Oct system

Abstract

An imaging control unit of this OCT system carries out determination processing for determining, when imaging OCT data, which of a first mode in which the retina surface of an eye to be examined is formed rearward relative to a zero delay position and a second mode in which the choroid back surface of the eye to be examined is formed forward relative to the zero delay position is an imaging mode suitable for detection of a prescribed tissue in the retina, and as a result of one of the first mode and the second mode being selected on the basis of the determination processing results, performs OCT data imaging after adjusting the optical path length in accordance with the selected imaging mode. An analysis processing unit detects the prescribed tissue using the OCT data imaged in the selected imaging mode, and additionally performs analysis processing which uses the position of the prescribed tissue as a reference on the OCT data.

Description

OCT system

[0001] The present disclosure relates to an OCT system that acquires (photographs) OCT data of a subject's eye.

[0002] Currently, most OCT devices used in ophthalmology facilities are Fourier-domain OCT devices, which perform predetermined processing including Fourier transform on a spectral interference signal between a measurement light and a reference light irradiated onto the subject's eye, thereby acquiring a tomographic image of the subject's eye.

[0003] In Fourier-domain OCT, the depth position where the optical path lengths of the measurement light and the reference light are the same is called the zero-delay position, and serves as the reference for the imaging range in the depth direction. In Fourier-domain OCT, the real image component and the virtual image component resulting from the Fourier transform are formed as symmetrical images with respect to the zero-delay position. An area including one of the symmetrical images is selectively displayed. In Fourier-domain OCT, the closer to the zero-delay position the higher the sensitivity, and the further away from the zero-delay position the lower the sensitivity.

[0004] Patent Document 1 discloses an apparatus capable of switching between a retina mode and a choroid mode. In the retina mode, a tomographic image (normal image) is acquired with the fundus positioned further back than the zero delay position, resulting in an image with higher sensitivity on the retina side than the choroid side. In the choroid mode, a tomographic image (inverted image) is acquired with the fundus positioned further forward than the zero delay position, resulting in an image with higher sensitivity on the choroid side than the retina side (see, for example, Patent Document 1).

[0005] Patent Literature 2 discloses an apparatus for performing analysis processing on captured OCT data by setting an analysis range based on the position of the fovea of ​​the fundus. As one method for determining the position of the fovea, it also discloses performing processing to detect the fovea in the OCT data.

[0006] Patent Document 3 proposes a spectral domain OCT, which is a type of Fourier domain OCT, in which the imaging range in the depth direction is 3 mm or more.

[0007] JP 2010-29648 A JP 2018-171141 A JP 2022-155352 A

[0008] Even though the OCT data was captured with the fundus positioned further back than the zero-delay position (retina mode), the retinal segmentation process (layer identification) sometimes failed. Even if the segmentation process was successful, the fovea detection sometimes failed. As a result, the retina analysis process was not performed properly.

[0009] In Fourier-domain OCT, which has a sufficiently wide imaging range in the depth direction as disclosed in Patent Document 3, the central part of the retina (the fovea centralis and its surrounding area) is imaged away from the zero-delay position, and as a result, the image quality of the central part of the retina becomes unsuitable for detection, which is thought to be one of the reasons for failure to detect tissue present in the retina.

[0010] The present disclosure has been made in consideration of the problems of the conventional technology, and has as its technical object to provide an OCT system that can effectively detect tissue present in the retina.

[0011] An OCT system according to a first aspect of the present disclosure is an OCT system including: an OCT optical system having a beam splitter that splits light from an OCT light source into a measurement beam path and a reference beam path; and a spectrometer that detects a spectral interference signal between the measurement beam guided to the fundus of the subject's eye via the measurement beam path and the reference beam from the reference beam path; an image processor that processes the spectral interference signal to acquire OCT data of the fundus; an imaging control unit that controls imaging of the OCT data; and an analysis processing unit that analyzes the captured OCT data, wherein the imaging control unit selects an imaging mode suitable for detecting a predetermined tissue present in the retina when the retinal surface of the subject's eye is located deeper than a zero delay position. When capturing the OCT data, a determination process is performed to determine whether the OCT data is captured in a first mode in which a posterior choroid of the test eye is formed anterior to a zero delay position, or a second mode in which a posterior choroid of the test eye is formed anterior to a zero delay position, and either the first mode or the second mode is selected based on the result of the determination process, and the OCT data is captured after adjusting the optical path length of either the measurement optical path or the reference optical path according to the selected capturing mode, and the analysis processing unit detects the specified tissue from the OCT data captured in the selected capturing mode, and further performs analysis processing on the OCT data based on the position of the specified tissue.

[0012] According to the present disclosure, tissue present in the retina can be detected well.

