Abstract:
An ophthalmological device ( 1 ) comprises an optical transmission system ( 5 ) for transmitting femtosecond laser pulses to a projection objective ( 3 ) for projecting the femto-second laser pulses onto or into eye ( 2 ) tissue. The ophthalmological device ( 1 ) further comprises an objective changing device ( 4 ) for changing and connecting the projection objective ( 3 ) to the optical transmission system ( 5 ). The objective changing device ( 4 ) comprises more than one different projection objectives ( 3 ) connected mechanically with each other, and the objective changing device ( 4 ) is configured to convey one of to the projection objectives ( 3 ) to the optical transmission system ( 5 ) for connecting the respective projection objective ( 3 ) to the optical transmission system ( 5 ). The objective changing device ( 4 ) makes it possible to adapt the laser-based ophthalmological device ( 1 ) for new applications without the need for extensive reconfigurations and/or costly vario-lense objectives.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of prior application Ser. No. 12/139,126 filed Jun. 13, 2008, entitled OPHTHALMOLOGICAL DEVICE, which is a continuation in part of prior application Ser. No. 11/822,401 filed Jul. 5, 2007, entitled OPHTHALMOLOGICAL DEVICE which claims benefit of and priority to European Patent Application No. 06405317.6 filed Jul. 21, 2006, the entire content of each of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to an ophthalmological device for projecting femtosecond laser pulses. The present invention relates, in particular, to an ophthalmological device is with an optical light projection module for projecting deflected femtosecond laser pulses onto a defined treatment surface into an image area extending from the optical axis of the light projection module. 
         [0004]    2. Prior Art 
         [0005]    Simple spherical lenses focus at the focal point only monochromatic light beams which run near the optical axis (paraxial beams). Beams running that are further removed from the optical axis are focused at another focal point. This most common image error is termed aperture error, or else spherical aberration. If the aim is to focus with a high numerical aperture in order to attain small spot sizes, it is possible to compensate these errors by aspheric lens shape, for example. This compensation provides no assistance for imaging locations lying off the optical axis. In addition, further aberrations such as coma, field curvature, astigmatism or distortions result during optical imaging. Furthermore, axial and lateral chromatic aberrations occur when polychromatic light is being used. 
         [0006]    It is normal to use a combination of a number of spherical lenses with different refractive properties to compensate these errors. Diffractive optical elements are also used for this purpose in a few cases. In general, the outlay on correction, and thus the number of optical elements (for the most part lenses and mirrors) and materials which are used rises with the numerical aperture and the field size (size of the sharply focused image area). However, the diameter and the weight of the optical systems also rise substantially with the numerical aperture and the field size. When the focal plane is additionally to be adjusted, the outlay on equipment rises further. This relationship is of great importance particularly in the design of femtolaser systems. For example, femtolaser systems, which have pulse widths of typically 10 fs to 1000 fs (1 fs=10−15 s), require numerical apertures of greater than 0.2 in an ophthalmological application, since otherwise the material removal at depth (for example in the cornea) is not accurately defined, and optical breakthrough already comes about partially on structures lying above the focal plane (for example in the epithel). A further undesired phenomenon outside the focal plane are streaky structures (so-called “streaks”) in the tissue along the propagation direction of the laser beam. There are breakthroughs above and below the focal plane even in the case of systems with numerical apertures around 0.3. Highly corrected systems with a working area of 10 mm with a numerical aperture of 0.3 require as many as ten and more lenses with a diameter of about 100 mm. Raising the numerical aperture is possible in practice only in conjunction with a reduced image field (image area). In addition, in the case of phases of femtosecond laser pulses which are affected by aberrations, there is the problem that not all light beams come into focus at the same instant, because of different transient times. Particularly in the case of very short pulses, the maximum intensity at the focus is therefore reduced. 
         [0007]    By way of example, Patent Application EP 1486185 describes such an ophthalmological device with an application head which can be used manually, and in this case the advantages of the small overall size and the low weight are bought at the expense of the disadvantage of a restricted image field. 
         [0008]    Patent Application DE 10358927 describes a laser device for material machining by means of laser radiation, in particular for refractive surgery on the human eye by means of deflected femtosecond laser pulses. The device according to DE 10358927 comprises a pulse selection device which modifies selected laser pulses such that the modified pulses either no longer pass into the material to be machined at all, or can at least no longer produce an optical breakthrough there. The modification of the laser pulses comprises influencing parameters such as phase, amplitude, polarization, beam direction and field distribution over beam cross section (beam profile). By means of wavefront modification, in particular, the selected laser pulses are defocused such that the energy density no longer suffices for optical breakthroughs. The pulse selection, and thus the modification, perform, in particular, in a fashion synchronized with the deflection rate. 
       SUMMARY 
       [0009]    It is an object of the present invention to propose an ophthalmological device for projecting deflected femtosecond laser pulses which does not have the disadvantages of the prior art. In particular, it is an object of the present invention to propose an ophthalmological device for projecting deflected femtosecond laser pulses which enable an enlarged image field in the case of a given projection optics, known from the prior art, in conjunction with retention of the central image quality even in the edge regions of the treatment surface (for example focal plane). It is, in particular, a further object of the present invention to propose an ophthalmological device which is of such a small design and such a low weight that it is suitable for manual application and positioning. Furthermore, the aim is to enable the use of different applanation elements and/or interchangeable objectives through the possibility of being able to adapt the optics. 
