland.

Adipose Body of the Orbit (ABO)

Fat, the adipose body of the orbit (ABO) is abundant within the confines of the orbital cavity [5] and around the outer orbital area. The ABO fills all spaces in the orbit left empty by the periorbita, connective tissue septa system, globe, muscles, neurovascular, lacrimal and glandular structures and represents almost half of the total orbital volume. It is not consistently unraveled yet whether the ABO is a continuous entity with ramified projections or if it is partitioned into single zones. This seems of interest because fat compartments might behave differently with aging or a disease process. The retrobulbar intraconal and extraconal part of the ABO accounts for most of the intraorbital fat.

The extraconal collection of fat continues anteriorly and distributes circumferentially around the globe (Fig. 3.28a, b). This peribulbar ABO area appears to furnish fine extensions next to the fornix margins into the upper and lower eyelids where they merge into two or three fat compartments, respectively.

2 intraoperative photographs of the left eye present dissected eyelids. 1. A surgical scissor is advanced inside the fine and transparent tissue layer. 2. Tweezers hold a fine tissue layer upward, exposing the fatty layer above the eyeball. — **Fig. 3.28**

Recently the lower, potentially also the upper, eyelid fat pads were reported as discrete compartments being separated from the posterior intraorbital ABO by kind of a fascial membrane, called the circumferential intraorbital retaining ligament. This ligamentous barrier is ascribed to the connective tissue system and the EOM pulleys. It attaches alongside the equator of the globe and along the perimeter of the orbital wall facing to it.

The quality of the ABO fat lobules, i.e., their size and shape, differs corresponding to their topography. The anterior peripheral orbital zones show a small packed and rather fibrous lobulation, while the retrobulbar central zone back into the apex presents large, egg-shaped lobules woven into a few thin fibrous septa.

Besides a cushioning function, a model of orbital mechanics based upon Finite-Element Analysis (FEA) confirms the theory that the supporting action of the orbital fat contributes to the suspension of the eyeball and to the stabilization of the rectus EOM gliding tracks.

Distinct preaponeurotic fat pockets are located directly deep to the septum.

The fat pockets are anterior extensions of extraconal orbital fat.

In the upper eyelid, two fat pockets are located anterior to the LPSM, divided in a medial and a larger central location and covered by a thin capsule. Interlobular septa are abundantly present. The lateral compartment is occupied by the lacrimal gland.

Cranial to the orbicularis muscle, the frontalis muscle is separated from the underlying periosteum by a fat pocket: the superior Retro-Orbicularis-Oculi Fat pocket (ROOF). This fat tissue extends from the supraorbital notch to the temporal ligament laterally. It is buried in a split of the deep galea layer. The fat pocket can descend into the upper eyelid through the orbicularis retaining ligament, projecting downward just anterior to the orbital septum and so behind the orbicularis muscle.

In the lower eyelid, there is a medial, central, and lateral fat pocket.

The arcuate expansion of Lockwood’s ligament spreads in between the central and lateral (temporal) fat pocket. The lateral fat pocket can be multilocular. Eisler’s “fat” pocket is a minor accessory fat pad located superficial to and immediately above Whitnall’s tubercle. The central and medial fat pockets are separated by the inferior oblique muscle (IOM).

Along the face, a system of several layers of fat pads is present. Superficially, there is the subcutaneous fat layer which is absent in the eyelids.

In the malar region, the Sub-Orbicularis-Oculi Fat (SOOF) pocket is located inferior to the inferior orbital rim. A medial component along the orbital rim, the medial SOOF is distinguished from a lateral SOOF compartment extending over the malar prominence. The lateral SOOF appears to connect by means of a temporal tunnel to the inferior temporal compartment. Superiorly it is bordered by the orbicularis retaining ligament, which separates it from the eyelid.

Neurovascular Anatomy of the Orbit

Optic Nerve (CN II)

It is essential to understand that the so called N. opticus is a white matter protrusion from the diencephalon which according to the current state of research is unlike other cranial or peripheral nerves incapable to regenerate in terms of a restitutio ad integrum. Even though a label such as “fasciculus opticus cerebralis” would appear more meaningful, the expression optic nerve is the conventional nomenclature. Each CN II is part of the afferent visual pathway (Functional Category: Special Somatic Afferent—SSA) composed of approximately 1.2 million retinal ganglion cell axons which are myelinated by oligodendrocytes posterior to the lamina cribrosa. CN II passes from the globe and the orbit via the optic canal to the optic chiasm with a total length of 45–50 mm and can be divided into four zones: intraocular, intraorbital, intracanalicular, and intracranial.

The intraocular component or optic nerve head (optic papilla) is only 1 mm thick. The axons leaving the retina to form the optic nerve posteriorly exit through the perforations in the sclera (lamina cribrosa) and become myelinated.

The intraorbital CN II portion or retrobulbar segment is 3–4 mm in diameter and 25–30 mm long. This portion runs a serptine course to cover the 20 mm spatial distance between the optic foramen and the posterior pole of the eyeball. This reserve length allows for movement and a certain limit of distension. Before entry into the canal, CN II passes through the superomedial annular foramen of Zinn’s ring. Meningeal layers (pia mater, arachnoidea, dura) envelope the CN II along its intraorbital and intracanalicular course. The subarachnoidal space around CN II contains cerebrospinal fluid and communicates with the intracranial subarachnoidal space (chiasmal cistern).The central retinal artery, originating from the ophthalmic artery, and an accompanying vein pierce the dural nerve sheath from inferomedially some 5–15 mm posterior to the globe, advance within the subarachnoid space, and penetrate the nerve stroma in a vertical direction on their way to the retina.

The intracanalicular CN II inside the LWS (optic canal—Table 3.1) is 5–8 mm long and supplied with pial branches of the ophthalmic artery which runs along the inferolateral surface of the nerve. Within the canal, the optic nerve is vulnerable to compression.

The two intracranial CN II parts, running along the medial aspect of the anterior clinoid process travel toward the optic chiasm (Fig. 3.29). Approximately 10 mm long, they lie in the subarachnoid cistern of the optic chiasm directly beneath the frontal lobes and with the internal carotid at their lateral surfaces.

A photograph of the coronal section of a dissected anatomical specimen. It presents the contents of orbital apices and retrobulbar optic nerve segments. Some labels read I C A, S S, U V, M T, and N F. — **Fig. 3.29**

The CN II contains the afferent, sensory limb for the light reflex. Anatomically, the afferent limb consists of the retina—optic nerve—pretectal nucleus in the midbrain (level superior colliculus). The efferent limb has nerve fibers running along the CN III.

Oculomotor Nerve (CN III)

The oculomotor nucleus is located in the midbrain in the gray substance of the floor of the cerebral aqueduct; the (accesory parasympathetic) nucleus Edinger-Westphal is located dorsal to the oculomotor nucleus and provides the autonomic function of the oculomotor nerve to the intrinsic eye-musculature. The somatic portion of the oculomotor nucleus of the midbrain contains a paired topographic individual ocular muscle localization of motor neurons.

CN III exits ventrally from the brain stem in front of the pons (interpeduncular space) and once it runs lateral to the posterior clinoid process, it pierces the dura mater at the top of the clivus and enters the lateral roof of the cavernous sinus lateral to the abducens nerve. It then runs through the lateral wall of the cavernous sinus just above the trochlear nerve, lateral to the intracavernous ICA (Fig. 3.30). Anteriorly in the cavernous sinus, the oculomotor nerves receive sympathetic fibers from the superior cervical sympathetic ganglion via the ICA plexus; there is no direct functionality with the CN III, however small branches communicate with the CN III as it passes through the cavernous sinus, finally reaching the end organ: the superior tarsal muscle, i.e., Müller’s muscle.

2 diagrams of the cavernous sinus. Diagram on the left presents the internal carotid artery and carotid plexus. Diagram on the right presents anterior clinoid process, C N 4, C N 3, n V 1, C N 6, and n V 2. — **Fig. 3.30**

It enters the orbit through the central part of the SOF (Table 3.1), the superolateral or oculomotor foramen of Zinn’s ring close to the lateral surface of the optic strut (Figs. 3.20, 3.21b, and 3.23).