[0013] FIG. 1 is a diagram illustrating the optical system and control system of the OCT device of the present embodiment. FIG. 2 is a schematic diagram of OCT data illustrating a state in which the zero delay position is set shallower than the retinal surface. FIG. 3 is a schematic diagram of OCT data illustrating a state in which the zero delay position is set deeper than the posterior surface of the choroid. FIG. 4 is a flowchart illustrating an example of the operation of the OCT device. FIG. 5 is a flowchart illustrating an example of optimization control. FIG. 6 is a flowchart illustrating an example of analysis processing. FIG. 7 is a diagram illustrating the relationship between the position of the fovea and the analysis range of the OCT data. FIG. 8 is a tomographic image captured with the zero delay position set shallower than the retinal surface. FIG. 9 is a tomographic image captured with the zero delay position set deeper than the posterior surface of the choroid. FIG. 10 is a diagram illustrating an analysis map as an example of the analysis results. FIG. 11 is a diagram illustrating an analysis chart as an example of the analysis results.

[0014] "Overview" An overview of an OCT system according to an embodiment of the present disclosure will be described.

[0015] An OCT system according to an embodiment of the present disclosure includes at least an OCT optical system, an image processor, an imaging control unit, and an analysis processing unit. The OCT system may be realized as a standalone device (OCT apparatus) having these components. Furthermore, for example, the OCT apparatus including the OCT optical system, the image processor, and the imaging control unit may be configured separately from the analysis processing device including the analysis processing unit.

[0016] The OCT optical system in this embodiment is a spectral-domain OCT optical system. The OCT optical system includes at least a beam splitter and a spectrometer. The beam splitter splits light from an OCT light source into a measurement beam path and a reference beam path. The spectrometer detects a spectral interference signal between the measurement beam guided to the fundus of the subject's eye via the measurement beam path and the reference beam from the reference beam path.

[0017] The image processor processes the spectral interference signal to obtain OCT data of the fundus, and performs predetermined processing including Fourier transform on the spectral interference signal to obtain the OCT data of the fundus.

[0018] In the OCT system of this embodiment, the imaging control unit controls the imaging of OCT data.

[0019] For example, the imaging control unit may adjust imaging conditions such as the OPL, focus, polarization state, and light intensity of imaging light or detector gain in the OCT optical system. In the OPL adjustment, the optical path length of at least one of the measurement optical path and the reference optical path is changed. The optical path length may be changed by moving an optical member disposed in at least one of the measurement optical path and the reference optical path, or by changing the distance between the subject's eye and the device. The OPL adjustment changes the zero delay position with respect to the fundus of the subject's eye.

[0020] Additionally, the OCT optical system may include a scanner that scans the fundus with measurement light, and the scanning control of the measurement light may be performed by the imaging control unit. The OCT system may additionally include an observation optical system, and the imaging control unit may control the observation optical system. The observation optical system acquires a front image of the fundus as an observation image. The observation image can be used for positioning the measurement position, tracking control of the scan position, etc.

[0021] The captured OCT data is analyzed by an analysis processor, and at least one of the thickness, length, area, volume, density, distribution, etc. of the tissue in the fundus is output as the analysis result.

[0022] The imaging control unit performs a determination process when capturing OCT data. When capturing OCT data, the determination process determines whether the imaging mode suitable for detecting a specific tissue present in the retina is the first mode or the second mode. The first mode is an imaging mode in which the retinal surface of the subject's eye is formed behind the zero delay position. The second mode is an imaging mode in which the posterior surface of the choroid of the subject's eye is formed ahead of the zero delay position.

[0023] The imaging control unit selects either the first mode or the second mode based on the results of the determination process, and then adjusts the optical path length of either the measurement optical path or the reference optical path according to the selected imaging mode, and then performs imaging of the OCT data.

[0024] The analysis processor detects a predetermined tissue from the OCT data captured in the selected imaging mode. The predetermined tissue is a tissue present in the retina at the center of the fundus. For example, the predetermined tissue may be the fovea, a predetermined layer, a layer boundary, or a lesion such as an NPA or a vascular aneurysm. An analysis process based on the transverse (XY) position of the predetermined tissue may be performed on the OCT data. If the position of the predetermined tissue can be identified in the transverse (XY) direction, such as the fovea, the OCT data may further be analyzed based on the transverse (XY) position of the predetermined tissue. The analysis process may determine any of the thickness, area, volume, density, and distribution of the tissue within an analysis range based on the position of the predetermined tissue. The analysis results may be output as numerical values, maps, or charts.

[0025] Here, it seems that the case where the retinal surface of the subject's eye is formed behind the zero delay position is more suitable for detecting tissue present in the retina than the case where the posterior choroid surface of the subject's eye is formed ahead of the zero delay position. However, when photographing a subject's eye with a highly curved fundus, such as a severely myopic eye, the retina may be located at a position far from the zero delay position even if the retinal surface of the subject's eye is formed behind the zero delay position.

[0026] In particular, devices with a wide imaging range in the depth direction can capture images from the center to the periphery of the fundus well, even when the fundus is significantly curvatured. In other words, it is easy to capture images from the center to the periphery of the fundus while avoiding image folding (the appearance of a virtual image) in the periphery. However, in the first mode, the center of the fundus is likely to be located far from the zero delay position, which may result in tissue detection failure, especially when a specific tissue is present in the center of the fundus. Furthermore, in the case of SD-OCT, which is prone to sensitivity attenuation in the depth direction, tissue detection may be likely to fail if the specific tissue to be detected is located far from the zero delay position. Due to at least one of the factors listed here, it may be impossible to ensure sufficient image quality for detection, even if a specific tissue is present in the retina of the fundus.

