Predicted light scattering from particles observed in human age-related nuclear cataracts using mie scattering theory.
OBJECTIVE
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 microm 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 microm radius) had low scattering efficiency over a wide range of particle refractive indices. Particles with radii 0.6 to 3 microm 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 microm) and, at an estimated 4000 particles/mm(3) of tissue, up to 18% of the incident light was scattered primarily within a 20 degrees 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.
Costello
M Joseph
MJ
Department of Cell and Developmental Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA. mjc@med.unc.edu
Johnsen
Sönke
S
Gilliland
Kurt O
KO
Freel
Christopher D
CD
Fowler
W Craig
WC
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D002386:Cataract / Q000473:pathology*; D006801:Humans; D002479:Inclusion Bodies / Q000528:radiation effects* / Q000648:ultrastructure; D007907:Lens Nucleus, Crystalline / Q000528:radiation effects* / Q000648:ultrastructure; D008027:Light; D008875:Middle Aged; D008962:Models, Theoretical; D010316:Particle Size; D012542:Scattering, Radiation