the extent of clouding of the lens of a human eye is measured and quantified by directing a beam of electromagnetic radiation through the iris and against the clouded portion of the lens so that the clouded portion disperses and reflects the incident radiation . a selected part of reflected radiation which makes an angle of 10 °- 40 ° with the beam of incident radiation is monitored for intensity by a photoelectronic transducer whose signals are transmitted to an ammeter or to a microprocessor which latter transmits modified signals to a display unit and / or to a printer . the clouded portion of the lens can be observed through an optical system with an ocular whose axis coincides with a portion of the path of incident radiation .