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Eye has Changes to Colored Part (Iris)

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    The iris is the colored part of the eye. It is a thin circular ring of muscle that constricts or dilates the size of the pupil according to light exposure, thus controlling the amount of light that reaches the retina.

    Most horses have a dark iris. However, horses with Pinto coloration and some horses from American Paint lines may have a blue iris, called a glass eye or blue eye. In some horses, the iris may lose pigment with age, resulting in a spotted or mottled appearance. This is usually normal.

    However, dark spots within the iris can be tumors or iris cysts. The corpora nigra is a normal growth on top and bottom of the pupil that changes in different light. The corpora nigra can also develop cysts.


    Given the importance of your horse’s sight, assess your horse’s eye and send a photo of your horse’s eye to your vet for discussion.


    Your vet considers this finding in the context of the rest of the eye exam, the appearance of the other eye in comparison, and considering the horse’s breed, age, color and other factors.

    Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health

    Author: Doug Thal DVM Dipl. ABVP


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