Optical tomographic imaging device

Abstract

This optical tomographic imaging device is a polarization sensitive optical tomographic imaging device. The optical tomographic imaging device includes: an imaging unit for capturing a tomographic image of an eye being examined; a designation means for designating a range in the depth direction of the tomographic image; and a calculation unit. The tomographic image includes a first tomographic image captured by irradiating the eye being examined with a first polarized light wave, and a second tomographic image captured by irradiating the eye being examined with a second polarized light wave having a vibration direction different from that of the first polarized light wave. The calculation unit is configured to be capable of executing, on the basis of the first tomographic image and the second tomographic image, image generation processing for generating at least one of an image indicating birefringence and an image indicating the fiber running mode with respect to the range in the depth direction of the tomographic image designated by the designation means.

Description

Optical tomography imaging device

[0001] The technology disclosed in this specification relates to a polarization-sensitive optical tomographic imaging apparatus.

[0002] Optical tomography devices are non-invasive and non-contact, and are therefore widely used in ophthalmologic devices and the like as a method for obtaining tomographic images of biological tissue. In recent years, polarization-sensitive optical tomography devices, which are one type of multifunctional optical tomography device, have been developed. Birefringence, which changes the polarization state, occurs in tissues in which molecules or fibrous tissues are aligned in a fixed direction. Using a polarization-sensitive optical tomography device, birefringence can be visualized. For example, Japanese Patent Application Laid-Open No. 2016-57197 discloses an example of a polarization-sensitive optical tomography device.

[0003] Using a polarization-sensitive optical tomographic imaging device such as that described in JP 2016-57197 A, various characteristics related to birefringence can be visualized. Therefore, the polarization-sensitive optical tomographic imaging device can generate images containing a wealth of information that cannot be obtained from tomographic images showing a cross section of the subject's eye (hereinafter also referred to as ordinary tomographic images), allowing for multifaceted analysis of the condition of the subject's eye. However, when images are generated using information acquired by a polarization-sensitive optical tomographic imaging device, the images are more complex than ordinary tomographic images, making it difficult to accurately interpret clinically useful information.

[0004] This specification discloses a technique for generating a simple and useful image from information acquired by a polarization-sensitive optical tomography apparatus.

[0005] In a first aspect of the technology disclosed in this specification, the optical tomography apparatus is a polarization-sensitive optical tomography apparatus. The optical tomography apparatus includes an imaging unit that captures a tomographic image of a subject's eye, a designation unit that specifies a depth range of the tomographic image, and a calculation unit. The tomographic image includes a first tomographic image captured by irradiating the subject's eye with a first polarized wave and a second tomographic image captured by irradiating the subject's eye with a second polarized wave having a vibration direction different from that of the first polarized wave. The calculation unit is configured to execute an image generation process that generates, based on the first tomographic image and the second tomographic image, at least one of an image showing birefringence and an image showing the running pattern of fibers within the depth range of the tomographic image specified by the designation unit.

[0006] In the optical tomography apparatus described above, a depth range can be specified, and at least one of an image showing birefringence in the specified range and an image showing the fiber orientation can be generated, thereby enabling the user to generate an image of only the depth range desired by the user. This allows the amount of information to be reduced by eliminating information in the depth range that is unnecessary for the user. This makes the image easier to view, allowing the condition of the subject's eye to be easily and accurately confirmed.

[0007] 1 is a diagram showing a schematic configuration of an optical system of an optical tomographic imaging apparatus according to Examples 1 to 7. FIG. 2 is a block diagram showing a control system of an optical tomographic imaging apparatus according to Examples 1 to 7. FIG. 3 is a block diagram showing the configuration of a sampling trigger / clock generator. FIG. 4 is a flowchart showing an example of a process for generating a birefringence intensity map for a desired depth range of an eye to be examined in Example 1. (a) is a tomographic image showing birefringence, (b) is an image in which layer boundaries are superimposed on (a), and (c) is an image showing a birefringence intensity map for only a selected depth range of the eye to be examined. FIG. 5 is a flowchart showing an example of a process for generating a fiber trajectory map for a desired depth range of the eye to be examined in Example 2. (a) is an image in which layer boundaries are superimposed on a tomographic image showing the fiber trajectory direction, and (b) is an image showing a fiber trajectory map for only a selected depth range r1 of the eye to be examined (optic nerve fiber layer (NFL) and Henle fiber layer). 1A is an image in which layer boundaries are superimposed on a tomographic image showing the direction of fiber travel, and 1B is an image showing a fiber travel map for only a selected depth range r2 (sclera) of the subject's eye. 1A is an image in which layer boundaries are superimposed on a tomographic image showing the direction of fiber travel, and 1B is an image in which streamlines are superimposed on a fiber travel map for a selected depth range r1 of the subject's eye. 1A is an image in which layer boundaries are superimposed on a tomographic image showing the direction of fiber travel, and 1B is an image in which streamlines are superimposed on a fiber travel map for a selected depth range r2 of the subject's eye. 1B is a flowchart showing an example of a process for displaying high birefringence regions superimposed on streamlines for a desired depth range of the subject's eye in Example 4. 1A is an image in which layer boundaries are superimposed on a tomographic image showing the direction of fiber travel, and 1B is an image in which high birefringence regions are superimposed on streamlines for a selected depth range r1 of the subject's eye. 10A is an image in which layer boundaries are superimposed on a tomographic image showing the direction of fiber travel, and FIG. 10B is an image in which high birefringence regions are superimposed on streamlines in a selected depth range r2 of the subject's eye. FIG. 10B is a flowchart showing an example of a process for generating a thickness map of high birefringence regions for a desired depth range of the subject's eye in Example 5.18A is an image in which layer boundaries are superimposed on a tomographic image showing birefringence, (b) is an image in which a high birefringence region is located in a selected depth range of the eye to be examined, and (c) is an image in which a thickness map of the high birefringence region is located only in a selected depth range of the eye to be examined. (a) is an image in which layer boundaries are superimposed on a tomographic image showing birefringence, (b) is an image in which a high birefringence region is located in a selected depth range of the eye to be examined, and (c) is an image in which a layer number map of high birefringence is located only in a selected depth range of the eye to be examined. (b) is a flowchart showing an example of a process for generating a relative angle map for a desired depth range of the eye to be examined in Example 7. (c) is a tomographic image showing birefringence. (d) is a tomographic image showing the direction of fiber travel corresponding to the main part XIX of FIG. 18A. (e) is a tomographic image showing the direction of fiber travel corresponding to the main part XX of FIG. 18A. (f) is an image in which a relative angle map of a selected depth range of the eye to be examined is located.

[0008] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0009] In a second aspect of the technology disclosed in this specification, the optical tomography apparatus of the first aspect described above may further include a display unit that displays an image showing the running pattern of fibers. The display unit may display, together with the image showing the running pattern of fibers, a line indicating the running direction of the fibers superimposed at a corresponding position on the image showing the running pattern of fibers. Images showing the running pattern of fibers generally display the running direction of fibers in different colors, making it difficult to read the running direction of fibers from the difference in color. By displaying the line indicating the running direction of fibers superimposed on the image showing the running pattern of fibers, it becomes easier to understand the running direction of the fibers.

