Imaging system

Abstract

Imaging systems are provided allowing examination of different object regions spaced apart in a depth direction by visual microscopy and by optical coherence tomography. An axial field of view and a lateral resolution is varied depending on which object region is examined by the imaging system. The proposed imaging systems are in particular applicable for thorough examination of the human eye.

Claims

1. A system comprising an OCT system and a lens system; wherein the OCT system comprises: an interferometer providing a measuring arm and a reference arm, an OCT measuring beam emitter for emitting a beam of OCT measuring light, OCT beam shaping optics disposed in a beam path of the measuring arm between the OCT measuring beam emitter and the lens system, an OCT scanner disposed in the beam path of the measuring arm between the beam shaping optics and the lens system; wherein the OCT beam shaping optics is configured such that the beam of OCT measuring light is focused at a beam focus, and wherein the OCT beam shaping optics is configured to change a lateral width of a beam waist of the beam of OCT measuring light at the beam focus; wherein the OCT beam shaping optics is configured such that before and after the changing of the lateral width, the beam of OCT measuring light is focused at a same distance from the lens system and/or at a focal plane of the lens system.

2. The system of claim 1, wherein the OCT beam shaping optics has a variable focal length; wherein the changing of the lateral width comprises changing a value of the variable focal length.

3. The system of claim 1, wherein before and after the changing of the lateral width, the OCT beam shaping optics forms a substantially parallel beam bundle of the OCT measuring light.

4. The system of claim 3, wherein a cross-sectional area of the substantially parallel beam bundle is different before and after the changing of the lateral width.

5. The system of claim 1, wherein the OCT beam shaping optics comprises a lens; wherein the changing of the lateral width comprises inserting or removing a lens from the beam path of the measuring arm.

6. The system of claim 1, wherein before and after the changing of the lateral width, the beam emitter is located in a focal plane of the OCT beam shaping optics.

7. The system of claim 1, further comprising a microscope system; wherein the microscope system is configured to image an object plane onto an image plane via an imaging beam path traversing the lens system.

8. A system comprising: a lens system; an OCT system, wherein the OCT system comprises: an interferometer providing a measuring arm and a reference arm, an OCT measuring beam emitter for emitting a beam of OCT measuring light, OCT beam shaping optics disposed in a beam path of the measuring arm between the OCT measuring beam emitter and the lens system, wherein the OCT beam shaping optics is configured such that the beam of OCT measuring light is focused at a beam focus, and wherein the OCT beam shaping optics is configured to change a lateral width of a beam waist of the beam of OCT measuring light at the beam focus; wherein the OCT beam shaping optics is configured such that before and after the changing of the lateral width, the beam of OCT measuring light is focused at a same distance from the lens system and/or at a focal plane of the lens system; wherein the beam shaping optics is configured so that the changing of the lateral width comprises inserting a first lens of the beam shaping optics into the beam path of the measuring arm and removing a second lens of the beam shaping optics from the beam path of the measuring arm.

9. The system of claim 8, wherein the OCT system further comprises an OCT scanner disposed in the beam path of the measuring arm between the beam shaping optics and the lens system.

10. The system of claim 8, wherein before and after the changing of the lateral width, the beam of OCT measuring light is focused at a same plane.

11. The system of claim 8, wherein before and after the changing of the lateral width, the OCT beam shaping optics forms a substantially parallel beam bundle of the OCT measuring light.

12. The system of claim 11, wherein a cross-sectional area of the substantially parallel beam bundle is different before and after the changing of the lateral width.

13. The system of claim 8, wherein before and after the changing of the lateral width, the beam emitter is located in a focal plane of the OCT beam shaping optics.

14. The system of claim 8, further comprising a microscope system; wherein the microscope system is configured to image an object plane onto an image plane via an imaging beam path traversing the lens system.

15. A system comprising: a lens system; an OCT system, wherein the OCT system comprises: an interferometer providing a measuring arm and a reference arm, an OCT measuring beam emitter for emitting a beam of OCT measuring light, OCT beam shaping optics disposed in a beam path of the measuring arm between the OCT measuring beam emitter and the lens system, an OCT scanner disposed in the beam path of the measuring arm between the beam shaping optics and the lens system; wherein the OCT beam shaping optics is configured such that the beam of OCT measuring light is focused at a beam focus, and wherein the OCT beam shaping optics is configured to change a lateral width of a beam waist of the beam of OCT measuring light at the beam focus; wherein the OCT beam shaping optics is configured such that before and after the changing of the lateral width, the beam of OCT measuring light is focused at a same distance from the lens system and/or at a focal plane of the lens system; wherein the OCT scanner comprises: a first mirror and a second mirror; and an imaging optics configured to image a point at the first mirror to a point at the second mirror.

