Merck Manual

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Pet Owner Version

Disorders of the Lens in Cats


Kirk N. Gelatt

, VMD, DACVO, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida

Reviewed/Revised Jul 2018 | Modified Oct 2022

The lens is a soft, transparent tissue that sits behind the iris. It helps focus incoming light onto the retina. Common disorders of the lens include those that affect its transparency (such as cataracts), and those that affect the placement of the lens.


A cataract occurs when the lens becomes cloudy or opaque, which effectively blocks light from reaching the retina. This causes a loss of eyesight that can range from mild vision problems to partial blindness. In contrast to dogs, most of the cataracts that develop in cats do not occur on their own. Instead, they often occur as the result of inflammation of the anterior uvea (called anterior uveitis Inflammation of the Anterior Uvea The uvea (or the uveal tract) is the colored inside lining of the eye consisting of the iris, the ciliary body, and the choroid. The iris is the colored ring around the black pupil. The ciliary... read more ). Cataracts can also be inherited; these types of cataracts are seen most often in young cats.

In general, treatment for cataracts involves surgery to remove the affected lens or lenses. Advances have been made in this procedure, but complications are possible. In animals in which cataract surgery is not performed, continued monitoring by a veterinarian is very important because cataracts can cause anterior uveitis, glaucoma Glaucoma in Cats Cats, like people, can develop glaucoma. Glaucoma occurs when an imbalance in production and drainage of fluid in the eye (aqueous humor) causes a buildup of fluid that increases eye pressure... read more , and a blind, shrunken eye. Follow your veterinarian’s recommendations for treatment of cataracts.

Lens Displacement

Lens displacement can occur in cats. The displacement may be due to trauma, longterm inflammation of the uvea, glaucoma, or changes associated with well-developed cataracts. Lens displacement also occurs in elderly cats.

Complete displacement of the lens into the front chamber of the eye produces sudden, severe signs and frequently is accompanied by glaucoma and swelling of the cornea. The only effective treatment is surgical removal of the lens.

Displacement backward into the main eye chamber (called the vitreous cavity) may cause no signs or be associated with inflammation of the eye or glaucoma. Partially dislocated lenses are recognized by a trembling of the iris and lens. The decision to remove partially dislocated lenses is based on the severity of the signs.

Procedures to remove the lens are associated with higher levels of postoperative complications of glaucoma and detachment of the retina. Your veterinarian will carefully evaluate your pet’s condition and recommend a program to provide your cat with the best possible outcome.

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