Table 3.1 Bony openings related to neuro and vascular anatomy

Full size table

The nerve splits into its two divisions within the SOF or sometimes in the anterior cavernous sinus already. The CN III innervates all EOM as well as the LPSM: functional category – General Somatic Efferent (GSE). The smaller superior division passes the oculomotor foramen next to the tendinous attachment of the superior rectus muscle and sends branches to the ocular (inferior) surfaces in the posterior third of the SRM and LPSM. The nerve fibers pass medially around the superior rectus muscle to insert into the LPSM.

The larger inferior division, as it enters the intraconal space divides in the orbital apex into the following three subdivisions: medial, central, and lateral, which initially all run lateral to the optic nerve. The medial branch crosses beneath the optic nerve to reach the ocular (lateral) surface of the MRM in its posterior third. The central branch runs anteriorly to innervate the IRM from its ocular (superior) surface, again posteriorly. The lateral branch is the longest and travels anteriorly along the lateral border of the IRM to enter the IOM near its midpoint (Fig. 3.23). The latter branch carries the parasympathetic fibers (functional category: General Visceral Efferent—GVE) which, after synapsing in the ciliary ganglion, continue within the short ciliary nerves to:

The involuntary musculus sphincter pupillae (pupillary constriction)
The involuntary ciliary muscle (accommodation control)
Regulate the flow of aqueous humor into Schlemm’s canal
Carry sensory proprioceptive neurons from the IOM which run with the lateral branch of the inferior CN III division

The CN III is responsible for the efferent limb of the light reflex: pretectal nucleus—Edinger Westphal (midbrain)—preganglionic parasympathetic fibers—ciliary ganglion (synapse)—postganglionic fibers—ciliary sphincter: control of the diameter of the pupil to regulate the light intensity entering the eye.

Clinical Implications

Interference of the oculomotor nerve results in a downward and outward deviation of the globe (functioning superior oblique and lateral rectus muscle) including ipsilateral ptosis of the upper eyelid. The pupil is dilated without reaction (direct and consensual) to light (musculus sphincter-constrictor pupillae) or accommodation (ciliary muscle).

The branch to the inferior oblique muscle is just underneath the periorbit and at risk for lesions by compression when the soft tissues are elevated e.g., lacerations of the periorbita during exploration of the orbital floor. The intraoperative mydriasis is not necessarily a direct effect from irritation of the ciliary ganglion but also from the compression of its parasympathetic root which derives from the CN III branch to the inferior oblique muscle. This parasympathetic root is located more anteriorly than the ciliary ganglion (compare Ciliary ganglion section).

Trochlear Nerve (CN IV)

CN IV is the single cranial nerve emerging from the dorsal aspect of the brain stem. It has the smallest caliber of all CNs and the longest intracranial course of approximately 40 mm; it is a somatic efferent nerve (functional category - GSE) that innervates the SOM. From the inferior tectal lamina, CN IV is curving around the cerebral peduncle above the pons and along the free edge of the cerebellar tentorium. The dura is penetrated inferior and lateral to the entry point of CN III into the cavernous sinus. Due to this long pathway [55], CN IV appears particularly vulnerable to injury from blunt head trauma.

Within the lateral sinus wall, CN IV moves up continuously on its way forward to finally cross over CN III before entrance into the SOF (Fig. 3.23). It runs outside Zinn’s ring, in classical terms through the superolateral narrow portion of the SOF (Table 3.1), accompanied by the frontal and lacrimal branches from the ophthalmic trigeminal division, overlaying it at first (Fig. 3.21b). Along its intraorbital course, CN IV remains entirely extraconal. The frontal and lacrimal nerves move to the lateral side of the CN IV. From a superomedial position in the orbital apex, CN IV turns medially across or rarely piercing the LPSM to run on the orbital (superolateral) SOM surface. The neuromuscular junction is commonly situated on the extraconal IOM surface in the posterior or middle one-third of the muscle. CN IV may separate consecutively in up to four branches with two branches in the majority. A recent study indicates that CN IV is not always a pure motor nerve but occasionally has a mixed nerve fiber composition conveying motor and sensory (nociceptive) information.

Clinical Implications

As CN IV partly runs adjacent to the medial bony wall, the nerve is prone for injury in case of midfacial trauma.

Trigeminal Nerve (CN V)

Somatosensory Innervation of the Orbit

The trigeminal nerve CN V represents the major sensory nerve of the face. Its sensory ganglion (synonym: Gasserian or semilunar ganglion) is seated in an impression near the apex of the petrous bone in the middle cranial fossa.

“Meckel’s cave” is a dural pocket that contains the sensory and motor roots of the trigeminal nerve, the trigeminal ganglion, and the trigeminal cistern.

The sensory nerves of the orbit come from the ophthalmic trigeminal division (V1) for the main part. The maxillary division (V2) contributes the zygomatic nerve and the infraorbital nerve, which pass through the inferior and lateral orbit.

Trigeminal Ophthalmic Division (CN V1)—Ophthalmic Nerve

The trigeminal ophthalmic division (CN V1) is the smallest of the three peripheral trigeminal divisions.

CN V1 is responsible for the sensory innervation of the eye [56], orbit, ocular adnexa, and forehead above the palpebral fissure, nasal dorsum and sidewalls, upper nasal cavity including the septum, ethmoid, sphenoid, frontal sinuses, and anterior cranial fossa. Of particular note is the cornea which is the most densely innervated tissue in the human body.

Within the lateral wall of the cavernous sinus, the ophthalmic nerve branches into the lacrimal, frontal, and nasociliary nerves which enter the orbit through the SOF. The lacrimal and frontal nerves run outside Zinn’s ring, the nasociliary nerve passes through the superolateral foramen of the ring.

The nasociliary nerve, inside the apex sends out a communicating branch, the sensory root as well as sympathetic fibers, to the ciliary ganglion. The sympathetic axons travel anteriorly in the orbit via the nasociliary and lacrimal nerves to innervate the sympathetic eyelid muscles; sensory fibers are carried from the iris, ciliary body, and cornea.

To arrive in the superomedial orbit, the nasociliary nerve exits the muscle cone in the interspace between the MRM below and the SOM and SRM above. Joined with branches of the ophthalmic artery, the anterior and posterior ethmoidal nasociliary nerve branches leave the orbit through the same named foramina. The terminal branch of the nasociliary is the infratrochlear nerve (ITN). This advances inferior to the SOM and trochlea to the medial palpebral commissure, where it splits into multiple terminal ramifications to the eyelid, lacrimal sac, caruncule, and the external nose. It exchanges fibers with the supratrochlear nerve (STN), the terminal branch of the frontal nerve.

The frontal nerve (FN), the largest CN V1 branch, runs outside Zinn’s ring (Fig. 3.21b) and passes through the narrow superior lateral SOF sector on the medial side of the lacrimal nerve, below the trochlear \nerve (CN IV) and above the superior ophthalmic vein. The frontal nerve runs forward on top of the LPSM surface covered by the periorbita just below the longitudinal midline of the orbital roof (Fig. 3.31). At this level, the nerve bifurcates into the supraorbital and supratrochlear nerves. The supraorbital nerve maintains the forwards course of the frontal nerve now on top of the LPSM and exits the orbit at the supraorbital notch or foramen. Its terminal branches, a singular lateral deep branch and several superficial branches fanning out medially, bundle sensory fibers from the middle upper eyelid, the conjunctiva, eyebrows, forehead, and scalp as far back as to the vertex. Compared with the supraorbital, the supratrochlear nerve has a smaller diameter. It turns medially and passes above the trochlea to leave the supraorbital rim medially of the supraorbital nerve either through a foramen or notch. It receives fibers from the medial upper eyelid and brow, lateral glabellar region, and the lower forehead up to the midline. The main branches of the FN and SON run deep to the orbicularis oculi muscle, from the supraorbital notch to the superior border of the tarsal plate. The STN and ITN run between the orbicularis muscle and the overlying skin. The lacrimal nerve continues to run forward between the orbicularis oculi muscle and the tarsal plate. The upper eyelid is primarily supplied by the SON and the FN while the medial extension is supplied by the STN and ITN and the lateral extension mainly by the lacrimal nerve.

