Ultrastructural immunocytochemical analysis of elastin in the human lamina cribrosa. Changes in elastic fibers in primary open-angle glaucoma.

The elastic fiber consists of several components: a central core of alpha-elastin and a microfibrillar sheath containing three components: fibrillin, microfibril-associated glycoprotein, and a 35-kD protein with amine oxidase activity. Elastin is a major component of the elastic fibers of the extracellular matrix (ECM) of the lamina cribrosa, and elastic fibers undergo marked changes in primary open-angle glaucoma (POAG). These changes, as demonstrated previously, include loss and fragmentation of elastic fibers at the bottom of the glaucomatous cup and disorganization in the peripheral walls of the cup. The author characterized the changes in elastic fibers with age and in POAG at the ultrastructural level, using colloidal gold immunostaining and anti-human alpha-elastin antibody. In fetal eyes, there was no detectable elastin in the ECM of the lamina cribrosa. In infant eyes, elastin was present in microfibrillar aggregates in the core of the plates. In young adults, thin elastic fibers were present that ran longitudinally in the core of the plates. With age, elastic fibers become thicker, tubular, and surrounded by densely packed collagen fibers. In mild POAG, tubular elastic fibers no longer were identifiable. Fragments of elastic fibers and microfibrillar aggregates stained positively for elastin suggested new synthesis of elastin that was not organized into tubular elastic fibers. In advanced POAG, masses of nonfibrillar elastin-positive material had a spotted appearance. Throughout the cribriform plates, there was a loss of collagen fibers, proliferation of basement membranes, and bundles of elastin-negative microfibrils not associated with collagen or elastic fibers. The progression of marked changes in elastic fibers and the disorganization of the ECM of the lamina cribrosa was associated with the loss of function and continuous remodeling of the optic nerve head in POAG.