SURGICAL MICROSCOPE HAVING AN ILLUMINATION APPARATUS

Abstract

A surgical microscope for visualizing a tissue region contains an illumination device with a light source and an illumination beam path for illuminating an object region with an object plane and an observation device having an observation beam path for imaging the object region with the object plane into an observation plane. A first polarizer can be coupled into the illumination beam path and is suitable for polarizing the illumination light in a first orientation. A polarizer, which can be coupled into the observation beam path, has a second orientation at an angle between 80° and 100° relative to the first orientation. In a first mode, the light source emits illumination light in a first wavelength range between 450 nm and 550 nm, the first polarizer is coupled into the illumination beam path, and the second polarizer is coupled into the observation beam path.

Claims

1. A surgical microscope for visualizing a tissue region, the surgical microscope comprising: an illumination device including a light source configured to emit illumination light to propagate along an illumination beam path and to illuminate an object region including an object plane; an observation device defining an observation beam path and being configured to image the object region into an observation plane; a first polarizer configured to be coupled into the illumination beam path and having a first orientation to polarize the illumination light; a second polarizer configured to be coupled into the observation beam path and having a second orientation at an angle between 80° and 100° relative to the first orientation, wherein, in a first mode: the light source emits the illumination light in a first wavelength range between 430 nm and 570 nm, the first polarizer is coupled into the illumination beam path, and the second polarizer is coupled into the observation beam path.

2. The surgical microscope as claimed in claim 1, wherein, in a second mode: the light source emits the illumination light as white light, the first polarizer is coupled out of the illumination beam path, and the second polarizer is coupled out of the observation beam path.

3. The surgical microscope as claimed in claim 1, wherein the first orientation of the first polarizer and the second orientation of the second polarizer are orthogonal relative to one another.

4. The surgical microscope as claimed in claim 1, wherein: the light source is a light-emitting diode light source and includes at least a first individual light source, a second individual light source, and a third individual light source, the first individual light source emits the illumination light in a red wavelength range between 600 nm and 640 nm, the second individual light source emits the illumination light in a green wavelength range between 500 nm and 570 nm, and the third individual light source emits the illumination light in a blue wavelength range between 430 nm and 480 nm.

5. The surgical microscope as claimed in claim 4, wherein: in the first mode, the light-emitting diode light source emits the illumination light only from the second individual light source and the third individual light source, and in the second mode, the light-emitting diode light source emits the illumination light from the first individual light source, the second individual light source, and the third individual light source.

6. The surgical microscope as claimed in claim 1, further comprising a red filter, wherein: the light source is a white light source which emits the illumination light in a wavelength range between 450 nm and 620 nm, in the first mode, the red filter is coupled into the illumination beam path and configured to cause an attenuation of larger than 90% of light having a wavelength longer than 620 nm.

7. The surgical microscope as claimed in claim 1, further comprising: a switch configured to switch between the first mode and the second mode.

8. The surgical microscope as claimed in claim 7, wherein the switch is an element of a graphical user interface or a member of a foot control panel.

9. The surgical microscope as claimed in claim 1, further comprising: at least one camera arranged in the observation beam path and configured to record the object plane.

10. The surgical microscope as claimed in claim 1, wherein, in the first mode, an intensity of the illumination light in a first wavelength range between 430 nm to 570 nm is larger than the intensity in the remaining wavelength ranges by at least a factor of 5.

11. The surgical microscope as claimed in claim 10, wherein, in the first mode, the light source emits the illumination light only in the first wavelength range between 430 nm and 570 nm.

12. A method for visualizing an object region with the surgical microscope as claimed in claim 1, the method comprising: coupling the first polarizer into the illumination beam path; orienting the first polarizer in the first direction to polarize the illumination light, illuminating the object region in the object plane with the illumination light in the first mode, wherein the illumination light is polarized in the first orientation and has a first wavelength range between 430 nm and 570 nm; coupling the second polarizer into the observation beam path; orienting the second polarizer to have the second orientation at the angle between 80° and 100° relative to the first orientation; and observing the illuminated object region with the observation device through the observation beam path.