16. The system of claim 15, wherein the OCT beam shaping optics has a variable focal length; wherein the changing of the lateral width comprises changing a value of the variable focal length.

17. The system of claim 15, wherein before and after the changing of the lateral width, the OCT beam shaping optics forms a substantially parallel beam bundle of the OCT measuring light.

18. The system of claim 17, wherein a cross-sectional area of the substantially parallel beam bundle is different before and after the changing of the lateral width.

19. The system of claim 15, wherein before and after the changing of the lateral width, the beam emitter is located in a focal plane of the OCT beam shaping optics.

20. The system of claim 15, further comprising a microscope system; wherein the microscope system is configured to image an object plane onto an image plane via an imaging beam path traversing the lens system.

21. The system of claim 1, wherein the OCT scanner comprises: a first mirror and a second mirror; and an imaging optics configured to image a point at the first mirror to a point at the second mirror.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A schematically illustrates an imaging system according to an embodiment of the present invention in a first operation mode;

(2) FIG. 1B schematically illustrates the imaging system according to FIG. 1A in a second operation mode;

(3) FIG. 2 schematically illustrates an imaging system, in particular a Spectral-Domain OCT facility according to an embodiment of the present invention;

(4) FIG. 3 schematically illustrates an imaging system, in particular a Swept-Source OCT facility, according to an embodiment of the present invention; and

(5) FIG. 4 illustrates a diagram of a spectrum of OCT measuring light that may be used in the Swept-Source OCT facility according to FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1A schematically illustrates an imaging system 1 according to an exemplary embodiment of the present invention in a first operation mode. Imaging system 1 provides a microscope feature embodies as a microscope portion 3 as well as an OCT feature embodied as an OCT portion 5. In the illustrates example, a human eye 7 is investigated using the imaging system 1. The microscope portion 3 allows visual inspection of the eye 7, in particular visual stereoscopic inspection of the eye 7. In particular, microscopic images of the eye 7 may be acquired. For this purpose, the eye 7 is illuminated by a microscopy illumination light source (not shown in FIG. 1A) generating microscopy illumination light having wavelengths in the visible wavelength range. Depending on the application, an angle of incidence of the microscopy illumination light and a colour temperature of microscopy illumination light may be varied. In spite of these possible adaptations regarding the microscopy illumination light, it is not easy to inspect the eye 7 by visual inspection only, since the eye comprises a number of transparent anatomical structures that can hardly be resolved or recognized. Therefore, for a thorough investigation of the eye 7 the imaging system 1 provides an OCT feature by the OCT portion 5. The OCT feature allows to acquire structural volume data of the eye 7. Thus, the OCT facility allows acquiring data across a lateral extension and a depth (or axial) extension of the eye 7.

(7) The imaging system 1 according to the illustrated example allows to inspect the eye 7 by visual microscopy and optical coherence tomography both in the anterior portion of the eye 7 and in the posterior portion of the eye 7. For this, the imaging system 1 is configured to provide a first operation mode for inspecting the anterior portion, as illustrated in FIG. 1A, and a second operation mode for inspecting the posterior, as illustrated in FIG. 1B.

