MANAGEMENT OF NON-HEALING CORNEAL ULCERS DR. SHELBY REINSTEIN, DACVO Veterinary Specialty & Emergency Center, Levittown, PA
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Normal corneal wound healing is accomplished via epithelial cell migration to cover the exposed stroma, followed by epithelial cell proliferation to restore the normal thickness of the epithelial layer. The epithelial cells develop firm attachments to the anterior corneal stroma via adhesion complexes. SCCEDs develop when the formation of these epithelial- stromal adhesions is inhibited. Thus, SCCEDs ulcers are often noted to epithelialize normally, however this newly formed epithelium is easily denuded contributing to the refractory nature of healing. SCCEDs have been studied histologically and multiple hallmark alterations in the normal healing process have been described. In almost all SCCEDs samples, the epithelial cells adjacent to the ulcer are poorly attached to the underlying stroma. Finally, there is formation of an acellular, hyalinized zone, which covers the exposed corneal stroma. This abnormal zone is now considered to contribute significantly to the pathophysiology of SCCEDs, as it interferes with the formation of strong epithelial-stromal adhesion complexes. 3 TREATMENT OF REFRACTORY CORNEAL ULCERS Superficial corneal ulcerations are quite painful, as the corneal nerve density is greatest in this region. Despite the underlying cause, refractory corneal ulcers should be treated with topical prophylactic antibiotic therapy (every 8-12 hours), and a topical cycloplegic (e.g. atropine). Oral non-steroidal anti-inflammatories or additional pain medications are beneficial in controlling the discomfort,
and a hard, plastic E-collar is necessary to prevent self-trauma. As previously discussed, refractory corneal ulcers have a variety of causes, and all efforts should be made to identify and treat any predisposing conditions. 4 TREATMENT OF SUPERFICIAL CHRONIC CORNEAL EPITHELIAL DEFECTS Both medical and surgical methods for the treatment SCCEDs have been described. The foundation and crucial first step in all successful SCCEDs treatment modalities is epithelial debridement. Using a sterile cotton-tipped applicator to remove the loose epithelium can be safely performed after application of topical anesthetic. Normal epithelium is quite firmly adhered, and thus will not be removed with gentle debridement. Epithelial debridement on its own has a reported success rate of about 50%. Techniques that aim to remove or disrupt the acellular, hyalinized superficial stromal zone have improved published success rates over epithelial debridement alone. The most recently reported therapy for SCCEDs is diamond burr debridement (DBD). DBD is performed using a handheld, battery powered polishing burr and has been described in human ophthalmology for the treatment of superficial, refractory ulcerations. The DBD technique was investigated histologically in dogs and shown to safely remove the epithelial basement membrane (and presumably the stromal hyalinized zone) without penetrating deeper into the corneal stroma. Recently, the DBD technique
in conjunction with bandage contact lens (BCL) placement was evaluated in a clinical setting in dogs with a success rate of 92.5% after a single treatment. Minimal complications were noted, and 95% of dogs retained the contact lens during the study. The BCL is thought to improve healing by protecting the migrating epithelial cells, as well as improve patient comfort by covering the exposed corneal nerves. Overall, DBD is considered advantageous due to the minimal cost, lack of specialized equipment needed, ease of the procedure, and little adverse effects. In clinical practice, the author treats SCCEDs in dogs with epithelial debridement, DBD, BCL placement, and oral doxycycline in addition to the standard topical antibiotic, and often oral NSAIDs therapy as for any corneal ulcer. Tetracyclines are known to modulate the expression of certain growth factors involved in corneal wound healing, and dogs that were treated with either topical oxytetracycline ophthalmic ointment or oral doxycycline healed faster than the control group. Anecdotally, a success rate of 90-95% is seen in the author’s practice, with an approximate 30% BCL retention rate.
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