13. The method as claimed in claim 12, further comprising: limiting a visualization of the object region in the first mode to a depth in a range between 300 μm to 800 μm.

14. The method as claimed in claim 12, wherein, in the first mode, an intensity of the illumination light in the first wavelength range between 430 nm to 570 nm is larger than the intensity in the remaining wavelength ranges by at least a factor of 5.

15. The method as claimed in claim 14, wherein, in the first mode, the light source emits the illumination light only in the first wavelength range between 430 nm and 570 nm.

16. A surgical microscope for visualizing a tissue region, the surgical microscope comprising: an illumination device including a light source configured to emit illumination light to propagate along an illumination beam path and to illuminate an object region including an object plane; an observation device defining an observation beam path and being configured to image the object region into an observation plane; a first polarizer configured to be coupled into the illumination beam path and having a first orientation to polarize the illumination light; a second polarizer configured to be coupled into the observation beam path and having a second orientation at an angle between 80° and 100° relative to the first orientation, wherein, in a first mode: the light source emits the illumination light with a wavelength within an absorption spectrum of hemoglobin and in a wavelength region below 570 nm, the first polarizer is coupled into the illumination beam path, and the second polarizer is coupled into the observation beam path.

17. The surgical microscope as claimed in claim 16, wherein, in the first mode, an intensity of the illumination light in the wavelength range above 570 nm is lower than the intensity in the remaining wavelength ranges by at least a factor of 5.

18. A method for visualizing an object region, the method comprising: providing an illumination device including a light source emitting illumination light to propagate along an illumination beam path and to illuminate an object region including an object plane and a first polarizer configured to be coupled into the illumination beam path; coupling the first polarizer into the illumination beam path and orienting the first polarizer in a first orientation to polarize the illumination light; illuminating, in a first mode, the object region in the object plane with the illumination light polarized in the first orientation, wherein a wavelength of the illumination light is in a first wavelength region within an absorption spectrum of hemoglobin and below 570 nm; coupling a second polarizer having a second orientation at an angle between 80° and 100° relative to the first orientation into an observation beam path of an observation apparatus; imaging the object region into an observation plane along the observation beam path; and observing the object region imaged into the observation plane with the observation apparatus.

19. The method as claimed in claim 18, wherein, in the first mode, an intensity of the illumination light in the wavelength range above 570 nm is lower than the intensity in the remaining wavelength ranges by at least a factor of 5.

20. The method as claimed in claim 18, further comprising: limiting a visualization of the object region in the first mode to a depth in a range between 300 μm to 800 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The disclosure will now be described with reference to the drawings wherein:

[0062] FIG. 1 shows a schematic illustration of typical optical components of a surgical microscope,

[0063] FIG. 2 shows a schematic illustration of a varioscope objective,

[0064] FIG. 3 shows the surgical microscope from FIG. 1 configured as a digital surgical microscope,

[0065] FIG. 4 shows a surgical microscope in a schematic illustration according to an exemplary embodiment of the disclosure,

[0066] FIG. 5 shows a diagram illustrating a radiation pattern of the individual light sources of the first light source and of the second light source in accordance with FIG. 4,

[0067] FIG. 6 shows a tissue region illuminated with conventional white light illumination in the second mode, and

[0068] FIG. 7 shows the tissue region in accordance with FIG. 6, illuminated in the multispectral mode.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0069] The present disclosure will be explained below by way of the example of a surgical microscope. With respect to FIGS. 1 and 2, the basic setup of the surgical microscope 2 is therefore described.

[0070] The surgical microscope 2 shown in FIG. 1 includes, as essential optical components, an objective 5 that is to face an object field 3, the objective, in particular, can be embodied as an achromatic or apochromatic objective. In the present exemplary embodiment, the objective 5 contains two partial lenses that are cemented to one another and form an achromatic objective. In the case of an apochromatic objective, at least three partial lenses would be present. The object field 3 is arranged in the focal plane of the objective 5 such that an observation object located in the object field 3 is imaged at infinity by the objective 5. Expressed differently, a divergent beam 7 emanating from the object field 3 is converted into a parallel beam 9 during its passage through the objective 5.

