Explaining the Types of Retinal Artery Occlusions and How they Occur

Like retinal vein occlusions, retinal artery occlusions (RAO) also are classified on the basis of whether they block the entire artery or only a branch of it. They may be thought of as a "retinal stroke".

The appearance of an artery occlusion (RAO) is different from a retinal vein occlusion (RVO). One does not see the dilated, tortuous veins and superficial retinal hemorrhages.

Instead, the retinal initially looks pale, an appearance caused by the swelling of the retina as a result of lack of blood.

The macula may have a "cherry-red spot" due to the thinner retina in that location. There are also often mild edema and splinter hemorrhages around the optic nerve.

Central Retinal Artery Occlusion (CRAO)

• Complete or nearly-complete blockage of this artery causes profound vision loss. This is classified as ischemic CRAO.
• The mildest form of CRAO is non-ischemic CRAO and occurs when the Central Retina Artery is only partially blocked.
• Some individuals have an "extra" artery from a different circulatory system that feeds the macula. Called the Cilio-Retinal Artery, it sometimes protects the macula from CRAO and preserves central vision.
• Studies have indicated that 90 minutes after the CRAO event the damage is irreversible.

Branch Retinal Artery Occlusion (BRAO)

• The portion of the vision that is lost will correspond to the amount of retina supplied by the affected artery.
• Unlike CRAO, in which the Central Retinal Artery is believed to form a blockage near the point where it enters the eye, a BRAO usually can be seen. They are commonly caused by clots referred to a "plaques", that travel down the artery until the opening becomes too small.
• Within a few months of the occurrence the retina will resume it's normal appearance, even though it may have permanent visual loss.