Surgical microscope

A surgical microscope for imaging structures of an eye includes: a front optical unit, an illumination device which has an illumination-radiation-emitting illumination source and which illuminates the retina of the eye with an illumination spot via an illumination beam path which extends through the front optical unit, a camera and an adjustable camera optical unit disposed upstream thereof, an imaging beam path which extends through the front optical unit and the camera optical unit, and a control device which controls the camera optical unit and sets the latter in such a way that the retina of the eye in the region of the illumination spot is imaged on the camera. The control device varies a focusing state of the camera optical unit and, as a result thereof, records a plurality of images of the retina in the region of the illumination spot, the images being focused in different depth planes, and establishes a refractive value of the eye from these images.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of German patent application no. 10 2015 115 106.5, filed Sep. 8, 2015, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a surgical microscope for interventions on the anterior chamber of the eye, for example for a cataract operation.

BACKGROUND OF THE INVENTION

Surgical microscopes for ophthalmic surgery are known from the prior art, for example from DE 10300925 A1. Such surgical microscopes are usually embodied in such a way that they generate a stereoscopic image of the eye such that the surgeon obtains a spatial impression of the eye to be operated.

In ophthalmic surgery, it is important for the surgeon to know the refractive state of the eye as present at the time of the intervention. By way of example, in the case of cataract operations, the refractive properties are required if the orientation of a toric lens needs to be set. Another problem in the case of cataract operation consists of an intraocular lens being inserted, the values of which were established on the basis of measurements which were carried out prior to the surgical intervention. However, such measurements may be erroneous due to the lens opacification caused by the cataract. Therefore, it is desirable to check the refractive properties of the eye once more prior to the insertion of the intraocular lens but after the removal of the eye lens, that is, on the aphakic eye, so that the lens selection can be corrected where necessary. It is also of interest to check the refractive values of the eye directly after the completion of the operation.

The prior art has disclosed intraoperative refraction measurements, which establish the wavefront emerging from the eye via parallel or time-sequential measurement systems and determine the refractive properties of the eye therefrom. However, these measurement methods are very complicated and require that additional, complex beam paths are coupled into the eye, as a result of which the outlay required for the surgical microscope increases.

The prior art has disclosed a method referred to as “phase retrieval”, which allows conclusions to be drawn about a transfer quality of an optical system by way of specific measurements.

SUMMARY OF THE INVENTION

It is an object to provide a surgical microscope with which the refractive properties of the eye can be established with little outlay.

According to the invention, this object is achieved by a surgical microscope for imaging structures of an eye, the surgical microscope including:a front optical unit,an illumination device which emits illumination radiation and which illuminates the retina of the eye with an illumination spot by way of an illumination beam path which extends through the front optical unit,a camera and an adjustable camera optical unit disposed upstream thereof,an imaging beam path which extends through the front optical unit and the camera optical unit, anda control device which controls the camera optical unit and sets the latter in such a way that the retina of the eye in the region of the illumination spot is imaged on the camera,wherein the control device varies a focusing state of the camera optical unit and, as a result thereof, records a plurality of images of the retina in the region of the illumination spot, the images being focused in different depth planes, and establishes a refractive value of the eye from these images.

The inventors recognized that the “phase retrieval” method, which was previously not used in ophthalmology, can be realized using a surgical microscope without substantial interventions on the existing surgical microscope being necessary. The surgical microscope should be configured in a comparatively simple manner to the extent that the refractive properties of the eye can be determined intraoperatively with the aid of the “phase retrieval” method. Here, the fact that a surgical microscope which is configured for cataract surgery usually illuminates the eye lens with a parallel beam is advantageously exploited. On account of the refractive properties of the eye, a beam which is incident in parallel onto the pupil of the eye generates an illumination spot on the retina. Such an illumination method of the eye lens for surgical microscopes is known by the term SCI illumination and realized, for example, in the surgical microscope OPMI Lumera 700 by Carl Zeiss Meditec AG.

