Ischemic Optic Neuropathy
Ischemic optic neuropathy is infarction of the optic disk. The only constant symptom is painless vision loss. Diagnosis is clinical. Treatment is ineffective.
Two varieties of optic nerve infarction exist: nonarteritic and arteritic. The nonarteritic variant occurs more frequently, typically affecting people about 50 yr and older. Vision loss tends not to be as severe as in the arteritic variant, which usually affects an older group, typically about 70 yr and older.
Most ischemic optic neuropathy is unilateral. Bilateral, sequential cases occur in about 20%, but bilateral simultaneous involvement is uncommon. Bilateral involvement is much more common among arteritic than nonarteritic cases. Atherosclerotic narrowing of the posterior ciliary arteries may predispose to nonarteritic optic nerve infarction, particularly after a hypotensive episode. Any of the inflammatory arteritides, especially giant cell arteritis, can precipitate the arteritic form.
Acute ischemia causes nerve edema, which further worsens ischemia. A small optic cup to optic disk ratio is a risk factor for nonarteritic ischemic optic neuropathy but not for the arteritic variety. Usually, no medical condition is found as the apparent cause of the nonarteritic variety, although factors contributing to atherosclerosis (eg, diabetes, smoking, hypertension), obstructive sleep apnea, certain drugs (eg, amiodarone, possibly phosphodiesterase-5 inhibitors), and hypercoagulable disorders are present in some patients and are thought to be risk factors. Vision loss on awakening leads investigators to suspect nocturnal hypotension as a potential cause of the nonarteritic variety.
Vision loss with both varieties is typically rapid (over minutes, hours, or days) and painless. Some patients notice the loss on awakening. Symptoms such as general malaise, muscle aches and pains, headaches over the temple, pain when combing hair, jaw claudication, and tenderness over the temporal artery may be present with giant cell arteritis; however, such symptoms may not occur until after vision is lost. Visual acuity is reduced, and an afferent pupillary defect is present.
The optic disk is swollen and elevated, and the swollen nerve fibers obscure the fine surface vessels of the optic nerve. Often hemorrhages surround the optic disk. The optic disk may be pale in the arteritic variety and hyperemic in the nonarteritic variety. In both varieties, visual field examination often shows a defect in the inferior and central visual fields.
Diagnosis is based mainly on clinical evaluation, but ancillary testing may be needed. Most important is to exclude the arteritic variety because the other eye is at risk if treatment is not started quickly. Immediate tests include ESR, CBC, and C-reactive protein. ESR is usually dramatically elevated in the arteritic variety, often exceeding 100 mm/h, and normal in the nonarteritic variety. CBC is done to identify thrombocytosis (> 400 × 103/µL), which adds to the positive and negative predictive value of using ESR alone.
If giant cell arteritis is suspected, temporal artery biopsy should be done as soon as feasible (at least within 1 to 2 wk because effects of the prednisone therapy may reduce the diagnostic yield of histopathology). Changes in C-reactive protein level are useful for monitoring disease activity and the response to treatment. For isolated cases of progressive vision loss, CT or MRI should be done to rule out compressive lesions.
For nonarteritic ischemic optic neuropathy, additional testing may be indicated based on the suspected cause or risk factor. For example, if patients have excessive daytime sleepiness or snoring or are obese, polysomnography should be considered to diagnose obstructive sleep apnea. If patients have vision loss on awakening, 24-h BP monitoring can be done.
The arteritic variety is treated with oral corticosteroids (prednisone 80 mg po once/day and tapered based on ESR) to protect the other eye. If vision loss is imminent, IV corticosteroids should be considered. Treatment should not be delayed while awaiting the biopsy procedure or its results. Treatment of the nonarteritic variety with aspirin or corticosteroids has not been helpful. Risk factors are controlled. Low-vision aids (eg, magnifiers, large-print devices, talking watches) may be helpful in both types.
Ischemic optic neuropathy is usually caused by giant cell arteritis or atherosclerosis.
Suspect ischemic optic neuropathy in patients 55 yr and older who have sudden, painless loss of vision.
Unless excluded, treat for giant cell arteritis to decrease the risk of contralateral involvement.
Prognosis tends to be poor.
Give corticosteroids if giant cell arteritis is possible.