The cornea of the eye is the transparent layer that makes up the front part of the eye. The cornea performs two important functions: it protects the eye from dust, germs, and other external substances; it also focuses and controls the amount of light that enters the eye, thus facilitating accurate vision. Because it is the outermost layer of the eye it is prone to scratches and tears. It is important to note that short faced breeds are more prone to eye injury as they have eyes that protrude as well as eyelids that may not cover the globe of the eye completely.
An ulcer occurs when there is damage to cornea, there are many things that can contribute to a corneal ulceration forming.
- Abrasion from plants, thorns, or bushes
- Scratches from contact with another animal
- Chemical irritation
- Foreign body injury
The first thing most owners notice is that their pet is squinting or rubbing at their eye. The white part of the eye (called the sclera) may also appear red and swollen, it may be watering excessively or the pet may be holding it shut entirely. Some breeds such as short faced breeds have decreased corneal sensitivity so they may not show any initial symptoms.
Diagnosis of a corneal ulcer relies on patient history as well as an ocular exam. The gold standard of testing is called a fluorescein stain. This is performed by placing a small drop of stain on the eye. Normally tears and water will roll off the intact surface of the eye, in the event there is a corneal ulcer the stain will stick to the damaged area and appear bright green under special lighting.
Treatment for a corneal ulceration involves both the use of an antibiotic and pain control. Most ulcers heal easily with appropriate treatment. Ocular antibiotics may be in either an ointment or a liquid drop. These will need to be administered 3 – 4 times a day. Atropine sulfate 1% is used for pain control. This medication works by temporarily causing the pupil to dilate and keep the iris from spasming. Most pain in the eye is caused by pupillary spasm. Because of the dilation of the pupil the pet may continue to squint or avoid bright areas. Because the tear duct system is connected to the nose and mouth cats will often drool after administration of this medication, dogs do not appear to be bothered as much. A cone collar is usually required to prevent further harm to the eye from rubbing.
In some cases complications may arise. There are 3 types of ulcers that require more intervention than antibiotics and pain control. The first of these is called an indolent ulcer. The tissue at the edge of these types does not adhere to the layer underneath thus causing the ulcer to be unable to heal. There are several treatment methods to treat an indolent ulcer. The second is called a melting ulcer. When the tissue of the cornea becomes infected the cornea will acquire a yellow or tan appearance. This is caused by the infection producing enzymes that attack the normal cornea. When this happens the cornea turns an opaque tan-yellow in color, these ulcers can actually perforate. Treatment of a melting ulcer may include sampling the eye for culture to aid in the selection of the appropriate antibiotic. Often treatment involves drawing blood from the patient and separating the serum to use as an eyedrop to inactive the enzymes that are damaging the collagen of the eye. The third complication is called a Descemetocoele. The innermost layer of the cornea is called the Descemet’s membrane, this type of ulcer has penetrated through the upper layers of the cornea and reached the last Descemet’s membrane. Animals with a descemetocele are at high risk for rupture of the globe of the eye. The typical treatment of a descemetocele is surgery.