The illumination spot is imaged with the camera of the surgical microscope, with different focusing states in the z-direction being realized. Therefore, there is a slight variation in the position of the image plane relative to the camera plane. This can be considered as “defocusing”, that is, as displacement of the object plane of the video camera in relation to the plane in which the illumination spot is focused. The plurality of images obtained thus constitute a so-called focus stack; they contain the images of the illumination spot with different defocusing states. Then, an image analysis of these various images according to the “phase retrieval” method supplies a refractive value of the eye.

The illumination spot is imaged by virtue of the camera optical unit being deliberately defocused for the purposes of recording the plurality of images. This deviates from the usual procedure in microscopy, in which an image which is focused to the best possible extent is obtained. Here, in an embodiment of the invention, provision is made for the camera optical unit for recording the images of the illumination spot to be set to an object plane, independently of which object plane of the surgical microscope is set for the purposes of examining the eye by microscopy. For the purposes of establishing the refractive value, the control device sets the camera optical unit into the object plane on the retina, without also adjusting the remaining imaging channels of the surgical microscope at the same time, for example, a tube eyepiece or eyepiece or a camera of a different stereo channel.

In an embodiment of this concept, for the purposes of establishing the refractive value, the control device intermittently switches the camera optical unit onto the object plane in which the focal spot lies and it records the focus stack there but keeps the other imaging channels of the surgical microscope with such a setting that a different object plane is examined by microscopy. In this manner, the camera optical unit and the camera are switched into a multiplex operation, in which the refractive value of the eye is established repeatedly during the examination of a different region, for example, the anterior chamber of the eye or eye lens, by microscopy. Naturally, during the recording of the plurality of images required for establishing the refraction value, the camera supplies image information which does not fit to the other imaging devices, for example a different stereo channel or a tube device and eye device. Therefore, provision is made in a preferred embodiment for the surgical microscope to be provided as a stereo surgical microscope and for the camera used to establish the refractive value to be the camera of a stereo channel of the stereo surgical microscope. Here, during the time period in which the camera is directed onto an object plane which differs from the object plane of the other stereo channel, it is particularly preferable either for the microscope to be switched into monocular mode of operation or, for the duration of the determination of the plurality of images, for the image information established during synchronous operation of the two cameras to be maintained for the channel whose camera is used for establishing the refractive value. If the microscope is switched into a monocular mode of operation in respect of the cameras, one of the two cameras can be used for microscopy in the object plane desired by the user; the other camera serves for the continuous establishment of the refractive value, that is, it is set to an object plane lying in the region of the illumination spot.

The surgical microscope can also realize a further operating state, to the effect that the camera optical unit has an adjustable embodiment and, in the further operating state, the control device sets the latter in such a way that an image of the anterior chamber or the eye lens of the eye is generated. In this way, a user can easily switch between the two operating states and either sees an image of the anterior chamber/eye lens, as is conventional for a cataract intervention, or uses the operating mode in which the surgical microscope automatically establishes a refractive value of the eye via the control device. Switching to and fro between the two modes of operation provides the user with the information about the current refractive state of the eye at any time during the surgical intervention, as a result of which the result of the surgical intervention is improved overall.

The illumination spot is formed on the eye from illumination radiation incident in parallel into the anterior chamber when an eye lens is present in the eye, either the natural intraocular lens or an intraocular lens inserted by surgery. However, additional optical measures are required to form the illumination spot in the case of an aphakic eye. Therefore, it is preferable in one embodiment of the surgical microscope for provision to be made of an adjustable optical unit and/or an optical unit which can be brought into the illumination beam path, the optical unit focusing the illumination radiation in such a way that an illumination spot is formed at the retina, even in the case of an aphakic eye.

