Abstract:
The invention relates to an optical measuring system comprising a wave front sensor for characterizing a shape of a wave front of measuring light and an imaging lens, wherein the imaging lens comprises a first optical assembly and a second optical assembly for imaging an object region in an entrance region of the wave front sensor. A distance between the object region and the first optical assembly is larger than a focal length of the first optical assembly. Furthermore, the optical measuring system can comprise an optical microscopy system and optionally an OCT system for carrying out different optical examination methods at the same time.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to and is a continuation-in-part of International Patent Application No. PCT/EP2009/006690, filed Sep. 16, 2009, which claims priority to German Patent Application No. DE 10 2008 047 400.2, filed Sep. 16, 2008, the disclosures of which are hereby incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a measuring system for ophthalmic surgery having a wavefront sensor and imaging optics. In particular, the invention relates to a measuring system for ophthalmic surgery having a wavefront sensor and imaging optics and which is suitable for use in surgery, in particular for use in eye surgery, by providing a sufficiently large distance between the imaging optics and the object under inspection. Furthermore, the invention relates to a measuring system for ophthalmic surgery having a wavefront sensor and an OCT system. 
     Wavefront sensors, which are configured to characterize the form of a wavefront of measuring light, are known in the art. Such wavefront sensors may in particular be used to measure aberrations of a human eye by using a Hartmann-Shack sensor, as described in the article of J. Liang, B. Grimm, S. Goelz, J. F. Bille, “Objective measurement of a Hartmann-Shack wavefront sensor”, J. Opt. Soc. Am. A 11 (1994) pp. 1949-1957. In such a system, the Hartmann-Shack sensor comprises in particular an array of microlenses which is arranged in a plane, wherein in a common focal plane of the microlenses, a position-sensitive light sensor is arranged. With such a Hartmann-Shack sensor, a form of a wavefront, which is incident onto the array of microlenses may be determined by measuring local inclinations of a wavefront in regions corresponding to each of the microlenses. 
     For measuring the optical properties of a human eye, an illumination spot, which is as small as possible, is generated on the retina of the human eye. A nearly spherical wave emanates from this point-like illumination spot, traverses the vitreous body, the lens and the cornea and leaves the human eye. The form of the wavefront is altered when it traverses the different optical interfaces of the human eye. This results in a deviation of the exiting wavefront from a plane wavefront. These deviations from a plane wavefront may be represented by local inclinations within a lateral region and thereby may be measured by using a Hartmann-Shack wavefront sensor. 
     Document US 2005/0241653 A1 discloses a wavefront sensor which can be arranged and mounted between an objective lens of a microscope system and an object under inspection. 
     Document U.S. Pat. No. 6,550,917 B1 discloses a wavefront sensor, which is designed such that a spherical wavefront is transformable into a plane wavefront. The spherical wavefront may for example be a wavefront, which exits an ametropic eye having a spherical aberration. Thereby, it is possible to increase a measuring range of the wavefront sensor. 
     The document DE 103 60 570 B4 discloses an optical measuring system, which comprises an OCT-system and a wavefront analysis system. Based on a measurement of a form of a wavefront, an adaptive optical element is controlled such that wavefronts, which are measured by a wavefront detector are substantially plane wavefronts. Thereby, it is possible to obtain an improved OCT signal. 
     However, the wavefront sensors, which are disclosed in the documents mentioned above are only of limited use in surgical operations, since they require a short distance between the object and the optical component which is located closest to the object. 
     Therefore, it is an object to provide an optical measurement system having a wavefront sensor and which is suitable for use in surgical operations. In particular, it is an object to provide a measuring system having a wavefront sensor and which is suitable for use in eye surgery, in particular cataract surgery. 
     It is a further object to provide an optical measuring system having a wavefront sensor and an OCT system and which allows to inspect an object by analyzing wavefronts, which emanate from the object, wherein the analysis is performed by measuring a three-dimensional structure data set. The measuring system further has to be suitable for surgical operations. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished taking the above problems into consideration. 
     Embodiments provide an optical measuring system, or a measuring system for eye surgery, which provides the surgeon with sufficient working space to perform surgical operations. 
     According to an embodiment, there is provided an optical measuring system, which comprises a wavefront sensor for characterizing a form of a wavefront of measuring light in an entry region of the wavefront sensor; and imaging optics having a first optical assembly and a second optical assembly for imaging an object region onto the entry region of the wavefront sensor by using the measuring light, wherein the following relation holds:
 
1.1 *f≦d , wherein
         f denotes a focal distance of the first optical assembly; and   d denotes a distance between the object region and the first optical assembly.       

     The wavefront sensor may comprise an extensive array of refractive or diffractive optical elements. The array of optical elements may be an array of microlenses. Each of these refractive or diffractive optical elements may be designed such that the measuring light is focused in a focal plane. In a common focal plane, which is formed from the individual focal planes of the refractive or diffractive optical elements, there may be provided a position-sensitive light sensor. The position-sensitive light sensor may for example be a CCD camera and/or a CMOS sensor or any other light sensitive sensor. The position-sensitive light sensor may be configured to resolve a spatial intensity distribution. The position-sensitive light detector may be arranged in a plane, which is oriented perpendicular to an optical axis of the wavefront sensor. The entry region of the wavefront sensor may be defined by a region, in which the array of refractive or diffractive optical elements is arranged. This region may have the form of a plane. This plane may for example be defined by fitting a plane to optical interfaces of the refractive or diffractive optical elements, wherein the optical interfaces comprise those optical surfaces of the wavefront sensor, which are located furthest away from the position-sensitive light sensor. 
     Depending on a form of a wavefront of measuring light, which is incident on the wavefront sensor, light ray bundles of this wavefront are imaged onto a corresponding array of regions on the position sensitive light detector by the array of refractive or diffractive optical elements. These regions of the focused light ray bundles may have the form of an ellipse or a circle. An average position or a position of a center of mass of each of the regions relative to a lateral position of the corresponding refractive or diffractive optical elements is indicative of a local inclination or tilt of the light ray bundle of the respective refractive or diffractive optical element, wherein the wavefront, which is incident on the wavefront sensor comprises this light ray bundle. 
     The position-sensitive light sensor may comprise a plurality of sensor segments or pixels. Depending on a light intensity, which is incident on each of the detector segments, electrical signals are generated by the wavefront sensor. Then, these electrical signals are transmitted to a processing unit. The processing unit is configured to determine from the electrical signals a position of the focused light ray bundles. The position may be a position of the center or center of mass, for example as a center of mass of a region, which extends over several detector segments and which is formed by an incident focused bundle of light rays, which has traversed one of the refractive or diffractive optical elements of the wavefront sensor. 
     According to embodiments, the wavefront sensor is a Hartmann-Shack sensor. Alternatively, the wavefront sensor may for example be an interferometer, a classic Hartmann-Test, a Ronchi test, Talbot interferometry, or a phase retrieval method. Furthermore, the optical measuring system may be configured such that a possible astigmatic aberration of the eye of the patient is pre-compensated by a variable cylindrical lens. The cylindrical lens may be rotatably supported. For example, the cylindrical lens may be a liquid lens. 
     The optical measuring system may further comprise a light source for illuminating an object under inspection. The measuring system may be configured to illuminate a region of the retina of the eye under inspection, wherein the region is as small as possible. A wavefront of measuring light, which is substantially parallel or spherical may be incident on the eye under inspection, and after the wavefront has traversed the cornea, the lens and the vitreous body of the eye under inspection, the wavefront is incident on the retina as a substantially spherical wavefront. Thereby, a region of the retina is illuminated, which has a small extent. Depending on an ametropia of the eye under inspection, this region may have the form of a circle or an ellipse. The difference between the length of the major axes of the ellipse may increase with the astigmatic aberration of the eye under inspection. 
     In order to measure the form of a wavefront which is emanating from an eye under inspection, the wavefront is directed onto the entry region of the wavefront sensor. For this purpose, the optical measuring system comprises imaging optics having a first optical assembly and a second optical assembly. The optical assemblies may comprise one or a combination of the following: refractive optical elements, diffractive optical elements, such as mirrors and/or lenses and/or gratings, and/or one or more electronically or mechanically controllable variable lenses or mirrors, which may be designed such that their optical refractive power is adaptable by varying their shape. Optical components of an optical assembly may have a fixed position relative to each other, such as cemented elements, or alternatively, individual lenses and/or cemented elements, which are mounted using lens mounts. 
     By traversing the first optical assembly, light, which emanates from a point in the focal region of the first optical assembly into different directions is transformed into a bundle of light, which is consists of substantially parallel light rays. By this fact, a position of the focal region of the first optical assembly is determinable. The focal region may have the form of a plane, which is located perpendicular to an optical axis of the first optical assembly. In this case, the focal region may be referred to as the focal plane. The focal point of the first optical assembly may be defined as the point, where the optical axis of the first optical assembly intersects the focal plane. An incident ray of light, which passes through the focal point of the first optical assembly and which forms a small angle with the optical axis, is transformed by the first optical assembly into an outgoing light beam, which runs parallel to the optical axis of the first optical assembly. A point of intersection of the extended outgoing light beam with the extended incident light beam is located in the principal plane of the first optical assembly. The focal length f of the first optical assembly is defined by the distance between the principal plane of the first optical assembly and the focal plane of the first optical assembly. 
     The distance d between the object region and the first optical assembly is defined by a distance between the object region and an optical surface of a component of the first optical assembly, wherein this optical surface may represent an optical surface of components of the first optical assembly, which is located closest to the object region along a beam path of the measuring light. This component of the first optical assembly is an optical component having the effect of a lens, i.e. a component which has a refractive power of greater than zero. For example, this component is not a plane-parallel plate or any other form of a component which does not modify a form of a wavefront of measuring light. Hence, further optical components may be arranged in the beam path of measuring light between the object region and the first optical assembly at a distance from the object region, which is smaller than d. These further optical components may have a refractive power of zero or a refractive power which is small compared to the refractive power of the first optical component, such as smaller than 5% or smaller than 1% of the refractive power of the first optical assembly. The refractive power of the first optical assembly is given by the reciprocal of the focal length, i.e. by 1/f. 
