Optical coherence tomography apparatus

Abstract

The object of the invention is to propose a device for performing optical coherence tomography, which is capable of capturing an image of a captured object or object structure with the simplest structure while reliably detecting the size of the object or object structure, thereby providing a device (10) for performing optical coherence tomography, comprising an interferometer having a light source (1), a reference arm (4) and a sample arm (5), the light emitted by the light source (1) being split by means of a light splitter (6a) such that a first light can be guided on the reference arm (4) and a second light can be guided on the sample arm (5), the first light and the second light being interferential, a detection device (3) being provided, the invention relates to a device for detecting and processing a signal in which first light interferes with second light, characterized in that an optical element (2) is provided, by means of which the first light in a reference arm (4) can be further split into primary light (I) and secondary light (II), the primary light (I) can be guided along a first light path (4a), and the secondary light (II) can be guided along a second light path (4b), the length of the second optical path is different from the length of the first optical path (4a).

Description

Technical Field

[0001] The invention relates to a device according to the subject-matter of claim 1. Background Art

[0002] The term "Optical Coherence Tomography" (often abbreviated to OCT) refers to an imaging method by which two-dimensional and three-dimensional images can be obtained from light-scattering structures.

[0003] In this method, light with a certain bandwidth is split into two beams, usually in a beam splitter. The first beam falls on the sample or object to be examined, and the second beam passes through a reference path.

[0004] The light reflected from the sample or object interferes with the reference beam. Using the interference signal, the sample can be analyzed with depth resolution, i.e. at the depth of the optical axis of the first partial beam, with the aid of a so-called A-scan.

[0005] In addition, the first partial light beam can be used to perform planar or transverse scanning on the sample to acquire an OCT image.

[0006] When performing OCT imaging of the posterior segment of the eye, the lateral scale of the image is often simply referred to as the field angle. To convert the field angle to an absolute length or distance, information about the length of the eye and the optical properties of the eye under examination is required. In addition, to correct the OCT image so that it is displayed in the correct proportion of the curvature, knowledge of the length of the eye is required.

[0007] In this context, there are currently two main methods for determining the length of the eyeball. With the aid of an eyeball model, the length of the eyeball can be estimated using the already set diopter and the manually entered corneal radius. It is also possible to measure the length of the eyeball directly using dedicated equipment. In this context, currently biometric instruments simultaneously record a rough image of the retina, and the eyeball length determined from this can be used to determine the scaling factor. However, such images are of poor quality and are not suitable for diagnostic purposes.

[0008] Separately measuring the length of the eyeball or the corneal curvature is an extra task for the user, so these measurements are not always performed and the results are not transferred to the software used to evaluate the posterior segment OCT images of the eyeball. If the values ​​are entered manually, transmission errors may also occur. Adding additional biometric technology to retinal OCT diagnostic equipment significantly increases the complexity of the system. Summary of the invention

[0009] In view of the above, an object of the present invention is to provide a device for performing optical coherence tomography, which can capture an image of an object or an object structure with the simplest structure and reliably detect the size of the object or the object structure.

[0010] In order to achieve the above object, the present invention provides the features described in claim 1.

[0011] The device comprises an interferometer having a reference arm and a sample arm, wherein each light beam guided on these arms can interfere with other light beams, and a detection device detects and processes the interference signal.

[0012] According to the invention, an optical element is provided, with which the light in the reference arm can be further divided or split, wherein primary light can be guided on a first optical path in the reference arm and secondary light can be guided on a second optical path in the reference arm, the length of the second optical path being different from the length of the first optical path.

[0013] According to the invention, such an OCT device has an interferometer with a beam splitting optical element for simultaneous or substantially simultaneous recording of OCT images at different distances from the device. According to the invention, the distance from the camera or lens of the device to the object, in particular to the eye, can also be measured simultaneously or substantially simultaneously with the imaging of a section of the object, preferably the posterior segment of the eye. This allows a very precise determination of the length of the object or the length of an object structure, in particular the optical eye length.

[0014] The detection device, in particular as part of a spectrometer, can detect and process the corresponding signals generated by the primary light or the secondary light from the corresponding first optical path or the second optical path, and generate A scans for the first optical path and the second optical path synchronously or at short intervals. This means that for each camera frame, A scans of the retina and the cornea can be created simultaneously. There is no need to use error-prone algorithms to align overlapping structures in the image.

