OBJECTIVE: Our principal research objective in this grant proposal is to design and fabricate a safe, clinical instrument with which to characterize quantitatively the origins of opacity in cataractous human lenses. The principle of the instrument is based on two types of laser light scattering: (1) the AC-DC method which determines separately the intensity of light scattered from soluble protein aggregates and that scattered from insoluble proteins, interdigitating membrane structures and swollen cells, and (2) laser light scattering spectroscopy, which determines the distribution of diffusivities of soluble protein aggregates. With this instrument we wish to classify precataractous lenses of patients. It will be used to detect cataract formation even before opacity becomes visible and to follow development and retreat of the lens opacity.