Device for performing optical coherence tomography

Abstract

In view of the problem of identifying an apparatus for performing optical coherence tomography that can reliably detect the dimensions of a target or a structure of the target during image acquisition of the target or the structure of the target and has a configuration as simple as possible, an apparatus (10) for performing optical coherence tomography includes an interferometer having a light source (1), a reference arm (4), and a sample arm (5). Light emitted from the light source (1) can be split by a beam splitter (6a), such that a first light is guided along the reference arm (4) and a second light is guided along the sample arm (5). The first light and the second light can be made to interfere, and a detection device (3) for detecting and processing signals of the interfering first light and second light is arranged. An optical element (2) capable of further splitting the first light in the reference arm (4) into primary light (I) and secondary light (II) is arranged. The primary light (I) can be guided along a first optical path (4a), and the secondary light (II) can be guided along a second optical path (4b) having a length different from that of the first optical path (4a).

Description

Technical Field

[0001] The present invention relates to an apparatus according to the preamble of claim 1.

Background Art

[0002] The term optical coherence tomography (usually abbreviated as OCT) is understood to be an imaging method. By this method, two-dimensional and three-dimensional images can be obtained from light-scattering structures.

[0003] In this method, light having a specific bandwidth is usually split into two partial beams at a beam splitter. The first partial beam is incident on the sample or object to be inspected, and the second partial beam passes through a reference section.

[0004] The light reflected from the sample or object interferes with the reference beam. Using the signal due to interference, the sample can be inspected with depth resolution, that is, at the depth of the optical axis of the first partial beam, by means of a so-called A scan.

[0005] Furthermore, an OCT image can also be obtained by scanning the surface of the sample with the first partial beam or scanning the sample laterally.

[0006] In posterior eye OCT imaging, the lateral scaling of the image is often simply known as the angular field of view. In order to convert the angular field of view into an absolute length or distance, information regarding the length of the eye and the optical characteristics of the individual eye to be examined is required. Furthermore, when it is an object to correct the OCT image and scale and display it with the correct curvature, it is necessary to know the length of the eye.

[0007] In view of such a background, currently, there are mainly two known methods for determining the eye length. The estimation of the eye length can be performed using an eye model based on the set refractive value and the manually input corneal radius. Also, it is possible to directly measure the eye length using an appropriate device. In view of such a background, a biometric device that simultaneously records a rough image of the retina is known, and the scaling of the image can be determined using the eye length determined thereby. However, since these images are of low quality, they are not suitable for diagnostic purposes.

[0008] Separately measuring the eye length or the corneal curvature places additional labor on the user. Therefore, these measurements are not always performed, and the results are not transferred to the software for evaluating the OCT image of the posterior segment of the eye. When values are input and the input is performed manually, there is also a possibility of transmission errors. Further integrating the biometer technology into the diagnostic retinal OCT device will significantly increase the complexity of the system.

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, the present invention is based on the object of providing an apparatus for performing optical coherence tomography that can reliably measure the dimensions of a subject or a structure of the subject with a simple configuration as much as possible during image acquisition.

Means for Solving the Problems

[0010] The present invention achieves the above object according to the features of claim 1.

[0011] The apparatus includes an interferometer having a reference arm and a sample arm, and the respective lights guided along these arms can be interfered with the respective other lights, and a detection device detects and processes the interference signal.

[0012] According to the present invention, an optical element capable of further splitting the light in the reference arm is provided, the primary light can be guided along the first optical path of the reference arm, and the secondary light can be guided along the second optical path of the reference arm having a length different from that of the first optical path.

[0013] According to the present invention, with such an OCT apparatus provided with an interferometer having a light splitting optical element, OCT images can be recorded simultaneously or almost simultaneously at various distances from the apparatus. According to the present invention, the distance from the camera or objective lens of the apparatus to the subject, particularly to the eye, can also be measured simultaneously or almost simultaneously with imaging of a part of the subject, preferably the posterior segment of the eye. Thereby, the length of the subject or the length of the structure of the subject, particularly the optical length of the eye, can be determined very accurately.