         [0010]    In accordance with the present invention, these objects are achieved, in particular, by means of the elements of the independent claims. Further advantageous embodiments proceed, furthermore, from the dependent claims and the description. 
         [0011]    The ophthalmological device comprises an optical light projection module for projecting deflected femtosecond laser pulses into an image area, extending from the optical axis of the light projection module, on a defined treatment surface. 
         [0012]    The above named objects are achieved with the aid of the present invention by virtue, in particular, of the fact that the ophthalmological device is also provided with a controllable optical correction element and a control module connected thereto, the controllable optical correction element being set up to modulate the wavefront of the femtosecond laser pulses in a variable fashion, and the control module being set up to control the correction element as a function of a deflection of the femtosecond laser pulses in such a way that the femtosecond laser pulses are focused in the image area. The controllable optical correction element and the control module are preferably set up to modulate the wavefront of the femtosecond laser pulses sequentially in each case for an image point lying inside the image area and onto which the deflected laser beam is projected. The sequential correction of the wavefront is performed image point by image point, in accordance with the scanning pattern of the deflected laser pulses, and is significantly less complex and complicated than a correction of an overall image with a multiplicity of image points which are to be projected simultaneously into the image area. The controlled modulation of the wavefront enables the focused projection of the femtosecond laser pulses onto the treatment surface in the entire extended image area arranged about the optical axis of the light projection module. The modulation of the wavefront enables even femtosecond laser pulses from pulsed laser beams which run that run at a distance from the optical axis of the light projection module to be imaged onto the machine surface in a fashion focused in the image area. It is possible by means of the adaptive and dynamic modulation of the wavefront of the deflected femtosecond laser pulses for the femtosecond laser pulses to be focused onto the treatment surface in an enlarged image area in conjunction with unchanged projection optics of the light projection module and so the image field can be enlarged in conjunction with an unchanging compact design of a light projection module suitable for manual application. The image quality of the optics of the light projection module can be generally improved by means of the corrective modulation of the laser pulse wavefronts. The controlled modulation of the wavefronts enables the more cost effective provision of a highly compensated optical system with a relatively small number of optical elements, a design that is smaller overall and a lesser resulting weight than optical systems of the prior art. In particular, the controlled correction module enables an ophthalmological device to be designed with a compact, manually positionable light projection module which is not felt to the patient to be threateningly large and has an image field of at least 10 mm and a numerical aperture of at least 0.3. Smaller image fields or image areas, for example with the diameter of 1 2 mm, 3 5 mm or 6 9 mm, can, in particular, be achieved with the design which is further reduced and yet more compact. Moreover, inaccuracies in fabrication and assembly, as well as aberrations can be compensated by means of lightweight optical superstructures in conjunction with regulated operation. 
         [0013]    In one embodiment, the ophthalmological device comprises a detector module with a wavefront detector and/or a light beam profile detector for determining a wavefront profile or a light beam profile of the femtosecond laser pulses, and the control module is set up to control the correction element as a function of the specific wavefront profile or light beam profile. The wavefront of the femtosecond laser pulses can be dynamically modulated, and therefore dynamically detected for focusing the femtosecond laser pulses in the image area by means of controlling the correction element on the basis of the detected wavefront profile or light beam profile. 
         [0014]    In a further embodiment, the ophthalmological device comprises optical elements for detecting the femtosecond laser pulses projected into the image area, and the control module is set up to control the correction element as a function of detected femtosecond laser pulses projected into the image area. The detection of the femtosecond laser pulses projected into the image area permits the projection quality actually produced in the image area, for example with the assistance of the abovementioned detector module, to be fed back and determined in a fashion as free from error as possible. 
         [0015]    In one embodiment, the ophthalmological device comprises optical elements for simulating a reference beam path corresponding to a beam path used for projecting the femtosecond laser pulses onto the treatment surface, and for detecting femtosecond laser pulses projected in the reference beam path. In addition, the control module is set up to control the correction element as a function of detected femtosecond laser pulses projected in the simulated beam path. The detection of the femtosecond laser pulses projected in the reference beam path permits the projection quality to be fed back and determined, for example with the aid of the abovementioned detector module, without intervening (that is to say inserting optical elements) in the beam path used for the machining. 
         [0016]    In one embodiment, the ophthalmological device comprises a laser source for generating a reference laser beam, and the control module is set up to control the correction element as a function of the reference laser beam deflected and projected in accordance with the femtosecond laser pulses. Depending on the variant, the reference beam path is led via the beam path used for the machining or the reference beam path. 
         [0017]    In one embodiment, the control module comprises control data with an assignment of control values to deflection values, and the control module is set up to control the correction element on the basis of the control values which are assigned to current deflection values. The control based on defined control data enables, inter alia, a control without feedback based on knowledge of the geometry of the ophthalmological device. 