The refractive value of the eye can be established via the “phase retrieval” method, which was already specified at the outset. A simplified establishment, which possibly has a sufficient, lower accuracy, is already obtained if an outline form of the illumination spot is evaluated in the images; that is, the control device establishes what outline the illumination spot has in the various defocused images. By way of example, the principal axis of an astigmatism can be established from this outline shape. For certain requirements, the specification of the principal axis as a refractive value suffices, for example if the surgeon should be provided with assistance in respect of the orientation in which a toric intraocular lens should be inserted. Therefore, the term refractive value includes the position of the principal axis of an astigmatism in some embodiments. In other embodiments, the refractive value is the value of a spherical and/or cylindrical deviation. In further embodiments, the refractive value is a specification of Zernike polynomials.

For such applications, it is particularly advantageous if the surgical microscope has a display device and the control device establishes the astigmatism axis as refractive value and plots the latter into an image of the eye on the display device. However, such an embodiment of the surgical microscope is naturally also advantageous if specifications going beyond the astigmatism axis are established for the refractive value of the eye.

In all cases where the eye is not aphakic, that is, either the natural eye lens or eye lens inserted by surgery is present, it is preferable, in view of a constructional outlay of the surgical microscope which is as small as possible, for a beam splitter to be disposed downstream of the front optical unit, the beam splitter coupling the imaging beam path into the illumination beam path, as a result of which the illumination beam path is then embodied as a parallel beam path between the front optical unit and the eye, like the illumination beam path as well.

In such cases, it is likewise preferable for the illumination device to illuminate the eye lens with a parallel illumination beam.

The refractive value of the eye is determined particularly precisely if the illumination spot has a minimal dimension. The dimension of the illumination spot can be set by a stop which is disposed upstream of the beam splitter in the illumination beam path. The dimension thereof directly influences the dimension of the illumination spot. Here, “directly” should be understood to mean that a reduction in the dimension of the stop also reduces the illumination spot. However, the dimension of the stop also directly influences the brightness with which the anterior chamber of the eye or eye lens is illuminated. Naturally, a user would like a brightness of the illumination of the anterior chamber or eye lens which is as high as possible for the cataract operations. Therefore, it is preferable in one embodiment for the control device to adjust the dimension of the stop depending on which mode of operation is used. If the camera is set for the anterior chamber or the eye lens, the stop is set to be larger than in the operating mode in which the refractive value of the eye is established. An optimization is possible for both modes of operation by adjusting the stop.

The determination of the refractive value is only reliable if the patient looks into the measurement beam, that is, fixates thereon in an appropriate manner, during the measurement. Therefore, an embodiment in which the illumination source simultaneously serves as fixation source is preferred. Alternatively, a light spot, for example from a laser or an SLD light source, which is additionally coupled into the illumination beam path is used as a fixation light.

It is particularly advantageous to select a wavelength in the short-wavelength range of the visible spectrum, for example, green, for the fixation light since an illumination spot then is smaller than in the case of radiation with a longer wavelength due to the reduced scattering in the retinal tissue.

The prior art, for example, US 2014/0024949, has disclosed the practice of additionally providing an OCT on an surgical microscope. Determining the refractive value was found to be particularly precise if the illumination spot lies as close as possible to the fovea. It is therefore preferable for the surgical microscope to additionally have an OCT (Optical Coherence Tomography), which is likewise controlled by the control device and the measured values of which are read by the control device, and for the control device only to establish the refractive value of the eye if the measured values of the OCT indicate that the illumination spot lies within predetermined surroundings of the fovea or directly on the fovea. Checking whether the illumination spot lies sufficiently close, or on, the fovea is known to the control device in the surgical microscope since the geometric relation between the beam path of the OCT and the illumination beam path is set and known. In this way, it is possible to ensure that the refractive value is only established when the eye is in a correct fixation state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1shows a surgical microscope M which is embodied for imaging an eye1during a surgical intervention, in this case a contract operation. The surgical microscope M illuminates the eye1with light from a light source2, which may be, for example, a halogen lamp, a xenon arc lamp, an LED, a laser or an SLD. An illumination optical unit3focuses the illumination radiation emanating from the light source2in such a way that, in combination with a main objective, a parallel beam is incident on the eye1. An eye lens15of the eye1brings about focusing of this parallel illumination beam onto an illumination spot16. The illumination optical unit3and the front optical unit and the main objective4therefore set an illumination beam path17, which runs over a beam splitter19in order to connect the illumination beam path17with an imaging beam path of the surgical microscope M.

