Morphology and immunohistochemistry of spontaneous chronic corneal epithelial defects (SCCED) in dogs

PURPOSE. To determine the morphologic features of the epithelium and extrac ellular matrix in spontaneous chronic corneal epithelial defects (SCCED) in dogs. METHODS. Forty-eight superficial keratectomy specimens were obtained after confirmation of the presence of a superficial corneal erosion for longer th an 3 weeks with no discernible underlying cause. Histologic samples were ex amined by fight microscopy, scanning electron microscopy, and transmission electron microscopy. Immunolocalization of laminin, Collagen IV, fibronecti n, and Collagen VU was performed. RESULTS Epithelial cells. adjacent to the defect were poorly attached to th e underlying extracellular matrix. A prominent superficial stromal hyaline acellular zone composed of Collagen fibrils, in the area of the erosion was present in most specimens. Samples exhibited a varying degree of fibroplas ia, vascularization, and leukocytic infiltrate. Laminin, Collagen IV, and c ollagen VII were usually either not present or were present only in discont inuous segments on the surface of the erosion. Fibronectin usually coated t he surface of the erosion, either as a continuous sheet or in discontinuous segments. Transmission electron microscopy. of 15 samples revealed that th e basement membrane was either absent in the area of the erosion or was pre sent only in discontinuous segments. Scanning electron microscopy of eight of nine samples confirmed the absence of continuous basement membrane. Epit helial and extracellular matrix components in the peripheral cornea appeare d normal. CONCLUSIONS. Most canine patients with spontaneous chronic corneal epitheli al defects do not have a normal basement membrane structure in the region o f the epithelial defect and have other abnormalities in the subjacent extra cellular matrix that may reflect a part of the underlying pathophysiology o f chronic and recurrent erosions.