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Spontaneous Chronic Corneal Epithelial Defects

SPONTANEOUS CHRONIC CORNEAL EPITHELIAL DEFECTS (SCCEDS) IN DOGS

A SCCED is a defect in the outer layer of the cornea, known as the epithelium. The normal
corneal epithelium is around 10-12 cell layers thick and is constantly being turned over. The
epithelial cells have their origin at the edge of the cornea and move towards the centre and
outwards towards the surface before they are shed as dead cells into the tear film. The
epithelium sits on a membrane called the basement membrane.


A superficial ulcer is defined as a defect where only the epithelium is missing but the
basement membrane is intact. Normally there is strong adhesion between the cells at the
base of the epithelium (basal cells) and the basement membrane. In a normal healthy cornea
with the normal healing mechanisms present, even large superficial defects should heal
rapidly, commonly within 3-4 days. These defects normally heal by the basal cells "sliding"
across and sticking down firmly to the basement membrane.


Unfortunately in some breeds, most commonly the Boxer, Samoyed, Welsh Corgi and the
Staffordshire Bull Terrier (although they can be seen in almost any dog) these superficial
ulcers fail to heal or show protracted poor healing over long periods of time. Sometimes they
can appear to have healed then suddenly appear as a new ulcer again. In these breeds we
know that there is a defect in the way the epithelium sticks down to the basement membrane
at a microscopic level. Unfortunately simple medication with antibiotic ointments will not heal
these defects as the problem is not due to bacterial infection. Procedures such as simple
debridement (rubbing the loose epithelium off) third eyelid flaps or sewing of the eyelids
together to protect the surface seem to be ineffective in most cases.


To get these ulcers to heal we need to do something which mechanically interferes with or
damages the basement membrane at a microscopic level so that the migrating epithelium can
be induced to stick down to the basement membrane. We will discuss various options with
you ranging from simple outpatient type procedures such as basement membrane burring to
more involved procedures requiring a general anaesthetic such as grid keratotomy and
superficial keratectomy, with the goal of achieving rapid resolution of this very frustrating
corneal condition.

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