The surgical microscope M images the eye1on cameras (5,6) by way of the main objective4, the cameras supplying their data to a control device S. The control device S can, for example, be or include a processor, CPU, electrical control circuit, computer, computer processor, a microprocessor or the like. The control device may include a memory/data storage unit. The cameras (5,6) are coupled on by way of a beam splitter such that the surgical microscope M supplies a stereo image of the eye1, even in a tube and eyepiece optical unit (9,10). Additionally, displays (7,8) are mirrored-in by way of beam splitters such that a user sees not only a stereo image of the eye1but also image information originating from the displays (7,8) when looking in through the tube and eyepiece optical unit (9,10). The displays are likewise supplied with appropriate data by the control device S.

In the illustration ofFIG. 1, the eye1has an eye lens15, that is, it is not in an aphakic state which may occur during the cataract operation. As a result, the illumination radiation incident in parallel is focused into the illumination spot16. Overall, the eye lens15participates in the illumination beam path17. If the eye does not have an eye lens15, an adjustment of the illumination optical unit3is provided, the latter ensuring that the illumination spot16nevertheless arises on the retina of the eye1.

The eye is imaged on the camera6by way of an imaging beam path18, which is formed, inter alia, by the main objective4and the camera optical unit11. Here, under the control of the control device S, the camera optical unit11is adjustable in such a way that a focus21of the image lies on the retina and hence at the location of the illumination spot16. The illumination spot16and the focus21coincide spatially since the imaging beam path18to the camera6is coupled into the illumination beam path17by way of the beam splitter19. The incidentally still plotted beam splitter20separates the imaging beam path onto the camera6from the imaging beam path onto the tube and eyepiece optical unit. This could also be inverted, that is, the beam splitter20separates the radiation for the tube and eyepiece optical unit (9,10). Since both the imaging beam path18and the illumination beam path17run through the objective4, an image of the illumination spot16arises on the camera6. In order to establish a refractive value of the eye1, the control device S sets the camera optical unit11into different positions and records a series of images13, which are shown inFIGS. 3A to 3F. The images13correspond to different focusing states, that is, different displacements of the image plane defined by the imaging beam path18and of the plane in which the camera6is situated.FIG. 3Acorresponds to defocusing of −4 mm,FIG. 3Bcorresponds to defocusing of −2 mm,FIG. 3Ccorresponds to a focusing state of 0 mm, that is, the image plane and the plane of the camera6coincide in this case,FIG. 3Dcorresponds to defocusing of +2 mm,FIG. 3Ecorresponds to defocusing of +4 mm andFIG. 3Fcorresponds to defocusing of +6 mm.

As shown inFIGS. 3A to 3F, the form of an illumination spot image14in the images13changes depending on the defocusing. The plurality of images13recorded in this manner by the control device S corresponds to a focus stack. The control device S calculates a refractive value of the eye therefrom. As explained in the general part of the description, the refractive value can merely specify the position of the principal axis of the astigmatism in the simplest case. In an embodiment, a qualitative measure for refractive error is also determined from the focus stack, for example in the form of Zernike polynomials.

FIG. 2shows a further operating state of the surgical microscope M, in which the focus21lies in the anterior chamber or at the eye lens15. This is achieved by virtue of the control device S accordingly setting the camera optical unit11in such a way that the object plane of the imaging beam path18lies or in the region of the eye lens15.

In other words, the control device S sets the camera optical unit11for the further operating mode in such a way that a different plane is conjugate to the plane of the camera6, namely the desired plane in the region of the eye lens15or in the anterior chamber. By contrast, in the operating mode ofFIG. 1, the camera optical unit11is set in such a way that the camera6is conjugate to a plane in which the retina lies.

