Distribution, spherical structure and predicted Mie scattering of multilamellar bodies in human age-related nuclear cataracts.

PURPOSE: To characterize multilamellar bodies (MLBs), determine their distribution along the optic axis and predict their potential Mie scattering within human age-related nuclear cataracts. Previous studies restricted to the equatorial plane have shown that MLBs are rare spherical objects that are 1-4 microm in diameter and covered by multiple layers of thin lipid-rich membranes.
METHODS: Eight human aged transparent lenses were obtained from eye bank donors and eight human 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. Light micrograph montages of the optic axis containing the juvenile, fetal and embryonic nuclei were examined. Mie scattering for random coated spherical particles was calculated based on assumed and measured particle parameters.
RESULTS: Cells along the optic axis of the cataract contained approximately 7.5 times more MLBs as similar regions of the aged transparent lens, although these MLBs occurred with extremely low frequency. Cells of the aged transparent lens contained 1.3 MLBs mm(-2), while those of the cataract contained 9.6 MLBs mm(-2), which are equivalent to calculated densities of 5.6 x 10(2) and 4.1 x 10(3)mm(-3), respectively. While some MLBs were located within the cytoplasm near cell membranes, others were found away from membranes. The MLBs are distinct from circular profiles resulting from finger-like projections between adjacent cells. MLBs displayed varying geometries and cytoplasmic textures, although predominately spherical with interiors similar to adjacent fiber cell cytoplasm. These results are in agreement with previous theoretical analysis of light scattering from human lenses and with previous morphological studies examining the equatorial plane of the lens. Potential Mie scattering of spherical particles with the average properties of the observed MLBs and assumed refractive index properties was calculated to be forward scattering of as much as 20% of the incident light.
CONCLUSIONS: The observed low frequency and absence of clustering of MLBs in the equatorial plane and along the optic axis suggests that MLBs are most likely uniformly distributed throughout the embryonic, fetal and juvenile nuclei of age-related cataracts. Because of their size, distribution, textured cytoplasm and calculated Mie scattering, MLBs probably cause local fluctuations in refractive index in human lens nuclei and, therefore, are potential sources of low-angle, forward light scattering that could impair image formation.