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Predicted Light Scattering from Particles Observed in Human Age-Related Nuclear Cataracts Using Mie Scattering Theory

¹From the Departments of Cell and Developmental Biology and ⁴Ophthalmology, University of North Carolina, Chapel Hill, North Carolina; the ²Departments of Biology and ³Pharmacology, Duke University, Durham, North Carolina.

PURPOSE. To employ Mie scattering theory to predict the light-scattering from micrometer-sized particles surrounded by lipid shells, called multilamellar bodies (MLBs), reported in human age-related nuclear cataracts.

METHODS. Mie scattering theory is applicable to randomly distributed spherical and globular particles separated by distances much greater than the wavelength of incident light. With an assumed refractive index of 1.40 for nuclear cytoplasm, particle refractive indices from 1.33 to 1.58 were used to calculate scattering efficiencies for particle radii 0.05 to 3 µm and incident light with wavelengths (in vacuo) of 400, 550, and 700 nm.

RESULTS. Surface plots of scattering efficiency versus particle radius and refractive index were calculated for coated spherical particles. Pronounced peaks and valleys identified combinations of particle parameters that produce high and low scattering efficiencies. Small particles (<0.3 µm radius) had low scattering efficiency over a wide range of particle refractive indices. Particles with radii 0.6 to 3 µm and refractive indices 0.08 to 0.10 greater (or less) than the surrounding cytoplasm had very high scattering efficiencies. This size range corresponds well to MLBs in cataractous nuclei (average MLB radius, 1.4 µm) and, at an estimated 4000 particles/mm³ of tissue, up to 18% of the incident light was scattered primarily within a 20° forward cone.

CONCLUSIONS. The calculated size of spherical particles that scatter efficiently was close to the observed dimensions of MLBs in cataractous nuclei. Particle refractive indices only 0.02 units different from the surrounding cytoplasm scatter a significant amount of light. These results suggest that the MLBs observed in human age-related nuclear cataracts may be major sources of forward light scattering that reduces contrast of fine details, particularly under dim light.

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