Patent Document

BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an ophthalmoscope having a housing in which there are arranged an observing unit and an illuminating unit between which there are/is arranged diaphragm means and/or filter means that can be set via a swivel lever means mounted outside on the housing.  
         [0003]     2. Description of the Background Art  
         [0004]     U.S. Pat. No. 4,684,227 discloses a generic binocular ophthalmoscope in whose lower housing part an observing unit is arranged by means of which an examiner can examine through a patient&#39;s pupil. An illuminating unit with a light source is accommodated in the upper housing part. An adjustable diaphragm is arranged between the light source and the observing unit. Also provided is a filter means by means of which optical filters can be moved into the illuminating path between the illuminating source and the observing unit. For the purpose of setting the diaphragm and the optical filters, there is respectively mounted on the side of the housing swivel lever means that comprises a rotary element, arranged in a bearing opening, on the outside of which a swivel lever is fastened. The swivel levers are kinematically connected to a mechanism for setting the diaphragm and/or the optical filters.  
         [0005]     The swivel lever means are mounted in a freely rotatable fashion in the bearing openings. As a rule, ophthalmoscopes are used by a single investigator who prefers a specific setting of the diaphragms and/or the optical filters. Other settings are carried out only rarely. Since the swivel lever means are supported in a freely rotatable fashion, the diaphragm or the optical filters are, however, displaced when the swivel levers are lightly touched, and this quickly comes about during improper handling. It is then necessary to reset the diaphragm and filters.  
       SUMMARY OF THE INVENTION  
       [0006]     It is the object of the invention to provide a reliable handheld ophthalmoscope with the aid of simple design means.  
         [0007]     This object is achieved according to the invention by means of an ophthalmoscope comprising a housing in which an observing unit and a light source are arranged between which there is positioned at least one of diaphragm means and filter means that can be adjusted by swivel lever means mounted outside on said housing, wherein said swivel lever means can be locked in several locking positions by locking means.  
         [0008]     In the case of the ophthalmoscope according to the invention, the respective swivel lever means can be locked in respective latch stages by locking means. This prevents the setting of the diaphragm and/or the filters from being changed when the swivel lever means is inadvertently touched. An investigator can lock the diaphragm and the filters in a position he desires.  
         [0009]     It is advantageous for the locking means to be designed in such a way that it unlocks when a predetermined torque exerted on the swivel lever means is exceeded. This prevents the swivel lever means from being damaged when an excessive force is exerted on it.  
         [0010]     In a preferred embodiment of the ophthalmoscope according to the invention, the swivel lever means comprises a rotary element that is rotatably supported in a bearing opening provided in the housing. A number of latching depressions are formed in the edge of the bearing opening at an angular distance from one another. In order to lock the rotary element in a desired position, a latching slide provided on the rotary element can optionally be brought into engagement with one of the latching depressions.  
         [0011]     In this embodiment, the latching depressions and a tip of the latching slide have inclined sidewalls that bear against one another in the locking position of the latching slide. The inclination angle of the sidewalls in selected such that the latching slide moves out of the latching depression when a predetermined torque is applied to the rotary element, such that damage to the swivel lever means during application of an excessively large force is prevented. 
     