     The distance d thereby represents a free space between the first optical assembly and the object under inspection. This free space is sometimes referred to as working space and the distance d is sometimes referred to as working distance. By fulfilling the condition 1.1*f≦d, it is ensured that the working distance d is greater than the focal length f of the first optical assembly. An increase in d thereby leads to an increase of the working distance, which ma be advantageous in surgical operations such as in surgical operations performed on the human eye. 
     Moreover, the range of focal lengths of the first optical assembly is limited by various constraints. One of such constraints is the magnification, which is necessary to image a region having the diameter of the pupil of the eye onto the entry region of the wavefront sensor. A further constraint is a total length of the imaging optics, which typically should be designed compact in size. Therefore, it is typically not possible to increase the focal length of the first optical assembly until a sufficient working distance is achieved. Consequently, it is advantageous to have an measuring system for ophthalmic surgery, which fulfills the condition 1.1*f≦d. 
     According to an embodiment, 1.5*f≦d holds, or 1.75*f≦d holds, or 2*f≦d holds. For particular applications, it is advantageous, to provide a comparatively small focal length of the first optical assembly. Also in this case, a sufficiently large working distance can be attained for conducting surgical operations. 
     According to an embodiment, d≧150 millimeters holds, or d≧175 millimeters holds, or d≧190 millimeters holds. Such working distances allow to conduct surgical operations under a variety of requirements, such as requirements, which result from conducting eye surgery. According to further embodiments, d≦500 millimeters holds, or d≦300 millimeters holds, or d≦200 millimeters holds. 
     According to an embodiment, at least one of the first optical assembly and the second optical assembly is a refractive optical assembly, such as for example a lens assembly. A lens assembly is a set of lenses, which comprises one or more lenses. A lens assembly may consist of cemented elements. Lenses of a lens assembly may be arranged at a fixed position relative to each other. 
     According to an embodiment, the optical measuring system further comprises a third optical assembly, which is arranged and configured to image the object region along a beam path of the microscope onto an image region, which is different from the entry region of the wavefront sensor. The image region may be located at a distance from the entry region of the wavefront sensor. Thereby, it is possible to perform optical microscopy of the object region in addition to performing an analysis of the wavefront. Performing optical microscopy may be helpful during conducting surgical operations. 
     According to an embodiment, the object region is located at a focal region of the first optical assembly. 
     According to an embodiment, the first optical assembly comprises a first optical subassembly and a second optical subassembly, which are located at a distance from each other. The first optical assembly consists of the first optical subassembly and the second optical subassembly. By way of example, the first optical subassembly and the second optical subassembly are arranged at a fixed position relative to each other. 
     According to an embodiment, an optical path, which is traversed by the measuring light along the beam path of the measuring light between the first optical assembly and the second optical assembly, is adaptable. The adaptability of the optical path has the advantage that a spherical aberration of a human eye under inspection is pre-compensatable. Thereby, it is possible to minimize a curvature of the wavefront, which is incident on the wavefront sensor and thereby to increase a measuring range or a dynamic range of the wavefront sensor. In case the wavefront of measuring light has a spherical form when being incident on the first optical assembly, the wavefronts in the entry region of the wavefront sensor may be transformed into wavefronts having a substantially plane form. This transformation may be adapted by increasing or decreasing the optical path between the first optical assembly and the second optical assembly, by increasing or decreasing the optical path between the second optical subassembly of the first optical assembly and the second optical assembly. 
     Even when varying the optical path between the first optical assembly and the second optical assembly, the focal region of the first optical assembly which may consist of the first optical subassembly and the second optical subassembly, is still imaged onto the entry region of the wavefront sensor. The varying of the optical path may comprise moving/displacing the second optical subassembly relative to the second optical assembly. In other words, the second optical subassembly may be configured such that it is displaceable or movable relative to the second optical assembly. There may be provided an actuator for varying the optical path, wherein the actuator is designed to provide a driving force for displacing or moving the second optical subassembly relative to the second optical assembly. The actuator may be a motor or an actuator, which may be configured to transmit a driving force for the displacement, such as an actuation mechanism like a screw. The displacement may be performed along a track or guide. An amount of the displacement, such as a distance of the displacement, may be detected and measured by a detector. The actuator may be in signal communication with a controller, such that the controller may activate the actuator. The controller may comprise or make use of a calibration curve, which allows to convert between the amount of a spherical aberration of the eye under inspection and a distance of a displacement for pre-compensating this ametropia. By using the calibration curve, it is possible to control the actuator for displacing the second optical subassembly relative to the second optical assembly based on a known ametropia of the eye under inspection. 
     According to an embodiment, the measuring system for ophthalmic surgery is configured to characterize a form of a wavefront of measuring light, which emanates from an eye, which is arranged in an object region, wherein the eye has a spherical aberration of between −5 dpt (diopters) to +25 dpt (diopters), by varying the optical path between the first optical assembly and the second optical assembly. The sign of the spherical aberration of the eye is defined such that an aphakic eye, i.e. an eye with the natural lens removed, has a spherical aberration of about +20 dpt. 
     According to an embodiment, the optical measuring system further comprises a reflector for deflecting the measuring light, for example by 180°, wherein the reflector is displaceably arranged between the first optical assembly and the second optical assembly in the beam path of the measuring light for varying the optical path traversed by the measuring light. By way of example, the reflector is displaceably arranged between the second optical subassembly of the first optical assembly and the second optical assembly in the beam path of the measuring light. 
     According to an embodiment, the reflector comprises at least two mirror surfaces, which are arranged at an angle different from zero. In other words, the two mirror surfaces are arranged at an angle relative to each other, which is different from zero. The reflector may for example comprise two or three mirrors, wherein the reflector does not comprise any further reflecting surfaces. It is advantageous to use exactly two mirrors due to the favourable polarization behavior. 
     According to an embodiment, the optical measuring system further comprises a retroreflector, which is arranged between the first optical assembly (for example the second optical subassembly of the first optical assembly) and the second optical assembly in the beam path of the measuring light. A retroreflector is an optical system, which substantially reverses a propagation direction of the measuring light. This feature is substantially independent from an orientation of a propagation direction of the measuring light relative to the retroreflector. By way of example, the measuring light is not reflected by the retroreflector along the beam path of the incident measuring light, but along a path, which is laterally displaced relative to the beam path of the incident measuring light. In other words, the reflected path of measuring light, which is outgoing from the retroreflector is parallel to and located at a distance from the path of measuring light which is incoming onto the retroreflector. By arranging a retroreflector between the second optical subassembly and the second optical assembly, it is possible to vary the optical path between the second optical subassembly and the second optical assembly by displacing the retroreflector. A displacement of the retroreflector in a direction parallel to the optical axis of the first optical assembly by a distance  1  results in an increase or decrease of the optical path between the second optical subassembly and the second optical assembly by 2*n*1, wherein n denotes a refractive index of a medium within the beam path of the measuring light between the second optical subassembly and the second optical assembly. Providing the retroreflector allows to design the optical measuring system very compact in size. This in turn allows the optical measuring system to be mounted within or beneath a microscope system. 
     According to an embodiment, the retroreflector comprises a corner cube. A corner cube comprises a transparent body, which substantially has a form of a three-sided pyramid. The three-sided pyramid may comprise three triangles which are oriented perpendicular to each other, each of which being in the form of an isosceles, right-angled triangle, and further a surface in the form of an equilateral triangle. With this corner cube, an incident light beam is reflected by the corner cube at three surfaces. The mirroring process may result from total internal reflection. However, it is also conceivable, that a reflective coating is applied to the surfaces at which a mirroring process occurs, for example by applying a metallic coating. Thereby, a possible polarization of the light is influenced in a different way. 
     According to an embodiment, the optical measuring system further comprises a beam splitter, which is arranged between the entry region of the wavefront sensor and the second optical assembly. The beam splitter may be designed as a polarization beam splitter. The beam splitter may advantageously be used for coupling measuring light into the beam path. Hence, the measuring light on the way from the beam splitter to the object in the focal region of the first optical assembly traverses substantially the same path as the light, which emanates from the object on the way to the beam splitter. On the way from the beam splitter to the object, the measuring light traverses the second optical assembly and the first optical assembly (for example the first optical subassembly and the second optical subassembly of the first optical assembly). On the way from the object to the beam splitter, the measuring light traverses the first optical assembly (for example the first optical subassembly and the second optical subassembly of the first optical assembly) and the second optical assembly. Furthermore, the measuring light reaches the wavefront sensor along a portion of the beam path, which is not traversed by the measuring light on the way from the beam splitter to the object. Thereby, it is for example ensured, that in the case of an eye under inspection, which has a spherical aberration, the measuring light, which illuminates the eye, is adaptable with respect of a curvature of the wavefront of the measuring light, such that the illumination spot on the retina of the eye under inspection is as small as possible. This may be performed by varying the optical path between the second optical assembly and the second optical subassembly. 
     According to an embodiment, the following relation holds: d(1,2)≧f1*d/(d−f1), wherein d(1,2) represents a distance between components of the first optical subassembly and components of the second optical subassembly and f1 represents a focal length of the first optical subassembly. The first optical subassembly and the second optical subassembly are located for example along the optical axis of the first optical assembly at a distance from each other, such that light beams, which emanate from a point in the focal region of the first optical assembly, intersect between the first optical subassembly and the second optical subassembly after having traversed the first optical subassembly. In a region of such an intersection, an intermediate image of the object region which is arranged in the focal region of the first optical assembly may be formed. d(1,2) represents a distance along an optical axis of the first optical assembly between an optical surface of a component of the first optical subassembly and an optical surface of a component of the second optical subassembly, wherein both components have an optical power different from zero and wherein both optical components are those optical components of the first and second optical subassembly, respectively, which have the smallest distance from each other. 
