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Arteriosclerotic Anterior Ischemic Optic Neuropathy
An acute disruption of the blood supply to the optic disk, i.e., optic disk infarc-tion, resulting from vascular changes in arteriosclerosis.
Arteriosclerotic AION is a common cause of sudden loss of visual acuity. The greatest incidence of this disorder is between the ages of 60 and 70. In contrast to arteritic AION, it can also occur in adults below the age of 60.
The causes of the disorder lie in acute disruption of the blood flowthrough the lateral branches of the short posterior ciliary arteries and the ring of Zinn in the setting of severe arteriosclerosis. A narrow scleral canal, i.e., a small optic disk, is a predisposing factor. The disorder known as diabeticpapillopathy also belongs to this group of disorders, although it has a betterprognosis in terms of vision.
Patients report asudden unilateral loss of visual acuity. This is dueto segmental or complete infarction of the anterior portion of the optic nerve. Severity is variable. The patient may present with wedge-shaped visual field defects (Fig. 13.12b) or horizontal visual field defects that correlate with seg-mental nerve fiber edemas. However, severe concentric defects progressing to total blindness can also occur. Vision may or not be impaired. An afferent pupillary defect is always present.
The patient will frequently have a history ofhypertension, diabetes mellitus, or hyperlipidemia.
Ophthalmoscopy will reveal edema of the optic disk, whose margin willbe accordingly obscured. The margin is often obscured in a segmental pat-tern, which is an important criterion in differential diagnosis (Fig. 13.12a). The head of the optic nerve is also hyperemic with marginal bleeding.
Obscured segments of the margin of the optic disk that correlate with visual field defects are a sign of AION.
Anterior ischemic optic neuropathy is nearly impossible to treat.Attempted methods include hemodilution (pentoxifylline infusions, acetyl-salicylic acid, and bloodletting depending on hematocrit levels) and systemic administration of steroids to control the edema. Diagnosis of the underlying cause is important; examination by an internist and Doppler ultrasound stud-ies of the carotid artery may be helpful. Underlying disorders such as diabetes mellitus or arterial hypertension should be treated.
The prognosis is usually poor even where therapy is initiatedearly. Isolated atrophy of the optic nerve will appear within three weeks, complex atrophy of the optic nerve is less frequent but may also be observed.
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