[0071] A magnification changer 11 is arranged on the observer side of the objective 5, which magnification changer can be embodied either as a zoom system for changing the magnification factor in a continuously variable manner as in the illustrated exemplary embodiment, or as what is known as a Galilean changer for changing the magnification factor in a stepwise manner. In a zoom system, constructed by way of example from a lens combination having three lenses, the two object-side lenses can be displaced in order to vary the magnification factor. However, the zoom system also can have more than three lenses, for example four or more lenses, in which case the outer lenses then can also be arranged in a fixed manner. In a Galilean changer, by contrast, there is a plurality of fixed lens combinations which represent different magnification factors, and which can be introduced into the beam path alternately. Both a zoom system and a Galilean changer convert an object-side parallel beam into an observer-side parallel beam having a different beam diameter.

[0072] In the present exemplary embodiment, the magnification changer 11 already is part of the binocular beam path of the surgical microscope 2, i.e., it has a dedicated lens combination for each stereoscopic partial beam path 9A, 9B of the surgical microscope 2. However, it is also possible in principle to use a “large magnification changer,” i.e., a magnification changer in which both stereoscopic partial beam paths pass through each lens.

[0073] A magnification factor is set, in the present exemplary embodiment, with the magnification changer 11 by way of a motor-driven actuator which, together with the magnification changer 11, is part of a magnification changing unit for setting the magnification factor.

[0074] The magnification changer 11 is adjoined on the observer side by an optical interface arrangement 13A, 13B, by which external appliances can be connected to the surgical microscope 2 and which includes beam splitter prisms 15A, 15B in the present exemplary embodiment. However, in principle, use can also be made of other types of beam splitters, for example partly transmissive mirrors. In the present exemplary embodiment, the optical interfaces 13A, 13B serve to couple a beam out of the beam path of the surgical microscope 2 (beam splitter prism 15B) and to couple a beam into the beam path of the surgical microscope 2 (beam splitter prism 15A).

[0075] In the present exemplary embodiment, the beam splitter prism 15A in the partial beam path 9A serves to mirror information or data for an observer into the partial beam path 9A of the surgical microscope 1 with the aid of a display 37, for example a digital mirror device (DMD) or an LCD display, and an associated optical unit 39 by the beam splitter prism 15A. A camera adapter 19 with a camera 21 fastened thereto, the camera being equipped with an electronic image sensor 23, for example with a CCD sensor or a CMOS sensor, is arranged at the interface 13B in the other partial beam path 9B. It is possible to record a digital image with the camera 21 and, in particular, a digital image of the object field 3.

[0076] The interfaces 13A, 13B are adjoined on the observer side by a binocular tube 27. The latter has two tube objectives 29A, 29B, which focus the respective parallel beam 9A, 9B onto intermediate image planes 31A, 31B, i.e., image the object field 3 onto the respective intermediate image planes 31A, 31B. The intermediate images situated in the intermediate image planes 31A, 31B are finally imaged at infinity in turn by eyepiece lenses 35A, 35B, such that an observer can observe the intermediate image with a relaxed eye. Moreover, an increase in the distance between the two partial beams 9A, 9B is effectuated in the binocular tube with a mirror system or by prisms 33A, 33B to adapt the distance to the interocular distance of the observer. In addition, image erection is carried out by the mirror system or the prisms 33A, 33B.

[0077] The surgical microscope 2 moreover is equipped with an illumination device, by which the object field 3 can be illuminated with illumination light. To this end, the illumination device in the present exemplary embodiment has a white light source 41, for example a halogen lamp or a gas discharge lamp. The light emanating from the white light source 41 is directed in the direction of the object field 3 via a deflection mirror 43 or a deflection prism to illuminate the field. Furthermore, an illumination optical unit 45 is present in the illumination device, the illumination optical unit ensuring uniform illumination of the entire observed object field 3.

