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When a person has a cherry-red spot, he or she has a symptom of one of several diseases. The spot is obvious only to an ophthalmologist, as it is located at the back of the eye. It arises when disease damages an area of the back interior wall of the eye, and allows the red color of underlying blood vessels to only shine through in one spot surrounded by damaged areas of opaque, whitish cells. Commonly, people with a cherry-red spot have a condition that prevents them from using and breaking down fats normally. Other potential causes include eye injury or problems with blood vessel constriction.
The back wall of the eye is called the retina, and it contains cells that recognize light and images. On the retina is a small area called the macula, which is yellow in color and is the spot at which the most efficient vision is located. If a cherry-red spot is present in a patient's eye, it will be on the macula.
Instead of being yellow and healthy tissue, the cherry-red spot appears in Caucasians either as a mild red or as a bright red color. The color of the spot depends on the color of the epithelial cells of the person, so people with Indian ancestry, for example, may have a reddish-brown spot, and native Australians can have a reddish-black spot. While the epithelial cells of the person present in the eye dictate the color variation, all have a red coloration due to the redness of the blood vessels at the back of the eye.
This redness arises from the fact that the cherry-red spot is an area where the blood in the vessels is visible, whereas the cells around the spot are damaged and not as transparent as normal. The damaged cells turn a whitish color and give the cherry-red spot a halo. If a disease continues to damage the area, this opaque area grows larger and the spot grows smaller.
Problems with metabolizing fats are an important cause of cherry-red spot damage. These conditions include genetic syndromes like Niemann-Pick syndrome, Hurler's syndrome and Sandhoff's disease, which can cause intellectual disability. A child with Tay Sachs disease was the first person to be identified with cherry-red spots that were related to disease, back in the late 1880s. An ophthalmologist named Warren Tay, who examined the baby, was the first to describe the spot.
As well as genetic disease, there are several other causes of a cherry-red spot. These include accidental injury to the eye, and issues with blood circulation or clots in the area. Poisoning, from carbon monoxide gas, methanol or quinine, for example, can also produce the symptom.