Sunday, November 13, 2011

Ocular Ischemic Syndrome

Signs and Symptoms
The patient with ocular ischemic syndrome (OIS) is elderly, ranging in age from the 50s to 80s. Males are affected twice as commonly as females. The patient is only rarely asymptomatic. Decreased vision occurs at presentation in 90 percent of cases, and 40 percent of patients have attendant eye pain. There may also be an attendant or antecedent history of transient ischemic attacks or amaurosis fugax. Patients also have significant known or unknown systemic disease at the time of presentation. The most commonly encountered systemic diseases are hypertension, diabetes, ischemic heart disease, stroke, and peripheral vascular disease. To a lesser extent, patients manifest OIS as a result of giant cell arteritis (GCA).

Unilateral findings are present in 80 percent of cases. Common findings may include advanced unilateral cataract, anterior segment inflammation, asymptomatic anterior chamber reaction, macular edema, dilated but non-tortuous retinal veins, mid-peripheral dot and blot hemorrhages, cotton wool spots, exudates, and neovascularization of the disc and retina. There may also be spontaneous arterial pulsation, elevated intraocular pressure, and neovascularization of the iris and angle with neovascular glaucoma (NVG). While the patient may exhibit anterior segment neovascularization, ocular hypotony may occur due to low arterial perfusion to the ciliary body. Occasionally, there is visible retinal emboli (Hollenhorst plaques).

The findings in OIS are caused by internal carotid artery atheromatous ulceration and stenosis at the bifurcation of the common carotid artery. Five percent of patients with internal artery stenosis develop OIS. However, OIS only occurs if the degree of stenosis exceeds 90 percent. Stenosis of the carotid artery reduces perfusion pressure to the eye, resulting in the above mentioned ischemic phenomena. Once stenosis reaches 90 percent, the perfusion pressure in the central retinal artery (CRA) drops only to 50 percent. Often, the reduced arterial pressure manifests as spontaneous pulsation of the CRA. The findings are variable and may include any or all of the above findings. Ninety percent of patients with OIS who develop neovascularization of the anterior segment manifest best corrected vision of finger counting within one year of diagnosis.

Ocular ischemic syndrome is best managed by addressing the causative factor, namely the carotid artery obstruction as well as the more serious ocular sequelae. In cases of retinal and anterior segment neovascularization, you must employ pan-retinal photocoagulation (PRP). PRP causes regression of anterior segment neovascularization in 36 percent of cases. As more of the angle becomes closed by the neovascularization, the success rate of PRP declines.

Carotid endarterectomy is frequently employed to surgically remove the carotid obstruction if the carotid artery is less than 99 percent obstructed. Following surgery, one-third of these cases improve, one-third remain stable, and one-third worsen.

Patients with OIS have significant systemic disease that must be assessed. Cardiac death is the primary cause of mortality in patients with OIS—the five-year mortality rate is 40 percent. For this reason, refer patients with OIS to a cardiologist for complete serology, EKG, ECG, and carotid evaluation.

As OIS may be caused by GCA, patients older than 60 years must immediately be evaluated with an erythrocyte sedimentation rate (ESR). Should the ESR be elevated, refer the patient to a neurologist experienced in the management of GCA.

Clinical Pearls

Idiopathic anterior uveitis is relatively rare in elderly patients. Suspect OIS in elderly patients presenting with an asymptomatic anterior uveitis.

OIS is a disease typified by asymmetry. Suspect OIS when patients present with asymmetric retinopathy, asymmetric cataracts, or a unilateral red eye.

Always consider OIS in elderly patients with neovascularization of the anterior segment.

Consider OIS when encountering ocular hypotony, especially if there is concurrent anterior chamber reaction and/or neovascularization.

The retinal veins in OIS will be dilated, but not tortuous. Tortuosity is a sign of retinal vein occlusion.

Always consider GCA as a cause of OIS and immediately evaluate the elderly patient with an ESR.

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