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OPHTHALMOLOGY: SUPERFICIAL CHRONIC CORNEAL EPITHELIAL DEFECTS

The following article is a direct copy of Dr Rhea Morgan's article in her textbook, Small Animal Practice Client Handouts, with only minor notations added by YVC (in italics). Dr Morgan is a board-certified specialist in both internal medicine and ophthalmology. In the article Dr Morgan uses the term "persistent corneal erosions", which is another name for the problem known as scced. 

Description   Persistent corneal erosions are superficial ulcers that do not heal and persist for at least 2 weeks beyond the expected healing time. Although the cornea successfully creates a new layer to cover the ulcer, it does not stick to the underlying layer. The new layer slides around, preventing the ulcer from healing. This condition is also known as a nonhealing ulcer, indolent ulcer, Boxer ulcer, or spontaneous chronic corneal epithelial defect.

Causes   In dogs, several different microscopic and/or neurologic defects can occur in the cornea to prevent the ulcer from healing. Corneas that are edematous (fluid in the middle layer of the cornea) are prone to these ulcers, because the surface layer becomes water-logged and soft. Herpesvirus has been incriminated in these ulcers in cats. 

We have found that many dogs and some cats perpetuate their ulcers by pawing at and/or rubbing their eye, but trauma is probably not the primary cause.

Signs   In some animals tearing may be the only sign. Other animals show signs of pain, including squinting or pawing at and rubbing the eye. The eye may be red and the third eyelid may be elevated. The cornea may be cloudy if edema is present, red if blood vessels are growing to the ulcer, or it may remain clear.

Diagnostic tests   Diagnosis is made by close examination of the eye. These ulcers are one layer deep and have loose tissue at their edges. Fluorescein stain highlights this. Other causes must be excluded, including trauma, eyelid abnormalities, dry eye, and bacterial infection. If both eyes are affected, further testing for underlying medical problems should be undertaken. 

Treatment options   These ulcers can be very difficult to heal, and healing may not occur for several weeks to months. No single therapy achieves healing in all ulcers, so many different types of treatment may be tried. Some treatments are done on an outpatient basis and some require hospitalization and general anesthesia. Some treatments are repeated multiple times. 

Debridement   Removal of the loose tissue is done on most of these ulcers, using a cotton swab or other device. In some cases, the pet may be taken to surgery so that all the abnormal layers of the cornea can be removed under anesthesia. 

Topical antibiotics   are used to prevent infection, and pain medications are also used. A protective collar is usually needed to prevent rubbing of the eye.

Keratotomy   is roughening of the surface of the cornea to promote bonding of the healing layer. Keratotomies are usually used in dogs. We often combine keratotomy with a third eyelid flap.

Bandage contact lenses and third eyelid flaps (the third eyelid is temporarily sutured over the eye - usually left in place for two weeks) protect the ulcer and prevent the edges of the eyelids from rubbing on it during healing. 

A wide variety of other topical therapies have been devised and can be tried, but have had mixed success. 

Ulcers that fail to heal with all other treatments may require surgical grafting.

Ulcers that arise in edematous corneas can be particularly stubborn. The application of topical 5% sodium chloride may be considered and a specialized cautery procedure (thermokeratoplasty) may be tried for unresponsive ulcers.

When these ulcers occur in cats, additional treatments for feline herpesvirus infection may be helpful.

Follow-up Care   Recheck visits are often scheduled every 7 to 14 days. If the ulcer persists beyond 21 days following initial treatment, then treatment is often modified, repeated, or a different treatment is tried. 

Prognosis   Although these ulcers are hard to heal, many do improve within 4 weeks.  (We believe this is true, but have found that a smaller but significant percentage of these ulcers persist for months - Dr Morgan mentioned this earlier in this article.) With persistence and diligent treatment, these ulcers will heal. Some corneas are left with cloudy scarring, but vision is usually unaffected. 

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