A photograph of a dissected eye in an anatomical specimen. It presents a lateral view of the exposed orbital contents. L R M, S R M, O A, P E A, C N 2, C G, and N C N are labeled posterior to the orbit of an eye. — **Fig. 3.31**

The intraorbital course, the occurrence, form, and position of the nerve exit points as well as the extraorbital distribution of both the surpraorbital and supratrochlear nerves and their branches/subbranches are highly diverse and the subject of numerous recent studies in the context of corneal neurotization, migraine surgery, and cosmetic filler injections.

The lacrimal nerve (LN), the smallest branch of CN V1 runs outside Zinn’s ring and passes the SOF on the lateral side of the frontal nerve. Its course in the superolateral orbital quadrant follows the superior border of the LRM. It provides the sensory innervation to the lacrimal gland, conjunctiva, and is variably involved in the parasympathetic secretomotor supply of the gland (see later). After switchover in the pterygopalatine ganglion, the postsynaptic parasympathetic fibers are carried within the zygomatic (= CN V2 branch) and zygomaticotemporal (ZTN) nerves to join the lacrimal sensory nerve across a communicating branch before they enter the gland. Different from this, least frequently occurring in classic textbook descriptions, a direct entry of the ZTN without a preceeding communication to the lacrimal nerve appears as the most commonly found variant. A dual connection via provision of a communicating branch to the lacrimal nerve and a direct ZTN contact to the gland takes the second place in frequency.

Trigeminal Maxillary Division (CN V2)—Maxillary Nerve

The maxillary nerve carries sensory information from the lower eyelid, the cheek, upper lip, anterior upper gingiva, nasal, palatal, pharyngeal mucosa, and maxillary, ethmoid, and sphenoid sinus.

After giving off the middle meningeal nerve once it leaves the Gasserian ganglion, the CN V2 enters the pterygopalatine fossa through the foramen rotundum and splits into three major branches: sphenopalatine nerve, the infraorbital nerve, and the zygomatic nerve; the zygomatic nerve may also divert from the infraorbital nerve during its course in the pterygoid fossa on its way toward the IOF.

The sphenopalatine (pterygopalatine) nerve courses straight downward. Some branches pass through the pterygopalatine ganglion without synapses, the main part continues below the ganglion and enters the pterygopalatine canal.

The infraorbital nerve, having reached the pterygopalatine fossa, turns anterolaterally to pass through the IOF sinkhole or the infratemporal fossa, respectively to ascend immediately toward the posterior end of the infraorbital groove. The opening to the groove is situated just below the bone level of the orbital floor. Running anteriorly, in the midorbit the infraorbital groove becomes roofed and converts into the infraorbital canal. The canal is minimally longer (average 14 mm; range 5–22 mm) than the groove (average 13 mm; range 7–22 mm). On its way anteriorly, the canal descends from the orbital floor progressively into the maxillary sinus. The common axis of the groove and canal follows a slight forward curvature with a posterolateral start from just anterior of the IOF isthmus directed to the infraorbital foramen as an anteromedial emerging point. As mentioned alongside this passage, the infraorbital nerve is accompanied by the infraorbital artery giving off multiple small branches (perforator vessels to IRM) from the open upside of the groove (Fig. 3.32). Inside the canal portion, the nerve delivers the middle and anterior superior alveolar rami. Outside the infraorbital foramen, the infraorbital nerve splits into a fan of branches, the inferior palpebral, the superior labial, and the internal and external nasal rami (Fig. 3.33).

A photograph of an anatomic specimen presents the orbital contents. Horizontal branches of muscles and nerves are exposed below the orbit. An inset presents a diagram of the skull highlighting the arteries below the orbit. — **Fig. 3.32**

A photograph of an anatomic specimen presents a dissected face. It exposes curved fat pads below both the eyelids, a dissected nose, and fine nerve branches on both cheeks. — **Fig. 3.33**

Parasympathetic and sympathetic fibers are associated with the course of the infraorbital nerve.

The arterial strand divides into several smaller branches which perforate to the periorbita and the rectus muscle along the top side of the infraorbital groove. These branches must be meticulously cauterized during subperiorbital dissection away from the orbital floor.

If not handled with great care, these perforater branches can be responsible for the occurrence of a retrobulbar hematoma, i.e., orbital compartment syndrome (Chap. 13).

The zygomatic nerve is a branch of the maxillary nerve (CN V2). It may appear to be a branch of the infraorbital nerve, exiting either just before or while the infraorbital nerve traverses the IOF.

The zygomatic nerve deviates laterally already beneath the IOF and periorbita level to turn toward the inside of the lateral orbital wall, entering the zygomatico-orbital foramen where it may subdivide into the zygomaticofacial (ZFN) and zygomaticotemporal (ZTN) nerves, departing the orbit (Table 3.1). The ZFN and ZTN may differ in their course and mutual conversion during the depart and exit between varying constellations and numbers of foramina inside and outside the orbital cavity. According to their openings at the facial and temporal surface of the zygoma, the nerves are sensory for a skin territory in the upper cheek, lateral lower eyelid, and lower temple.

Clinical Implications

In a superior orbital fissure (SOF) syndrome [57, 58], the neural structures passing through the fissure may be involved to a different degree. In the complete clinical picture, the combination of motor impairment due to CN III–CN IV–CN VI lesions results in ophthalmoplegia and subsequently proptosis due to decreased tension of the EOM. Ptosis will occur due to loss of function of the LPSM & loss of sympathetic input to Müllers superior tarsal muscle (long ciliary nerves). Focus impairment (loss of accommodation) and a fixed, dilated pupil (loss of parasympathetic innervation by ciliary nerves—inferior div. CN III to ciliary and sphincter pupillae muscle) are present. The corneal reflex is absent due to loss of afferent input (long-short ciliary nerves) from the CN V1 (ophthalmic division).There is paresthesia of the upper eyelid and lacrimal hyposecretion (CN V1 frontal, lacrimal, and nasociliary branches) (Fracture sites compare—Fig. 3.34a, b). Loss of vision indicates involvement of the orbital apex (superomedial foramen of Zinn’s ring) and the condition is called orbital apex syndrome.

2 illustrations present fractures in the wing of a sphenoid. Illustration 1 presents a lateral fracture while illustration 2 presents a medial fracture. — **Fig. 3.34**

Abducens Nerve (CN VI)

The abducens nerve exits the brain stem ventrally at the pontomedullary junction. The neurons arise in the paired motor nuclei in the pons. After an ascending prepontine intracranial course, it pierces the dura of the posterior cranial fossa on the clivus. CN VI advances from its petroclival entrance point surrounded by a dural sleeve which is situated in between the sphenopetroclival venous confluence and the lateral wall of the cavernous sinus. CN VI runs rather in the body then in the lateral wall of the cavernous sinus (Fig. 3.30). The sleeve represents a short osteofibrous tube named Dorello’s canal, which passes below the butterfly-shaped petrosphenoid ligament. The vulnerability of CN VI in severe cranial and cervical trauma or by increased intracranial pressure cerebral herniation and downward migration of the brainstem is attributed to its firm rostral tethering within Dorello’s canal. Within the cavernous sinus, CN VI continues forward on the lateral side of the posterior vertical segment of the internal carotid artery and medial to the ophthalmic nerve (CN V1) (Fig. 3.30). The SOF is passed inside the superolateral part of Zinn’s ring inferior to the superior CN III divison, inferolateral to the nasociliary nerve, and lateral to the inferior CN III division (Table 3.1). In the orbital apex, CN VI shifts laterally to spread several subbranches along the ocular (medial) LRM aspect (Figs. 3.23, 3.26, 3.31). The neuromuscular junction is located in the posterior or middle one-third of the muscle. Sympathetic fibers are carried along with CN VI.

