Diplopia

Abstract

Binocular single vision is based upon the fusion of two retinal images, one perceived by each eye, into a single percept. This phenomenon is called fusion, one of the stages of an intricate system of processes taking place in the brain. In order to direct our eyes to a focus of attention, six extraocular muscles per eye—each innervated by three extracranial nerves—control ocular movement. This operating system can be disrupted easily. Orbital diseases may impede the function of these muscles and nerves leading to strabismus and, eventually, (gaze-dependent) diplopia.

Orthoptic investigation and diagnosis can help in the treatment of this group of patients. Orthoptic investigation is constructed by several steps which will lead to a full picture of the binocular system, and includes determining ocular deviation, binocular function, and ocular motility.

Based upon these results, the orthoptist may provide temporary measures, such as prisms or occlusion to lessen the burden of diplopia. In case of lasting diplopia, strabismus surgery can alleviate part of this diplopia. However, restricted eye movements, incomitant deviation, and severe cyclotorsion may hamper the field of binocular single vision, even despite the availability of various surgical options. Careful explanation and a multidisciplinary treatment of orbital patients is necessary to guide them through the treatment process.

FormalPara Learning Objectives

• Diplopia can be either monocular, binocular, or gaze dependent.

• Be aware of the possibility of pre-existing strabismus.

• The absence of diplopia in an individual does not automatically imply that this person has binocular single vision.

• Careful examination of the ocular movements is necessary to differentiate neurogenic from mechanic causes of diplopia and to diagnose any pre-existing strabismus.

• During follow-up, patients may be helped with some form of occlusion or Fresnel prisms to prevent diplopia.

• Different surgical procedures are available to create a useful field of binocular single vision.

• If a significant amount of cyclotorsion is measured, a poorer prognosis for both adjusting to the Fresnel prism as well as for the outcome of strabismus surgery is given.

• A full field of binocular single vision may not be reached despite surgical treatment in patients with orbital pathology.

Introduction

Each of us has double vision. Our eyes allow us to see the world as it is; our minds allow us to see the world as it can be.—Patti Dawn Swansson

The perception of depth through the use of two eyes is a naturally occurring visual process, which is often taken for granted. The importance of binocular single vision becomes painfully apparent once it is lost. Once a diagnosis is made, requiring quick surgical or medicinal intervention and especially in case of multidisciplinary approach, the complexity of diplopia often fades into the background. However, the basis of the binocular system plays an important role during the course of treatment, especially when different medical specialists are to decide on the treatment, sometimes based upon the presence or absence of diplopia. Extricating the true cause of diplopia may be difficult. The orthoptist, however, is trained in examining ocular movement and binocular single vision. The orthoptist may play a crucial role in the early stages of diagnosing in orbital disorders and certainly in the follow-up through the different stages of treatment, whether conservative or surgical.

Levels of Binocular Single Vision and Diplopia

Physiology Binocular Vision: The Cyclopean Eye

Binocular single vision is the simultaneous use of both eyes to give a single mental impression in normal visual conditions. Normal binocular vision is possible when the left and right fovea fixate on the same point and there is no manifest deviation (Fig. 6.1a). The two images of both fovea are perceived as one: The brain combines the images of both eyes to a single three-dimensional percept. This combining of the two images from each fovea is called the cyclopean eye (Fig. 6.1b). Double vision occurs when either two eyes perceive two separate images or when the perceived images are of dissimilar quality (Fig. 6.1c, d). Binocular double vision or diplopia is an indication that at least both eyes perceive an image.

Fig. 6.1

(a–d) Normal binocular single vision when the candle is perceived on the fovea of the right and left eye (a) shown as one candle in the cyclopean eye (b). Diplopia when the candle is perceived on the fovea of the left eye (FOS) and point A of the right eye (AOD) (c) showing two candles in the cyclopean eye (d). OS left eye, OD right eye, FOD fovea right eye, AOD other point of right eye, FOS fovea left eye

Different Levels of Binocular Vision

Binocular single vision is the result of a complicated system that consists of several levels. The first level is simultaneous perception, i.e. the ability to perceive an image with both eyes at the same time. The second level is fusion, which is the ability to appreciate two images that are alike and to interpret them as one. The highest grade of binocular single vision is stereoscopic vision, which is the perception of relative depth of objects in space. This can be tested in a clinical setting through the use of stereoscopic tests, such as the stereofly test or the TNO stereopsis test (Fig. 6.2).