[0014] The detection device, particularly as part of a spectrometer, separately detects and processes the respective signals generated by the primary or secondary light in each of the first or second optical paths, and can generate A-scans for both the first optical path and the second optical path simultaneously or at short time intervals. As a result, A-scans of the retina and the cornea can be generated simultaneously in each camera frame. In order to register each overlapping structure in the image, an algorithm prone to errors is not required.

[0015] In view of such a background, light in the first spectral range can be guided along the first optical path, and light in the second spectral range can be guided along the second optical path. As a result, the light is split into light beams of various spectral ranges, that is, light beams having various wavelengths. Therefore, signals in at least two spectral ranges can be recorded by a line scan camera of the detection device in the detection arm of the interferometer and processed separately for the two spectral ranges. Thereby, OCT images can be recorded simultaneously or almost simultaneously at various distances from the apparatus in two spectral ranges.

[0016] The spectral ranges of the respective optical paths may not overlap with each other or may overlap only slightly. Alternatively, the spectral ranges of the respective optical paths may be separated from each other by a wavelength range or a spectral range. The line scan camera can detect the optical wavelengths with a first interval much better or completely separated from the optical wavelengths with other intervals and with good signal quality.

[0017] Light in the second spectral range can be guided along the second optical path, and light in each of the two spectral ranges can be guided along the first optical path, but the latter two spectral ranges are separated from each other by a wavelength range. In this way, the line scan camera can separate the optical wavelengths with two different separated first intervals from the optical wavelengths with a second interval and can detect them particularly well. The two spectral ranges of the first optical path may not overlap with the spectral range of the second optical path or may overlap only slightly. In this way, a very good or sufficiently good signal quality can be achieved.

[0018] Using the detection device, the distance from each structure of the object to the device can be confirmed simultaneously or at short time intervals from the axial position of each structure in the A-scan and the lengths of the first and second optical paths. In this way, the optical path can be specifically assigned to the specific structure to be detected.

[0019] The length of the object to be examined and / or the distances between each structure within the object, particularly from each other or from the device, may be confirmable from the confirmed distances. In this way, the object can be examined not only with respect to its spatial extent but also with respect to its internal spatial configuration.

[0020] The length of the eye can be determined by the device described in this specification. Alternatively or in addition, the distance between the cornea and the retina of the eye can be determined by the device. These data can be used by a doctor for further diagnosis.

[0021] In view of such a background, the image generation device can generate and / or display an image scaled in the horizontal direction of the retina based on the confirmed eye length. As a result, since all important information is visually displayed in the image, the doctor can make a particularly good diagnosis.

[0022] The detection device may include a line scan camera. Alternatively or in addition, the light source may be a broadband light source. With a broadband light source, light in a very wide spectral range can be emitted, and this can also be divided into light beams in various spectral ranges, where these latter spectral ranges are partial ranges of the above-mentioned wide spectral range. The line scan camera can detect light in various spectral ranges very selectively and specifically.

[0023] The device may be switchable between two image generation modes, namely, a first mode in which images of the eye's retina and cornea can be simultaneously recorded and / or displayed, and a second mode in which only an image of the eye's retina can be recorded and / or displayed. The switchable recording mode can be realized by a switching device that enables switching between a spectrally divided simultaneous mode and a mode in which the full spectral bandwidth is available for the retinal image. In contrast to the prior art, this switching device does not switch alternately between various z ranges.

[0024] In view of such a background, the optical element can be connectable or rotatable into the beam path of the reference arm and removable or rotatable out therefrom. The rotation-in process can be easily implemented mechanically, for example, by an electric motor that moves the optical element around a rotation axis.

[0025] The optical element may have or be formed as a beam splitter, particularly a dichroic beam splitter. Thereby, light or a light beam can be split into two light beams traveling along different optical paths. The dichroic beam splitter splits the incident light beam into light beams in various spectral ranges.

[0026] The optical element may be designed as a dichroic element or may include a dichroic element. Thereby, light can be split into partial beams having various wavelengths. As the dichroic element, for example, instead of separate beam splitters and mirrors, a dichroic mirror directly disposed in the beam path of the reference arm and reflecting only for a first spectral range of the primary light can be used.

