FIELD OF THE INVENTION 
   The invention relates to an optical device for releasable attachment to a microscope suited for contact-free observation of the eye. 
   BACKGROUND OF THE INVENTION 
   In ophthalmology, and particularly with vitreous body surgery, specific devices in combination with correspondingly suited microscopes are used, in order to makes possible a contact-free, wide-angle observation of the eye. In particular, with operations on the eye, optical devices are used, with which the surgeon can observe the movements performed with the operating implements, whereby, by the adjustment of the lens in the region between the objective of the microscope and the eye, focusing in different planes is made possible. 
   Such a device is known, for example, from EP 11 99 591 A1. With this device, the driving movement of a drive motor provided on the microscope can be transferred with the assistance of a flexible drive shaft on a linear gear provided on the device. 
   Since the devices are used in the direct operating area in the eye, sterilization of the devices, for example, by heating and aerating in autoclaves is of the greatest importance. One disadvantage associated with the device known from EP 11 99 591 A1 is that for transferring of the drive movement, a relatively rigid drive shaft is required. Based on the rigidity of the drive shaft, this can be fixed only inadequately flexibly along suitable attachment points, so that an unwanted contamination of the shaft by contact with non-sterilized objects, for example, the housing of the microscope, can occur. A further disadvantage of the drive by means of a drive shaft is that the device can be pivoted relative to the microscope only within determined limits, since the drive shaft can snap off easily. In addition, the maximum distance between the drive motor and the device is limited by the drive shaft. 
   An object of the present invention, therefore, starting from this state of the art, is to propose a new, optical device for releasable attachment to a microscope, whose manipulation and hygienic qualities are improved compared with the known devices. 
   SUMMARY OF THE INVENTION 
   According to the present invention, the drive motor for remotely controlled adjustment of the lens in the region between the eye and objective of the microscope is integrated in the device, so that the device is released entirely together with the drive motor from the microscope and by suitable methods, can be sterilized. By the integration of the drive motor in the device, the drive shaft for transmission of the drive moment from the drive motor to the device can be eliminated. In addition, the drive movement required for adjustment of the lens within the device is produced by conversion of electrical energy into mechanical energy. 
   In order to achieve a sufficient sterilization of the device of the present invention, known methods, for example, autoclave under pressure and temperature effects or steam can be used. These sterilization methods represent a potential risk of damage for the electromechanical components of the electric motor. In particular, damage to the drive motor can result from thermal strain and corrosion. In order to reliably eliminate this type of damage by sterilization methods over long periods of use, the drive motor is encapsulated in a gas- and moisture-sealed housing according to a preferred embodiment of the invention. As a result, the drive motor is insular against the atmosphere of the surrounding environment, so that in the frame of the typical sterilization methods, no gas or moisture can access the electro-mechanical components of the drive motor. 
   Each opening in the housing for encapsulated accommodation of the drive motor represents a potential source of malfunction, which requires the use of correspondingly suited sealing features, so that also with longer periods of use, gases or moisture can not enter the interior of the housing. Housing openings that are particularly difficult to seal are those through which a drive movement, for example, with the use of a drive shaft provided on the drive motor, is transferred from the interior of the housing outwardly. According to a preferred embodiment, this problem can be solved by use of a contract-free coupling, in particular, a magnetic coupling. This type of contact-free coupling has a drive part and an output part, whereby the drive movement between the drive part and output part is transferred contact-free, for example, by magnetic fields. In order to avoid a housing opening transferring the drive movement of the drive motor from the interior of the housing outwardly, the drive part of the contact-free acting coupling is encapsulated together with the drive motor. The drive part of the contract-free acting coupling, in contrast, is arranged outside of the housing and thereby makes available the drive moment transferred from the drive motor to the drive part of the coupling outside of the housing. 
   In order to provide the drive motor with electrical energy, an electrical cable can be provided, which passes through an opening in the housing and is connected to the drive motor to be electrically conductive. Since the electrical cable itself transfers no movement, the through opening for entry of the electrical cable can be sealed relatively simply from gases and moisture by suitable sealing means. In addition, electrical cables can be fixed in a simple manner along any principle paths on which the cable is laid. Also, the pivoting of the device relative to the microscope is not prevented by the high flexibility of the electrical cable. For sealing of the sealing gap between the housing and the electrical cable, a sealing ring can be provided, which, for example, is fixed by a suitable press nut. 
