The technique of photon correlation spectroscopy has been used to measure scattered light intensity fluctuations from the corneal stroma of diabetics and nondia-betics. The fluctuations in light intensity result from Brownian motion of the scattering elements in the cornea. Analysis of the resulting autocorrelation function provides information on these scatterers. Changes in stromal measurements were noted in response to aging. There were also significant changes measured in those diabetics exhibiting proliferative diabetic retinopathy. Patients in the proliferative retinopathy class who had had prior laser photocoagulation therapy showed measurements more characteristic of nondiabetics and diabetics with no or background retinopathy. This technique provides a sensitive, quantitative, and noninvasive method for clinical monitoring of corneal changes at the molecular level.