(8) The imaging system 1, comprises an objective lens system 9 having adjustable optical power that is located in a beam path of both the microscope portion 3 and the OCT portion 5. The microscope portion 3 comprises a stereoscopic optical system downstream the objective lens system. This stereoscopic optical system comprises a zoom system 11 comprising a zoom lens 11.sub.1 and zoom lens 11.sub.2 and an ocular system 13 comprising an ocular lens 13.sub.1 which is viewed by a left eye 14.sub.1, and an ocular lens 13.sub.2. which is viewed by a right eye 14.sub.1 of an observer. In the first operation mode illustrated in FIG. 1A the objective lens system is adjusted to have a focal length fo.sub.1. In a focal plane 15.sub.1 of the objective lens system 9 adjusted to have a focal length fo.sub.1 the object region 17.sub.1 is arranged. The object region 17.sub.1 includes the anterior portion of the eye 7. The anterior portion of the eye comprises for example the cornea, the anterior chamber, the posterior chamber and a crystal lens 8 of the eye 7. Microscopy illumination light is scattered and reflected from the object region 17.sub.1 and emerges therefrom as light 19. The light 19 traverses the objective lens system 9. One part of light 19 traverses the zoom lens 11.sub.1 and thereafter the ocular lens system 13.sub.1, to enter e.g. the left eye 14.sub.1 of the observer. Another part of the light 19 having traversed the objective lens system 9 traverses the zoom lens 11.sub.2 and the ocular system 13.sub.2 to enter the right eye 14.sub.2 of the observer, such that the observer perceives a stereoscopic image of the object region 17.sub.1. The microscope portion may comprise a beam splitter 121 arranged downstream of the objective lens in the beam path of one or both parts of the light 19 to direct these parts of light 19 to image sensors 123, such as a CCD detectors, in order to record and store electronic representations of images of the object region 17.sub.1. These recorded images can be displayed via displays, such as a monitor, in particular a stereo display, or a head mounted display 125 carried by the observer.

(9) The OCT portion 5 includes a spectrometer 21 which includes a light source, a beam splitter, a reference arm and a detector. The measuring arm of the interferometer carries OCT measuring light 23 that is supplied to an optical fiber 25. The optical fiber 25 guides the OCT measuring light 23 to a tip 27 of the optical fiber 25 which represents an exit area of the light source comprised in OCT spectrometer 21. The exit area at the tip 27 of the optical fiber 25 may correspond to a tip end of the core of the optical fiber 25 which guides the OCT measuring light 23. The OCT measuring light 23 emanates from the exit area at the tip 27 of the optical fiber as a divergent beam.

(10) The exit area at the tip 27 of the optical fiber from which the OCT measuring light 23 emanates is arranged in a focal plane 28 of a collimating lens 29.sub.1. The focal length of the collimating lens 29.sub.1 amounts to fc.sub.1. The OCT measuring light 23 traverses the collimating lens 29.sub.1 and is collimated to form a substantially parallel beam bundle having a cross sectional diameter d.sub.1. Thereafter, the collimated OCT measuring light enters a scanning system 31 including a first scanning mirror 33 pivotable about a first axis and a second scanning mirror 35 pivotable about a second axis extending in a direction different from a direction of extension of the axis of the first mirror. The scanning system 31 is provided to enable scanning of the OCT measuring light across the object region 17.sub.1.

(11) After being reflected at the scanning mirrors 33 and 35 the OCT measuring light is reflected at a mirror 37 to direct the OCT measuring light 23 towards the objective lens system 9. In the illustrated example, the mirror 37 is arranged between the two stereoscopic beam paths traversed by the microscopy light 19. According to other examples, the mirror 37 is a semi-transparent mirror traversed by the microscopy light 19.

(12) After being reflected from the mirror 37, the OCT measuring light 23 traverses the objective lens system 9 to be focused at the focal plane 15.sub.1 of the objective lens system 9 being adjusted to have the focal length fo.sub.1. Thus, the exit area at the tip 27 of the optical fiber 25 is imaged by the collimating lens 29.sub.1 and the objective lens system 9 onto a part of the image region 17.sub.1. A size of the image of the exit area at the tip 27 of the optical fiber 25 determines a lateral width of the beam of the OCT measuring light 23 illuminating at least part of the object region 17.sub.1. The lateral width of the beam of the OCT measuring light 23 illuminating part of the object region 17.sub.1 limits a lateral resolution of the OCT portion.

(13) The objective lens system 9 and the collimating lens 29.sub.1 form the illumination optics of the OCT portion 5 in the first operation mode. A magnification of this illumination optics, i.e. a ratio of a size of an image of an object and a size of the object, is given as a ratio between the focal length of the objective lens system 9, i.e. fo.sub.1, and the focal length of the collimating lens 29.sub.1, i.e. fc.sub.1. Thus, the magnification is fo.sub.1/fc.sub.1.

(14) The magnification of the illumination optics can be varied by varying the focal length fo.sub.1, the focal length fc.sub.1 or both focal lengths fo.sub.1 and fc.sub.1. Such variation results in a variation of the lateral width of the OCT measuring light illuminating the object region 17.sub.1. It follows that the lateral resolution of the OCT portion of the imaging system can be varied by such variation of the one or both of the focal lengths fo.sub.1 and fc.sub.1.