     According to an embodiment, the first optical subassembly comprises a fist lens group, which may comprise or consist of an objective lens; and he first optical subassembly further comprises a second lens group, which is arranged at a distance from the first lens group, wherein the microscope beam path traverses the first lens group of the first optical subassembly and wherein the third optical assembly comprises a zoom system. Thereby, the beam path of the measuring light for the wavefront sensor as well as the microscope beam path traverses the first lens group of the first optical subassembly. Thereby, it is possible to provide an optical measuring system, which allows to perform an analysis of the wavefront and at the same time optical microscopy, wherein the first lens group of the first optical subassembly is used for both purposes. Thereby, it is possible, to provide an integration of the components of the optical measuring system, which is compact in size. 
     According to an embodiment, a mirror surface, such as a mirror surface of a folding mirror is arranged in the beam path of the measuring light between the first lens group and the second lens group of the first optical subassembly. The mirror surface is provided for spatially separating the beam path of the measuring light from the microscopy beam path. 
     According to an embodiment, the second lens group of the first optical subassembly and the second optical subassembly form an afocal system. The measuring system may comprise an afocal system, which consists of the second lens group of the first optical subassembly and the second optical subassembly. The afocal system may be a Kepler telescope. By traversing an afocal system, light, which consists of plane wavefronts is transformed into light which also consists of plane wavefronts. A Kepler telescope is an optical system which consists of two lenses or lens systems. The two lenses or lens systems are arranged at a distance from each other along the optical axis, wherein the distance may correspond to the sum of the focal lengths of both lenses or lens systems. 
     According to an embodiment, the object region is located in a focal region of the first lens group of the first optical subassembly. The first lens group of the first optical subassembly may be referred to as a main objective lens of a microscopy system. Hence, the object region is located in the focal region of the main objective lens of the microscopy system. This is advantageous in case further optical components are used downstream of the main objective lens, such as a zoom system or an eye-piece. 
     According to an embodiment, the third optical assembly comprises an objective lens and a zoom system, wherein the beam path of the measuring light is free from traversals of the objective lens and wherein a mirror surface is arranged in the beam path of the measuring light between the object region and the first optical subassembly. In other words, the beam path of the measuring light does not traverse the objective lens. According to this embodiment, none of the components of the optical measuring system, mentioned so far, are provided for an analysis of the wavefront and for conducting optical microscopy. This may have the advantage that the components for an analysis of the wavefront may be designed such that they are detachably mountable on an optical microscopy system and hence may be dismounted for performing an analysis of the wavefront. Furthermore, the components may be designed such that they are mountable on different optical microscopy systems without requiring significant optical components of the optical microscopy system or without having to adapt significant optical components of the optical microscopy system. 
     According to an embodiment, the object region is located in a focal region of the objective lens. 
     According to an embodiment, the object region is different from a focal region of the first optical assembly. The object region may be located at a distance from the focal region of the first optical assembly. 
     According to an embodiment, the first optical assembly and the second optical assembly together form an afocal system, such as for example a Kepler telescope. The measuring system comprises an afocal system, which consists of the first optical assembly and the second optical assembly. 
     According to an embodiment, a beam splitter is displaceably arranged between the first optical assembly and the second optical assembly in the beam path of the measuring light. Through the beam splitter, illumination light is directable to the object region. For example, the measuring system may comprise an actuator, which is attached to the beam splitter, and which is configured to displace the beam splitter upon receiving control signals from a control unit of the measuring system. 
     According to an embodiment, a mirror surface is arranged between the first optical assembly and the object region. Thereby, the optical measuring system is combinable with a microscopy system, wherein the beam splitter decouples from the light, which is used for microscopy a portion, which forms the measuring light for wavefront analysis. 
     According to an embodiment, the measuring system for ophthalmic surgery further comprises an OCT system having an OCT light source for generating an OCT measuring light, wherein in a beam path of the OCT measuring light between the first optical assembly and the second optical assembly or between the second optical assembly and the entry region of the wavefront sensor, there is arranged an OCT beam splitter such that OCT measuring light is directed to at least the first optical assembly for illuminating the object region. In case the OCT beam splitter is arranged between the first optical assembly and the second optical assembly, the OCT measuring light is directed only through the first optical assembly and not through the second optical assembly for illuminating the object region. In case the OCT beam splitter is arranged between the second optical assembly and the entry region of the wavefront sensor, the OCT measuring light traverses the first optical assembly as well as the second optical assembly for illuminating the object region. The OCT measuring light may interact with the OCT beam splitter, wherein the interacting may for example comprise a transmitting or reflecting. The OCT beam splitter may be configured to arrange the beam path of the OCT measuring light such that it is identical, at least in a portion thereof, with the beam path of the measuring light, which is used for an analysis of the wavefront. Thereby, the measuring light, which is used for the analysis of the wavefront may traverse or be reflected by components of the system which are also traversed by OCT measuring light or at which also OCT measuring light is reflected, wherein the optical components of the system may comprise the first optical assembly. Additionally, the components may also comprise the second optical assembly. Thereby, a set-up, which is cost-effective and compact in size may be obtained. 
     Optical coherence tomography (OCT) is a method based on interferometry for obtaining structural information of an object in a volumetric portion by reflecting light at different depths of an object under examination. 
     The OCT light source may be configured to provide OCT measuring light having wavelengths in the visible and/or near infrared range of wavelengths, wherein a bandwidth of the OCT light source is adjusted such that a coherence length of the OCT measuring light, which is emitted from the OCT light source, is between several micrometers and several tenths of micrometers. A portion of the OCT measuring light, which is emitted from the OCT light source is guided along an OCT beam path which comprises mirrors, lenses and/or fiber optics to an object, which is located in the object region. The OCT measuring light penetrates into the object, depending on the wavelengths and the material within the object, to a certain penetration depth. A portion of the penetrated OCT measuring light is reflected depending on a reflectivity within the object and is superimposed on a second portion of OCT measuring light, which has been emitted from the OCT light source and which has been reflected at a reference surface. The superimposed light is detected by a detector and converted into electrical signals, which correspond to an intensity of the detected superimposed light. Due to a comparatively short coherence length of the OCT measuring light, constructive interference is only observed when a difference between the optical path which has been traveled by the OCT measuring light to and back from the object and the optical path which has been traveled by the second portion of the light, which has been emitted by the OCT light source and has been reflected by the reference surface, is less than the coherence length of the OCT measuring light. 
     Different embodiments provide different variants of an OCT system. The different variants of the OCT system are different from each other in the way, structural information is obtained from a scanning along a depth direction (axial direction) as well in the way the superimposed light is detected. According to an embodiment of a time domain OCT (TD-OCT), the reference surface, at which the second portion of light, which has been emitted by the light source, is reflected, is displaced for obtaining structural information of the object from different depths. In this case, an intensity of the superimposed light may be detected by a photo detector. 
     In Frequency-Domain-OCT (FD-OCT), the second portion of the OCT measuring light, which is emitted by the OCT light source is also reflected at a reference surface. However, the reference surface does not have to be displaced for obtaining structural information from different depths within the object. Rather, superimposed light is spectrally dispersed into spectral portions by a spectrometer, wherein the spectral portions are detected for example by a position sensitive detector, such as a CCD camera. Through a Fourier-Transform of the obtained spectrum of the superimposed light, structural information of the object along the depth direction is obtainable (Fourier-Domain-OCT). 
     Further variants of FD-OCT is Swept-Source-OCT (SS-OCT). A spectrum of superimposed light is sequentially recorded by continuously varying a mean wavelength of OCT measuring light having a very narrow band width. At the same time, the superimposed light is recorded by using a photo diode. 
     The OCT system may for example be used to inspect the structure of an anterior chamber or posterior chamber of the human eye, or the retina of the human eye. 
     According to an embodiment, the measuring system for ophthalmic surgery further comprises at least one scanning mirror, which is pivotably arranged between the OCT light source and the OCT beam splitter for scanning the OCT measuring light over the object region. The OCT system may further comprise collimating optics for collimating OCT measuring light, which is generated by the OCT light source. By pivoting the at least one scanning mirror, the collimated OCT measuring light may be guided as a focused OCT measuring beam over the object region. Thereby, structural information may be obtained from a laterally extended portion of the object region. The system may comprise more than one scanning mirror, such as two scanning mirrors, which are pivotable about different axes. 
     According to an embodiment, the at least one scanning mirror, the second lens group of the first optical subassembly and the second optical subassembly are configured and arranged to image a region close to the at least one scanning mirror onto a region close to the mirror surface. The first optical assembly comprises, as described above, the first optical subassembly and the second optical subassembly, wherein the first optical subassembly comprises a second lens group. The second lens group of the first optical subassembly and the second optical subassembly may form an afocal system for imaging a region which is located close to the scanning mirror to a region, which is located close to the mirror surface. 
     A detailed description of the design and arrangement of the scanning mirrors, the mirror surface and how the region close to the at least one scanning mirror is imaged onto the region close to the mirror surface by the first optical subassembly and the second optical subassembly is given in US 2009/0257065, the whole contents of which is incorporated herein by reference in its entirety. 
     The mirror surface is arranged between the first lens group of the first optical subassembly and the second lens group of the first optical subassembly in the beam path of the measuring light for analyzing a wavefront. The mirror surface, which is for example part of a folding mirror may reflect the measuring light such that it traverses a further lens such as an objective lens of a microscope on the path to the object region. For an optimal adjusted system, a center of the at least one scanning mirror is imaged onto a center of the mirror surface by the second lens group of the first optical subassembly and by the second optical subassembly. Such an optical imaging process has the advantage that for different pivoting positions of the at least one scanning mirror, the OCT measuring light which emanates from a point on the scanning mirror is imaged onto a point in the center of the mirror surface, i.e. without beam walk-off. Thereby, it is prevented that the OCT measuring light fails to impinge on the mirror surface. Hence, it is possible to design the mirror surface comparatively compact in size. 
