I have a beautiful long haired tabby/ tortoiseshell cross 1 year old but her right eye pupil is wide open and does not dilate, the left eye is similar but not as bad, the vet finds this ‘strange’ but is obviously not familiar with the problem. Can anyone help please?
Hi Derek: I am not sure that you have described the problem accurately. If the pupil is wide open it is dilated. Perhaps you mean that the pupil does not change shape or narrow. The pupil is the opening in the center of the eye through which the light passes and which is narrowed or enlarged to control the amount of light entering the eye. The iris (a muscular structure) opens and closes the pupil. In the cat the pupil is slit like and the amount of light entering the eye can be further controlled by the eye half closing and going over the slit.
Iris not responding to light input
If the iris is not responding to different light levels by closing and opening the pupil it might indicate that your cat is blind or partially blind i.e. light is not being received and no signal is being sent to the brain to regulate its impact on the retina. Blind or partially sighted cats can cope very well and therefore hide the problem.
Sudden blindness is often caused by untreated feline hypertension. Early signs to watch for include dilated pupils which don’t respond to light. It appears that this is what is happening with your cat but I am not a veterinarian. Seek veterinary advice please.
Hypertension can damage the blood vessels in the retina and it can cause the retina to detach which in turn can cause partial or complete blindness on my understanding of this disease.
Any disease that reduces the sensitivity of the retina to light impulses such as retinal atrophy or a disease which affects the optic nerves or that part of the brain which processes information from the optic nerve (e.g. brain trauma) can produce visual disturbance including blindness which can cause the operation of the irises to change which in turn can lead to the pupil being in an always dilated position.
High blood pressure (hypertension) is one of the most common causes of retinitis which is a disease of the eye in which inflammation of the retina leads to the degenation and destruction of the light receptors. There are various causes including toxoplasmosis, feline infectious peritonitis, lymphoma, and systemic fungus infections but, as mentioned, one of the most common causes is high blood pressure.
Shining a light into your cat’s eyes is not a guaranteed test of whether they are partially or completely blind. It is not exact enough because the pupil may become smaller because of a reflex action. In which case it doesn’t tell you if the brain is receiving visual images.
Perhaps a more general way to diagnose if a cat is blind is through their behaviour and activity. Activities that require good body coordination such as jumping from a sofa to a chair may show that the cat’s abilities are impaired. And sometimes in a dimly lit room cats with limited or no vision may bump into furniture. They may hold their noses close to the ground and feel ahead with their whiskers which are pointed forward.
Sometimes, with older cats their eyesight might fail soon after they become deaf. They then have to rely more on memory to find their way around their home. Many blind cats get along quite well because they are familiar with the surroundings and they can use their other senses. Everything in the home should be kept in its place this reason.
Of couse there is no substitute for a good vet providing advice on the spot.