A cat’s eyes are remarkable in that they respond to light levels, allowing the cat to see in near-darkness in order to hunt prey. A cat’s eyes are also a ‘window into their soul’, and they can give you a good sense of how your cat is feeling – emotionally and physically.

Narrow pupils signal that a cat is aroused and its senses are heightened. Watch your cat’s pupils become narrow slits the next time they spot a bird through the window, or when they sit on your lap and purr for attention.

Wide pupils, on the other hand, can be a sign of both excitement and fear, and so you will need to look for other body language clues such as a ‘bottle-brush’ tail, which indicates that a cat is scared. Wide pupils can also be a sign of abject terror, something which many cats experience when they have to travel in a car.

What if a cat’s eyes are different sizes? When one pupil is larger than the other this indicates that a cat has a condition called anisocoria. Anisocoria is a symptom of a medical problem, and not a disease in itself, and it can indicate that the cat has:

• a brain injury due to trauma, such as a fall or being hit by a car
• an injury to the surface of the eye
• a problem with the nerves running to the affected eye
• glaucoma, a very painful build up of pressure in the eye
• a retinal disease, and possibly cancer.

Different sized pupils can also be a sign of the feline leukemia virus, which affects a cat’s immune system and for which there isn’t a preventative vaccine.

You should seek immediate veterinary advice is you notice your cat’s pupils have developed anisocoria to lessen the chance that your cat’s vision will be permanently affected, or an otherwise undetectable head injury is left untreated.

A cat’s pupils are an incredibly expressive part of your feline’s body language repertoire, and help you to know how they are reacting to certain stimuli – enabling you to do more of the good things and to avoid unnecessary fear. They could also help you to save your cat’s life.