Just as CN III and CN IV, the abducens carries sensory fibers from proprioceptive receptors in the EOM.

Clinical Implications

Because of its long and tortuous course along the cranial base, the CN VI is vulnerable especially for compressive and/or traumatic injuries, intracranial tumor lesions, and infections [59].

Since CN VI does not lie within the lateral wall of the sinus as do the oculomotor and trochlear nerves but runs in the sinus itself lateral to the internal carotid artery, it is generally affected first in case of increased pressure within the cavernous sinus (Fig. 3.30). Sympathetic fibers from the carotid plexus to the dilator pupillae muscle run with the abducens for a short distance: thus a fixed pupillary constriction in combination with abducens palsy may occur.

Autonomic Nervous System

The autonomic nervous system of the orbit and eye has many functional tasks, which are mediated via parasympathetic and sympathetic pathways and their interrelated or antagonistic action:

Pupil dilatation/constriction
Control of ocular accommodation
Influence on light reflex circuits and convergence
Width control of the palpebral aperture (STM and ITM)
Regulation of intraocular pressure—aqueous humor homeostasis
Modulation of lacrimal secretion—tear flow production
Control of ocular blood flow

Parasympathetic Pathways

The head has four parasympathetic ganglia: the ciliary-, the pterygopalatine-, the otic ganglion and the submandibular ganglion. The orbita related ciliary- and pterygopalatine ganglion will be discussed.

Parasympathetic innervation of the eyes commences from two origins:

Edinger Westphal Nucleus (EWN):

EWN is the accessory subdivision of CN III nucleus lying in the rostral mesencephalon.
Superior Salivatory Nucleus (SSN):

SSN is the parasympathetic (lacrimal) constituent of CN VII nucleus lying in the medulla oblongata.

The preganglionic neurons originating in EWN gather with the oculomotor nerve, to proceed along the “IIIrd CN Parasympathetic Pathway,” to the ciliary ganglion (CG) and synapse there to their postganglionic projections via short ciliary nerves.

The preganglionic neurons from the SSN course within the intermediate nerve (parasympathetic and sensory part of CN VII) to the geniculate ganglion and along the greater petrosal nerve following the “VIIth CN Parasympathetic Pathway” to synapse in the pterygopalatine ganglion (PPG). The greater petrosal nerve unites with the deep petrosal nerve, which consists of postganglionic sympathetic fibers from the ICA plexus, to form the pterygoid nerve (Vidian) inside the same-named canal. On this way, the fibers for the parasympathetic root as well as for the sympathetic root are conveyed to the PPG.

The sensory fibers of the maxillary nerve directly pass the PPG without synaptic contacts except for some short fibers which constitute the sensory root of the PPG. Vasodilator and secretomotor fibers from PPG are distributed conjoining with the sensory branches of the maxillary nerve (zygomatic nerve [− occasionally communicating with lacrimal nerve], greater and lesser palatine nerves, the nasopalatine, and the pharyngeal nerve) to the lacrimal gland and mucous membranes of the nose, hard palate, upper lip and gums, soft palate, tonsils, and upper part of the pharynx, respectively.

The IOF provides the intraorbital entrance for the “VIIth CN parasympathetic pathway” and postganglionic sympathetic fibers.

Sympathetic Pathways

The sympathetic innervation starts from the posterolateral hypothalamus and descends inferomedial cell column of the gray substance extending within the C8–T2 segments of the spinal cord. The neurons give rise to preganglionic fibers that connect to the paravertebral sympathetic chain ganglia and continue to ascend in the sympathetic trunk to the superior cervical ganglion (SCG) where they synapse. The complete sympathetic supply of the head emerges from SCG.

The final postganglionic sympathetic pathways follow the ICA through the foramen lacerum/carotid canal into the cavernous sinus, the departure region for the terminal passage into the orbit [60] is both through the optic canal and the SOF.

Still proximal to Zinn’s ring, a plexus of sympathetic nerve surrounds the ophthalmic artery. The main sympathetic access route into the orbit is by means of the sensory ophthalmic nerve branches (CN V1)—frontal, lacrimal, and nasociliary, while the extraocular motor nerves—oculomotor (CN III), trochlear (CN IV), abducens (CN VI), and the ophthalmic artery plexus are only partly involved in the sympathetic supply. Orbital arteries are closely associated with orbital sensory nerves.

The nasociliary nerve trunk gives off small sympathetic ramifications traveling anteriorly toward the ophthalmic artery, the extraocular motor nerves, and the CG.

The tunica media muscle layers of the ophthalmic artery and all branches including the central retinal artery, frontal artery, and lacrimal artery, are innervated by sympathetic axons in contrast to the venous drainage system (superior ophthalmic vein). This suggests sympathetic control of the arterial flow within the eye and orbit.

The common path of extraocular motor nerves and sympathetic fibers may be explainable by the provision of sympathetic input for the regulation of the MRM and LRM muscle pulleys.

The long ciliary nerves (from the nasocliary nerve) carry sympathetic axons anteriorly through the suprachoroidal space to innervate the ciliary body, iris (dilator pupillae), and trabecular meshwork.

Apart from sympathetic nasociliary branches, the CG receives sympathetic fibers directly from extensions of the ICA plexus and the ophthalmic artery.

The delicate fascicles of the short ciliary nerves arise from the CG and transport these sympathetic nerve fibers as well as parasympathetic fibers. While the parasympathetic fibers innervate the ciliary body (i.e., ciliary muscle) and iris (sphincter pupillae), the sympathetic fiber subset is nonspecific and provides vasoconstriction for the uveal blood vessels. The ocular adnexal structures such as the tarsal muscles and lacrimal gland are further destinations of sympathetic efferents in the orbit.

The sympathetic innervation to the superior (Müller) and inferior tarsal muscles [61] derives most likely from the lacrimal and infratrochlear branches of the ophthalmic nerve. The long ciliary nerves bring in additional sympathetic supply to Müllers superior tarsal muscle. The perivascular sympathetic plexus around the lacrimal artery continues with the vasculature into the lacrimal gland and appears to modulate its secretory function by regulation of the blood flow and direct innervation of the acini. Moreover some sympathetic fibers pass along the external carotid artery, through the pterygopalatine fossa to enter the orbit with the maxillary artery and the infraorbital nerve.

Sympathetic innervation of the inferior orbitalis muscle of Müller, the smooth muscle across the IOF and adding to the inferior tarsal muscle is conveyed from the PPG and travels along branches of the infraorbital nerve, such as the zygomatic nerve.

Clinical Implications

Horner’s syndrome [59, 62, 63] is caused by an interruption of the oculosympathetic pathway (pointed out above). Depending on the extra-, intracranial or intraorbital location of the “sympathetic disruption,” it may result in ipsilateral miosis (pupillary constriction/anisocoria due to paresis of dilatator muscle) and mild ptosis (due to paresis of Müller’s superior tarsal muscle), both contributing to pseudoenophthalmus (sinking back of the eye in the orbit). Ipsilateral impairment of sweating and vasoconstriction in the face (facial anhidrosis) ensues from damage at the thoracic/cervical level. In contrast, lesions at the height above the superior cervical ganglion—after the sudomotor and vasomotor fibers have branched off—show only limited involvement of the face.

Important note: Careful observation will reveal that the reaction of the pupils to direct and consensual light and to accommodation is preserved since these functional circuitries do not rely on sympathetic nerve action.

Ciliary Ganglion (CG)

The CG represents one of the four (submandibular, otic, pterygoplatatine and ciliary ganglia) parasympathetic cranial ganglia, and is associated with the ophthalmic division of the CN V (nasociliary) and the inferior division of CN III.

It is the pre-postganglionic relay center of the “IIIrd CN Parasympathetic Pathway.”

CG lies embedded in fat at the orbital apex, between the lateral aspect of CN II and the LRM most often in the midhalf between Zinn’s ring and the back of the eyeball, 1 cm anterior to the SOF (Fig. 3.31).

