Multilamellar bodies as potential scattering particles in human age-related nuclear cataracts

To characterize within human age-related nuclear cataracts rare spherical objects covered by multiple membranes, termed multilamellar bodies (MLBs).

Adult human normal, transparent lenses were obtained from eye bank donors and age-related nuclear cataracts were obtained immediately after extracapsular extraction. Each sample was Vibratome sectioned fresh into 200 microm thick sections that were fixed and embedded for light or electron microscopy. Confocal images were recorded from sections stained with the lipid soluble dye, DiI.

Light micrograph montages of the equatorial plane containing the fetal and embryonic nuclei were examined. Rare, but distinct, circular 1-3 microm diameter objects were observed consistently in the cataracts. These objects did not appear to be components of the complex intercellular interfaces. Serial sections indicated that the objects were spherical, or contained a spherical component. For about 20,000 fiber cell cross-sections in each lens, the frequency of MLBs was 10 times higher in cataracts than in the normal lens nuclei. Although extensive searching with the electron microscope was necessary, the size, circular profile and multiple layers of thin (5 nm) membranes easily identified the MLBs. Interiors of the MLBs displayed variable textures. Confocal images indicated that the coverings were enriched in lipid compared to the adjacent plasma membranes. The calculated density of the MLBs in the cataractous nuclei was about 3800/mm3, which represents a volume fraction of 0.00003.

Because the MLBs are large compared to the wavelength of light, display interiors with variable staining textures and have lipid-rich coverings, they appear to be ideal candidates for large scattering particles that may contribute to the forward light scattering in nuclear cataracts.