Fig. 6.2

TNO stereopsis test (a) and Titmus stereofly test (b)

Diplopia in Childhood

In order to appreciate double vision, there are several conditions that have to be met. Binocular vision must be present since the early years of childhood. If adults have strabismus since an early age, the binocular system has adjusted to this binocular abnormality. This means that the brain is used to an ocular deviation and that the visual cortex develops an adaptation called suppression. In case of suppression, an eye is able to see in monocular condition. In binocular condition, however, the suppressed eye does not consciously perceive an image.

In some cases, this suppression also leads to amblyopia, i.e. a lower visual acuity caused by a continued state of suppression, in which the visual system delays or even stops its visual development.

If there is a sudden change in eye position in children, they might perceive a double image very shortly. The plasticity of the young brain will almost immediately adapt to this new situation, in which case suppression and amblyopia arise. Objective examination is therefore crucial in young children.

Strabismus But No Diplopia

In orbital diseases, loss of binocular single vision resulting in diplopia is a common phenomenon, but loss of binocular single vision does not always result in diplopia. Examples of the absence of diplopia in combination with absent or abnormal binocular single vision are:

• 1. Pre-existing strabismus since childhood, in which case the image of the deviating eye is suppressed.

• 2. Amblyopia in one eye.

• 3. Significantly reduced visual acuity due to a coexisting eye disease.

• 4. Significant visual field defect due to a coexisting eye disease.

• 5. An ocular torticollis, i.e. patients adapt an abnormal head posture to avoid double vision.

Monocular or Binocular Diplopia

Diplopia must first be sorted in either binocular or monocular diplopia. Binocular diplopia means that there is a change in eye position of one eye relative to the other, a condition to which the patient is not used to. With one eye closed, the diplopia disappears. Monocular diplopia is a form of blurred vision, but usually considered as double vision by the patient. Monocular diplopia is in almost all causes produced by abnormalities of the ocular globe, such as the ocular surface or the ocular lens.

Acquired or Long-Standing?

Once it has been established that there is indeed binocular double vision, orthoptic examination can then clarify whether double vision is caused by long-standing or recently acquired strabismus. Strabismus that has been present since childhood is most often concomitant, i.e. an ocular deviation that remains unchanged, regardless the direction of gaze. In case of incomitant strabismus, the ocular deviation changes depending on the direction of gaze (Fig. 6.3). Examining the ocular movements will distinguish between both types of strabismus (see Eye movement). It does not mean that incomitant strabismus is always acquired. If incomitant strabismus is present without diplopia in the absence of ophthalmological abnormalities, it may be assumed to be long-standing. Whether the long-standing strabismus is concomitant or incomitant, the binocular system has adjusted to this situation, as is seen in the presence of suppression fitting the previously existing deviation.

Fig. 6.3

Straight eye position with concomitant eye movements (a) and left hypotropia with incomitant eye movements (b)

Pre-existing strabismus may be disrupted in the presence or absence of mechanical or neurogenic damage and may consequently cause diplopia. Once an eye position is changed, a patient may experience double vision just as is seen in patients with acquired strabismus without an orthoptic history. This can be explained by a previously adapted binocular system or suppression that is not sufficient anymore. Patients may not even be aware of long-standing strabismus and report it as recently acquired.

In case of acquired strabismus, the type of diplopia (horizontal, vertical, cyclotorsion, or combined) will give an indication of the involved ocular muscles. Through orthoptic examination, it is possible to specify the type of diplopia as well as to determine whether ocular motility is concomitant or incomitant. Most often it is possible to define whether motility disorders are long-standing or acquired, mechanical, or neurogenic in nature. In follow-up consultations, it is possible to record whether ocular motility is stable or changing over time.

Causes of Diplopia

The different types of diplopia may have several causes. Before orbital and often mechanic causes are assumed in orbital abnormalities, one also must consider a neurological cause of diplopia.

Diplopia Due to Head Trauma

Head trauma may lead to ocular nerve damage which is expressed as ocular muscle paralysis, such as lateral rectus paralysis in case of a nuclear lesion of the VIth cranial nerve. Even on a more peripheral level, one can find an ocular muscle paresis. The trochlear nerve (IVth cranial nerve) is most vulnerable to damage due to its long trajectory from the brainstem to the superior oblique muscle (Fig. 6.4). Either internuclear nerve failure or peripheral nerve damage will lead to an ocular motility disorder with diplopia. Nerve damage may be caused by disruption of the nerve in case of direct damage by, for example, bone fragments, bruising of a nerve by brain movement, interrupted blood supply, and/or hemorrhage or compression from or within the nerve.

