A retinal artery occlusion is an obstruction of a vessel that carries blood to the retina, the photosensitive layer that lines the back, inner surface of the eye. Occlusions in the retinal arterial system can occur in the main, central retinal artery, which accounts for 57 percent of retinal artery occlusions, or in its smaller tributaries. These blood vessels supply the nourishment to the inner third of the retina. A patient who experiences a retinal artery occlusion presents with a history of a sudden, painless visual deficit. In most cases, a retinal artery occlusion is caused by an embolus, which is a floating blood clot, cholesterol plaque, or fat globule that lodges in the inner bore of the artery.
Typical findings when a patient experiences a retinal artery occlusion include pallor of the retina in the area affected by the obstruction and a cherry-red spot in the macula. Another sign of a retinal artery occlusion is a relative afferent papillary defect, with unexpected pupil dilation on the affected side when swinging a flashlight from the unaffected side to the affected side. The cherry-red spot results from an alternative blood flow to the macula that keeps it perfused with blood, hence red, against the backdrop of a blood-starved, surrounding retina. Cherry red spots do not develop until at least one hour after the blockage occurs. Animal studies suggest that irreversible damage occurs within 105 minutes after an occlusion takes place, but humans may recover to some extent even days after the event.
The causes for a retinal artery occlusion vary with the age of the patient. On average, patients with retinal artery occlusions are in their sixth or seventh decade of life, but patients who are considerably younger may also develop an occlusion. Most of embolic cases stem from cardiovascular disease or cholesterol plaques in the main neck vessels. Other causes include migraine, sickle cell anemia, inflammatory arterial disease, infections, and talc from intravenous drug abuse. Glaucoma may also increase the risk for blockages in the retinal circulation.
Studies have shown that early intervention improves the prognosis after a retinal artery occlusion. Measures that dilate or open the artery, including ocular massage, inhalation of five-percent carbon dioxide, and removal of fluid from the eye by a needle, all dislodge the obstructing debris and allow it to move further down the vascular supply to a smaller blood vessel. Medications that dilate blood vessels or break up blood clots may also be used. Some physicians us hyperbaric oxygen, oxygen delivered at high pressures, to force oxygen into the blood-starved tissues and prevent retinal damage.