         [0018]    In one embodiment, the ophthalmological device comprises optical elements for detecting the femtosecond laser pulses projected into the image area, and a calibration module for generating and storing the control data as a function of detected femtosecond laser pulses projected into the image area. In one variant, the calibration module is set up to generate the control data as a function of the wavefront profile or light beam profile determined by the detector module. By means of the calibration, the control data can, on the one hand, be readjusted and, on the other hand, be adapted upon application to circumstances and requirements specific to machining. 
         [0019]    In a number of embodiments, the optical correction element is set up such that during the modulation of the wavefront of the femtosecond laser pulses it varies phase distribution, amplitude distribution, polarization distribution and/or propagation directions in the beam cross section of the femtosecond laser pulses. 
         [0020]    In a further embodiment, the ophthalmological device comprises a holding element for changeably holding at least one objective element of the optical light projection module. The holding element enables, for example, the interchanging of the entire light projection module or of an objective or objective element (for example one or more lenses) of the light projection module. In particular, the holding element enables the holding or the interchanging of various light projection modules, objectives or objective elements, which are set up for the (focused) projection of deflected femtosecond laser pulses into image areas of different size and/or onto various treatment surfaces, which machine surfaces are, for example, defined (that is to say shaped) by various contact elements to be flat (applanation surface) or curved (spherically, convexly). The controllable optical correction element and the control module are, moreover, set up to modulate the wave-front of the femtosecond laser pulses such that projection errors resulting from the mechanical interchange of the light projection modules, objectives or objective elements are compensated or corrected. 
         [0021]    In a number of embodiments, the optical correction element comprises a deformable mirror, a spatial transient time delay element, moveable lenses, moveable prisms, a diffractive optical element, and an anamorphotic optical module, a photonic crystal, a lens array, a spatial polarization plate, a diaphragm and/or a spatial light modulator. 
         [0022]    In a further aspect of the present invention, the ophthalmological device for treating eye tissue using femtosecond laser pulses comprises an optical transmission system for transmitting the femtosecond laser pulses to a projection objective for projecting the femtosecond laser pulses onto or into the eye tissue. The above-mentioned holding element is implemented as an objective changing device, i.e. the ophthalmological device further comprises an objective changing device configured for changing and connecting the projection objective to the optical transmission system. The objective changing device makes it possible to adapt the laser-based ophthalmological device for new applications without the need for extensive reconfigurations and/or costly vario-lense objectives. The objective changing device makes it possible for a user to interchange flexibly and efficiently the projection objective, so that the projection objective can be interchanged without significant time delay in between different applications and treatment steps. Particularly, the objective changing device makes it possible to adapt the system to new applications which were not known or in use at the time the system was manufactured. Compared to the use of vario-lense objectives, interchanging projection objectives is further advantageous in that there is no need for controlled settings of objective parameters, and thus no requirement of respective components and modules for parameter feedback and control. 
         [0023]    In a preferred embodiment, the objective changing device comprises more than one different projection objectives connected mechanically with each other, and the objective changing device is configured to supply one of the projection objectives to the optical transmission system for connecting the respective projection objective to the optical transmission system. For example, the projection objectives differ in their focal length, field size, field curvature, numerical aperture, focus diameter, focus shape, focus extension in projection direction, and/or beam divergence. In different embodiments, the objective changing device is configured to interchange the projection objectives through rotary or translatory motion, in each case, one of the projection objectives is supplied to the optical transmission system through rotary or translatory motion for connecting the respective projection objective to the optical transmission system. An objective changing device having multiple projection objectives makes possible a particularly efficient interchange by way of simple manipulations, without the necessity of attaching new projection objectives to the ophthalmological device during the treatment. 
         [0024]    In further embodiments, the projection objectives comprise in each case an application element for applying the projection objective onto an eye, and/or the ophthalmological device comprises a common application element for applying the projection objective onto an eye, whereby the objective changing device is configured to combine the projection objective with the application element when connecting the respective projection objective to the optical transmission system. The variant with multiple application elements, in each case connected to a projection objective, has the advantage that different application elements can be interchanged by way of simple manipulations, independently from the projection objective, e.g. application elements having different contact forms or working distances. In a combination embodiment, it is possible to interchange different application elements and/or projection objectives as well as to provide a common application element, e.g. used for fixing onto the eye. 
         [0025]    In a further embodiment, the objective changing device comprises at least one connecting module for removably receiving and connecting the projection objective to the optical transmission system. A combination of the connecting module with an objective changing device makes it possible to load, before an operation, the objective changing device with suitable, application and/or patient-specific projection objectives and/or application elements, and to interchange a selected element during the operation without further manipulations by way of a rotary or translatory motion. An objective changing device with only one connecting module makes possible a particularly simple device embodiment which permits the selection and interchanging of different projection objectives during the operation. 
         [0026]    Preferably, the optical transmission system is configured to convey the femtosecond laser pulses to the projection objective by way of beams which are essentially parallel. Beams which enter the projection objective in parallel have the advantage that imprecision of the mechanical interchanging of different projection objectives (mounting tolerances) do not have an impact on the focal depth achieved with the projection objective. 