     In case the system comprises two scanning mirrors, which are arranged at a distance from each other, the system may be designed and adjusted such that the point in the middle of a connecting line between the two scanning mirrors is imaged onto a center of the mirror surface, or at least onto a region which is located close to the mirror surface, such as onto a region, which is located along the OCT beam path at a distance from the center of the mirror surface at most 100 times, 10 times or 2 times of the lateral extent of the mirror surface. The lateral extent of the mirror surface may be a diameter of the mirror surface. The connecting line may be oriented along the OCT beam path of the optical system, which consists of the second lens group of the first optical subassembly and the second optical subassembly. A distance of the region from the mirror surface may depend on an optical magnification of the system, which consists of the second lens group of the first optical subassembly and the second optical subassembly, such that the distance increases with a higher magnification. This dependence may be linear. 
     A region, which is located close to the scanning mirror may comprise spatial points, which have a distance to the scanning mirrors of the system, which is smaller, for example smaller by a factor of 10, or smaller by a factor of 5 or smaller by a factor of 2, as an extent one of the scanning mirrors, which the system comprises. The extent of the scanning mirror may be a diameter of the scanning mirror. 
     A region close to the mirror surface may comprise spatial points which have a distance to the mirror surface, which is smaller in particular by a factor of 10, by a factor of 5 or by a factor of 2, as an extent of the mirror surface. The distance may be measured along the OCT beam path. The mirror surface and the OCT beam path may form an angle of between 30° and 60°. The extent of the mirror surface may for example be a diameter of the mirror surface. 
     According to an embodiment, the measuring system for ophthalmic surgery further comprises a wavefront light source for generating measuring light which is used for analyzing the wavefront, wherein at least 80% of a total intensity of the generated measuring light consists of light having wavelengths of between 800 nm and 870 nm, or of between 820 nm and 840 nm. In other words, at least 80% of a total intensity of the generated measuring lights consists of wavelengths of between 800 nm and 870 nm, or of between 820 nm and 840 nm. The measuring light may for example be generated by a superluminescence diode (SLD). Measuring light of such a wavelength is in particular suitable to traverse the human eye until the retina such that it forms an illumination spot on the retina. Then, after diffuse reflection, the light leaves the eye and is inspected in view of its form of the wavefront by the wavefront sensor. It is advantageous to use light of these wavelength ranges, since this light is not perceived by the eye of the patient, such that the patient is not blinded and the iris of the eye of the patient does not contract. A contracted iris would impair the measurement. 
     According to an embodiment, at least 80% of a total intensity of the generated OCT measuring light consists of light having wavelengths between 1280 nm and 1320 nm, or of between 1300 nm and 1320 nm. OCT measuring light of these wavelengths is in particular suitable to enter a region of the interior chamber of the eye and being reflected by this region. Thereby, structural information from the anterior chamber may be obtained. Moreover, it is possible to obtain structural information from the posterior chamber of the eye and/or the retina. 
     For examining or observing the retina by OCT, a wavelength range between 800 nm and 870 nm is well suitable, since this light reaches the retina. In this case, spectra of the wavefront light source and the OCT light source may overlap such that at least 60%, or at least 80% of an intensity of the measuring light for the analysis of the wavefront is located in a wavelength range, in which 80% of an intensity of the OCT measuring light is located. The measuring light for the analysis of the wavefront may comprise essentially the same wavelengths as the OCT measuring light. In this case, it is possible to use a single light source which generates the measuring light for the analysis of the wavefront and also the OCT measuring light. 
     According to an embodiment, a least 60%, or at least 80% of a total intensity of the measuring light consists of wavelengths, which define a wavelength range of measuring light, in which at least 80% of a total intensity of the OCT measuring light is located. 
     In other words, a spectral intensity distribution of the measuring light and a spectral intensity distribution of the OCT measuring light are configured such that in an overlapping wavelength range of these intensity distributions, at least 60% or at least 80% of a total intensity of the measuring light is located and at least 80% of a total intensity of the OCT measuring light is located. 
     According to embodiments, at least 70%, or at least 90% of the intensities of the measuring light, which is used for the wavefront analysis and the OCT measuring light are not located in overlapping wavelength ranges. In other words, at least 70%, or at least 90% of a total intensity of a spectral intensity distribution is not located in an overlapping wavelength range of the spectral intensity distribution of the measuring light and the spectral intensity distribution of the OCT measuring light. Although, the measuring light, which is used for the wavefront analysis, and the OCT measuring light traverse or interact with optical components of the measuring system for ophthalmic surgery, those measuring lights may be separated from each other, for example by dichroic elements, due to their different wavelength ranges. The optical components, with which the measuring lights interact or which are traversed by the measuring lights, may for example be the first optical assembly and optionally also the second optical assembly. Thereby, it is prevented that a measurement of the wavefront influences a measurement with the OCT-system. However, both measuring lights may comprise common wavelength ranges and their spectra may overlap to a large extent. 
     According to an embodiment, the OCT beam splitter comprises a dichroic mirror, wherein a transmission of the dichroic mirror in a wavelength range of between 800 nm and 870 nm, or of between 820 nm and 840 nm is at least twice as high or at most half as high as the transmission in a wavelength range of between 1280 nm and 1340 nm or of between 1300 nm and 1320 nm. 
     According to embodiments, at least 80% of an intensity of the measuring light for wavefront analysis or of the OCT measuring light is transmitted through the OCT beam splitter. 
     According to an embodiment, the OCT beam splitter comprises a dichroic mirror, wherein a reflectivity of the dichroic mirror in a wavelength range of between 1280 nm and 1340 nm, or of between 1300 nm and 1320 nm is at least twice as high or at most half as high as a reflectivity in a wavelength range of between 800 nm and 870 nm, or of between 820 nm and 840 nm. 
     According to an embodiment, at least 80% of an intensity of the measuring light for wavefront analysis or of the OCT measuring light is reflected by the OCT beam splitter. 
     The dichroic mirror may be coated with layers of materials having different dielectric constants. These layers may be configured such that constructive interference is generated for the reflected measuring light or the transmitted measuring light in case the measuring light impinges onto the dichroic mirror. 
     According to an embodiment, a major part, or at least 70% of an intensity of OCT measuring light which impinges onto the OCT beam splitter is reflected at the OCT beam splitter. Additionally or alternatively, a major part, or at least 70% of an intensity of measuring light for wavefront analysis, which impinges onto the OCT beam splitter, is transmitted through the OCT beam splitter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The forgoing as well as other advantageous features of the invention will be more apparent from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. It is noted that not all possible embodiments of the present invention necessarily exhibit each and every, or any, of the advantages identified herein. 
         FIG. 1A  schematically illustrates an embodiment of an optical measuring system, wherein an illumination beam path or wavefront beam path, respectively, is illustrated; 
         FIG. 1B  schematically illustrates the embodiment, which is illustrated in  FIG. 1A , wherein an object beam path is illustrated; 
         FIG. 1C  schematically illustrates a section of the embodiment illustrated in  FIGS. 1A and 1B  of an optical measuring system; 
         FIG. 2A  schematically illustrates a further embodiment of an optical measuring system, wherein an illumination beam path or wavefront beam path, respectively, is illustrated; 
         FIG. 2B  chematically illustrates the embodiment, which is illustrated in  FIG. 2A , wherein an object beam path is illustrated; 
         FIG. 3  chematically illustrates a further embodiment of an optical measuring system; 
         FIG. 4  schematically illustrates a further embodiment of an optical measuring system; 
         FIG. 5A  schematically illustrates a further embodiment of an optical measuring system, wherein an illumination beam path or wavefront beam path, respectively, is illustrated; 
         FIG. 5B  schematically illustrates the embodiment, which is illustrated in  FIG. 5A , wherein an object beam path is illustrated; 
         FIG. 6  shows an optical measuring system according to a further embodiment, wherein an OCT beam path is illustrated; and 
         FIG. 7  shows an optical measuring system according to a further embodiment, wherein an OCT beam path is illustrated. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the invention should be referred to. 
       FIG. 1A  schematically illustrates an optical measuring system  1  according to an embodiment. Measuring system  1  comprises a light source  3 , which generates measuring light  5 . Measuring light  5  is collimated by collimating optics  7  for generating measuring light  9 , which substantially consists of plane wavefronts. Measuring light  9  is reflected at the beam splitter  11  and traverses cemented element  13 . The measuring light, which is converged by cemented element  13  passes through aperture  15  and is deflected by 180° by reflector  17  which comprises two mirror surfaces  17 ′ and  17 ″, which are oriented orthogonal to each other. Thereby, measuring light  9  is deflected in a substantially reverse direction and displaced in a lateral direction, i.e. in a direction which is perpendicular to a propagation direction of the measuring light  9 . 
     In further embodiments, the reflector  17  may be a corner cube. The corner cube comprises a body made of glass, having the form of a three-sided pyramid. The outer surfaces of the pyramid consists of isosceles, right-angled triangles, wherein each pair of these triangles is oriented perpendicular to each other. Furthermore, the corner cube comprises a basis surface, which is in the form of an equilateral triangle. In case the corner cube is used in the measuring system, the measuring light  9  is reflected at the three isosceles, right-angled, triangular surfaces. 
     The reflector  17  is displaceable in directions which are denoted by the double arrow  20 . The aperture  15  is arranged in a focal region of the cemented element  13 , wherein the position of the cemented element is independent of a displacement position of the reflector  17 . 
     The measuring light  9 , which is reflected by the reflector  17 , traverses a cemented element  19 , whereby convergent measuring light is formed. In the plane  21 , the measuring light  9  is substantially converged to a point, a crossover, and continues as a divergent measuring light. The divergent measuring light  9  traverses a further cemented element  23  and is transformed into plane wavefronts. The plane measuring light  9  traverses a quarter wave plate  24  and impinges onto an eye  25  in the form of a plane wavefront. The pupil of the human eye  25  is located in the object plane  28 . The image of the iris is referred to as the pupil of the eye  25 . Typically, the pupil is located about 2.7 to 3 mm behind the vertex of the cornea  33 . In this embodiment, the object plane  28  is located at the focal plane  29  of the first optical assembly  31 , which consists of the cemented element  23  and the cemented element  19 . Hence, the pupil of the eye  25  is located in the focal plane  29 . 
