Basal linear deposit in the human macula.

We used electron microscopy and immunohistochemistry to study the macular regions of nine enucleated elderly human eyes and to document the various abnormalities present in the so-called basal linear deposit. These changes include bush-like strands of electron-dense material, which project from the basement membrane of the retinal pigment epithelium, deposition of wide-banded collagen, vesiculoid elements, membrane-bound structures and occasional melanin granules. Fibronectin was also identified in the basal linear deposit and in Bruch's membrane, but mucopolysaccharides could not be demonstrated. The presence of electron-empty space suggests a disturbance in water permeability. Our studies also showed neovascularisation beneath the retinal pigment epithelium in locations where the basal linear deposit was abundant, as well as erosion of Bruch's membrane by macrophages and endothelial cell processes. Our findings suggest that the basal linear deposit is an important precursor of neovascularisation. Possible pathogenetic mechanisms are discussed.