Eye Care for Animals - The Leaders in Veterinary Ophthalmology

Corneal Ulcers

The cornea is the transparent windshield-like structure of the eye. It serves to protect the eye while allowing light to enter for vision. The normal cornea is composed of several layers. An outer layer of epithelial cells lines the surface and protects the rest of the cornea. The thicker middle layer is called the stroma and contains multiple supportive cells, fibers and nerves. The inner lining is called the endothelial layer, which functions to maintain corneal clarity. A corneal ulcer is defined as a break in the outer epithelial layer of the cornea. Although initially painful, uncomplicated ulcers should heal within three to five days with appropriate therapy.

Complicated Ulcers

Corneal ulcers that either fail to heal within three to five days, deepen and/or become infected can be considered complicated ulcers. These can be broadly categorized as follows:

1. Ulcers that fail to heal due to external causes, including ongoing trauma, unresolved foreign bodies, and abnormally located eyelashes that rub against the cornea
2. Ulcers that fail to heal due to ocular diseases such as dry eye, glaucoma or inflammation (uveitis)
3. Ulcers that become deeper or progress due to secondary bacterial, fungal or viral infections. These ulcers may rapidly worsen and even cause the eye to rupture. Severe infections may cause the cornea to “melt” by breaking down the supportive structures of the stroma

Recurrent or Spontaneous Chronic Corneal Epitheal Defects (SCCEDS)

Indolent ulcers occur when the epithelium fails to adhere to the underlying stroma. Essentially, what happens is that the attachment sites for the epithelial cells start to flatten out with age. Therefore, the epithelial cells will form loose flap-like sheets that lay over the ulcer instead of attaching to it. This condition is common in dogs 7 years or older.  In addition, indolent ulcers are more common in certain breeds, such as the Boxer, which has led to the nickname "Boxer ulcer." Indolent ulcers can also occur in dogs with underlying metabolic conditions such as hypothyroidism, diabetes mellitus or Cushing's syndrome.

These ulcers often have a recurrent course. If they heal on their own, the epithelial cells may remain loose, and be predisposed to spontaneously peel off again. Therefore, these ulcers usually require surgery to allow for permanent healing (see "Treatment for Indolent Ulcers" below).

Diagnosis

Evaluating a patient with a complicated corneal ulcer requires several diagnostic procedures, tests and techniques.

Among the most important instruments required to evaluate a corneal ulcer is a hand-held microscope called a slit lamp. The slit lamp permits our veterinary ophthalmologists to carefully evaluate the patient’s cornea with a high degree of magnification and resolution. Sometimes, we are able to find the cause of an ulcer (such as an aberrant eyelash or a foreign body stuck in the eye). In this case, the ulcer will generally heal uneventfully after removal of the inciting cause.

To further evaluate a complicated corneal ulcer, we might obtain samples for bacterial culture, viral testing and/or cytology.

Treatment for Indolent Ulcers

Arguably the most frustrating ulcer is the indolent ulcer. Although these ulcers do not typically threaten a patient’s sight, they run a protracted course. Medical therapy for indolent ulcers consists of preventative antibiotics and often a hyper-osmotic (salt) agent. At best, medications alone offer only a poor chance of success.

The recommended treatment for indolent ulcers is a surgical procedure called a keratotomy. The purpose of this procedure is to first remove all of the loose epithelial cells that are not able to remain attached to the stroma. A very fine needle is then used to make a series of microgrooves or grid-like streaks into the superficial aspect of the corneal stroma. This will help create new attachment sites, which will allow new epithelial cells to adhere onto the underlying cornea. This can be performed either awake (using a topical anesthesic) or under general anesthesia, depending on the patient's temperament and the size and duration of the ulcer. Most indolent ulcers will heal after this procedure; however, refractory ulcers might require the procedure to be repeated or a more invasive surgical procedure called a superficial keratectomy. With the latter procedure, the outer unhealthy layers of the cornea are surgically removed.  Superficial keratectomies are considered to have the highest success rate, however, they tend to cause permanent corneal scars.

Treatment for Deep Ulcers

Corneal ulcers that are deeper than 50% of the cornea's thickness will cause the eye to be very fragile and at risk for rupture. Therefore, these ulcers require aggressive medical treatment and often need surgical intervention to save the eye.

We use various surgical techniques to treat deep corneal ulcers. Some of the more common techniques include conjunctival pedicle grafts and corneoscleral transpositions. Conjunctival pedicle grafts involve harvesting a piece of conjunctiva (the pink tissue covering the “white” of the eye) and suturing it over the corneal defect. We may also place a second graft composed of a biological disc to further increase support. Corneoscleral transpositions involve separating a layer of the patient's cornea and sliding it over ulcer's defect.

After the surgical procedure is complete, we often temporarily suture the eyelids partially closed for the initial healing period. This allows the closed eyelids to act as a supportive patch over the delicate graft while it is healing. It will decrease friction over the graft site and promote comfort much like a bandage would.

It is important to realize that, although graft procedures are considered to have low risk, the chance for complication is possible. For example, there is always a risk associated with being under general anesthesia. Other potential complications include, but are not limited to:

• Inflammation of the pink tissue (conjunctivitis)
• Break down of the tissue or suture (wound dehiscence/graft retraction/rejection)
• Surgical site infection
• Corneal ulcerations (superficial to deep)
• Corneal scarring, vascularization, or mineralization
• Rupture of the eye
• Inflammation inside the eye (uveitis)
• High pressure within the eye (glaucoma), secondary to uveitis
• Retinal detachment or degeneration, secondary to uveitis or infection
• Ocular or orbital pain, secondary to uveitis, glaucoma or infection
• Eyelid rubbing
• Bleeding inside the eye (hyphema)
• Excessive tearing
• Lens luxation, secondary to uveitis, glaucoma or infection

In rare instances, some of these complications can lead to blindness.

If you have any questions regarding corneal ulcers, please call Eye Care for Animals.