     The reflector  17  may be configured to be displaceable or movable along a direction, which is parallel to the optical axis of the first optical assembly ( 31 ) and/or the optical axis of the second optical assembly ( 13 ). In particular, the reflector may be configured such that it is displaceable or movable forward and backward parallel to the optical axis of the first optical assembly ( 31 ) and/or the optical axis of the second optical assembly ( 13 ). 
     Measuring light  9  traverses the cornea  33  and the lens  35  of the eye  25 , and is focused onto a spot  37  on the retina  39 . At the beam splitter  11 , the measuring light consists of plane wavefronts, i.e. of a bundle of parallel light ray beams. Measuring light is imaged onto a spot  37  on the retina of the eye  25  when the optical components are at a fixed position relative to each other only in case of an emmetropic eye having no spherical aberration. In this case, the reflector is positioned such that the total system consisting of the three optical assemblies  23 ,  19  and  13  is an afocal system. However, in case the eye has a spherical aberration, it is possible to displace the reflector  17  or the corner cube  17 , respectively, along a direction, which is indicated by double arrow  20 , for generating slightly convergent measuring light  9  or slightly diverging light  9 , which is incident on the eye  25 . Thereby, it is possible, even in case the eye has a spherical aberration, to generate an illumination spot of the measuring light on the retina, which is as small as possible. By displacing the corner cube  17  along a direction, which is indicated by double arrow  20 , an optical path of the measuring light between the cemented element  13  and the cemented element  19  is varied. Therefore, in case of a spherical aberration of the eye  25  being within a certain range, measuring light  9  is focusable on a point on the retina  39  of the ametropic eye  25 . 
     The illumination spot  37  is a diffuse light source on the retina  39  of the eye  25  which emits light  41 , which consists of substantially spherical wavefronts. Light  41  traverses the vitreous body, the lens  35  and the cornea  33  and forms light  43 . Depending on optical properties and the shape of the lens  35  and the cornea  33 , a wavefront of the light  43  deviates from a plane wavefront. The form of the wavefronts, which form light  43 , is indicative of an ametropia of the optical components or the interfaces of the eye  25 , i.e. for example of the optical properties and the form of the lens  35  and the cornea  33 . 
     Light  43  traverses cemented element  23  and forms convergent light. In a spatial region of the plane  21 , in which an image of the retina is formed, light  43  is converged to a minimum extent and thereafter diverges. Furthermore, measuring light  43  traverses cemented element  19 , is reflected and laterally displaced by reflector  17 , passes aperture  15 , traverses cemented element  13  and forms light, which substantially consists of plane wavefronts. A deviation of the wavefronts of the measuring light  43  from plane wavefronts is indicative of an ametropia of the eye  25 . 
     Measuring light  43  enters the entry region  45  of a Hartmann-Shack sensor  47 . The entry region  45  is formed by an array of microlenses, wherein in a common focal plane of the microlenses, an electronic imaging sensor such as a chip of a CCD camera is arranged. The electronic imaging sensor comprises a plurality of pixels, each of which converts intensity values of incident light into electrical signals. The electrical signals are transmitted via data line  49  to a processing unit, which is not illustrated. For each of the microlenses of the array of microlenses of the Hartmann-Shack sensors  47 , the processing unit determines a displacement position of the light, which is focused by the respective microlens. Thereby, a form of a wavefront of the measuring light  43  in the entry region  45  of the Hartmann-Shack sensor is determinable. With reference to  FIG. 1B , it is described, that a region of the focal plane  29  is imaged onto the entry region  45  of the Hartmann-Shack sensor  47 . Thereby, a form of a wavefront of light  43 , which is emitted from the eye  25  is determinable. With reference to  FIG. 1B , further properties and advantages of the optical measuring system  1  are described. The pupil of the eye  25  in the object plane  28  is arranged in the focal plane  29  of the first optical assembly  31 , which consists of the cemented elements  23  and  19 . Three light beams  53   a ,  53   b ,  53   c , emanate from a focal point  53  in the focal plane  29  along the object beam path, traverse the quarter wave plate  24  and the cemented element  23  and are converged to a minimum extent in an intermediate image region  55 . Beams  53  emanate from the intermediate image region  55  as divergent beams, traverse cemented element  19  and exit the cemented element  19  as substantially parallel beams  53   a ′,  53   b ′,  53   c ′. The parallel beams  53   a ′,  53   b ′,  53   c ′ are reflected and laterally displaced by reflector  17 , pass the aperture  15 , traverse cemented element  13  and are focused to a point after having traversed the beam splitter  11 . This point is defined by the optical axis of the measuring system  1  and the entry region  45  of the Hartmann-Shack sensor  47 . Thereby, a point in the focal plane  29  is imaged onto a point in the entry region  45  of the Hartmann-Shack sensor  47 . Displacement of the corner cube  17  along a direction, which is indicated by double arrow  20  does not modify this imaging properties, since light beams, which emanate from a point in the focal plane  29  are oriented parallel between cemented element  19  and cemented element  13 , where the reflector  17  is arranged in the beam path. Hence, a form of a wavefront, which exits from an ametropic or emmetropic eye may be inspected with high precision. 
       FIG. 1C  schematically illustrates a portion of the optical measuring system  1  of the schematically illustrated embodiment of  FIGS. 1A and 1B . The light beams  53   a ,  53   b  and  53   c  emanate from the focal point  51 , traverse cemented element  23  and are focused onto the intermediate image region  55 . From the intermediate image region  55 , three light beams emanate and are deflected by cemented element  19  such that three parallel light beams  53   a ′,  53   b ′ and  53   c ′ are formed, which run parallel to the optical axis  10 . Cemented elements  23  and  19  form the first optical assembly  31 , as described above. A focal length f of the first optical assembly  31  may be determined as described in the following: 
     The light beam  53   a ′, which is parallel to the optical axis  10  is extended in a direction towards the focal plane  29  and beyond the focal plane  29  such as illustrated by dashed line  55   a ′. Accordingly, the light beam  53   b , which is incident on the first optical assembly  31  and which is transformed into beam  53   a ′ after having traversed the optical system  31 , is extended beyond focal plane  29 , such as illustrated by dashed line  55   a . The line  55   a  and the line  55   a ′ intersect in a point  57   a . The point  57   a  is located in a principal plane  59  of the first optical assembly  31 . The principal plane  59  is located at a distance f away from the focal plane  29 , which is parallel to the principal plane  59 . In the principal plane, there is also located point  57   c , which is analog to point  57   a , wherein the point  57   c  is defined by the intersection of lines  55   c ′ and  55   c . Hence, light beams  53   a  and  53   c  appear to be refracted at points  57   a  or  57   c , respectively, which are located in the principal plane  59 . After having traversed the first optical assembly  31 , light beams  53   a  and  53   c  run parallel to the optical axis. 
     The light beams  53   a ′,  53   b ′ and  53   c ′ are reflected by corner cube  17 , as schematically illustrated, and are focused by cemented element  13  onto the entry region  45  of the wavefront sensor  47 . The entry region  45  is formed by those surfaces of the microlenses  46 , which are located closest to the cemented element  13 . An object region  28 ′ in the object plane  28  in the focal plane  29  of the first optical assembly  31  is therefore imaged onto the entry region  45  of the wavefront sensor  47 . Each of the microlenses  46  has a focal length  1 . At a distance  1  from the entry region  45  of the wavefront sensor  47 , there is arranged a CCD  48  for a position sensitive detection of light intensities. As described above, a detection of a distribution of light intensities and an analysis thereafter allows to determine a form of a wavefront of the measuring light, which emanates from the object region  28 ′. The object region  28 ′ in the focal plane  29  of the first optical assembly  31  is located at a distance d away from an optical surface of the first optical assembly  31 , wherein this optical surface is the optical surface which is closest to the focal region  29 . In the exemplary embodiment, which is illustrated, the distance d is about 2.5 times the focal length f of the first optical assembly  31 . 
     The optical measuring system  1  is especially suited for eye surgery, such as for example cataract surgery. The cornea or the pupil of the eye under surgery is arranged at the object region  28 ′. The distance d between the cornea or the pupil of the eye under inspection and a component of the first optical assembly  31  is 220 mm in the exemplary embodiment  1 . Hence, the surgeon has enough working space for performing surgical operations with his hands. 
     The embodiment  1  of an optical measuring system, as illustrated in  FIGS. 1A ,  1 B and  1 C, may be mounted at a fixed position relative to an optical microscopy system. For example, the optical measuring system is supported upstream of the objective lens of the optical microscopy system in a beam path of measuring light which emanates from the object under inspection. In this embodiment, measuring light  43 , which emanates from the object region  28 ′, may be reflected by a folding mirror  61 , which is schematically indicated. After reflection at the folding mirror  61 , the measuring light is incident on the entry region  45  of the wavefront sensor  47  after having traversed the first optical assembly  31  and being reflected at the corner cube  17  and having traversed the cemented element  13 . In  FIGS. 1A and 1B , the position of the folding mirror  61  is indicated. Another part of the light, which emanates from the object region  28 ′ is guided through an objective lens of the microscopy system for performing microscopic imaging. Therefore, it is possible for a surgeon to obtain a microscopic image of an object under surgery as well as to conduct an analysis of a form of a wavefront of measuring light, which emanates from the object region  28 ′. According to embodiments, the folding mirror  61  is located close to the objective lens of the microscopy system. Thereby, a free working space is reduced as little as possible. 
       FIGS. 2A and 2B  schematically illustrate a further embodiment  1   a  of an optical measuring system. Some components of the optical measuring system  1   a  are analog to components of the optical measuring system  1 , which is illustrated in  FIGS. 1A ,  1 B and  1 C. Thereby, for a detailed description of these components, it is referred to the corresponding description of the embodiment  1 . For example, cemented elements  19   a  and  13   a  of the embodiment  1   a  correspond to cemented elements  19  and  13  of the embodiment  1 . Furthermore, light source  3 , collimating optics  7  and wavefront sensor  47  of the embodiment  1  correspond to light source  3   a , collimating optics  7   a  and wavefront sensor  47   a  of the embodiment  1   a.    