[0010] In a third aspect of the technology disclosed herein, in the second aspect described above, the display unit may further superimpose an image showing a region where the birefringence intensity is greater than a predetermined value at a position corresponding to the image showing the fiber running mode. This configuration makes it easier to understand the relationship between the fiber running direction and the region where the birefringence intensity is high. While it is useful to evaluate the birefringence intensity and the fiber running direction separately, it is also important to evaluate both in an integrated manner. By superimposing an image showing a region where the birefringence intensity is greater than a predetermined value on the image showing the fiber running mode, it becomes easier to evaluate the birefringence intensity and the fiber running direction in an integrated manner.

[0011] In a fourth aspect of the technology disclosed in this specification, the optical tomography apparatus according to the first aspect may further include a display unit that displays an image showing birefringence. The display unit may display a thickness map showing the thickness of regions where birefringence is higher than a predetermined value. This configuration makes it easier to grasp the thickness of regions with high birefringence. For example, while an intensity map showing the intensity of birefringence can identify the location of regions with high birefringence, it is necessary to check each tomographic image to determine the thickness of the regions with high birefringence. By displaying a thickness map showing the thickness of regions where birefringence is higher than a predetermined value, the thickness of the regions with high birefringence can be easily grasped.

[0012] In a fifth aspect of the technology disclosed in this specification, the optical tomography apparatus of the first aspect may further include a display unit that displays an image showing birefringence. The calculation unit may be configured to further perform a layer identification process that identifies each layer in the subject's eye and a determination process that determines whether the birefringence of each layer identified in the layer identification process is higher than a predetermined value. The display unit may display a layer number map that indicates the number of layers determined to have birefringence higher than the predetermined value in the identification process. This configuration makes it easy to determine the number of layers with birefringence higher than the predetermined value.

[0013] In a sixth aspect of the technology disclosed herein, in the first aspect described above, the calculation unit may be further configured to perform a layer identification process for identifying each layer in the subject's eye, a first calculation process for calculating the relative angle between each layer identified in the layer identification process and an adjacent layer, and a second calculation process for calculating the sum of the relative angles calculated in the first calculation process for a depth-wise range of the tomographic image specified by the designation means. The optical tomographic imaging apparatus may further include a display unit that displays an angle map indicating the sum of the relative angles calculated in the second calculation process. This configuration makes it easier to understand the state of the relative angles in the subject's eye. Information on the extent to which the fiber directions in adjacent layers differ has clinically important implications, such as whether the subject has stress resistance to axial length progression. Displaying the relative angle map makes it easy to understand the distribution of the sum of the relative angles.

[0014] An optical tomography apparatus according to the present embodiment will be described with reference to the drawings. The optical tomography apparatus according to the present embodiment is a polarization-sensitive OCT (PS-OCT) apparatus that uses a wavelength-swept light source and is capable of capturing the polarization characteristics of a test object using swept-source optical coherence tomography (SS-OCT).

[0015] As shown in Figure 1, the optical tomographic imaging apparatus of this embodiment includes a light source 11, a measurement light generation unit (21 to 29, 31, 32) that generates measurement light from the light of the light source 11, a reference light generation unit (41 to 46, 51) that generates reference light from the light of the light source 11, interference light generation units 60 and 70 that generate interference light by combining reflected light from the test eye 500 generated by the measurement light generation unit with reference light generated by the reference light generation unit, and interference light detection units 80 and 90 that detect the interference light generated by the interference light generation units 60 and 70.

[0016] (Light Source) The light source 11 is a wavelength sweep type light source, and the wavelength (wave number) of the emitted light changes at a predetermined cycle. Because the wavelength of the light irradiated onto the subject's eye 500 changes (sweeps), the intensity distribution of the light reflected from each portion in the depth direction of the subject's eye 500 can be obtained by performing Fourier analysis on a signal obtained from the interference light between the reflected light from the subject's eye 500 and the reference light.

[0017] The light source 11 is connected to a polarization control device 12 and a fiber coupler 13, and the fiber coupler 13 is connected to a PMFC (polarization-maintaining fiber coupler) 14 and a sampling trigger / clock generator 100. Therefore, the light output from the light source 11 is input to the PMFC 14 and the sample trigger / clock generator 100 via the polarization control device 12 and the fiber coupler 13. The sampling trigger / clock generator 100 uses the light from the light source 11 to generate sampling triggers and sampling clocks for signal processors 83 and 93, which will be described later.

[0018] (Measurement Light Generator) The measurement light generator (21-29, 31, 32) includes a PMFC 21 connected to the PMFC 14, two measurement light paths S1 and S2 branching from the PMFC 21, a polarization beam combiner / splitter 25 connecting the two measurement light paths S1 and S2, and a collimator lens 26, galvanometer mirrors 27 and 28, and a lens 29 connected to the polarization beam combiner / splitter 25. An optical path length difference generator 22 and a circulator 23 are disposed in the measurement light path S1. Only a circulator 24 is disposed in the measurement light path S2. Therefore, the optical path length difference ΔL between the measurement light paths S1 and S2 is generated by the optical path length difference generator 22. The optical path length difference ΔL may be set longer than the measurement range in the depth direction of the test eye 500. This prevents interference light with different optical path length differences from overlapping. The optical path length difference generating unit 22 may be, for example, an optical fiber or an optical system such as a mirror or a prism. In this embodiment, a 1-m PM fiber is used for the optical path length difference generating unit 22. The measurement light generating unit further includes PMFCs 31 and 32. The PMFC 31 is connected to the circulator 23. The PMFC 32 is connected to the circulator 24.

[0019] One of the beams (i.e., the measurement beam) split by the PMFC 14 is input to the measurement beam generators (21 to 29, 31, 32). The PMFC 21 splits the measurement beam input from the PMFC 14 into a first measurement beam and a second measurement beam. The first measurement beam split by the PMFC 21 is guided to a measurement beam path S1, and the second measurement beam is guided to a measurement beam path S2. The first measurement beam guided to the measurement beam path S1 passes through the optical path length difference generator 22 and the circulator 23 and is input to the polarization beam combiner / splitter 25. The second measurement beam guided to the measurement beam path S2 passes through the circulator 24 and is input to the polarization beam combiner / splitter 25. The PM fiber 304 is connected to the polarization beam combiner / splitter 25 in a state rotated 90 degrees circumferentially relative to the PM fiber 302. As a result, the second measurement light input to the polarized beam combiner / splitter 25 has a polarization component orthogonal to that of the first measurement light. Because the optical path length difference generating unit 22 is provided in the measurement light path S1, the first measurement light is delayed relative to the second measurement light by the distance of the optical path length difference generating unit 22 (i.e., an optical path length difference ΔL is generated). The polarized beam combiner / splitter 25 superimposes the input first measurement light and second measurement light. The light output from the polarized beam combiner / splitter 25 (the superimposed light of the first measurement light and the second measurement light) is irradiated onto the test eye 500 via a collimator lens 26, galvanometer mirrors 27 and 28, and a lens 29. The light irradiated onto the test eye 500 is scanned in the x-y directions by the galvanometer mirrors 27 and 28.

[0020] Light irradiated onto the test eye 500 is reflected by the test eye 500. The light reflected by the test eye 500 is scattered on the surface and inside the test eye 500. The reflected light from the test eye 500 travels in the opposite direction to the incident path through the lens 29, the galvanometer mirrors 28 and 27, and the collimator lens 26, and is input to the polarization beam combiner / splitter 25. The polarization beam combiner / splitter 25 splits the input reflected light into two polarized components that are orthogonal to each other. For convenience, these are referred to here as horizontally polarized reflected light (horizontally polarized component) and vertically polarized reflected light (vertically polarized component). The horizontally polarized reflected light is then guided to the measurement optical path S1, and the vertically polarized reflected light is guided to the measurement optical path S2.