(15) The OCT measuring light 23 penetrates the object region 17.sub.1, i.e. the anterior portion of the eye 7, in a depth direction, i.e. a direction substantially orthogonal to the focal plane 15.sub.1. The OCT measuring light 23 interacts with tissue material within a volume portion defined by the lateral width of the OCT measuring light. Portions of the OCT measuring light are reflected at different positions with different strength depending on optical properties of tissue material located in this volume portion. Having interacted with the object region 17.sub.1 the OCT measuring light emerges as light 39 from the eye 7. The light 39 traverses the objective lens system 9, is reflected from the mirror 37, is reflected from the scanning mirrors 35 and 33, traverses the collimating lens 29.sub.1, enters the tip 27 of the optical fiber 25 and is guided to the beam splitter of the interferometer 21. At the beam splitter, the light 39 is superimposed with reference light having traversed the reference arm of the interferometer 21. The superimposed light generates an interference on a detector of the OCT portion.

(16) According to time-domain OCT, a length of the reference arm of the interferometer is varied, and the detected light intensities are recorded in dependence of the length of the reference arm. The intensities recorded in dependence of the length of the reference arm are analyzed to obtain volume data representing the tissues of the anterior portion of the eye 7.

(17) According to spectral-domain OCT, the superimposed light is guided to a spectrometer which disperses the superimposed light based on its wavelength and detects intensities of plural spectral portions of the superimposed light. Thereby, a spectrum of the superimposed light is obtained. Electrical signals corresponding to the spectrum are then supplied via signal line 41 to a control and processing system 43. The control and processing system 43 processes the electrical signals, such as performing a Fourier transformation, sampling, normalization and the like to compute volume data representing tissues of the eye 7 within the object region 17.sub.1.

(18) Moreover, other embodiments can use other OCT methods, such as swept source OCT for obtaining the volume data representing tissues of the eye 7 within the object region 17.sub.1.

(19) In order to allow communication with a user, an input unit 45, such as a keyboard and a mouse, and a display unit 47 for visualizing the volume data, such as a monitor, can be connected to the control and processing system 43. Via a signal line 49 the control and processing system 43 is also connected to the scanning unit 31, to control rotational movements of the mirrors 35 and 33, in order to scan the beam of OCT measuring light 23 across the object region 17.sub.k.

(20) Further, the control and processing unit 43 controls via the signal line 41 the spectrometer comprised in the interferometer 21 in order to adjust a dispersion strength of the spectrometer. The dispersion strength of the spectrometer is related to the spectral resolution of the detected spectrum of the dispersed superimposed light, and thus to the spectral width of the detected plural spectral portions of the dispersed superimposed light. This spectral resolution is related to an axial field of view (FOV) of the obtained OCT data. The spectral width is also related to an axial field of view of the OCT data. The field of view corresponds to a depth range within the object region from which structure information can be obtained by the OCT portion. In the first operation mode the dispersion strength of the spectrometer is adapted by the control and processing system 43 such that the field of view is FOV.sub.1, as indicated in FIG. 1A.

(21) In a time-domain OCT system, the field of view is FOV.sub.1 is adjusted by controlling a scanning movement of a mirror in the reference arm of the interferometer.

(22) Further, via signal line 51 the control and processing unit 43 controls an actuator 53 being adapted to rotate a carrier or shaft 55 on which the collimating lens 29.sub.1 and a further collimating lens 29.sub.2 are attached. In other embodiments, the collimating lenses 29.sub.1, 29.sub.2 are attached to a slider moved by the actuator to be translated in a linear direction.

(23) The actuator 53 is controlled by the control and processing unit 43 to arrange either the collimating lens 29.sub.1 or the collimating lens 29.sub.2 into a beam path of the OCT measuring light 23 downstream the exit area at the fiber tip 27 of the optical fiber 25. The collimating lenses 29.sub.1 and 29.sub.2 have different focal lengths, the collimating lens 29.sub.1 has focal length fc.sub.1 and the collimating lens 29.sub.2 has focal length fc.sub.2 that is greater than the focal length fc.sub.1. As explained above, changing the focal length of the collimating lens changes the lateral width of the OCT measuring light 23 illuminating the object region 17.sub.1 or object region 17.sub.2 as explained below.