[0027] Alternatively, the dichroic element may be designed as a dichroic lens or a dichroic coated lens. The lens can be used together with a switching device that must enable the rotation in and out of a single compact optical component.

[0028] Furthermore, the use of a dichroic lens is advantageous especially when adjustment for single-mode fibers is required. A dichroic lens or a dichroic coated lens that causes little or no refraction in the transmitted light as a whole can be disposed in the beam path of the reference arm. When light is input into the reference arm via a fiber, there is an advantage that adjustment becomes easy, but more light is lost. For non-critical adjustment, since there is an advantage that the lens can be easily rotated in and out of the beam path, a simple and robust switching between the "complete spectrum for visualizing the retina" mode and the "simultaneous display of the cornea and retina for determining the optical eye length" mode can be realized.

[0029] The dichroic element may be designed as a dichroic mirror that reflects only for a specific wavelength range or spectral range. Such a mirror can reflect a specific spectral range of the incident light and transmit other spectral ranges.

[0030] A configuration for adjusting the working distance from the objective lens to the object to be inspected and / or for adjusting the objective lens laterally may be included in the types of devices described herein. The devices described herein can be integrated into a fully automated retinal diagnostic system as a Z sensor of an automatic adjustment device for setting the correct working distance between the objective lens and the tip or the eye vertex.

[0031] The devices described herein can be used not only in spectral domain OCT but also in swept source OCT systems. When the device is implemented in a specific system, a discontinuous range of the optical spectrum can be used. Thereby, the spatial resolution can be significantly improved at the expense of higher sidebands.

[0032] The beam path and the optical path described herein can be implemented not only within the framework of a free beam optical unit but also at least partially in a fiber optic system. Therefore, the device may have an optical fiber.

[0033] The measurement of the distance between the device described herein and the eye to be inspected can be performed during the acquisition of an OCT image at the posterior segment of the eye for measuring the dimensions of the eye, particularly the length of the eye. With the device described herein, there is no need to separately measure the length of the eye, and there is no cause for errors due to data transmission or unentered data. This improves the absolute scaling specification of the retinal OCT record and the average accuracy of the simultaneously recorded cSLO images of the confocal scanning laser ophthalmoscope.

[0034] In the prior art, the corneal curvature and refractive value are currently used to estimate the axial length and thereby determine the scaling. However, the determination of the axial length becomes inaccurate when the eye parameters not considered, such as the corneal curvature of another surface, the anterior chamber depth, and the lens parameters, deviate from the used model eye. This is particularly applicable when the refractive error of the patient is corrected using an intraocular lens (IOL). Therefore, directly measuring the axial length provides a more robust parameter for determining the scaling.

[0035] By making the scaling more consistent between the test data and the reference data, the classification method can achieve better test intensity. Although a dense volume is not recorded, using a scanning pattern with a certain scaling also has the advantage that the recording location of the recorded OCT tomographic image and the target position are more consistent. For example, in a circular scan with a certain radius, the actual radius variation within the eye is reduced.

[0036] Even more advantageously, by measuring the distance, it is possible to confirm whether the relative position between the camera of the device and the eye is correct during recording.

[0037] Using this information, the camera can be adjusted manually or automatically. The OCT signal of the retina can be used as a direct operating variable for automatic distance setting (retinal signal at the sweet spot with respect to the reference arm length optimally set for the optical eye length) assuming the optical eye length is known.

[0038] When the eye length is unknown, the automatic distance setting can be performed based on the corneal signal, and then the reference arm can be optimally set for the retinal signal in a second automatic process.

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

[0040] When changing the scan direction and performing alternating radial scans in different directions, for example, in the case of two orthogonal scans, the position information can also be utilized in 2D.

[0041] A further potential use of the device is the measurement of the curvature of the retina, which may be relevant to various pathologies, particularly in myopic patients. The curvature of the retinal signal depends on the working distance between the vertex of the objective lens and the vertex of the cornea. If the optical length of the eye is known, the working distance can be reliably determined from the "reference arm length" and the "sample arm length to the vertex of the objective lens", which are known parameters. In this way, the true curvature of the retina can be determined even more accurately with an appropriate eye model.

