or surgery for sleep apnea, or tumor management may be successful. In the case of IIH, initiation of a supervised weight loss program may diminish the need for supportive therapy.

Patients with good central visual function, no edema in the macula, and visual field changes limited to enlargement of blind spot size can be watched. The clinician should conduct visual field tests on three visits, each 1 month apart. If function is stable or improves, future visits can be spaced further apart.

Medical

At the first evidence of optic nerve compromise, patients should receive systemic medical therapy. Acetazolamide decreases cerebrospinal fluid production and is the usual first choice. The standard initial daily dosage would be 1 gram divided in two to four doses per day. If visual function stabilizes or improves within a week, continue this dose. If optic nerve function deteriorates, one may increase the dosage by a gram daily up to 4 grams total per day. Once patients exceed a gram per day, however, the side effects of gastric upset, tingling in the hands and feet, and electrolyte imbalance result in sufficient patient discomfort to lead to poor compliance. Topiramate is a new carbonic anhydrase inhibitor that may be effective. Furosemide at 40 mg twice daily is a possible alternative to acetazolamide and topiramate with fewer systemic side effects. Both medications may result in bone marrow suppression; patients should be checked by complete blood count at regular intervals to look for anemia, leukopenia, and thrombocytopenia. Both medications may also cause problems for patients with sulfonamide allergies and may cause kidney stones.

Treatment with corticosteroids is controversial. Corticosteroids may lower ICP, but potentially dangerous rebound and further elevation of ICP may occur as corticosteroids are tapered. Corticosteroids may cause weight gain and thwart a supervised weight loss program.

Surgical

Lumboperitoneal shunting or ventriculoperitoneal shunting may result in rapid improvement in patients with both headaches and visual loss.

Optic nerve sheath decompression (ONSD) may be effective but the mechanism of its effect is unclear. It is often preferred in patients with visual loss but minimal headache complaints. Decompression of one optic nerve may relieve optic disc edema in the contralateral disc but this result is not guaranteed.

REFERENCES

Corbett JJ, Jacobson DM, Mauer RC, Thompson HS: Enlargement of the blind spot caused by papilledema. Am J Ophthalmol 105:261–265, 1988.

Friedman DI, Jacobson DM: Diagnostic criteria for idiopathic intracranial hypertension. Neurology 59:1492–1495, 2002.

Galvin JA, Van Stavern GP: Clinical characterization of idiopathic intracranial hypertension at the Detroit Medical Center. J Neurol Sci 223:157–160, 2004.

Jacobson EE, Johnston IH, McCluskey P: The effect of optic nerve sheath decompression on CSF dynamics in pseudotumor cerebri. J Clin Neurosci 6:375–377, 1999.

McGirt MJ, Woodworth G, Thomas G, et al: Cerebrospinal fluid shunt placement for pseudotumor cerebri-associated intractable headache: predictors of treatment response and an analysis of long-term outcomes. J Neurosurg 101:627–632, 2004.

318 TRAUMATIC OPTIC NEUROPATHY

377.49

Leonard A. Levin, MD, PhD

Montreal, Canada and Madison, Wisconsin

Traumatic optic neuropathy is diagnosed when there is clinical evidence of an optic neuropathy that is temporally related to head or ocular trauma in the absence of another etiology.

ETIOLOGY/INCIDENCE

Traumatic optic neuropathies are generally classified by location of injury (anterior or posterior) and type of injury (direct or indirect). Because the central retinal artery and vein enter and exit the optic nerve approximately 10 mm posterior to the globe, anterior injuries are usually associated with vascular changes in the retina. More posterior injuries do not cause acute fundus changes. Anterior direct optic nerve injuries result from penetrating ocular or orbital trauma that damages the anterior optic nerve, e.g. a knife wound that transects the optic nerve. Posterior direct optic nerve injuries result from penetrating orbital or cerebral trauma that damages the posterior optic nerve, e.g. a bullet that passes just anterior to the chiasm.

Indirect injuries are caused by forces transmitted at a distance from the optic nerve, e.g. blunt head trauma without penetration. Anterior indirect injuries are usually associated with sudden rotation of the globe from blunt trauma, such as falling and hitting the eye on the corner of a table. These commonly cause partial or total avulsion of the optic nerve, with associated bleeding and central retinal artery occlusion.

Posterior indirect optic nerve injuries result from blunt head trauma, usually transmitting a concussive force to the optic nerve and resulting in contusion or even transection. There may or may not be bone fracture(s).