[0078] Reference is made to the fact that the illumination beam path illustrated in FIG. 1 is highly schematic and does not necessarily reproduce the actual course of the illumination beam path. In principle, the illumination beam path can be embodied as what is known as oblique illumination, which comes closest to the schematic illustration in FIG. 1. In such oblique illumination, the beam path extends at a relatively large angle (6° or more) with respect to the optical axis of the objective 5 and, as illustrated in FIG. 1, may extend completely outside the objective. Alternatively, however, there is also the possibility of allowing the illumination beam path of the oblique illumination to extend through a marginal region of the objective 5. A further option for the configuration of the illumination beam path is what is known as 0° illumination, in which the illumination beam path extends through the objective 5 and is coupled into the objective 5 between the two partial beam paths 9A, 9B, along the optical axis of the objective 5 in the direction of the object field 3. Finally, it is also possible to embody the illumination beam path as what is known as coaxial illumination, in which a first illumination partial beam path and a second illumination partial beam path are present. The partial beam paths of the illumination beam path are coupled into the surgical microscope in a manner parallel to the optical axes of the observation partial beam paths 9A, 9B by way of one or more beam splitters, such that the illumination extends coaxially in relation to the two observation partial beam paths.

[0079] In the exemplary embodiment of the surgical microscope 2 shown in FIG. 1, the objective 5 consists only of an achromatic lens. However, use can also be made of an objective lens system made of a plurality of lenses, in particular what is known as a varioscope objective, by which it is possible to vary the working distance of the surgical microscope 2, i.e., the distance between the object-side focal plane and the vertex of the first object-side lens surface of the objective 5, also referred to as front focal distance. The object field 3 arranged in the focal plane is imaged at infinity by the varioscope objective 50, too, and so a parallel beam is present on the observer side.

[0080] One exemplary embodiment of a varioscope objective is illustrated schematically in FIG. 2. The varioscope objective 50 includes a positive member 51, i.e., an optical element having positive refractive power, which is schematically illustrated as a convex lens in FIG. 2. Moreover, the varioscope objective 50 includes a negative member 52, i.e., an optical element having negative refractive power, which is schematically illustrated as a concave lens in FIG. 2. The negative member 52 is situated between the positive member 51 and the object field 3. In the illustrated varioscope objective 50, the negative member 52 has a fixed arrangement, whereas, as indicated by the double-headed arrow 53, the positive member 51 is arranged to be displaceable along the optical axis OA. When the positive member 51 is displaced into the position illustrated by dashed lines in FIG. 2, the back focal length increases, and so there is a change in the working distance of the surgical microscope 2 from the object field 3.

[0081] Even though the positive member 51 has a displaceable configuration in FIG. 2, it is also possible, in principle, to arrange the negative member 52 to be movable along the optical axis OA instead of the positive member 51. However, the negative member 52 often forms the last lens of the varifocal objective 50. A stationary negative member 52 therefore offers the advantage of making it easier to seal the interior of the surgical microscope 2 from external influences. Furthermore, it is noted that, even though the positive member 51 and the negative member 52 in FIG. 2 are only illustrated as individual lenses, each of these members may also be realized in the form of a lens group or a cemented element instead of in the form of an individual lens, for example to embody the varioscope objective to be achromatic or apochromatic.