[0042] Compared with methods of sequentially measuring the distances from the retina and the cornea, such as by varying the reference arm length, the advantage of using the device described herein is that the measurements are performed simultaneously. Thus, errors due to axial eye movement during length measurement are almost eliminated.

[0043] By using the device described herein, advantages can be obtained in the following aspects. The accuracy of the classification method depending on scaling is improved. Manual adjustment is assisted by specifying the interpupillary distance or derived indices, and as a result, the image quality is improved on average. An automatic adjustment function is supported. A display of the actual size of the retina with the actual curvature becomes possible.

Brief Description of the Drawings

[0044]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiment for Carrying Out the Invention

[0045] FIG. 1 is a schematic diagram of a recording of the posterior segment of the human eye 8 by OCT or cSLO, in which the angular field φ is shown as an apparatus parameter, and since the optical properties and size of the eye under examination 8 are unknown, it shows that direct access to the size of the recording area at the fundus d is not possible. A prior art apparatus 10' is used for recording the posterior segment.

[0046] In view of such a background, FIGS. 2 and 3 each show, as partial schematic diagrams, an apparatus 10 for performing optical coherence tomography, including an interferometer having a broadband light source 1, a reference arm 4, and a sample arm 5. The light emitted from the light source 1 is split by a beam splitter 6a, and the first light is guided along the reference arm 4, and the second light is guided along the sample arm 5.

[0047] The first light and the second light are interfered, and a detection device 3 for detecting and processing the signals of the interfering first light and second light is arranged.

[0048] An optical element 2 for further splitting the first light in the reference arm 4 into primary light (I) and secondary light (II) is arranged. The primary light (I) is guided along the first optical path 4a in the reference arm 4, and the secondary light (II) is guided along the second optical path 4b in the reference arm 4, but the length of the second optical path 4b is different from the length of the first optical path 4a.

[0049] In this regard, the first light includes the primary light (I) and the secondary light (II) in different optical paths 4a, 4b, and interferes with the second light in each case.

[0050] In FIG. 2, the detection device 3 separately detects and processes the respective signals generated by the primary and secondary lights (I, II) of each of the first and second optical paths 4a, 4b, and generates an A-scan for both the first optical path 4a and the second optical path 4b simultaneously or at short time intervals.

[0051] The detected primary light (I) in the first spectral range 7a is guided along the first optical path 4a, and the detected secondary light (II) in the second spectral range 7b is guided along the second optical path 4b.

[0052] The spectral ranges 7a, 7b of the primary light (I) and the secondary light (II) along the optical paths 4a, 4b do not overlap with each other.

[0053] The detection device 3 includes a line scan camera 3a. The signals in both spectral ranges 7a, 7b are recorded by the line scan camera 3a in the detection arm of the interferometer and processed separately for both spectral ranges 7a, 7b or wavelength ranges. Each spectral range 7a, 7b corresponds to a wavelength range containing light of a specific interval of optical wavelengths.

[0054] As a result, an A-scan of the retina and the cornea of the eye 8 can be obtained simultaneously in each camera frame. In order to register each overlapping structure such as the cornea and the retina in the image, an algorithm that is prone to errors is not required.

[0055] The absolute distance from the cornea to the objective lens of the device 10 or the camera of the device 10 can be determined from the OCT image of the first spectral range 7a.

[0056] The optical distance from the retina to the objective lens of the device 10 or the camera of the device 10 can be determined from the position of the retina in the OCT image of the second spectral range 7b.

[0057] The difference in position between the cornea and the retina is the optical eye length. Using the obtained eye length, the horizontal scaling of the retinal image can be estimated or confirmed more accurately.

[0058] Ultimately, in the reference arm 4, broadband light from the light source 1 is split by the optical element 2 into optical paths 4a and 4b of different lengths, such that the length of the reference arm 4a for the first part (I) of the optical spectrum corresponds to the distance from the device 10 to the cornea of the eye 8, and the length of the reference arm 4b for another second part (II) of the optical spectrum corresponds to the optical distance from the device 10 to the retina.

