Detecting the Ocular Ischemic SyndromeWritten By: Gary C. Brown, MD, MBA, and Melissa M. Brown, MD, MN, MBA
Edited by Ingrid U. Scott, MD, MPH, and Sharon Fekrat, MD
In 1963, Kearns and Hollenhorst1 described the ocular features of a syndrome they observed in 5 percent of their patients with carotid artery obstruction. Characterized by retinal hemorrhages and dilated retinal veins, the entity was named “venous stasis retinopathy” by the authors. Regrettably, this term has also been used to describe nonischemic central retinal vein obstruction, a disease with a very different etiology. Because of the potential for confusion, other authors have promoted the term “ocular ischemic syndrome” to refer to the ocular symptoms and signs attributable to severe carotid artery obstruction.2 This latter term has since gained widespread usage.
It is estimated that the ocular ischemic syndrome occurs in about 2,100 patients per year in the United States. The disease is highly unusual in patients who are younger than 50 years, and the mean age at presentation is 65 years. Men outnumber women by a ratio of 2:1 and the incidence of bilaterality is 20 percent.
The most common cause is atherosclerosis of the carotid artery, although inflammatory conditions such as giant cell arteritis occasionally can be responsible. Ophthalmic artery obstruction accounts for fewer than 5 percent of cases.
It has been shown that blood flow to the eye is relatively unaffected until carotid obstruction exceeds 70 percent. When the obstruction reaches 90 percent—the minimum typically needed to cause the ocular ischemic syndrome —the perfusion pressure within the central retinal artery decreases by 50 percent. Approximately 50 percent of people with the ocular ischemic syndrome have total ipsilateral carotid artery obstruction, and about 10 percent have bilateral total carotid artery obstruction.
Signs and Symptoms Visual loss. Ninety percent of patients complain of visual loss, usually occurring over a period of days to weeks, while the remaining 10 percent have no visual symptoms at presentation. In about 12 percent of patients, the visual loss is abrupt and a cherry-red spot is present on funduscopic examination, indicating acute central retinal artery occlusion.
In these instances, iris and angle neovascularization often is present, which leads to increased IOP. This rise in IOP predisposes to an arterial obstruction when it exceeds the already compromised perfusion pressure within the central retinal artery. Pain. Present in about 40 percent of patients, the pain of ocular angina is generally described as a dull ache in the orbital region and may occur secondary to ocular ischemia, increased IOP from neovascular glaucoma and/or ipsilateral dural ischemia. Other symptoms. Delayed recovery of vision following bright light exposure is a symptom particularly suggestive of ocular ischemia. Anterior segment signs. Iris neovascularization is observed in two-thirds of eyes at the time of initial examination. Anterior chamber flare is present in most eyes with iris neovascularization, and there is a mild (1+ to 2+ on a 4+ scale) anterior chamber cellular response in about 20 percent of affected eyes. Keratic precipitates are generally absent. Despite the fact that the anterior chamber angle is synechially closed in many eyes with iris neovascularization, IOP may be normal, or even decreased, due to poor ciliary body perfusion. When iris neovascularization is present, 90 percent of eyes deteriorate to counting fingers vision or less within a year. Posterior segment signs. These include narrowed retinal arteries, dilated or beaded (but not tortuous) retinal veins and microaneurysms. Intraretinal hemorrhages are present in 80 percent of eyes, neovascularization of the retina and/or optic disc in 35 percent, macular edema in 12 percent, cotton-wool spots in 5 percent and spontaneous retinal arterial pulsations in 4 percent of eyes.
Associated Systemic Illnesses
Systemic arterial hypertension is present in about two-thirds of cases, while diabetes is found in about 50 percent. Fifty percent of patients have ischemic heart disease, about 25 percent have had a previous stroke and about 20 percent have had peripheral arterial disease requiring surgery. The five-year mortality is approximately 40 percent, with cardiac disease being the most common cause of death.3
Fluorescein angiography reveals delayed choroidal filling (>5 seconds) in 60 percent of eyes, delayed arteriovenous transit time (>11 seconds) in 95 percent of eyes, and large retinal vessel staining (usually arterial) in 85 percent of eyes. The electroretinogram usually reveals decreased amplitudes of the b-wave and the a-wave due to retinal vascular and choroidal hypoperfusion, respectively.2
The differential diagnosis includes diabetic retinopathy, nonischemic central retinal vein occlusion, parafoveal telangiectasis and radiation retinopathy. Light digital pressure on the globe through the eyelid often produces arterial pulsations in eyes with ocular ischemic syndrome, while this is not the case with the other diseases in the differential diagnosis.
When iris neovascularization is present and the anterior chamber angle is open, panretinal laser photocoagulation should be considered, as it causes regression of the iris and angle vessels in about 35 percent of eyes. If the anterior chamber angle is already closed and glaucoma filtering surgery is being considered, panretinal photocoagulation should be performed first to retard intraocular bleeding at the time of surgery.
The most definitive treatment is carotid endarterectomy. While no clinical trial concerning endarterectomy and the ocular ischemic syndrome has been performed, data suggest that approximately one-third of patients have improved vision after carotid surgery, one-third are visually unchanged and the remaining third progress to worsening vision despite the surgery. It should be noted that endarterectomy can be performed with a 99 percent stenosis; however, with a 100 percent stenosis, there is typically a clot propagating the length of the internal carotid that precludes successful surgery.
An important aspect of treatment that is often overlooked is referral to an internist if the patient is not already being followed. Since there is a very high risk of cardiac death, the status of the heart should be investigated and monitored in patients with the ocular ischemic syndrome.
In the general population, carotid endarterectomy has been shown to be beneficial in symptomatic patients (those with a nondisabling stroke, amaurosis fugax and/or a transient ischemic attack) with 70 to 99 percent ipsilateral carotid artery stenosis. Surgery decreases the two-year incidence of stroke in such patients from
26 to 9 percent.4
However, endarterectomy has not been shown to be of benefit compared with antiplatelet agents in patients who have less than 70 percent carotid artery stenosis.
The largest trial in asymptomatic patients shows a 1.5 percent perioperative chance of stroke or death, but 83 patients must be treated to prevent one stroke over a two-year period.5 Additional studies of carotid surgery in asymptomatic patients are under way.
1 Mayo Clin Proc 1963;38:304–312.
2 Brown, G. C. and L. E. Magargal. Int Ophthalmol 1988;11(4):239–251.
3 Sivalingam, A. et al. Int Ophthalmol 1989; 13(3):187–191.
4 North American Symptomatic Carotid Endarterectomy Trial Collaborators. N Engl J Med 1991;325(7):445–457.
5 Barnett, H. J. et al. CMAJ 2002;166(9): 1169–1179.
______________________________ Drs. Brown and Brown are codirectors of the Center for Value-Based Medicine in Flourtown, Pa., and adjunct senior fellows at the Leonard Davis Institute at the University of Pennsylvania. Dr. Gary Brown also is director of the Retina Service at Wills Eye Hospital, Philadelphia.
For Further Reading
Sharma, S. and G. C. Brown. “Ocular Ischemic Syndrome.” Chap. 89 in Retina (Baltimore: CV Mosby, 2000).