The effect of freezing on human cortical cataracts.

To ascertain a direct relationship between the light scattering intensity and the particle scattering the light, thin (6-20 micrometers) sections were cut from frozen human cataracts. Freezing for 15 min (-10 C) and then thawing had no effect on the clarity or light scattering properties of nuclear cataracts. Cortical cataracts treated in the same manner appeared to be much clearer than they were prior to freeze-thawing. Light scattering measurements were obtained as a function of scattering angle, both in the I parallel and I perpendicular mode; a He-Ne laser was used. Results showed a reduction in the light scattering intensity in the I parallel and I perpendicular modes with repeated cyclical freezing and thawing and that this decrease was most pronounced at higher scattering angles. Morphologic data showed that much of the anatomical heterogeneity present in the human cortical and rat lens osmotic cataract disappeared upon freeze-thawing. However, even though the anatomical heterogeneity was less, there was persistence of serious cellular anatomical disorganization in grossly transparent parts of the cortex. This suggests that transparency is not dependent upon the presence of intact fiber cells. The importance of these findings to studies of light scattering, cataract classification and analysis of cryoextracted human lenses is discussed.