Abstract:
The invention relates to a device for observing the ocular fundus, in particular to a fundus camera. Said device comprises a light source ( 1   b ) for the provision of illumination radiation, an illumination optical path for directing the illumination radiation onto the ocular fundus and observation optics for reproducing the illuminated ocular fundus, the observation optics comprising a module ( 16   b ), whose refractive power can be electrically adjusted.

Description:
FIELD OF THE INVENTION 
   The invention relates to a device for examining the ocular fundus by means of an optical system and in particular by means of electronic sensors for recording images, preferably a fundus camera. The invention furthermore relates to an astigmatism compensation device, in particular for a fundus camera. 
   BACKGROUND OF THE INVENTION 
   Normally when using a fundus camera, depending on the defective vision of the patient, the optical observation system in the fundus camera is changed from one patient to the next such that a highly focused image of the ocular fundus is reproduced on the image recording sensor. In order to be able to examine as many patients as possible the focusing range is selected with no less than ±25 dpt. In known fundus cameras, either a part of the optical system is displaced along the optical axis of the lens, or the image recorder is displaced along the optical axis (see  FIGS. 1   a ,  1   b ). 
   It has been demonstrated that the known fundus cameras require precise mechanical components that are expensive in and of themselves and in addition are subject to wear, and that furthermore it is not possible to obtain focused images of the ocular fundus in all patients using this camera. 
   However, the object of the invention is to provide a device for observing the ocular fundus that makes it possible, in a simpler manner and/or for a greater majority of patients, to obtain focused images of their ocular fundus. 
   SUMMARY OF THE INVENTION 
   This object is attained using the device for observing an ocular fundus in accordance with claim  1 , using the astigmatism compensation device in accordance with claim  7 , and using the adjustable lens in accordance with claim  10 . 
   One aspect of the invention provides a device for observing an ocular fundus that has observation optics with a lens that is electrically adjustable with respect to its refractive power. The refractive power that can be adjusted in this manner can be a spherical or/and cylindrical refractive power; in the latter case, the axis position for the cylindrical refractive power can also be adjustable. The device can include in particular an electronic image recording sensor and/or can be embodied for direct visual observation. The electrically adjustable lens can have liquid crystal layers or two fluids contained in a container, between which fluids a phase boundary surface is embodied that can be deformed by applying a voltage. 
   A second aspect of the invention provides an astigmatism compensation device that includes a lens with adjustable radially asymmetric refractive power, the lens including two electrodes between which an electrical field is embodied when a voltage is applied. 
   A third aspect of the invention provides an adjustable lens, the lens including two fluids contained in a container, between which fluids is embodied a phase boundary surface that can be radially asymmetrically deformed by applying a voltage. 
   Additional advantageous details and aspects proceed from the subordinate claims, the following description, and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  depicts a conventional fundus camera with an optical system to be displaced; 
       FIG. 1   b  depicts another conventional fundus camera with image recorder to be displaced; 
       FIG. 2  depicts another conventional fundus camera with a Stokes lens as astigmatism compensation device; 
       FIG. 3  depicts an inventive fundus camera with an electrically controllable lens; 
       FIG. 4  depicts another inventive fundus camera with an electrically controllable astigmatism compensation device; 
     
       FIG. 5 
       a  
     
       FIG. 5   b  depict a cross-section and elevation of an electro-optical lens with a liquid crystal basis; 
       FIG. 6  depicts a cross-section of an electro-optical lens with a fluid basis; 
       FIG. 7  is a diagram of an electrode arrangement for the lens depicted schematically in  FIG. 6 ; 
       FIG. 8  is another electro-optical lens with a fluid basis. 
   

   DETAILED DESCRIPTION 
   In the known camera in accordance with  FIG. 1   a , light from a light source  1  is directed through a lens  3  onto a perforated mirror  5 . From the perforated mirror  5 , the illuminating light  6  is directed through a front lens  7  of the fundus camera onto the eye  9 , and thus through the eye lens  11 , onto the fundus  13  of the eye. The beam going out from the fundus  13  of the eye is directed through the eye lens  11  and the front lens  7  of the fundus camera onto the aperture  15  in the aperture mirror  5 . A compensation lens  17  can be pivoted behind the aperture  15 . Finally, the observation beam  8  is reproduced on an image recording sensor  21  through a main lens group  19  that is displaceable in the direction of the beam path. 
   In the known variant, in accordance with  FIG. 1   b , the components are basically arranged in the same manner, but the image recording sensor  21 ′, rather than the main lens group  19 ′, is displaceable in the direction of the beam path. In both variants, ZB is an intermediate image plane. 
   In another known variant, in accordance with  FIG. 2 , the compensation lens is embodied as a Stokes lens pair  17 ″ with which an astigmatism of the eye  9  can be compensated according to rate and direction by mechanically adjusting the axis position of the two lenses. In this case, the main lens group  19 ″ produces a second intermediate image ZB 2 , which using multi-part imaging optics O 1  is first reproduced on a folding mirror  31  and then either through rangefinder optics O 2  on the CCD sensor of a rangefinder camera  21 ′ or through documentation optics O 3  on the CCD sensor of a documentation camera  21 ″. In addition, a flash light  25  with associated optics  27  is provided in the illuminating beam path, and its light can be directed via an illuminating folding mirror  29  and additional illuminating optics  23  onto the aperture mirror  5 . 