There are numerous variations in size, shape, number, and location of CG [64].

So it can have a round, ovoid or an irregular, star-like flattened shape. The mean size approximates to 2.5 mm in horizontal diameter, 1.5 mm in vertical height, and 0.5–1 mm in thickness.

Rarely the CG may be located in close contact with the inferior division of the oculomotor nerve (Fig. 3.35). It is most often located lateral to the CN II, variable in the area between retrobulbar and ventral to the maxillary strut, i.e., apex orbitae (Fig. 3.36).

A lateral-view illustration of a face presents the orbital contents. The nerves, muscles, and glands are labeled around the orbit. — **Fig. 3.35**

A diagram of an eye presents the location of the ciliary ganglion. It labels 5%, 55%, 37.5%, and 2.5% from inside out on the medial rectus. — **Fig. 3.36**

The CG has inputs by sensory, parasympathetic, and sympathetic fiber projections, which join it from the posterior aspect and why they are named roots; it is associated with roots from the nasociliary (CN V1) and oculomotor nerve (CN III) as well as with direct sympathetic rami from the internal carotid plexus (Fig. 3.37).

A diagram presents the nerve system of an eye. The orthosympathetic pathway is indicated between the cornea and the maxillary vein. The parasympathetic pathway is indicated between the pterygopalatine ganglion and the zygomaticotemporal vein. Ciliary ganglion actions are also illustrated. — **Fig. 3.37**

The sensory CG root is provided by a single branch diverting from the nasociliary nerve (CN V1) proximal to Zinn’s ring. It carries sensory fibers from the globe as short posterior ciliary nerves, which convey sensation from the eyeball and cornea, enters the ciliary ganglion, and without synapse transmits to the nasociliary nerve. Some sensory fibers directly enter the nasociliary nerve within the long ciliary nerves.

The parasympathetic or so called motor CG root consists of a commonly single fiber strand leaving from the inferior division of the oculomotor nerve (CN III) or more specifically from its longest branch supplying the inferior oblique muscle.

Within the CG, the preganglionic parasympathetic fibers synapse (Fig. 3.37). The postganglionic parasympathetic output passes into the short ciliary nerves numbering up to 20 branches. In their initial course, the short ciliary nerves stay in a lateral position to CN II; finally they pierce the sclera at the posterior globe close to the entrance of the optic nerve. Within the globe, they run anteriorly in the suprachoroidal space, innervating the ciliary muscle (regulation of ocular accommodation) while a minor (3–5%) portion innervates the sphincter pupillae muscle (regulation of pupil constriction).

The sympathetic CG root fibers arise from the carotid plexus, pass the SOF, and travel through the ciliary ganglion without synapsing to assort within the short posterior ciliary nerves. They are in charge of vasoconstriction of the uveal vasculature. Some other sympathetic fibers travel with the nasociliary nerve initially and proceed as long posterior ciliary nerves to the superior tarsal muscle (Müller) and dilatator pupillae muscle, as mentioned above (Fig. 3.37).

Clinical Implications

The knowledge of the anatomic functional basis of pupillary control is important in orbital surgery. During intraorbital surgery, too much pressure may be exerted within the orbital apex, i.e., next to the ciliary ganglion.

Parasympathetic fibers synapse in the ciliary ganglion and continue within the short ciliary nerves to innervate the sphincter pupillae. The sympathetic fibers cross the ciliary ganglion uninterruptedly and continue as well in the short ciliary nerves but have no relevance for pupillary function.

Increased pressure during intraorbital procedures within the orbital apex next to the ciliary ganglion may lead to interferences with the synapting parasympathetic CG fibers. It is assumed that the parasympathetic synapses within the CG are particularly susceptible to pressure, what may result in pupillary dilatation.

To distinguish whether the function of the CN II is affected or not in case of intraoperative mydriasis, the swinging flashlight test can be carried out. When a flashlight is shown onto the eye with the dilated pupil, pupillary constriction will result in the opposite eye provided that CN II function is intact. When the flashlight is swung over to the undisturbed contralateral eye, this will react with pupillary constriction, while the pupil of the affected eye will remain wide. This confirms an undisturbed bilateral CN II Function and impairment of the CG or CN III as the cause of the mydriasis.

Intraoperative mydriasis may also be due to compression of the parasympathetic CG root which derives from the CN III branch to the inferior oblique muscle (Figs. 3.31 and 3.37). This parasympathetic root is located more anteriorly than the CG.

CN III lesions proximal of the CG, involvement of the CG synaptic sites or compression of the distal parasympathetic CG root cannot be differed intraoperatively.

Intraoperative pupillary dilatation must be appreciated as a specific warning sign of too much and/or too long pressure on the delicate neurovascular orbital tissue portions. If this pressure continues, it may eventually result in a dilated pupil (sphincter pupillae muscle disturbance) and may occur in combination with a loss of the accommodation reflex owing to CN III paresis or ciliary muscle disturbance, what constitutes a serious permanent complication.

Adie’s myotonic pupil (Holmes-Adie Syndrome) is the result of postganglionic parasympathetic denervation in the CG. The reaction of the abnormally mid-dilated pupil to light is sluggish and poor and much less than the response to accommodation. The pupil remains constricted and will dilate very slowly only.

So there is a light-near dissociation, though the accommodation is impaired (tonic near constriction and hyperopia). Other features may consist of decreased deep tendon reflexes secondary to degeneration of dorsal root ganglia in the spinal cord.

Pterygopalatine Ganglion (PPG)

The PPG also known as sphenopalatine, nasal or Meckel’s ganglion is the largest cranial parasympathetic ganglion and the pre-postganglionic switchover of the “VIIth CN Parasympathetic Pathway” (Figs. 3.37, 3.38, and 3.39). It receives input from a sensory, parasympathetic, and sympathetic roots, which reach it via the maxillary nerve branches and the pterygoid (Vidian) nerve. It is located in the pterygopalatine fossa [65], where it lies lateral to the sphenopalatine foramen, medial to the foramen rotundum and anterior to the aperture of the pterygoid (Vidian) canal.

A photograph of an anatomical specimen presents the dissected head and eye. It exposes the muscles, nerves, arteries, and contents labeled L R M, I R M, O A, N L D, M A S, H P, D P N, P O A T, D P N, P P G, C N, V 2, C 5, I C A, and C N 2. — **Fig. 3.38**

A photograph of an anatomical specimen presents the pterygopalatine ganglion. It exposes the muscles, nerves, arteries, and ganglion. Labels read L R M, O N, M R M, I C A, and D P N. — **Fig. 3.39**

Looking from the front to the bony orbit, the PPG projects medio-posteriorly underneath the orbital process of the palatine bone where it clings along the transition from the perpendicular plate.

It can be of oval, triangular or square shape with a mean size of 5 mm in horizontal and 6.5 mm in vertical dimension. PPG may be bipartite and there may be a number of associated microganglia.

The sensory PPG root connections descend from the maxillary division of the trigeminal nerve (CN V2 and rr. ganglionares n. maxillaris) after entering the pterygopalatine fossa (PPF) through the foramen rotundum (Fig. 3.39). These maxillary rami pass the PPG and do not synapse. In the PPF, they emerge as nasopalatine, pharyngeal, greater and lesser palatine nerves. Together these nerves conduct sensation (General Somatosensory Afferents—GSA) from the mucosa of the hard palate, upper gums, soft palate, tonsils, and the naso- and upper orpharyngeal walls.

The parasympathetic PPG root is brought about by the nerve of the pterygoid canal (Vidian). The Vidian nerve enters the PPF posteriorly and conglomerates with the PPG (Figs. 3.38 and 3.39). Within the PPG, the preganglionic parasympathetic fibers originating from the greater petrosal partition of the Vidian nerve synapse with postganglionic parasympathetic secretomotor neurons, which meet with the maxillary and ophthalmic divisions of the trigeminal nerve (CN V1 and V2) to travel to their destinations in the mucosa of the nasal cavity, naso- and oropharynx, and the upper oral cavity as well as to the lacrimal gland. The parasympathetic supply to the lacrimal gland is presently debated and may be reached within the zygomatic nerve, the ZTN, and possibly the lacrimal nerve itself.

