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Medications: Atropine and tropicamide cause mydriasis in the pupil, while pilocarpine causes miosis.

When this is the case, we refer to ophthalmologic or ocular causes. Ocular causesĪnisocoria can be a condition secondary to diseases of the eye or dysfunctions in the optic nerve, which is responsible for transmitting visual stimuli from the retina to the brain.Īsymmetry in pupil size can also appear as a result of the dog’s eye contact with certain plants and substances. This means that the difference in pupil size in your dog may be a manifestation of some disorder that may occur in the visual or nervous systems. Causes of anisocoria in dogsĪssociate professor at the University of Arizona College of Veterinary Medicine, Ryane Englar, states in her book Common Clinical Presentations in Dogs and Cats published in 2019, that “anisocoria may be a result of primary ocular disease or primary neurologic disease.” Pupil dilation is known as mydriasis and occurs as a response to light. When there are too many light stimuli, the parasympathetic nervous system (PNS) is responsible for closing the pupil to reduce the entry of light into the pupil. The opposite occurs in pupillary constriction. In response, the sympathetic nervous system (SNS) is responsible for increasing the size of the pupil in order to obtain as much light as possible. The first occurs when there’s a very poor light stimulus. It does this through two processes known as pupillary dilation and contraction. It has the function of regulating the entrance of light into the eye, especially into the retina. In dogs, its shape is always round, and it’s similar to the diaphragm opening of a camera. The pupil is the black structure found in the center of the iris. Discover all the aspects related to this unusual pupillary disorder. Although it isn’t a pathology in itself, its appearance is related to alterations in the ocular, nervous, and auditory systems.įor this reason, it’s important for you to know the origin of anisocoria in your pet, in order to provide timely care. That is, one pupil is more dilated or contracted than the other. In essence, anisocoria in dogs could be defined as asymmetry in pupil size.