Fig. 6.4

The trochlear nerve (green) passes from the midbrain onto the lateral surface of the crus of the cerebral peduncle. It runs through the lateral dural wall of the cavernous sinus, then crosses the oculomotor nerve and enters the orbit through the superior orbital fissure, above the common tendinous ring of the recti muscles. Here, it lies above the levator palpebrae superioris muscle and medial to the frontal and lacrimal nerves [1]

Diplopia is also seen in patients with superior orbital fissure syndrome, in which case the IIIrd, IVth, VIth, and Vth cranial nerves are involved in the event of bone accident in this region. In case of intraorbital damage, one may also find diplopia caused by nerve damage when near the apex of the orbit.

Of course, diplopia may be caused by direct damage to the ocular muscles as is seen in facial trauma or may be iatrogenic in nature after orbital surgery. Muscles may be contused in case of shifting bony fragments, swelling due to intramuscular hemorrhage, muscle damage due to laceration, or changed muscle mechanics due to muscle displacement. In some cases, however rare, there may even be muscle entrapment in an orbital fracture. In case of mechanical damage after an orbital blow-out fracture, the mechanism of damage leading to diplopia is quite similar to that caused by an orbital decompression operation. In case of a fracture, damage to the muscles is rarely the cause of diplopia. It may partly be due to the herniation of orbital fat and connective tissue into the surrounding sinus with subsequent traction on the muscle sheaths. In case of an orbital decompression, diplopia may be induced by means of change in the support system of the orbital content after removal of orbital walls.

Diplopia Due to Abnormal Structure

Another major cause of diplopia is the presence of an abnormal lesion in the orbit. Any abnormal volume in the region of the muscle or of the muscle itself may limit both the contraction and the relaxation of that specific movement (Fig. 6.5). Ocular muscles that have been affected by orbital pathology—such as orbital myositis, intraorbital space-occupying lesions, or inflammatory conditions such as Graves’ orbitopathy (GO)—show a change in function depending on the level of involvement. In case of mild inflammation, ocular function may not be hampered at all. However, as may be seen in GO, some patients show edema of the orbital tissue including the ocular muscles, in which case there is a structural change of muscular tissue and, hence, function and mechanics.

Fig. 6.5

MRI scan of a patient showing enlargement especially of the inferior rectus muscle of the left eye

Depending on the amount of swelling, one will find impaired muscle movement caused by tightness or contraction of the muscle. The typically enlarged eye muscles cause a limitation of eye movement in the opposite direction due to their inability to relax.

Orthoptic Investigative Procedures

In order to determine the presence and the degree of strabismus, ocular motility disorders, and/or the level of binocular single vision, the orthoptist has an array of investigative procedures to select from. At the start of the investigation, the presence of an abnormal head posture to compensate for gaze-dependent strabismus must be noted. All observations and measurements are performed with the patient assuming the primary sitting position (sitting upright, shoulders back and head upright).

Eye Position

The corneal light reflex informs about the position of the globe. Using the light reflex, an impression of the angle of deviation (strabismus) can be achieved (Fig. 6.6).

• A light reflex on the border of the pupil indicates strabismus of roughly 15°.

• A light reflex between the border of the pupil and the limbus (corneoscleral transition) indicates strabismus of about 30°.

• A light reflex on the limbus means a strabismus of about 45°.

Fig. 6.6

Symmetrical light reflex with the potential of binocular single vision

This estimation of the angle of deviation is called the ‘Hirschberg method’.

An asymmetric corneal reflex is indicative of strabismus and may be accompanied by diplopia (Fig. 6.7). We can distinguish four different types of strabismus:

• Esotropia = inward displacement of one eye.

• Exotropia = outward displacement of one eye.

• Hypertropia = upward displacement of one eye.

• Hypotropia = downward displacement of one eye.