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0012]     An exemplary embodiment of the invention is explained in more detail below with the aid of drawings, in which:  
         [0013]      FIG. 1  shows an ophthalmoscope in a perspective fashion,  
         [0014]      FIG. 2  shows a cross section through the upper part of the ophthalmoscope of  FIG. 1 ,  
         [0015]      FIG. 3  shows a perspective longitudinal view of a swivel lever means of the ophthalmoscope of  FIG. 1 ,  
         [0016]      FIG. 4  shows a schematic of the engagement of a latching slide of the locking means of  FIG. 3  in latching depressions,  
         [0017]      FIG. 5  shows a perspective illustration of the swivel lever means of  FIG. 3 , and  
         [0018]      FIG. 6  shows a sectional side view of the swivel lever means of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     As shown in  FIG. 1 , the ophthalmoscope  10  according to the invention comprises a lower housing part  14  in which an observing unit is arranged behind a central glass pane  42 . The observing direction of the observing unit can be set by a setting rod  26 .  
         [0020]     Provided above the glass pane  24  is an upper housing part  12  in which an illuminating unit with an illuminating source, for example LEDs, is accommodated. Although it is not shown in the drawings for reasons of clarity, in the case of the ophthalmoscope according to the invention, as in the case of the opthalmoscope known from U.S. Pat. No. 4,684,227, there is firstly arranged between the light source and the observing unit an adjustable diaphragm means, after which there is arranged a filter means with optical filters in the illuminating path. The diaphragm means can be set by a swivel lever means  16  via a mechanism that is not shown. The setting of the filters is enabled by a swivel lever means  17  via a mechanism (likewise not shown).  
         [0021]     Two swivel lever means  16 ,  17  are of identical design. For this reason, the construction of the swivel lever means  16 ,  17  is described with the aid of the swivel lever means  16  for the diaphragm means. A circular bearing opening  32  is provided in the corresponding sidewall  28  of the top housing part  12 . An overall cylindrical bearing section  34  of a rotary element  33  is rotatably supported in the bearing opening  32 . By means of a coaxial screw  36 , the bearing section  34  is connected inside in a rotationally fixed fashion to the diaphragm means in order to adjust it.  
         [0022]     Guided in the bearing section  34  such that it can be displaced in the radial direction of the bearing section  34  is a locking body  40  of a locking element  41  that extends beyond the outside of the bearing section  34  and has on its outside a fluted gripping surface  42 .  
         [0023]     Upwardly extending outside the upper housing part  12  from the bearing section  34  is a lever  38  that has in the region of the locking body  40  a downwardly extending shoulder  46  that, in the unlocking position, shown in  FIG. 2 , of the locking body  40 , engages in a recess  44  on the top side of the locking body  40 , and bears against the base thereof.  
         [0024]     Extending radially downward approximately from the axis of rotation of the bearing section  34  at a distance from the vertically running inside of the locking body  40  is a narrow latching slide  52  designed integrally with the locking body  40 . There is formed as a result between the locking body  40  and latching slide  52  a downwardly open U-shaped cutout  48  that extends radially downward and extends longitudinally. The latching slide  52  is guided radially at the side in a slot  59  in the bearing section  34 .  
         [0025]     As is to be seen in  FIG. 4 , there are formed in the edge  35  of the bearing opening  32  a number of latching depressions  54   a ,  54   b ,  54   c ,  54   d  that are open toward the axis of rotation and outwardly and have sidewalls  64 ,  66  that are inclined to the radial of the bearing opening  32  through the middle of the corresponding latching depression  54   a ,  54   b ,  54   c ,  54   d  at an angle α, and are bounded by a tangentially running base  70 . At its tip, the latching slide  52  has lateral surfaces  62 ,  68  that are inclined at the same angle as the lateral surfaces  64 ,  66  of the latching depressions  54   a  to  54   d.    
         [0026]     It is to be seen in  FIG. 3  that a transversely running blind hole  37  in which a helical spring  39  is arranged is formed in the locking body  40 . It is shown in  FIG. 6 , in which the locking body  40  is omitted for the purpose of clarity, that there is fastened at the end of the helical spring  39  a ball  43  which projects from the blind hole  37  in the unloaded state. Arranged at a distance from one another in the bearing section  34  in a fashion opposite the ball  43  are two substantially concave recesses  51 ,  53  in the displacement direction of the locking body  40 , in which the ball  43  engages in the unlocking position or in the locking position of the locking body  40 .  
         [0027]     The ball  43  biased by the spring  39  ensures that the locking body  40  automatically latches in the unlocking position or in the locking position as soon as the ball  43  has overstepped the edge of the corresponding recess  51 ,  53 .  
         [0028]     If the diaphragm is to be fixed in a specific position, for the purpose of locking the swivel lever means  16  the locking body  40  is displaced downward in the radial direction until the tip of the latching slide  52  strikes the base of the corresponding latching depression  54   a  to  54   d , and the sidewalls  62 ,  68  of the latching slide  52  bear against the sidewalls  64 ,  66  of the corresponding depressions  54   a  to  54   d . The swivel lever means  16  is thereby locked. As a result, an inadvertent misadjustment of the swivel lever means  16 , and thus of the diaphragm is prevented. The inclination of the lateral surfaces  62 ,  64 ,  66 ,  68 , and the resistance of the locking body  40  in the radial direction are, however, selected such that in the event of a force that exceeds a previously determined force, the latching slide  52  is moved out of the corresponding latching depression  54   a  or  54   d . This prevents damage to the swivel lever means  16 . The inclination angle α is a function of the coefficient of friction between the lateral surfaces  62 ,  64 ,  66 ,  68  and the force that is required in order to move the locking body  40  in the unlocking direction. The angle α is preferably between 10 and 80 degrees.  
         [0029]     As the swivel lever means  17  is designed like the swivel lever means  16 , the filters can be fixed in the same way as described above.

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