Description
Anterior ischemic optic neuropathy entails swelling of the anterior portion of the optic nerve in association with visual disturbance, and may relate to occlusion of the short posterior ciliary arteries. When associated with giant cell arteritis (GCA, temporal arteritis), the condition is referred to as arteritic ischemic optic neuropathy (AION). NAION (i.e., without evidence of arteritis) occurs mostly in patients aged over 45 years. Patients are usually otherwise well, although many have associated cardiovascular risk factors including hypertension, diabetes, hyperlipidaemia and smoking. Since over half of patients first notice the visual deficit upon awakening, it has been suggested that nocturnal hypotension may contribute its onset.
Symptoms
The usual presentation is sudden, painless, unilateral loss of vision with no preceding visual symptoms. The clinician should inquire specifically regarding symptoms consistent with giant cell arteritis (GCA) e.g., fever, myalgias, temporal headache and scalp tenderness.
Signs
Visual acuity loss is usually maximal at onset; occasionally it continues to deteriorate for several weeks. Acuity is 6/18 or better in approximately half of patients, and worse than 6/60 in one-third. The inferior visual field is preferentially involved, and a relative afferent papillary defect is expected. Fundoscopy reveals segmental or generalised pale disc swelling with peripapillary flame-shaped haemorrhages. After several weeks to months, the swelling and hemorrhage resolve, with residual optic disc pallor.
It has been suggested that examination of the fellow eye may assist in the diagnosis of NAION: the optic cup is often small or absent in NAION, and usually normal in association with giant cell arteritis. This has given rise to the notion of the ‘disc at risk’ of NAION, in which axons within a crowded optic nerve are susceptible to infarction. Occasionally the fellow eye has signs of optic atrophy, presumptively from a previously undetected episode of NAION.
Incidence
Rare (approximately 1 per 10,000).
Significance
The presentation of acute, severe and painless loss of vision in association with pale disc swelling is a medical emergency requiring immediate exclusion of GCA, since the prognosis of the latter is improved by immediate corticosteroid therapy.
Differential Diagnosis
Arteritic Ischemic Optic Neuropathy (AION, GCA), Optic Neuritis (papillitis), Central Retinal Vein Occlusion, Optic Nerve Tumor, Hypertensive Retinopathy
See Also
Papilloedema
Management
Urgent
Immediate erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) estimation are required to exclude GCA. Less urgent blood tests are performed to exclude underlying cardiovascular or hematological conditions, and may include fasting lipids and glucose, full blood examination, vasculitic and procoagulant screens.
Additional tests
Fluorescein angiography may be helpful when the diagnosis is unclear, and typically demonstrates increased retinal circulation time and late staining of the optic disc. .
Oral medications
Unfortunately, no treatment has been proven to improve the visual prognosis of NAION. Long-term, low-dose aspirin may provide minimal protection against involvement of the second eye; it may also reduce the risk of other cardiovascular events in selected patients.
Review
Initial review is conducted at 1 month. Approximately 20 to 30 percent of patients experience mild improvement in vision, usually over the following several months. NAION can become bilateral in at least 30 percent of patients over subsequent years.
Figure 1.
Acute NAION: [Left] Grey swelling of optic disc with vascular dilation of superficial capillaries. Generalized field constriction although central vision was relatively spared. The other eye was unaffected. [Right] The same eye 9 months later, with resolution of the optic disc edema in one quadrant and partial resolution in the remainder. The condition was idiopathic.
Figure 2.
Chronic NAION: Segmental disc pallor and atrophy, with superior loss of nerve fibre layer. There is a corresponding inferior altitudinal field loss (inset).