Fig. 6.7

Asymmetrical light reflex with an exotropia (a) and hypotropia (b) of the left eye

Measurement of Strabismus

More precisely than with the Hirschberg method, the amount of deviation can be captured through the use of prism bars at several distances or even in different directions of gaze. When measuring strabismus, the prism bar is used to divert incoming light rays of a fixation light to meet the amount of ocular deviation. When combined with the cover test, the examiner can objectify the degree of strabismus. The patient is asked to fixate on a light, while the eyes are alternately covered (Fig. 6.8). If strabismus is present, an eye will have to make a corrective movement after it is uncovered. If the amount of strabismus is equal to the strength of the prism used, the movement of the eyes is neutralized. If the strength is equal to the amount of deviation, light will fall on to the fovea and an eye does not have to adjust its position upon fixation.

Fig. 6.8

Alternating cover test in combination with one prism basing temporal (in front of right eye) and the other prism basing down (in front of left eye) measuring and esodeviation and left hyperphoria or left hypertropia

Binocular Single Vision

Once strabismus has been established, one can examine the ability of binocular single vision by means of adjusting the incoming image through a prism bar. This prism bar, adjusted in the specific amount that meets the ocular deviation, will cause an image to be interpreted as one (Fig. 6.9). Once fusion has been established, one is then able to report on the ability to hold on to the single image, while changing the amount of horizontal and vertical prisms. This will, then, give rise to a horizontal and vertical fusional range. The size of this range can clarify complaints. A high range may conceal ocular deviations, whereas a small range may give rise to complaints that do not seem fitting in case of a small deviation. This fusion range helps to decide whether prisms are beneficial in alleviating diplopia during daily life (see conservative treatment).

Fig. 6.9

Prism bars in front of the patient’s eye to perceive binocular single vision

Field of Binocular Single Vision

In acquired strabismus, diplopia is often only present in some directions of gaze. In other directions of gaze, binocular single vision exists. The localization and the extent of the area of diplopia determines the inconvenience in daily life. For instance, a patient with an orbital floor fracture may have diplopia only if looking up. As the need for looking up in everyday life circumstances is limited, especially for tall people, the impact of the diplopia will be acceptable. Generally, single vision in primary (gaze straight ahead) and reading position will often be acceptable for the patient and is often the best to be obtained, i.e. in patients with severe GO.

In case a patient reports diplopia as well as binocular single vision, a field of binocular single vision can be determined and this is very useful in decision making and follow-up. A field of binocular single vision can be attained and quantified in several manners. In literature, Goldman perimetry is considered to be the golden standard (Fig. 6.10). One must keep in mind, however, that this device does not depict natural viewing conditions because of limited fusion. The measurement performed with the Harmswand or Maddox tangent screen (Fig. 6.11) results in a field of binocular single vision in more natural conditions.

Fig. 6.10

The Goldman perimeter

Fig. 6.11

The Maddox tangent screen

In either approach, the patient is asked to report at what point he/she notices diplopia. In case of Goldman perimetry, the patient is asked to follow a light from a point of single vision with his/her head fixated. In the other two approaches, the patient will be asked to move his/her head while focusing on a fixated light. The field of binocular single vision is a means of quantifying double vision. Scoring a field of binocular single vision may be done with the Sullivan score [2] (Fig. 6.12). The quantitative score ranges from 0 (no binocular single vision) to 100 (no double vision). This scoring system easily clarifies the progression of improvement (Fig. 6.13), worsening or change after surgery. The use of the Sullivan score field in combination with the field of binocular single vision simplifies progress in treatment and allows comparison between study groups accessible [3].

Fig. 6.12

Score field according to Sullivan et al. (1994) [2] for quantifying the field of binocular single vision ranging from 0 (no binocular single vision) to 100 (no double vision)

Fig. 6.13

Progress of the field of binocular single vision during follow-up measurements. White = binocular single vision; pink = diplopia

Eye Movement

Different types of eye movements can be distinguished:

• Versions: binocular and symmetrical eye movements. Both eyes look in a particular direction and move in a synchronized manner.

• Ductions: monocular eye movement of one eye in a specific direction:

  • Abduction: temporal movement.

  • Adduction: nasal movement.

  • Elevation: upward movement.

  • Depression: downward movement.

• Concomitant: No change in ocular deviation despite change in direction (Fig. 6.3a).

• Incomitant: A change of ocular deviation per direction; one eye is restricted in its movements and the other will overcompensate while moving in the same direction (Fig. 6.3b).

To determine whether strabismus is concomitant or incomitant, the ocular deviation must be judged in the nine positions of gaze. Each ocular muscle has a different function per gaze. The axis of rotation of the normal functioning eye muscles depends on the muscle insertion to the globe. The horizontal muscles, the medial and lateral rectus, all have an almost purely horizontal action (Fig. 6.14).

