An ulcer is similar to a corneal abrasion, except that an ulcer is deeper and involves the middle and sometimes the inner layer of the cornea.
Most corneal ulcers are caused by trauma, but some are associated with keratoconjunctivitis sicca, corneal dystrophy, diabetes mellitus, Addison’s disease, or hypothyroidism.
Corneal ulcers are extremely painful and cause severe tearing, squinting, and pawing at the eye. Dogs frequently avoid light. Large ulcers are visible to the naked eye as dull spots or dished-out depressions on the surface of the cornea. Small ulcers are best seen after the eye has been stained with fluorescein.
Treatment: Early veterinary consultation and treatment is vital to prevent serious complications and even loss of the eye. Medical treatment is similar to that described for a corneal abrasion (page 191), except that ulcers take more time to heal. Your veterinarian may recommend injecting antibiotics directly into the eye beneath the conjunctiva.
Surgical treatment involves suturing the third eyelid or a flap of conjunctiva over the surface of the eye to protect the cornea during healing. Soft contact lenses and collagen shields are other methods of protecting a damaged cornea. The advantage of a contact lens is that it can be changed weekly to observe and treat the ulcer. Collagen shields need to be replaced periodically because they degrade and disappear within a few days. Your dog may need to wear an Elizabethan or BiteNot collar while the eye is healing to prevent rubbing or pawing at the eye.
Rupture of the eye into the anterior chamber can be anticipated if the cloudy central portion of a deep ulcer begins to clear, or the endothelial layer protrudes like a bulging tire. This can be recognized by your veterinarian. It is an emergency. Immediate surgery is necessary to prevent loss of the eye.