[0015] In this context, light of a first spectral range can be guided on a first optical path, and light of a second spectral range can be guided on a second optical path. In this way, the light can be split into light beams of different spectral ranges, i.e., light beams of different wavelengths. In this way, a line scan camera of a detection device in the detection arm of the interferometer can record signals from at least two spectral ranges and process them separately for the two spectral ranges. Thus, OCT images in two spectral ranges can be recorded simultaneously or substantially simultaneously at different distances from the device.

[0016] The spectral ranges of the optical paths may not overlap or only slightly overlap. Alternatively, the spectral ranges of the optical paths may be separated from each other by a certain wavelength range or spectral range. In this way, line scan cameras are particularly good at capturing most or all wavelengths of light from a first wavelength interval of different wavelength intervals with good signal quality.

[0017] Light of a second spectral range may be guided on a second optical path, wherein light of two spectral ranges may be guided on a first optical path, the latter two spectral ranges being separated from each other by a wavelength range. In this way, the line scan camera is particularly good at capturing light wavelengths from two different independent first intervals, which light wavelengths are distinguishable from light wavelengths of the second interval. The two spectral ranges of the first optical path may not overlap or only slightly overlap with the spectral range of the second optical path. In this way, a very good or sufficiently good signal quality may be achieved.

[0018] By means of the detection device, the distance of the structures from the device can be determined synchronously or at short intervals based on the axial position of the structures in the A-scan and the length of the first and second light paths. This allows the light paths to be specifically assigned to specific structures to be detected.

[0019] Based on the determined distances, the length of the object to be inspected and / or the distances of structures within the object, in particular the distances between structures or between structures and the device, can be determined. In this way, not only the spatial extension of the object but also the spatial structure within the object can be analyzed.

[0020] The device described herein can be used to determine the length of the eyeball. Alternatively or additionally, the device can be used to determine the distance between the cornea of ​​the eyeball and its retina. These data can be used by doctors for further diagnosis.

[0021] In this context, the image generating device can generate and / or display a horizontally scaled image of the retina based on the determined length of the eyeball. In this way, all important information can be intuitively presented to the doctor through the image, so that the doctor can make an accurate diagnosis.

[0022] The detection device may include a line scan camera. Alternatively or additionally, the light source may be a broadband light source. A broadband light source may emit light in a very wide spectral range, which may be split into light beams in different spectral ranges, which are sub-ranges of the aforementioned wide spectral range. A line scan camera may very selectively capture light from different spectral ranges.

[0023] With the device, it is possible to switch between two image generation modes, wherein in a first mode, synchronized images of the retina and cornea of ​​the eyeball can be recorded and / or displayed, and in a second mode, only images of the retina of the eyeball can be recorded and / or displayed. The switchable recording mode can be achieved by a switching device, which allows switching between a spectral splitting synchronization mode and a full spectral bandwidth retinal imaging mode. Compared with the prior art, such a switching device does not need to switch back and forth between different Z ranges.

[0024] In this context, the optical element can be switched into the beam path of the reference arm or pivoted into it and out of it. The pivoting process can be easily realized mechanically, for example by a motor that pivots the optical element.

[0025] The optical element can have or be designed as a beam splitter, in particular a dichroic beam splitter. In this way, light or a light beam can be split into two beams that propagate along different optical paths. A dichroic beam splitter splits an incident light beam into beams of different spectral ranges.

[0026] The optical element can be designed as a dichroic element or include a dichroic element. In this way, the light can be split into partial beams of different wavelengths. Instead of a separate beam splitter and a reflector, for example, a dichroic mirror can also be used as a dichroic element, which is arranged directly in the beam path of the reference arm and has a reflective effect only for the first spectral range or the first spectral range of the main light.

[0027] Alternatively, the dichroic element may be designed as a dichroic lens or a dichroic coated lens. The lens may be used with a switching device that is required to pivot a single compact optical component in and out.

[0028] Furthermore, the use of dichroic lenses is particularly advantageous when alignment is required for single mode fibers. A dichroic lens or a dichroic coated lens can be placed in the beam path of the reference arm with little or no refraction of the transmitted light in general. If the light is fed into the reference arm using an optical fiber, this has the advantage of being easier to align, but with increased light losses. The advantage of non-critical alignment is that the lens can be easily pivoted in and out of the beam path, allowing for simple and robust switching between the two modes of imaging the full spectrum of the retina and simultaneous imaging of the cornea and retina to determine the optical eye length.