The sympathetic PPG root corresponds to fibers from the deep petrosal nerve having made their way within the Vidian nerve. These postganglionic sympathetic fibers traverse the PPG interruptedly. They are mainly distributed to the nasal and pharyngeal mucosa with a few fibers reaching the lacrimal gland.

Sympathetic innervation to Müller’s inferior orbital muscle and to the inferior tarsal muscle derives from the PPG via the infraorbital nerve CN V2. Among the numerous PPG outlets, there are delicate sensory orbital rami which are supplemented by sympathetic fibers from the ICP. This doublet leaves into the orbital apex and forms the retroorbital plexus, which again send out fine rami eventually targeting for the lacrimal gland.

Arterial Supply to the Orbit

The arterial system supplying the orbit, eyeball, and adnexa features an extensive collateral circulation system interconnecting the branches of the ophthalmic artery (OA) originating from the internal carotid artery (ICA) and linking with the external carotid artery (ECA) [66].

The ICA-/ECA-derived network is set up in between the:

Frontal branches of superficial temporal artery—supraorbital/supratrochlear arteries
Facial/angular artery—medial palpebral/dosal nasal arteries
Maxillary/sphenopalatine artery—ethmoid arteries
Transverse facial and deep temporal artery—lacrimal artery

External Carotid Artery (ECA)

The infraorbital artery, one of the terminal branches of the maxillary artery represents the only direct supply of the ECA system to the orbit. It leaves from the pterygopalatine fossa and enters the orbit through the IOF (Table 3.1) to follow the same course as the infraorbital nerve (CN V2). During passage through the infraorbital groove, it gives off small branches (perforators) extending into the fat and muscles (IRM and IOM) of the lower orbit (Fig. 3.32a, b).

The middle meningeal artery (MMA), another terminal branch of the maxillary artery, that enters the middle cranial fossa through the foramen spinosum may connect via a recurrent meningeal branch of the lacrimal artery (LA) or give off the OA. The recurrent vessel connection is oriented backward and passes through the outermost part of the superior lateral SOF sector or a distinctive foramen in the greater wing of the sphenoid (GWS) lying anterolaterally to the upper end of the SOF, which is called the meningo-orbital or cranio-orbital foramen (COF). The direction of flow for an aberrant OA is downstream from the MMA, of course.

Internal Carotid Artery (ICA)

Ophthalmic Artery (OA)

The OA is the primary source of arterial blood supply to the orbit. In general, it is the first intracranial branch of the ICA and exits off from superomedial convexity of the supraclinoid/ophthalmic ICA segment (C 6) in the subarachnoid space above the cavernous sinus. At this origin, the OA lies medial to the anterior clinoid process [67] and on the inferior side of CN II.

Within the optic canal (Table 3.1), the artery is fixed to the dural sheath and still kept in an inferolateral position. The orbit is entered through the supermedial foramen of Zinn’s ring. Different from this typical textbook arrangement, some variants can be encountered in terms of the OA following a separate course through an additional proximal access foramen to the optic canal or through a duplicate bony passage below the canal. As a special feature the OA and or the lacrimal artery (LA) can arise from the middle meningeal artery (MMA) [68] (Fig. 3.40a–c).

3 diagrams present the origin of O A and L A in the orbit of an eye. The arteries and nerves are labeled. — **Fig. 3.40**

Or the OA and LA may loop between the ICA and the MMA (Fig. 3.40c) as a baseline for all other branches. The OA may also be duplicated. In as much as the OA exclusively exits from the MMA, the entire arterial supply of the orbit will depend on the ECA. Therefore an arterial branch traversing a GWS foramen or the upper lateral end of the SOF occurring during a deep lateral periorbital dissection should be preserved unless its provenance is clarified beyond any possible doubt.

The vessel variations [69, 70] are reflected in diversified courses through the bony gateways (superior lateral SOF sector and/or COF). In the rare case that the MMA originates from the OA instead of the maxillary artery, the foramen spinosum will not exist.

Once inside the orbital apex, the OA typically crosses over the CN II from a posterolateral to an anteromedial location between the MRM and the SOM.

The intraorbital course of the OA is characterized by tortuosity and extensive arborization (Figs. 3.31 and 3.41).

The branches and subbranches can be grouped according to their topography (orbital, ocular, extraorbital) and supply area, based on the site of origin from the stem vessel (medial, lateral, etc.) or in line with their sequence of origin (orbital apex toward aditus/rims, initial to terminal branches). In a posterior–anterior direction, the OA distributes the following branches (Fig. 3.41).

Central Retinal Artery (CRA): is the first ocular branch from the OA originating at the ramification of the OA and the lacrimal artery near the anterior orbital apex. The CRA turns inferiorly to pierce the optic nerve sheath from its lower-medial aspect.

The distance from the CN II/eyeball junction posteriorly to the CRA entry point into the CN II sheath is between 7 and 10.5 mm. The CRA travels then a short distance in the subarachnoid space and zigzags vertically into the nerve stroma and forward again to the optic disc.
Posterior Ciliary Arteries: two or infrequently three lateral and medial long posterior ciliary arteries (lpca) originate from the lacrimal artery and/or from the OA itself. These vessels pass forward next to CN II, enter the sclera, and course between choroid and sclera around the lateral and medial orbital circumference to reach and penetrate the ciliary muscle. By anastomoses among one another and with the anterior ciliary arteries, they form the greater arterial circle of the iris. A bundle of 15–20 short posterior ciliary arteries (spca) emanates from the long posterior ciliary nerves near the posterior globe and pierces the sclera in a ring around CN II (= Zinn-Haller ring) and branches to supply the choroid and the optic nerve.
Muscular Arterial Branches to Rectus EOMs and Anterior Ciliary Arteries: the muscle arteries (m) for the rectus musculature depart in the proximity of the OA and lacrimal artery divergence. They run forward along the ocular surfaces or inside the muscular substance to enter the globe at the scleral tendinous insertions. Here the muscular branches subdivide into pairs of anterior ciliary branches except for the LRM, which carries only one anterior ciliary artery. The Lacrimal Artery (LA): an early larger branch diverges laterally into the superotemporal orbit at the OA crossing site over CN II. LA first runs intraconally, then accompanies the lacrimal nerve (CN V1) along the superior LRM border and distributes to the lacrimal gland, and to the conjunctiva and lids in the lateral corner of the eye via the superior and inferior lateral palpebral arteries. Proximal to the lacrimal gland, already a descending branch divides into the zygomaticotemporal and zygomaticofacial arteries. These run along the lateral orbital wall and exit the orbit together with the homonymous nerves (ZTN and ZFN) through the respective foramina.

The lateral long posterior ciliary artery branches off medially to parallel CN II together with the medial long posterior ciliary artery.

The recurrent meningeal artery branch returns laterally to communicate with a frontal branch of the middle meningeal artery (MMA) via the SOF or the COF.

Supraorbital artery (SA): is given off from the OA at the crossroads over CN II. It courses with the supraorbital nerve (CN V1) on top of the LPSM underneath the periorbita to leave the orbit through the supraorbital notch or foramen to the skin of the eyebrows and forehead.
Ethmoidal Arteries: the posterior ethmoidal artery (PEA) and the anterior ethmoidal artery (AEA) rise from the OA along its anterior course vis-a-vis the medial orbital wall in transverse direction with a given distance in between them. The vessels penetrate the periorbita to enter their foramina at the frontoethmoidal suture together with the homonymous nasociliary nerve branches (CN V1). PEA usually passes over the SOM or between the MRM and SOM. It is variable in size, topographic location, and may even be absent.

The AEA is a more constant and somewhat larger vessel. It runs between the MRM and SOM. The AEA is the first transverse element to be encountered in a subperiorbital dissection of the superonasal quadrant.