[0082] FIG. 3 shows a schematic illustration of an example of a digital surgical microscope 48. In this surgical microscope, the main objective 5, the magnification changer 11 and the illumination system 41, 43, 45 do not differ from the surgical microscope 2 with the optical view that is illustrated in FIG. 1. The difference lies in the fact that the surgical microscope 48 shown in FIG. 3 does not include an optical binocular tube. Instead of the tube objectives 29A, 29B shown in FIG. 1, the surgical microscope 48 depicted in FIG. 3 includes focusing lenses 49A, 49B, by which the binocular observation beam paths 9A, 9B are imaged onto digital image sensors 61A, 61B. Here, the digital image sensors 61A, 61B can be, e.g., charge-coupled device (CCD) sensors or complementary metal-oxide semiconductor (CMOS) sensors. The images recorded by the image sensors 61A, 61B are transmitted digitally to digital displays 63A, 63B, which may be embodied as light-emitting diodes (LED) displays, as liquid-crystal display (LCD) displays, or as displays based on organic light-emitting diodes (OLEDs). Like in the present exemplary embodiment, eyepiece lenses 65A, 65B can be assigned to the displays 63A, 63B, by which the images displayed on the displays 63A, 63B are imaged at infinity such that an observer can observe the images with relaxed eyes. The displays 63A, 63B and the eyepiece lenses 65A, 65B can be part of a digital binocular tube; however, they can also be part of a head-mounted display (HMD) such as, a pair of smartglasses.

[0083] Even though FIG. 3, like FIG. 1, only illustrates an achromatic lens 5 with a fixed focal length, the surgical microscope 48 shown in FIG. 3 may include an apochromatic objective or a varioscope objective instead of the achromatic lens 5, like the surgical microscope 2 illustrated in FIG. 1. Furthermore, FIG. 3 shows a transfer of the images recorded by the image sensors 61A, 61B to the displays 63A, 63B by cables 67A, 67B. However, instead of in a wired manner, the images can also be transferred wirelessly to the displays 63A, 63B, especially if the displays 63A, 63B are part of a head-mounted display.

[0084] FIG. 4 shows a surgical microscope in a schematic illustration according to an exemplary embodiment of the disclosure.

[0085] A surgical microscope system 100 includes a surgical microscope 101, a light source unit 140 and a control unit 150. The surgical microscope includes an observation device having an observation beam path 112 and an illumination device having an illumination beam path 113.

[0086] The observation device includes a main objective 102, a magnification changer 103, a first beam splitter 104, and an eyepiece 105, which are arranged along the observation beam path 112. An object region 110 with an object plane 111 can be observed by an observer, illustrated by a schematically illustrated eye 106, through the eyepiece 105.

[0087] The observation device is illustrated schematically. The observation beam path 112 is stereoscopic and includes two partial beam paths (not illustrated).

[0088] The first beam splitter 104, arranged in the observation beam path 112, couples out part of the observation light and images it, via the camera beam path 107, onto the sensor of a camera 108, with the result that the object region 110 with the object plane 111 is capturable by the camera 108. The camera 108 can have a stereoscopic embodiment.

[0089] The light source unit 140 includes a first light source 141 and a second light source 142. The first light source 141 is embodied in the form of a light-emitting diode light source and includes three individual light sources for the colors red, green, and blue. The light-emitting diode light source is also referred to as an RGB light source. The light source unit 140 is connected to the control unit 150 via a first line 151, with the result that each individual light source is separately actuable.

[0090] The illumination light emitted by the first light source 141 is guided via a second beam splitter 143 along an illumination-light beam path 144 and coupled into an optical waveguide 146, for example a fiber-optic cable. The illumination light of the second light source 142 is coupled into the illumination-light beam path 144 via the beam splitter 143. The second light source 142 can be formed for example by an individual light source emitting violet light.

[0091] The optical waveguide 146 is connected to the surgical microscope 101. The illumination light is guided along the illumination beam path 113 to the object region 110 with the object plane 111. An illumination optical unit 120 is arranged in the illumination beam path 113. The illumination beam path 113 is deflected via a deflection mirror 122 and guided through the main objective 102 to the object plane 111.

[0092] A first polarizer 130 is arranged in the illumination beam path 113 between the illumination optical unit 120 and the deflection mirror 121. The first polarizer 130 can be coupled into and out of the illumination beam path 113. To this end, the first polarizer 130 is movable by way of a first actuator 132. The first actuator 132 is connected to the controller 150.