[0029] The dichroic element can be designed as a dichroic mirror that reflects only a specified wavelength range or spectral range. With such a mirror, incident light in a specified spectral range can be reflected, while light in other spectral ranges can be transmitted.

[0030] An arrangement for adjusting the working distance of a lens to an object to be examined and / or for lateral adjustment of a lens may comprise a device of the type described herein. The device described herein may be integrated into a fully automated retinal diagnostic system and used as a Z sensor of an automatic adjustment device in order to set the correct working distance between the lens and the vertex or apex of the eyeball.

[0031] The device described in this article can be used not only in spectral domain OCT, but also in swept source OCT systems. If the device is implemented in a specific system, non-contiguous spectral regions can be used. This can greatly improve the spatial resolution, but at the expense of higher sidebands.

[0032] The beam paths and optical paths described herein can be realized not only in the context of free beam optics but also at least partially in the context of fiber optics. Thus, the device can be provided with an optical fiber.

[0033] During the capture of the posterior segment OCT image of the eyeball, the distance between the device described in this article and the eyeball to be examined can be measured to record the size of the eyeball, especially the length of the eyeball. With the device described in this article, there is no need to measure the length of the eyeball separately, and there is no error caused by transmitting data or not entering data. This improves the absolute scaling average accuracy of retinal OCT images and cSLO images collected simultaneously with confocal scanning laser fundus examination.

[0034] In the prior art, corneal curvature and refraction are currently used to estimate the axial length, thereby determining the scaling ratio. However, if the unconsidered eye parameters (such as the second surface corneal curvature, anterior chamber depth and lens parameters) deviate from the model eye used, the determination of the axial length will be wrong. This is especially true when the patient's refractive error is corrected by using an intraocular lens (IOL). Therefore, directly measuring the axial length is a more robust parameter for determining the scaling ratio.

[0035] Classification methods can achieve higher test power due to a better scaling match between the test and reference data. Methods that do not record dense volumes but use scan patterns with fixed scaling can also benefit from a better match between the recorded OCT slice image positions and the target positions. For example, using a circular scan with a fixed radius, the actual radius will vary less in the eye.

[0036] It is also advantageous that the distance measured during recording can be used to check whether the relative position of the device camera to the eyeball is correct.

[0037] This information can be used to adjust the camera manually or automatically. If the optical eye length is known, the OCT signal from the retina can be used as a direct control variable for automatic distance adjustment (reference arm length to the retinal signal at the best match of eye length).

[0038] If the length of the eyeball is unknown, the distance can be adjusted automatically using the corneal signal, and the reference arm can then be optimally adjusted in a second automatic step based on the retinal signal.

[0039] The position of the available corneal signal in the B-scan can also be used to obtain information about the lateral adjustment of the camera in the scanning direction.

[0040] If the scanning direction is changed and radial scans in different directions are performed alternately, such as two orthogonal scans, the position information can also be in a two-dimensional form.

[0041] Another potential application of the device is the measurement of retinal curvature, which can be relevant for various pathologies, especially in myopic patients. The curvature of the retinal signal depends on the working distance between the lens vertex and the corneal vertex. If the photosphere length is known, the working distance can be reliably determined from the known parameters "reference arm length" and "length of the sample arm to the lens vertex". This allows the real curvature of the retina to be determined more accurately using an appropriate eyeball model.

[0042] Compared to methods that measure the distance to the retina and cornea sequentially, for example by changing the length of the reference arm, the advantage of using the device described herein is that the measurements can be performed simultaneously. Therefore, errors in length measurement caused by axial movements of the eyeball are largely excluded.