Naturally, the second camera5and the mirroring-in of the data from the display (7,8) are optional.

The illustrations ofFIGS. 3A to 3Fshow the change in the spot form depending on the defocusing of the camera optical unit11for an astigmatic error of the eye of 1 diopter, wherein the focal length of the main objective is 200 mm and the focal length of the camera optical unit11is 50 mm.

The illumination spot16on the retina can also be generated differently to what is depicted inFIGS. 1 and 2. As an alternative to the SCI illumination used there, it is also possible to use a laser light source or an SLD light source coupled into the beam path, as is known, for example, for realizing an OCT in surgical microscopes.

The camera optical unit11allows the control device S to switch between the modes of operation ofFIG. 1andFIG. 2, that is, to place the object planes imaged on the camera6in the region of the eye lens or in the region of the retina, depending on the setting of the camera optical unit11. This adjustment possibility permits the integration of the determination of the refractive values of the eye1into the surgical microscope M.

In order to generate an illumination spot16on the retina1which is as small as possible, it is preferable to dispose a stop (not depicted inFIGS. 1 and 2) in front of the light source2and to set the spot differently for determining the refractive value or for imaging the eye lens, as was already explained in the general part of the description.

Intraoperative refraction measurements are only reliable if the patient looks into the measurement beam during the measurement. The fixation sources mentioned in the general part of the description are therefore advantageous for an optional embodiment of the surgical microscope M. If an OCT system is used for fixation or illumination, care has to be taken that visible radiation, that is, light, is coupled into the OCT interferometer.

For the purposes of aligning a toric lens during the cataract operation, the refractive value of the eye must be established virtually in real time so that the surgeon rotates the toric intraocular lens under control of the surgical microscope M, that is, with the current display of the refractive value, for example the principal axis of the astigmatism. Therefore, an embodiment in which the control device S places the surgical microscope M to and fro between the two modes of operation in a multiplex mode is preferred, that is, in which the control device alternately shifts the camera optical unit11between two basic positions, in which the object plane lies in the region of the eye lens and in the region of the retina, respectively, and records the focus stack for the basic position with the position of the object plane in the region of the retina.

An embodiment of the multiplex operation includes one of the two cameras, for example, the camera6, being set in terms of the camera optical unit thereof, in this case the camera optical unit11, in such a way that the refractive value of the eye is determined, while the other camera, for example, the camera5, is set in terms of the camera optical unit thereof, in this case the camera optical unit12, in such a way that the object plane lies in the region of the eye lens15. Therefore, there is a deliberate difference in the settings of the camera optical units (11,12) assigned to the stereo channels, which are always set the same during stereo operation. The deliberate deviation from the prescription of the stereo operation renders it possible to continuously establish the refractive value, as already explained in the general part of the description.

The “phase retrieval” method renders it possible to measure the properties of the whole optical system including eye and surgical microscope M. Provision is therefore made in an embodiment for the optical properties of the surgical microscope M to be measured and accordingly subtracted from the measurement result such that only the optical properties of the eye1are established as refractive value.

In place of the integration into the beam path of the surgical microscope M, shown inFIGS. 1 and 2, provision can also be made of a separate module below the main objective4, the separate module including a camera for recording the focus stack and the adjustable camera optical unit required therefor. Either a light source used in the surgical microscope M or a light source integrated into the additional module can be used as a light source for generating the illumination spot.

The position of the principal axis of an astigmatism can be established from the outline shape of the illumination spot image14. For this, two images are already sufficient, that is, a focus stack having two images13.

For the purposes of generating the focus stack, provision is made in one embodiment of a lens with a variable focal length and without mechanically moving elements being used instead of an adjustment of the camera optical unit11, the lens particularly preferably only being provided in the camera optical unit11for the adjustment for recording the focus stack.