Ischemic optic neuropathy is infarction of the optic disk. It can be arteritic or nonarteritic. The only constant symptom is painless acute vision loss. Diagnosis is clinical. Treatment for the nonarteritic variety is ineffective. Treatment for the arteritic variety does not restore vision but can help protect the unaffected eye.
Two varieties of optic nerve infarction exist: nonarteritic and arteritic.
The nonarteritic variant occurs more frequently, typically affecting people about 50 years and older. Vision loss tends not to be as severe as in the arteritic variant, which usually affects an older group, typically about 70 years 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
Symptoms and Signs of Ischemic Optic Neuropathy
Vision loss with both varieties of optic nerve infarction 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 an altitudinal and/or central defect.
Diagnosis of Ischemic Optic Neuropathy
Erythrocyte sedimentation rate (ESR), C-reactive protein, and complete blood count (CBC)
Computed tomography (CT) or magnetic resonance imaging (MRI) of the brain and orbits if vision loss is progressive
Diagnosis of optic nerve infarction 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/hour, and normal in the nonarteritic variety. C-reactive protein is also elevated and is more sensitive than ESR in diagnosing giant cell arteritis. CBC is done to identify thrombocytosis (> 400 × 103/mcL), which adds to the positive and negative predictive value of using ESR alone.
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-hour blood pressure monitoring can be done.
Prognosis for Ischemic Optic Neuropathy
There is no effective treatment for the nonarteritic variety of optic nerve infarction; however, up to 40% of patients spontaneously recover some useful vision.
In the arteritic variety caused by giant cell arteritis, losses of visual acuity and visual field are typically greater. Prompt treatment does not restore lost vision in the affected eye but protects the unaffected eye. Inadequate treatment risks relapses and additional vision loss.
Treatment of Ischemic Optic Neuropathy
Pearls & Pitfalls
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Treatment reference
1. Stone JH, Tuckwell K, Dimonaco S, et alN Engl J Med 377(4):317-328, 2017. doi: 10.1056/NEJMoa1613849
Key Points
Ischemic optic neuropathy is usually caused by atherosclerosis, but giant cell arteritis should always be ruled out.
Suspect ischemic optic neuropathy in patients 55 years and older who have sudden, painless loss of vision.
If giant cell arteritis is suspected, treat it with corticosteroids to decrease the risk of contralateral involvement.
Visual prognosis tends to be poor.