[0043] Several advantages can be achieved by using the device described herein. The accuracy of classification methods that rely on scaling is improved. Manual adjustment is aided by specifying an interpupillary distance or a derivative indication, thereby improving image quality on average. Automatic adjustment functions are supported. The actual curvature of the retina can be displayed in true proportion. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of recording the posterior segment of the eyeball is shown, where the field angle is shown as an instrument parameter. Since the optical and size conditions of the examined eyeball are unknown, the size of the recorded area at the fundus d cannot be directly obtained;

[0045] Figure 2 A schematic diagram of a device for performing optical coherence tomography is shown, the device having an interferometer, wherein an optical element is arranged in a reference arm, a first spectral range is used on a first channel of a detection device and a second spectral range is used on a second channel of the detection device to generate an image;

[0046] Figure 3 A further schematic diagram of an apparatus for performing optical coherence tomography is shown, wherein an optical element is arranged in the reference arm, two discontinuous spectral ranges at two ends of the spectrum are used on a first channel of the detection device to generate an image, and a second spectral range is used on a second channel to generate an image;

[0047] Figure 4 The left figure in the middle shows a schematic diagram of a dichroic mirror as an optical element arranged in the beam path of the reference arm, and the right figure shows a schematic diagram of a dichroic coated lens as an optical element arranged in the beam path of the reference arm. DETAILED DESCRIPTION

[0048] Figure 1A schematic diagram of recording the posterior segment of a human eye 8 by OCT or cSLO is shown, wherein the field of view angle φ is shown as a device parameter. Since the optical and size conditions of the eye 8 under examination are unknown, the size of the recording area at the fundus d cannot be directly obtained; a prior art device 10' is used to record the posterior segment of the eye.

[0049] In this context, Figure 2 and Figure 3 Detailed schematic diagrams of a device 10 for performing optical coherence tomography are shown respectively, wherein the device 10 includes an interferometer having a broadband light source 1, a reference arm 4 and a sample arm 5, and light emitted from the light source 1 is split by a beam splitter 6a, thereby guiding the first light on the reference arm 4 and the second light on the sample arm 5.

[0050] The first light and the second light are caused to interfere with each other, and the detection device 3 is arranged to detect and process a signal of the interference between the first light and the second light.

[0051] An optical element 2 is provided to further split the first light in the reference arm 4 into primary light (I) and secondary light (II). The primary light (I) is guided along a first optical path 4a in the reference arm 4, and the secondary light (II) is guided along a second optical path 4b in the reference arm 4, wherein the length of the second optical path 4b is different from that of the first optical path 4a.

[0052] In this regard, the first light includes primary light (I) and secondary light (II) on different light paths 4a, 4b, both of which interfere with the second light.

[0053] like Figure 2 As shown, the detection device 3 detects and processes the corresponding signals generated by the primary light (I) or the secondary light (II) from the corresponding first optical path 4a or the second optical path 4b, and generates A scans for the first optical path 4a and the second optical path 4b synchronously or at short intervals.

[0054] Primary light (I) of a first spectral range 7a to be detected is guided on a first beam path 4a, and secondary light (II) of a second spectral range 7b to be detected is guided on a second beam path 4b.

[0055] The spectral ranges 7a, 7b of the primary light (I) and the secondary light (II) on the optical paths 4a, 4b do not overlap with each other.

[0056] The detection device 3 includes a line scan camera 3a. The line scan camera 3a in the interferometer detection arm records the signals of two spectral ranges 7a, 7b, and processes the two spectral ranges 7a, 7b or wavelength ranges separately. The wavelength range corresponding to each spectral range 7a, 7b includes light of a specific wavelength interval.

[0057] This creates an A-scan of the retina or retina and cornea or cornea of ​​the eye 8 simultaneously with each camera frame 8. No error-prone algorithms need to be employed to register overlapping structures in the images, such as the cornea and retina.

[0058] From the OCT image of the first spectral range 7a, the absolute distance of the cornea from the device 10 or from the camera lens of the device 10 can be determined.

[0059] From the position of the retina on the OCT image of the second spectral range 7 b , the optical distance of the retina to the device 10 or to a camera lens of the device 10 can be determined.

[0060] The difference between the corneal position and the retinal position is the optical eye length. The eye length determined in this way can be used to more accurately estimate or determine the lateral scaling of the retinal image.

[0061] In the reference arm 4, the broadband light from the light source 1 is divided into optical paths 4a and 4b of different lengths by the optical element 2, so that the length of the reference arm 4a of the first part of the spectrum (I) corresponds to the distance from the device 10 to the cornea of ​​the eyeball 8, and the length of the reference arm 4b of the second part of the spectrum (II) corresponds to the optical distance from the device 10 to the retina.

[0062] Even with this extremely small wavelength range, the resolution is sufficient to adequately determine the position of the cornea, with only a slight loss in depth resolution for diagnostic images.

