Ocular Ischemic Syndrome
Ocular ischemic syndrome (OIS) involves a constellation of posterior and anterior segment findings, and is commonly mistaken for diabetic retinopathy or CRVO. OIS typically affects the elderly, and is more common in men than women. 34.

OIS involves atheromatous ulceration and stenosis of the carotid artery. Most patients have an underlying disease such as hypertension, diabetes, hyperlipidemia, cardiac disease or clotting abnormalities. Besides carotid artery occlusion, OIS may result from collagen–vascular disease, endarteritis or giant cell arteritis. For patients over 60, order a sedimentation rate for giant cell arteritis.

As perfusion pressure to the eye decreases, several things happen. Blood flow shunts through the external carotid system, leading to a unilateral red eye. Anterior segment ischemia leads to cataract, a breakdown of the blood–aqueous barrier and an anterior chamber reaction. Rubeosis may lead to neovascular glaucoma, but usually won’t because ciliary body ischemia halts aqueous production. Hypotony, due to poor perfusion pressure, is more common.

Retinal findings include mid–peripheral dot and blot hemorrhages, microaneurysms, narrow arterioles and dilated veins. You may see spontaneous arterial pulsation and neovascularization of the disc and retina. 34–36.

The signs mimic non–ischemic CRVO. The biggest difference is that in CRVO the retinal veins are dilated and tortuous, in OIS the veins are dilated but not tortuous (owing to decreased blood flow). OIS is also frequently confused with diabetic retinopathy, especially since these patients are often diabetic. The main difference is asymmetry of disease. Diabetic retinopathy typically develops symmetrically in both eyes, OIS is unilateral in 80 percent of cases, and in the others will show profound retinopathy only in one eye.

OIS may cause anterior segment changes: conjunctival and episcleral injection, anterior chamber reaction, cataract, rubeosis irides (and possibly neovascular glaucoma), corneal edema and keratic precipitates. IOP may either be elevated due to neovascular glaucoma or, more likely, reduced. The eye may be painful due to neovascular glaucoma, ocular angina or dural ischemia.

If you see asymmetric retinopathy, ocular hypotony, asymmetric cataract and/or anterior uveitis in an elderly patient, check for OIS. Ophthalmodynomometry can help by showing reduced perfusion pressure to the eye. Carotid Doppler ultrasound can confirm your diagnosis.

The prognosis for OIS is poor. About 90 percent of patients who develop iris neovascularization from OIS will have finger–counting vision within a year. These patients usually receive panretinal photocoagulation, but the results are poor. 37, 38 OIS patients have about a 40 percent chance of dying within five years, most often from myocardial infarction.

Refer these patients to a cardiologist. Blood thinning therapy with aspirin or warfarin (Coumadin) may have modest success. Carotid endarterectomy is the surgery of choice, but the risks are significant.