The cornea is the clear portion at the very front of the eye. The cornea has three layers: epithelium, stroma and endothelium. The outside layer is epithelium just like our skin but without hair and normally without pigment. The epithelial layer is thicker in the cornea of the dog than the cat. The epithelium is water-tight so that neither tears outside the cornea nor fluid from within the eye can get past the epithelium. Lining the cornea is one cell layer of endothelium similar to the cells that line blood vessels. Between the epithelium and the endothelium is the thickest layer of the cornea, the stroma.
A corneal ulcer is a break in the outer layer of the cornea. Ulcers may occur from a variety of conditions such as scratches by other pets, foreign material in the eye (pieces of grass, sand or dirt), lack of tear production, or failure of the eyelids to remain completely closed during sleep. Uncomplicated ulcers, although painful, should heal in 3 to 10 days (depending on the size) when appropriate treatment is used. Those ulcers that persist are considered complicated.
Corneal ulcers fail to heal for either external or internal reasons. External causes include: ongoing trauma, unresolved infection, foreign material embedded within the eyelid or in the cornea itself, the failure of the patient to close its eyes fully during sleep, the lack of tear production and abnormally placed eyelashes. These ulcers require treatment of the external cause as well as the ulcer to allow healing to occur. Ulcers that fail to heal for internal reasons are usually primary tissue healing problems or other conditions inside the eye that prevent healing. Primary tissue healing problems refer to conditions at the cellular level in which the cornea itself fails to heal in a normal fashion. This process is recognized in older dogs and in certain breeds, like the Boxer, and is sometimes referred to as a boxer ulcer. Another term for this type of ulcer is indolent ulcer. Other ocular conditions that can prevent corneal healing are unresolved glaucoma or inflammation within the eye.
Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from corneal ulcers or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.
Evaluation of a patient with a corneal ulcer requires a number of specialized diagnostic instruments and techniques. The most common instrument is 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 of a corneal ulcer is dependent on the results of the diagnostic procedures. Removal of inciting external causes, when appropriate, results in rapid healing. Those ulcers that involve ocular diseases will require treatment of the underlying diseases to permit healing of the ulcer. The most frustrating ulcer to treat may be those with healing defects. These ulcers, although generally not sight threatening, take a long time to heal. If healing is prolonged, severe scarring and possible vision loss may occur. Treatment consists of stripping the surface off the cornea and roughening the corneal surface. Treatment with antibiotics, medications to dilate the pupil and agents that increase the adherence of the surface to the next layer is then begun. If these therapies do not work a surgical procedure known as a superficial keratectomy is recommended.
If the ulcer becomes deep, the cornea may become perforated. These ulcers require aggressive surgical intervention and subsequent medical treatment. Various surgical techniques have been used to treat deep corneal ulcers. The most common procedures are a corneal graft or pedicle conjunctival graft. A corneal graft may be used when the ulcer is along the center of the cornea or for very large, sight-threatening ulcers. The advantage of a corneal graft is that it provides an immediate seal to the corneal ulcer with a healthy piece of ocular tissue. The graft will scar to some degree, yet vision is possible through the graft. The pedicle conjunctival graft involves stitching a piece of conjunctiva (the moveable white tissue of the eye) into the corneal defect. The advantage of this procedure is that it also provides an immediate seal and that it brings healing blood vessels to the area. The tissue remains in place for 4-to-6 weeks. Once healed, the graft may be trimmed after applying a local anesthetic.