Depth-dependent forward light scattering by donor lenses.

PURPOSE To determine quantitatively forward light scattering in the human lens as a function of depth. To use this to explain the psychophysical result, verified earlier in vitro, showing total light scattering in the human lens to decrease with scattering angle according to an approximate power law (power -2). METHODS The amount of light scattered by donor lenses (n = 15; age range, 43 to 82 years) from a 1 mm x 0.1 mm white slit beam was measured as a function of depth in the lens for seven angles from 10 degrees to 165 degrees and for four wavelengths from 400 to 700 nm. Absolute values for light scattering (Rayleigh ratios) were derived. RESULTS Light scattering of the total lens corresponded quantitatively to psychophysically determined in vivo stray light data. Powers were approximately -2.2. An important source of forward scattered light is located superficially at the anterior and the posterior poles. Nuclear forward light scattering varied over 2 log units, more or less in line with clinical assessment of nuclear opacity (LOCS III NO score). Nuclear powers were approximately -1.4. CONCLUSIONS In vitro forward light scattering of donor lenses as a whole corresponded with in vivo data, but different depths in the lens contributed differently. Studies on functionally relevant light scattering by the human lens proteins should be conducted to explain true (in vivo) lenticular light scattering.