[0063] In this context, Figure 3 A device 10 is shown, in which secondary light (II) of a second spectral range 7b to be detected is guided on a second optical path 4b, and primary light (I) of two first spectral ranges 7.1a and 7.2a to be detected can be guided on a first optical path 4a, respectively, wherein the latter two first spectral ranges 7.1a and 7.2a are spaced apart from each other by a certain wavelength range and do not overlap with the second spectral range 7b of the second optical path 4b.

[0064] Therefore, two discontinuous first spectral ranges 7.1a, 7.2a at two ends of the spectrum are used on the first channel of the detection device 3 to generate an image.

[0065] A continuous second spectral range 7b is used on the second channel to generate an image.

[0066] Therefore, the first channel has a higher resolution, but also has strong sidebands. The second channel has a slightly lower signal-to-noise ratio and resolution.

[0067] With the help of Figure 2 and Figure 3The detection device 3 of the device 10 shown can determine the distances of the structures from the detection device 3 or the device 10 synchronously or at short intervals based on the axial positions of the structures in the A scan and the lengths of the first optical path 4a and the second optical path 4b.

[0068] Based on the determined distance between the structure and the device 10 , the length of the object to be inspected and / or the distances between structures within the object, in particular the distances between the structures, can be determined.

[0069] use Figure 2 and Figure 3 The device 10 shown can determine the length of the eyeball 8 and / or the distance between the cornea of ​​the eyeball 8 and its retina.

[0070] The image generating device may generate and / or display a lateral zoomed image of the retina based on the determined length of the eyeball 8 .

[0071] like Figure 2 and Figure 3 In the device shown, it is possible to switch between two image generation modes, wherein in the first mode synchronized images of the retina and cornea of ​​the eye 8 can be recorded and / or displayed, and in the second mode only images of the retina of the eye 8 can be recorded and / or displayed.

[0072] For this purpose, the optical element 2 can be switched into the beam path of the reference arm 4 or can be moved into the beam path of the reference arm 4 and then moved away from or out of it.

[0073] like Figure 2 and Figure 3 As shown, the optical element 2 has a dichroic beam splitter 6b and guides the primary light (I) and the secondary light (II) in different directions onto respective optical paths 4a, 4b.

[0074] Figure 4 Two alternative reference arms 4 ′, 4 ″ are shown in detail, in which the optical element 2 is designed as a dichroic element or comprises a dichroic element.

[0075] Figure 4 The left side shows a dichroic element designed to reflect only a specified spectral range or wavelength range. Specifically, the primary light (I) is allowed to be reflected while the secondary light (II) is transmitted. This creates two light paths 4a, 4b of different lengths.

[0076] Figure 4 The right side shows that the dichroic element is designed as a dichroic lens or a dichroic coated lens. The dichroic coated lens is arranged in the beam path of the reference arm 4 ″ and generally does not refract or only slightly refracts the transmitted secondary light (II).

[0077] Since optical fiber 9 is used to feed light into reference arm 4", adjustment is more convenient. The figure schematically shows optical fiber 9, which can be designed as a single-mode optical fiber.

[0078] In the OCT reference arms 4, 4', 4", the broadband light from the light source 1 is preferably divided into optical paths 4a, 4b of different lengths by the dichroic optical element 2, so that the length of the reference arm 4a of the first part of the spectrum (I) corresponds to the distance from the device 10 to the cornea of ​​the eyeball 8, and the length of the reference arm 4b of the second part of the spectrum (II) corresponds to the optical distance from the device 10 to the retina.

[0079] Figure 2 and Figure 3 The optical distance plane R where the cornea is located is shown I and the optical distance plane R where the retina is located II . Distance plane R I , R II The distance therebetween corresponds to the length of the eyeball 8 .

[0080] Using the device 10 described herein, OCT imaging of the posterior segment of the eye can be performed and the distance from the device 10 to the eye 8 can be determined simultaneously or substantially simultaneously. This is achieved by using a reference arm 4 having a dichroic element.

