Anterior Ischemic Optic Neuropathy (AION) Workup

Updated: May 09, 2017
  • Author: Andrew A Dahl, MD, FACS; Chief Editor: Hampton Roy, Sr, MD  more...
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Workup

Laboratory Studies

The erythrocyte sedimentation rate (ESR) is commonly obtained in patients with anterior ischemic optic neuropathy (AION). In patients with arteritic AION, the ESR is usually elevated, although 10% of patients may have a normal ESR. In nonarteritic anterior ischemic optic neuropathy (NAION), the ESR is more likely to be normal, assuming no comorbid condition is present. The Westergren ESR is thought to be more reliable than the Wintrobe ESR.

A hematology group is useful. Mild anemia may be present.

Other blood tests, such as the C-reactive protein (CRP), have been found useful in diagnosing giant cell arteritis (GCA). In a few patients with GCA, the CRP level has been shown to be elevated despite the finding of a normal ESR.

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Imaging Studies

Ultrasonography of the temporal arteries and ocular Doppler ultrasonography have been described, but the utility of ultrasonographic evaluation in the differentiation between arteritic anterior ischemic optic neuropathy (AION) and nonarteritic anterior ischemic optic neuropathy (NAION) has not been proven.

Ocular plethysmography (OPG) findings have been described as being abnormal in patients with arteritic AION.

MRI is useful in younger individuals in identifying unilateral visual loss of optic nerve with possible demyelinating disease. It is not useful in older age groups, in either the arteritic or nonarteritic form of AION.

CT scanning is not useful in either the arteritic or nonarteritic form of AION.

Fluorescein angiography has been suggested as a possible method of distinguishing arteritic AION from NAION. With arteritic AION, a markedly prolonged choroidal filling time is usually present.

Angiography of the cerebral circulation has been useful in giant cell arteritis (GCA), showing segmental stenosis or even occlusion of the extracranial vessels. However, angiography is rarely used because of its invasive nature. CT angiography has been described as sometimes revealing segmental stenosis in GCA.

Optical coherence tomography (OCT) has been used in patients with AION with success. [7]  

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Procedures

Temporal artery biopsy is used to diagnose giant cell arteritis (GCA). It is especially useful in patients with any of the symptoms of GCA or in patients with visual loss and a high ESR. A normal result of the temporal artery biopsy is often used to exclude the diagnosis of GCA in older patients with anterior ischemic optic neuropathy (AION).

Whenever possible, a biopsy specimen of at least 2-3 cm should be obtained to minimize the possibility of skip lesions. Bilateral temporal artery biopsies increase the yield of positive results. A second temporal artery biopsy should be considered if GCA is still suspected despite an initial negative result of the first temporal artery biopsy. Delaying the second side a few weeks may improve the yield of a positive biopsy result on that second side.

Biopsy should generally be performed either before or soon after the initiation of steroid therapy, although positive biopsy results can sometimes be obtained months after steroids have begun. 

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Histologic Findings

The idiopathic form of ischemic optic neuropathy has no characteristic pathology other than obliterative occlusion of the cilioretinal arteries and ischemic necrosis of the optic nerve head in variable degree.

Giant cell arteritis (GCA) has a characteristic inflammatory infiltrate that has a granulomatous appearance, sometimes with giant cells. Complete occlusion of the ophthalmic artery within the orbit may result in ischemic changes of the globe in its entirety. The use of frozen section for temporal artery biopsy is very useful in determining arteritis, and it may establish the diagnosis with a single temporal artery biopsy. Rarely, if the initial temporal artery biopsy result is negative, the contralateral biopsy result may be positive due to minimal involvement or skip areas. Inflammatory infiltrate in the adventitia often is considered to be sufficient evidence for diagnosis, even with the elastica intact. 

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