   Compared to the known fundus camera in accordance with  FIG. 1   a  or  1   b , the first embodiment depicted in  FIG. 3  and the main lens group  19   a  as well as the image recording sensor  21   a  are securely mounted. Depending on their structure or function, components comparable to the components described in the foregoing will now and hereafter be labeled with the same numbers, but for purposes of differentiation these will be followed by lower-case letters. In this example, a pivotable compensating lens  17   a  for roughly adapting to the refractive power of the patient eye is also provided, but it can be omitted. In this example, an electrically adjustable lens  16  is arranged between aperture  15   a  and compensating lens  17   a . The position between aperture  15   a  and main lens group  19   a  is preferred for the arrangement of the adjustable lens  16  because at this location the observation beam  8   a  has a relatively small diameter and therefore it is possible for the adjustable lens  16  to have a smaller free diameter. However, instead of the aperture mirror  5   a , another beam splitter can be used to inject the illuminating light into the observation beam path, for instance a geometric beam splitter such as for instance a simple mirror, without an aperture, arranged in a lateral half of the beam. 
   In the second embodiment, illustrated in  FIG. 4 , in contrast to the known variant in accordance with  FIG. 2 , an electrically adjustable lens  16   b  is arranged between the aperture  15   b  of the aperture mirror  5   b  and the main lens group  19   b  instead of the Stokes lens pair. This electrically adjustable lens  16   b  is embodied such that it has two adjustable refractive powers that can be adjusted independent of one another and the main directions of which are perpendicular to one another. For instance, the refractive power adjustment can be based on liquid crystal layers such as are described in U.S. Pat. Nos. 4,795,248 and 5,815,233. Full disclosure of these publications is included in the present application by reference. 
     FIG. 5   a  is a cross-section of an assembly  16   c  that has variable optical effect. The assembly  16   c  includes a first liquid crystal layer  103  and a second liquid crystal layer  105  that are arranged on either side of a common transparent continuous electrode  107 . A likewise transparent electrode structure  109  is provided on a side of the common electrode  107  that opposes the liquid crystal layer  103 , as is depicted in  FIG. 5   b . The electrode structure  109  provides a plurality of controllable pixels  111  that are arranged, for instance, in a rectangular grid. A control  113  is provided in order to apply an adjustable voltage to each pixel  111  via a driver  115  that feeds the voltage to the individual pixels as is already known for liquid crystal displays. Because of this, an electrical field is adjustable between each pixel  111  and the common electrode  107 , and depending on the adjusted electrical field the liquid crystal layer  103  provides for a beam of light 
     117  passing there through a variable optical path length for a polarization direction of the beam  117 . Arranged on a side of the liquid crystal layer  105  that faces away from the common electrode  107  is another transparent electrode structure  109  having the structure depicted in  FIG. 5   b  that is likewise controlled by the control  113 . While the liquid crystal layer  103  provides the variable optical path length for a polarization direction indicated by an arrow  119  in  FIG. 5   a  in the plane of the figure, the liquid crystal layer  105  provides a correspondingly variable optical path length for a polarization direction orthogonal thereto, as is indicated by the symbol  121  in  FIG. 5   a.    
   Thus, using appropriate control of the electrode structure  109 , it is possible to provide for both polarization directions of the beam  117  optical path lengths of the two liquid crystal layers  103 ,  105  that are adjustable as a function of a position on the layers  103 ,  105 . Thus the assembly  16   c  can be controlled overall in order to provide adjustable optical effects for the beam  117 , such as for instance, a round lens effect with positive or negative refractive power in terms of a selectable optical axis, or even a cylinder lens effect with positive or negative refractive power in terms of an adjustable plane of symmetry. 
