Fundus reflectance and the measurement of crystalline lens density.

We have developed an optical technique for measuring the in vivo absorption of the human crystalline lens based on using the retina as a reflector for a double-pass measurement of lens density. We compare results obtained by the reflectometric technique with results obtained in the same subjects by a psychophysical method. We find that the estimates obtained with the two techniques are highly correlated, and both measure similar effects of aging on the optical density of the lens. In addition, we show that the significant variations in retinal reflectance attributable to differences in ocular pigmentation and drusen have only a minor effect on the estimate of lens optical density. However, correcting retinal reflectances for the effect of lens absorption shows that the effect of lens absorption may be overestimated with both methods. The overestimation may arise from inaccuracies in the shape of the assumed lens spectrum.