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 approximately 15% of patients with nonarteritic ischemic optic neuropathy within 5 years (1), 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
General reference
1. Newman NJ, Scherer R, Langenberg P, et al: The fellow eye in NAION: Report from the ischemic optic neuropathy decompression trial follow-up study. Am J Ophthalmol 134(3):317-328, 2002. doi: 10.1016/s0002-9394(02)01639-2
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. In arteritic ischemic optic neuropathy due to giant cell arteritis, 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 are usually present; however, such symptoms may be absent in up to 20% of cases (1). Visual acuity is usually 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.
Symptoms and signs reference
1. Chen JJ, Leavitt JA, Fang C, et al: Evaluating the incidence of arteritic ischemic optic neuropathy and other causes of vision loss from giant cell arteritis. Ophthalmology 123(9):1999-2003, 2016. doi: 10.1016/j.ophtha.2016.05.008
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 corticosteroid treatment is not started quickly. Immediate tests include ESR, CBC, and C-reactive protein. ESR is usually 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. Only 4% of biopsy proven GCA have normal values for both C-reactive protein and ESR. CBC is done to identify thrombocytosis (> 400 × 103/mcL), which adds to the positive and negative predictive value of using ESR alone (1).
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.
Diagnosis reference
1. Walvick MD, Walvick MP: Giant cell arteritis: Laboratory predictors of a positive temporal artery biopsy. Ophthalmology 118(6):1201-1204, 2011. doi:10.1016/j.ophtha.2010.10.002
Treatment of Ischemic Optic Neuropathy
1). There is no established treatment of the nonarteritic variety. Vascular risk factors should be optimized. Low-vision aids (eg, magnifiers, large-print devices, talking watches) may be helpful in both types.
Pearls & Pitfalls
|
Treatment reference
1. Stone JH, Tuckwell K, Dimonaco S, et alN Engl J Med 377(4):317-328, 2017. doi: 10.1056/NEJMoa1613849
Prognosis for Ischemic Optic Neuropathy
There is no effective treatment for the nonarteritic variety of optic nerve infarction; however, up to 40% of patients have mild spontaneous recovery of vision (1).
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.
Prognosis reference
1. Singh S, Zimmerman MB: Nonarteritic anterior ischemic optic neuropathy: natural history of visual outcome. Ophthalmology 115(2):298-305.e2, 2008. PMID: 17698200
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.