     Unlike embodiment  1  of the optical measuring system, which is illustrated in  FIGS. 1A ,  1 B and  1 C, and which comprises cemented element  23 , the embodiment  1   a , which is illustrated in  FIGS. 2A and 2B  comprises a lens group  23   a  which consists of lens system  63   a  and lens system  65   a . Furthermore, embodiment  1   a  does not comprise a reflector  17  or a corner cube  17 , respectively, as is the case for embodiment  1 . Rather, aperture  15   a , cemented element  13   a , beam splitter  11   a , collimating optics  7   a , light source  3   a  and the wavefront sensor  47   a  are arranged at a fixed position relative to each other and may together be displaceable in a direction along the optical axis  10   a  of the measuring system  1   a . This is illustrated by the dashed box  67   a , which is displaceable along directions, which are indicated by the double arrow  69 . As is explained with reference to embodiment  1 , which is illustrated in  FIGS. 1A ,  1 B and  1 C, a variation of the optical path between cemented elements  19  and  13  or  19   a  and  13   a , respectively, of the measuring light, which is incident on the object region  28 ′, as well as measuring light  43 , which emanate from the object region  28 ′ allows a compensation of a spherical aberration of an eye under inspection  25 . The compensation effects the illumination as well as the analysis of the wavefront of the measuring light, which exits the eye  25 . Thereby, a dynamic measuring range of the wavefront sensor  47  may be extended. 
     Instead of providing a displaceable unit  67   a  for this purpose in the embodiment, there may be provided an arrangement by using a reflector  17  or a corner cube  17 , respectively, as is illustrated in  FIGS. 1A and 1B  in a corresponding way. Accordingly, the embodiment  1  of the optical measuring system, as illustrated in  FIGS. 1A ,  1 B and  1 C may not comprise a reflector  17 . Instead, the components aperture  15 , cemented element  13 , beam splitter  11 , collimating optics  7 , light source  3  and wavefront sensor  47  may be supported at a fixed position relative to each other and are designed to be displaceable together along the optical axis  10 , such as it is illustrated in  FIGS. 2A and 2B  in a corresponding way. These components also may be designed not to be displaceable. In case these components are not displaceable, there is provided a wavefront sensor  47  having a large dynamic range since in this case a pre-compensation is not possible when eyes having a spherical aberration are inspected. 
     In the object region  28 ′ in the object plane  28   a  within the focal plane  29   a , the cornea  33  or the pupil of an eye  25  of an emmetropic eye without spherical aberration is arranged. The light  5   a , which is generated by the light source  3   a  is transformed by collimating optics  7   a  into measuring light  9 , which substantially consists of plane wavefronts. Measuring light  9  is incident as plane wavefront on the eye  25  after having been reflected by beam splitter  11   a , having traversed cemented element  13   a , having passed aperture  15   a , having passed the cross-over, having traversed cemented element  19   a , having passed the cross-over of the measuring light  9  in plane  21   a , having traversed lens system  65   a  and having traversed lens system  63   a . The ametropic eye, having no spherical aberration, focuses measuring light  9  onto a point  37  of the retina  39  of the eye  25 . From point  37 , spherical wavefronts emanate and exit the eye as measuring light  43  having plane wavefronts in the object region  28 ′ after having traversed the vitreous body, the lens  35  and the cornea  33 . Measuring light  43  traverses lens system  63   a , traverses lens system  65   a , traverses cemented element  19   a , traverses cemented element  13   a  and traverses beam splitter  11   a  and is incident on the wavefront sensor  47   a . There, the CCD detector, which is not illustrated, records distribution of light for determining a form of a wavefront of measuring light  43  which emanates from the object region  28 ′. 
     The working distance d between the object region  28 ′ and a surface of the lens system  63   a , which is located closest to the object region  28 ′ is about three times as large as the focal length f of the first optical assembly  31   a , which consists of the lens system  63   a , lens system  65   a  and cemented element  19   a . Thereby, embodiment  1   a  of the optical measuring system provides a sufficiently large working distance d for providing sufficient free working space for performing surgical operations. 
       FIG. 2B  illustrates embodiment  1   a  of the optical measuring system, wherein an object beam path, i.e. a beam path, which emanates from object plane  28   a , is illustrated for demonstrating further properties of the measuring system  1   a . The pupil of the eye  25  is arranged in the object plane  28  in the illustrated example of using the optical measuring system  1   a  for examining the eye  25 . Therefore, the object beam path corresponds to a pupil beam path. Light beams  53   a ,  53   b  and  53   c , of light  43 , which emanate from a focal point  51   a  are transformed by lens system  63   a  into light beams  53   a ″,  53   b ″ and  53   c ″, each of which runs parallel to the optical axis  10   a  of the optical measuring system  1   a . The focal point  51   a  is also located in the object region  28   a ′. Hence, the distance between the principal plane  63   a ′ of the lens system  63   a  and the object region  28   a ′ is equal to the focal length f ( 63   a ) of the lens system  63   a . The focal length f ( 63   a ) of the lens system  63   a  substantially corresponds to a working distance d between the object region  28   a ′ and a surface of the lens system  63   a , which is located closest to the object region  28   a ′. Lens system  65   a  and cemented element  19   a  are arranged at a distance along the optical axis  10 , which correspond to a sum of their focal length, i.e. f( 65   a )+f( 19   a ). Thereby, the lens system  65   a  and the cemented element  19   a  form a so-called Kepler telescope. The Kepler telescope is an example of an afocal system, which transforms incident parallel light beams into outgoing parallel light beams. Accordingly, the parallel light beams  53   a ″,  53   b ″ and  53   c ″ are transformed by lens system  65   a  and cemented element  19   a  into parallel light beams  53   a ′,  53   b ′ and  53   c ′. After light beams  53   a ′,  53   b ′ and  53   c ′ have traversed cemented element  13   a , they are focused onto the entry region  45   a  of the wavefront sensor  47   a . Thereby, the object region  28   a ′ is imaged onto the entry region  45   a  of the wavefront sensor. Since the light beams between the cemented element  19   a  and the cemented element  13   a  are parallel, such an imaging is independent from a modification of the optical path of the measuring light between the cemented elements  19   a  and  13   a . Such a modification is achieved by displacing the system  67   a , along directions, which are indicated by arrow  69 . 
       FIG. 3  shows a further embodiment  1   b  of an optical measuring system. The structure and the orientation of the elements  63   b ,  65   b ,  19   b ,  13   b ,  11   b ,  7   b ,  3   b  and  47   b , relative to each other, substantially correspond to the structure and the relative arrangement of the elements  63   a ,  65   a ,  19   a ,  13   a ,  11   a ,  7   a ,  3   a  and  47   a , respectively, which are illustrated in  FIGS. 2A and 2B . Compared to the embodiment illustrated and described so far, the optical measuring system  1   b  comprises further lens elements  71 ,  73  and  75 , which are arranged in this order between the object region  28   b ′ in the focal plane  29   b  of the first optical assembly  31   b  which consists of the lens system  63   b , the lens system  65   b  and the cemented element  19   b . The lens element  71  comprises a focal length of 40 mm, the lens element  73  comprises a focal length of 18.5 mm and the lens element  75  comprises a focal length of 75 mm. These lens elements  71 ,  73  and  75  are arranged to inspect an aphakic eye  25 , i.e. an eye, the lens of which has been removed and which is therefore omitted in  FIG. 3 . Light beams  43   a ,  43   b  and  43   c  are illustrated, which diverge from a point  37  of the retina  39  of the eye  25  and exit the eye  25 . In the illustrated embodiment, the aphakic eye has 19 diopters. The divergent light beams  43   a ,  43   b  and  43   c , which emanate from the object region  28   b ′ and which represent spherical wavefronts, are imaged by the optical imaging system of the optical measuring system  1   b  as parallel wavefronts onto the entry region  45   b  of the wavefront sensor. Thereby, it is possible by inserting the lens elements  71 ,  73  and  75 , to further increase the dynamic measuring range of the wavefront sensor  47 , such that even aphakic eyes may be inspected in view of spherical and non-spherical aberrations. Lens elements  71 ,  73  and  75  may also be provided in embodiments, which are illustrated in  FIGS. 1A ,  1 B,  1 C,  2 A and  2 B. 
       FIG. 4  illustrates a further embodiment  1   c  of an optical measuring system. The optical measuring system  1   c  comprises a wavefront analysis system  77  and an optical microscopy system  79 . Many of the components of the wavefront analysis system  77  have a similar structure and a similar relative orientation as the optical measuring system  1   a , as shown in  FIGS. 2A and 2B . A detailed description of these components is therefore omitted. The lens system  63   a  of the optical measuring system  1   a  is also an objective lens  63   c  of the optical microscopy system  79  in the optical measuring system  1   c . In the embodiment, shown in  FIG. 4 , the objective lens  63   c  has a diameter of 53 mm. Light beams  43   a ,  43   b  and  43   c , which emanate as parallel beams from the object region  28   c ′ in the focal plane  29   c  of the first optical assembly  31   c , which consists of the lens system  19   c , the lens system  65   c  and the objective lens  63   c , and which therefore form plane wavefronts, are incident on the wavefront sensor  47   c  as plane wavefronts after having traversed the first optical assembly  31   c , the cemented element  13   c  and the beam splitter  11   c . Parallel light beams, which emanate from the object region  28   c ′ and which therefore do not represent plane wavefronts, are incident on the wavefront sensor  47   c  as non-plane wavefronts. As described above, a form of such non-plane wavefronts may be determined by detecting an intensity distribution by the wavefront sensor  47   c  and by a subsequent analysis. 
     Furthermore, the optical measuring system  1   c  allows to acquire microscopic images of the object region  28   c ′. From a point  51  in the object region  28   c ′ in the focal plane  29   c  of the first optical assembly  31   c  (and the objective lens  63   c ), light beams  81  and  83  emanate. Light beams  81  and  83  form a stereo angle α. Light beams  81  traverse a region  85  of the objective lens  63   c  and light beams  83  traverse a region  87  of the objective lens  63   c  and thereafter propagate as parallel light beams. Then, light beams  81  traverse a zoom system  89  and light beams  83  traverse a zoom system  91 . Downstream of the objective lens,  63   c , there may be located an ocular system and/or a camera for imaging the object region  28   c ′ into an image region. 