         [0027]    In an embodiment, the ophthalmological device comprises a measurement system for determining for the projection objective connected to the optical transmission system its position relative to the device. The measuring system makes possible the detection, indication and/or correction of imprecise positioned projection objectives. 
         [0028]    In a further embodiment, the ophthalmological device comprises a detector for determining an objective type identifier provided by the projection objective connected to the optical transmission system. Preferably, the detector is connected to the control module, the detector is configured to transmit to the control module the objective type identifier of the projection objective connected to the optical transmission system, and the control module is further configured to control the laser source and/or the optical transmission system, e.g. the deflection module and/or the optical correction element, based on the objective type identifier. For example, the objective type identifier is implemented as a mechanical, optical, electrical or radio based identifier. Through assignment and recognition of an objective type, the laser beam can be controlled in its condition, transmission, direction and/or deflection, depending on the optical characteristics of the used projection objective. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    A design of the present invention is described below with the aid of an example. The example of the design is illustrated by the following attached figures: 
           [0030]    FIG.  a  shows a block diagram which illustrates schematically an ophthalmological device being used to treat an eye by means of a focused pulsed laser beam. 
           [0031]      FIG. 1   b  shows a plan view of a treatment surface, machined by the ophthalmological device, and an image area lying thereupon. 
           [0032]      FIGS. 2   a ,  2   b ,  2   c  and  2   d  respectively show a block diagram which diagrammatically illustrates an embodiment of the ophthalmological device being used to treat an eye by means of a focused pulsed laser beam. 
           [0033]      FIG. 3   a  shows two pulsed laser beams of which the laser beam running further removed from the optical axis is not imaged in a focused fashion onto a treatment surface. 
           [0034]      FIG. 3   b  shows two pulsed laser beams which are both imaged in a focused fashion onto a treatment surface by means of a “corrected” light projection module. 
           [0035]      FIG. 4  shows a block diagram which illustrates schematically an embodiment of the ophthalmological device having an objective changing device. 
           [0036]      FIG. 5  shows a block diagram which illustrates schematically a front view of an embodiment of the ophthalmological device having a number of projection objectives connected mechanically with each other. 
           [0037]      FIG. 6  shows a block diagram which illustrates schematically a top view of an embodiment of the ophthalmological device having a number of projection objectives connected mechanically with each other. 
           [0038]      FIG. 7   a  shows a block diagram which illustrates schematically an embodiment of the ophthalmological device having a number of application elements connected in each case to one of the projection objectives. 
           [0039]      FIG. 7   b  shows a block diagram which illustrates schematically an embodiment of the ophthalmological device having a common application element for a number of projection objectives. 
           [0040]      FIG. 7   c  shows a block diagram which illustrates schematically a combined embodiment of the ophthalmological device having a number of application elements connected to the projection objectives and having a further common application element. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0041]    In  FIGS. 1   a ,  2   a,    2   b,    2   c,    2   d,    4 ,  5 ,  6 ,  7   a,    7   b  and  7   c  the reference symbol  1  denotes an ophthalmological device or an ophthalmological device arrangement with a laser source  17  and an optical light projection module  11 , optically connected to the laser source  17 , for generating and projecting in a focused fashion a pulsed laser beam L′ for the punctiform breakdown of tissue at a focus F (focal point) in the interior of the eye tissue  21 , for example in the cornea. The laser source  17  comprises, in particular, a femtosecond laser for generating femtosecond laser pulses which have pulse widths of typically 10 fs to 1000 fs (1 fs=10−15 s). The laser source  17  is arranged in a separate housing or in a housing common to the light projection module  11 . For the purpose of holding and applying the ophthalmological device  1  or the optical light projection module  11  manually, the ophthalmological device  1  has a diagrammatically illustrated handle  18 . As is also illustrated diagrammatically in Figure la, the ophthalmological device  1  comprises a holding element  19  for interchangeably holding various optical light projection modules  11  or at least various objective element(s) of the light projection module  11 . The holding element  19  is designed, for example, as a bayonet catch or screw plug. 
         [0042]    For the purpose of better understanding, it is to be stated here that  FIGS. 1   a,    2   a,    2   b,    2   c ,  2   d,    4 ,  5 ,  6 ,  7   a,    7   b  and  7   c  illustrate the ophthalmological device  1  diagrammatically and in a simplified fashion. For example, the figures do not reproduce precisely that the optical light projection module  11  has a high numerical aperture of, for example, at least 0.3, that the ophthalmological device  1  is fastened on the eye  2  by means of a suction ring, and that the ophthalmological device  1  comprises a contact element (for example an applanation element) for the contact based deformation (for example for applanation) of the eye  2  when the ophthalmological device  1  is being applied. 
