Patent Publication Number: US-2002005934-A1

Title: Device for testing visual functions of the human eye

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to a device for the examination of visual functions of the human eye which is at a viewing point and is oriented along a viewing axis. Means associated with a first light source are used for the temporally staggered generation of stimuli at selectable locations on the background of the viewing axis. The background around the viewing axis is uniformly illuminated with a second light source.  
       [0003] 2. Description of the Related Art  
       [0004] A device of the prior art of the type described above is described in CH-A-677 599. In this device of the prior art, the stimuli are offered to the patient on an image plane around the viewing axis. The three-dimensional background around this viewing axis is uniformly illuminated. For this purpose, in the viewing axis there is a partly light-permeable mirror that is directed toward the image plane, which on one hand lets through the light of the stimulus light source and on the other hand deflects the light generated by the second light source toward the image plane. The second light source used is a halogen lamp which is optionally cooled by means of a ventilator.  
       [0005] The prior art also includes a full-field perimeter in the field of electrophysiology by means of which a flickering background can be generated. The flickering background is generated by means of a halogen lamp and a mechanical shutter which interrupts the light of the halogen lamp at a defined frequency. A mechanical shutter is relatively complex and expensive and is also prone to defects and malfunctions. SUMMARY OF THE INVENTION  
       [0006] The invention relates to a device for the examination of visual functions of the human eye which is at a viewing point and is oriented along a viewing axis. A first light source is equipped for the temporally staggered generation of stimuli at selectable locations on the background of the viewing axis. A second light source generates light that is distributed evenly on the background of the viewing axis.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a schematic illustration of the device of the present invention; and  
     [0008]FIG. 2 is a schematic illustration of an alternate embodiment of a second light source. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0009] The object of the invention is to create a device for testing visual functions of the human eye which can be manufactured more easily and economically.  
     [0010] The invention teaches that the second light source has at least one LED (Light Emitting Diode). Associated with the LED there are preferably timing elements that allow the LED to be turned on either constantly or to flicker at selectable timed ratios. The frequencies that can be selected are essentially unlimited and thus cover even the ranges in which the critical flicker fusion frequencies occur.  
     [0011] The device claimed by the invention has the advantage that there is no need for moving mechanical parts to generate the flickering background. LEDs also generate no waste heat, which means that active cooling by means of a ventilator is unnecessary. In contrast to electrophysiology, where expensive amplifiers are necessary to evaluate the flicker ERGs, the subject responds by pressing a response button.  
     [0012] In one development of the invention, the second light source has at least two LEDs that are located in different planes and at least one colored filter. The light from the one LED thereby passes through the colored filter and generates a correspondingly colored background. In this case, the essential advantage is that the colored filter can be installed in a stationary manner. In the prior art, such colored filters had to be mounted so that they were movable and could be pivoted into the beam path when necessary. In this invention, to generate a white background, the LED, the light from which does not go through the colored filter, is turned on. To generate a colored background, the other LED is turned on. In this case, realizations with a plurality of colored filters are possible.  
     [0013] The perimeter that is illustrated schematically in FIG. 1 has an optical system  60 , on the optical axis  40  of which there are on one hand a viewing point  41  and on the other hand a first light source  42  to generate stimuli. The stimuli are brief pulses of light that are presented to the subject at different points in the subject&#39;s field of vision. The light from the first light source  42  is focused by a condenser lens  43  on a diaphragm  44  and is deflected behind the diaphragm  44  into a parallel beam path  45 . The beam path  45  is limited toward the diaphragm  44  by a field lens  46  and toward the viewing point  41  by a convex lens  53 . The viewing point  41  is then realized so that the convex lens  53  focuses the light that exits the beam path  45  onto the center of the pupil of the subject&#39;s eye. Sight defects of the subject&#39;s eye therefore have no influence on the stimulus image on the retina. In the parallel beam path  45 , perpendicular to the viewing axis  40 , there is a diaphragm  47  which blocks the entire cross section, with a diaphragm opening  48  which limits the stimulus in terms of shape and size. The diaphragm  47  can be displaced in a plane in two directions that are oriented perpendicular to each other with respect to viewing axis  40  by means of a drive which is not shown here and is controlled by a computer which is also not shown here. Consequently, the diaphragm opening  48  can be displaced by said drive to any desired location in the diaphragm plane and defined in terms of coordinates. The stimuli are presented in the parallel beam path  45  in the image plane, from which they are projected by the convex lens  53  onto the retina of the subject&#39;s eye.  
     [0014] The background is illuminated by means of a second light source  49 , the light from which is deflected by means of a partly light-permeable deflecting mirror  50  in the beam path  45  toward the convex lens  53 . By means of two additional partly light-permeable deflecting mirrors  51  and  52 , a fixation mark can be superimposed onto the background on one hand and the subject&#39;s eye is monitored by means of a camera on the other hand.  
     [0015] The second light source  49  used is an LED that is actuated so that on one hand a continuous background light and on the other hand a flickering background light can be generated. Programming strategies can be used to modify both the intensity and the characteristic of the flickering background light, so that the critical flicker fusion frequency can be determined by means of calibration methods based on bracketing or by continuous approximation. The perception of the flickering background is indicated by the subject pushing a response button. The background light can be white or colored. In FIG. 1, the second light source  49  is formed by a single LED. However, realizations are also possible in which the second light source  49  is formed by a plurality of LEDs.  
     [0016] In the realization of a second light source  49 ′ illustrated in FIG. 2, a plurality of LEDs  57  and  58  are located on a bracket  55  in different planes A and B. A colored filter  56  is fastened to the bracket so that the LEDs  58  are located above this filter and the LEDs  57  are located below this filter  56 . To generate white background light, only the LEDs  58  are operated. To obtain colored background light, the LEDs  57  but not the LEDs  58 , are operated. Because the LEDs  57  are located below the colored filter  56 , as shown in the accompanying illustration, their light falls through this colored filter  56  and thereby generates the corresponding color. To change the color, all that is necessary is to reverse the switching of the LEDs  57  and  58 . The colored filter  56  can be installed in a stationary manner and therefore need not be moved to change the color. Because the LEDs  57 - 59  emit essentially no heat during operation, there is need for active cooling of the second light source  49  or  49 ′.