   Alternatively or in addition to the use of a sealing ring, also a sealing coupling can be used for encapsulated sealing of the drive motor in the housing, with which hollow chambers in the interior of the housing can be lined to be gas- and moisture-impermeable. As far as necessary, the sealing compound can be pressed in also under pressure into the housing, in order to reliably fill hollow chambers and to close sealing gaps. 
   In order to enable application of the sealing compound into the housing in a simple manner, the housing can have at least one fill opening. In this manner, it is possible, in particular, to mount the drive motor first completely in the housing and after conclusion of the mounting, to seal the housing by application of the sealing compound. 
   Since with the sterilization of the device in normal cases, the electrical connection cable must also be sterilized, preferably a plug suitable for sterilization can be provided on the end of the electrical cable. 
   Alternatively to using an electrical cable for supply the drive motor with electrical drive energy, also accumulators can be provided on the device, which permit a network free energy supply of the drive motor. If, in addition, also a wireless data transmission to the device is provided, over which the control data necessary for the control of the device can be transmitted, then, apart from the mechanical attachment of the device to the microscope, a complete decoupling between the sterilized parts of the device and the non-sterilized parts of the microscope is provided. 
   The type of lenses that can be attached to the device of the present invention is essentially as desired. Since, however, the lens is the part of the device that lies closes to the eye, which must be arranged with only minimal distance above the eye, the highest specifications as to the sterility of the lens and lens-adjacent components are required. According to a preferred embodiment, therefore, one-way lenses are used, which together with the holding mechanism provided for attachment of the lens, are disposed of after each operation. 
   Particularly suited for use on the proposed optical devices are lenses, which are embodied in the form of magnifiers. Preferably, higher-refracting, aspherical magnifiers are used, which project a transversely inverted, upside down image, which is righted and horizontally corrected by either a parallel optical path or alternatively, an inversion system arranged beneath the objective. 
   In order to enable production with the associated holding mechanism with regard to the only one-time use with justifiable costs, the lens and/or the holding mechanism preferably are made from plastic. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the device of the present invention is shown in the drawings and will be explained in greater detail by way of example. 
     In the drawings: 
       FIG. 1  shows a microscope with an optical device according to the present invention attached thereon in a side view; 
       FIG. 2  shows the microscope with the device of the present invention of  FIG. 1  in a view from behind; 
       FIG. 3  shows the device according to the present invention in an enlarged perspective view; 
       FIG. 4  shows the drive motor of the device according to  FIG. 3  in cross section; and 
       FIG. 5  shows the drive motor of the device according to  FIG. 3  in an exploded representation. 
   


   DETAILED DESCRIPTION 
   In  FIG. 1 , a microscope  01  with a housing  02 , an ocular  03 , and an objective  04  is shown. The microscope  01  can be used for wide-angle observation of an eye  05  (represented only schematically) during an eye operation. The optical axis  06  can be oriented to the operating area in the eye  05 , in order to enable the enlarged observation of the operating area in the ocular  03 . 
   On the lower side of the housing  02  of the microscope, a holder  07  is attached to the microscope. By means of the holder  07 , an optical device according to the present invention can be releasably attached to the microscope  01 . The device  08  serves to enable fixing of a lens  09  in the optical path along the optical axis  06 . In order to make possible an accurate side to side observation of the movement of the operating instruments in the eye, an inversion prism  39  is also provided in the optical path of the microscope  01 . Alternatively thereto, also another suitable inversion device can be used, which also can be arranged beneath the objective  04 , for example. The holder  07  can be aligned specifically on the microscope type of different manufacturers, in order to make possible the attachment of similarly constructed optical devices  08  to various microscope types. 
   The lens  09  can be attached by means of a holding device  10  to a holding arm  11  of the device  08 . It is advisable in this regard if the lens  09  and/or the holding device  10  are made of plastic and can be discarded after each individual operation. 
   The holder arm  11  comprises a guide tube  12  and a telescoping rod  13  elastically supported therein. In this manner, it is permitted that with undesired contact between the eye  05  and the lens  09 , the lens  09  can be drawn aside upwardly, so that an injury to the eye is avoided. The holder arm  11  is attached to a traverse  14 , which is longitudinally displaceable in the direction of the optical axis  06  on a fixed bar  15  and which is engaged with a threaded spindle  16 . 
   The device  08  is pivotably and rotatably supported on the holder  07 , so that the device  08 , when needed, can be pivoted out from the optical path of the microscope and, in addition, can be rotated into different positions. The structural details related thereto are known in the art and not specifically shown in the drawings. The threaded spindle  16  is rotatably supported on a base plate  17  and can be rotatingly driven by means of a drive motor  24  (see  FIG. 4 ) arranged in a housing  18  via a drive belt  19 . In addition, a handwheel is provided for rotary driving of the threaded spindle  16  by hand, which is non-rotatably connected with the threaded spindle  16 . 