(24) Thus, the control and processing unit 43 is capable of controlling the lateral width of the OCT measuring light illuminating the object region, and thus of adjusting the lateral resolution of structural data acquired by the OCT portion 5.

(25) According to a particular example in the first operation mode, the exit area at the tip 27 of the optical fiber 25 may have a diameter of around 5 m, and a lateral width of the OCT measuring light 23 at the object region may be around 60 m, thus requiring a magnification of the illumination optics comprising the collimating lens 29.sub.1 and the objective lens system 9 of around 10. This magnification may for example be achieved, if the focal length fo.sub.1 of the objective lens system 9 is around 200 mm and the focal length fc.sub.1 of the collimating lens 29.sub.1 is around 20 mm. The dispersion strength of the spectrometer of the OCT facility may be adjusted such that the field of view in the first operation mode, i.e. FOV.sub.1, is around 3 to 7 mm.

(26) Further, via signal line 57 the control and processing system 43 can control by appropriate actuators a magnification of the zoom system 11. The magnification of the zoom system 11 may in particular be controlled depending on a size of a scanning area of the OCT measuring light 23 which is defined by maximum rotations of the scanning mirrors 33 and 35. In particular, the control and processing system 43 may be adapted to substantially match a size of a microscopic field of view determined by a magnification of the zoom system 11 and the size of the scan area of the OCT measuring light. For example, if a user manually changes the magnification of the zoom system 11, the control and processing system 43 can automatically control the scanning unit 31 to match the scan area of the OCT measuring light with the microscopic field of view.

(27) FIG. 1B schematically illustrates the imaging system 1 illustrated in FIG. 1A in the second operation mode. In the second operation mode an object region 17.sub.2, i.e. the posterior portion of the eye 7, is investigated. For this purpose, several components of the imaging system 1 have been readjusted compared to their condition during the first operation mode illustrated in FIG. 1A: An actuator 61, which can be manually controlled or controlled via signal line 59 by the control and processing system 43, mounts an ophthalmic lens 63 between the objective lens system 9 and the eye 7. Optionally, the focal length of the objective lens system 9 has been manually adjusted or adjusted via signal line 10 by the control and processing system 43 to be fo.sub.2. Further, an inversion system 65 has been introduced into the beam path of the light 19 to compensate up-down and right-left inversion caused by introducing the ophthalmic lens 63 such that the image perceived by the user looking into the oculars 13 is an upright image.

(28) Further, the collimating lens 29.sub.1 has now been replaced by collimating lens 29.sub.2 to be arranged in the beam path of the OCT measuring light 23 downstream the exit area at the tip 27 of the optical fiber 25. Collimating lens 29.sub.2 has a focal length fc.sub.2 and the exit area at the tip 27 is arranged in the focal plane 28 of the collimating lens 29.sub.2. The focal length fc.sub.2 is greater than the focal length fc.sub.1. In the illustrated example, the focal length fc.sub.2 is two times the focal length fc.sub.1. In particular, the focal length fc.sub.2 may be about 30 mm to 50 mm. The effect of the change from the collimating lens 29.sub.1 in the first operation mode to the collimating lens 29.sub.2 in the second operation mode is that the lateral width of the OCT measuring light illuminating now the object region 17.sub.2 is decreased, for example by a factor of more than 2.

(29) The OCT measuring light 23 emanating as a divergent beam from the tip of the optical fiber 25, traverses the collimating lens 29.sub.2, is reflected from the scan mirrors 33 and 35 as substantially parallel beam bundle, is reflected by the mirror 37, traverses the objective lens system 9 to be focused at the focal plane 15.sub.2 which is arranged a distance fo.sub.2 away from the objective lens system 9. At the focal plane 15.sub.2 the convergent OCT measuring light 23 crosses, and traverses the ophthalmic lens 63, to form a substantially parallel beam bundle. This substantially parallel beam bundle of OCT measuring light 23 traverses the crystal lens 8 of the eye to be focused on the retina 18 of the eye in the object region 17.sub.2. The OCT measuring light 23 interacts with the object region 17.sub.2 in a depth range corresponding to the axial field of view FOV.sub.2 and leaves the object region 17.sub.2 as light 39. Light 39 traverses the crystal lens 8, the ophthalmic lens 63, the objective lens system 9, the inversion system 65, is reflected at the folding mirror 37, the two scanning mirrors 35 and 33, traverses the collimating lens 29.sub.2 and is supplied to the optical fiber 25 which guides the light 39 to the interferometer 21 of the OCT facility 5, as described above.