Fig. 6.14

Schematic view of horizontal eye movement of the medial and lateral rectus muscles [4]

The vertical and oblique muscles, however, have a more complicated action of movement due to their oblique position on the globe; not only moving the eye up and down, but also causing movement around the visual axis of the eye, which is called cyclotorsion. The visual axis is the line that connects a point in the outside world through the center of the pupil to the fovea centralis (center) of the retina.

The vertical and oblique ocular muscles have a primary, secondary, and tertiary action (Table 6.1). Depending on the position of the ocular globe, the position of the muscle will change relative to the visual axis leading to a different action. The superior oblique muscle/tendon is at an angle of 51° with the visual axis (Fig. 6.15). This means that if the eye is adducted, the visual axis is perfect aligned with the superior oblique muscle and will have a vertical action (depression).

Table 6.1 Actions of external eye muscles in primary position [5]

Fig. 6.15

The anatomical position of the superior oblique muscle [6]

Measurement of Incomitant Strabismus

Once it has been established that there is a form of incomitant strabismus due to a motility disorder, ocular movements will have to be documented more precisely. There are three essential components of this documentation: ductions, eye position in nine directions of gaze, and cyclotorsion. These three components are necessary for a proper diagnosis as well as essential in decision making with regard to further treatment.

Ductions

Ductions are a measurement of monocular ocular movement, more specifically of the horizontal and vertical eye muscles. Muscle function can be evaluated by means of a grading system. A grading scale from −4 to +4 is often used to quantify muscle function (+ is degree of overaction, and − is degree of underaction). In this manner, oblique muscle function can also be roughly classified. This grading system is completely subjective—and therefore observer dependent—and much less precise to a deviometer such as the Goldman perimeter or a motility meter as developed by Mourits (Fig. 6.16), although the latter cannot evaluate or grade oblique muscle function. The patient follows a moving light on an arc, while the examiner pays attention to the corneal light reflex of the patient. Maximal duction is recorded from the digital screen as seen in the picture. Though much more precise, the grading is derived from an observation of the corneal light reflex and, therefore, also subjective and observer dependent. Normal values of the ductions are shown in Table 6.2.

Fig. 6.16

Motility meter developed by Mourits

Table 6.2 Normal values of ductions [7]; OD is oculus dexter, i.e. the right eye: OS is oculus sinister, i.e. the left eye

Nine Positions of Gaze

Once the function or limitation of an ocular muscle has been documented, the eye position should be measured in nine positions of gaze. This can be achieved through the use of a Maddox rod in combination with a tangent screen at 2.5 m (Figs. 6.11 and 6.17), a Hess motility screen (50 cm) or a Lancaster screen (1 m). Each will give the same result, although measured at different distances. Overaction and underaction of muscle function can be schematically depicted and followed over time (Fig. 6.18).

Fig. 6.17

Maddox rod in front of the right eye. The patient perceives a red line through the red lens of the Maddox rod. The red line is perceived on the right side of the light on the tangent screen at 2.5m in case of this esodeviation. The red line is projected onto the tangent screen at 2.5m, the distance between the light and the line can then be recorded in degrees

Fig. 6.18

Amsterdam motility diagram: The red lines are a depiction of the points of each reported placement of the red line on the tangent screen at 2.5m in the nine directions of gaze. The red lines show a right hypotropia (the circle in the middle of the square on the right side of the diagram is lower in ratio to the black lines which would be normal) in a patients with Graves’ orbitopathy caused by a restricted elevation. On right gaze the inferior oblique muscle overacts (red line formed from the circle in the middle on left side (OS) which is deviated to the right upper corner and shows the inferior oblique function), which results in an increased right hypotropia. Cyclotorsion is recorded in three directions of gaze next to the diagram. Exc excyclotorsion, OS left eye, OD right eye

Cyclotorsion

Another function of ocular motility that is essential in diagnosis and therapeutic deliberation is cyclotorsion. Cyclotorsion is a rotation of the eye around the visual axis. The majority of patients will not spontaneously report abnormal cyclotorsion, unless specifically asked for. However, cyclotorsion is often indispensable in diagnosing and plans for surgical treatment especially in acquired strabismus. Measurement of torsion is helpful in identifying oblique muscle weakness or overaction, such as can be found in acquired fourth nerve palsy in which case excyclotorsion will be found. In case of congenital strabismus, cyclotorsion will not be noticed by the patient. The presence or absence of cyclotorsion can be crucial in differentiating between congenital or acquired lesions and the need for further neurological examination. Incyclotorsion, on the other hand, is often found secondary to orbital injury or orbital surgery [8]. Measurement of cyclotorsion can be performed in different positions of gaze using the Harms tangent screen or the cycloforometer of Franceschetti (Fig. 6.19).

