If you've been noticing that your cat is starting to bump into things or that its pupils are staying dilated no matter how brightly lit the room is, it's possible that your cat is going blind. The first thing to do is to make an appointment with a vet. Your vet may be able to put a stop to the deterioration in your cat's vision and maybe even be able to correct it. At the least, your vet can give you tips on how to help your cat navigate its surroundings with limited vision.
Cats can lose their vision due to a number of reasons, including disease, birth defects, lack of enough oxygen during birth, and due to reactions to certain medications. Additionally, if a cat's diet does not include enough of the amino acid, taurine, the cat's retinas (the light-sensitive cells inside the eyeballs that transmit messages about sight to the brain) can become damaged, which can lead to blindness. Altering your cat's diet accordingly may limit but not reverse the damage.
If a cat's blindness is caused by cataracts (cloudiness in the eyes), the condition can be remedied through surgery. Expect that once your cat reaches middle age (six to ten years of age), its vision, along with its other senses and body functions will begin to deteriorate. If your cat has limited vision, the vet will probably suggest keeping your cat restricted to a few familiar rooms. Try not to change the furniture layout of the room, as your cat uses and relies on cues and landmarks that are on its level. Even something as simple as a child's toy left on the floor one morning can disorient a blind cat. Keep your cat away from stairs (in order to prevent accidental falls) and from doors to the outside. A blind cat in an unfamiliar outside environment has little chance of surviving.