The most common site of posterior indirect optic nerve injury is the optic canal; the intracranial optic nerve is the next most common site of injury. Posterior indirect injury is the most common cause of traumatic optic neuropathy. There may be little or no evidence of significant head trauma; a fall from a bicycle may suffice. In most cases there is multisystem trauma or significant brain injury.

Loss of consciousness occurs in 40 to 72% of patients with traumatic optic neuropathy. Motor vehicle and bicycle accidents are the most frequent causes of traumatic optic neuropathy, accounting for 17 to 63% of cases. Traumatic optic neuropathy may also be iatrogenic, especially after maxillofacial or endoscopic surgery, as a result of inadvertent direct injury to the optic nerve or transmitted force fracturing the optic canal.

Traumatic optic neuropathy in children is similar to that in adults.

COURSE/PROGNOSIS

The prognosis for recovery from optic nerve injuries depends in part on whether the injury is direct or indirect. Direct injuries tend to produce severe and immediate visual loss with little likelihood of recovery. Patients with indirect optic neuropathies may have spontaneous visual recovery, at variable times after injury. In some cases, visual loss only begins several hours to days after the injury. If this happens, the possibility of an

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Nerve Optic • 28 SECTION

intrasheath hemorrhage should be entertained, and neuroimaging repeated.

The severity of initial visual loss in patients with traumatic optic neuropathy varies dramatically from no light perception to better than 20/20 with only a visual field defect as functional evidence of disease. Patients with only light perception vision or with no light perception are less likely to improve, regardless of therapy, than are patients with vision better than light perception.

DIAGNOSIS

Clinical signs and symptoms

Injuries to the proximal portion of the optic nerve within 10 mm of the globe, anterior to where the central retinal artery enters and the central retinal vein leaves the nerve, produce a variety of disturbances that are immediately apparent in the ocular fundus, including an ophthalmoscopic picture of a central retinal or branch artery occlusion, central retinal vein occlusion, or anterior ischemic optic neuropathy. More posterior optic nerve injuries produce no immediate change in the appearance of the ocular fundus. Almost always the optic disk remains normal in appearance for at least 3 weeks and then becomes progressively paler.

Both anterior and posterior traumatic optic neuropathies are characterized by varying degrees of visual acuity loss, decreased color vision, and visual field defects. An afferent pupillary defect should be present in all cases of traumatic optic neuropathy unless there has been symmetric injury to both optic nerves. In unconscious patients, this sign is often the only clinical evidence for a posterior optic nerve injury. Occasionally there is injury to the chiasm, in which case there may be unilateral or bilateral temporal visual field defects respecting the vertical meridian. Chiasmal injury can be seen with posterior avulsion of the optic nerve, e.g. traumatic enucleation.

Laboratory findings

Neuroimaging, particularly computed tomography (CT) scanning, is important in the evaluation of a patient with traumatic optic neuropathy. CT scanning is clearly superior to magnetic resonance imaging (MRI) in delineating fractures of bone. MRI is better for imaging soft tissue, particularly the intracranial optic nerve and chiasm, and may be useful for delineating intrasheath hemorrhage or optic nerve transection within intact meninges. CT should be done with thin sections, and reconstructions performed.

From 20 to 50% of patients with posterior traumatic optic neuropathy have evidence of an optic canal fracture by neuroimaging. Even in the absence of a fracture, blood in the sphenoid sinus should raise suspicion for optic nerve injury. MRI should be performed only after a metallic intracranial, intraorbital, or intraocular foreign body has been ruled out by CT scanning or conventional radiography.

Patients with large fractures involving the optic canal are also at risk for carotid-cavernous fistulas, and may need CT angiography.

TREATMENT

Medical

Respiratory and cardiovascular resuscitation and stabilization are the first priorities in all cases of trauma, regardless of the severity of ocular injury; thus, care of the patient with a

traumatic optic neuropathy often requires a team approach, involving emergency physicians, trauma surgeons, head and neck surgeons, neurosurgeons, and ophthalmologists. Medical therapy for traumatic optic neuropathy is controversial, as there is no evidence from good quality randomized trials to guide decision-making. Because visual function can spontaneously improve, observation without medical or surgical treatment is a valid option.

