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.