[0021] The optical path of the horizontally polarized reflected light is changed by the circulator 23 and input to the PMFC 31. The PMFC 31 splits the input horizontally polarized reflected light and inputs it to the PMFCs 61 and 71, respectively. Therefore, the horizontally polarized reflected light input to the PMFCs 61 and 71 includes a reflected light component due to the first measurement light and a reflected light component due to the second measurement light. The optical path of the vertically polarized reflected light is changed by the circulator 24 and input to the PMFC 32. The PMFC 32 splits the input vertically polarized reflected light and inputs it to the PMFCs 62 and 72. Therefore, the vertically polarized reflected light input to the PMFCs 62 and 72 includes a reflected light component due to the first measurement light and a reflected light component due to the second measurement light.

[0022] (Reference Light Generator) The reference light generator (41-46, 51) includes a circulator 41 connected to the PMFC 14, reference delay lines (42, 43) connected to the circulator 41, a PMFC 44 connected to the circulator 41, two reference light paths R1, R2 branching from the PMFC 44, a PMFC 46 connected to the reference light path R1, and a PMFC 51 connected to the reference light path R2. An optical path length difference generator 45 is disposed in the reference light path R1. No optical path length difference generator is provided in the reference light path R2. Therefore, the optical path length difference ΔL′ between the reference light path R1 and the reference light path R2 is generated by the optical path length difference generator 45. For example, an optical fiber is used for the optical path length difference generator 45. The optical path length ΔL′ of the optical path length difference generator 45 may be the same as the optical path length ΔL of the optical path length difference generator 22. By making the optical path length differences ΔL and ΔL′ equal, the depth positions of a plurality of interference lights, which will be described later, with respect to the subject's eye 500 become the same. In other words, it is not necessary to align the positions of a plurality of acquired tomographic images.

[0023] The other light (i.e., reference light) branched by the PMFC 14 is input to the reference light generating unit (41 to 46, 51). The reference light input from the PMFC 14 passes through a circulator 41 and is input to a reference delay line (42, 43). The reference delay line (42, 43) is composed of a collimator lens 42 and a reference mirror 43. The reference light input to the reference delay line (42, 43) is irradiated onto the reference mirror 43 via the collimator lens 42. The reference light reflected by the reference mirror 43 is input to the circulator 41 via the collimator lens 42. Here, the reference mirror 43 is movable toward or away from the collimator lens 42. In this embodiment, before measurement begins, the position of the reference mirror 43 is adjusted so that the signal from the subject's eye 500 falls within the measurement range of the OCT in the depth direction.

[0024] The reference light reflected by the reference mirror 43 has its optical path changed by the circulator 41 and is input to the PMFC 44. The PMFC 44 splits the input reference light into a first reference light and a second reference light. The first reference light is guided to the reference light path R1, and the second reference light is guided to the reference light path R2. The first reference light passes through the optical path length difference generating unit 45 and is input to the PMFC 46. The reference light input to the PMFC 46 is split into a first split reference light and a second split reference light. The first split reference light passes through a collimator lens 47 and a lens 48 and is input to the PMFC 61. The second split reference light passes through a collimator lens 49 and a lens 50 and is input to the PMFC 62. The second reference light is input to the PMFC 51 and is split into a third split reference light and a fourth split reference light. The third branched reference light passes through a collimator lens 52 and a lens 53 and is input to the PMFC 71. The fourth branched reference light passes through a collimator lens 54 and a lens 55 and is input to the PMFC 72.

[0025] (Interference Light Generator) The interference light generators 60 and 70 include a first interference light generator 60 and a second interference light generator 70. The first interference light generator 60 includes PMFCs 61 and 62. As described above, the PMFC 61 receives horizontally polarized reflected light from the measurement light generator and the first branched reference light (light having an optical path difference ΔL′) from the reference light generator. The horizontally polarized reflected light includes a reflected light component due to the first measurement light (light having an optical path difference ΔL) and a reflected light component due to the second measurement light (light without an optical path difference ΔL). Therefore, the PMFC 61 combines the reflected light component due to the first measurement light (light having an optical path difference ΔL) and the first branched reference light to generate the first interference light (horizontally polarized component).

[0026] The PMFC 62 also receives vertically polarized reflected light from the measurement light generator and second branched reference light (light having an optical path difference ΔL′) from the reference light generator. The vertically polarized reflected light includes a reflected light component due to the first measurement light (light having an optical path difference ΔL) and a reflected light component due to the second measurement light (light without an optical path difference ΔL). Therefore, the PMFC 62 combines the reflected light component due to the first measurement light (light having an optical path difference ΔL) and the second branched reference light to generate second interference light (vertically polarized component).

[0027] The second interference light generation unit 70 has PMFCs 71 and 72. As described above, the horizontally polarized reflected light is input to the PMFC 71 from the measurement light generation unit, and the third branched reference light (light without optical path length difference ΔL′) is input to the PMFC 71 from the reference light generation unit. Therefore, in the PMFC 71, the reflected light component of the horizontally polarized reflected light due to the second measurement light (light without optical path length difference ΔL) is combined with the third branched reference light to generate the third interference light (horizontally polarized component).

[0028] Furthermore, the PMFC 72 receives vertically polarized reflected light from the measurement light generator and receives fourth branched reference light (light without optical path difference ΔL′) from the reference light generator. Therefore, the PMFC 72 combines the reflected light component (light without optical path difference ΔL) of the vertically polarized reflected light due to the second measurement light with the fourth branched reference light to generate fourth interference light (vertically polarized component). The first interference light and the second interference light correspond to the measurement light that has passed through the measurement light path S1, and the third interference light and the fourth interference light correspond to the measurement light that has passed through the measurement light path S2.

[0029] (Interference light detection unit) The interference light detection units 80, 90 include a first interference light detection unit 80 that detects the interference light (first interference light and second interference light) generated by the first interference light generation unit 60, and a second interference light detection unit 90 that detects the interference light (third interference light and fourth interference light) generated by the second interference light generation unit 70.

[0030] The first interference light detection unit 80 includes balanced photodetectors 81 and 82 (hereinafter simply referred to as "detectors 81 and 82") and a signal processor 83 connected to the detectors 81 and 82. The PMFC 61 is connected to the detector 81, and the signal processor 83 is connected to the output terminal of the detector 81. The PMFC 61 splits the first interference light into two interference lights with a phase difference of 180 degrees and inputs them to the detector 81. The detector 81 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees input from the PMFC 61, converts them into an electrical signal (first interference signal), and outputs the first interference signal to the signal processor 83. That is, the first interference signal is an interference signal HH between the horizontally polarized reflected light from the test eye 500 and the reference light due to the horizontally polarized measurement light. Similarly, the PMFC 62 is connected to the detector 82, and the signal processor 83 is connected to the output terminal of the detector 82. The PMFC 62 splits the second interference light into two interference lights with a phase difference of 180 degrees, and inputs them to the detector 82. The detector 82 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees, converts them into an electrical signal (second interference signal), and outputs the second interference signal to the signal processor 83. That is, the second interference signal is an interference signal HV between the vertically polarized reflected light from the subject's eye 500 and the reference light due to the horizontally polarized measurement light.

