Corneal ulcers in cats are an erosion of the various layers which make up the outer protective surface of the cat's eye called the cornea. When an ulcer develops, it can be very serious because part of the inside of the cat's eye is now exposed.
Most commonly, corneal ulcers are caused by some sort of trauma to the eye. This may be a blunt impact, or possibly a scratch from another animal. In somewhat rarer cases, a chemical infection may trigger the ulcer - such as if the cats gets shampoo or some other irritant in its eye. Finally, ulcers may also be caused by bacterial infections or viral infections such as feline herpes, according to VCA Animal Hospitals.
Corneal ulcers are very painful, so owners will likely notice the issue when the cat begins squinting or pawing at its eye. The eye may also take on a cloudy appearance as the ulcer begins to develop. The cat may also keep its eye shut or blink repeatedly.
It's important owners bring their cats to a veterinary clinic as soon as possible if a corneal ulcer is suspected. In many cases, ulcers can be treated with medication if caught early enough. However, an ulcer that erodes through all protective layers to the eyeball itself may irreparably damage the eye and cause blindness.