A central retinal artery occlusion is the result of a blockage of the main artery supplying blood to the retina (the light sensitive membrane lining the inner wall of the back of the eye) acting like the photographic film of the eye leading to a sudden loss of vision of the affected eye.
Incidence/age

Central retinal artery occlusion most commonly occurs between the age of 50 and 80.

Causes of central retinal artery occlusion

The main causes of central retinal artery occlusion are emboli (fragments) from atherosclerosis in the carotid artery of the neck in older patients, heart valve disease in younger patients or thrombosis (clot formation) from atherosclerosis (disease of the arterial walls). Between 2 and 10% of central retinal artery occlusions are secondary to giant cell arteritis (GCA) which if left untreated may lead to bilateral loss of vision.

Signs/symptoms

The patient presents with a sudden, painless, unilateral loss of either the entire vision or of part of the visual field. The pupil reaction of the affected eye may be abnormal. Examination of the retina on the inside layer of the back of the eye will show a characteristic appearance of a pale retina with a central cherry red spot and interruption of the blood flow through the blood vessels of the retina.

Complications of disorder

Interruption of the blood flow through the central retinal artery may lead to irreversible damage to those parts of the retina which do not receive an adequate blood supply. Irreversible damage will occur to those parts of the retina where the blood supply has been interrupted for a period of more than two hours.

Complete occlusion of the central retinal artery circulation is, however, rare and retinal recovery may be possible even days after a retinal artery occlusion. Between 5 and 15% of patients with a central retinal artery occlusion are at risk of subsequently developing iris or retinal neovascularisation (the growth of new friable blood vessels on the surface of either the retina or the iris). The growth of such vessels can lead to the development of glaucoma (raised pressure within the eye).

Tests

Investigations to determine the cause of the central retinal artery occlusion may include blood tests for anaemia, thickening of the blood, clotting disorders or an abnormal viscosity of the blood. A blood sugar, cholesterol, triglyceride and lipid profile assessment is undertaken to evaluate atherosclerotic disease.

Blood cultures may be indicated to look for causes of infective emboli to the central retinal artery. Imaging studies may include a carotid Doppler ultrasound examination of the blood vessels within the neck. An electrocardiogram to look for heart arrhythmias and an echocardiogram to look for disease of the heart valves may be required. In some cases a magnetic resonance angiogram may be helpful in examining the blood vessels leading to the eye.

Treatment of central retinal artery occlusion

Medical
The immediate treatment of a central retinal artery occlusion is aimed at restoring the blood circulation to the retina as quickly as possible by increasing the perfusion of blood through the artery. It is reasonable to treat all cases of central retinal artery occlusion seen within 48 hours in this way. Treatment includes massage of the eye for periods of 5-15 seconds repeated for up to 15 minutes.

An intravenous injection of Azetozolamide to lower the pressure in the eye may be used. Other measures which may be considered include inhalation of a mixture of 5% carbon dioxide and 90% oxygen and tapping fluid from the anterior chamber of the eye to lower the pressure within the eye. The results of such treatment are unfortunately usually disappointing.

Further treatment will depend on the cause of central retinal artery occlusion. If the occlusion is the result of emboli from blood vessels elsewhere in the body then treatment of the cause of the emboli is important to reduce the chances of further emboli to the same or the other eye resulting in further loss of vision or further emboli to the brain resulting in stroke. Such treatment may include the use of anticlotting agents such as aspirin or Warfarin.

If the cause of the retinal artery occlusion is atherosclerosis then risk factors for artery disease such as hypertension, diabetes, hypercholesterolaemia and smoking should be identified and treated appropriately. Where the cause of the occlusion is due to giant cell arteritis then immediate treatment with high dose steroid is required to prevent the involvement of the other eye.

Surgical
Surgical treatment is usually confined to a limited number of patients where disease of the carotid artery within the neck is found to be the cause of the retinal artery occlusion. A minority of such patients may benefit from a carotid endarterectomy (an arterial graft to bypass a severe blockage of the blood vessel within the neck).

Outcome

The recovery of useful vision in the affected eye is related to the level of vision at the time the patient presents with the condition and the rapidity with which treatment is sought. Unfortunately the prognosis for recovery of vision after a central retinal artery occlusion is generally poor. It is important to realise that the changes in vision are often the result of a systemic disease which requires investigation and treatment to prevent a further recurrence or other complication.