There is no evidence that medical treatment of anterior or direct optic nerve injuries is efficacious. For posterior indirect traumatic optic neuropathy, intravenous corticosteroids can be used. Some practioners use ‘megadose’ intravenous methylprednisolone, i.e., a 30 mg/kg loading dose followed by 5.4 mg/kg/ hour continuous infusion for 48 to 72 hours. However, such a large dose appears to be toxic in animals, and this approach is falling into disfavor. A dose of 250 mg methylprednisolone, administered every 6 hours for 48 to 72 hours, is probably safer. Dexamethasone may be substituted for methylprednisolone, based on one trial demonstrating its equivalency in this setting.

If medical therapy produces no improvement, surgery can be considered in centers with expertise in optic canal decompression. If vision improves with treatment, the patient is placed on oral prednisone at a tapering dose. If vision deteriorates during the taper, high-dose intravenous methylprednisolone is reinstituted, diagnostic imaging is performed, and surgical decompression is considered.

Surgical

Surgical therapy for both anterior and posterior traumatic optic neuropathy is controversial, as there is no evidence from good quality randomized trials to guide decision-making. Surgery should only be considered in centers with experience with the procedures. Because of the possibility that the carotid may be iatrogenically injured, there must be informed consent regarding the risk of death or stroke.

Surgery should not be performed on an unconscious patient because of the difficulty in assessing visual function. A possible exception is when the pupil in the affected eye is amaurotic (nonreactive to light but reactive to light in the contralateral eye). The presence of a relative afferent pupillary defect indicates only that an optic neuropathy is present; it does not indicate the severity. A patient with a relative afferent pupillary defect may have 20/20 visual acuity.

An optic nerve sheath fenestration should be performed in cases of anterior traumatic optic neuropathy associated with neuroimaging evidence of an enlarged optic nerve sheath. The procedure is performed in the hopes of evacuating an intrasheath hematoma.

Decompression of the intracanalicular optic nerve via an endoscopic transnasal or transethmoidal route may be performed in cases of traumatic posterior optic neuropathy that do not respond to a 48to 72-hour initial course of intravenous systemic corticosteroids. The procedure must include (1) removal of at least 50% of the circumference of the osseous canal, (2) removal of bone along the entire length of the canal, and (3) total longitudinal incision of the dural sheath, including the annulus of Zinn.

REFERENCES

Chuenkongkaew W, Chirapapaisan N: A prospective randomized trial of megadose methylprednisolone and high dose dexamethasone for traumatic optic neuropathy. J Med Assoc Thai 85 (5):597–603, 2002.

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patients taking oral contraceptives who developed ischemic optic neuropathy. Hemoglobin electrophoresis should be performed to exclude sickle cell anemia in young black patients with disk swelling and visual loss.

PION can occur secondarily to intracranial artery or internal carotid ophthalmic artery atherosclerosis. It may also present with tumors that disrupt the blood supply to the optic nerve. Trauma can injure the pial vessels within the optic canal that supply the optic nerve, resulting in PION. The ophthalmic artery may also be disrupted by penetrating injuries or iatrogenically during paranasal sinus surgery. The fundus then will show a cherry-red spot with massive pallid edema of the optic nerve. Optic nerve vascular damage has also been implicated in radiation-induced optic neuropathy. The exact mechanism of visual loss is very complex and includes cytopathic, chromosomal, and immunologic factors, as well as vascular compromise. The common denominator of all of these PIONs is optic atrophy without antecedent disk swelling. PION is a diagnosis of exclusion.

Differential diagnosis

●Inflammatory optic neuropathies.

●Ischemic optic neuropathies.

●Metabolic optic neuropathies.

●Toxic optic neuropathies.

●Demyelination.

●Axonal degenerations.

●Traumatic optic neuropathy.

●Normal tension glaucoma.

●Sleep apnea associated optic neuropathy.

●Cross-over syndromes.

PROPHYLAXIS

Patients are counseled against smoking. They are started on a regimen of one aspirin per day. Prolonged tapering of steroids is necessary to decrease the incidence of recurrences of GCA.

TREATMENT

Systemic

The treatment for GCA is systemic corticosteroids; there are no effective treatments for NAION. The evaluation and treatment of an elderly patient with profound visual loss, pallid edema, temporal pain, and tenderness proceeds in the following manner:

●An intravenous line is started immediately, and the patient is given 500 mg methylprednisolone IV.

●The patient is next given 150 mg ranitidine or a comparable H2 blocker or proton pump inhibitors and hospitalized. Prednisone 120 mg PO is started concurrently.

