VARIATIONS IN REFRACTIVE-INDEX AND ABSORBANCY OF 670-NM LIGHT WITH AGE AND CATARACT FORMATION IN HUMAN LENSES

A newly-developed fibre-optic sensor (wavelength of 670 nm) was used to measure the index gradient in 16 human lenses ranging in age from 38 to 78 years. Two of these lenses had nuclear cataract. The refractive index, calculated from the proportion of reflected light at the sensor/sample interface, appeared to increase with age and further with cataract formation. This was not consistent with previous studies. The increased losses of reflected light, which gave apparent increased values of refractive index, were reconsidered to be resulting from light absorption and an estimate of relative absorption was made by deducting excess light loss from a base level expected to yield the maximum index value. The characteristics of the relative absorption are similar to those of a red fluorophor reported in other studies.