[0093] A second polarizer 131 is arranged in the observation beam path 112 between the magnification changer 103 and the first beam splitter 104. The second polarizer 131 can be coupled into and out of the observation beam path 112. To this end, the second polarizer 131 is movable by way of a second actuator 133. The second actuator 133 is connected to the controller 150.

[0094] In a white light mode, the second made, the first polarizer 130 is coupled out of the illumination beam path 113 and the second polarizer 131 is coupled out of the observation beam path 112. The first light source 141 emits white illumination light. This is attained by way of all individual light sources, i.e., the red, green, and blue individual light sources, being switched on. In this second mode, a tissue region located in the object plane 111 is illuminated with white light. The observer can observe the tissue region in normal view without specific structures, capillaries or blood vessels being particularly highlighted.

[0095] The control unit 150 is connected to a switching element 153. Upon actuation of the switching element 153, the first mode, the multispectral mode, is activated by way of the control unit 150. To this end, the red individual light source of the first light source 141 is switched off, while the green and blue individual light sources remain switched on. At the same time, the first polarizer 130 is coupled into the illumination beam path by way of the first actuator 132, and the second polarizer 131 is coupled into the observation beam path by way of the second actuator 132. This multispectral mode thus results in good visualization and significantly improved contrast of the capillaries and blood vessels in the mucosa and in the underlying tissue.

[0096] The observer observes the image filtered by the second polarizer 131 directly through the eyepieces. The camera 108, which is optional, records a single channel or both channels of the stereoscopic image. No additional digital filtering is necessary to produce the contrast between tissue and blood vessel in the video signal.

[0097] Another actuation of the switching element 153 once again sets the white light mode. To this end, the red individual light source of the first light source 141 is switched on again. The first polarizer 130 is coupled out of the illumination beam path by way of the first actuator 133, and the second polarizer 131 is coupled out of the observation beam path by way of the second actuator 133. These procedures are performed at the same time. In an alternative aspect, they may also be performed successively in time.

[0098] The surgical microscope 101 can be a conventional optical stereo surgical microscope with eyepieces or may be embodied in the form of a purely digital surgical microscope only with cameras. The surgical microscope 101 can be embodied in the form of a hybrid system, a mixture of a conventional surgical microscope and a digital surgical microscope with the camera 108.

[0099] FIG. 5 shows a diagram 200 illustrating an exemplary embodiment of a radiation pattern of the individual light sources of the first light source and of the second light source in accordance with FIG. 4.

[0100] An abscissa 201 indicates the wavelength range of the emitted light between 200 nm and 800 nm. An ordinate 202 indicates an intensity.

[0101] A first curve 210 shows the radiation pattern of the second light source 142 with respect to the exemplary embodiment according to FIG. 4.

[0102] A second curve 211 shows the radiation pattern of the blue individual light source of the first light source 141 with respect to the exemplary embodiment according to FIG. 4. The emitted light of the first blue individual light source is emitted in a wavelength range between 420 nm and

[0103] A third curve 212 shows the radiation pattern of the green individual light source of the first light source 141 with respect to the exemplary embodiment according to FIG. 4. The emitted light of the green individual light source is emitted in a wavelength range between 480 nm and 600 nm.

[0104] A fourth curve 213 shows the radiation pattern of the red individual light source of the first light source 141 with respect to the exemplary embodiment according to FIG. 4. The emitted light of the red individual light source is emitted in a wavelength range between 600 nm and 640 nm.

[0105] FIG. 6 shows a tissue region illuminated with conventional white light illumination. The surgical microscope in accordance with FIG. 4 is set in a second mode.

[0106] FIG. 7 shows the tissue region in accordance with FIG. 6, illuminated in the multispectral mode. The FIG. 7 shows the improved contrast between tissue and blood vessels in the multispectral mode.

