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

摘要

The transparent human lens focuses light on the retina. When the lens becomes opaque, it is known as a cataract, a condition in which light is scattered instead of focused. Cataract, the leading cause of blindness worldwide, may be a multifactorial disease with many sources of light scattering. One particular source of light scattering in human age-related nuclear cataracts is likely to be rare spherical objects within the cytoplasm known as multilamellar bodies (MLBs). Studies were designed to characterize and quantify these structures. Adult human normal, transparent lenses were obtained from eye bank donors, and age-related nuclear cataracts were obtained immediately after extracapsular extraction. Samples were Vibratome sectioned and prepared for light, electron, and confocal microscopy. Light micrograph montages were used to examine cells of both the equatorial plane and the optic axis. Rare but distinct circular 1–3μm diameter objects were observed consistently in the cataracts. For about 20,000 fiber cell cross-sections in each lens, the frequency of MLBs was approximately 7.5 times higher in cataracts than in the normal lenses. 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. The calculated density of the MLBs in the cataracts was about 4000/mm3 , which represents a volume fraction of 3 × 10−5 . 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 cataract.