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Canine keratitis: Ulcers to KCS (Proceedings)

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Aug 01, 2010

Spontaneous Chronic Corneal Epithelial Defect (SCCED/Indolent Ulcer/Recurrent Erosion)

The SCCED represents a specific unique type of corneal ulcer that is frustrating for veterinarians and clients alike. They are chronic, superficial, non-infected, and present with the patient minimally to severely painful. Most are characterized by a superficial erosion of the corneal epithelium with loose epithelial edges and variable corneal vascularization. Histopathology shows that in cases of SCCED the epithelium is poorly attached to the corneal stroma and that the normal epithelial architecture is lost. Epithelial to basement membrane and basement membrane to stroma adhesion complexes are absent or minimized in this condition. Additionally a thin, hyalinized, acellular zone develops between the epithelium and the underlying stroma. A SCCED should be suspected when a superficial ulcer persists for more than 7-10 days with no obvious cause or predisposing factor. Any breed can be affected, but most affected dogs are middle-aged or older. These dogs have no predisposing cause for a chronic ulcer and may or may not have had a known trauma.

Appropriate topical treatment should include a prophylactic antibiotic (e.g., neo-poly-bac or tobramycin) q 12 to q 8 hours and 1% atropine once or twice daily for comfort. Oral tramadol and a non-steroidal anti-inflammatory are also helpful to keep these patients comfortable. Topical hyperosmotic treatment with 5% sodium chloride ointment may facilitate healing in cases that have significant corneal edema associated with the lesion. Polysulfated glycosaminoglycans, epidermal growth factor, and fibronectin have also be used, but studies show that they do not increase the rate of healing beyond conventional medical and surgical treatments. Inhibition of destructive corneal enzymes with doxycycline and tetracycline has been shown to be ineffective in the canine patient.

Corneal epithelial debridement is a mainstay of treatment and can be repeated at 7-14 days intervals. Success rates after debridement alone averages 50%. Linear grid or superficial punctuate keratotomy are most often recommended to facilitate healing. Success rate after linear grid or punctuate keratotomy increases up to 80%. The result of these procedures is an increase the extracellular matrix components that are important in epithelial adhesion to the underlying The keratotomy procedures should only be performed on superficial, non-infected ulcers that have minimal edema. Success rate after complete superficial keratectomy is consistently 100%. This procedure works by completely removing the abnormal superficial layer of the cornea stroma. The linear grid and superficial punctuate keratotomies can be performed under general anesthesia, with sedation, or under topical anesthesia alone dependent upon the compliance of the patient and the experience level of the surgeon. The complete superficial keratectomy requires general anesthesia and an operating microscope for accurate dissection.

Corneal Stromal Ulcers

Ulcerative keratitis that extends into the corneal stroma normally is secondary to trauma or involves a microbial infection that initiated corneal destruction. Any visible defect in the corneal surface suggests stromal involvement. Most superficial ulcers are not visible with the naked eye, except some cases of SCCED. This being said, any ulcer that appears to involve the stroma should have a corneal cytology, culture and sensitivity evaluated. These tests should be performed prior to the application of fluorescein as which has been shown to inhibit bacterial growth.

Stromal ulcers may be progressive or non-progressive, the problem is telling the difference. Any stromal ulcer should be monitored closely for response to treatment to assure that it is not progressing. Medical intervention should be aggressive as these lesions, if progressive, are vision and globe threatening. Antibiotics can be chosen based on cytology and gram stain results and altered as necessary based on culture results. Topical atropine can be used to minimize ciliary spasm induced pain. Systemic antibiotics, anti-inflammatories, and pain medications are all recommended as well. If stromal melting is present, antibiotic and anti-collagenase/anti-protease therapies should be given every 1-2 hours. Surgical intervention to provide tectonic support is recommended in stromal lesions that are greater than 50% of the corneal depth. Tectonic support can be via conjunctival graft, corneal conjunctival transposition, amniotic membrane graft, or synthetic membrane graft. Tissue adhesives have also been used in the treatment of stromal ulcers. The procedure can be done under topical anesthesia, with sedation, or under general anesthesia dependent upon the compliance of the patient. The cornea is dried with a cotton swab or warm air and a very thin layer of adhesive is applied to the cornea. The adhesive needs 15 to 60 seconds to dry without allowing blinking of the lids. If the application of adhesive is too thick it can cause irritation or it can be sloughed prematurely. Tissue adhesive use in cases of descemetoceles is not recommended due to the potential for ocular toxicity.