Your veterinarian will consider your cat’s history, perform a thorough physical exam, and recommend diagnostic tests to help determine the underlying cause. Unlike in dogs, Horner’s Syndrome in cats should not be expected to resolve on its own. Head (e.g., traumatic injury, middle ear infection).Neck or chest (e.g., bite wound, mediastinal cancer).Midbrain or cervical spine (e.g., tumor or blood clot) this is uncommon in cats.This is usually quite obvious in cats, due to the contrast provided by their brightly colored irises, and the fact that their unequal pupils will have different shapes.Īnisocoria is always abnormal, but it may not be immediately apparent whether the larger or smaller pupil is the cause for concern.Ĭats with anisocoria should be examined promptly by a veterinarian (especially if it occurs suddenly).

The term anisocoria refers to having two differently sized pupils. Normally, both pupils dilate or constrict at the same time, but in some cases, one pupil remains fixed in an open or closed position. This process is not under conscious control it occurs in response to signals from the sympathetic and parasympathetic nervous systems. Pupils change size to regulate how much light enters the eyes. They even have special pupils that change shape! When fully open (dilated), their pupils are round, but when constricted, they have a vertical ellipse shape.

Unequal pupil size in cats