Corneal Ulcer

By: Dr. Stephanie Permenter

The horse’s eye is large, beautiful, expressive, and it is also set prominently on the side of their head. Because of it’s anatomic location horses frequently scratch or damage the clear portion of the eye which is the cornea. The cornea has a large number of nerve endings throughout it and even very small injuries or ulcerations can be extremely painful, causing the horse to squint and have an increase in tear production. To compound the problem, the horses’ environment is full of bacteria increasing the risk of contamination and infection.

The horse’s eye is a complex structure with its own microenvironment and protective mechanisms. Every structure in the eye works together to protect the eye and allow the horse to see the world around them. The clear portion of the eye, the cornea, is made up of base layer of cells that provide nutrients to the numerous clear flattened cells make up the bulk of the cornea. Coating the top of the cornea is a tear film which helps keep the cornea moist and protects it from bacteria and small debris.

Once the top layers of the cornea have been damaged, the protective tear film that eyefunctions to remove bacteria and old cells can actually work against healing of the eye. The tear film includes specialized enzymes that help break down old cells and bacteria and as the body tries to remove damaged corneal cells and invading organisms it can actually damage the healthy cells around the injury creating a larger ulcer. If the body is left to deal with the damage on its own, overtime it can cause the cornea to become overly thin and even rupture. For this reason it is very important to treat ulcers quickly and they should be seen as an equine emergency.

The longer the eye is left without treatment, the larger the ulcer is likely to become. This delay can significantly increase the length of treatment and the risk of complications. Larger ulcers lead to an increased amount of scarring in the cornea, which appear as white areas that can alter vision.

It is important to make sure your veterinarian evaluates the eye before treatment begins to ensure that the correct antibiotics are used. Inadvertent treatment with an ointment or medication containing steroids can rapidly degrade the cornea leading to a sight threatening ulcer. Corneal ulcers often require treatment with topical antibiotics 4-6 times a day as well as other medications, both topically and orally, to help reduce inflammation and discomfort within the eye. Rapid identification and treatment can reduce discomfort as well as treatment time and cost, allowing your horse to return to its normal activities.