Corneal erosion or ulceration is a defect in the clear protective membrane covering the iris and the lens of the eye. It can be caused by physical trauma, a chemical injury, or chronic irritation as occurs in the case of keratoconjunctivitis sicca (KCS or “dry eye”) or entropion (hereditary inward rolling of the eyelids). Deep ulcers are considered ocular emergencies.
A corneal ulcer is painful. It usually causes photophobia (avoidance of light), squinting, and rubbing / pawing at the eye. There may be a mucousy discharge from the affected eye. Because the barrier provided by the epithelium, or the outer layers of the cornea, is compromised, the eye becomes susceptible to bacterial infection. Left untreated, an ulcer can lead to permanent scarring and vision loss. It is possible that a small ulcer in the cornea could eventually progress to complete eye-loss.
Damage to the cornea is not always obvious to the pet’s owner; symptoms are evidence enough that the eye needs immediate veterinary attention. The doctor will first instill a local anesthetic into the painful eye to alleviate discomfort and facilitate a thorough examination. Then, several tests are performed including a fluorescein stain uptake test. A sterile fluorescent dye is introduced onto the surface of the cornea, then gently rinsed away with saline. A healthy, intact cornea is smooth and non-porous and will not absorb any stain. Any defect in the smooth surface however, no matter how superficial, will retain the fluorescent dye. The eroded area will subsequently glow bright green under a wood’s lamp (black light).
Superficial erosions and minor ulcers usually heal rapidly with some protection from a topical antibiotic eye-drop or ointment. Because the cornea is constantly rinsed by the cleaning action of tears, the medication must be reapplied often. It is critical, especially during the first 48 hours of treatment, to apply the antibiotic as prescribed. This may be as frequent as four or more times a day and should be continued throughout the night as well. The clear cornea normally contains no blood vessels; therefore, systemic antibiotics like those taken orally are ineffective and useless at this stage.
The eye is treated for pain with a topical medication as well. Some medications may cause pupil dilation as an intended effect, and the pet may shy from bright light as a consequence. Also, the tear ducts drain into the nasal cavity and the oral cavity; drooling may be seen for a short time after treatment due to a bitter tasting medication applied in the eye.
The veterinarian will ask for a recheck appointment within 2 days to one week depending on the initial presentation and severity. Routine ulcers will usually resolve in about 7 to 10 days; prolonged healing despite diligent treatment will warrant further testing, a change in medications, or a referral to an ophthalmologist.
Deep ulcers, indolent ulcers (will not heal), and descemetoceles (read on) are not routine and are indeed ocular emergencies. A descemetocele (pronounced dez-met-o-seal) is an ulcer with the deepest membrane protruding through the opening in the cornea. Descemet’s membrane is the last covering that retains the fluid of the inner chambers of the eye. The pet may be referred immediately to a specialist in ophthalmology, even after-hours, for surgery to save the eye at-risk for blindness.
It should be noted that brachycephalic breeds of dogs and cats are especially predisposed to eye injuries and ailments such as corneal ulcers. Brachycephalics are animals with pushed in muzzles and protruding eyes, such as Pugs, Boston Terriers, Persians, and Himalayans.