The cornea is a transparent barrier that covers the front of the eye, and consists of the outer epithelium, the stroma, Descemet’s membrane, and the endothelium. The cornea protects the eye against external substances, such as dust and germs, and also functions to focus and control how much light enters the eye. This tissue is extremely sensitive, and can easily be damaged, jeopardizing your pet’s vision. Our Veterinary Vision Center team explains conditions that can cause your pet’s cornea to ulcerate.
Corneal ulcers in cats
Corneal ulcers in pets can be caused by numerous factors, including scratches, ingrown eyelashes, foreign bodies under the eyelid, exposure to caustic chemicals, and viral or bacterial infection. The most common cause in cats is recurrent feline herpesvirus infection (FHV). An infected cat may seem to clear the virus, but the pathogen can recur during stressful periods, allowing the virus to attack the cornea, and cause ulceration. Signs include tearing, redness around the cornea, and squinting. Treatment focuses on controlling the inflammation, and reducing the pain. If FHV is causing the ulcer, an antiviral medication may also be prescribed.
Simple superficial ulcers in pets
Simple, uncomplicated ulcers are superficial, and affect only the corneal epithelium, which is five to seven cell layers thick, and can regenerate when injured. About an hour after the tissue injury, new epithelial cells begin to migrate to the defect, to begin the healing process. With no complicating factors, such as infection or trauma, the lesion should heal in five to seven days. The new cells will be loosely attached, and can be easily disrupted if rubbed, so Elizabethan collars are helpful to keep pets from interrupting healing. Antibiotic eye drops or ointment also are typically prescribed. If you notice your pet squinting more, or their eye changing color, you should have your pet evaluated by a veterinary professional, to ensure the lesion has not become infected.
Melting ulcers in pets
Enzymes called matrix metalloproteinases are responsible for removing dead cells and debris from the ocular surface. In a melting ulcer, these enzymes become excessive, and can be released by certain pathogens, as well as white blood cells, resulting in rapid corneal stroma destruction. The bacteria that most commonly produce these enzymes are Pseudomonas aeruginosa, Staphylococcus species, and Streptococcus species, and they may also be produced by fungal organisms. Other risk factors that put pets at higher risk for developing a melting ulcer include topical and systemic corticosteroid use, pre-existing keratoconjunctivitis sicca (i.e., dry eye), diabetes mellitus, and hyperadrenocorticism.
Eyes affected by melting ulcers usually have a gelatinous appearance, and possibly a yellow or grey discoloration. A purulent discharge is also often present. These lesions cause significant pain for most pets, but brachycephalic breeds, such as boxers, have a reduced corneal sensitivity, and they may appear comfortable. To salvage your pet’s eye, treatment should be aggressive, and include:
- Hospitalization — These lesions require frequent, around the clock treatments, and most pets have a better prognosis if they are hospitalized for treatment and monitoring.
- Antibiotics and antifungals — The lesion should be cultured, to determine which antibiotic or antifungal is appropriate.
- Enzyme inhibitors — Medications to counteract the damaging enzymes are an important treatment factor.
- Nonsteroidal anti-inflammatories (NSAIDs) — Topical NSAIDs are contraindicated, but systemic NSAIDs are important, to control your pet’s discomfort.
- Surgery — If medical management is not successful, surgical intervention may be necessary to salvage your pet’s eye.
Spontaneous chronic corneal epithelial defects in dogs
Spontaneous chronic corneal epithelial defects (SCCED) are also known as indolent ulcers or boxer ulcers, because boxers are predisposed to developing these lesions, and also are more likely to develop a SCCED in the contralateral eye. These lesions differ from simple, uncomplicated ulcers, because a hyalinized membrane forms over the stroma, preventing epithelial cells from adhering to the defect, and healing the ulcer. These ulcers will not heal without debridement. Techniques include:
- Cotton swab — After administering a topical anesthetic, a dry, sterile cotton swab is used to remove the loose epithelium. Healthy corneal epithelium is firmly attached to the underlying stroma, and cannot be easily removed, so debridement is continued until all loose epithelium is detached. This procedure’s overall success rate is about 50 percent.
- Grid keratectomy — This technique involves making linear scratches on the superficial stroma, which likely allows the epithelial cells to penetrate the abnormal hyalinized area. Success rate for this procedure is about 60 to 70 percent.
- Diamond burr debridement — This procedure involves using a low powered, hand-held polishing burr, to remove the abnormal tissue. Success rate for this procedure is about 70 to 80 percent.
- Superficial keratectomy — This procedure requires general anesthesia, and the abnormal tissue is surgically excised, to allow the ulcer to heal normally. This procedure’s success rate is 95 to 100 percent.
Wearing an Elizabethan collar after debridement is critical to your dog’s healing, because the epithelial cells adjacent to the defect are poorly attached, and rubbing the eye before complete healing occurs can remove all the newly laid cells.
Corneal ulcers are a concerning issue for your pet, and prompt veterinary attention is needed. If your pet has a complicated corneal ulcer, contact our team at Veterinary Vision Center, so we can help save their sight.