Lens opacity was quantified in 85 cataractous patients, using a new instrument: the lens opacity meter 701 (LOM; Interzeag, Schlieren, Switzerland). Cataracts were classified as nuclear, cortical, subcapsular and mixed forms. Sensitivity, specificity and reproducibility of the results were evaluated by statistical analysis. Visual acuity was correlated with LOM values in patients with nuclear and mixed cataracts. Moreover, the instrument gave a good degree of reproducibility only in patients who presented these forms of lens opacities. Our findings demonstrate that the LOM 701 is able to detect and to measure only lens opacities which affect the central area of the lens.