[0031] The signal processor 83 includes a first signal processing unit 84 to which the first interference signal is input, and a second signal processing unit 85 to which the second interference signal is input. The first signal processing unit 84 samples the first interference signal based on a sampling trigger and a sampling clock input from a sampling trigger / clock generator 100 to the signal processor 83. The second signal processing unit 85 samples the second interference signal based on a sampling trigger and a sampling clock input from the sampling trigger / clock generator 100 to the signal processor 83. The first interference signal and the second interference signal sampled by the first signal processing unit 84 and the second signal processing unit 85 are input to a calculation unit 202, which will be described later. A known data acquisition device (so-called DAQ) can be used as the signal processor 83.

[0032] Similar to the first interference light detection unit 80, the second interference light detection unit 90 includes balanced photodetectors 91 and 92 (hereinafter simply referred to as "detectors 91 and 92") and a signal processor 93 connected to the detectors 91 and 92. The PMFC 71 is connected to the detector 91, and the signal processor 93 is connected to the output terminal of the detector 91. The PMFC 71 splits the third interference light into two interference lights with a phase difference of 180 degrees and inputs them to the detector 91. The detector 91 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees, converts them into an electrical signal (third interference signal), and outputs the third interference signal to the signal processor 93. That is, the third interference signal is an interference signal VH between the horizontally polarized reflected light from the subject's eye 500 and the reference light due to the vertically polarized measurement light. Similarly, the PMFC 72 is connected to the detector 92, and the signal processor 93 is connected to the output terminal of the detector 92. The PMFC 72 splits the fourth interference light into two interference lights whose phases differ by 180 degrees, and inputs them to the detector 92. The detector 92 performs differential amplification and noise reduction processing on the two interference lights whose phases differ by 180 degrees, converts them into an electrical signal (fourth interference signal), and outputs the fourth interference signal to the signal processor 93. That is, the fourth interference signal is an interference signal VV between the vertically polarized reflected light from the test eye 500 due to the vertically polarized measurement light and the reference light.

[0033] The signal processor 93 includes a third signal processing unit 94 to which the third interference signal is input and a fourth signal processing unit 95 to which the fourth interference signal is input. The third signal processing unit 94 samples the third interference signal based on a sampling trigger and a sampling clock input from a sampling trigger / clock generator 100 to the signal processor 93. The fourth signal processing unit 95 samples the fourth interference signal based on a sampling trigger and a sampling clock input from the sampling trigger / clock generator 100 to the signal processor 93. The third interference signal and the fourth interference signal sampled by the third signal processing unit 94 and the fourth signal processing unit 95 are input to a calculation unit 202 (described later). A known data acquisition device (so-called DAQ) can also be used for the signal processor 93. This configuration allows for acquisition of interference signals representing four polarization characteristics of the subject's eye 500. Note that, although the present embodiment uses signal processors 83 and 93 each having two signal processing units, the present invention is not limited to such a configuration. For example, one signal processor having four signal processing sections may be used, or four signal processors each having one signal processing section may be used.

[0034] Next, the configuration of the control system of the optical tomographic imaging apparatus according to this embodiment will be described. As shown in FIG. 2 , the optical tomographic imaging apparatus is controlled by a calculation device 200. The calculation device 200 is composed of a calculation unit 202, a first interference light detection unit 80, and a second interference light detection unit 90. The first interference light detection unit 80, the second interference light detection unit 90, and the calculation unit 202 are connected to the measurement unit 10. The calculation unit 202 outputs a control signal to the measurement unit 10 and drives the galvanometer mirrors 27 and 28 to scan the incident position of the measurement light on the subject's eye 500. The first interference light detection unit 80 acquires first sampling data based on the sampling clock 1 input from the measurement unit 10, using a sampling trigger 1 as a trigger, in response to the interference signals (interference signals HH and HV) input from the measurement unit 10, and outputs the first sampling data to the calculation unit 202. The calculation unit 202 performs calculation processing such as Fourier transform processing on the first sampling data to generate HH tomographic images and HV tomographic images. The second interference light detection unit 90 acquires second sampling data based on a sampling clock 2 input from the measurement unit 10 in response to the interference signals (interference signals VH and VV) input from the measurement unit 10, using a sampling trigger 2 as a trigger, and outputs the second sampling data to the calculation unit 202. The calculation unit 202 performs calculation processing such as Fourier transform processing on the second sampling data to generate VH tomographic images and VV tomographic images. Here, the HH tomographic image, VH tomographic image, HV tomographic image, and VV tomographic image are tomographic images of the same position. Therefore, the calculation unit 202 can generate tomographic images of four polarization characteristics (HH, HV, VH, VV) representing the Jones matrix of the subject's eye 500.

[0035] 3, the sampling trigger / clock generator 100 includes a fiber coupler 102, sampling trigger generators (140 to 152), and sampling clock generators (160 to 172). Light from a light source 11 is input to the sampling trigger generator 140 and the sampling clock generator 160 via the fiber coupler 13 and the fiber coupler 102, respectively.

[0036] (Sampling Trigger Generator) The sampling trigger generator 140 may generate a sampling trigger using, for example, an FBG (Fiber Bragg Grating) 144. As shown in FIG. 3 , the FBG 144 reflects only a specific wavelength of light incident from the light source 11 to generate a sampling trigger. The generated sampling trigger is input to the distributor 150. The distributor 150 distributes the sampling trigger into sampling trigger 1 and sampling trigger 2. The sampling trigger 1 is input to the calculation unit 202 via a signal delay circuit 152. The sampling trigger 2 is input directly to the calculation unit 202. The sampling trigger 1 serves as a trigger signal for the interference signals (first interference signal and second interference signal) input from the first interference light detection unit 80 to the calculation unit 202. The sampling trigger 2 serves as a trigger signal for the interference signals (third interference signal and fourth interference signal) input from the second interference light detection unit 90 to the calculation unit 202. The signal delay circuit 152 is designed so that sampling trigger 1 is delayed in time relative to sampling trigger 2 by the optical path length difference ΔL of the optical path length difference generation unit 22. This makes it possible to make the frequency at which sampling of the interference signal input from the first interference light detection unit 80 starts the same as the frequency at which sampling of the interference signal input from the second interference light detection unit 90 starts. Here, only sampling trigger 1 may be generated. Since the optical path length difference ΔL is known, when sampling the interference input from the second interference light detection unit 90, sampling can be started so as to be delayed in time by the optical path length difference ΔL from sampling trigger 1.

[0037] (Sampling Clock Generator) The sampling clock generator may be configured, for example, with a Mach-Zehnder interferometer. As shown in FIG. 3 , the sampling clock generator generates sampling clocks of equal frequency using a Mach-Zehnder interferometer. The sampling clock generated by the Mach-Zehnder interferometer is input to a distributor 172. The distributor 172 distributes the sampling clock into sampling clock 1 and sampling clock 2. Sampling clock 1 is input to the first interference light detector 80 via a signal delay circuit 174. Sampling clock 2 is input directly to the second interference light detector 90. The signal delay circuit 174 is designed to delay the time by the optical path length difference ΔL of the optical path length difference generator 22. This allows sampling at the same timing even for interference light delayed by the optical path length difference generator 22. This prevents misalignment of multiple acquired tomographic images. In this embodiment, a Mach-Zehnder interferometer is used to generate the sampling clock. However, a Michelson interferometer or an electrical circuit may be used to generate the sampling clock, or a light source equipped with a sampling clock generator may be used to generate the sampling clock.