[0027] In contrast, it has been found that tissue detection is more likely to be successful in an imaging mode (second mode) in which the posterior choroidal surface of the test eye is formed anterior to the zero-delay position. Therefore, in this embodiment, when capturing OCT data, it is determined whether the imaging mode suitable for detecting a specific tissue present in the retina is the first mode or the second mode. This makes it easier to properly detect the specific tissue during analysis. As a result, analysis processing based on the position of the specific tissue is more likely to be performed appropriately.

[0028] The determination of this embodiment is particularly useful, for example, when the depth-direction imaging range of the OCT optical system is 3 mm or more (more preferably 4 mm or more) and the transverse imaging range is sufficient (e.g., at least 9 mm square, capable of performing a map scan, more preferably 12 mm or more square, and even more preferably 15 mm or more square). For example, if the long side is approximately 15 mm and the short side is approximately 12 mm, 3D OCT data including both the perifoveal and perioptic disc regions can be captured in a single image. In this case, analysis results for the perifoveal and perioptic disc regions can be obtained based on a single 3D OCT data set. However, in this case, in OCT data acquired when the retinal surface of the test eye is positioned further back than the zero-delay position, the image quality of the retina in the central fundus is further degraded, making it even more difficult to detect retinal layers and tissues such as the fovea in the central fundus.

[0029] In the above-described imaging mode determination process, it may be determined whether the imaging mode suitable for detecting a predetermined tissue present in the retina is the first mode or the second mode, based on an image of the fundus in a tomographic image. The tomographic image used for the determination may be acquired with the optical path length adjusted so that the retinal surface is located behind the zero delay position or the choroidal posterior surface is located in front of the zero delay position. Since the determination is made based on the tomographic image acquired with the optical path length adjusted, the determination is likely to be made appropriately. In this case, the determination may be made based on the position or range of the image of the fundus in the tomographic image. Alternatively, the determination may be made based on the shape of the image of the fundus.

[0030] Furthermore, in the above-described imaging mode determination process, determination may be made based on the axial length of the subject's eye. The axial length may be acquired in advance by a device separate from the OCT system, or may be an actual measurement value measured by the OCT system. For a method of measurement using an OCT system, see, for example, Japanese Patent Application Laid-Open No. 2023-18548 filed by the present applicant.

[0031] The imaging control unit may also include a scan pattern selection unit that selects one of two or more different scan patterns. When a scan pattern in which a scan line is set for a predetermined tissue is selected from the two or more scan patterns, the imaging control unit may set the imaging mode based on a determination process. The predetermined scan pattern may be a pattern corresponding to an analysis process including a detection process for the predetermined tissue. The imaging mode may be appropriately selected depending on the content of the analysis process. Furthermore, when a scan pattern is selected whose imaging range includes a first analysis region in the center of the fundus and a second analysis region at least partially different from the first analysis region, the imaging mode may be set based on a determination process. With this scan pattern, scans are performed without changing any of the fixation light presentation position, optical path length, focus state, etc. between scans for the first analysis region and scans for the second analysis region. For example, the scan pattern may be a scan pattern that scans a wide area including the first analysis region and the second analysis region in a single operation (scanning the first analysis region and the second analysis region without distinguishing between them). This makes it possible to prevent a decrease in the accuracy of tissue detection and analysis even when analyzing an image of a wide imaging range that includes not only the first analysis region but also the second analysis region.

[0032] In the case of follow-up imaging, the same imaging mode as that used in previous imaging (e.g., baseline imaging) may be selected and imaging performed without determining the imaging mode, or even if a determination is made, regardless of the determination result. The imaging mode used in previous imaging may be stored in a storage unit in advance, and in the case of follow-up imaging, the imaging mode used in previous imaging stored in the storage unit is referenced and the same imaging mode as that imaging mode is set. In this way, when performing follow-up observation of the same eye to be examined, different imaging modes result in the same image state, analysis method, etc., making it easier to perform follow-up observation appropriately.

[0033] "Example" Hereinafter, as an example, an optical coherence tomography (OCT) device shown in Fig. 1 will be described. The OCT device according to this example has, for example, a spectral domain OCT (SD-OCT) as its basic configuration.

[0034] The OCT apparatus 1 according to the embodiment acquires OCT data of the subject's eye. In this embodiment, unless otherwise specified, the OCT apparatus 1 captures OCT data of the fundus.

[0035] First, the configuration of the OCT apparatus 1 will be described with reference to Fig. 1. In the description of the embodiment, the axial direction of the subject's eye E will be referred to as the Z direction, the horizontal direction as the X direction, and the vertical direction as the Y direction.

[0036] The OCT apparatus 1 according to the embodiment includes a photographing unit 2, a driving unit 5, a face support unit 7, and a control unit 70.