     In the illustrated embodiment, the distance d between a surface, which is located closest to the object region  28   c ′ of the objective lens  63   c  and the object region  28   c ′ amounts to 20 cm. In the illustrated embodiment, this distance corresponds to the focal length f( 63   c ) of the objective lens. Further embodiments comprise an objective lens having a focal length of 15 cm or 25 cm. A focal length f of the optical assembly  31   c , which consists of the lens system  19   c , lens system  65   c  and the objective lens  63   c , amounts to about 70 mm in the illustrated embodiment. Thereby, a sufficiently large working space is provided for conducting a surgical operation, wherein the focal length f is much smaller. 
     In the embodiment  1   c  of the optical measuring system, which is illustrated in  FIG. 4 , light rays  43   a ,  43   b  and  43   c , which are used for an analysis of the wavefront, traverse the objective lens  63   c  of the optical microscopy system  79 . The objective lens  63   c  is traversed in a region  86  of the objective lens  63   c , which is different from the regions  85  and  87  through which light beams  81  and  83  pass, which are used for microscopic imaging. Light beams  43   a ,  43   b  and  43   c , which are used for an analysis of the wavefront, are decoupled from further components of the optical microscopy system  79  by folding mirror  61   c.    
     As an alternative to this method of decoupling, light beams  43   a ,  43   b  and  43   c  may be decoupled between the object region  28   c ′ and the objective lens  63   c  of the optical microscopy system  79  through a folding mirror  61 , which is indicated by a dashed line. Thereby, embodiment  1  of an optical measuring system, which is illustrated in  FIGS. 1A ,  1 B and  1 C, may be combined with the optical microscopy system  79  or with the embodiment  1   d , which is illustrated in  FIGS. 5A and 5B . This is illustrated in  FIGS. 1A ,  1 B,  5 A and  5 B by folding mirror  61 . 
     Instead of simultaneously displacing the components, which are surrounded by box  67   c  of the wavefront analysis system  77 , the optical path between lens system  19   c  and cemented element  13   c  may be varied by providing a displaceable corner cube  17 , such as is illustrated in  FIGS. 1A and 1B . This way of pre-compensation of a spherical aberration of an eye under inspection may be used in combination with the decoupling of measuring light  47  with folding mirror  61   c  as well as the decoupling of the measuring light  43  by using folding mirror  61 . 
     The optical measuring system  1   c  provides to the surgeon a microscopic image of the anterior chamber of the eye and at the same time allows to analyze a wavefront of measuring light which is emitted from the eye. Thereby, an accurate measurement of a refraction is possible by using the wavefront sensor. Due to the large working space, the wavefront analysis system does not have to be removed during the surgical operation and does not have to be inserted in case it is needed. Thereby the handling is significantly simplified and the wavefront analysis system does not need to be pivotably supported. 
     The object region  28   c ′ is also located in the focal plane of the objective lens  63   c . Downstream of the objective lens  63   c , light beams  81  and  83  which emanate from a point  51  of the object region  28   c ′, are parallel, which result in further advantages for the subsequent components and the microscopic imaging. In the wavefront analysis system  77  of the optical measuring system  1   c , further lens elements  71 ,  73  and  75  may be provided in an analogy to the embodiment  1   b  of an optical measuring system, which is illustrated in  FIG. 3 , for analyzing wavefronts, which exit from an aphakic eye. Therefore, it is possible, to inspect eyes having spherical aberrations of 14 diopters, 19 diopters, 24 diopters and values therebetween. In case the lens elements  71 ,  73  and  75  are not provided, eyes having spherical aberrations of at least in the range between −5 dpt and +5 dpt may be inspected by varying the optical path between elements  13  and  19 ,  13   a  and  19   a , or  13   c  and  19   c , respectively. 
     The Kepler telescope, which is formed by the lens system  65   a  and the cemented element  19   a , which is illustrated in  FIGS. 2A and 2B , may be replaced by a Galilei telescope or another afocal system. 
     According to an embodiment, the entry region of the wavefront sensor has an extent of 6.34 mm*6.34 mm. In alternative embodiments, other extents may be provided. The light source  3 ,  3   a ,  3   b  and  3   c , respectively, typically comprises a superluminescence diode and acts as a point light source. Also, the optical measuring system  1   c  may be designed such that an optical path is variable for a pre-compensation of a spherical aberration. Optical elements, which interact with a polarization of light such as for example quarter wave plates or a beam splitter, which is configured as a polarization beam splitter, may be used for separating the reflected light, which is generated at optical surfaces from measuring light, which emanates from the illumination spot  37  on the retina  39 . 
       FIGS. 5A and 5B  schematically illustrate a further embodiment of an optical measuring system  1   d . Again, in  FIG. 5A , an illumination beam path or a wavefront beam path is illustrated and in  FIG. 5B , an object beam path is illustrated. The optical measuring system  1   d  comprises a first optical assembly  31   d , which in this embodiment is a cemented element, a second optical assembly  13   d  which in this embodiment is a cemented element and a wavefront sensor  47   d.    
     For illuminating the eye  25 , the optical measuring system  1   d  further comprises a light source  3   d , which emanates light  5   d . Light  5   d  is converted by beam shaping optics  7   d  into convergent measuring light  9  and focused into the region of the aperture  12   d  after being reflected at the beam splitter  11   d . In case an emmetropic eye is inspected, aperture  12   d  is arranged in a focal plane of cemented element  31   d . After having traversed the cemented element  31   d , measuring light  9  substantially comprises plane wavefronts which are incident on the eye  25 . After having traversed the cornea  33 , the natural lens  35 , measuring light  9  is focused onto a point  37  of the retina  39 . 
     Light  41  emanates from point  37  and form measuring light  43  after having traversed the natural lens  35  and the cornea  33 . In case of an emmetropic eye, measuring light  43  substantially consists of plane wavefronts. The pupil of the human eye is arranged in the object plane  28   d  in the object region  28   d ′. The distance between the object plane  28   d  and the cemented element  31   d  is denoted as distance d and the focal length of the cemented element  31   d  is denoted as distance f in  FIG. 5A . Measuring light  43 , which emanates from the object region  28   d ′ traverses cemented element  31   d , passes the cross-over in a plane of the aperture  12   d , traverses beam splitter  11   d , traverses cemented element  13   d  and impinges onto the entry region  45   d  of the wavefront sensor  47   d  as plane wavefronts in case of an emmetropic eye. 
     Cemented element  31   d  and cemented element  13   d  form an afocal system, such as for example a Kepler system. For achieving this, the cemented element  31   d  and the cemented element  13   d  are arranged at a distance along the optical axis  10   d , wherein the distance corresponds to the sum of the focal length of the cemented element  31   d  and the cemented element  13   d.    
     Through displacing of the component along the optical axis  10   d  which are surrounded by box  14   d , as indicated by double arrow  16   d , (i.e. the light source  3   d , the beam shaping optics  7   d , the beam splitter  11   d  and the aperture  12   d ), it is possible even in case an eye having a spherical aberration is investigated, to generate an illumination spot  37  which has a small extent on the retina  39  of the eye  25 . In this case, measuring light  43 , which emanates from the object region  28   d ′ does not consists of substantially plane wavefronts. Therefore, it is possible for the wavefront sensor  47   d , which is used in embodiment  1   d , to measure wavefronts having a comparatively small curvature. 
       FIG. 5B  illustrates an object beam path of the optical measuring system  1   d . Light beams, which emanate from a point  28   d ″ in the object region  28   d ′ in the object plane  28   d  traverse cemented element  31   d , beam splitter  11   d  and cemented element  13   d  and impinge onto a point  45   d ′ in the entry region of the wavefront sensor  47   d . It is obvious that the distance d between cemented element  31   d  and the object plane  28   d  is much larger than the focal length f of the cemented element  31   d.    
     The optical measuring system  1   d  may comprise a folding mirror  61 , which allows to combine the optical measuring system  1   d  with an optical microscopy system  79 , as illustrated in  FIG. 4 . In  FIG. 4 , the position of the folding mirror  61  is schematically indicated. 
       FIG. 6  schematically illustrates an optical measuring system  1   e  according to an embodiment. The optical measuring system  1   e , as illustrated in  FIG. 6 , is configured to inspect an object region  28   e ′ by an analysis of a wavefront which emanates from an object region and by optical coherence tomography (OCT). To this effect, the measuring system  1   e , as illustrated in  FIG. 6 , comprises in addition to the measuring system  1 , as illustrated in  FIGS. 1A and 1B , an OCT system  93  and an OCT beam splitter  95 . The OCT system  93  comprises OCT components  97 , which comprise an OCT light source for generating OCT measuring light  99 , an optical coupler for dividing and combining OCT measuring light, a reference mirror, a spectrometer, a position sensitive detector and an analysis system. 
     The OCT light source emits OCT measuring light  99  which traverses collimating optics  101  and enters as collimated OCT measuring light beam a scanner, which comprises two scanning mirrors  103  and  105 . The scanning mirrors  103 ,  105  are pivotable about axes, which are oriented perpendicular to each other for scanning OCT measuring light  99  over the object region  28   e ′. For illustrative purposes, the elements  97 ,  101  and  103  are illustrated in  FIG. 6  as being tilted about the connecting line between the two scanning mirrors  103  and  105 . The OCT measuring light  99  may comprise as a major part wavelengths of light between 1290 nm and 1330 nm. 