(30) In the second operation mode the dispersion strength of the spectrometer (within interferometer 21) for wavelength dispersion of the light 39 superimposed with reference light has been set to be smaller than in the first operation mode. Thus, the axial field of view in the second operation mode, i.e. FOV.sub.2, is smaller, in particular more than two times smaller, than the field of view in the first operation mode, i.e. FOV.sub.1. Thus, for switching from the first operation mode to the second operation mode the control and processing system 43 has at least controlled the actuator 53 to cause switching from the collimating lens 29.sub.1 to the collimating lens 29.sub.2. The control and processing system 43 may also control the spectrometer to change the dispersion strength. The control and processing system 43 may also control the objective lens system 9 to change from the focal length from fo.sub.1 to fo.sub.2. The control and processing system 43 may also control the actuator 61 to place the ophthalmic lens 63 in a beam path of the OCT measuring light and the microscopic light thereby changing from the object region 17.sub.1 to the object region 17.sub.2 which is located farther away from the objective lens system 9 than the object region 17.sub.1.

(31) FIG. 2 schematically illustrates another embodiment 1a of an imaging system. As will be explained below, the imaging system 1a may also be used to provide the OCT portion 5 of the embodiment illustrated with reference to FIGS. 1A and 1B above. The imaging system 1a provides an OCT feature embodied as a Spectral Domain OCT. The OCT portion 5a comprises a light source 67 for generating a beam of OCT measuring light 23 which is guided by an optical fiber 69 to a beam splitter/coupler 71. The beam splitter/coupler 71 splits the OCT measuring light 23 into a portion 23 and a portion 24. Portion 24 of the OCT measuring light is guided via an optical fiber 69 to a reference mirror 73 which can be displaced in directions indicated by double arrow 74. Portion 24 of the OCT measuring light is reflected from the reference mirror 73 and is guided as light 24 to the optical splitter/coupler 71. Portion 23 of the OCT measuring light is guided by optical fiber 25a to a tip 27a of the optical fiber 25a from which the portion 23 of the OCT measuring light emanates as a divergent beam and traverses a collimating optics 29a having adjustable optical power. The collimating optics 29a may be constructed as a zoom system such that a focal length thereof can be changed continuously or in one or more steps. The OCT measuring light 23 is collimated by collimating optics 29a, is reflected from mirrors 33a and 35a of a scanning system 31a, traverses a lens system 9a to be focused in a focal plane 15a of the lens system 9a in object region 17. Light 39 emanating from the object region traverses lens system 9a, is reflected from the scanning mirrors 35a and 33a, traverses the collimating optics 29a, enters the optical fiber 25a and is guided to the beam splitter/coupler 71, where it is superimposed with the light portion 24, to form superimposed light 26. Superimposed light 26 is guided via optical fiber 69 to a spectrometer 75.

(32) Spectrometer 75 includes a dispersion apparatus 77, imaging optics 79 and a spatially resolving detector 81. The dispersion apparatus 77 may comprise diffractive and/or refractive optical elements for dispersing the superimposed light 26. Dispersing the superimposed light 26 typically comprises deflecting spectral portions of the superimposed light 26 in different directions depending on wavelengths comprised in the spectral portions. The dispersion apparatus 77 may for example comprise a diffraction grating including a substrate having plural diffractive elements arranged thereon, in particular arranged in a periodic manner. The dispersion apparatus 77 disperses the superimposed light 26 into plural spectral portions 83. The plural spectral portions 83 traverse the imaging optics 79 having adjustable optical power. The detector 81 is arranged in the focal plane 84 of the imaging optics 79. Thus, a distance between an effective surface 82 of the detector 81 and a principal plane of the imaging optics 79 corresponds to the focal length fi of the imaging optics 79. When the focal length fi of the imaging optics 79 is changed, the detector 81 is shifted in directions indicated as double arrow 85 to keep the effective surface 82 of the detector 81 arranged in the changed focal plane 84 of the imaging optics 79. The detector 81 comprises plural detector segments each receiving a particular spectral portion 83 of the dispersed superimposed light 26. By changing the focal length fi of the imaging optics 79 and displacing the detector 81 as explained above, a width of a wavelength range comprised in a spectral portion received and detected by a single detector segment can be controlled. This width of a wavelength range detected by a single detector segment is related to the axial field of view provided by the OCT facility 5a. Thereby, the OCT facility 5a is enabled to adjust an axial field of view to for example a value of FOV.sub.1 or a value of FOV.sub.2, as indicated in FIG. 2.