         [0043]    As is illustrated diagrammatically in Figure la, the ophthalmological device  1  comprises a deflection module  16 , that is to say an optical scanning module or scanner module which is set up to deflect the femtosecond laser pulses L 1  generated by the laser source  17  in at least one direction, and thereby to move the focus F of the pulsed laser beam L′ in accordance with a scanning pattern (scan pattern) at least in one direction x, y of the (continuous or discontinuous) defined treatment surface w in the tissue  21  of the eye  3 . With the motionless light projection module  11  (static), a deflection of the femtosecond laser pulses L effects a movement of the focus F of the pulsed laser beam L′ in the image area p which is situated on the treatment surface w and extends from the optical axis z of the light projection module  11  (see  FIG. 1   b ). The image region p is thus scanned image point by image point in accordance with the scanning pattern, individual image points also being able to overlap one another partially or completely. In the applied state of the ophthalmological device  1  or the light projection module  11 , the image area p runs substantially normal to the optical axis z, at least at the point of intersection with the optical axis z. It may be maintained here that the treatment surface w and the image area p can be more simply flat, but also curved. The image area p has different possible shapes, depending on the control of the deflection module  16 . For example, together with the laser source  17  the deflection module  16  is arranged in a separate housing or in a housing common to the light projection module  11 . 
         [0044]    In addition, in one variant the ophthalmological device  1  comprises a drive module  15  for moving the light projection module  11  along the directions x and/or y and/or a normal to these directions (for example along the optical axis z). Thus, the drive module  15  can likewise move the focus F of the pulsed laser beam L′ in one or more directions. The focus F of the pulsed laser beam L′ can also form the normal (z) by means of moveable lenses, for example inside the light projection module  11 . 
         [0045]    As is illustrated in  FIG. 1   a , the ophthalmological device  1  additionally comprises a controllable optical correction element  14  which is arranged in the diagrammatically illustrated beam path L between the laser source  17  and the exit of the light projection module  11 . The optical correction element  14  is set up for the variable modulation of the wavefront of the femtosecond laser pulses. The phase transient times and/or the propagation directions are varied over the beam cross section of the femtosecond laser pulses by the controllable modulation of the wavefront. Furthermore, the polarization and the amplitude distribution can be varied. Since, given an unchanged spectral distribution, the wavefront can be dependent in general on the amplitude distribution, the polarization distribution and the phase distribution in the beam cross section, or can be influenced by these, it is intended below to talk of a wavefront modulation in place of amplitude, polarization and phase modulation. The term wavefront modulation further comprises the modulation of the propagation directions. The optical correction element  14  is designed, for example, as a deformable mirror, as a spatial transient time delay element, by means of moveable lenses, by means of moveable prisms, and/or as a diffractive optical element. Radially moveable lenses can be integrated, for example, in polar coordinate scanner systems which deflect at a high annular, but comparatively low radial speed. The optical correction element  14  can also be designed by means of an anamorphotic optical module, a chromatic crystal, a lens array, a spatial polarization plate, a diaphragm and/or a spatial light modulator (for example a conventional mirror array or LCD array). 
         [0046]    The reference symbol  13  in  FIGS. 1   a ,  2   a,    2   b,    2   c,    2   d  and  4  denotes a control module which is designed by means of software and/or hardware as a programmed logic module. The control module  13  is connected to the optical correction element  14  for the purpose of transmitting control signals. The control module  13  is arranged in a separate housing or in a housing common to the light projection module  11 . The control module  13  is set up to control the optical correction element  14  such that the wavefront of the femtosecond laser pulses is modulated so that the deflected femtosecond laser pulses of the pulsed laser beam L′ are respectively focused at the image point, this being, specifically, on the treatment surface w for image points inside the entire image area p. 
         [0047]    The image of two pulsed laser beams L 3 , L 4  by the “uncorrected” light projection module  11  is illustrated in  FIG. 3   a . As indicated by the focus F 3 , the laser beam L 3  running in the vicinity of the optical axis z is imaged in a fashion focused onto the treatment surface w. By contrast, the laser beam L 4  deflected further from the optical axis z is imaged onto an (unsharp) focal area F 4 ′ lying outside the treatment surface w.  FIG. 3   b  illustrates the imaging of the pulsed laser beams L 3 , L 4  by the “corrected” projection system  11 - 14 , which comprises the light projection module  11  and the optical correction element  14 , the correction element  14  being controlled by the control module  13  such that the wavefront of the femtosecond laser pulses is modulated such that both the laser beam L 3 , at the focus F 3 , and the laser beam L 4 , at the focus F 4 , are imaged in a focused fashion onto the image area p of the treatment surface w. The control of the optical correction element  14  is performed dependent on the deflection of the femtosecond laser pulses L 1 , generated by the laser source  17 , by the deflection module  16 . The deflection of the femtosecond laser pulses L 1  is defined, for example, by x/y coordinates in the image area p, or by one or more deflection angles. Data on the deflection are, for example, transmitted by the deflection module  16  to the control module  13 , or are already known to the control module  13  from internal control data. In addition, the control of the optical correction element  14  is performed as a function of stored control data  131  and/or feedback relating to the projection of the pulsed laser beam L′ in the image area p on the treatment surface w. For the different deflections (deflection values), the control data comprise control values for controlling the optical correction element  14 . The control data are permanently defined, for example on the basis of the calculation of the optical system, or of a calibration of the optical system after its assembly, by means of external measuring instruments, or are generated by means of an optional calibration module  132  on the basis of feedback relating to the projection of a laser beam into the image area p on the treatment surface w. 