[0081] Reference numerals

[0082] 1 Equipment light source

[0083] 2 Optical elements of the reference arm

[0084] 3 Detection device

[0085] 3b Line Scan Camera

[0086] 4,4',4” Reference Arm

[0087] 4a The first optical path in the reference arm

[0088] 4b Second optical path in the reference arm

[0089] 5 Sample Arm

[0090] 6a First beam splitter

[0091] 6b Second beam splitter (dichroic)

[0092] 7a First spectral range

[0093] 7b Second spectral range

[0094] 7.1a The first spectral range

[0095] 7.1b Second first spectral range

[0096] 8 Eyeball

[0097] 9. Fiber Optics

[0098] 10,10' Equipment

[0099] I Primary light of the first light path

[0100] II Secondary light of the second optical path

[0101] R I The distance plane between cornea and device

[0102] R II Retina distance from device plane

Claims

1. An apparatus (10) for performing optical coherence tomography, comprising: An interferometer having: a light source (1); Reference arm (4); as well as Sample arm (5), The light emitted by the light source (1) can be split by a beam splitter (6a), so that the reference arm (4) can guide the first light and the sample arm (5) can guide the second light. wherein the first light and the second light can interfere with each other, A detection device (3) is provided for detecting and processing a signal of interference between the first light and the second light. It is characterized in that An optical element (2) is provided, whereby the first light in the reference arm (4) can be further split into primary light (I) and secondary light (II), wherein the primary light (I) can be guided along a first light path (4a), and Wherein, the secondary light (II) can be guided along a second light path (4b), and the length of the second light path (4b) is different from the length of the first light path (4a).

2. The device according to claim 1, characterized in that The detection device (3) detects and processes the corresponding signals generated by the primary light or the secondary light (I, II) from the corresponding first optical path (4a) or the second optical path (4b), and generates A scans for the first optical path (4a) and the second optical path (4b) synchronously or at short intervals.

3. The device according to claim 1 or 2, characterized in that The first optical path (4a) can guide light (I) in a first spectral range (7a), and the second optical path (4b) can guide light (II) in a second spectral range (7b).

4. The device according to claim 3, characterized in that The spectral ranges (7a, 7b) of the optical paths (4a, 4b) do not overlap or only slightly overlap and / or are spaced apart from each other by a certain wavelength range.

5. The device according to any one of the preceding claims, characterized in that The second optical path (4b) can guide light (II) in the second spectral range (7b), wherein the first optical path (4a) can guide light (I) in two respective spectral ranges (7.1a, 7.2a), wherein the latter two spectral ranges (7.1a, 7.2a) are spaced apart from each other by a certain wavelength range and / or do not overlap or only slightly overlap with the spectral range (7b) of the second optical path (4b).

6. The device according to any one of the preceding claims, characterized in that With the aid of the detection device (3), the distance of the structure to the detection device (3) or the apparatus (10) can be determined synchronously or at short intervals based on the axial position of the object structure in the A scan and the lengths of the first optical path (4a) and the second optical path (4b).

7. The device according to claim 6, characterized in that Based on the determined distances, the length of the object to be examined and / or the distances of structures within the object, in particular the distances of the structures from one another, can be determined.

8. The device according to any one of the preceding claims, characterized in that This allows the length of the eyeball and / or the distance between the cornea of ​​the eye and its retina to be determined.

9. The device according to claim 8, characterized in that Based on the determined eyeball length, the image generating device generates and / or displays a lateral zoomed image of the retina.

10. The device according to any one of the preceding claims, characterized in that The detection device (3) comprises a line scan camera (3a), and / or the light source (1) is a broadband light source.

11. The device according to any one of the preceding claims, characterized in that It is possible to switch between two image generation modes, wherein in a first mode, synchronized images of the retina and cornea of ​​the eye can be recorded and / or displayed, and in a second mode, only images of the retina of the eye can be recorded and / or displayed.

12. The device according to claim 11, characterized in that The optical element (2) can be switched into the beam path of the reference arm (4), or can be rotated into the beam path of the reference arm (4) and then moved away from or out of it.

13. The device according to any one of the preceding claims, characterized in that The optical element (2) has a beam splitter (6b).

14. The device according to any one of the preceding claims, characterized in that The optical element (2) is designed as a dichroic element or comprises a dichroic element.

15. The device according to claim 14, characterized in that The dichroic element is designed as a dichroic lens or a dichroic coated lens.

16. The device according to claim 14 or 15, characterized in that The dichroic element is designed as a dichroic mirror that reflects only within a specified wavelength range.

17. An arrangement for adjusting the working distance of a lens to an object to be inspected and / or for lateral adjustment of a lens, comprising a device according to any one of the preceding claims.

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