[0038] Next, with reference to FIGS. 4 and 5 , a process for generating an image showing the birefringence intensity (hereinafter also referred to as a birefringence intensity map) for a desired depth range of the test eye 500 will be described. When the test eye 500 is photographed using the optical tomography apparatus of this embodiment, various birefringence-related characteristics can be visualized. The depth range of the test eye 500 that a user (e.g., a medical professional such as a doctor) wants to understand varies depending on the type of disease being examined. If information outside the depth range desired by the user is included in the image, the amount of information contained in the image increases, making it difficult to grasp the desired information about the test eye 500. Below, an image showing birefringence (birefringence intensity map) is generated only for the depth range desired by the user. In particular, since the polarization-sensitive optical tomography apparatus of this embodiment acquires a large amount of information, generating an image excluding unnecessary ranges allows the user to display only the information within the desired range, making the image easier to view and more effective.

[0039] In this embodiment, an example will be described in which a process for superimposing and displaying a tomographic image of the fundus of the subject's eye 500 is described. Note that the tomographic image is not limited to an image of the fundus of the subject's eye 500. The tomographic image may be an image of a part other than the fundus of the subject's eye 500, for example, an image of the anterior segment of the eye.

[0040] As shown in FIG. 4 , the calculation unit 202 first acquires a tomographic image showing the birefringence of the fundus of the subject's eye 500 (S12). The process of acquiring a tomographic image showing the birefringence of the fundus of the subject's eye 500 is performed as follows: First, the examiner operates an operating member such as a joystick (not shown) to align the optical tomographic imaging apparatus with respect to the subject's eye 500. That is, the calculation unit 202 drives a position adjustment mechanism (not shown) in response to the examiner's operation of the operating member. This adjusts the position of the optical tomographic imaging apparatus in the x- and y-directions (vertical and horizontal directions) and the z-direction (direction of forward and backward movement) relative to the subject's eye 500. Next, the calculation unit 202 captures a tomographic image of the fundus of the subject's eye 500. In this embodiment, this is performed using a raster scan method. In the raster scan method, the B-scan direction is set horizontally relative to the subject's eye 500, and the C-scan direction is set vertically, and a tomographic image is captured. This allows a tomographic image of the fundus of the subject's eye 500 to be acquired over the entire area. Note that the method for capturing a tomographic image of the fundus of the subject's eye 500 is not limited to the raster scan method. Any method may be used as long as a tomographic image of the fundus of the subject's eye 500 can be acquired over the entire area, and for example, a radial scan method may be used. In the radial scan method, a tomographic image is captured by setting the B scan direction as a radial direction from the corneal apex of the subject's eye 500 and the C scan direction as a circumferential direction.

[0041] As described above, the optical tomography apparatus of this embodiment is a polarization-sensitive optical tomography apparatus, and therefore can simultaneously acquire a tomography image captured by irradiating the test eye 500 with a vertical wave and a tomography image captured by irradiating the test eye 500 with a horizontal wave. By using these two types of tomography images, the calculation unit 202 can generate not only a tomography image showing the tissue in the test eye 500 based on the scattering intensity (so-called a normal tomography image), but also a tomography image showing the birefringence in the test eye 500. In this embodiment, the tomography image showing the birefringence is generated using four interference signals HH, HV, VH, and VV. The tomography image showing the birefringence can be generated using a known method. For example, the tomography image showing the birefringence can be acquired by the following method. When capturing a tomography image, speckles are generated due to interference of scattered light generated by fine structures below the OCT resolution. The phase difference between the polarized signals of the generated speckles is displayed. This results in a tomography image showing the birefringence.

[0042] Next, the calculation unit 202 identifies (segments) the boundaries between adjacent tissues (for example, the boundaries between the nerve fiber layer and the ganglion cell layer) in each tomographic image within the subject's eye 500 (S14). Note that the segmentation can be performed using a known method such as that disclosed in Japanese Patent Application Laid-Open No. 2019-88957, and therefore detailed description thereof will be omitted.

[0043] Next, the calculation unit 202 superimposes the layer boundaries identified in step S14 on the tomographic image acquired in step S12 and displays the result on the monitor 120 (S16). Fig. 5(a) shows the tomographic image acquired in step S12, and Fig. 5(b) shows an image in which the boundary lines identified in step S14 are superimposed on the tomographic image of Fig. 5(a). As shown in Fig. 5(b), by superimposing the layer boundaries on the tomographic image, the user can easily visually grasp each layer of the subject's eye 500.

[0044] Next, the calculation unit 202 determines whether a depth range has been selected (S18). Specifically, the user uses an input device (not shown) such as a mouse to input a specific (desired) depth range for the tomographic image displayed on the monitor 120 in step S16. For example, the user designates one or more layers from among the layers whose boundaries were identified in step S14. The designated one or more layers are then selected. Alternatively, when the user designates a specific layer, a predetermined depth range may be selected from the front and / or back surface of the designated layer. Alternatively, the user may input the name of the layer to be selected (e.g., optic nerve fiber layer (NFL)) using an input device (not shown) such as a keyboard, and the calculation unit 202 may select one or more layers corresponding to the input layer. If a depth range has not been selected (NO in step S18), the calculation unit 202 waits until the user selects a depth range.

[0045] When the depth range is selected (YES in step S18), the calculation unit 202 generates a birefringence intensity map for the depth range selected in step S18 (S20). The birefringence intensity map is an image (en-face image) obtained by calculating the maximum, minimum, or average value of birefringence intensity in the depth direction for each A-scan of the three-dimensional data and compressing the three-dimensional data into a two-dimensional front image. The calculation unit 202 generates the en-face image using only the tomographic images (tomographic information) for the depth range selected in step S18. This generates a birefringence intensity map for only the depth range selected in step S18.

[0046] Next, the calculation unit 202 displays the birefringence intensity map generated in step S20 on the monitor 120 (S22). As shown in FIG. 5C, the birefringence intensity map calculated using the tomographic information of only the one or more layers selected in step S18 is displayed on the monitor 120. The birefringence intensity map includes only information on the one or more layers selected in step S18, and does not include information on other layers. Since information on birefringence in unnecessary ranges is not included and only information on birefringence in the desired range (birefringence intensity map) is displayed, unnecessary information is reduced, making the image easier to view. It is known that fiber density correlates with birefringence. By checking the birefringence intensity distribution of the test eye 500, the fiber density in the test eye 500 can be indirectly evaluated.

[0047] Example 2 In Example 1, the calculation unit 202 generated a birefringence intensity map for a desired depth range of the subject's eye 500. However, other images related to birefringence may be generated for the desired depth range of the subject's eye 500. For example, the calculation unit 202 may generate an image showing the orientation of fibrous tissue for the desired depth range of the subject's eye 500 (hereinafter also referred to as a fiber orientation map). In this example, the fiber orientation map shows horizontal fiber orientation in a first color, vertical fiber orientation in a second color different from the first color, and the intermediate portion is displayed with a gradation between the first and second colors (see FIGS. 7(b) and 8(b)). By displaying the image in this manner, the orientation of the fibers can be visually determined from the difference in color.