         [0048]    Feedback via the projection into the image area p on the treatment surface w is performed by means of optical elements and of the optional detector module  12 . In particular for the purpose of calibration before operational use, the femtosecond laser pulses of the projected laser beam L′, or an auxiliary reference laser beam from the optional reference laser source  171 , are detected by removable or moveable optical elements, for example mirrors, semitransparent mirrors and/or lenses, at the level of the treatment surface w, and then optically to the detector module  12 . For feedback during operational use, the femtosecond laser pulses which are reflected onto the treatment surface w are fed to the detector module  12  via optical elements, for example by means of reflecting and/or semitransparent mirrors and/or lenses. In an alternative embodiment, the device  1  comprises optical elements, for example mirrors, semitransparent mirrors and/or lenses, which simulate a reference beam path corresponding to the beam path used for projecting the femtosecond laser pulses onto the treatment surface w such that the detector module  12  can be fed femtosecond laser pulses whose wavefront and/or beam profile correspond to those of femtosecond laser pulses of the laser beam L′ in the image area p on the treatment surface w. It will be understood by the person skilled in the art that, as in the case of calibration, feedback during operational use is generated in alternative embodiments on the basis of an additional auxiliary reference laser beam which is generated by the optional reference laser source  171 . 
         [0049]    In a number of embodiments, the detector module  12  comprises a wavefront detector and/or a light beam profile detector for determining the wavefront profile or the light beam profile of the femtosecond laser pulses fed via the optical elements. The wave-front detector is, for example, designed as a Shack-Hartmann sensor, for example according to US 2003/0038921, or as an interferometer, for example as a shearing interferometer. Further possible embodiments of the wavefront detector are described in Jos. J. Rozema, Dirk E. M. Van Dyck, Marie-Jose Tassignon, “Clinical comparison of 6 aberrometers. Part 1: Technical specifications”, J Cataract Refract Surg, Volume 31, June 2005, pages 1114-1127. The light beam profile detector comprises, for example, a CCD (Charge Coupled Device) chip. The detector module  12  is connected to the control module  13  for feeding back the specific wavefront profile or the light beam profile. The control module  13  is set up to generate control signals on the basis of the feedback, and to lead them to the optical correction module  14  in order to modulate the wavefront of the femtosecond laser pulses by means of the optical correction module  14  such that a desired, defined wavefront profile or a desired, defined light beam profile results in the image area p on the treatment surface w, and the deflected femtosecond laser pulses are adequately focused on the treatment surface w over the entire image area p in accordance with a defined degree of focus. Depending on the machining method, there can be a number of quality criteria for the degree of focus. For example, the maximum intensity at the focus can be defined as degree of focus (important for initiating an optical breakthrough). Furthermore, the shape of the focus (for example circular for a defined machining zone, elliptical as a function of scanning patterns), the diameter thereof (important in the case of uniform spot spacing) or else the intensity profile (for example flat top) can serve as a criterion for the degree of focus. If the focus shape (spot shape) is the decisive criterion, this can be readjusted in the event of an unsatisfactory intensity at the laser source. The readjustment can also be undertaken as a function of the focal position. The readjustment can be required, for example, when the wavefront modulator gives rise to fluctuating intensities. 
         [0050]    In the embodiment according to  FIG. 2   a , the controllable optical correction element  14  is inserted into the beam path between the laser source  17  and the deflection module  16 . The femtosecond laser pulses L 1  generated by the laser source  17  are fed to the correction element  14 , which modulates the wavefront of the femtosecond laser pulses L 1  in accordance with the control signals of the control module  13 , doing so in each case for the image point onto which they are deflected and projected in the image area p. The femtosecond laser pulses L 2  generated by the correction element  14  and having a modulated wavefront are fed to the deflection module  16 . The deflection module  16  deflects the femtosecond laser pulses L 2  in at least one scanning direction. The femtosecond laser pulses L 2 ′ deflected by the deflection module  16  are fed to the light projection module  11  for the purpose of focused projection. 
         [0051]    In the embodiment according to  FIG. 2   b , the controllable optical correction element  14  is integrated in the deflection module  16 . The femtosecond laser pulses L 1  generated by the laser source  17  are fed to the deflection module  16 . In the internal beam path of the deflection module  16 , the correction element  14  modulates the wavefront of the femtosecond laser pulses L 1  in accordance with the control signals of the control module  13 , doing so in each case for the image point onto which they are deflected and projected in the image area p. The femtosecond laser pulses L 2 ″ with modulated wavefront, which are modulated by the correction element  14  and deflected by the deflection module  16  in at least one scanning direction, are fed to the light projection module  11  for focused projection. 
