The central retinal artery is a branch of the ophthalmic artery and supplies the retina.
Central retinal artery occlusion (CRAO) refers to blockage of the central artery of the retina, which leads to a profound and acute loss of vision. It is also associated with increased risk of the development of cerebral stroke and ischemic heart disease.
It is due to the development of atherosclerosis in the systemic and ocular arteries.
CRAO is usually caused by thromboembolism due to atherosclerotic plaques in the carotid artery, though it may also arise from carotid artery stenosis or from plaques in the coronary vessels.
Types of CRAO
CRAO may be of the following types:
- Non-arteritic permanent: this is the most common type, seen in two of every three patients. Risk factors include:
- Diabetes mellitus
- Atherosclerotic disease of the carotid or coronary arteries
- Transient ischaemic attacks (TIAs) or cerebrovascular accidents
- v=Vascular disease such as the connective tissue disorders, use of oral contraceptives, or myeloproliferative disease, in younger patients
- Non-arteritic transient: similar to a TIA, this condition is associated with an acute but transient attack of visual loss due to short-lived occlusion of the central retinal artery which is quickly and spontaneously relieved. Serotonin-induced vasospasm may be one way in which this type of occlusion occurs, because platelets present in association with atherosclerotic plaques release this neurochemical.
- Non-arteritic CRAO with cilioretinal sparing: an additional cilioretinal artery is found in almost half of all individuals, and supplies the retina to a variable extent. With the onset of CRAO, the presence of this artery may spare the retina from extensive damage if it supplies a sizable area of the retina.
- Arteritic CRAO due to giant cell arteritis – this is found in about 5% of cases.
The diagnosis of CRAO is based upon the following clinical features:
- A history of loss of vision in one eye, not associated with pain, and of sudden onset
- Eliciting risk factors for CRAO as listed above
- Findings of the physical examination such as atrial fibrillation which predisposes to thromboembolic phenomena, and scalp tenderness in temporal arteritis
- Findings from an ocular examination such as posterior pole retinal opacity in approximately 58% of patients, while cherry-red spot is seen in 9 of every 10 individuals. Retinal arterial attenuation is found in a third of patients.
- Results of ocular testing and other tests: fundoscopy may show the presence of thrombi in the vessels, the appearance of which varies with the type of clots. The type of vascular disorder may also be suggested as hypertensive retinopathy or pre-retinal arterial loops. Fluorescein angiography of the fundus shows the cattle-trucking sign of the blood column inside the branches of the retinal artery, with impaired filling of the involved blood vessels.
The condition is treated in a variety of ways but none have been shown to be more effective than placebo. Available options for acute phase management include:
- Isosorbide dinitrate sublingually
- Systemic pentoxiffylline
- Carbogen inhalation
- Hyperbaric oxygen
- Ocular massage
- Intravenous acetazolamide
- Intravenous mannitol
- Paracentesis of the anterior chamber
- Systemic corticosteroids such as methylprednisolone
- Eyeball compression
- Tissue plasminogen activator to dissolve the clots and restore retinal circulation
Subacute phase management is concerned with the prevention of neovascularization and associated complications such as further visual loss.
Future prevention of cerebrovascular accidents or recurrent occlusive events in the eye is also initiated.