Ulcers of the cornea in dogs and cats
Ulcers of the cornea in dogs and cats is a common occurrence, and a potentially dangerous affliction. Any abrasion to the cornea, including an bee sting, rub from a paw, a scratch from a claw or thorn or an invasive infection can abrade the cells on the surface of the dog or
cat cornea. Once the surface cells are disrupted the smooth surface of the cornea becomes rough, infective organisms can invaded the spaces between the cells and the area becomes a source of pain and irritation to the animal. Dogs and cats with corneal ulcers commonly will have increased tear production, will squint (called blepharospasm) and rub at their eye. The irritated tissues often become infected.
If infection progresses into the thin cellular layers of the cornea, the ulcer may deepen and widen and eventually break through the membrane at the back of the cornea called Descemet's membrane. In these severe cases, the fluid from the anterior chamber of the eye can escape and the front of the eye collapses. When this occurs, called a descemetocele, the iris will often seal the hole in the cornea. If the iris tissue adheres to the opening and acts as a plug, the anterior chamber may refill and eventually the ulcer may heal and seal the opening in the cornea. This could take many weeks to occur. In unfortunate cases, the interior of the eye can become infected and eventually the eye may be damaged beyond repair.
Once the cornea is abraded, the entire cornea suffers from swelling (called edema) and the cornea takes on a slight haze. Then tiny capillaries begin to move over the cornea from the white of the eye (called the sclera) and seek out the damaged tissue. Within days of the abrasion these tiny vessels are on their way to bring healing tissues and fluid to the ulcer. As specialized corneal cells slide into and fill the defect, the ulcer eventually heals and the surface of the cornea returns to normal. Then the healing capillaries dry up and go away!
Clinical Signs
Corneal ulcers are extremely painful and may cause your pet to avoid bright lights. Clinical signs also include squinting, watering or redness of the eye and a visible cloudy spot on the surface of the eye.
Diagnosis
The most immediate diagnosis of a corneal ulcer is a fluoroscein dye test. The dye is placed on the surface of the eye to "highlight" the corneal ulcer. This test helps your veterinarian determine the size and depth of the ulcer. If your veterinarian suspects an underlying cause, like dry eye, other tests may also be recommended
Treatment
Most veterinarians will begin treating corneal ulcers in dogs and cats with appropriate antibiotic ointment or drops. The use of cortisone or cortisone-related medications may not be a good choice to use due to the possibility of delayed healing and a worsening of the ulcer. It pain is evident, Atropine or other antispasmodic medications may also be dispensed.
The dog or cat's dewclaw, if present, may need to be bandaged to prevent the dewclaw from doing further damage to the irritated cornea as the patient wipes across the offending eye.
Rechecking the eye in five days and then another five days usually demonstrates that proper healing has taken place. A negative stain uptake upon use of the Fluorescein stain will indicate if additional treatment is needed.
Some breeds of dogs, notoriously Boxers and Boston Terriers, often have very unresponsive corneal healing activity.
hese cases of poorly healing corneal ulceration need to be monitored closely and special selection of adjunctive medications, such as topical Vitamin E and other medications, may need to be tried to stimulate corneal epithelium regeneration.
Third eyelid flap surgery
Occasionally when a corneal ulcer fails to heal or when a very deep or wide ulcer is present a third eyelid flap procedure is performed.
Under general anesthesia the patient's Nictitating Membrane...also spelled Nictating Membrane... (called the third eyelid) that originates in the medial corner of the eye opening and under the lower lid, is pulled up and over the cornea.
It is sutured to the inside of the upper eyelid, thus forming a protective and nourishing layer of tissue over the damaged cornea. Medications can still be applied to the eye between the eyelids, but the surface of the cornea will not be exposed and cannot be visualized while the third eyelid flap is in place.
The sutures are removed in 10 to 28 days and the corneal healing is assessed. This procedure is commonly done and be very helpful in generating a healing response in severely damaged corneas.