A method of classifying cataractous changes in excised human lenses, based on separate and independent photographic documentation, with consequent quantitative evaluation of lens opacification is proposed. The degree of lens clouding was evaluated quantitatively by measuring the optical density index and the area of the zones of clouding with certain optical density parameters (equidensities) by use of an image analyser. This technique produced an image in which contrast represented different zones of lens clouding in the frontal projection, and allowed their contribution to the total lens area to be determined. The precise topography of the opacities was established. The classification data obtained for different clinical types of cataracts can be simplified according to the needs of the scientist in his effort to measure clinically or scientifically significant quantitative associations between laboratory measures and cataractous changes.