[0059] Even in a very short wavelength range, a resolution sufficient to determine the position of the cornea well enough so that the depth resolution of the diagnostic image does not decrease as much as possible can be achieved.

[0060] In view of such a background, FIG. 3 shows a device 10 in which the secondary light (II) in the detected second spectral range 7b is guided along the second optical path 4b, and the primary light (I) in each of the two detected first spectral ranges 7.1a, 7.2a can be guided along the first optical path 4a, but these latter two first spectral ranges 7.1a, 7.2a are separated from each other by a wavelength range and do not overlap with the second spectral range 7b of the second optical path 4b.

[0061] Therefore, in the first channel of the detection device 3, two non - continuous first spectral ranges 7.1a, 7.2a at both ends of the spectrum are used for image generation.

[0062] In the second channel, the continuous second spectral range 7b is used for image generation.

[0063] Therefore, the first channel shows a higher resolution, but stronger sidebands are generated. The second channel shows a slight decrease in the signal - to - noise ratio and resolution.

[0064] The detection device 3 of the device 10 in FIGS. 2 and 3 can confirm the distance from each target structure to the detection device 3 or the device 10 simultaneously or at short time intervals from the axial position of each structure in the A-scan and the lengths of the first and second optical paths 4a, 4b.

[0065] The length of the object to be inspected and / or the distances between each structure within the object, especially between each other, can be confirmed from the confirmed distances from each structure to the device 10.

[0066] The device 10 in FIGS. 2 and 3 can determine the length of the eye 8 and / or the distance from the cornea to the retina of the eye 8.

[0067] Based on the confirmed length of the eye 8, the image generation device can generate and / or display an image scaled in the lateral direction of the retina.

[0068] In the device according to FIGS. 2 and 3, it is switchable between two image generation modes, namely, a first mode in which images of the retina and cornea of the eye 8 can be recorded and / or displayed simultaneously, and a second mode in which only an image of the retina of the eye 8 can be recorded and / or displayed.

[0069] For this purpose, the optical element 2 can be connected to or rotatably inserted into the beam path of the reference arm 4, and can be removed from or rotatably taken out from there.

[0070] FIGS. 2 and 3 show that the optical element 2 has a dichroic beam splitter 6b and guides the primary light (I) and the secondary light (II) in different directions along the respective optical paths 4a, 4b.

[0071] FIG. 4 shows that the optical element 2 is designed as a dichroic element or includes a dichroic element by two sections of alternative additional reference arms 4', 4".

[0072] The left side of FIG. 4 shows that the dichroic element is designed as a dichroic mirror that reflects only for a specific spectral range or wavelength range. Specifically, the primary light (I) is reflected and the secondary light (II) is transmitted. As a result, two optical paths 4a and 4b of different lengths are obtained.

[0073] The right side of FIG. 4 shows that the dichroic element is designed as a dichroic lens or a dichroic coated lens. The dichroic coated lens is disposed in the beam path of the reference arm 4”, and causes almost no or no refraction in the transmitted secondary light (II) as a whole.

[0074] Since light is input to the reference arm 4” by the optical fiber 9, adjustment becomes easy. The optical fiber 9 shown as a schematic diagram can be designed particularly as a single mode fiber.

[0075] In the OCT reference arms 4, 4’, 4”, the broadband light derived from the light source 1 is split by the dichroic optical element 2 into optical paths 4a and 4b of different lengths, and the length of the reference arm 4a for the first part (I) of the optical spectrum corresponds to the distance from the device 10 to the cornea of the eye 8, and preferably the length of the reference arm 4b for another second part (II) of the optical spectrum corresponds to the optical distance from the device 10 to the retina.

[0076] FIGS. 2 and 3 show the optical distance plane R I where the cornea is located and the optical distance plane R II where the retina is located. The distance between the distance planes R I and R II corresponds to the length of the eye 8.

[0077] With the device 10 described in this specification, OCT imaging of the posterior eye can be performed while measuring the distance from the device 10 to the eye 8 simultaneously or almost simultaneously. This is achieved by using the reference arm 4 having a dichroic element.

