Corneal sequestrum is a disease affecting the cornea (the clear curved transparent part of the front the eye). The sequestrum is usually an area of degenerated or non-living corneal tissue. This develops after an area of the cornea becomes ulcerated and the ulcer is long standing or non-healing. The area of corneal degeneration often turns light brown to dark brown or black in color. The sequestrum may affect only the outer layers of the corneal stroma (tissue), but in some cases the sequestrum extends deeper into the cornea and may lead to deep ulceration, pain and possibly, corneal rupture.

Conjunctivitis and keratitis are common eye problems in all ages of cats. Conjunctivitis refers to the inflammation of the pink membranes surrounding the eye whereas keratitis refers to the inflammation of the cornea. Signs of conjunctivitis may be coupled together with keratitis and is then termed keratoconjunctivitis. A number of infectious agents, namely viruses and bacteria have been identified as possible underlying causes of these two conditions. These infections may be contracted as a kitten from the mother or from other cats.

Feline herpesvirus (FHV-1) is a common cause of eye and upper respiratory infection in the cat. This virus is very common in the cat population, but it is not contagious to people and other species of animals such as dogs. Herpesvirus is easily passed from one cat to another through sneezing, coughing, grooming and/or simply being in close contact with an infected cat. Clinical signs associated with infection can vary greatly between cats. Some cats affected with FHV-1 may only have mild conjunctivitis of one or both eyes. Other cats with more severe forms of the disease may show ocular (eye) and nasal (nose) discharge, conjunctivitis (inflammation of the white part of the eye), coughing, sneezing and corneal ulcers. Corneal ulcers can be very painful and serious enough to cause noticeable scarring on the normally clear cornea. An infected corneal ulcer may even progress to cause perforation (rupture) of the eye.

Proliferative keratoconjunctivitis is an inflammatory condition affecting the cornea and/or the conjunctiva. This condition is unique to the domestic cat and the horse. The lesions of the cornea and/or conjunctiva are comprised of specific white blood cells, which invade these tissues and result in a white to pink plaque that is visible on the surface of the eye. This disease is progressive and can grow to involve the entire surface of the eye causing blindness and discomfort. Often it is initially detected in one eye; however, the disease often progresses to involve both eyes.