(33) Further, by varying the focal length fc of the collimating optics 29a and arranging the fiber tip 27a in the focal plane 28a of the collimating optics 29a the lateral width of the beam of OCT measuring light 23 illuminating the object region 17 can be controlled. Thus, the OCT facility 5a is also capable of adjusting a lateral resolution.

(34) As explained above, the imaging system 1a providing an OCT feature may be employed as the OCT portion 5 in the imaging system 1 illustrated with reference to FIGS. 1A and 1B above. For this purpose, the OCT measuring light 23 may be guided through the objective lens system 9 instead of the lens system 9a by providing a mirror 37a instead of the lens system 9a as indicated by double arrow 38.

(35) The imaging system 1a also comprises a control and processing system 43a performing similar functions as the control and processing system 43 of imaging system 1 illustrated in FIGS. 1A and 1B illustrated with reference to FIGS. 1A and 1B above. In particular, the control and processing system 43a obtains data from the detector 81 via signal line 41a and controls also displacing the detector 81 in directions indicated by double arrow 85. Further, system 43a controls adjusting of the focal length fi of the imaging optics 79 and thus controls adjusting the dispersion strength of the spectrometer 75. Further, via signal line 51a the control and processing system 43a controls adjusting the focal length fc of the collimating system 29a.

(36) FIG. 3 illustrates another embodiment of an imaging system 1b accordingly. In particular, FIG. 3 schematically illustrates an imaging system 1b providing an OCT feature embodied as a swept-source OCT. The swept-source OCT 5b illustrated in FIG. 3 can be used to provide the OCT portion in the embodiment illustrated with reference to FIGS. 1A and 1B above. In particular, also the swept-source OCT 5b illustrated in FIG. 3 can be controlled to adjust an axial field of view of the OCT imaging as well as a lateral resolution of the OCT imaging.

(37) The swept-source OCT 5b comprises an optical amplifier 87 for amplifying light waves in a predetermined wavelength range. For this purpose, the optical amplifier 87 can be a semi-conductor optical amplifier pumped by a current source 89. The optical amplifier 87 is optically connected to a ring fiber 91 for guiding light amplified by the optical amplifier 87. In a beam path provided by the optical fiber 91 routing switches 93 and 95 are configured to guide light propagating within the optical fiber 91 to optical fiber 91.sub.1, 91.sub.2, and 91.sub.3. Optical fiber 91.sub.1 guides light received from routing switch 93 or routing switch 95 to a first sweepable filter 97.sub.1. After traversing the first sweepable filter 97.sub.1 the filtered light is again coupled into the fiber ring 91 via routing switch 93 or 95.

(38) Alternatively to traversing the first sweepable filter 97.sub.1 the routing switches 93 and 95 may cause the light in the ring 91 to be guided through a second sweepable filter 97.sub.2 or a third sweepable filter 97.sub.3. The first, second and third sweepable filters 97.sub.1, 97.sub.2, and 97.sub.3 may be spectral filters of the Fabry-Prot type comprising two opposing reflecting surfaces arranged parallel to each other. A distance between the two reflecting surfaces can be controlled by a piezo-electric element controlled by a ramp generator 99 connected to the three spectral filters. Only light having a wavelength satisfying a resonance condition depending on a distance between the two opposing reflecting surfaces of the spectral filter arranged in the beam path of the ring 91 will constructively interfere. Light having other wavelengths will substantially be attenuated. By changing the distance between the two opposing reflecting surfaces of the Fabry-Prot type filter using the ramp generator 99, a peak wavelength of light satisfying the resonance condition can be varied. Depending on the optical properties of the opposing reflecting surfaces of the Fabry-Prot type filter arranged in the beam path of the ring fiber 91 not only a single wavelength will satisfy the resonance condition but a range of wavelengths around the peak wavelengths. Thus, a particular Fabry-Prot type spectral filter is characterized by a particular transmission spectrum whose characteristics depends on at least a reflectivity of the reflecting surfaces.

