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Anisocoria is the term that describes the condition when pupils are unequal in size. It can result from lesions in the eye, the pathway between the eye and the brain or in the brain. The size of the pupil is determined by the muscles in the iris that can produce pupillary dilation or constriction. Sometimes no cause is found for anisocoria and other times it is caused by very serious conditions. Mild inequality of pupils in cats is very common and is related to the difference in muscle tone between the two eyes. Persistent, marked anisocoria warrants ocular and neurological examination as well as blood testing to determine the proper treatment as well as the prognosis. Pupil size is examined in bright and dim light. Generally if the difference in size remains the same in both levels of lighting the anisocoria is physiologic or anatomic and not pathologic.
Some of the conditions that have been associated with anisocoria:
- Trauma (eye, nerves, brain)
- Infections (eye, nerves, brain)
- Protozoan (Toxoplasmosis)
- Fungal (Histoplasmosis)
- Viral (Feline immunodeficiency virus, Feline Leukemia virus, Feline Infectious Peritonitis, Feline herpes virus)
- Mass lesions (eye, nerves, brain)
- Malignant
- Benign
- Feline ischemic encephalopathy
- Ocular causes
- Anterior uveitis
- Glaucoma
- Painful corneal lesions
- Some eye medications
- Systemic hypertension
- Idiopathic
The first tests that generally follow a thorough examination are tests for feline leukemia and feline immunodeficiency viruses and measurement of the kitty’s blood pressure. If a lesion is suspected to primarily involve the eye, fluorescein stains may be applied to look for an injury and the ocular pressure may be measured. A complete blood count and a blood chemistry profile may also be recommended to evaluate for systemic disease. Referral to a veterinary ophthalmologist or neurologist may be necessary to reach a final diagnosis.
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