[0048] As shown in FIG. 6 , first, the calculation unit 202 acquires a tomographic image showing the direction of fiber travel in the fundus of the subject's eye 500 (S112). In this embodiment, the tomographic image showing the direction of fiber travel is generated using four interference signals HH, HV, VH, and VV. The tomographic image showing the direction of fiber travel can be generated using a known method. For example, the tomographic image showing the direction of fiber travel can identify the direction of birefringence by calculating the axis of birefringence, thereby visualizing the direction of fiber travel in the subject's eye 500.

[0049] Next, the calculation unit 202 identifies the boundaries of each layer in the subject's eye 500 for each tomographic image (S114), and displays the boundaries of each layer superimposed on the tomographic image on the monitor 120 (S116). The calculation unit 202 then waits for the user to select a depth range (S118). Note that the processing in steps S114 to S118 is substantially the same as the processing in steps S14 to S18 in the first embodiment, and therefore detailed description thereof will be omitted.

[0050] Once a depth range is selected (YES in step S118), the calculation unit 202 generates a fiber trajectory map for the depth range selected in step S118 (S120). Specifically, the calculation unit 202 generates an en-face image using only the tomographic images (tomographic information) for the depth range selected in step S118. This generates a fiber trajectory map for the depth range selected in step S38. In this embodiment, too, a fiber trajectory map is generated using only the tomographic information for the layer selected by the user. Because information about birefringence (fiber trajectory map) for only the desired range is displayed, unnecessary information is reduced, making the image easier to view.

[0051] For example, when the user selects the area r1 representing the optic nerve fiber layer (NFL) and Henle fiber layer as shown in FIG. 7(a), a fiber trajectory map showing the fiber direction of only the optic nerve fiber layer (NFL) and Henle fiber layer is displayed as shown in FIG. 7(b). Furthermore, when the user selects the area r2 representing the sclera as shown in FIG. 8(a), a fiber trajectory map showing the fiber direction of only the sclera is displayed as shown in FIG. 8(b). As shown in FIGS. 7(b) and 8(b), the fiber trajectory direction varies depending on the layer of the fundus of the subject's eye 500. If a fiber trajectory map of the entire fundus of the subject's eye 500 is generated, information on multiple layers with different fiber trajectories is compressed into a frontal image, making it difficult to grasp the fiber trajectory direction. Generating a fiber trajectory map consisting of only the desired depth range selected by the user makes it easier to grasp the fiber trajectory direction in that range (layer). Understanding the fiber trajectory direction in a specific range (layer) is useful for understanding how the fiber trajectory direction affects the shape of the subject's eye 500. For example, by comparing the changes in the direction of fiber travel before and after the eyeball shape develops or deforms due to severe myopia or pathological myopia, it is possible to better understand the disease of the subject eye 500 and use this information to consider treatment plans.

[0052] (Example 3) In the above Example 2, the calculation unit 202 generated a fiber running map for a desired depth range of the subject's eye 500, but it is also possible to display a line (hereinafter also referred to as a streamline) indicating the fiber running direction (direction of the birefringence axis) superimposed on the fiber running map for a desired depth range of the subject's eye 500.

[0053] In this embodiment, the calculation unit 202 first executes the same processes as steps S112 to S118 in the second embodiment. Next, the calculation unit 202 executes the same process as step S120 in the second embodiment to generate a fiber trajectory map and generate streamlines. Generally, algorithms and software for rendering streamlines are readily available. For example, streamlines in the birefringence axis direction can be rendered using the Advanced Plotting Toolkit from Heliosphere Research LLC, which is provided as an add-on to National Instruments' LabVIEW. Alternatively, similar processing may be performed using the open-source software Matplotlib.

[0054] Next, the calculation unit 202 superimposes the generated fiber trajectory map and streamlines on the monitor 120. In this embodiment, a fiber trajectory map consisting of only the layers selected by the user is generated. Because information about birefringence (fiber trajectory map) for only the desired range is displayed, unnecessary information is reduced, making the image easier to view. Furthermore, as shown in FIGS. 9( b) and 10( b), in this embodiment, streamlines are superimposed on the fiber trajectory map. Fiber trajectory maps that show axial directions in color require the fiber trajectory direction to be determined from the color difference, making it difficult to intuitively interpret the fiber trajectory direction. Superimposing streamlines on the fiber trajectory map makes it easy to understand the fiber trajectory direction. In this embodiment, streamlines are superimposed on the fiber trajectory map and displayed on the monitor 120. However, the user may be able to switch between displaying and hiding streamlines (i.e., displaying only the fiber trajectory map) using an input device.

[0055] Example 4 In Example 3 above, the calculation unit 202 generates a fiber trajectory map for a desired depth range of the subject's eye 500 and displays streamlines superimposed on the generated fiber trajectory map, but information about regions where the birefringence intensity is higher than a predetermined value (hereinafter also referred to as high birefringence regions) may be superimposed on the fiber trajectory map or streamlines for a desired depth range of the subject's eye 500. Below, an example will be described in which information about high birefringence regions is superimposed on streamlines, but information about high birefringence regions may also be superimposed on the fiber trajectory map.

[0056] As shown in FIG. 11 , first, the calculation unit 202 acquires a tomographic image showing the birefringence of the fundus of the subject's eye 500 (S212). Since the process of step S212 is the same as the process of step S12 in the first embodiment, detailed description thereof will be omitted. Next, the calculation unit 202 acquires a tomographic image showing the direction of fiber distribution in the fundus of the subject's eye 500 (S214). Since the process of step S214 is the same as the process of step S112 in the second embodiment, detailed description thereof will be omitted. Furthermore, step S214 may be executed before step S212. Next, the calculation unit 202 identifies the boundaries of each layer in the subject's eye 500 for each tomographic image (S216), and displays the boundaries of each layer superimposed on the tomographic image on the monitor 120 (S218). The calculation unit 202 then waits for the user to select a depth range (S220). The processes in steps S216 to S220 are substantially the same as the processes in steps S14 to S18 in the first embodiment, and therefore detailed description thereof will be omitted.

[0057] Next, the calculation unit 202 generates a fiber trajectory map and streamlines for the depth range selected in step S220 using the tomographic image showing the direction of fiber trajectory in the fundus of the subject's eye 500 acquired in step S214 (S222). Note that the processing in step S222 is substantially the same as the processing for generating the fiber trajectory map and streamlines in Example 3, and therefore a detailed description thereof will be omitted.

[0058] Next, the calculation unit 202 identifies a high birefringence region within the depth range selected in step S220 in the tomographic image showing the birefringence of the fundus of the subject's eye 500 acquired in step S212 (S224). The predetermined value for determining whether or not a region is a high birefringence region is a value set by the user. That is, the user sets a value at which the intensity of birefringence is determined to be high as the predetermined value (i.e., threshold value).

[0059] Next, the calculation unit 202 superimposes the high birefringence regions identified in step S224 on the streamlines generated in step S222 and displays them on the monitor 120 (S226). For example, as shown in Figures 12(b) and 13(b), in this embodiment, the high birefringence regions are displayed in a color (highlighted) different from that of the streamlines. That is, the color indicating the high birefringence regions is displayed superimposed on the streamlines.

