Why Do Cats Eyes Get Smaller. While every cat has magnificent eyes, there are a few breeds of cats which are known for having particularly round eyes. Obviously, just like human pupils your cat’s pupils will always react to light, this means that when there is brighter light or a lack of light the pupils will dilate.

Readers answer other readers' questions on subjects ranging from trivial flights of fancy to profound scientific concepts. For your cat, their pupil size is dictated by light and emotion. Some illnesses, drugs and other chemicals affect the behavior of the iris.