[0037] <Photographing Unit> The photographing unit 2 has the main optical systems in the OCT apparatus 1. In this embodiment, the photographing unit 2 has an OCT optical system (interference optical system) 10, a light-guiding optical system 10a, a fundus observation optical system (SLO optical system) 30, and an anterior eye observation optical system 40 (anterior eye observation optical system). The optical paths of the OCT optical system 10, the fundus observation optical system 30, and the anterior eye observation optical system 40 are split and combined by beam splitters / combiners 16 and 17.

[0038] <OCT Optical System> The OCT optical system 10 detects a spectral interference signal between the measurement light and the reference light irradiated onto the fundus of the subject's eye E. The OCT optical system 10 may be, for example, an SD-OCT, an SS-OCT, or an OCT based on another imaging principle.

[0039] The OCT optical system 10 includes at least an OCT light source 11, a beam splitter 12, a reference optical system 20, and a detector 25. Note that although the reference optical system 20 in this embodiment is described as being a reflective optical system, it may also be a transmissive optical system.

[0040] The OCT light source 11 emits low-coherence light. The light emitted from the OCT light source 11 is split into measurement light and reference light by the beam splitter 12. In this embodiment, a coupler (splitter) is used as the beam splitter 12. The measurement light is guided to the subject's eye E via the light-guiding optical system 10a, and the reference light is guided to the reference optical system 20. The measurement light returned from the subject's eye E and the reference light passed through the reference optical system 20 are incident on the beam splitter 12. As a result, the measurement light returned and the reference light are combined by the beam splitter 12 and guided to the detector 25. As a result, the detector 25 detects a spectral interference signal (spectral intensity data) between the measurement light (return light) and the reference light. In SD-OCT, a spectrometer is used as the detector 25.

[0041] A depth profile (A-scan signal) in a predetermined range is acquired by Fourier transform of the spectral intensity data detected by the detector 25. Scanning the fundus with the measurement light along one scan line is called a "B-scan." Two-dimensional OCT data of the fundus is obtained by one B-scan. Three-dimensional OCT data of the fundus is obtained based on scanning the measurement light along multiple scan lines. The three-dimensional OCT data may be acquired based on, for example, raster scanning.

[0042] Furthermore, dispersion correction processing is performed on the spectral intensity data output from the detector 25. For details, please refer to, for example, U.S. Patent No. 6,980,299, JP-A-2008-501118, and JP-A-2010-29648. Dispersion correction causes a difference in image quality between the real image and the virtual image. In this embodiment, dispersion correction is performed so that the real image has higher image quality than the virtual image. However, the present invention is not necessarily limited to this.

[0043] A light-guiding optical system 10a is formed on the optical path between the light splitter 12 and the subject's eye E. In this embodiment, the light-guiding optical system 10a includes at least a focusing lens 14, a scanning unit (optical scanner) 15, and an objective lens 60.

[0044] In this embodiment, the focus position in the OCT optical system 10 is changed by displacing the focusing lens 14 in the optical axis direction.

[0045] The scanning unit 15 is used to change the acquisition position of the OCT image. The scanning unit 15 may be used to two-dimensionally scan the fundus of the subject's eye E with the measurement light. The scanning unit 15 may include, for example, two optical scanners having different scanning directions. Each optical scanner may be a galvanometer mirror or another type of optical scanner.

[0046] The objective lens 60 guides the measurement light to the fundus of the subject's eye. The measurement light is rotated via the objective lens 60, with a position conjugate with the scanning unit 15 as the rotation point. As shown in FIG. 1 , when the anterior segment of the subject's eye is located at the rotation point, the measurement light reaches the fundus without being vignetted by the iris, and the measurement light scans the fundus based on the driving of the scanning unit 15. In this case, the condensing plane of the measurement light is formed on the fundus.

[0047] In this embodiment, the reference optical system 20 is provided with a mirror (not shown) that is movable along the optical axis. The optical path length of the reference light path is changed depending on the position of the mirror. However, this is not necessarily limited to this, and the optical path length in the light-guiding optical system 10a may also be variable. The zero delay position moves in the depth direction depending on the optical path length difference between the measurement light and the reference light. The zero delay position serves as the reference for the imaging range. The sensitivity in Fourier-domain OCT is higher the closer to the zero delay position and decreases the further away it is. The OCT optical system 10 can image a certain range in front of or behind the zero delay position.

[0048] <Real and Virtual Images in Tomographic Images> Here, with reference to Figures 2A and 2B, a tomographic image acquired via the OCT optical system 10 will be described. Figures 2A and 2B each show image data of a tomographic image (B-scan image) after Fourier transform. Z is the zero delay position on the image. The first region G1 is an image region corresponding to the imaging range on the rear side from the zero delay position Z, and the second region G2 is an image region corresponding to the imaging range on the front side from the zero delay position Z.

[0049] 2A and 2B, in Fourier-domain OCT, real and virtual image components resulting from the Fourier transform are formed as symmetric images with respect to the zero-delay position Z. A real image R and a virtual image M (mirror image) are formed.

[0050] 2A, the optical path length is adjusted so that the zero delay position Z is formed anterior (shallower) to the retinal surface, and in this case, a normal image is acquired as the real image R. The retinal surfaces face each other between the first region G1 and the second region G2. In this case, the real image R is formed in the first region G1, and the virtual image M is formed in the second region G2.

