Random Distribution of Multilamellar Bodies in Human Age-Related Nuclear Cataracts

Abstract

Abstract: : Purpose: We reported previously that some of the cells of human age-related nuclear cataracts contain multilamellar bodies (MLBs), which are seldom-occurring spherical particles surrounded by multiple layers of tightly-packed thin lipid membranes (Gilliland et al., Molecular Vision, 2001, 7:120-30). Because MLBs are large (2-3 µm in diameter) with comparison to the wavelength of light and are 10 times more numerous in the cataract compared to the normal, they are considered to be potential contributors to the forward scattering of light. Whereas previous studies have characterized MLBs only in the equatorial plane of the lens, the goal of the current study is to quantify MLBs along the optic axis. Methods: Human normal lenses and age-related nuclear cataractous nuclei were sectioned with a Vibratome, fixed, and embedded for light microscopy. For each sample, 1.5 mm₂ of TBO-stained tissue along the optic axis in the embryonic and fetal nuclei was examined by light microscopy. MLBs were quantified and their morphology was studied. Results: Cells along the optic axis of the cataract contained approximately 8 times as many MLBs as similar regions of the normal lens, although these MLBs occurred with extremely low frequency. Cells of the normal lens contained approximately 2 MLBs/mm₂, while those of the cataract contained approximately 15 MLBs/mm₂. While some MLBs were located within the cytoplasm near cell membranes, others were found away from membranes. These MLBs, which are distinct from circular profiles resulting from finger-like projections of one cell into an adjacent cell, displayed varying geometries and cytoplasmic textures. Conclusion: The similar frequency of MLBs in the equatorial plane and along the optic axis suggests that MLBs are distributed randomly throughout the embryonic and fetal nuclei of cataracts. The size, frequency, and random distribution of MLBs agree with that predicted in theoretical experiments based on actual light scattering. The continued support of the fact that MLBs are approximately 10 times more numerous in the cataract compared to the normal lens indicates that MLBs may be potential light scattering particles. Because of their size, distribution, and textured cytoplasm, MLBs are likely to cause local fluctuations in refractive index and to scatter light in the forward direction toward the retina.

Keywords: 338 cataract • 342 cell membrane/membrane specializations • 474 microscopy: light/fluorescence/immunohistochemistry