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CRAO causes a sudden, painless loss of vision, typically finger counting or barely light perception. You'll also note an APD. The inner retina will appear edematous and milky-white, as the underlying choroidal blood flow is obscured. You'll see a "cherry-red spot" in the macula as some choroidal blood does show through. The retinal edema and opaque appearance disappear over time, leaving a normal-looking retina, attenuated retinal arterioles and an atrophic and pale optic nerve.15,16
In BRAO you may see an embolus on ophthalmoscopy. Patients remain asymptomatic if the macula is not affected. Usually, though, they experience a severe reduction of visual acuity and/or field.
There's little we can do to improve visual outcomes in CRAO or BRAO. In CRAO some doctors have had success dislodging the embolus-by anterior chamber paracentisis, compressing the globe or increasing blood CO2 levels-thereby restoring blood flow and function to the retina. Yet, research shows that these measures have no greater effect than no treatment at all.
Retinal artery occlusion carries profound systemic implications, most commonly arteriosclerosis. Others include myocardial infarction, hypertension, carotid artery disease, diabetes, cardiac valve abnormalities and giant cell arteritis.32,33 Refer these patients to a cardiologist.
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.
Sickle Cell Retinopathy
Seen mostly in blacks, this disease is an inherited disorder involving abnormal hemoglobin, the principal protein of erythrocytes. Normal erythrocytes appear as pliable, biconcave discs; in sickle cell disease they lose their biconcave shape. The sickled cells become rigid and restrict blood flow, causing hypoxia. Tissues deprived of oxygen then undergo pathologic changes.
Sickle cell retinopathy, like diabetic retinopathy, may be proliferative or non-proliferative. Non-proliferative sickle cell retinopathy represents necrosis of retinal vessel walls. Findings include dark-without-pressure, intraretinal ("salmon-patch") hemorrhages, hemosiderin deposits combined with RPE hyperplasia ("black sunburst"), venous tortuosity and angioid streaks (with possible choroidal neovascularization).
Proliferative sickle retinopathy results from peripheral arteriolar occlusion. Hypoxia leads to neovascularization with a "sea fan" appearance. Fibrotic proliferation and scaffolding associated with the neovascularization can lead to vitreal hemorrhage and tractional retinal detachment.39 Often, the neovascularization will spontaneously regress, leaving a characteristic whitish tuft.40
The Sickledex test as well as hemoglobin electrophoresis can be helpful. Non-proliferative retinopathy requires only observation. Refer those with proliferative retinopathy for possible laser treatment.
Retinal Macroaneurysm
Patients with retinal macroaneurysms are typically in the 50-80 age range, female and hypertensive.41,42 The condition involves a focal dilatation of a major retinal arterial (or, rarely, venous) branch.
Weakening of the vessel wall leads to the aneurysm. There's no associated microvasculopathy as seen in diabetic retinopathy, but there is a strong association with hypertension. The condition is less commonly associated with retinal embolization, arteriosclerosis and cardiovascular disease.
Patients are frequently asymptomatic, but if the macula is involved they will present with reduced visual acuity and field.41,42 Often there is significant leakage, with exudates and extensive intraretinal or subretinal hemorrhage around it. The vascular dilatation may be obscured by hemorrhage. Fluorescein angiography can aid in this diagnosis. The aneurysm will hyperfluoresce early with a balloon-like appearance.
Asymptomatic, non-leaking macroaneurysms simply require monitoring every 4-6 months. If hemorrhage or exudation occurs but does not threaten the macula, monitor every 1-3 months. If hemorrhage does involve or threatens the macula, or if macular edema persists, photocoagulation may be indicated. The laser treatment scleroses the macroaneurysm but leaves the vessel patent. If a non-hemorrhaging macroaneurysm spontaneously pulsates, photocoagulation may prevent rupture. Since these patients have a predilection for systemic vascular disease, refer for evaluation.
Retinal Telangiectasia
Three conditions involve retinal telangiectasia: Leber's miliary aneurysm, Coats' disease and idiopathic juxtafoveal telangiectasia. Each occurs due to abnormal retinal capillaries. Coats' disease and Leber's miliary aneurysm share a similar appearance and origin; they may be different forms of the same disease.
Leber's miliary aneurysm involves an aneurysm and telangiectasia in the retinal periphery. It's more common in males, and is typically discovered in the first decade of life. In Leber's, the vessels remain patent with minimal leakage.
When the telangiectatic vessels lead to extensive leakage and exudation, the condition is diagnosed as Coats' disease. A growth hormone may stimulate these changes, which may explain why most Coats' disease cases are diagnosed in the first two decades of life.43
In Coats' disease cystic cavities develop in response to a breakdown in the blood-retinal barrier due to the telangiectasis. These cystic cavities fill with proteins and lipids on and below the retina. There's also a macrophage response, with lipids migrating deep within the retina. This brings subretinal accumulation of exudates and a retinal detachment.
Retinal edema may also be persistent, causing decreased acuity when it reaches the macula. Ischemia may develop as well, with neovascularization and subsequent vitreal hemorrhage and retinal detachment.
Leber's miliary aneurysm calls for periodic monitoring. Coats' disease, if left unchecked, will lead to total retinal detachment. Treatment consists of laser photocoagulation or cryoretinopexy to destroy the abnormal vessels, as well as scleral buckling to repair any retinal detachment.
Idiopathic juxtafoveal retinal telangiectasia (IJRT) is not associated with Leber's miliary aneurysm or Coats' disease, but may be a variation of the same disease process. IJRT, which is more benign than Coats' disease, involves a capillary malformation at the edge of the foveal avascular zone.44
IJRT may be unilateral or bilateral. The unilateral form only affects men, and typically is not discovered until after age 40.44 Patients with unilateral IJRT are usually asymptomatic. However, leakage may cause macular edema and reduced visual acuity. Fundus assessment often reveals parafoveal dot and blot hemorrhages and, rarely, exudates.
Bilateral IJRT affects women as well as men, typically between ages 40 and 60. The presentation is often symmetrical, and involves retinal edema, parafoveal hemorrhaging, RPE hyperplasia and possibly choroidal neovascularization. Despite these changes, vision tends to be 20/30 or better.
Clinicians frequently overlook IJRT as a cause of retinal edema, parafoveal hemorrhages and exudates. For diabetic or hypertensive patients, doctors often wrongly attribute the parafoveal findings to these diseases. Suspect IJRT when you note parafoveal hemorrhaging, particularly when there is no peripheral hemorrhaging in diabetics, or no systemic ischemic vascular disease.
Occasionally, you may observe the juxtafoveal telangiectasia on ophthalmoscopy. The parafoveal vessels may take an irregular course, like they're being dragged toward the foveal avascular zone. Angiography will readily reveal the details.
The prognosis of IJRT is excellent. Most cases present only with several isolated, unexplained parafoveal dot and blot hemorrhages. Once you've ruled out diabetes, anemia and hypertension as possible causes, you can simply monitor the condition, particularly if vision is unaffected. In cases of unremitting macular edema, focal photocoagulation may help. Since no systemic conditions are associated with IJRT, you don't need to refer to a primary care physician.
Many systemic diseases manifest in readily observable retinal vascular changes. By understanding the complexities of retinal vascular disease, you can take steps to reduce morbidity not only to the eye, but to the patient as a whole.
Dr. Sowka is an associate professor at the Nova Southeastern University
College of Optometry. Dr. Kabat is an assistant professor there.
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