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Ulcerative Corneal Disease
Corneal Ulcers

 

A corneal ulcer is a break in the outer layer or epithelium of the cornea. Uncomplicated ulcers, although initially painful, should heal in 3 to 4 days with appropriate treatment. Those ulcers that persist longer than this period of time often prove to be complicated ulcers.

Complicated Ulcers

Corneal ulcers fail to heal for two broad categories of reasons. The first category is comprised of those that fail to heal due to external causes. These causes include ongoing trauma such as entropion - an abnormal rolling in of the eyelid, or trichiasis - facial hair which is in contact with the eye as a result of facial conformation. Also, foreign bodies lurking behind the third eyelid, embedded within the eyelid or in the cornea itself, and abnormally placed eyelashes - ectopic cilia - are causes of ongoing corneal trauma. In addition, some breeds of dogs which, due to facial conformation have a decreased ability to blink and spread the tearfilm over the cornea, may develop corneal ulceration due to excessive evaporation of the tearfilm and exposure of the corneal surface. Finally, unresolved infections which may be seated in the conjunctiva, in the glands of the eyelid margin or within the tear duct may cause corneal ulceration.

These corneal ulcers will not heal unless the external cause is treated at the same time as the ulcer is treated.

The second category of non-healing ulcers is those that fail to heal for internal reasons. These causes include other ocular diseases and primary tissue healing problems. Other ocular diseases that would prevent corneal healing would be the lack of tear production, glaucoma, and intraocular inflammation. Primary tissue healing problems refer to conditions in which the tissue itself fails to heal in a normal fashion. This process is recognized in certain breeds, like the Boxer, Samoyed, Corgi but may occur in any older dog and is referred to as an "idiopathic epithelial erosion" Other terms for this type of ulcer is "indolent ulcer" or "boxer ulcer."

Diagnosis

Evaluation of the patient with a complicated corneal ulcer requires a number of diagnostic instruments and techniques. Probably the most important in the evaluation of a corneal ulcer is using the slit lamp-biomicroscope. This instrument permits the veterinary ophthalmologist to carefully evaluate the cornea and ocular structures with a high degree of magnification and resolution. Stains are used to determine the size of the ulcer and if the edges are undermined. Frequently, specimens are obtained for bacterial culture, virus isolation and cytological evaluation.

Treatment

Treatment of a non-healing corneal ulcer is dependent on the results of the diagnostic procedures. Ulcers that involve external causes require those causes be treated and normally healing rapidly follows. Those that involve other ocular diseases will require those ocular diseases to be treated in an effort to permit healing of the ulcer.

Corneal Ulcer

The most frustrating ulcer may be the idiopathic epithelial erosion ulcer (indolent ulcer). These ulcers, although generally not sight threatening, take a long time to heal. Treatment consists of stripping the surface off of the cornea - this is called corneal debridement; scratching the corneal surface with a needle to 'roughen' it - this is called a crosshatch or grid keratotomy (see figure); and then treatment with antibiotics, medications to dilate the pupil and hyperosmotoc agents which increase the adhesion of the epithelial surface layer to the underlying corneal stroma. In some cases, a soft contact lens or a collagen shield is applied to the cornea to act as a bandage. A collagen shield is like a contact lens but will dissolve in 72 hours. If medical therapy doesn't work, a surgical procedure known as a superficial keratectomy is recommended. Third eyelid flaps are generally not as effective in the treatment of this type of corneal ulcer.

Eye Threatening Ulcers

If the ulcer becomes deep, a perforation of the cornea may be the result. Such ulcers require aggressive medical and surgical intervention. Various surgical techniques have been used to treat deep corneal ulcers. The most common procedures used are a conjunctival pedicle graft and a corneal graft. In a conjunctival pedicle graft, a patch of healthy conjunctival tissue is harvested in a way that it remains attached at its base and the graft is sutured into the corneal defect once all of the unhealthy corneal tissue has been debrided away. The advantage of this procedure is that it provides an immediate seal to the corneal defect and that it brings healing blood vessels to the area. The graft remains in place for a period of 4 to 6 weeks, and once healed well the pedicle may be trimmed under local anesthetic. The graft will scar to some degree, yet vision is possible through the graft.

A corneal graft may be used when the ulcer is along the center of the cornea or in cases of very large, sight-threatening ulcers. The advantage of this procedure is that it provides an immediate seal to the corneal ulcer with a healthy piece of ocular tissue. The donor cornea may be harvested from healthy corneal tissue adjacent to the corneal defect, or in some centres corneal tissue from donor animals is used.

Summary

Corneal ulcers are a frequent problem in veterinary medicine. Your regular veterinarian is equipped to evaluate and manage most of the non-complicated problems. Patients with complicated ulcers should be referred for evaluation to the veterinary ophthalmologist who is especially trained and equipped to treat complex ocular diseases in pets.