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How is the cause of anisocoria diagnosed? In other cases, depending on the underlying cause, the white part of the affected eye might be red, the cornea (outer surface of the eye) might be cloudy or bluish in color, there might be a discharge from the eye, the eyelid on the affected eye might be droopy, the dog might be squinting or rubbing at its eye, or you might notice that your pet is less active than usual. In some cases, that might be all that you notice. In all cases of anisocoria, the pupil in one eye will be bigger or smaller than the one in the other eye. If anisocoria occurs suddenly, you should consider this an emergency and seek veterinary care immediately to lessen the chance that your dog's vision will be permanently affected. Congenital defect of the iris, in which the iris tissue does not develop properly.Iris atrophy, or a decrease in the amount of tissue within the iris, usually a degenerative change associated with aging.Scar tissue formation between the iris and the lens (called posterior synechia), a condition that may develop subsequent to uveitis.Uveitis, or inflammation of the interior of the eye (the pupil in the affected eye will usually be constricted).
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Disease or injury to the brain or to the nerves running to the affected eye such as Horner’s syndrome.In some cases, the abnormal pupil may be the one that is smaller and in other cases the abnormal pupil may be the one that is larger.Īnisocoria is a sign of a disease or condition, therefore there can be several different causes, including: What is anisocoria?Īnisocoria is a condition in which the pupils of the dog’s eyes are different sizes in other words, one pupil is larger than the other. The pupil constricts or dilates (enlarges) according to the amount of light that enters the eyes, with both pupils normally dilating in dim light and constricting in bright light. In dogs, about 75% of optic nerve fibers cross to the opposite cerebral cortex at the optic chiasm.The pupil is a round opening in the middle of the iris (colored part of the eye) that allows light to pass through the eye to the retina. Optic radiations relay the visual information from the LGN to the occipital cortex. This information travels along cranial nerve (CN) II via the optic chiasm to the optic tracts and then the LGN. When light enters the eye, it activates the retinal photoreceptors. The visual pathway ( Figure 2) is composed of the retina, optic nerve (also known as cranial nerve II), lateral geniculate nuclei (LGN) in the thalamus, and occipital cortex in the cerebrum. Miosis refers to smaller than normal pupil size, while mydriasis refers to larger than normal pupil size. Localize the lesion responsible for anisocoria.Determine whether one or both pupils are abnormal in size.
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When evaluating patients with asymmetric pupils, the practitioner needs to: Heidi Barnes Heller, DVM, Diplomate ACVIM (Neurology), and Ellison Bentley, DVM, Diplomate ACVOĪnisocoria is defined as pupil asymmetry, and may be seen with ocular or neurologic dysfunction ( Figure 1).1When anisocoria is caused by neurologic disease, unequal pupil size may result from malfunction of the sympathetic, parasympathetic, or visual systems.įIGURE 1.