Red eye is a condition in which the conjunctiva, the clear membrane that lines the eyelid and covers the white of the eye, becomes inflamed and red.
Conjunctivitis is the most common cause of red eye in cats. It is caused by an infection or an allergic reaction.
Allergies can also cause red eye in cats. Common allergens include pollen, dust mites, and food.
Foreign bodies, such as dust or dirt, can also get into a cat's eye and cause redness and irritation.
Eye injuries, such as scratches or cuts, can also cause red eye.
Systemic diseases, such as FeLV or FIV, can also cause red eye in cats.
If your cat's eye is red and you are not sure of the cause, you should see a vet.