fig1 shows a cross section of an eye - ball 1 , with a cornea 2 , a conjunctiva 3 , an iris 4 , a pupil 5 , a lens 6 , and a retina 7 . adhering to the eye 1 is a contact glass 8 consisting of a transparent material , preferentially a plastic ( organic ) glass , whose contact surface is adapted to the form of the eye under investigation . between the eye 1 and the contact glass 8 a thin layer of fluid 9 has been placed in known manner , thus providing optical contact . two light sources 10 and 11 are rigidly fixed to the contact glass 8 , source 10 emitting illumination light and source 11 stimulus light . also rigidly fixed to the contact glass 8 are several detectors 12 , two of them being shown in the figure . the mounts of the light sources and the detectors are not shown , for clarity . such mounts may , for example , be fixed to a case that can be slid over and fixed to the contact glass 8 , said case making , however , no optical contact with those surfaces of the contact glass 8 which act as reflecting surfaces for the illumination light as described below . electrical leads 13 , 14 and 15 for the sources 10 , 11 and the detectors 12 are indicated . whereas the emission of the stimulus light source 11 must lie within the visible range of the spectrum since the retina 7 is expected to respond to it , the contrary applies to the emission of the light source 10 . for the latter , therefore , light that is not perceived by the human eye , e . g . infrared radiation , is suitable . the detectors 12 , then , have to be sensitive to this same spectral range . such a separation of the spectral ranges of the illumination and stimulus lights has the additional advantage that stray light from the stimulus source ( if any ) may easily be withheld from the detectors 12 by optical filters , not shown . for the illumination and stimulus light sources 10 and 11 the use of so - called light - emitting diodes is of advantage ; these can be obtained commercially . such diodes , although not being of high intensity , have a relatively small radiating area , which is favorable for the present device . on the other hand their low intensity is compensated by the fact that the light path from the source to the detectors is relatively short . nevertheless , it is of interest to use as great a part of the illumination light 10 as possible , in order to make the signal , that is , the variation of the pupil size , as high as possible relative to the unavoidable noise ( stray light , instabilities of the detector and the amplifiers ). for that purpose the contact glass 8 of the device according to the present invention is conceived as an optical collecting system of a special type which will be described below . moreover , it is of advantage to provide not only one but several detectors 12 that may work independently or in series . miniature photo diodes may be used which are commercially available . their signals are processed electronically in known manner and may be displayed for example by a pen recorder . the contact glass 8 of fig1 as an optical system , exhibits a polished toroidal surface 16 and a polished cylindrical surface 17 . ( the latter may also be given a slightly conical shape if so required by production necessities ). the hollow light cone impinging on said refracting toroidal surface 16 , emitted by source 10 , is collimated and directed towards the iris by total reflection on said polished cylindrical surface 17 . the light is thus concentrated on the plane of measurement as defined by the iris 4 and the pupil 5 . part of the light striking the iris 4 is absorbed , another part is diffusely reflected . a certain percentage of the reflected light reaches the detectors 12 and is recorded . if now the size of the pupil changes , e . g . as a reaction to a light stimulus reaching the retina 7 from the source 11 in the form of the beam 18 , the surface of the iris lying within the illuminated area , and therefore the amount of reflected light , change too . the signals of the detectors thus vary as to sign and quantity according to the variation of the pupil size , and their temporal course can be recorded . any movements of the eye 1 do not influence the results of the measurement because the contact glass 8 and hence all measuring elements as described take part in such movements . good adherence of the contact glass 8 to the eye 1 can be provided in known manner by slight suction . the bore channel of small diameter necessary for this is not shown in fig1 . another form 19 of the contact glass is shown in fig2 . here the functions of the collimating and the totally reflecting surfaces 16 and 17 of fig1 are taken over by one single polished toroidal mantle surface 20 , whereas the entrance surface 21 for the light from source 10 is conical . fig3 shows a third variant of the contact glass . the contact glass 22 differs from the contact glass 8 of fig1 insofar as lenses 23 are provided , each lens forming an image of a certain sector of the iris 4 on one of the detectors 12 . in contrast to this , light reflected from any point of the iris can reach all the detectors in the case of fig1 . with the device of fig3 it is therefore possible to differentiate the pupillary reaction in respect to certain sectors of the iris . this too is of clinical interest since the coordination of the various muscle bundles responsible for iris movements may be out of order . according to fig3 the lenses 23 of the contact glass 22 are part of a removable body 24 . if required , the body 24 may be exchanged for another piece without such lenses . said body 24 consists of a mount 25 that may be formed , for example , out of an opaque plastic material . this mount serves as a support for a lens body 26 of transparent material , e . g . glass or transparent plastic . the lenses 23 may be given an aspherical form . the detectors 12 are located above the lenses 23 on the upper surface of mount 25 . the lens body 26 comprises , in addition , a central lens 27 that serves to direct the stimulus light from source 11 towards the retina ( not shown here , see fig1 ) through the pupil 5 . the advantage of providing such a lens is that it can be devised to form an image 27 &# 39 ; of the small radiating area of source 11 in the pupil plane , as shown . since that image will be smaller than the smallest diameter the pupil is able to contract to , the retinal area covered by the stimulus light will be independent of the pupil size , whereas for the device of fig1 it does depend on that size ; this is not desirable , however , for well - defined investigations . as for the rest , the contact glass 22 of fig3 corresponds to the contact glass 8 of fig1 especially so concerning the course of the light beams from source 10 to iris 4 . as can be seen on the plan view , fig4 of body 24 ( without detectors 12 ), four lenses 23 may be provided , for example . the use of the device described above in several examples is made difficult or impossible when measurements on prematurely or newly born infants are intended , because in these instances the lid fissure is too small to adapt the cylindrical optical system of the contact glass as shown in fig1 to 3 . in fig5 and 6 a modification of the contact glass is shown that avoids this difficulty . the contact glass 28 possesses a cup - like contact part 29 of similar form to those described above , except that its radius is smaller , thus being adapted to the smaller radius of infantile corneas . the cross section ( fig5 ) of the optical system collecting the light from the illumination source ( not shown ) is of the same form as that of the contact glasses described above in fig1 and 3 ; that is , there is a collimating toroidal surface 30 and a totally reflecting cylindrical surface 31 . however , as shown in fig6 the part of the contact glass delimited by these two surfaces is partially cut off . the remaining sectors of the optical system have a width 32 of 5 . 5 mm , for example , which conforms to the lid fissure of prematurely or new - born infants . besides , the contact glass 28 , like that of fig3 is provided with a recess 33 into which a body with lenses of appropriate dimensions may be fitted , as shown in fig3 . other parts of the device , especially the illumination source and the detectors , not shown in fig5 and 6 , correspond to those described above . experience has shown that with the device described , measurements of the pupil size on prematurely and new - born infants are possible . it will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification .
a device for measuring the size of an eye pupil , particularly with non - cooperating patients , has a body which contacts the eye and carries on it an illuminating light source , a series of light detectors and an optical system for collecting the divergent light from the illuminating source and directing such light towards the iris of the eye . a stimulus light source can also be included for directing stimulus light through the pupil and onto the retina .