Morphology of the aging human lens. II. Ultrastructure of clear lenses.

Clear human post mortem lenses, varying in age between 23 and 82 years, were investigated using scanning and transmission electron microscopy. The lenses were obtained from the Corneabank Amsterdam. The post mortem delay ranged from 8-24 hours. Apart from some minor mitochondrial changes no hypoxic post mortem disturbances in epithelial cells and lens fibers were observed. In the lens fibers three main age-related fine structural alterations were found: i) membrane ruptures, ii) watervacuoles and iii) multilamellar bodies. The frequency of these alterations increased with age and they remained restricted to the superficial equatorial cortex. They were absent in the anterior and posterior cortex, supranuclear equatorial cortex and nucleus. The relevance of these observations in relation to the etiology and early pathogenesis of senile cataract is discussed. The membrane ruptures and watervacuoles are in morphological support of the view, based on biochemical evidence, that oxidative stress leads to destabilization and desintegration of membranes and consequently disturbs the waterbalance of fibers. It is postulated that the lamellar bodies are involved in the repair of ruptured membranes and breakdown of affected proteins thus explaining the late onset of senile cataractous changes.