Ultrastructure of Age–Related Changes in Human Bruch's Membrane as Seen by Quick–Freeze/Deep–Etch (QFDE)

Abstract

Abstract: : Purpose: To characterize age–related ultrastructural changes in human macular Bruch's membrane (BrM). Methods: The ultrastructure of macular BrM of 11 normal eyes from 11 human donors (age 27 – 82 yr) was visualized by QFDE. Tissue blocks were processed for thin–section TEM following post–fixation in osmium–tannic acid–paraphenylenediamine (OTAP, n=3) for visualization of neutral lipid. Results: Lipoprotein–like particles (LLPs) and small granular structures (SGs) accumulated with age in the inner collageneous (ICL) and elastin layers (EL). Similar regions in OTAP preparations contained electron–dense particles, confirming that the LLPs seen by QFDE contained neutral lipid. LLPs were often surrounded by SGs that connected to other ultrastructural materials by fine filaments. LLPs and SGs accumulated to such an extent that no open space was visible in the EL of eyes >58 yr and the ICL of eyes >72 yr. Four of 6 eyes >72 yr had a confluent "lipid wall" in the plane between the basal lamina of the retinal pigment epithelium (RPE–BL) and the ICL. The only apparent age–related change in the RPE–BL was a small number of LLPs. LLPs and SGs were more widely spaced in the outer collageneous layer (OCL) than in the EL and ICL. One replica from a 59 yr old eye showed a drusenoid deposit. The deposit contained LLPs, SGs, and fibril–like structures interconnected by fine filaments. The fibril–like structures were usually curved and differed morphologically from collagen Type I and III seen in the ICL. Conclusions: Two–thirds of eyes >72 yr had the "lipid wall" aggregation between the RPE–BL and ICL, supporting previous evidence that it is a common characteristic of older eyes. Our data suggest that the EL and ICL were consecutively populated by SGs and LLPs with age. Perhaps these layers play more important roles than does the RPE–BL or OCL in the age–related decline of the hydraulic conductivity of BrM.

Keywords: Bruch's membrane • lipids • aging