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What is Central retinal artery occlusion and explain in detail?
Central retinal artery occlusion (CRAO) is a disease of the eye where the flow of blood through the central retinal artery is blocked (occluded). There are several different causes of this occlusion; the most common is carotid artery atherosclerosis.

Signs and symptoms
Central retinal artery occlusion is characterized by painless, acute vision loss in one eye. Upon fundoscopic exam, one would expect to find: cherry-red spot  (90%) (a morphologic description in which the normally red background of the choroid is sharply outlined by the swollen opaque retina in the central retina), retinal opacity in the posterior pole (58%), pallor (39%), retinal arterial attenuation (32%), and optic disk edema (22%). During later stages of onset, one may also find plaques, emboli, and optic atrophy.

Diagnosis
One diagnostic method for the confirmation of CRAO is Fluorescein angiography, it is used to examine the retinal artery filling time after the fluorescein dye is injected into the peripheral venous system. In an eye with CRAO some branches of the retinal artery may not fill or the time it takes for the branches of the retinal artery to fill will be increased, which is visualized by the leading edge of the fluorescein moving slower than normal through the retinal artery branches to the edges of the retina. Fluorescein angiography can also be used to determine the extent of the occlusion as well as classify it into one of four types non-arteritic CRAO, non-arteritic CRAO with cilioretinal artery sparing, transient non-arteritic CRAO and arteritic CRAO. Optical coherence tomography (OCT) may also be used to confirm the diagnosis of CRAO.

Causes
CRAO can be classified based on it pathogenesis, as arteritic versus non-arteritic. Non-arteritic CRAO is most commonly caused by an embolus and occlusion at the narrowest part of the carotid retinal artery due to plaques in the carotid artery resulting in carotid retinal artery atherosclerosis. Further causes of non-arteritic CRAO may include vasculitis and chronic systemic autoimmune diseases. Arteritic CRAO is most commonly caused by giant cell arteritis. Other causes can include dissecting aneurysms and arterial spasms, and as a complication of patient positioning causing external compression of the eye compressing flow to the central retinal artery (e.g. in spine surgeries in the prone position).

Mechanism
The ophthalmic artery branches off into the central retinal artery which travels with the optic nerve until it enters the eye. This central retinal artery provides nutrients to the retina of the eye, more specifically the inner retina and the surface of the optic nerve