Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl has a dilated pupil that does not respond to light, even bright light, and she cannot see with that eye. Things that can cause dilated pupils that are unresponsive to light stimuli include diseases that affect the eye itself, especially the retina (the back of the eye that collects light stimuli and sends the information to the brain), the nerves that take information to the brain or the brain itself.This can be related to trauma including a penetrating foreign body or scratch or bite wound.In older cats hypertension, which can lead to retinal bleeding or detachment, is the most common cause of dilated pupils. Hypertension in cats is usually due to hyperthyroidism
(a tumor of the thyroid gland that secretes excess thyroid hormones) or kidney
failure. Less commonly it can be due to primary hyperaldosteronism, which is often due to an adrenal gland tumor.Other possible causes of dilated pupils include systemic infections like Toxoplasmosis, feline leukemia, feline immunodeficiency virus or feline infectious peritonitis, a toxin ingestion, or a brain tumor or stroke (fairly rare in cats) or glaucoma (increased eye pressure).Were her eye pressures checked?Was her blood pressure checked?Any history of trauma to her eye?Did they look into her eye to check for bleeding, a detached retina or evidence of a mass?Was she checked for feline leukemia and feline immunodeficiency viruses?Was she checked for toxoplasmosis?Were her kidney enzyme levels normal?Was her urine checked for high levels of protein which could indicate early kidney failure?Was her thyroid level checked?Did they send in a sample to measure serum aldosterone? If she does not have a history of trauma, her eye pressure is normal, her kidney enzyme levels are normal, she is concentrating her urine well and not spilling excess protein, and her thyroid levels are normal but she has high blood pressure then the next step would be measuring her aldosterone levels, and an abdominal ultrasound to assess her adrenal glands.If she does not have high blood pressure then referral to a veterinary ophthalmologist would be best. They can assess her eye further and discuss possible causes and treatment. Please let me know if you have any further questions.