Explanation of Reference Numerals

[0078] Light source from 1 to 10 Optical element at 2 to 4 3 Detection device 3b Line scan camera 4, 4’, 4” Reference arm 4a First optical path at 4, 4’, 4” 4b Second optical path at 4, 4’, 4” 5 Sample arm 6a First beam splitter 6b Second beam splitter, dichroic 7a First spectral range 7b Second spectral range 7.1a First first spectral range 7.1b Second first spectral range 8 Eye 9 Optical fiber 10, 10’ Device I Primary light along 4a II Secondary light along 4b R I Corneal distance plane at a distance from 10 R II Retinal distance plane at a distance from 10

Claims

1. An apparatus (10) for performing optical coherence tomography, comprising an interferometer having a light source (1), a reference arm (4) and a sample arm (5), wherein light emitted from the light source (1) can be split by a beam splitter (6a), such that a first light is guided along the reference arm (4) and a second light is guided along the sample arm (5), the first light and the second light can be made to interfere with each other, a detection device (3) is arranged for detecting and processing signals of the interfering first light and second light, an optical element (2) is arranged in the reference arm (4) which can further split the first light into a primary light (I) and a secondary light (II), the primary light (I) can be guided along a first optical path (4a), and the secondary light (II) can be guided along a second optical path (4b) having a length different from that of the first optical path (4a).

2. The detection device (3) separately detects and processes the respective signals generated by the primary or secondary light (I, II) in each of the first or second optical paths (4a, 4b), and generates an A-scan for both the first optical path (4a) and the second optical path (4b) simultaneously or at short time intervals. The apparatus according to claim 1.

3. Light (I) in a first spectral range (7a) can be guided along the first optical path (4a), and light (II) in a second spectral range (7b) can be guided along the second optical path (4b). The apparatus according to claim 1 or 2.

4. The spectral ranges (7a, 7b) of the optical paths (4a, 4b) do not overlap or only slightly overlap, and / or are separated from each other by a wavelength range. The apparatus according to claim 3.

5. Light (II) in a second spectral range (7b) can be guided along the second optical path (4b), and light (I) in each of two spectral ranges (7.1a, 7.2a) can be guided along the first optical path (4a), and these latter spectral ranges (7.1a, 7.2a) are separated from each other by a wavelength range, and / or do not overlap or only slightly overlap with the spectral range (7b) of the second optical path (4b). The apparatus according to claim 3.

6. The apparatus according to claim 2, characterized in that the distance from each structure of the object to the detection device (3) or the device (10) can be determined simultaneously or at short time intervals from the axial position of each structure in the A-scan and the lengths of the first and second optical paths (4a, 4b).

7. The apparatus according to claim 6, characterized in that the length of the object to be examined and / or the distances between the structures within the object, in particular to each other, can be confirmed from the confirmed distances.

8. The apparatus according to claim 7, characterized in that it can be used to determine the length of the eye and / or the distance from the cornea of the eye to the retina.

9. The apparatus according to claim 8, characterized in that the image generation device generates and / or displays an image scaled in the lateral direction of the retina based on the confirmed length of the eye.

10. The apparatus according to claim 1, characterized in that the detection device (3) includes a line scan camera (3a) and / or the light source (1) is broadband.

11. The apparatus according to claim 1, characterized in that it is switchable between two image generation modes, namely a first mode in which images of the retina and cornea of the eye can be recorded and / or displayed simultaneously and a second mode in which only an image of the retina of the eye can be recorded and / or displayed.

12. The apparatus according to claim 11, characterized in that the optical element (2) is connectable or rotatable into the beam path of the reference arm (4) and removable or rotatable out therefrom.

13. The apparatus according to claim 12, characterized in that the optical element (2) has a beam splitter (6b).

14. The apparatus according to claim 12, characterized in that the optical element (2) is designed as a dichroic element or includes a dichroic element.

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

16. The apparatus according to claim 14 or 15, characterized in that the dichroic element is designed as a dichroic mirror that reflects only for a specific wavelength range.

17. A configuration for adjusting the working distance from the objective lens to the object to be inspected and / or for adjusting the objective lens laterally, the configuration including the apparatus according to any one of claims 1 to 2 and 6 to 15.

Images