In 50 eyes with nuclear cataract, posterior subcapsular cataract and cortical cataract and 34 normal eyes, the amount of scattered light was determined using the Opacity Lensmeter 701 to determine its accuracy in distinguishing between clear and cataractous lenses. Taking as a basis the manufacturer's statement that normal lenses show Opacity Lensmeter readings of less than 25 and that cataractous lenses show Opacity Lensmeter readings of more than 30, 94% of the nuclear cataract cases, 62% of the posterior subcapsular cases and 66% of the cortical cataract cases were identified as being pathologically opaque. Of the normal eyes, 88% had an Opacity Lensmeter reading of less than 25. Among the types of cataract examined, a significant linear relationship (P < 0.05) between visual acuity loss due to cataract and scattered light measurements could be found only in eyes with nuclear cataract, with the individual results heavily scattered around the linear regression. In the case of nuclear cataracts, measuring scattered light with the Opacity Lensmeter is suitable for making general statements on visual loss due to cataract for a whole group of patients. However, in individual cases the results can only be used together with other clinical examinations.