THE COMPOSITION OF WIDE-SPACED COLLAGEN IN NORMAL AND DISEASED DESCEMETS-MEMBRANE

Descemet's membrane, the specialised basement membrane of the corneal endothelium, contains a form of extracellular matrix described as wide -spaced collagen. In healthy human Descemet's membrane, wide-spaced co llagen forms a highly ordered array in a region called the anterior ba nded zone. However, in corneal endotheliopathies such as Fuchs' endoth elial dystrophy and the iridocorneal-endothelial syndrome large amount s of wide-spaced collagen are deposited posterior to Descemet's membra ne in a grotesque parody of the anterior banded zone termed a posterio r collagenous layer. The purpose of this study was to identify the com position of the wide-spaced collagen found in the Descemet's membrane of normal and diseased human corneas. Tissue from three normal human c orneas, three from patients with Fuchs' endothelial dystrophy and five from patients with the iridocorneal-endothelial syndrome was prepared for immunoelectron microscopy by freezing or embedding in Lowicryl K4 M resin. Immunocytochemistry on ultrathin sections was performed with antibodies to collagen Types I, III, V, VI and VIII, fibronectin, lami nin, P component and tenascin. Ultrastructural labelling of the wide-s paced collagen in the anterior banded zone of normal and diseased corn eas and also of the wide-spaced collagen in the posterior collagenous layer of all the diseased corneas was demonstrated with antibody to co llagen Type VIII. Wide-spaced collagen was not labelled by any of the other antibodies used. Large amounts of Type VIII collagen are present in discrete regions of healthy and diseased Descemet's membrane. The deposition of Type VIII collagen may significantly influence the patho biology of the corneal endotheliopathies.