   By the rotating drive of the threaded spindle  16  by means of the drive motor  24  or by means of the handwheel  20 , the traverse  14  is lifted or lowered, so that by corresponding adjustment of the lens  09  in the optical path of the microscope  01 , focusing in different high planes of the eye  05 , is made possible. For supplying the drive motor arranged in the housing  18  with electrical energy, an electrical cable  21  is provided, which can be connected releasably to a voltage source provided in the inversion prism  39  by means of a sterilizable plug  22 . 
   In  FIG. 2 , the microscope  01  and the device  08  are shown with the different components in a view from behind. 
     FIG. 3  shows the device  08  in an enlarged representation in perspective inclined from below. One recognizes that a holding ring  23  is provided on the device  08 , with which additional lenses can be fixed in the optical path of the microscope  01 . 
   In  FIG. 4 , the encapsulated housing  18  is shown in cross section with the drive motor  24  arranged therein and a magnetic coupling  25  provided for transmitting the drive movement to the drive belt  19 . The housing  18  is combined from an upper housing part  18   a  and a lower housing part  18   b , whereby both housing parts  18   a  and  18   b  are connected to one another in a gas- and moisture-sealed manner, for example, by adhesive. The lower housing part  18   b  has an attachment projection  26 , with which the housing  18  can be fixed to the base plate  17  by screwing in of an attachment screw  27  to the base plate  17 . 
   The housing  18  has an opening  28  on its upper end for passage of the electrical cable  21  into the interior of the housing  18 . The drive motor  24  is shown only schematically in  FIG. 4 , so that the wire windings of the drive motor  24  are not recognizable in detail. The magnetic coupling  25  comprises a drive part  25   a  and an output part  25   b , on which, respectively, four permanent magnets are provided. The output part  25   b  of the magnetic coupling is rotatably supported on the base plate  17  outside of the housing  18 . The drive part  25   a  is enclosed within the housing and is non-rotatably connected with the drive shaft of the drive motor  24 . If the drive part  25   a  of the magnetic coupling  25  is rotatingly driven by the drive motor  24 , the drive movement produced thereby is transmitted contact-free by the alteration of the magnetic field to the output part  25   b . A through opening in the housing  18  for implementation of the adjustment movement produced by the drive motor therefore can be eliminated. 
   For sealing of the through opening  28 , a sealing ring  29  is provided, which is fixed in the sealing gap between the cable  21  and the housing wall of the housing  18  by means of a pressing nut  30  that can be screwed onto the housing  18 . In addition, for sealing of the housing  18  in the region above the drive motor  24 , in which the electrical connection between the drive motor  24  and the different lines of the cable  21  is made, is lined with a sealing compound  31 . 
     FIG. 5  shows the drive motor  24  and the housing  18  in an exploded view. One recognizes the cable  21  with the plug  22  attached thereon, which is suitable for sterilization. On the drive motor  24 , two connection terminals  32  are provided, on which the line ends of the electrical lines  33  guided in the cable  21  can be soldered. The drive shaft  34  of the drive motor  24  is non-rotatably attached by means of a threaded pin  35  on the drive part  25   a  of the magnetic coupling  25 . The upper end of the drive shaft  34  is covered outwardly with a corrugated covering  36 . 
   In  FIG. 5 , the sealing compound  31  is shown in a hardened state. It should also be noted, however, that the sealing compound  31  is not added as a hardened component in the housing  18 . In addition, the drive motor  24  is first completely electrically and mechanically mounted in the housing  18  and next, the housing  18  is closed by application of the sealing ring  29  and the pressing nut  30 . Next, the sealing compound  31  is applied in a not yet hardened form in the housing  18 , in order to permit a hermetic encapsulation of the drive motor from the outside. For application of the first, still fluid sealing compound  31  in the housing  18  in the upper housing part  18   a , a fill opening  37  is provided. Subsequently, the fill opening  37  is closed from outside by screwing into the threaded pin  38 .
A removable optical device with at least one lens for releasable attachment to a microscope suited for contact-free observation of an eye, which can be arranged between the objective of the microscope and the eye in the optical axis of the microscope. A drive device is provided, with which the lens can be adjusted along the optical axis of the microscope, whereby an electric drive motor is integrated in the removable device, which, together with the device, can be detached from the microscope and sterilized by suitable methods.