Just like you, your cat has a pupil in her eye. Though her vision is vastly different from yours, her pupil serves the same purpose, to regulate the amount of light received by her eye. As the light changes, her pupils constrict and dilate to help her see better. Sometimes, however, it's more than a matter of light causing her pupils to grow and shrink.
Keeping Your Eye on Her Eyes
If it's a bright and sunny day and your cat's pupils are large, you may be wondering what's up with that. After all, it makes sense that they're dilated in a darker setting, allowing her eyes to soak in as much light as possible. However, there are a variety of reasons why her pupils may dilate despite the bright light. It could be a matter of mood -- she may be frightened by something, or she may be happy and frisky. Her demeanor will give you a clue you which it is. Sometimes her dilated pupils are an indicator of health. Hypertension, glaucoma, sudden onset blindness and retinal detachment are a few of the medical conditions that present dilated pupils as a symptom. If her pupils continue not to respond to light or if you see other symptoms, such as a sudden change in eye color, unusual spots on the cornea or iris, discharge, squinting or pawing at her eye or forward-facing whiskers, take her to the vet.