Fig. 6.19

The cycloforometer of Franceschetti

Evaluation

After orthoptic assessment, diagnosis, and multidisciplinary consultation, it is important to evaluate these findings in light of the patient’s experience. A patient with a field of binocular single vision of 80 points can be fully incapacitated when he/she is a plasterer and uses the remaining 20% of upper field of gaze for more than 70% of the day, while a similar patient working an administrative job will report no complaints at all, although presenting with equal measurements. Several quality-of-life questionnaires are available to quantify this.

Treatment of Diplopia

The treatment of diplopia can be either conservative or surgical.

Conservative Treatment

While waiting for spontaneous improvement, nonsurgical treatment can start once a patient is presented to the orthoptist. Primarily, three options may be considered: abnormal head posture, prisms, and occlusion.

A fourth form of treatment must be contemplated in case of orbital fractures: eye movement exercises. No clinical studies have been performed to analyze the effect of monocular eye muscle exercises in patients with orbital fracture. It is, however, the golden standard and the first line of treatment in these patients. During the first few weeks after trauma, the affected eye has to be actively moved in all gaze directions with the sound eye covered.

Abnormal Head Posture

Most patients with acquired strabismus and some form of binocular single vision will naturally adapt and assume an abnormal head posture to avoid double vision. Some patients, however, must be actively pointed to this possibility.

Prisms

In case of strabismus with diplopia, to achieve binocular single vision, a patient sometimes can be helped with prisms (Fig. 6.20). By means of a prism bar, ocular deviation can be neutralized and the particular prism strength can be prescribed. With changing deviation, Fresnel prisms (a ribbed piece of silicone foil that can be applied to the spectacle lens) can be used (Fig. 6.21). Fresnel prisms are available at a range from low to high power, both for horizontal and vertical diplopia (not for torsional diplopia).

Fig. 6.20

Exotropia of the right eye (a) with diplopia shown in the cyclopean eye (b). Prism base nasal in front of deviated eye (c) gives single vision for the patient a shown in the cyclopean eye (d)

Fig. 6.21

Fresnel prism foil on the right spectacle lens to correct horizontal diplopia

The foil is prescribed for the eye with the lowest vision and/or the most restricted eye movements. Prism foils will always lead to some amount of reduced vision due to the line pattern and hence if applied in front of the eye with the lowest vision will limit complaints. It is imperative to inform the patient about this. Even when ocular movement shows an incomitant pattern, prisms are often well accepted [9]. In theory, incomitant strabismus would require different prism strength, depending on the direction of gaze. The advantage of a Fresnel prism is that binocular single vision is restored. Once single vision is achieved, most patients can make use of their innate fusional strength to maintain this single vision in most directions. During follow-up, the strength of the Fresnel prism can be adjusted, according to the eye position. The prism can eventually be grinded into the lenses as a permanent solution.

If binocular single vision cannot be achieved by means of prisms, one must be aware of cyclotorsion hampering fusion.

Occlusion

In some unfortunate cases, no acceptable field of binocular single vision can be gained with prisms or after strabismus surgery (see explanation below). Some patients can adjust to this situation and actively ignore the second image. It may help if the vision of one eye is reduced. Diplopia can be very frustrating and extremely debilitating and, therefore, may lead to the extreme choice of permanent occlusion. This can be achieved through the use of an occlusion patch or by means of fully or partially occluding a spectacle lens (Fig. 6.22) by means of a matted foil or grinded lens. If occlusion of a spectacle lens is an unacceptable option for the patient, a painted contact lens (Fig. 6.23) or even an intraocular occlusion lens is a more sophisticated solution. Explanation has to be given that the visual field is significantly narrowed especially in case of a (intraocular)lens.

