QUASI-ELASTIC LIGHT-SCATTERING STUDY OF THE LIVING HUMAN LENS AS A FUNCTION OF AGE

Purpose. To determine contributions of molecular scattering elements t o the increase with age in the light scattered from the human ocular l ens in vivo. Methods. We used quasielastic light scattering to measure autocorrelation functions of the intensity of light scattered in vivo from three locations (anterior, nuclear and posterior) along the opti c axis in ocular lenses of 225 subjects, ranging from 17 to 63 years o f age. We deduced probability distributions of key parameters (I-s, I- f, I-i, I-T), which describe contributions of slowly diffusing (I-s), rapidly diffusing (I-f) and relatively immobile (I-i) scattering eleme nts to the total light intensity (I-T) scattered into the collection o ptics. We deduced characteristic times tau(s) and tau(f) that describe the Brownian motion of scattering elements. Results. Probability dist ributions for each age decile show clearly defined shifts in key param eters with age. I-T at the nucleus increases by a factor of three from age 20 to 60 years. This increase is produced principally by an appro ximate five-fold increase in I-s. I-T and I-s and can be detected with an accuracy of similar to +/- 10%. We estimate threshold values for I -T, which mark the boundary beyond which clinical cataract becomes man ifest. This boundary represents 6 to 8 times the light scattering effi ciency expected from the newborn lens. Conclusions. This methodology p ermits a sensitive, quantitative, clinically useful representation of the pre-cataractous molecular changes associated with aging in the liv ing human lens.