[0060] Although birefringence intensity and fiber direction are both characteristics of the birefringence of fibrous tissue, they have different clinical significance. While evaluating birefringence intensity and fiber direction individually is useful, it is also important to integrate and evaluate them comprehensively. When evaluating birefringence intensity and fiber direction comprehensively, displaying them as separate images requires users to compare the two images, which is inconvenient for users. Superimposing high birefringence regions on streamlines makes it easier for users to comprehensively evaluate birefringence intensity and fiber direction. For example, high birefringence intensity suggests high fiber density, and in high birefringence regions, fiber direction may be more important than in regions with low birefringence intensity (i.e., regions with sparse fiber density). Superimposing high birefringence regions on streamlines makes it easier to understand the fiber direction in high birefringence regions. This makes it easier for the user to focus on the direction of fibers in high birefringence regions, which are likely to be of particular clinical importance.

[0061] In this embodiment, the entire high birefringence region is displayed in a color different from the streamlines, but this configuration is not limited to this. It is sufficient that the high birefringence region can be easily visually recognized. For example, the color of the streamlines in the high birefringence region may be displayed in a color different from that in other regions. Furthermore, the thickness of the streamlines in the high birefringence region may be displayed with a different thickness from that in other regions, or the brightness of the streamlines in the high birefringence region may be displayed with a different brightness from that in other regions. Furthermore, the predetermined value may be configured to be changeable by the user after the high birefringence region is displayed superimposed on the streamlines.

[0062] (Example 5) In the above Example 1, the calculation unit 202 generated a birefringence intensity map for a desired depth range of the test eye 500, but it may also generate a thickness map of a region where the birefringence intensity is higher than a predetermined value (hereinafter also referred to as a thickness map of a high birefringence region) for a desired depth range of the test eye 500.

[0063] 14, the calculation unit 202 first acquires tomographic images showing the birefringence of the fundus of the subject's eye 500 (S312), identifies the boundaries of each layer in the subject's eye 500 for each tomographic image (S314), and displays the tomographic images with the boundaries of each layer superimposed on them on the monitor 120 (S316). The calculation unit 202 then waits for the user to select a depth range (S318). Note that the processing in steps S312 to S318 is substantially the same as the processing in steps S14 to S18 in the first embodiment, and therefore detailed description thereof will be omitted.

[0064] Next, the calculation unit 202 identifies a region where the birefringence intensity is higher than a predetermined value (high birefringence region) in the tomographic image showing the birefringence of the test eye 500 acquired in step S312 (S320). The predetermined value is a value set by the user. That is, the user sets a value that determines the birefringence intensity as high as the predetermined value (i.e., threshold value). For example, assume that the user selects a range deeper than the choroid-sclera interface (CSI). Also assume that the predetermined value is set to 0.12 deg / μm (see the range in the lower diagram of FIG. 15( a)). Then, the calculation unit 202 identifies a region where the birefringence intensity is 0.12 deg / μm or greater in the range deeper than the CSI.

[0065] Next, the calculation unit 202 calculates the thickness of the high birefringence region identified in step S320 for the depth range selected in step S318 (S322). For example, as shown in Fig. 15B, for each tomographic image, the calculation unit 202 calculates the thickness of the region where the birefringence intensity is 0.12 deg / µm or more for each A-scan within the depth range selected by the user.

[0066] Next, the calculation unit 202 generates a thickness map of the high birefringence region from the calculated thickness of the high birefringence region (S324) and displays the generated thickness map of the high birefringence region on the monitor 120 (S326). For example, as shown in FIG. 15C, the thickness map of the high birefringence region is displayed in different colors depending on the thickness. In this embodiment, the thickness map of the high birefringence region is displayed only for the depth range selected by the user. Because the thickness map of the high birefringence region uses the depth range selected by the user, information about depth ranges unnecessary for the user is excluded. This allows the user to grasp the thickness of the high birefringence region only for the required depth range. Furthermore, because the thickness map of the high birefringence region is a thickness map of only regions where the birefringence intensity is higher than a predetermined value, information about layers with low birefringence intensity is excluded. This makes it easier to grasp regions with high birefringence intensity.

[0067] Areas with high birefringence intensity suggest high fiber density. In layers with high fiber density, the fibers may have aligned in the same direction due to stress caused by axial length extension, resulting in increased fiber density. Alternatively, high fiber density layers may have a naturally high fiber density, making them highly resistant to axial length extension. Thus, layers with high fiber density are considered to be areas requiring clinical attention. For example, a birefringence intensity map (see Figure 5) can identify the location of high birefringence regions, but it cannot determine their thickness. Therefore, to determine the thickness of the high birefringence regions, it was necessary to check each tomographic image. Displaying a thickness map of the birefringence layer allows the thickness of the high birefringence regions to be determined at a glance.

[0068] (Example 6) In the above Example 5, the calculation unit 202 generated a thickness map of the high birefringence region for a desired depth range of the test eye 500, but it may also generate a map indicating the number of layers whose birefringence intensity is higher than a predetermined value for a desired depth range of the test eye 500 (hereinafter also referred to as a high birefringence layer number map).

[0069] In this embodiment, first, the calculation unit 202 executes the same processes as steps S312 to S320 in the fifth embodiment.

[0070] Next, the calculation unit 202 calculates the number of layers including the high birefringence regions identified in step S320 for the depth range selected in step S318. For example, as shown in Fig. 16B, for each tomographic image, the calculation unit 202 calculates the number of layers including regions where the birefringence intensity is 0.12 deg / µm or more for each A-scan within the depth range selected by the user.

[0071] Next, the calculation unit 202 generates a high birefringence layer number map from the calculated number of layers including the high birefringence region, and displays the generated high birefringence layer number map on the monitor 120. For example, as shown in FIG. 16( c), the high birefringence layer number map is displayed in different colors depending on the number of layers. In this embodiment, too, the high birefringence layer number map is displayed only for the depth range selected by the user. This eliminates information unnecessary for the user (information about depth ranges unnecessary for the user and information about layers with low birefringence intensity), making it easier to grasp the high birefringence intensity region. Furthermore, by displaying the high birefringence layer number map, the number of layers in the high birefringence intensity region can be grasped at a glance.

[0072] (Example 7) In the above Example 2, the calculation unit 202 generated a fiber course map for a desired depth range of the test eye 500, but it may also generate an angle map (hereinafter also referred to as a relative angle map) that indicates the sum of relative angles between adjacent layers for a desired depth range of the test eye 500.

[0073] 17 , the calculation unit 202 first acquires a tomographic image showing the birefringence of the fundus of the subject's eye 500 (S412), and also acquires a tomographic image showing the direction of fibers in the fundus of the subject's eye 500 (S414). Next, the calculation unit 202 identifies the boundaries of each layer in the subject's eye 500 for each tomographic image (S416), and displays the tomographic image on the monitor 120 with the boundaries of each layer superimposed on the tomographic image (S418). The calculation unit 202 then waits for the user to select a depth range (S420). Note that the processing in steps S412 to S420 is substantially the same as the processing in steps S212 to S220 in the fourth embodiment, and therefore detailed description thereof will be omitted.

[0074] Next, the calculation unit 202 uses the tomographic images showing the birefringence of the fundus of the test eye 500 acquired in step S412 to identify layers (high birefringence layers) in which the birefringence intensity is higher than a predetermined value for the depth range selected in step S420 (S422). Specifically, for each tomographic image showing the birefringence of the fundus of the test eye 500 acquired in step S412, the calculation unit 202 identifies regions (high birefringence regions) in which the birefringence intensity is higher than a predetermined value for the depth range selected in step S420. Then, the calculation unit 202 identifies high birefringence regions located at different depth positions as different high birefringence layers. Therefore, the high birefringence layers are different from the layers formed for each tissue identified in step S416, and multiple high birefringence layers may exist within the same tissue.