[0107] In an alternative exemplary embodiment of the disclosure, the object region with the object plane is illuminated in the first mode using the light source 141 with illumination light in a wavelength range within the absorption spectrum of hemoglobin and below 570 nm. The intensity of the illumination light in the wavelength range above 570 nm is here lower than in the remaining wavelength ranges typically by at least a factor 5, in particular by at least a factor 10. In addition, the first polarizer 131 is introduced in the illumination beam path 113 with a first orientation, with the result that the illumination light is polarized with the first orientation. In addition, the second polarizer 131 is coupled into the observation beam path 112. The second polarizer 131 has a second orientation at an angle between 80° and 100° relative to the first orientation of the first polarizer.

[0108] Owing to the illumination light having wavelengths <570 nm, the penetration depth of the illumination light in mucosal tissue is less than 800 μm. Removing the red wavelengths from the illumination spectrum, i.e., wavelengths >570 nm, and illuminating with blue and green illumination light, i.e., with wavelengths <570 nm, limits the representation substantially to surface layers with a depth of less than 800 μm. In addition, hemoglobin absorption in the green and blue wavelength ranges is significantly greater than in the red wavelength above 570 nm, as a result of which a dark-light contrast between blood-filled vessels and surrounding tissue is obtained. The polarizers additionally have the effect that the light that is scattered back by the mucosal tissue comes from penetration depths of 300 μm and more, with the result that the image information obtained with the observation beam path is limited to a range between 300 and 800 1 μm of tissue located under the skin surface.

[0109] The foregoing description of the exemplary embodiments of the disclosure illustrates and describes the present invention. Additionally, the disclosure shows and describes only the exemplary embodiments but, as mentioned above, it is to be understood that the disclosure is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art.

[0110] The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of.” The terms “a” and “the” as used herein are understood to encompass the plural as well as the singular.

[0111] All publications, patents and patent applications cited in this specification are herein incorporated by reference, and for any and all purposes, as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.

LIST OF REFERENCE SIGNS

[0112] 2 Surgical microscope [0113] 3 Object region [0114] 5 Objective [0115] 7 Divergent beam [0116] 9 Beam [0117] 9A, 9B Stereoscopic partial beam path [0118] 11 Magnification changer [0119] 13A, 13B Interface arrangement [0120] 15A, 15B Beam splitter prism [0121] 19 Camera adapter [0122] 21 Camera [0123] 23 Image sensor [0124] 27 Binocular tube [0125] 29A, 29B Tube objective [0126] 31A, 31B Intermediate image plane [0127] 33A, 33B Prism [0128] 35A, 35B Eyepiece lens [0129] 37 Display [0130] 39 Optical unit [0131] 41 White light source [0132] 43 Deflection mirror [0133] 45 Illumination optical unit [0134] 48 Digital surgical microscope [0135] 49A, 49B Focusing lens [0136] 50 Varifocal objective [0137] 51 Positive member [0138] 52 Negative member [0139] 53 Displacement path [0140] 100 Surgical microscope system [0141] 101 Surgical microscope [0142] 102 Main objective [0143] 103 Magnification changer [0144] 104 First beam splitter [0145] 105 Eyepiece [0146] 106 Eye of an observer [0147] 107 Camera beam path [0148] 108 Camera [0149] 110 Object region [0150] 111 Object plane [0151] 112 Observation beam path [0152] 113 Illumination beam path [0153] 120 Illumination optical unit [0154] 121 Deflection mirror [0155] 130 First polarizer [0156] 131 Second polarizer [0157] 132 First actuator [0158] 133 Second actuator [0159] 140 Light source unit [0160] 141 First light source [0161] 142 Second light source [0162] 143 Second beam splitter [0163] 144 Illumination-light beam path [0164] 146 Optical waveguide [0165] 150 Control unit [0166] 151 First line [0167] 152 Second line [0168] 153 Switching element [0169] 200 Diagram [0170] 201 Abscissa [0171] 202 Ordinate [0172] 210 First curve [0173] 211 Second curve [0174] 212 Third curve [0175] 213 Fourth curve