   On the other hand, the refractive power setting can be based on lenses with two fluids separated by a phase boundary surface, as is sold by the Varioptic Company, 69007 Lyon, France. The way such lenses function is described, for instance, in international patent application WO 1999/018456; full disclosure of this publication 
   is included in the present application by reference.  FIG. 6  illustrates a section through such an optical assembly  16   d  that has an adjustable optical effect. The assembly  16   d  includes a housing  221  with two inlet and outlet windows  223 , between which are enclosed two non-miscible liquids  225  and  227  that have different refractive indices. The one liquid  225  is, for instance, water or salt water and the other liquid  227  is, for instance, oil or a methylphenyl siloxane mixture with a density that is preferably the same as or similar to that of the water or salt water. The housing  221  provides for the two liquids  225 ,  227  a conical wall  231  that is symmetrical with respect to an optical axis  229  of the assembly and against which a boundary surface  233  is positioned between the two liquids at a contact angle θ. A likewise conical electrode  235  is arranged inside the wall  231 , and an annular electrode  236  is arranged in the volume of the liquid  225  in the vicinity of the window  223 . The liquid  225  is electrically conducting, while the liquid  227  is largely not electrically conducting. A voltage can be adjusted between the electrodes  235  and  236  using a control  213 . A change in the voltage between the electrodes  235  and  236  alters the angle θ, which the boundary surface  233  creates between the two liquids  225 ,  227  with the wall  231 . Thus, by changing the voltage between the electrodes  235 ,  236 , it is possible to change the shape and curvature of the boundary surface  233 , as is schematically depicted with a broken line  233 ′ in  FIG. 6 . Due to the different refractive indices of the two liquids  225 ,  227 , a lens effect of the assembly  16   d  can be changed for a light beam passing therethrough along the optical axis  229 . If the conical electrode  235  is divided into a plurality of separately controllable sectors  235   e   1  through  235   e   8 , as is depicted schematically in  FIG. 7 , another contact angle can be embodied in each sector  235   e   1  through  235   e   8 . For providing a cylindrical or toroidal boundary surface with different refractive indices in main planes of curvature that are perpendicular to one another, diametrically opposing sectors are activated by a control  33  with an equal, maximum voltage (for instance, sectors  235   e   1  and  235   e   5 ), and the sectors arranged perpendicular thereto (for instance, sectors  235   e   3  through  235   e   7 ) with a minimum voltage that is the same for each of them (for instance, 0 V). Sectors located therebetween (for instance, sectors  235   e   2 ,  235   e   4 ,  235   e   6 , and  235   e   8 ) are actuated by the control  33  with voltages therebetween. The more sectors provided, the finer the voltage graduation can be and the more exact the toroidal boundary surface that can be produced. However, it is preferred to provide at least 4 and up to 64 sectors; furthermore it is preferred to provide an even number of sectors, in particular a number of sectors that is divisible by four. The lens arrangement  16   d  can also be mounted such that it is rotatable in order to facilitate coarse adjustment onto the axis position of an astigmatism of a patient&#39;s eye; in this case the control  33  would only provide the fine adjustment for the voltage. 
   However, it is also possible to provide a cuboid geometry  16   f  instead of the radially symmetrical geometry for the assembly  16   d , and to arrange a flat electrode  235   f , through  235   f   4  in each of the four vertically stacked circumferential walls instead of a sectored, conically shaped electrode (see  FIG. 8 ). The electrodes are each insulated from the adjacent electrode, but can be connected in an electrically conducting manner to the respective opposing electrode. For creating 
   a cylindrical boundary surface between the fluids  225   f  and  227   f , a contact angle of 90° is set on two mutually opposing walls (for instance, electrodes  235   f   1  and  235   f   3 ), while another contact angle θ is set on the two other walls (for instance electrodes  235   f   2  and  235   f   4 ). This results in a cylindrically shaped boundary surface that can compensate an eye astigmatism in a patient according to the rate. In order to be able to adjust this arrangement onto the axis position of the eye astigmatism of the patent, it is preferably rotatably borne about its optical axis  35 . 
   Compared to known devices for compensating cylindrical defects of the eye, the inventive device is clearly more simple to manufacture and to use. The optical components are simpler and do not require any rotary movement or require only a rotary movement that is simple to produce. In particular the optical components and the image recorder do not have to be displaceable, that is, they can be fixed and are therefore easier to adjust. 
   For instance, in the known device in accordance with  FIG. 2 , the rate of the cylindrical refractive power provided by the Stokes lens  17 ″ for astigmatism compensation is determined by the angle of the relative arrangement of the Stokes lenses  17 ″; this relative angle must therefore be precisely adjusted. Consequently, the axis positions of both lenses in the Stokes lens pair  17 ″ must be able to be precisely adjusted independent of one another. In contrast, in the present invention only the axis position of the overall arrangement must be adjusted, relative to the patient&#39;s eye, by rotating the device, for which lower precision is sufficient. The rate of the cylindrical refractive power for compensating astigmatism, however, can be adjusted electrically using the amount of voltage applied and therefore does not require such a precise mechanism. 
   Moreover, in contrast to the known devices, the actually adjusted cylinder value, including rate, [mathematical] sign, and axis position in the form of the control voltages, for the electrically activated lens and via the position of the activated electrodes or the adjusted angle of the adjustable lens assembly is easily evaluated and simply accessible for a follow-on documentation or computing process (for instance measurements, focusing, automatic focusing, etc.). The control can provide an output signal for this as well. 
   In addition, with the inventive device it is possible, using a differently measured refractive power of the patient&#39;s eye, to automatically adjust the compensation lens of the fundus camera electrically such that an optimally focused image of the ocular fundus can be recorded and/or observed. For this, the control can also have an input interface and/or a keyboard. In the latter case, data representing the refractive power of the patient&#39;s eye can be stored for instance in an electronically stored table together with identifying information for the patient; inputting the patient identification and an activation command can then initiate camera focusing. This makes it much easier to perform a series of examinations on a number of patients one after the other, even if the examinations of both eyes of the same patient normally require different settings for the compensation optics. 
   The invention can be employed not only for adult human patients, but also, due to its temporal advantages because the camera can be focused more rapidly, is particularly advantageous for children and vertebrate animals in general, especially mammals, in particular house pets such as dogs and cats, because the behavior of both children and animals (pets) during lengthy examinations can be problematic.