Morphologic characteristics and chemical composition of Christmas tree cataract.

PURPOSE Christmas tree cataract consists of highly refractile multicolored "needles" crisscrossing the lens fibers of the deep cortex. The fact that the colors vary according to the angle of the incident light, and that in retroillumination only a dim outline of the cataract is seen, would suggest that Christmas tree cataract is a diffractive phenomenon. This study was performed to unravel the ultrastructure and chemical composition of the Christmas tree needles. METHODS Eight lenses from donor eyes and four extracapsularly extracted lenses with Christmas tree cataract were investigated by scanning and transmission electron microscopy. The chemical composition was studied with energy-dispersive x-ray microanalysis and Raman microspectroscopy. RESULTS Scanning electron microscope examination showed that the needles are smooth, rectangular, plate-like elements bordered by membranes and amorphous material and running crisscross through the lens. In the specimens for transmission electron microscopic examination, the needles proved to be largely dissolved, but the remains showed regular spacings of approximately 5 nm. Material identical in spacing and electron density was found in neighboring cells bound to a reticular membranous network originating from the fiber-limiting membranes. Energy-dispersive x-ray and Raman microanalysis showed that the needles have a high sulfur content and pronounced S-S, CS-SC, and C-S vibrations. The cytoplasm adjacent to the needles and reticular meshwork had an elevated Ca++ content. CONCLUSIONS It is concluded that cystine is the most likely candidate for the Christmas tree needles and that the needles probably are formed as the result of an age-related aberrant breakdown of crystallins induced by elevated Ca++ levels.