         [0052]    In the embodiment according to  FIG. 2   c , the controllable optical correction element  14  is inserted into the beam path between the deflection module  16  and the light projection module  11 . The femtosecond laser pulses L 1 ′, generated by the laser source  17  and deflected by the deflection module  16 , are fed to the correction element  14 . The correction element  14  modulates the wavefront of the deflected femtosecond laser pulses L 1 ′ in accordance with the control signals of the control module  13 , doing so in each case for the image point onto which they are deflected and projected in the image area p. The femtosecond laser pulses L 2 ′″ with modulated wavefront, which are deflected by the deflection module  16  in at least one scanning direction and are modulated by the correction element  14 , are fed to the light projection module  11  for focused projection. In the case of a deflecting mirror in the deflection module  16 , said mirror can also simultaneously be designed with a capacity to be deformed or to modulate intensity, and can thus also serve as optical correction element. Furthermore, in addition to correction based on wavefront modulation it is also possible, for example, to use a deformable mirror for adjusting (positioning) the focus. 
         [0053]    In the embodiment according to  FIG. 2   d , the controllable optical correction element  14  is integrated in the light projection module  11 . The femtosecond laser pulses L 1  generated by the laser source  17  are fed to the deflection module  16 , which deflects the femtosecond laser pulses L 1  in at least one scanning direction. The deflected femtosecond laser pulses L 1 ′ are fed to the correction element  14  in the light projection module  11 , which modulates the wavefront of the deflected femtosecond laser pulses L 1 ′, doing so in each case for the image point onto which they are deflected and projected in the image area p. The femtosecond laser pulses with modulated wavefront, which are generated by the correction element  14 , are projected in a focused fashion by the light projection module  11 . 
         [0054]      FIG. 4  shows an embodiment of the ophthalmological device  1  with the holding element  19  being implemented as an objective changing device  4 . In  FIGS. 4 ,  5 ,  6 ,  7   a ,  7   b ,  7   c  reference numeral  5  refers to the optical transmission system for transmitting the femtosecond laser pulses from the laser source  17  to a projection objective  3  of the projection module  11 . Preferably, the optical transmission system  5  is configured to convey essentially in parallel the laser beams L to the projection objective  3 , which is not the case for interchangeable objectives used in photography, for example. Depending on the embodiment, the optical transmission system  5  comprises the deflection module  16 , the optical correction module  14  and/or the detector module  12  described above. 
         [0055]    The objective changing device  4  is configured for changing the projection objective  3  and to connect the currently selected projection objective  3  to the optical transmission system  5 . Different embodiments of the objective changing device  4  are illustrated in  FIGS. 4 ,  5 ,  6 ,  7   a ,  7   b  and  7   c.    
         [0056]    In the embodiment according to  FIG. 4 , the objective changing device  4  comprises a connecting module  41  for removably inserting, receiving and connecting the projection objective  3  to the optical transmission system  5 . For example, the connecting module  41  comprises a thread or bayonet connector for receiving and fixing the projection objective  3  to the ophthalmological device  1 . When it is in the fixed state, the projection objective  3  is connected optically with the optical transmission system  5 . 
         [0057]    In the embodiments according to  FIGS. 5 ,  6 ,  7   a ,  7   b  and  7   c , the objective changing device  4   a,    4   b  comprises in each case a number of different projection objectives  3 ,  3 ′ which are connected mechanically with each other (e.g. two, three or more projection objectives). The projection objectives  3 ,  3 ′ are provided in each case with an objective type identification, and differ in their optical characteristics, such as numerical aperture, focal length, field size, field curvature, focus diameter, focus shape, focus extension in projection direction and/or beam divergence. 
         [0058]    In the embodiment according to  FIG. 5 , the objective changing device  4   a  is configured to change the projection objectives  3 ,  3 ′ by way of rotary motion φ about a rotation axis r. The projection objectives  3 ,  3 ′ are fixed to a carrier (support) which is rotatable about the rotation axis r. For example, the objective changing device  4   a  is implemented in form of revolver optics. By way of a rotary motion φ, a selected one of the projection objectives  3 ,  3 ′ is conveyed (supplied) and connected optically to the optical transmission system  5 . 
         [0059]    In the embodiment according to  FIG. 6 , the objective changing device  4   a  is configured to change the projection objectives  3 ,  3 ′ by way of translatory motion t. The projection objectives  3 ,  3 ′ are fixed to a carrier slide which is movable along an axis. By way of a translatory motion t, a selected one of the projection objectives  3 ,  3 ′ is conveyed (supplied) and connected optically to the optical transmission system  5 . 
         [0060]    Preferably, when it is connected to the optical transmission system  5 , the selected projection objective  3 ,  3 ′ is fixed in its rotation or translation, respectively, for example, mechanically by means of a locking or blocking mechanism. 
         [0061]    In an embodiment, the carrier of the objective changing device  4   a,    4   b  has one or more connecting modules for removably receiving in each case one projection objective  3 ,  3 ′, as described in the context of  FIG. 4 . Thereby, the objective carrier can be loaded with different sets of projection objectives  3 ,  3 ′, provided, for example, for different treatment steps and applications performed during treatment of a patient. 