[0051] On the other hand, if the optical path length is adjusted so that the zero delay position Z is formed behind the retinal surface, an inverse image is acquired as a real image R, as shown in Figure 2B. In this case, the retinal surfaces of the first region G1 and the second region G2 face in opposite directions. In this case, a real image R is formed in the second region G2, and a virtual image M is formed in the first region G1.

[0052] Returning to FIG. 1, the description of the device configuration will be continued.

[0053] <Fundus Observation Optical System> The fundus observation optical system 30 is used to obtain a front image of the fundus as an observation image. The front image of the fundus is obtained as an observation image via the fundus observation optical system 30.

[0054] 1 illustrates an SLO optical system as an example of the fundus observation optical system 30. The fundus observation optical system 30 may include at least an illumination optical system and a light-receiving optical system. The illumination optical system illuminates the imaging site of the subject's eye with observation light. The light-receiving optical system receives fundus reflection light resulting from the observation light using a light-receiving element 39. Observation images are sequentially acquired based on output signals from the light-receiving element 30.

[0055] The fundus observation optical system 30 further includes a focus adjustment unit, which includes a focusing lens 34.

[0056] The observation light source 31 may be, for example, a laser diode light source. In addition to the focusing lens 34, a scanning unit 35 and an objective lens 60 are arranged in the observation light path. The scanning unit 35 scans the imaging region of the subject's eye two-dimensionally with light. The scanning unit 35 may include, for example, a combination of a polygon mirror and a galvanometer scanner.

[0057] A beam splitter 33 is disposed between the observation light source 31 and the focusing lens 34. A confocal aperture 37 and a light receiving element 39 are disposed in the transmission direction of the beam splitter 33.

[0058] The observation light is reflected by the beam splitter 33 and then passes through a focusing lens 34 to reach a scanning unit 35. The light passing through the scanning unit 35 passes through a beam splitter 17 and then passes through an objective lens 60 to be irradiated onto the fundus of the subject's eye.

[0059] The light reflected from the fundus is guided back along the light projection path to the beam splitter 33. The light reflected from the fundus passes through the beam splitter 33 and is received by the light receiving element 39 via the confocal aperture 37. A front image of the fundus is formed based on a light receiving signal from the light receiving element 39. The formed front image may be stored in the memory 72.

[0060] <Anterior Eye Segment Observation Optical System> The anterior eye segment observation optical system 40 is used to observe a front image (referred to as an observation image) of the anterior eye segment of the subject's eye E. The anterior eye segment observation optical system 40 has at least an image sensor 45. In this embodiment, an image of the anterior eye segment is formed on the image sensor 45. The observation image of the anterior eye segment acquired via the anterior eye segment observation optical system 40 is used for alignment and tracking of the photographing unit 2 with the subject's eye E when photographing the fundus.

[0061] <Fixation Projection Optical System> The OCT device 1 further includes a fixation target projection optical system. The fixation target projection optical system may be an internal fixation lamp. The fixation target projection optical system projects a fixation target (fixation light beam) onto the subject's eye E, thereby guiding the gaze direction of the subject's eye E. In this embodiment, the fixation target projection optical system can change the presentation position of the fixation target two-dimensionally, and can guide the subject's eye E in multiple directions. As a result, the imaging location is changed. In this embodiment, the fixation projection optical system is also used by the fundus observation optical system 30, which is an SLO optical system. A visible light source different from the observation light source is provided, and the timing of projecting the visible light is controlled, so that the fixation target is projected onto the subject's eye E.

[0062] <Driver> The driver 5 moves the photographing unit 3 in each of the X, Y, and Z directions relative to the subject's eye E. The driver 5 has an actuator for moving the photographing unit 2 in each direction, and is driven based on a control signal from the controller 70.

[0063] <Face Support Unit> The face support unit 7 supports the face of the subject so that the subject's eye E faces the photographing unit 2. The face support unit 7 may include, for example, a chin rest 7a. The subject's face is placed on the chin rest 7a. In this embodiment, the face support unit 7 has an actuator that moves the position of the chin rest 7a in the vertical direction. The chin rest 7a may also have a sensor that detects that the subject's face has been placed on it.

[0064] <Control System> Next, the control system of the OCT apparatus 1 will be described.

[0065] The control unit 70 of the OCT apparatus 1 controls various operations in the OCT apparatus 1. In this embodiment, the control unit 70 also serves as an image processor and an analysis processor. The control unit 70 may be configured with, for example, a CPU, a RAM, a ROM, etc.

[0066] In this embodiment, the control unit 70 is connected to a monitor 80 and controls the display of the monitor 80. Furthermore, the control unit 70 is connected to a memory 72, an operation unit 85, and the like.

[0067] In this embodiment, the operation unit 85 may include a pointing device such as a mouse. The monitor 80 may also be a touch panel display, in which case the monitor 80 may also serve as the operation unit 85. The monitor 80 and the operation unit 85 may be located at a remote location from the OCT apparatus 1 via a network or the like.