Fig. 6.22

Occlusion foil on the right spectacle glass

Fig. 6.23

Occlusion contact lens

Surgical Treatment

It is important that repeated examinations show a stable outcome before considering any surgical treatment to resolve diplopia. However, this waiting-for-stability period can be extremely frustrating from the patient’s perspective. Care professionals should be aware of this and are urged to address the reason of postponing surgery. The goal of this waiting period is to make an optimal surgical plan with a more predictable outcome based upon a stable condition. In general, at least two similar orthoptic examinations over a period of several months are necessary to decide upon which strabismus surgery is most suitable. Most authors suggest a period of 6 months of stability, this however depends on the cause of strabismus, i.e. in case of GO a stable period of 3 months can be maintained [10].

Treatment of Patients with Graves’ Orbitopathy

One of the hallmarks of GO is swelling and inflammation of one or more extraocular muscles. This often results in fibrosis and loss of power of relaxation of the involved muscles.

In GO, the severity of incomitance of ocular motility results in different treatment strategies. Recession of the most affected muscle (i.e. reinsertion of the tendon of that muscle posterior to its original insertion) is the preferred choice, rather than resection (i.e. surgically shortening of the muscle) of an unaffected muscle. Depending on the degree of angular deviation, one or two muscles are recessed. The recession of the muscle will decrease its original function, yet it will increase the opposite action. For instance, a swollen medial rectus muscle leads to an abduction deficiency. Through recession this muscle’s ability to abduct will increase, but its opposite function, adduction, will be diminished and although the horizontal duction range remains unchanged, ocular deviation will have shifted [10]. In all cases, resection of the muscle has to be avoided, since this would lower the total duction range and increase the incomitancy.

In severe cases, in which normal recessions (maximum of 5 mm) are not sufficient to correct the large angle of squint, elongation material (such as fascia lata or Tutopatch^® implants) can be used to obtain the same effect as a recession without excessive reduction of a muscle’s action [11, 12].

In approximately 70% of the GO patients that need surgery to correct their diplopia, one surgical intervention is sufficient to reach a functional field of binocular single vision [13]. However, especially in the more complex cases, a minimum of two subsequent sessions of strabismus surgery is often necessary to achieve a comfortable field of binocular single vision, e.g. in primary gaze, downgaze, and side gaze. The patient has to be informed that a full field of binocular single vision cannot be achieved.

We can distinguish a few typical ocular motility schemes in GO patients:

• GO patients with severe esotropia (esotropia of 24°) due to extensive fibrosis of both medial recti muscles: The large esodeviation is due to enlarged medial rectus muscles with limited abduction of both eyes. In the ocular motility screen, one will see the missing secondary gaze directions due to impaired ductions of both eyes (Fig. 6.24; diagram a.). Surgical plan: Recession of both medial rectus muscles is the surgery of choice [10]. Diagram 6.24b. shows the post operative result with significant improvement of the field of BSV Fig 6.24c and d.

• GO patients with a large concomitant vertical deviation (left hypertropia of 25°) due to extensive fibrosis of the inferior rectus muscle of the right eye with limited elevation and fibrosis of the superior rectus muscle of the left eye with limited depression: There is also a small esodeviation (Fig. 6.25). Surgical plan: Recession of the enlarged inferior rectus of the right eye and the superior rectus of the left eye. Diagram a of Fig. 6.25 shows the preoperative ocular deviation, diagram b shows the postoperative result.

• GO patients with abnormal head posture (chin up) due to an incomitant vertical deviation caused by asymmetric fibrotic inferior rectus muscles (Fig. 6.26): The left inferior rectus muscle is more severely affected than the right. In primary position, the patient has a left hypotropia of 9° and in downgaze no deviation. This patient perceives single vision in downgaze. Surgical plan: Asymmetrical inferior rectus muscle recession with more recession of the vertically lowered eye (left). When recession of both inferior rectus muscles is considered, one has to be aware of an increase of in cyclotorsion [14].

Fig. 6.24

Amsterdam motility diagram preoperative (a) and postoperative (b) recession of the medial rectus muscles. Field of binocular single vision before (c) and after (d) strabismus surgery. OS left eye, OD right eye, inc incyclotorsion, exc excyclotorsion

Fig. 6.25

Amsterdam motility diagram preoperative (a) and postoperative (b) inferior recession of the right eye and superior recession of the left eye. OS left eye, OD right eye, inc incyclotorsion, exc excyclotorsion

Fig. 6.26

Amsterdam motility diagram preoperative (a) and postoperative (b) asymmetrical rectus inferior recession of both eyes. OS left eye, OD right eye, inc incyclotorsion, exc excyclotorsion

Treatment of Strabismus and Diplopia in Orbital Fractures

Diplopia treatment of patients with an orbital fracture differs in several ways from patients suffering from GO. A major cause of diplopia in case of orbital trauma is edema within the orbit or within the extraocular muscles. Edema will eventually disappear. Hence, an initial wait-and-see policy is highly recommended [15, 16]. While waiting for spontaneous recovery, as mentioned earlier in this chapter, ocular eye movement exercises are key.

