Aging Increases Collagen Cross Linking and Pore Size Within the Inner Collagen Layer of Human Bruch’s Membrane

Abstract

Abstract: : Purpose: To determine the effects of aging on the collagen framework within the inner collagen layer (ICL) of human Bruch's membrane Methods:Explants of human Bruch's membrane were prepared from 20 donor human cadaver eyes (23-80 years old), and the ICL was exposed by mechanical removal of the basal lamina. Scanning electron microscopy was used to image the ICL framework and random images were analyzed morphometrically using NIH image analysis software. We determined the following morphometric parameters: average diameter of collagen fibers (nm), fractal dimension of collagen fibers, total pore area (nm² per µ²), number of pores (per µ²), area of deposits (nm² per µ²), number of deposits (per µ²) and percent deposit coverage of the surface. We determined the correlation between donor age each morphometric parameter by deriving best-fit curves. Results:Aging results in thickening of individual collagen fibers (r = + 0.36). Increased cross-links among collagen fibers are evidenced by a decrease in number of individual fibers (r = - 0.40) with increasing age. The total area (r = + 0.64) and number (r = +0.42) of pores within the ICL increases with age. The number of the deposits among collagen fibers increase slightly with aging (r = + 0.19), however age-related deposits were larger in size (r = + 0.48) and occupied a greater percentage of the total area (r = + 0.52). Conclusions: Aging of the ICL of human Bruch's membrane is characterized by increased cross-linking of thickened collagen fibers and accumulation of large debris. This suggests that the decrease in hydraulic conductivity reported previously may be due to increased deposition of lipophilic debris.

Keywords: Bruch's membrane • extracellular matrix • age-related macular degeneration