Corneal ulcer and abscess
Corneal ulcers are common in horses due to the environment in which they live. The cornea is the clear, front part of the eye. When you have a corneal ulcer there is a break in the top layer of cells or epithelium. It is essential that this top layer remain intact as this is what prevents infections. There are many types of ulcers that can happen in a horse; superﬁcial or deep.
Superﬁcial ulcers only involve the top layer of cells. Superﬁcial ulcers can occur from trauma or an infection. There are even superﬁcial nonhealing ulcers called indolent ulcers. Superﬁcial nonhealing ulcers usually occur in aged horses. Superﬁcial ulcers often respond very well to basic, broad spectrum antibiotic therapy. In the case of a nonhealing ulcer, additional minor procedures may be necessary to facilitate healing.
Deep corneal ulcers can develop if a superﬁcial ulcer becomes infected with a more aggressive bacteria or even a fungus. If this occurs these ulcers can become very deep within hours. Ulcers that are all the way down to the last layer of cells are called a descemetocele. There are even ulcers called melting ulcers. This type of ulcer develops when a bacteria or fungus turns the normally ﬁrm cornea to a gelatinous substance and it has the appearance of melting from the surface of the eye. Deep, infected corneal ulcers need aggressive therapy to stop the progression of the infection with the goal of preventing rupture of the eye. Lastly there are abscesses that can develop in the horse cornea. When there is an ulcer that heals up quickly there may be infection left underneath that top layer of cells. This infection slowly multiplies resulting in an abscess.
When presented with a corneal ulcer there are two diagnostic tests that should be performed. The ﬁrst one is a culture. A swab is used to obtain a sample which is grown in a laboratory to determine which bacteria or fungal organism is causing the infection and exactly what medication will work most eﬀectively. The next test that is performed is cytology. Cytology is where a sample from the ulcer is placed on a slide and it is looked at under a microscope. This test allows Dr. Tolar to see what type of organisms are present immediately. After these tests are performed the goal is stopping the infection.
Medical therapy uses topical antibiotics and topical antifungals administered directly into your horses eye to stop the infection. Depending on the type of ulcer your horse has the medications may be administered as little as four times daily or as frequently as every hour around the clock. Most horses will get upset with hourly therapy so a special catheter placed under the eyelid is used to administer the medications eﬀectively. This catheter is called a subpalpebral lavage tube. The lavage tube is easily placed in a sedated horse.
Additional therapeutic options to treat infections include, cross linking, cryoablation, injections directly into the cornea and even the anterior chamber (front chamber) of the eye and surgery. Cross linking is used in melting ulcers to arrest the melting process and make the cornea more ﬁrm. Cryoablation uses extreme cold to destroy the bacterial and fungal cells. This therapy is used most often for fungal infections. Injections directly into the cornea are used for fungal infections. This allows a very concentrated amount of medication to be placed immediately at the site of the infection.
Surgery is the last treatment option. The goal with surgery is to preserve the integrity of the eye and save vision. Surgery involves removing the diseased tissue and patching or rebuilding the corneal surface. Materials such as amnion or porcine small intestinal submucosa can be sutured directly on the cornea to maintain integrity until they are able to heal the area on their own. A conjunctival graft involves rotating the pink tissue surrounding the eye over the cornea and suturing it in place over the ulcer. This delivers a blood supply to the ulcer which aids in healing as well as maintaining structural integrity of the eye. When the thickness of the cornea is compromised a full thickness corneal transplant may be necessary.
Infected corneal ulcers and abscesses can develop very quickly from what is thought to be a simple problem. It is imperative that an ulcer in a horse is attended to immediately and rechecked frequently. If your horse has an ulcer and you would like to discuss treatment options please call Dr. Erica Tolar.