       FIG. 6  shows in an exemplary way three light beams of OCT measuring light which are reflected at a point A of the scanning mirror  105  when the scanning mirror is positioned at three different pivoting positions which are obtained by pivoting the pivoting mirror about a pivoting axis which is oriented perpendicular to the paper plane and which intersects point A. The light beams of OCT measuring light  99  are incident on the OCT beam splitter  95  which comprises a dichroic mirror  96 . The dichroic mirror  96  comprises layers which are deposited on a mirror surface of the dichroic mirror  96 , wherein the layers have different dielectric properties for reflecting the incident OCT measuring light  99  with a high effectivity and to transmit only a small portion, such as less than 30%. The OCT measuring light  99  traverses the lens  19   e  after having been reflected at the dichroic mirror  96 . For example, the lens  19   e  may be designed as a cemented element and an additional individual lens. Then, the OCT measuring light  99  traverses cemented element  23   e . Cemented element  23   e  and lens  19   e  form the first optical assembly  31   e . The first optical assembly  31   e  images the point A in the center of the scanning mirror  105  onto a point A′ between the first optical assembly  31   e  and the object region  28   e ′, in which the focal point  51   e  of the first optical assembly  31   e  is located. Similarly, a point P in the center of the connecting line between the scanning mirror  103  and the scanning mirror  105  is imaged by the first optical assembly  31   e  onto a point P′. At this position, an optional folding mirror  61  may be located for deflecting OCT measuring light  99 , which propagates towards the object region  28   e ′ and OCT measuring light, which returns from the object region  28   e ′. This may be advantageous in case the optical measuring system  1   e  is used in combination with an optical microscope. In this case a folding mirror  61  may be arranged in the beam path of the microscope between the main objective lens of the microscope and the object region  28   e′.    
     In such a case, it may be advantageous that the optical measuring system  1   e  images the point P onto the point P′, which is located on the folding mirror  61 , since for different pivoting positions of the mirrors  103 ,  105 , a walk-off of the point P′ from the center of the folding mirror  61  is minimized. Hence, it is possible to design the folding mirror  61  compact in size such that vignetting of the beam path of the microscope is prevented. In order to achieve this, all scanning mirrors of a scanner (in this case the scanning mirrors  103  and  105 ) have to be arranged as close as possible to the point P and the folding mirror  61  has to be located as close as possible to the point P′. 
     The three light beams of OCT measuring light which correspond to three different pivoting positions of the scanning mirror  105  are incident at the three different points within the object region  28 ′ at which they interact with the object, which is arranged in the object region  28   e ′. In  FIG. 6 , there are shown only three scanning points. However, by continuously pivoting the scanning mirrors  103 ,  105  the entire object region  28   e ′ is scanned. 
     OCT measuring light, which emanates from the object region  28   e ′ has been reflected at different layers within the object and thereby contains structural information of the object under inspection. The reflected OCT measuring light  100  traverses cemented element  23   e , lens  19   e  and a major part is reflected at the dichroic mirror  96  of the OCT beam splitter  95 . After further reflections at the scanning mirrors  105 ,  103 , the returning OCT measuring light traverses collimating optics  101  and enters an optical fiber of the OCT components  97 , which is not illustrated. Then, the returning OCT measuring light is superimposed on reference light and spectrally dispersed by a spectrometer and detected by a position sensitive detector. A spectrum of the returning OCT measuring light, which is interferometrically superimposed on reference light, is processed for obtaining structural information from the lateral object region  28   e ′ of the object under inspection along a depth direction, i.e. perpendicular to the object plane  28   e.    
     Such as the embodiment  1  of an optical measuring system, as illustrated in  FIGS. 1A and 1B , also the optical measuring system  1   e , as illustrated in  FIG. 6 , comprises components for analyzing a wavefront, as described above. For simplicity of illustration, in  FIG. 6 , a beam path of measuring light  9 , which is guided towards the object region  28   e ′ through cemented element  13   e , lens  19   e  and cemented element  23   e , as well as returning measuring light  43  are not illustrated. These beam paths are illustrated in  FIGS. 1A and 1B  from which it may be seen that also in the embodiment of an optical measuring system  1   e , which is illustrated in  FIG. 6 , the object region  28 ′, which may comprise the focal point  51   e  of the first optical assembly  31   e  is imaged onto the entry region  45   e  of the Hartmann-Shack sensor  47   e.    
     Therefore, the embodiment  1   e  allows to simultaneously inspect the object region  28 ′ by analyzing wavefronts, which emanate from this region and by acquiring OCT structural data. The wavefront light source  3   e  may be configured such that a central portion of measuring light which is generated by light source  3   e  is located within a range of wavelengths of about 830 nm to 870 nm. The OCT beam splitter  95 , or its dichroic mirror  96  is designed such that a substantial portion of light of a wavelength range of about 830 nm to 870 nm is transmitted. Thereby, it is possible to separate the OCT measuring light from the measuring light for inspecting a wavefront in order to reduce disturbances. 
     According to a further embodiment, no reflector  17   e  is provided between lens  19   e  and cemented element  13   e , such that a beam path of measuring light  9 ,  43  which is used for an analysis of the wavefront propagates in a straight line along an optical axis of cemented elements  19   e ,  23   e , i.e. an optical axis of the first optical assembly  31   e , without being deflected. 
     According to a further embodiment, the OCT beam splitter  95  may be arranged between the second optical assembly  13   e  and the Hartmann-Shack sensor  45   e , instead of being located between the first optical assembly  31   e  and the second optical assembly  13   e . This is indicated by the dashed box  95   a . Accordingly, the OCT system  93  is illustrated as an alternative with a dashed box having reference sign  93   a . This embodiment is advantageous in case structural information is to be obtained from the posterior portion of the eye by using the OCT system. This arrangement of the OCT beam splitter  95   a  or the OCT system  93   a  may be used when the optical measuring system does not have a reflector  17   e , as described above. 
       FIG. 7  schematically illustrates an optical measuring system if according to a further embodiment. The optical measuring system  1   f , as illustrated in  FIG. 7 , is designed in a similar way as the optical measuring system  1   c , as illustrated in  FIG. 4 , in so far as the optical measuring system if also comprises components  67   c  of a wavefront analysis system  77  as well as a microscopy system  79 . The microscopy system  79  comprises an objective lens  63   c  for imaging the object region  28   c ′, which is located in a focal plane  29   c , after having traversed zoom systems  89 ,  91 . Also, the wavefront analysis system  77  is designed such that wavefronts, which emanate from the object region  28   c ′ or which traverse the object region  28   c ′ are inspectable in view of their form, as has been described with reference to  FIG. 4 . 
     In addition to the functionalities of the optical measuring system  1   c , as illustrated in  FIG. 4 , the optical measuring system  1   f , as illustrated in  FIG. 7 , allows to inspect the structure of an object region  28   c ′ along a depth direction, i.e. perpendicular to the focal plane  29   c  by using the OCT system  93   a . To this effect, the OCT system  93   a  comprises similar components as the OCT system  93 , which is illustrated in  FIG. 6 . 
     In  FIG. 7 , there is schematically illustrated a beam path of the OCT measuring light  99   a  for three different pivoting positions of the scanner, which consists of the scanning mirrors  103   a ,  105   a . For simplicity of illustration, OCT measuring light  99   a  which emanates in three different directions from the point P between the scanning mirrors  103   a ,  105   a  is illustrated. Alternatively, at this point P, a center of a 3D-scanner may be arranged. In case a scanner comprises more than one mirroring surface, the point P is advantageously arranged such that distances to mirror surfaces of the scanner are minimized. 
     Light beams of OCT measuring light  99 , which emanate from the point P, are reflected at the scanning mirror  105   a , are reflected at dichroic mirror  96   a  to a major part and traverse the afocal system, which consists of the cemented element  19   c  and the cemented element  65   c , and is imaged onto the point P′, which is arranged in the center of the folding mirror  61   c . Point P is imaged by the cemented element  19   c , i.e. the second optical subassembly of the first optical assembly  31   c  and through cemented element  65   c , i.e. the second lens group of the first optical subassembly of the first optical assembly onto the point P′ which is located at the center of the folding mirror  61   c . Hence, for different pivoting positions of the scanner, which consists of scanning mirrors  105   a ,  103   a , there is a minimal walk-off of the point P′. In case of an ideally arranged 3D-scanner having only one reflecting surface, there is expected to be no beam walk-off. This allows to design the folding mirror  61   c  compact in size, such that beam paths of the microscope  81  and  83  can pass the folding mirror  61  and enter the respective zoom system of the stereo microscope system  79 . 
     As an alternative to the arrangement of the OCT beam splitter  95   a  and the OCT system  93   a , as illustrated in  FIG. 7 , these components or at least the OCT beam splitter  95   a  may be arranged between cemented element  65   c  and the folding mirror  61   c.    
     As an alternative to the embodiments, which are illustrated in  FIGS. 6 and 7 , the OCT beam splitter  95 ,  95   a  or the dichroic mirror  96 ,  96   a  may be designed such that OCT measuring light  99 ,  99   a  may be transmitted with a higher effectivity than reflected. They further may be designed such that measuring light  9 , which is used for the measurement of the wavefront is reflected with a higher effectivity than transmitted. Hence, in alternative embodiments, the spatial arrangement of the wavefront analysis system  77  and the OCT system  93 ,  93   a  may be interchanged. 
     According to further embodiments, a range of wavelengths, which comprises 70% of a total intensity of OCT measuring light may overlap with a range of wavelengths, which comprises 70% of a total intensity of measuring light for inspecting the wavefront. Thereby, light of the same wavelength range may be used for inspecting the wavefront and for inspection by using OCT light. In this case, the OCT beam splitter  95 ,  95   a , having a dichroic mirror  96 ,  96   a  is not necessary. In this case, it is advantageous to successively conduct a measurement for determining the wavefront and a measurement for determining the structure by using OCT. Thereby, an interference is prevented. However, it is also possible to conduct both measurements simultaneously. Optical elements having a polarization effect, such as quarter wave plates may be inserted into the beam path. For example, the elements  11 ,  11   a ,  11   b ,  11   c ,  11   d ,  11   e  may be configured as a polarization beam splitter. 
     According to further embodiments, the light beam of OCT measuring light  99  is not focused onto the object region  28   c ′,  28   e ′ but focused onto a region, which is located deeper, such as onto the retina of the eye under inspection. 
     While the invention has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present invention as defined in the following claims.