Picosecond light scattering measurements of cataract microstructure

A picosecond range-gated light scattering technique is used to measure the microstructure of cataracts in the living eye, with a resolution of the order of the wavelength of light. The cataract is illuminated with ultrashort pulses of light derived from a mode-locked Nd:glass laser. The pulses backscattered by the opacity are collected at several angles simultaneously by an array of fiber-optic light guides whose outputs are sequentially sampled by a multichannel picosecond Kerr shutter. This shutter transmits only that light which is scattered from the desired depth in the eye, while blocking from the detector any light scattered by foreground or background tissue and reducing multiple scattering effects. The size distribution of scatterers in the cataract is deduced from the angular distribution of scattering intensities by application of Mie theory. The results of experiments with suspensions of latex microspheres and with rabbit cataracts in vivo are presented. Cataract microstructure down to 0.5 microm has been measured in a rabbit eye and verified with electron microscopy.