(39) FIG. 4 is a diagram showing transmission characteristics T of the first and second sweepable filters 97.sub.1 and 97.sub.2. Depending on the wavelength , a transmission of the first sweepable filter 97.sub.1 is shown as a curve 101.sub.1, and a transmission of the second sweepable filter 97.sub.2 is shown as a curve 101.sub.2. Typically, each Fabry-Prot type filter exhibits several transmission peaks. In FIG. 4 two such transmission peaks P, P are shown, one having a mean wavelength of 1000 nm and another having a mean wavelength of 1100 nm. Plural transmission peaks occur, because the resonance condition may be satisfied by plural wavelengths according to different orders. Here, only the first transmission peak P located around 1000 nm is of interest, since the second transmission peak P located around 1100 nm is located outside the working range of the semi-conductor optical amplifier 87 and is therefore not amplified.

(40) As first spectral width 105.sub.1 of the transmission spectrum 101.sub.1 of the first sweepable filter 97.sub.1 may be obtained by forming a minimum of a difference between two wavelengths 102.sub.1 and 104.sub.1 within which 90% of the transmission 101.sub.1 of the first sweepable filter 97.sub.1 is comprised, whereby transmission peaks of higher order wavelengths outside the wavelength range of the semi-conductor optical amplifier 87 are disregarded. In the illustrated example, the first spectral width 105.sub.1 amounts to about 50 pm. Similarly, a second spectral width 105.sub.2 of the transmission spectrum 101.sub.2 of the second sweepable filter 97.sub.2 may be obtained amounting to about 20 pm.

(41) Referring again to FIG. 3, when the first sweepable filter 97.sub.1 is arranged to be traversed by light guided within the ring fiber 91, only light will be amplified by the semi-conductor optical amplifier 87 that substantially has a spectrum given by the transmission spectrum 101.sub.1 of the first sweepable filter 97.sub.1, as illustrated in FIG. 4. Thus, a spectrum of light guided within the ring fiber 91 will be largely defined by the transmission characteristics of the spectral filter 97.sub.1 arranged within the ring fiber 91. Light thus amplified will be denoted as OCT measuring light 107. A portion of the OCT measuring light 107 is extracted by splitter 109 and is guided to interferometer 111. In the interferometer 111, the OCT measuring light is split into two portions, wherein one portion is reflected by a reference mirror and the other portion is directed to collimating optics 29b. The collimating optics 29b has an adjustable optical power similar to the collimating optics 29 illustrated in FIGS. 1A and 1B and collimating optics 29a illustrated in FIG. 2. Thus, these different embodiments of collimation optics provide a similar function in controlling a lateral width of OCT measuring light illuminating the object region 17 where the object 7 is arranged.

(42) After having traversed the collimating optics 29b the OCT measuring light 107 traverses the lens system 9b to be focused at the object region 17. The OCT measuring light 107 illuminating the object region 17 interacts with the object 7, and light 39 emanates from the object, traverses the lens system 9b, collimating optics 29b and is guided to interferometer 111. Here, light 39 is superimposed with reference light to form superimposed light 26b. Superimposed light 26b is guided to photo detector 113 which detects an intensity of the superimposed light 26b.

(43) Similar to the other embodiments of imaging systems illustrated above, the imaging system 1b comprises a control and processing system 43b that controls operation of the imaging system 1b. In particular, control and processing system 43b controls, via a signal line 98, the ramp generator 99 to enable sweeping of the peak wavelength of the OCT measuring light 107. Further, the system 43b may control adjusting the focal length of the collimating optics 29b and may also control the routing switches 93 and 95, thereby controlling a spectrum of the OCT measuring light 107 illuminating the object region 17. Thus, the control and processing system 43b may control and change an axial field of view and/or a lateral resolution of the OCT portion 5b.

(44) When the lens system 9b is substituted with folding mirror 37 of the imaging system 1 illustrated in FIGS. 1A and 1B the OCT facility 5b may be used as OCT facility 5 in the imaging system 1 illustrated in FIGS. 1A and 1B.

(45) Embodiments of the present invention provide imaging systems enabling examination of both the anterior portion of the eye and the posterior portion of the eye by visual microscopy and optical coherence tomography. In particular, these imaging systems allow switching of OCT components and microscopy components when examining the one or the other object region. In particular, an axial field of view and a lateral resolution of the OCT method are varied when switching the object regions.

(46) While the present invention has been shown and described herein in what is believed to be the most practical and preferred embodiments, it is recognized that departures can be made therefrom within the scope of the invention, which is therefore not be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent methods and apparatus.