[0068] <Explanation of Operation> Next, the operation of the device in this embodiment will be described with reference to Figures 3 to 10. The flowchart in Figure 3 shows the flow of a series of photographing operations.

[0069] <Alignment> In the flowchart of Fig. 3, first, the device is aligned with the subject's eye (S1). The subject is first instructed to gaze at a fixation target, and the positional relationship between the subject's eye and the measurement optical axis is adjusted based on an anterior segment observation image captured by an anterior segment observation camera (not shown). For example, the adjustment is performed so that the pupil center of the subject's eye coincides with the measurement optical axis. The alignment may be adjusted manually or automatically. Once the alignment adjustment is complete, a front image of the fundus may be acquired as an observation image via an observation optical system (not shown), and the image may be displayed on the monitor 80.

[0070] <Scan Pattern Selection> Next, the control unit 70 selects one of multiple scan patterns prepared in advance (S2). Each scan pattern differs in the position on the fundus where an OCT image is acquired and the number of OCT images acquired. Examples of scan pattern types include line scan, cross scan, multi-scan, radial scan, and raster scan (also called map scan). Furthermore, multiple scan patterns with different positions on the tissue and scan lengths may be prepared for each type. Furthermore, for example, an example of a combo pattern including multiple imaging operations may be a pattern that combines multiple imaging operations of different image types. For example, the combo pattern may include a pattern in which an OCT image and a frontal fundus image are successively captured, or a pattern in which an intensity OCT image and a motion contrast image are successively captured.

[0071] In this embodiment, as shown in FIG. 4 , the following description will be given assuming that a map scan of a wide area of ​​the fundus is selected. Specifically, the map scan capture range includes an analysis region (first analysis region) based on the fovea Mc and an analysis region (second analysis region) based on the optic disc. In FIG. 4 , the map scan capture range is indicated by the symbol A1. For example, the map scan range A1 of the fundus is set based on the position of the fixation target. A region measuring 15 mm horizontally and 12 mm vertically is scanned with the midpoint between the fovea Mc and the optic disc aligned with the optical axis of the OCT optical system 10. However, the scan pattern is not limited to the map scan described above. Any scan pattern in which one or more scan lines are set on the fovea Mc and in which analysis processing based on the fovea Mc is performed on the OCT data captured using the scan pattern may be selected.

[0072] <Optimization Control> Next, optimization control is executed (S3). Optimization control enables acquisition of highly accurate (e.g., highly sensitive and high-resolution) OCT data at a desired fundus site. For example, optimization control is started in response to an optimization start operation on the operation unit 85.

[0073] The optimization control in this embodiment will be described below as an example with reference to the flowchart in FIG. 5 . The optimization control adjusts the OPL, focus, and polarization to predetermined states. The adjustments may be performed sequentially, or at least some of them may be performed in parallel. In the following description, the adjustment of the OPL will be described, and the adjustment of the focus and polarization will not be described.

[0074] First, a coarse adjustment is performed. In the coarse adjustment, the optical path length is adjusted so that an image of the subject's eye appears in the imaging range in the depth direction (regions G1 and G2). In this embodiment, as an example, the optical path length is changed stepwise by a predetermined value, and an evaluation value related to the signal intensity of the tomographic image obtained at each step is obtained, and the position at which the evaluation value is maximized is searched for (S21). By adjusting to the position at which the evaluation value is maximized, the image of the subject's eye appears in the imaging range in the depth direction. In this embodiment, a value B expressed by the following formula is used as the evaluation value in the coarse adjustment.

[0075] B = L1 - L2 / σ2 where L1 is the "average maximum luminance value of the image," L2 is the "average luminance value of the background region of the image," and σ2 is the "standard deviation of the luminance values ​​of the background region." However, the evaluation value is not necessarily limited to this.

[0076] <Real / Imaginary Determination> Next, the control unit 70 determines whether the fundus image generated in the region G1 behind the zero delay position Z is a real image R or a virtual image M (S22). If it is determined to be a virtual image M, the real image R exists in the region G1. In this embodiment, the real / imaginary determination is performed by utilizing the difference in image quality between the real image R and the virtual image M. For example, the control unit 70 may perform the determination by comparing the half-width of the peak of the brightness distribution of the tomographic image in the depth direction with a threshold value. If the half-width is smaller than the threshold value, the image may be determined to be a real image R, and if the half-width is equal to or greater than the threshold value, the image may be determined to be a virtual image M. However, the method for determining real / imaginary is not necessarily limited to the above method. For example, various information such as image contrast, edge rise, and image shape may be used instead of the above-described half-width to perform the determination.

[0077] In this embodiment, when the true / false determination is completed, it is determined which of the two imaging modes, retinal mode and choroidal mode, the OCT data captured in is suitable for detecting tissues present in the retina. Here, the tissues present in the retina mainly refer to the layers and layer boundaries of the retina and the fovea.

[0078] Incidentally, it seems that the RETINAL mode can capture images of tissues present in the retina at the fundus, such as the fovea Mc, with higher image quality and facilitate proper detection. However, when capturing images of a subject's eye with a highly curved fundus, such as a severely myopic eye, the center of the fundus may be located at a position far from the zero delay position.

