A challenging case: A dog with nonhealing corneal ulcers - Veterinary Medicine
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A challenging case: A dog with nonhealing corneal ulcers
Corneal ulcers usually heal rapidly with appropriate treatment, but this Labrador developed two that were slow to heal. A technique used commonly in people—diamond burr superficial keratectomy—appeared to help in this case.


VETERINARY MEDICINE


Treatment

Numerous strategies, including medical and surgical options, have been proposed and investigated to promote the healing of SCCEDs. Conventional, conservative medical treatment consists of the administration of prophylactic topical antibiotics. It is usually ineffective as it fails to remove or ameliorate the cause of the problem.9 Thus, effective therapy must remove the loose epithelium that is not adhering to the stroma, promote the normal adhesion of the new epithelium to the underlying stroma, and protect the delicate, newly forming epithelium.

Débridement. Débridement with a cotton-tipped applicator is an effective way of removing nonattached epithelium. In most dogs, the débriding can be done without sedation if a topical anesthetic is applied. It is important to remove all the loose epithelium even though this procedure generally creates a defect that is much larger than the original ulcer and in some cases the entire corneal surface becomes denuded of epithelium. Normal epithelium cannot be removed with a cotton-tipped applicator, so if the epithelium comes off, it is unhealthy. In the case presented here, we used a cotton-tipped applicator that had been dipped in dilute povidone-iodine solution to kill any organisms that might be adhering to the ulcer.

Keratotomy. Once the ulcer has been débrided, promotion of the adherence of the newly forming epithelium will increase the healing ability of the cornea.9 For example, use of a hypodermic needle to make small punctures (anterior stromal micropuncture, punctate keratotomy) or linear scratches (grid keratotomy) in the anterior stroma has been extensively used to promote adherence,8 and the success rate of these keratotomy techniques is about 80%.9 These methods physically provide a surface in the stroma for epithelial adherence and also increase collagen IV and laminin, molecules that are important in epithelial adhesion.12

Surgical keratectomy. Surgical, superficial keratectomy removes the nonhealing epithelium and anterior stroma more extensively than grid keratotomy does and has been reported to have a 100% success rate, but it requires general anesthetic and a surgical microscope to complete. It often leads to corneal scarring.8,9

Diamond burr ketatectomy. Diamond burr polishing of the anterior stroma is a method of removing loose epithelium and the anterior stroma that has been used in human medicine for several years to treat recurrent corneal erosions.15 The studies of this technique in people show that it is a safe, convenient, inexpensive, and effective method of débridement.16 The diamond burr is being used in dogs as well. A retrospective study comparing the diamond burr superficial keratectomy with two methods of grid keratotomy suggested that the diamond burr method allows for faster healing than either method of grid keratotomy does.4 In addition, the procedure had low complication rates.

We chose to treat the dog in this report with this method after the failure of the grid method in the left eye, and it proved to be noninvasive, easy-to-perform, and effective. The diamond burr was used in the right eye but not used initially in the left eye based solely on ophthalmologist preference.

Corneal protection. Methods of protecting the newly forming epithelium that have been described include bandaging contact lens placement, temporary tarsorrhaphies, and third eyelid flaps. These methods not only protect the cornea but also may help relieve discomfort associated with these procedures.

Tissue glue. A technique involving placement of a thin layer of topical cyanoacrylate tissue glue (Tissuemend II—Veterinary Products Laboratories) over the ulcerated area after débridement has been reported.17 The glue remains in place until the epithelium grows under it at which time it is elevated off the corneal surface. This technique appears to be effective, with healing times that range between two and eight weeks.17

Topical medical therapy. In addition to topical antibiotics that act only to prevent infection of uninfected corneal ulcers but do nothing to heal them, topical medical therapies that promote healing have been investigated. These include polysulfated glycosaminoglycans and aprotinin (which inhibit proteolytic enzymes),18,19 epidermal growth factor,20 substance P,7 and fibronectin.21 Although many of these substances promote healing, none is considered a standard therapy.

A recent study of clinical cases of dogs with SCCEDs demonstrated that topical tetracycline (Terramycin Ophthalmic Ointment—Pfizer Animal Health) significantly shortened healing times compared with a placebo.22 It was hypothesized that increasing the expression of growth factors and signaling targets increased the corneal epithelial cell migration, which promoted healing. The authors concluded that this method would be a safe, effective, and relatively inexpensive way of increasing the ulcers' healing ability.22

The authors' approach. Although much is still unknown about the pathophysiology of SCCEDs and the most effective treatment regimen is under debate, the high rates of healing we have achieved using the diamond burr technique has led us to use this as our first-line therapy (directly after removing the epithelial edges with a cotton-tipped applicator). If this procedure fails after two débridements, we will then use the more invasive grid keratotomy technique once before we resort to performing a superficial keratectomy.

Concurrent with the débridement and diamond burr method, prophylactic topical antibiotics should be administered three to four times a day and the dog should wear an Elizabethan collar at all times to prevent self-trauma until the defect has healed. Even occasional rubbing of the eye may inhibit healing.


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Source: VETERINARY MEDICINE,
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