fig1 shows the retina 1 , the iris 2 and the lens 3 of a human eye . the lens 3 has a clouded portion 4 which is or can be attributable to the age of the patient or to a disease ( cataract ). the clouded portion 4 is assumed to be of such nature that it adversely affects the effectiveness of the eye even if the retina 1 is intact . the apparatus for measuring the extent of clouding or obscuring of the lens 3 comprises a radiation source 5 which emits a beam of radiation along a first path 6 extending through the diaphragm of the iris 2 and impinging upon the clouded portion 4 . the latter disperses and reflects the incident beam of radiation and some of the dispersed and reflected radiation propagates itself along a second path 7 which is inclined with reference to the first path 6 . the extent to which the clouded portion 4 disperses the beam which impinges upon it after having advanced along the path 6 is proportional to the cloudiness of the lens 3 , i . e ., the diffusion of incident radiation is more pronounced if the clouded portion 4 is more pronounced . the improved apparatus further comprises means for monitoring the reflected radiation , and such monitoring means includes a photoelectronic transducer 8 which is installed in the second path 7 and generates signals denoting at least one characteristic of the reflected light , namely a characteristic which is indicative of the degree of dispersion of incident radiation by the clouded portion 4 . the signals which are transmitted by the transducer 8 form a photocurrent which is supplied to a simple signal processing device in the form of a nanoamperemeter 9 with a pointer and a suitably calibrated scale to indicate the seriousness of the clouding of the lens 3 in appropriate units . the apparatus of fig1 further comprises ( or can further comprise ) a host of additional components including mirrors which direct radiation along selected paths , filters and / or other optical elements . some of these optical elements are shown in fig2 . the radiation source 5 is or can be selected in such a way that it emits monochromatic light . fig1 further shows a modulator 10 which can influence the beam of radiation in the path 6 , e . g ., to modulate the intensity of radiation which is being emitted by the source 5 toward the iris 2 . for example , the radiation source 5 can emit a bundle of light which is used as an orientation beam and the modulator 10 can periodically increase the intensity of emitted light in pulsating fashion . the source 5 can emit radiation in the infrared or in the ultraviolet range of the spectrum or in the visible light range . the angle alpha between the paths 6 and 7 is preferably less than 91 °, more preferably between 5 and 90 ° and most preferably between 10 and 40 °. the radiation source 5 can constitute the light source of a slit lamp which includes means ( such as binoculars ) for permitting observation of the clouded portion 4 along the second path 7 . to this end , the slit lamp includes an ocular 107 whose axis coincides with the path 7 . a portion of radiation which is reflected by the clouded portion 4 of the lens 3 into and propagates itself along the path 7 can be deflected between the observation objective and one of the two oculars of the slit lamp by a partially transmitting mirror to impinge upon the photoelectronic transducer 8 . it is equally within the purview of the invention to replace one ocular of the slit lamp with a light measuring head which includes the transducer 8 . it is presently preferred to employ a transducer 8 wherein the spectral sensitivity distribution is the same as that of the human eye and to place the transducer behind a suitable filter . this ensures that the quantification of cloudiness of the lens corresponds to the subjective sensation of the patient . the photoelectronic transducer 8 can be replaced with a video camera whose images are electronically stored in a suitable memory . the camera can be used in conjunction with a computer which processes the signals from the camera and displays them in the form of curves , or which integrates or otherwise averages the signals and transmits a single averaged signal . the nanoamperemeter 9 of fig1 can be replaced with a more sophisticated ( e . g ., electronically controlled ) signal receiving and processing device of any known design . fig2 shows a modified apparatus wherein all such parts which are identical with or clearly analogous to corresponding parts of the apparatus of fig1 are denoted by similar reference characters . the radiation source 5 comprises a light emitting diode which is designed to emit light in the dark red range ( approximately 690 nm ). the light beam transfer from the source 5 through an adjustable diaphragm 11 and is deflected by a mirror 12 to impinge upon a partially light transmitting prismatic beam splitter 17 . the thus deflected beam of radiation passes through the main objective 14 of an optical system 13 whose axis coincides with the first path portion extending to the clouded portion 4 of the lens 3 behind the iris 2 of the eye of the patient . the diaphragm 11 can be set to permit the passage of a beam having a diameter of 1 . 3 - 3 mm . if desired , the aperture of the diaphragm 11 can have a noncircular outline in order to reduce the likelihood of excessive reflection of the beam of incident radiation by the cornea of the eye of the patient . the main objective 14 serves to image the iris 2 in the ocular 15 of the optical system 13 ( e . g ., a suitable telescope ), and to image the beam of red light which is directed toward the iris 2 along the path 6 . the beam splitter 17 of the optical system 13 mixes the radiation in the respective portion of the path 6 . an abbe prism 18 of the optical system 13 is disposed between the beam splitter 17 and the ocular 15 to reverse the image . a fixation point 19 is provided in the first path to enable the patient to look in the direction toward the beam splitter 17 . the clouded portion 4 can constitute a cataract which disperses and reflects some of the incident radiation into the path 7 wherein the reflected radiation impinges upon the photoreceiver 20 of a transducer 8 . the receiver 20 can include an optical element and a preamplifier which directs signals to a second component 21 of the transducer 8 , preferably a combined amplifier and band pass filter whose output is connected with a demodulator 22 having an output connected with the corresponding input of a microprocessor 23 . the band pass filter of the component 21 eliminates or reduces the influence of undesirable factors , and the amplifier of the component 21 intensifies the signals to a level which is required for convenient processing in the microcomputer 23 . the demodulator 22 serves to relieve the signals of noise and to demodulate the signals so that they are devoid of radiation which is attributable to daylight or artificial light , i . e ., the signals which reach the microcomputer 23 are derived solely from radiation which is emitted by the source 5 . an analog - digital converter ( not specifically shown ) is installed between the demodulator 22 and the microprocessor 23 which latter is equipped with a keyboard 24 . the microprocessor 23 of the transducer 8 processes the digital signals in accordance with selected mathematical algorithms before the signals reach an alphanumerical display unit 25 . if desired , the output of the microcomputer 23 can be connected with the input of a printer 26 which can be used with or in lieu of the display unit 25 . the components 25 , 26 together constitute a functional equivalent of the amperemeter 9 of fig1 . an output of the microcomputer 23 is connected with the modulator 10 for the beam of radiation issuing from the source 5 . the apparatus of the present invention can be designed to measure the polarization of light which is attributable to the presence of a cataract 4 . such polarization measurement ( in the path 7 ) can take place in addition to or in lieu of a measurement of intensity of reflected radiation . this is often desirable and advantageous if the source 5 emits nonpolarized light . the monitoring means ( transducer 8 ) can further comprise means for monitoring the electric or magnetic field of radiation in the path 7 to ascertain the energy density which is directly proportional to the rate of dispersion of radiation by the cataract 4 . if the source 5 emits monochromatic light , the monitoring means can operate in accordance with fresnel interference principles to ascertain the extent to which the dispersion of light affects the monochromaticity of light ( nonelastic dispersion ) which is an indication of the rate of dispersion of light by the cataract 4 . slit lamps which can be used in the apparatus of the present invention are manufactured and sold by haag - streit ag , hess - str . 27 , ch - 3097 liebefeld , switzerland . without further analysis , the foregoing will so fully reveal the gist of the present invention that others can , by applying current knowledge , readily adapt it for various applications without omitting features that , from the standpoint of prior art , fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and , therefore , such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims .