TESTS AND PROCEDURES THAT MAY BE DONE IN PATIENTS WITH AION

Visual acuity testing: The ophthalmologist needs to know at every visit just how much the patient can see, so that changes in the amount of affected vision can be determined. In addition to reading the eye charts for distance and near visual acuity, patients will often have visual field testing.

Visual field testing: A visual field test measures both central (straight ahead) and peripheral (side) vision. A defect in the visual field test shows which optic nerve fibers are affected by the disease (see Fig. 3). An eye with normal 20/20 (or 6/6) visual acuity can have fairly marked visual field loss in the periphery, so a normal visual acuity does not guarantee that there is no visual loss.

Relative afferent pupillary defect: The pupil, located in the center of the iris, is the part of the eye which gets larger and smaller according to the amount of light. The optic nerve plays an important role in this reaction to light, so if the pupil is changing more slowly or less than normal it shows that there is damage to the optic nerve or the retina. The pupils are tested by shining a light into each eye, causing the pupils to constrict. As the light is moved from one eye to the other, the pupils should constrict to about the same size. If they do not, a relative afferent pupillary defect is present in the involved eye.

Tonometry (Glaucoma Testing): The pressure in the eye (intraocular pressure) is measured with an instrument called a tonometer. This simple, painless procedure is essential to obtain full information about the circulation in the eye. If there is any doubt about whether the pressure is high the patient may need to be tested several times over a whole day, because intraocular pressure can vary at different times of the day. A person may not know he/she has high pressure in the eye until after visual loss has occurred.

Fundus Photograph and Fluorescein fundus Angiography: Photographs of the optic disc and the back of the eye may be taken on several occasions during the course of the disease to find out the amount of swelling of the optic disc and its resolution (Figs. 4, 5, 6, 7, 8). Fluorescein fundus angiography is a routine dye test, done to find out the state of circulation in the back of the eye and optic disc (Fig. 9).

To read more about fundus photography, click here.
To read more about fluorescein angiography, click here.

Blood Tests and Referrals to Specialists in Other Areas: Blood tests which will be done immediately are the Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP). The results of these tests are available within a couple of hours. The results are usually abnormally high in giant cell arteritis.

Many other blood studies may be needed to find out if there is anything else wrong with the patients, and may help in finding the reason for the development of AION, such as diabetes or collagen vascular disease. Cholesterol and/or triglyceride levels will be checked because high levels lead to "hardening of the arteries." The results of these blood studies may indicate a need for follow-up by a local physician or referral to a specialist in hematology.

Blood pressure: will be taken to determine if the patient has high blood pressure (hypertension). A cardiologist or cardiovascular specialist may be consulted if it seems that the cause of AION was a blood clot from somewhere else in the body, or that the heart, carotid arteries, or generalized "hardening of the arteries" may be contributing to the ischemia in the eye. Our recent studies have shown that abnormal fall of blood pressure during sleep can be a serious risk factor.^{28,33,47,50,58} This can be tested by recording the blood pressure every 10 to 20 minutes over a 24 hour period, with an ambulatory blood pressure monitor (Fig. 2).

Temporal Artery Biopsy: When the patient’s symptoms, the eye examination, elevated ESR and CRP, and fluorescein angiography make it seem likely that he/she has giant cell arteritis, a temporal artery biopsy will be done. The temporal artery lies just under the skin on the side of the forehead, or temple. The area is anesthetized and a small cut made in the skin to expose the artery. About an inch of the artery is removed for examination and the area is sutured with several stitches (which will be removed in about a week). This sample of the artery is examined under a microscope by a pathologist to determine whether there is inflammation of the artery. It may take several days before this result is known; however, treatment for arteritis may be started even before the biopsy is done, because of the very high risk of blindness if adequate treatment is not given soon enough. Starting treatment before the biopsy is done does not interfere with the results.

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