[0079] For example, the OCT device 1 of this embodiment has a wide imaging range in the depth direction of 3 mm or more, so it can capture images of the fundus from its center to its periphery even when the fundus is significantly curvatured. In other words, it is easy to image the fundus from its center to its periphery while avoiding image folding (the appearance of a virtual image) in the periphery. However, in this case, the center of the fundus is likely to be located far from the zero delay position. Furthermore, the OCT device 1 of this embodiment is an SD-OCT, which is generally more prone to sensitivity attenuation in the depth direction than SS-OCT. Due to at least one of the factors listed here, it may not be possible to ensure sufficient image quality for detection even when a target is present in the retina at the fundus.

[0080] In contrast, it has been newly discovered that images taken in CHOROIDAL mode, which was previously thought to be disadvantageous for detecting retinal tissue in the center of the fundus, can sometimes capture retinal tissue in the center of the fundus with high image quality.

[0081] In this embodiment, as an example, in one of the regions G1 and G2 on which the real image R exists, the ratio of the depth direction area in which the real image R exists to the one region is derived (S23), and a judgment is made based on this ratio (S24).

[0082] As an example, the ratio is compared with a threshold value. In detail, in this embodiment, if the depth direction area in which the real image R exists in the region G1 or the region G2 is 2 / 3 or less, the imaging mode suitable for detecting the retinal tissue in the center of the fundus is determined to be the retinal mode (S24: Yes), and if it exceeds 2 / 3, the imaging mode is determined to be the choroidal mode (S24: No). However, the threshold value is not necessarily limited to this.

[0083] The determination method is not necessarily limited to the above-described method, as long as the determination is made using information correlated with the depth-wise position of retinal tissue at the central part of the fundus, such as the fovea Mc in region G1 or region G2. Position information of the fundus image may also be used as information correlated with the depth-wise position of retinal tissue at the central part of the fundus. The position information of the image may be, for example, position information of the edge of the image in the depth direction, position information of a specific part, or an average of position information from each A-scan.

[0084] In the fine adjustment, the optical path length is further adjusted so that an image is detected at a predetermined target position in the region G1 or region G2 (S25 to S27).

[0085] In the RETINAL mode, the optical path length is adjusted so that the retinal surface of the subject's eye is formed behind the zero delay position (S25 → S27). In this case, the area G1 behind the zero delay position is extracted and displayed.

[0086] If it is determined in the process of S22 that the image appearing in the region G1 is a real image R, the optical path length is changed by a value corresponding to the distance between the image position and the target position.

[0087] If the process of S22 determines that the image appearing in region G1 is virtual image M, the control unit 70 changes the optical path length in the direction in which real image R is acquired in that region. The optical path length is changed by the distance from zero delay position Z to the upper end of real image R, and further, the optical path amount is changed from zero delay position Z to the target position. As a result, real image R is positioned at the target position in region G1.

[0088] In the choroidal mode, the optical path length is adjusted so that the posterior choroidal surface of the subject's eye is formed anterior to the zero-delay position (S26 → S27). In this case, the region G2 anterior to the zero-delay position is extracted and displayed. For example, the amount of adjustment of the optical path length is calculated using a position a predetermined distance (e.g., 500 μm) away from the lower end of the RPE (IS / OS) detected by segmentation as the target zero-delay position, and the optical path length is changed according to the amount of adjustment.

[0089] If the process of S22 determines that the image that appears in the region G1 behind the zero delay position Z is a virtual image M, a real image R appears in the region G2. In this case, the optical path length is changed by a value corresponding to the distance between the target position set in the region G2 and the image position.

[0090] If the process of S22 determines that the image that appears in the region G1 behind the zero delay position Z is a real image R, a virtual image M is generated in the region G2. In this case, the control unit 70 changes the optical path length in the direction in which the real image R is acquired in the region G2. The optical path length is changed by the distance from the zero delay position Z to the bottom edge of the real image R, and then the optical path length is changed from there by the distance of the target position.

[0091] <Capture Process> After the adjustment is completed, photography is performed (S4). The photographing scan may be triggered by an operation input by the examiner. In this embodiment, as shown in FIG. 4 , an area (e.g., an area 15 mm wide x 12 mm long) including an analysis area (first analysis area) based on the fovea Mc and an analysis area (second analysis area) based on the optic disc is scanned by map scanning. As described above, in this embodiment, the map scanning range is set based on the presentation position of the fixation target. However, this is not necessarily limited to this. For example, the positions of characteristic features on the fundus (e.g., the positions of the fovea Mc and the optic disc) may be detected by image processing of a tomographic image or an observation image, and the map scanning range may be set based on the detected positions.

[0092] Note that the above-described determination of the appropriateness of the imaging mode and the setting of the imaging mode according to the determination of appropriateness are performed when some scan patterns are selected, but are not performed when the remaining scan patterns are selected. As described above, some scan patterns may be scan patterns in which one or more scan lines are set on the fovea Mc, and analysis processing based on the fovea Mc is performed on the OCT data captured using the scan pattern. For example, when a scan pattern in which analysis processing based on the papilla is performed is selected, the above processing may not be performed.