Inside the ethmoid, it ascends to enter the upper nasal cavity and to penetrate the roof to direct across the anterior cranial fossa to the cribriform plate.

Both the AEA and PEA (Fig. 3.31) are supplemented with anastomoses via the sphenopalatine artery as well as the angular/facial artery provide the blood supply of a widespread area, the entire ethmoidal sinuses, the infundibulum of the frontal sinus, the upper nasal cavity including the septum and the skin over the cartilaginous nasal vault with additional descending branches.
Medial Palpebral Arteries: the superior and inferior medial palpebral arteries arise from the OA below the trochlea and descend to the lacrimal sac and the upper and lower eyelids, where they form rows of marginal and peripheral arcades connecting with the lateral palpebral arteries of the LA.
Frontonasal artery: corresponds to the distal OA end that splits into the following terminal branches.
Supratrochlear artery: it runs above the trochlea and over the medial upper orbital rim to the paramedian forehead (formerly known as medial frontal artery).
Dorsal nasal artery: it comes to lie midway in between the trochlea and the medial canthal tendon and continues anteriorly for the supply of the lacrimal sac and the skin of the nasal sidewall and dorsum.

Venous Outflow of the Orbit

The venous drainage from the orbit [71, 72] can be organized into three routes—upstream return into the cavernous sinus, downward return into the pterygoid plexus, and anterior leave by communication with the venous system of the face. The veins of the orbit are suggested to be valveless. Other than the veins elsewhere in the body, the orbital veins are not as closely associated with their arterial counterparts.

Two principal venous systems and their tributaries deal with the outflow from distinct distributions: the superior ophthalmic vein (SOV) drains the superomedial orbit, whereas the inferior ophthalmic vein (IOV) drains the inferolateral orbit (Fig. 3.42).

Nasofrontal Vein: corresponds to the confluence of the supratrochlear and angular veins and their union to the SOV.
Superior Ophthalmic Vein (SOV): begins medially above the anterior eyeball in continuation of the nasofrontal, passes the SOF (Table 3.1), and empties into the cavernous sinus. In the anterior section, the course of the SOV coincides with parts of the OA.

The SOV passes backward alongside the trochlea and the SOM. It crosses above CN II toward the lateral SRM border to bend down into the lateral orbital apex, which it leaves between the heads of the SRM and LRM for the SOF. Usually the SOF runs through the narrow superior lateral sector outside Zinn’s ring. At the SOF level, the SOV meets with the IOV. Fused to a common conduit, they merge with the anteroinferior extensions of the cavernous sinus.
Ethmoidal Veins: most often there are two veins paralleling their corresponding arteries over some part. The anterior ethmoidal vein drains into the SOV, the posterior ethmoidal vein joins a venous webbing under the orbital roof.
Muscular Venous Branches from the EOMs: The venous branches from SOM and SRM consistently drain into the SOV. The MRM and LRM branches may drain into the SOV, IOV or lacrimal vein (LV).The IRM and IOM branches connect to the venous plexus relating to the orbital floor.
Vorticose/Vortex veins (VVs): a set of commonly four, occasionally up to eight VVs drain the choroid. Each eyeball quadrant has at least one VV emanating posterior of the prime meridian. The superior medial VV empties either into the SOV or the lacrimal vein LA. The inferior medial and lateral VVs feed into the SOV or IOV either separately or joined together.
Lacrimal Vein: accompanies the LA and usually opens into the SOV from the lateral side further posteriorly than the other tributaries. It may be large enough to rank as a third main orbital vein, in particular if it enters the cavernous sinus separately. It is usually joined by muscular branches from the SRM and LRM and by a vortex vein.
Collateral Veins: the upper and lower orbital venous divisions communicate via several collateral veins. They all run a course from the floor to the roof. With regard to their topographical position inside the orbit, they are called anterior, medial, lateral, and posterior collateral veins.
Ciliary Veins: accompany their corresponding arteries. The anterior ciliary veins drain the ciliary body and greater circle of the iris into the muscular branches.
Central Retinal Vein: leaves the meningeal optic nerve sheath nearer behind the globe than the central retinal artery and passes into the orbital apex to open directly into the cavernous sinus or less frequently into the SOV, IOV or posterior collateral vein.
Inferior Ophthalmic Vein (IOV): develops from the posterior end of a venous plexus which relates to the orbital floor by covering around the IRM and underneath CN II in the midorbit. The anterior part of the plexus receives the VVs from the lower globe hemisphere and inferior muscular branches, the posterior part connects with the collateral veins.

The IOV runs posteriorly in parallel to the CN III branch to the IOM and to the IRM, respectively before it may divide into two or three branches. A consistent superior branch passes into the cavernous sinus in common with the SOV. Another direct branch connects to the cavernous sinus through the inferior SOF sector below Zinn’s ring. A variable third lower branch may communicate with the pterygoid plexus through the IOF.

The infraorbital vein accompanies the infraorbital artery and nerve. It passes along the canal/grove and through the IOF (Table 3.1) to drain into the pterygoid plexus. Its tributaries emerge from tissues close to the orbital floor and communication with the IOV.

A diagram of the orbit of an eye with exposed arteries and branches. Some of the labeled branches are medial posterior ciliary, posterior ethmoidal, lateral posterior ciliary, and lateral palpebral. — **Fig. 3.41**

Clinical Implications

The IOV and/or SOV are the terminations of the angular vein plexus from the facial vein system; since the majority of these veins are valveless permitting flow in both directions, it has long been assumed that dentofacial infections may easily spread along these veins in a retrograde fashion into the cavernous sinus carrying the risk of a cavernous sinus thrombosis. Recently, it has been shown that various vascular mechanisms in the head & neck region may be involved in the context of inadvertent spread of cosmetic facial fillers and embolic material into the orbit [73]. There is a rich interconnection of anatomic territories (angiosomes) which are linked together by functional anastomotic (“choke”) vessels. So links between the ophthalmic-, facial-, superficial temporal-, and maxillary arteries are present. A plexus of a large caliber facial venous network drains into the orbits along the inner canthus concurrently with arteriovenous shunting and true anastomoses between ophthalmic artery—angular facial artery. According to current hypothesis, different vascular pathways—separately or in combination—may contribute to the spread of infectious emboli into the cavernous sinus and dural veins.

Cavernous Sinus

The cavernous sinus (CS) (Figs. 3.30 and 3.42) or the “lateral sellar compartment” belongs to the cranial dural venous sinuses [72, 74, 75]. The paired CS expand on each side of the sella turcica, the pituitary gland, and the lateral aspect of the sphenoid body including the adjacent part above the petrous apex. The architecture of the CS walls is composed of meningeal and periosteal/periorbital layers [76]. The CS walls surround a system of three longitudinal venous axes and the C4 segment of the ICA with a sympathetic nerve plexus around it. The oculomotor (CN III), trochlear (CN IV), and ophthalmic nerves (CN V1) course in the lateral wall (Fig. 3.30). The abducens nerve (CN VI) passes forward within the sinus in between the medial side of CN V1 and the lateral side the ICA. The longitudinal “intermediate venous axis” laying between the ICA and cranial nerves contributes to the venous drainage from the directly adjacent orbit [77]. The sinus is larger posteriorly and gets more narrow anteriorly, where it reaches into the orbital apex at the SOF [78]. The lower SOF margin, made up by the junction of the sphenoid body and GWS, is located at the same level as the lower acute angled CS edge. The medial and lateral CS walls meet along the lower edge, so that the sinus obtains a triangular cross section. The lower CS edge extends from across the base of the GWS to the lateral border of the dorsum sellae leaning against the lateral margin of the sella turcica. The transitional region between the orbital apex and the lateral sellar compartment via the SOF has been conceptualized in terms of a “lateral sellar orbital junction” (LSOJ) which is situated in the wide inferomedial SOF portion. According to the LSOJ concept, the SOF is not a mere portal but a three-dimensional structure contributing to a sequence of compartments from the cone of the orbital apex over a neural compartment into the intracranial venous compartment corresponding to the cavernous sinus. The PPF has an extension via the IOF and the SOF. Though it is addressed as the pterygopalatine compartment subjacent to the LSOJ, it is not counted as a constituent of it.

