Abstract
Abstract: :
Purpose:To employ Mie scattering theory to predict the light scattering from particles in nuclei of human age–related cataractous lenses. Methods: Mie scattering theory is applicable to random spherical particles separated by distances much greater than the wavelength of light. Scattering from particles of various sizes and composition was calculated based on previous studies of the human lens interior, including the predicted scattering from spherical, micron–sized particles surrounded by thick lipid shells, called multilamellar bodies (MLBs), implicated as a major source of forward light scattering in human nuclear cataracts (Mol Vis 7, 120–30, 2001). Literature values for refractive indices of nuclear cytoplasm and particle refractive index variation from 1.33 to 1.55 were used to calculate scattering efficiencies for a range of particle sizes (0.1–6 µm) and wavelengths (400–700 nm) using MatLab (Mathworks, Natick, MA). Results: Surface plots of scattering efficiency versus particle size and refractive index were calculated at different wavelengths for theoretical coated spherical particles. Pronounced peaks and valleys in the plots identified combinations of particle parameters that produce high and low scattering efficiencies. Small particles (<1 µm) had low scattering efficiency over a wide range of particle refractive indices. Particles that were 1.5 to 4 µm in diameter with refractive indices 0.08 to 0.10 greater than the surrounding cytoplasm had very high scattering efficiency. This size range matches the range observed for MLBs in cataractous nuclei (average MLB diameter is 2.7 µm). TEM images of MLB interiors often differ in staining density compared to the surrounding cytoplasm, suggesting differences in refractive index. The calculated Mie scattering intensity for particles matching the characteristics of MLBs (at the calculated 4000 particles/ mm3 of tissue) was concentrated in the forward direction, mainly within a 10º scatting angle and up to 20% of the incident light. Conclusions: The calculated size range of spherical particles that would produce the maximum amount of light scattering matched the observed dimensions of MLBs in cataractous nuclei. The Mie scattering plots indicate that the particle refractive index needs to be only 0.02 units different from the surrounding cytoplasm to produce an important increase in scattering. These results suggest that the MLBs observed in human age–related nuclear cataracts are a major source of forward light scattering that can impair image formation.
Keywords: cataract • microscopy: electron microscopy • microscopy: light/fluorescence/immunohistochemistry