MORPHOLOGIC CHARACTERISTICS AND CHEMICAL-COMPOSITION OF CHRISTMAS TREE CATARACT

Purpose. Christmas tree cataract consists of highly refractile multico lored ''needles'' crisscrossing the lens fibers of the deep cortex. Th e fact that the colors vary according to the angle of the incident lig ht, and that in retroillumination only a dim outline of the cataract i s seen, would suggest that Christmas tree cataract is a diffractive ph enomenon. This study was performed to unravel the ultrastructure and c hemical composition of the Christmas tree needles. Methods. Eight lens es from donor eyes and four extracapsularly extracted lenses with Chri stmas tree cataract were investigated by scanning and transmission ele ctron microscopy. The chemical composition was studied with energy-dis persive x-ray microanalysis and Raman microspectroscopy. Results. Scan ning electron microscope examination showed that the needles are smoot h, rectangular, plate-like elements bordered by membranes and amorphou s material and running crisscross through the lens. In the specimens f or transmission electron microscopic examination, the needles proved t o be largely dissolved, but the remains showed regular spacings of app roximately 5 nm. Material identical in spacing and electron density wa s found in neighboring cells bound to a reticular membranous network o riginating from the fiber-limiting membranes. Energy-dispersive x-ray and Raman microanalysis showed that the needles have a high sulfur con tent and pronounced S-S, CS-SC, and C-S vibrations. The cytoplasm adja cent to the needles and reticular meshwork had an elevated Ca++ conten t. Conclusions. It is concluded that cystine is the most likely candid ate for the Christmas tree needles and that the needles probably are f ormed as the result of an age-related aberrant breakdown of crystallin s induced by elevated Ca++ levels.