●Laboratory requests include an ESR by the Westergren method, a C reactive protein, complete blood cell count, platelets, prothrombin time, partial thromboplastin time, anticardiolipin antibodies, antinuclear antibodies, fluorescent treponemal antibody absorption test, VDRL syphilis test, electrolytes, blood urea nitrogen, and creatinine. The ESR is only one piece of information that can lead to the diagnosis of GCA; its specificity is extremely poor. Malignancies, infection, cardiovascular, and collagen-vascular diseases may raise the ESR. A rough estimate is that if the ESR is half the patient’s age plus 10 for a woman, it is

abnormal (just half the age for a man). The platelet count is extremely important. Giant cell arteritis is unlikely without thrombocytosis. Interleuken 6 can also be measured.

●Two hours after the first dose of methylprednisolone, the patient is started on a course of 250 mg methylprednisolone IV every 6 hours for 48 hours and is continued on 120 mg prednisone PO and 150 mg ranitidine b.i.d.

●If the temporal artery biopsy is positive, the patient is discharged on 120 mg/day prednisone plus ranitidine.

●Steroids are slowly tapered over a period of 6 months for healed arteritis and 24 months for active arteritis. This treatment is performed in conjunction with an internal medicine colleague or a rheumatologist. A systemic work-up is essential.

●Serial ESR and CRP results guide the tapering of steroids.

●If the biopsy is negative, steroids are tapered relatively quickly depending on the clinical suspicion as well as the ESR and CRP. Patients with persistent elevation of acute phase-reactants, such as platelets, will often need a biopsy of the temporal artery on the opposite side.

●Patients with a lower clinical probability of GCA are started on 80 mg prednisone with ranitidine, and a temporal artery biopsy is scheduled within the next several days.

●Patients with a higher probability of GCA are admitted to the hospital, started on a regime intravenous steroids and ranitidine, and scheduled for a temporal artery biopsy expeditiously.

COMPLICATIONS

Patients with hypertension and diabetes are at the highest risk for developing AION. There is a 15% incidence of a second event in the fellow eye. Eyes with small cup-to-disk ratios are at particular risk. Rarely, a patient will have a second event in the same eye.

Patients may awaken from major surgery bilaterally blind. It is important to differentiate blindness secondary to occipital strokes from blindness secondary to optic nerve infarcts. Initially, there may be no sign other than minimal optic disk swelling; however, if optic nerve infarction has occurred, pallid edema will ensue over the next 24 hours. The prognosis is very poor.

Some patients may have protein S or C deficiencies, antiphosphylipid syndrome, an antithrombic III deficiency, factor V laden deficiencies or hyperhomocystemia. Consideration should be given in consultation with a hematologist for systemic anticoagulation with warfarin. The ciliary circulation is made up of very small vessels and may respond better to Plavix or aspirin. In patients who have progressed on aspirin, Plavix is added. There are inflammation conditions that can also lead to ischemia, such as sarcoid and lupus. These cross-over syndromes require corticosteroid therapy.

COMMENTS

A prospective randomized clinical trial that compared observation with optic nerve sheath decompression showed that decompression was not effective treatment for NAION. Current treatments are designed as prophylaxis against second events, such as nicotine patches for smokers, aspirin, Plavix, lowering intraocular pressure, increasing ocular blood flow with drozol-

amide, steroids for patients whose disease includes inflammatory component, warfarin in those with coagulation defects, altering the timing of antihypertensive medication in patients with elevated blood pressure and continuous positive airway pressure in patients with sleep apnea. While 40% of patients improve, 40% also worsen.

REFERENCES

Bogen DR, Glaser JS: Ischemic optic neuropathy: the clinical profile and history. Brain 98:689–708, 1975.

Borchert M, Lessell S: Progressive and recurrent nonarteritic anterior ischemic optic neuropathy. Am J Ophthalamol 106:443–449, 1988.

Clearkin L, Caballero J: Recovery of visual function in anterior ischemic optic neuropathy due to giant cell arteritis. Am J Med 92:703–704, 1992.

Costello F, Zimmerman MB, Podhajsky PA, Hayreh SS: Role of thrombocytosis in diagnosis of giant cell arteritis and differentiation of arteritic from non-arteritic anterior ischemic optic neuropathy. Eur J Ophthalmol 14(3):245–257, 2004.

Egan R: Prothrombotic and vascular risk factors in NAION. Ophthalmology 107(12):2116–2117, 2000.

Hayreh SS: Posterior ischaemic optic neuropathy: clinical features, pathogenesis, and management. Eye 18(11):1188–1206, 2004.

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