         [0062]    As illustrated schematically in  FIG. 4 , the ophthalmological device  1  comprises an objective detector  6  for detecting the objective type identifier of the connected projection objective  3 . For example, the objective type identifier is implemented as a mechanical, optical, electrical or radio based identifier, and indicates a type code assigned to the objective type identifier. Corresponding to the embodiment of the objective type identifier, the objective detector  6  comprises a sensor for detecting and reading a mechanically implemented identifier, e.g. a code implemented by way of structural elements, for capturing an optically implemented identifier, e.g. a bar code or a blind coding, for reading an electrically implemented identifier, e.g. a capacitive or ohmic code, or for receiving and recognizing a radio based identifier, e.g. an RFID (Radio Frequency Identification). 
         [0063]    The objective detector  6  is connected to the control module  13  and is configured to transmit the determined objective type identifier to the control module  13 . For transmitting control signals (control commands, control programs), the control module  13  is connected to the deflection module  16 , the controllable optical correction element  14 , and the laser source  8 . The control module  13  is arranged in a separate housing or in a housing shared with the objective changing device  4 . For different objective types, the control module  13  comprises in each case assigned physical nominal values, which indicate optical characteristics of the respective objective type, e.g. numerical aperture, focal length, field size, field curvature, focus diameter, focus shape, focus extension in projection direction and/or beam divergence, and/or assigned control program modules. The control module  13  is configured to control the laser source  8  and the optical transmission system  5 , particularly the deflection module  16  and the correction element  14 , based on the detected objective type identifier, by transmitting to the laser source  8 , the correction element  14 , the deflection module  16  and/or other controllable elements of the optical transmission system  5 , e.g. movable lenses and controllable blinds, control commands from assigned control program modules and/or in dependence of assigned physical nominal values. Thus, depending on the objective type used, adapted and changed automatically is the laser beam L of the laser source  8 , e.g. its energy level, pulse rate, and/or pulse width, as well as its transmission, direction and/or deflection. 
         [0064]    In  FIG. 4 , the reference numeral  9  refers to a measuring system for determining the position of the projection objective, connected to the optical transmission system  5 , relative to the ophthalmological device  1 , and particularly relative to the optical transmission system  5 . In different embodiments, the measuring system  9  is configured to determine the relative position in a capacitive, inductive, ohmic or optical fashion. The measuring system  9  is connected to the control module  13  and configured to transmit to the control module  13  the determined relative position. Depending on the embodiment, the control module  13  indicates to the user via a user interface, e.g. acoustically and/or optically, deviations of the relative position from a defined range of tolerance, and/or adapts according to the deviation from a defined target value the controlling of the laser source  8  and/or the optical transmission system  5 , particularly the deflection module  16 . 
         [0065]    Although this is not illustrated explicitly in the simplified  FIGS. 4 ,  5 ,  6 ,  7   a ,  7   b  and  7   c , in respective embodiments, the ophthalmological device  1  shown in these Figures also comprises a control module  13 , an objective detector  6 , and/or a measuring system  9  for determining type and position, as well as for controlling the laser beam L based thereon. 
         [0066]      FIGS. 7   a ,  7   b ,  7   c  show embodiments in which the ophthalmological device  1  has one or more application elements  30 ,  31 ,  31 . For example, the application elements  30 ,  31 ,  31  comprise contact bodies, e.g. applanation bodies which are at least in places or partially transparent, or concave/convex form bodies. Depending on the embodiment, the application elements  30 ,  31 ,  31  further comprise a suction ring or other fastening devices for fixing on the eye  2 . 
         [0067]    In the embodiment according to  FIG. 7   a , the application elements  30 ,  31 ,  31  are in each case attached to the projection objectives  3 ,  3 ′ in a fixed or interchangeable manner, and can be implemented differently, for example, e.g. as an applanation body, a concave form body or different distance bodies for different treatment steps, and/or with, without or with different fixing means for fixing on the eye  2 . 
         [0068]    In the embodiment according to  FIG. 7   b , the ophthalmological device  1  has a common fixed or interchangeable application element  30 , and the objective changing device  4  is configured and arranged such that the different projection objectives  3 ,  3 ′ can be interchanged such that they can be combined with the application element  30 , without contact or with mechanical contact, when the projection objectives  3 ,  3 ′ are connected to the optical transmission system  5 . 
         [0069]    The embodiment according to  FIG. 7   c  is a combination of the embodiments according to  FIGS. 7   a  and  7   b , whereby, on one hand, different application elements  31 ,  31 ′ are attached to the projection objectives  3 ,  3 ′ in each case, and, on the other hand, the ophthalmological device  1  has a common application element  30 . In the combined embodiment according to  FIG. 7   c , it is possible during an operation to select and interchange different projection objectives  3 ,  3 ′ and/or application elements  31 ,  31 ′, on one hand, and, on the other hand, a common application element  30  can be kept during the treatment, for example a suction ring for fixing on the eye  2 , a distance body and/or a protection blind. 
         [0070]    Although this is not illustrated, the application elements  30 ,  31 ,  31 ′ can also be combined with the embodiments according to  FIGS. 4 and 6 . 
         [0071]    In a further embodiment, the objective changing device  4 ,  4   a,    4   b  further comprises an optional drive module for interchanging in a motorized manner the projection objectives  3 ,  3 ′ and/or the application elements  31 ,  31 ′.