The efficacy of a new clinical instrument which measures light backscatter from the crystalline lens--the Opacity Lensmeter 701--was assessed. Repeated measurements were made on 83 normal subjects in the age range 15 to 82 years, and on 38 eyes of subjects with cataract but normal retinal and neural function. The cataract scores were compared against results of Logmar visual acuity (VA) and glare disability measurements from the same subjects. The Lensmeter was found to be simple to use and gave quick, repeatable, objective measurements of light backscatter. Scores correlated well with normal age changes in noncataractous lenses and in cataracts of pure nuclear morphology, but not in cortical or posterior subcapsular cataracts.