In case of stable orthoptic measurements, surgery can be considered. However, diplopia treatment has to follow orbital treatment. Any orbital repair can change ocular mechanics and diplopia, and this means that after orbital treatment one must again wait for orthoptic stability before deciding on further treatment of diplopia [17]. When surgical treatment is addressed, only a few options are available. In case of secondary orbital revision, any improvement of the motility should not be expected by removing or revising an implant [18]. Also, no improvement of the ductions is expected when adhesiolysis of the affected tissue is performed.

Mechanically injured, or even paretic, muscles cannot be repaired. To obtain more concomitant ocular movement and, hence, an improved field of binocular single vision, the healthy eye is the one to receive surgical treatment. In general, the overacting muscle of the other eye is recessed and/or a posterior fixation suture is placed 10–12 mm behind the insertion of the muscle (Fig. 6.27). A posterior fixation suture (e.g. Faden operation) does not affect muscle movement in primary position, but it limits an overacting muscle in the direction of its maximum action. The suture acts as a brake on the action of the healthy muscle, once the eye moves past the field of action in which the overaction takes place.

Fig. 6.27

Amsterdam motility diagram before (a) and after (b) posterior fixation suture of the superior rectus of the right eye

Case Report

A 68-year-old man with a medial wall fracture of the right orbit after head trauma is presented. He has no diplopia. As a child, he underwent strabismus surgery of his left eye. Large exotropia and small hypertropia of the left eye were observed (Fig. 6.28). The left eye showed impaired adduction (Table. 6.3). Visual acuity was 1.6 on the right versus 1.0 on the left, slightly amblyopic eye. Orthoptic diagnosis is a consecutive (preoperative esotropia) exotropia with adduction impairment in the left eye due to strabismus surgery with suppression. The impaired adduction and strabismus are not related to the orbital wall fracture on the right side. The patient renounced surgery as he, because of the lack of diplopia, did not consider his exotropia to be (cosmetically) disturbing.

Fig. 6.28

Patient photographed 1 day (a) and 3 months (b) after trauma showing an alternating exotropia and a limitation of adduction of the left eye

Table 6.3 Ductions of patient shown in Fig. 6.28. OD right eye, OS left eye

Treatment of Strabismus Causes by Other Orbital Conditions

There are numerous other orbital conditions that may affect the mechanics of ocular movement or the ocular deviation in primary position. In general, the golden rule in decision making is to reach orthoptic stability before deciding on surgical treatment to alleviate diplopia. It is important to determine the cause of the motility disorder. Treatment can then be adapted according to the principles as mentioned in the section on GO if muscles have become fibrotic. Alternatively, treatment can be adjusted in a manner as mentioned in the example of orbital fracture. There are numerous types of strabismus surgery that can improve symmetry in ocular movement, of which only a few are mentioned in this chapter.

Conclusion

Orthoptic examination is diverse and comprises of several components. Examination may lead to a different conclusion regarding the cause of diplopia as would be expected by only external impression and/or subjective experience of the patient. Although orthoptic measurement may not be leading in initial therapeutic decisions, it can be very useful in case of doubt regarding the cause, type or even the absence of diplopia in orbital pathology.

One must be aware of the complexity of binocular single vision and consider possible pre-existing strabismus, complex cyclodeviations, and mechanical abnormalities as well as neurogenic disruption of the oculomotor system once ophthalmological pathologies are eliminated as causative factors.

Orthoptists can play an important supportive role in case of extensive treatment to alleviate binocular complaints. Stability of ocular movement can only be captured through orthoptic follow-up. Orthoptic conclusions are eminent in decision making for strabismus surgery.

In light of all orthoptic measurements and therapeutic options, whether conservative or surgical, one must always remember that objective findings may be miles away from subjective complaints. Double vision may be objectified in a protocolled manner, but it should be emphasized that each patient is different in mindset and his/her meaning of life.