Senior Hyperthyroid Cat Is Deteriorating

Q: Our black and white tabby, Holstein, is about 17 years old. She is very thin (always has been), but now we can see her hip bones and spinal bones. She eats like a horse, wet food twice a day and dry food all day. She is constantly thirsty, but will only drink out of the tub spigot. She is an indoor cat with rare jaunts outside to eat some grass. Her eyes are hazed over so you can barely see the color of her irises (which is sad, because she had such beautiful eyes). Could these be cataracts? It is clear she cannot see as well anymore and is deteriorating due to age. She was diagnosed with hyperthyroidism a year or two ago. She eats and sleeps, is lovable, and plays occasionally with her stuffed mice. She is comfortable now, but I am wondering if there is anything we can do about her eyes to help her see better?

A: You did not say in your letter whether you are giving your cat medication for her hyperthyroidism. I’m wondering how well controlled your cat’s hyperthyroidism is, since she “eats like a horse” and is “constantly thirsty.” A cat with well-controlled hyperthyroidism would not be expected to have such dramatic clinical signs. Some cats with hyperthyroidism will have hypertension (high blood pressure), and if uncontrolled, it can lead to retinal hemorrhage and/or retinal detachment, resulting in vision impairment.

Some cats, however, will experience a decrease in vision simply as a matter of aging. I can’t be certain from your description exactly what is causing the hazy appearance of her eyes. It is very likely to be something called “lenticular sclerosis,” another aging change that occurs in the lens of the eye as cats get older. Clients often see this and think that their cat has cataracts, when in fact it is just a benign cloudy appearance in the lens.

I would have your cat’s thyroid re-evaluated, and consider having a blood pressure measurement performed as well. Your cat should have a complete eye exam by your veterinarian, including a good look at the retinas. If the blood pressure is normal and the ophthalmologic exam is normal, then your cat’s diminished eyesight is likely to be due to aging. I’d be careful when you let her outside to nibble the grass. If her vision is diminished, she should not be allowed outside unless closely supervised.