The cornea is the clear, front part of the eye that acts like a windshield, protecting the inside of the eye while allowing light to pass through. The normal cornea is composed of several layers. An outer layer of epithelial cells lines the surface and protects the rest of the cornea from the atmosphere. The thick middle layer is called the stroma and this layer contains multiple supportive cells and nerve fi bers. The inner lining is called the endothelial layer and it functions to help keep the cornea clear. A corneal ulcer is a break in the outer layers of the cornea. Although initially painful, uncomplicated ulcers should heal with limited care in three to four days. Ulcers that persist beyond this period of time frequently prove to be complicated ulcers.

Complicated Ulcers
Corneal ulcers that fail to heal within a reasonable period of time can be sorted into two broad categories:
1. Ulcers that fail to heal due to external causes, including ongoing trauma, unresolved infections, foreign bodies embedded within the eyelid, and abnormally placed eyelashes.
2. Ulcers that fail to heal due to internal causes, including ocular diseases and primary tissue healing defects.

Ocular diseases that prevent corneal healing include dry eye syndrome, glaucoma, and intraocular infl ammation.

Primary tissue healing defects are conditions in which the tissue itself fails to heal in a normal fashion. This condition is common in middle-aged and older dogs as well as certain breeds, such as the Boxer. This type of ulcer is sometimes called a Boxer ulcer or an indolent ulcer. The basic defect with this condition is that the outer epithelial cells lose the ability to form supportive “anchors” to the underlying corneal stroma. Thus, they attempt to grow over and cover the ulcer, but are periodically be rubbed away by the eyelids with normal blinking or due to active rubbing of the eye by the animal.

Corneal ulcers, including those caused by foreign bodies, can lead to corneal scarring, corneal vascularization, and ocular infections that may extend to other internal and/or external areas of the eye (intraocular/extraocular infections), as well as secondary complications similar to those to which surgery for treating ulcers can give rise, as discussed in the section titled “Treatment”.

Diagnosis
Evaluating a patient with a complicated corneal ulcer requires several diagnostic instruments and techniques. Among the most important instruments required to evaluate a corneal ulcer is the slit lamp, a biomicroscope. The slit lamp permits our veterinary ophthalmologists to carefully evaluate the patient’s cornea with a high degree of magnifi cation and resolution. Sometimes, a cause for the ulcer, such as an aberrant eyelash or foreign material stuck in the eye, can be found. The ulcer will generally heal rapidly upon removal of the inciting cause. To further evaluate a complicated corneal ulcer, we might obtain samples for bacterial culture, virus isolation, and cytological evaluation.

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 prolonged course. Medical therapy for indolent ulcers consists of antibiotics and hyper-osmotic agents and offers only a 15% success rate.

The recommended treatment for indolent ulcers is a surgical procedure called a linear grid keratotomy. The purpose of this procedure is to first remove all of the unhealthy epithelial cells that are not able to attach to the cornea. A very fi ne needle is then used to make a series of microgrooves into the corneal stroma. This will help to disrupt the abnormal portion of the cornea and allow new epithelial cells to anchor down to healthy cornea deeper in the stroma. This can be performed either awake under topical anesthesia or under general anesthesia, depending on the patient. Most indolent ulcers will heal after this procedure; however, refractory ulcers might require a repeat of the procedure or a more invasive surgical procedure called a superficial keratectomy, where the outer layers of the cornea are surgically removed.

Treatment For Deep Ulcers
If a corneal ulcer progresses to the point that it occupies 50% or deeper of the corneal thickness, the risk of perforation, which could lead to loss of the eye, is high. Therefore, these deep ulcers require aggressive medical treatment and often will need surgical intervention.

We use various surgical techniques to treat deep corneal ulcers. The surgical techniques we perform most commonly include conjunctival pedicle grafts, corneoconjunctival transpositions, and the application of cyanomethylmethacrylate surgical glue.

For the conjunctival pedicle graft, we transplant a piece of conjunctiva (the loose tissue covering the “white” of the eye) into the corneal defect. With this procedure and the corneoconjunctival transposition, we are able to seal the corneal ulcer with a healthy piece of ocular tissue, which we leave in place and allow to integrate into the cornea.

Alternatively, a medical grade of glue, cyanomethylmethacrylate may be applied to the ulcer following the careful removal of degenerative tissue.

Frequently after the surgical procedure the eyelids are sutured partially closed. This sutured closing serves as a soft bandage over the weakened tissue.

Again, although not all corneal ulcer patients require surgical intervention, with pets who do, owners need to be aware of potential complications. Any surgical procedure can introduce complications, including potential anesthetic risks. Surgical procedures that involve the cornea seldom give rise to complications, which occur in less than 5% of these cases. Nevertheless, 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)

Infections at the surgical site, which may extend to other internal and/or external areas of the eye (intraocular/extraocular infections)

Corneal ulcerations (superfi cial to deep)

Corneal scarring, vascularization, or mineralization

Rupture of the eye, secondary to ulceration

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

Some of these complications can lead to blindness.

Occasionally, a sequestrum may occur in the other eye, depending on the underlying cause.

If you have any questions about Corneal Ulcers, please do not hesitate to call us at Eye Care for Animals.