Glossary

Cataracts

Cloudiness in the lens of the eye that blocks light and can lead to blindness, often inherited or linked to diabetes.

Also called: canine cataracts, cloudy lens, cloudy eyes, lens opacity

A cataract is a cloudy area in the lens, the clear structure behind the pupil that focuses light. A small cataract may hardly affect sight, while a mature one makes the pupil look white or milky and the dog may bump into things.

Causes include inheritance, diabetes, age and injury, and cataracts that start in young dogs are often hereditary. Cataracts can also sit alongside other eye diseases.

Do not confuse them with nuclear sclerosis, a bluish haze that is a normal aging change in the lens of most older dogs and usually does not block sight much. Only a veterinarian can tell the two apart with an eye exam. Surgery by a veterinary eye specialist can restore vision in suitable dogs, and a cataract that moves or inflames the eye needs prompt attention.

Last reviewed November 8, 2026

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Related terms

Diabetes mellitus A disease in which the body cannot make or use enough insulin, so blood sugar stays high, with increased thirst and urination. Glaucoma Raised pressure inside the eye that damages the optic nerve; it is painful and can cause permanent blindness within hours or days. Progressive retinal atrophy A group of inherited diseases in which the retina slowly degenerates, causing night blindness first and then total blindness, without pain.