In vivo dynamic light scattering characterization of a human lens: Cataract index

Purpose. To characterize the cataractous state of the living lens by a single parameter, derived from in vivo dynamic light scattering measurements. Methods. Dynamic light scattering, in conjunction, with a fiber optic transmitter/receiver, was used for measuring the intensity autocorrelation of the light scattered in the backward direction from the living human lens. The fiber optic transreceiver provided a rapid means for active positioning and collection of the back scattered light from any point inside the lens. Intensity autocorrelation, spanning seven decades of delay time, was acquired, in vivo, from the lenses of volunteers ranging in age from 10 to 85. The number weighted size distribution, recovered from the autocorrelation data, was found to be a consistent means of characterizing the aging living lens. Results. The cataract index, representing the average of the number weighted size distribution, varied from five, for clinically clear lenses, to 10,000 for cataractous lenses. Repeated measurements, over a period of two years, on the lens of the same subject established the efficacy of the measurement. In the precataractous stage a single point measurement in the nuclear region of the lens was sufficient to characterize the state of the whole lens. Conclusion. The cataract index is a quantitative measure of the cataractous state of any small volume element (50 x 250 μm ) inside the human lens. This index is useful for characterizing lenses at any stage of development, that is, from infancy through visual impairment.