New components of 'basal laminar deposits' in age-related macular degeneration

Two new components of basal laminar deposit (BlamD) occurring in samples of submacular neovascular membranes surgically removed from patients with a wet (exudative) form of age-related macular degeneration are described. They are: (1) minute ribbon-like structures which occur singly and/or in a bunch and extend from the inner surface of the BlamD layer into the extracellular matrix (ECM) beneath the retinal pigment epithelium (RPE). The ribbons are composed of polarized molecules, aggregating in parallel, aligned transversally in register, morphologically similar to isolated collagen molecules of the short-chain type. Deeper in the BlamD but always close to its inner surface, aspects suggesting a transition between ribbons and (2) long-spacing collagen (LSC)-like aggregates characterized by periods bordered by a single dense band were observed. This band could arise from the globular domains of the polarized monomers, which assemble in parallel and display all their terminal extensions at the same end of each period resulting in the single dense band. The presence of ribbons and of LSC-like aggregates in the BlamD layer and the concomitant choroidal neovascularization (CNV) suggest that the events might be correlated. The newly formed vessels crossing Bruch's membrane and invading the BlamD layer could induce physicochemical changes in the ECM of the RPE, providing the required environmental conditions for the polymerization of collagen molecules into aggregates with the LSC-like pattern. With the deposition of new components, the thickness of BlamD increases and further impairs the supply of nutrients and oxygen, thus sustaining CNV.