Retinal artery occlusion refers to the closure of the central retinal artery and usually results in complete loss of vision in one eye. Occlusion of its branches causes loss of vision in only a portion of the field of vision.
Description
Retinal artery occlusion (RAO) occurs when the central retinal artery, the main source of blood supply to the retina, or one of its branches becomes blocked.
Causes and symptoms
The main causes of RAO are the following:
embolism (the sudden obstruction of a blood vessel by a blood clot)
atherosclerotic disease that results in the progressive narrowing of the arteries over time
endarteritis (the chronic inflammation of the inner layer of arteries)
angiospasm (a spasmodic contraction of a blood vessel with increase in blood pressure)
The most common symptom of RAO is an acute, painless loss of vision in one eye. The degree of loss depends on the location of the occlusion. If the occlusion occurs in the central artery of the retina, damage usually results in complete loss of vision in the affected eye. If occlusion occurs in a branch artery, vision loss will be partial and may even go unnoticed if only a section of the peripheral vision is affected.
People affected by RAO typically have high blood pressure, heart disease, or diabetes as an underlying condition. Other conditions that may increase the risk of RAO include high cholesterol and glaucoma. Incidence is slightly more common in men and in people age 60 or older.
Diagnosis
RAO is diagnosed by examination of the retina with an ophtalmoscope.
Treatment
Central retinal artery occlusion (CRAO) is an emergency. If treatment begins within an hour, the patient has the highest possibility of regaining vision in the affected eye, although complete restoration is unlikely.
A common treatment is inhalation of carbon dioxide so as to dilate the retinal vessels and move the occlusion from the central retinal artery to a branch artery. This movement reduces the area of the retina affected and may restore a certain amount of vision. Eyeball massage may also be performed, also in an effort to remove the occlusion. The physician may also consider puncturing the eyeball.
Drug therapy includes the use of carbonic anhydrase inhibitors to reduce the internal eye pressure and enhance movement of the occlusion. Both of the treatments would be used within the first 24 hours of noticeable vision loss.
Alternative treatment
Hyperbaric oxygen therapy may be beneficial if started within 90 minutes of the onset of symptoms. Some studies indicate a 40% improvement of visual acuity using this method.
Prognosis
The prognosis for central retinal visual acuity is poor with only about one-third of patients recovering useful vision. The longest delay in getting treatment that has been associated with significant visual recovery was approximately 72 hours.
Branch retinal artery occlusions (BRAO) have a recovery rate of 80% where vision is restored to 20/40 or better.
Angiospasm—Spasmodic contraction of a blood vessel with increase in blood pressure.
Arterioles—Small blood vessels that carry arterial (oxygenated) blood.
Atherosclerotic disease—The progressive narrowing and hardening of the arteries over time.
Central retinal artery—A branch of the ophthalmic artery that supplies blood to the retina and branches to form the arterioles of the retina.
Embolism—The sudden obstruction of a blood vessel by a blood clot.
Endarteritis—Chronic inflammation of the inner layer of arteries.
Hyperbaric oxygenation—Administration of oxygen in a compression chamber at an ambient pressure greater than 1 atmosphere, in order to increase the amount of oxygen in organs and tissues.
Occlusion—Momentary complete closure of some area or channel of the body.
Ophthalmic artery—The artery supplying the eye and adjacent structures with blood.
Ophthalmoscope—An instrument used for viewing the inside of the eye that consists of a concave mirror with a hole in the middle through which the physician examines the eye, and a light source that is reflected into the eye by the mirror.
Retina—Light sensitive layer of the eye, that consists of four major layers: the outer neural layer, containing nerve cells and blood vessels, the photoreceptor layer, a single layer that contains the light sensing rods and cones, the pigmented retinal epithelium (PRE) and the choroid, consisting of connective tissue and capillaries.
