ANTERIOR ISCHEMIC OPTIC NEUROPATHY (AION)

SIGNS AND SYMPTOMS
The patient will typically be elderly and will present with a unilateral, painless loss of vision and visual field. The field defect traditionally is a superior, altitudinal defect. Visual acuity may in rare instances be quite good; however, acuity is usually in the range of 20/200 to no light perception. Visual loss may progress rapidly over several days.

The patient generally has significant systemic disease. In the case of non-arteritic anterior ischemic optic neuropathy, the patient usually has a systemic vascular disease (hypertension, diabetes, atherosclerosis) or collagen vascular disease. In the arteritic form of the disease, the patient will usually present with early signs of anorexia, weight loss, decreased appetite, jaw claudication, scalp tenderness and malaise.

Often several instances of amaurosis fugax (transient blindness) may precede the arteritic AION by up to six months. This is due to giant cell arteritis (GCA), an idiopathic systemic inflammation of medium-sized arteries. The patient with arteritic AION is, on average, 75 years old while the patient with non-arteritic AION is, on average age, 62 years old. Non-arteritic patients will present with a relative afferent pupil defect and a swollen, hyperemic optic disc. Patients with the arteritic form will present also with afferent pupil defect, but the swollen disc is usually pale with associated splinter hemorrhages.

PATHOPHYSIOLOGY
Anterior ischemic optic neuropathy is caused by infarction of the short posterior ciliary arteries supplying the anterior optic nerve. In the non-arteritic form, these vessels are compromised by vascular disease and arteriolosclerosis. In the case of arteritic AION, these vessels, as well as the ophthalmic and central retinal arteries, are compromised by an idiopathic infiltration of the vessels walls by inflammatory macrophages, lymphocytes, and multinucleate giant cells. As most arteries are affected in GCA, there usually is a constellation of systemic symptoms. Due to the widespread involvement in GCA, there is a propensity for the fellow eye to become similarly involved within days, causing severe bilateral vision loss.

MANAGEMENT
Collect a thorough ocular and systemic history and immediately order an erythrocyte sedimentation rate (ESR). Typically, this will be grossly elevated in arteritic AION and normal in non-arteritic AION. If the ESR is elevated and you suspect GCA and arteritic AION, have the patient undergo a temporal artery biopsy to examine for inflammatory cells in the arteries.

If the patient is either suspected to have, or diagnosed with, GCA and arteritic AION, begin treatment with systemic steroids to prevent vision loss from progressing to the other eye. Typically, it's best to hospitalize the patient and place him or her on 1-2g I.V. methylprednisolone for two to three days, followed by oral steroids (60 to 100mg QD of prednisone). Following hospital release, taper the oral steroids but maintain therapy for two to four years. Despite aggressive therapy, GCA frequently progresses to the fellow eye, giving this disease a poor prognosis.

In the case of non-arteritic AION, the prognosis is guarded but much better than with arteritic AION. The rate of progression to bilateral involvement is significantly lower (32 months, on average). There is no direct treatment for non-arteritic AION or the vasculopathy that causes it. The systemic vascular diseases that precipitate the condition must be well controlled by the patient's internist in hopes of preventing or delaying bilateral involvement.

CLINICAL PEARLS

Suspect GCA and arteritic AION in any patient over age 65 with sudden unilateral vision loss and a swollen disc. This is a true emergency, and warrants immediate consultation with a neurologist or neuro-ophthalmologist. You also must evaluate any elderly patient presenting with headache, head pain or, especially, amaurosis fugax for giant cell arteritis.

Central retinal artery occlusion (CRAO), while usually caused by embolism, occurs due to GCA in two to 10 percent of cases. Assume that any patient over age 65 presenting with CRAO has giant cell arteritis until proven otherwise. This means that the patient must immediately have an ESR. If the ESR is abnormal, or if there are systemic signs or symptoms of GCA, the patient must undergo temporal artery biopsy.