Lymphatic Drainage

In the eyelids, lymphatic drainage [79, 80] is restricted to the region anterior to the orbital septum and provided by a superficial pretarsal and a deep posttarsal system.

The superficial system drains the lymph fluid from the OOM and the overlying skin.

The deep system drains the tarsus and conjunctiva. Drainage is into preauricular and submandibular nodes. The retaining ligament at the infraorbital rim separates lymphatic drainage locations: lower eyelid edema stops “acutely” at the rim.

Orbital edema resolves via the conjunctival lymphatic system. Edema in the posterior orbit drains into the cavernous sinus, also carrying the risk of infectious spread intracranially and the risk of cavernous sinus thrombosis.

The retina and cornea lack lymphatic vessel systems.

Periorbital Dissection—Deep Orbit Versus Rule of Halves: 24 to 12 to 6

The anterior IOF loop has been proposed as an anatomic landmark to define the point of entrance into the deep orbit in post-traumatic surgical dissection and repair, with the two arguments that the frontal orbital cross section begins to taper backward continuously from there on, making a subperiosteal (periorbital) dissection progressively difficult and with the high frequency at which it is involved by relevant traumatic defects.

The concept of the deep orbit [81] suggests using the following four hard and soft tissue structures for orientation and pathfinding during dissection of the inferior and lateral wall: infraorbital nerve (canal groove/sulcus)/IOF / GWS (central trigone part/sphenotemporal buttress) / upper plate of the orbital process of the palatine bone.

These structures concenter at the confluence of the orbit, which corresponds to the area in direct proximity of the IOF isthmus.

Often, orbital depth gauging data derived from anthropometric studies cannot provide appropriate guidelines for safe distance dissection because of variation, particularly in trauma due to severe multifragmentation, displacement, soft tissue disruption, and fat herniation. So, the preference is to dissection in a subperiosteal (subperiorbital) plane to identify the leading structures [82, 83]. Apart from the EF, the medial orbit does not feature any reliable orientation aid to prevent interference with the optic foramen and the optic nerve [84].

Despite the well-known uncertainties in terms of number and zonal location of the EF, their potential distances in relation to the lacrimal crest, among each other, and to the optic foramen (Fig. 3.43a) are referred to by a well-known mnemonic, the rule of halves: 24 mm to 12 mm to 6 mm by Rontal [85] brings one to remind the distances (Fig. 3.43b) [81].

A diagram of the orbit of an eye with exposed vessels. The labels read superior ophthalmic, cavernous sinus, inferior ophthalmic, and vortex. — **Fig. 3.42**

2 illustrations. 1. A photograph of an anatomical specimen with downward-pointing arrows labeled O F C, P E C, I E F, and A E F. 2. A 3D model of medial orbital wall presents 3 measurements of distances labeled 6, 12, and 24 millimeters. — **Fig. 3.43**

Conclusion

Anatomy has and will always be one of the most important and challenging fundaments of Medicine. Its contribution is indispensable.

When surgery is performed, knowledge of basic anatomy is a conditio sine qua non.

We realize that this chapter on soft tissue in and around the orbit is far from complete. The different types of tissues involved in the orbital contents are highly complex. Even today, despite the tremendous amount of existing information accumulated by well-respected medical researchers in the past, new insights are still continuously coming. We have presented a brief compilation of some anatomic issues here and hope that it will supply the reader with useful information to facilitate surgical interventions within the orbit.

Change history

20 March 2024
A correction has been published.

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AcknowledgementsSpecial thanks to Dr. Serge Steenen who has taken care of drawing several illustrations in this Chap. 3, in which he tried to reflect anatomical reality in a truthful manner. Big thanks go to Gerhard Poetzel and Rudolf Herzig, the photographers at the OMFS Departments, LMU Munich, for their excellent support in editing the anatomic images.

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Department of Oral and Maxillofacial Surgery, Amphia Hospital Breda, Breda, The Netherlands
Peter J. J. Gooris
Amsterdam University Medical Centers, Amsterdam, The Netherlands
Peter J. J. Gooris
Department of Oral and Maxillofacial Surgery, University of Washington, Seattle, WA, USA
Peter J. J. Gooris
Department of Oral and Maxillofacial Surgery, Facial Plastic Surgery, Ludwig Maximilians University, Munich, Bavaria, Germany
Carl-Peter Cornelius

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Affiliate Professor, Department of Oral and Maxillofacial Surgery, Amphia Hospital Breda, Breda, The Netherlands
Peter J.J. Gooris
Professor Emeritus, Department of Ophthalmology, Amsterdam University Medical Centers, Location AMC, Amsterdam, The Netherlands
Maarten P. Mourits
Professor, Department of Oral and Maxillofacial Surgery, Amphia Hospital Breda, Breda, The Netherlands
J.Eelco Bergsma

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Gooris, P.J.J., Cornelius, CP. (2023). Anatomy of the Orbit: Overall Aspects of the Peri- and Intra Orbital Soft Tissues. In: Gooris, P.J., Mourits, M.P., Bergsma, J. (eds) Surgery in and around the Orbit. Springer, Cham. https://doi.org/10.1007/978-3-031-40697-3_3

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DOI: https://doi.org/10.1007/978-3-031-40697-3_3
Published: 29 December 2023
Publisher Name: Springer, Cham
Print ISBN: 978-3-031-40696-6
Online ISBN: 978-3-031-40697-3
eBook Packages: MedicineMedicine (R0)

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Anatomy of the Orbit: Overall Aspects of the Peri- and Intra Orbital Soft Tissues

Abstract

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Anatomy of the Orbit and Periorbital Region

Orbit

Orbital Anatomy

Keywords

Introduction

The Protective Curtain System of the Ocular Globe

The Eyelids

Tarsal Plates

Motor Innervation Eyelids

Clinical Implications

Upper Eyelid

Musculature

Clinical Implications

Whitnall’s Ligament

Lower Eyelid

Lid Retractors

Clinical Implications

Canthal Ligaments

Medial Canthal Ligament (MCL)

Lateral Canthal Ligament (LCL)

The Periorbita and Orbital Septum

Periorbita

Orbital Septum

Lacrimal Functional Unit

Tear Producing Glands

Main and Accessory Aqueous Lacrimal Glands

Conjunctival Goblet Cell (CGC) Population

Tarsal Glands

Ciliary Glands

Ocular Tear Film

Lacrimal Drainage Pathway—Nasolacrimal Sac/Duct

Plica Semilunaris

Lacrimal Caruncle

Clinical Implications

The Ocular Globe

The Globe—Gross Anatomical Outline/Overview

Clinical Implications

Zinn’s Ring and Extraocular Muscle System

Zinn’s Ring

Clinical Implications

Topographic Spaces of the Orbit

Adipose Body of the Orbit (ABO)

Neurovascular Anatomy of the Orbit

Optic Nerve (CN II)

Oculomotor Nerve (CN III)

Clinical Implications

Trochlear Nerve (CN IV)

Clinical Implications

Trigeminal Nerve (CN V)

Somatosensory Innervation of the Orbit

Trigeminal Ophthalmic Division (CN V1)—Ophthalmic Nerve

Trigeminal Maxillary Division (CN V2)—Maxillary Nerve

Clinical Implications

Abducens Nerve (CN VI)

Clinical Implications

Autonomic Nervous System

Parasympathetic Pathways

Sympathetic Pathways

Clinical Implications

Ciliary Ganglion (CG)

Clinical Implications

Pterygopalatine Ganglion (PPG)

Arterial Supply to the Orbit

External Carotid Artery (ECA)

Internal Carotid Artery (ICA)

Ophthalmic Artery (OA)

Venous Outflow of the Orbit

Clinical Implications

Cavernous Sinus

Lymphatic Drainage

Periorbital Dissection—Deep Orbit Versus Rule of Halves: 24 to 12 to 6

Conclusion

Change history

20 March 2024

References

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