HETEROGENEITY IN ULTRASTRUCTURE AND ELEMENTAL COMPOSITION OF PERINUCLEAR LENS RETRODOTS

Purpose. To unravel the cataractogenic process(es) leading to the bire fringent lenticular bodies known as perinuclear retrodots. Methods. Te n human lenses containing biomicroscopically verified perinuclear retr odots were systematically screened and analyzed using scanning electro n microscopy and energy dispersive x-ray microanalysis to verify their ultrastructure and elemental composition. Results. Three types of ret rodots were distinguished, different in size, ultrastructure, and orig in. Two of them contained calcium phosphate, the third probably contai ned calcium oxalate. All three types were separated from surrounding n ormal fibers and the crystalline inclusions were sequestered within me mbrane-lined bodies. Conclusions. Because of these observations and da ta found in the literature it is postulated that elevated free calcium is the initiating factor in the formation of retrodots, trapped by ei ther oxalate or phosphate and sequestered in the retrodots. It is sugg ested that the oxalate is derived from ascorbate because of impaired p rotection against oxidative stress in the older lens. Phosphoric acid is believed to be released by calcium-induced hydrolysis of membrane p hospholipids.