Traumatic Optic Neuropathy
A 44-year-old male sustained a fall with right brow injury about 3 weeks prior to admission to a local hospital for visual loss in the right eye. He received intravenous pulse steroid therapy for 3 days under the impression of traumatic optic neuropathy OD. His vision did not improve much after therapy. He came to our clinic for a second opinion. His best-corrected visual acuity was hand motion at 15 cm OD and 6/6 OS. Intraocular pressures and anterior segments were normal on exam. There was a relative afferent pupillary defect (RAPD) in the right eye. Ophthalmoscopic examination showed mild optic disc pallor in the right eye (Fig. 6.1). OCT showed mild thinning of the peripapillary retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GC-IPL) in the right eye when compared to the left eye (Fig. 6.2). One month later, his vision remained stable, but both the peripapillary RNFL and macular GC-IPL were shown to be moderately impaired (Fig. 6.3).
6.1 Case Report
Traumatic optic neuropathy (TON) is an optic nerve injury caused by either direct or indirect trauma . In direct TON, the optic nerve axons or its vascular supply is directly injured by mechanical forces such as avulsion by stretching injury, transection by penetrating injury, or compression by hematoma . Indirect TON refers to optic nerve injury caused by impact distant from the optic nerve . The exact mechanism of injury is not understood but is presumed to be due to the transmission of forces from a blunt head concussion or injury to the region of the optic canal, without any overt damage to the surrounding tissue structures. The impact is most commonly located over the temporal brow region. Because the optic nerve dura is tightly adhered to the periosteum of the optic canal, the intracanalicular segment of the optic nerve is highly susceptible to the concussive forces and tissue edema arising from possible resultant optic nerve compartment syndrome [1, 3, 4].
Indirect TON is an uncommon event with an approximate incidence of 2.3% in patients with head injuries . The injury can sometimes be subtle, making gathering a thorough history critical . Ophthalmoscopic examination demonstrates reduced visual acuity spanning a wide range, depending on the severity of the injury. Color vision is typically affected. An assessment of the visual field will usually show central scotoma or a totally obscured field. Relative afferent pupillary defect (RAPD) can be seen on the side of the lesion but is generally absent in bilateral symmetric cases. RAPD is an important indication of optic nerve injury, especially at early phase without any optic disc changes. The optic disc is commonly normal in appearance initially, though pallor or atrophy may develop 4–6 weeks later [1, 2]. Sometimes, disc swelling with hemorrhage may occur. OCT may detect a slight increase of peripapillary retinal nerve fiber layer (RNFL) thickness in the initial 2 weeks in severe cases, and this is commonly followed by eventual progression to an atrophic state . Visual evoked potential (VEP) is usually not needed to establish the diagnosis but could be helpful in questionable cases .
6.2.1 Diagnostic Tests
CT and plain X-rays are helpful to detect optic canal fractures or other associated findings such as orbital fractures, intraorbital or intraocular foreign bodies, and orbital or optic nerve sheath hematomas. In addition, prior literature has described an association between radiographic findings of posterior orbital fractures and poorer prognoses for indirect TON; this may be helpful to keep in mind for treatment planning . On the other hand, studies have indicated that neither the presence nor absence of an optic canal fracture seems to correlate with a severity of visual loss or visual prognosis [8, 9].
6.2.2 Differential Diagnosis
RAPD sign and OCT examination are important findings that help to establish the diagnosis. Malingering should be considered in the differential diagnosis. A fogging test may help in detecting true acuity in cases of suspected malingering (please refer to Chap. 53).
In cases of optic canal fractures with fragments of bone incarcerated in the optic nerve or optic nerve sheath hematoma compressing the nerve, surgery is indicated to remove the bone chip and drain the hemorrhage [1, 10, 11]. However, in patients with a normal CT scan of orbit and optic nerves, controversy exists regarding the optimal treatment for indirect TON. There are several treatment options as follows: (1) clinical observation alone, (2) systemic steroids, and (3) surgical decompression of the optic canal. Systemic steroids and optic canal decompression do not provide better visual outcomes when compared to each other or to clinical observation alone and may even result in potential side effects [1, 2, 8, 9, 10, 11].
Election of optic canal decompression is dependent on the expertise available locally and has generally shifted toward an endoscopic approach recently . When considering the use of steroids for treatment, the possible benefits and side effects should be clearly explained to patients. However, a few conditions like concurrent severe craniofacial injury, CSF leakage, or conscious disturbance are contraindicated/unsuitable for high-dose steroids [1, 13, 14, 15].
Indirect TON typically has a relatively high spontaneous recovery rate of up to 57% . However, many patients still end up with poor vision. Baseline visual acuity is the most important prognostic indicator , as it reflects the severity of the traumatic impact. Other prognostic factors for poor outcome include no light perception at presentation, loss of consciousness, lack of visual recovery after 48 h, and the presence of blood in posterior ethmoidal cells .
Tests for TON: visual acuity, RAPD, visual field, and CT scan of orbit.
Management: clinical observation, systemic steroids, and optic canal decompression.
Protect your patients and others: explain clearly the benefits and side effects of treatment options.
DO NOT use high-dose steroids in patients with concurrent severe brain injuries.
Follow up visual acuity and visual field.
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