The central retinal artery is one of the two principal sources of blood for the ocular retina, which is the light-sensitive membrane lining the back of the eye. It is the first branch off the ophthalmic artery, which is, in turn, the first branch off the internal carotid artery after it enters the base of the brain. After leaving the ophthalmic artery, the retinal artery joins the optic nerve approximately 1 centimeter (0.45 inch) posterior to the eye, courses within the sheath of the optic nerve into the eye, and divides into four main arcuate branches at the optic disc. These branches of the central retinal artery supply blood to the inner two thirds of the retina. Occlusions of the central retinal artery result in sudden, profound vision loss.
In addition to the central retinal artery, the eye receives blood from the short posterior ciliary arteries, also branches of the ophthalmic artery. The short posterior ciliary arteries supply the outer third of the retina and the peripheral vascular layer of the eye, which is called the choroid. In about 14 percent of the population, a cilioretinal artery arises from one of the short posterior ciliary arteries. A cilioretinal artery, if present, provides additional blood supply to the central, inner retina, called the macula. In the setting of central retinal artery occlusion (CRAO) with a cilioretinal artery present, the alternative blood supply to the central retina allows a gain in visual acuity to 20/50 or better in almost 80 percent of cases over a few weeks.
Central retinal artery occlusion is usually the result of blockage of the blood vessel due to a blood clot or a cholesterol plaque. The most common symptom of CRAO is a sudden, enduring loss of vision in the affected eye, with the patient only able to see raised fingers on a hand or in some cases, light exclusively. Some patients report prior episodes of transient loss of vision, which resolved within minutes. Within 15 minutes of a CRAO, the retina becomes swollen, pale, and yellowish-white in color. The very center of the retina, called the foveola, will have a distinct cherry-red color in contrast to the surrounding opaque retina.
Studies show that irreversible, catastrophic damage occurs to the inner retinal layers within 90 to 100 minutes after a complete blockage of the retinal artery. Most ophthalmologists agree that patients must receive any treatments for CRAO within the first 24 hours of onset in order to obtain any benefit. Treatments to restore blood flow include the use of blood thinners, inhaled CO2, medications to dilate the blood vessels, and massage of the eye. Physicians must also address associated, predisposing illnesses and conditions, such as hypertension, diabetes, atherosclerosis, intravenous drug use, and oral contraceptive use. In cases of CRAO, the patient life expectancy drops to only 5.5 years.