[0075] For example, FIG. 18 is a tomographic image showing birefringence. FIG. 19 shows a tomographic image showing the running direction of fibers corresponding to main portion XIX in FIG. 18, and FIG. 20 shows a tomographic image showing the running direction of fibers corresponding to main portion XX in FIG. 18. In main portion XIX in FIG. 19 (the portion shown in FIG. 19, hereinafter also referred to as region A), two high birefringence regions exist at different positions in the depth direction. The calculation unit 202 identifies these two high birefringence regions as high birefringence layers L1 and L2, respectively. Furthermore, in main portion XX in FIG. 18 (the portion shown in FIG. 20), three high birefringence regions exist at different positions in the depth direction. The calculation unit 202 identifies these three high birefringence regions as high birefringence layers L3, L4, and L5, respectively. The high birefringence layers L3 and L5 are located across the entire width in the left-right direction of Fig. 20, while the high birefringence layer L4 is located only on the left side of Fig. 20. That is, three high birefringence layers L3, L4, and L5 are located in the depth direction on the left side (hereinafter also referred to as region B) of the main part XX (the part shown in Fig. 20), and two high birefringence layers L3 and L5 are located in the depth direction on the right side (hereinafter also referred to as region C) of the main part XX (the part shown in Fig. 20).

[0076] Next, the calculation unit 202 calculates the relative angle between adjacent high birefringence layers in the depth direction (S424). Specifically, the calculation unit 202 identifies the fiber running direction (angle) of each high birefringence layer identified in step S422 and calculates the difference between the fiber running directions (angles) of adjacent high birefringence layers in the depth direction for each A-scan. This calculates the relative angle. The fiber running direction of each high birefringence layer is identified using the tomographic image showing the fiber running direction acquired in step S414. Note that if the fiber running direction is not constant within a single high birefringence layer, the average of the fiber running directions within that high birefringence layer is calculated and used as the fiber running direction within that high birefringence layer. Alternatively, if the fiber running direction is not constant within a single high birefringence layer, the fiber running direction at the center position of that high birefringence layer may be used as the fiber running direction within that high birefringence layer.

[0077] For example, as shown in FIG. 19 , in region A, two high birefringence layers L1 and L2 are identified in step S422. The running direction of the fibers in high birefringence layer L1 is 0 degrees, and the running direction of the fibers in high birefringence layer L2 is 45 degrees. Therefore, the calculation unit 202 calculates that the relative angle between adjacent high birefringence layers L1 and L2 in region A is 45 degrees (45 degrees - 0 degrees). Furthermore, as shown in FIG. 20 , in region B, three high birefringence layers L3, L4, and L5 are identified in step S422. The running direction of the fibers in high birefringence layer L3 is 0 degrees, the running direction of the fibers in high birefringence layer L4 is 45 degrees, and the running direction of the fibers in high birefringence layer L5 is 90 degrees. Therefore, in region B, the calculation unit 202 calculates the relative angle between adjacent high birefringence layers L3 and L4 to be 45 degrees (45 degrees - 0 degrees), and the relative angle between adjacent high birefringence layers L4 and L5 to be 45 degrees (90 degrees - 45 degrees). Furthermore, in region C, two high birefringence layers L3 and L5 are identified in step S422. Therefore, in region C, the calculation unit 202 calculates the relative angle between adjacent high birefringence layers L3 and L5 to be 90 degrees (90 degrees - 0 degrees).

[0078] Next, the calculation unit 202 calculates the sum of the relative angles for each depth direction (S426). For example, as shown in FIG. 19, in region A, the relative angle calculated for each depth direction in step S424 is only one, the 45-degree relative angle between the high birefringence layers L1 and L2, so the sum of the relative angles is 45 degrees. Also, as shown in FIG. 20, in region B, the relative angles calculated for each depth direction in step S424 are two: the 45-degree relative angle between the high birefringence layers L3 and L4 and the 45-degree relative angle between the high birefringence layers L4 and L5, so the sum of the relative angles is 90 degrees (45 degrees + 45 degrees). Furthermore, in region C, the relative angle calculated for each depth direction in step S424 is only one: the 90-degree relative angle between the high birefringence layers L3 and L5, so the sum of the relative angles is 90 degrees.

[0079] Next, the calculation unit 202 generates a relative angle map from the sum of the relative angles for each depth direction calculated in step S426 (S428), and displays the generated relative angle map on the monitor 120 (S430). For example, as shown in Fig. 21, the relative angle map is displayed in different colors depending on the sum of the relative angles (angles).

[0080] In this embodiment, the relative angle map is displayed only for the depth range selected by the user. Therefore, unnecessary information for the user (information about the depth range unnecessary for the user and information about layers with low birefringence intensity) is excluded, making it easier to grasp the relative angle of the region with high birefringence intensity. When multiple regions with high birefringence intensity exist in the depth direction, it is thought that the clinical significance, for example, of stress resistance to axial length progression, will differ depending on whether the fiber direction is the same or different. Displaying the relative angle map makes it easier to grasp the state of the relative angle.

[0081] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility.

Claims

1. A polarization-sensitive optical tomographic imaging device comprising: an imaging unit that captures a tomographic image of a test eye; a designation means for designating a depth-wise range of the tomographic image; and a calculation unit, wherein the tomographic images include a first tomographic image captured by irradiating the test eye with a first polarized wave and a second tomographic image captured by irradiating the test eye with a second polarized wave having a vibration direction different from that of the first polarized wave, and the calculation unit is configured to execute an image generation process that generates at least one of an image showing birefringence and an image showing the running pattern of fibers, for the depth-wise range of the tomographic image designated by the designation means, based on the first tomographic image and the second tomographic image.

2. An optical tomographic imaging device as described in claim 1, further comprising a display unit that displays an image showing the running pattern of the fibers, the display unit displaying the image showing the running pattern of the fibers together with a line indicating the running direction of the fibers superimposed at a corresponding position on the image showing the running pattern of the fibers.

3. An optical tomography apparatus as described in claim 2, wherein the display unit further superimposes and displays an image showing an area where the birefringence intensity is greater than a predetermined value at a position corresponding to the image showing the course of the fibers.

4. The optical tomography apparatus according to claim 1, further comprising a display unit for displaying an image showing the birefringence, the display unit displaying a thickness map showing the thickness of a region in which the birefringence is higher than a predetermined value.

5. An optical tomographic imaging device as described in claim 1, further comprising a display unit that displays an image indicating the birefringence, wherein the calculation unit is further configured to execute a layer identification process that identifies each layer in the test eye, and a determination process that determines whether or not the birefringence of each layer identified in the layer identification process is higher than a predetermined value, and the display unit displays a layer number map indicating the number of layers determined in the identification process to have birefringence higher than the predetermined value.

6. The optical tomographic imaging device of claim 1, further comprising a display unit configured to display an angle map showing the angle for the sum of the relative angles calculated in the second calculation process, the calculation unit being further configured to execute a layer identification process for identifying each layer in the test eye, a first calculation process for calculating a relative angle between each layer identified in the layer identification process and adjacent layers, and a second calculation process for calculating a sum of the relative angles calculated in the first calculation process for the depth direction range of the tomographic image specified by the designation means.

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