[0093] <Analysis Processing> After the imaging is completed, the analysis processing shown in the flowchart of Fig. 6 is executed at an appropriate time. The analysis processing may be executed, for example, when a report on the imaging results is generated, or at other times. In this embodiment, analysis processing related to tissue thickness is executed. The two-dimensional distribution of the measured values ​​of tissue thickness and / or the two-dimensional distribution of the comparison results between the tissue thickness of a normal eye and the measured values ​​is output as the analysis processing result. However, the content of the analysis processing is not limited to analysis processing related to layer thickness (details will be described later).

[0094] During the analysis process, a reference position of the analysis range is set (S11). As shown in Fig. 7, the position of the captured fovea Mc is used as the reference position Ac of the analysis range A2. The position of the fovea Mc may be detected by, for example, image processing of the OCT data.

[0095] For example, the control unit 70 performs image processing (e.g., segmentation processing) on ​​the OCT data to divide the OCT data into layers, detects the retinal thickness and a depression in the shape of the detected ILM (internal limiting membrane), and detects the point in the depression where the score for foveal resemblance is equal to or greater than a threshold as the fovea. The position of the detected point may be acquired as the position of the fovea Mc. The method for detecting the fovea Mc is not limited to this, and any detection process may be used.

[0096] In this embodiment, the position of the nipple is also detected as the reference position of the nipple and the analysis region around it (second analysis region).

[0097] 8A and 8B show tomographic images that can be captured in the retinal mode and the choroidal mode, respectively, using the OCT device 1 according to this embodiment. Fig. 8A is a tomographic image captured in the retinal mode, and it can be seen that the retina, particularly the periphery of the fovea, is depicted unclearly in the center of the fundus. In contrast, Fig. 8B is a tomographic image captured in the choroidal mode, and it can be seen that the retina is depicted more clearly in the center of the fundus than in Fig. 8A. When such an OCT image is acquired, as described above, capturing the image in the choroidal mode is considered to facilitate successful detection of retinal tissue (retinal layers, layer boundaries, fovea Mc, etc.) in the center of the fundus.

[0098] As described above, in this embodiment, when photographing, it is determined which of the two photographing modes, the retinal mode or the choroidal mode, the OCT data captured in is suitable for detecting retinal tissue in the center of the fundus, and the suitable photographing mode is selected for photographing. Therefore, the retinal tissue in the center of the fundus can be appropriately detected in the detection process.

[0099] Next, the control unit 70 executes an analysis process. In this embodiment, the analysis process involves analyzing the layer thickness (S12). In this case, the control unit 70 may perform image processing (e.g., segmentation processing) on ​​the OCT data to divide the OCT data into layers and measure the thickness of each layer based on the spacing between layer boundaries. As described above, an imaging mode that makes it easy to detect retinal tissue in the center of the fundus is selected for imaging, making it easy to perform accurate retinal segmentation processing.

[0100] The control unit 70 generates a layer thickness map (see FIG. 9 ) and a layer thickness chart (see FIG. 10 ) as the analysis results (S13). FIGS. 9 and 10 show the layer thickness map and layer thickness chart generated by analyzing the fovea Mc and its surrounding area (analysis area A2). The layer thickness map and layer thickness chart are two-dimensional distributions of thickness in the analysis area. The fovea Mc, which is the reference position, is used, for example, as the center of the layer thickness map and layer thickness chart. The thickness measurements at each position in the fundus area are compared with normal eye data to generate a comparison map and comparison chart with the normal eye as a two-dimensional distribution of the comparison results. The generated layer thickness map and layer thickness chart are displayed on the screen (S14). Similarly, the analysis area of ​​the optic optic disc and its surrounding area (second analysis area) are also analyzed as appropriate, and maps, etc. are generated.

[0101] These analysis results may be displayed together with the tomographic image. As described above, the image quality of the retina in the central part of the fundus has improved, and the success rate of the segmentation process has also improved, making it easier to detect the fovea Mc more accurately. As a result, it is easier to generate appropriate layer thickness maps and layer thickness charts regardless of the degree of curvature of the eye.

[0102] In particular, in this embodiment, when a map scan is performed once on an area including an analysis area A2 based on the fovea Mc and an analysis area (not shown) based on the papilla, an appropriate imaging mode is set based on the determination process. Therefore, even with OCT data that has undergone a wide-area map scan, the accuracy of tissue detection and analysis is unlikely to decrease.

[0103] "Modifications" The present disclosure has been described above based on the embodiments and examples, but the present disclosure is not necessarily limited to these.

[0104] In the above embodiment, in the case of the choroidal mode, the target zero delay position is set based on the lower end position of the RPE (IS / OS). However, this is not necessarily limited to this, and the target zero delay position may be set based on the lower end position of the boundary between the choroid and the sclera. The lower end position of the boundary between the choroid and the sclera may be detected by segmenting the OCT image obtained in the choroidal mode. The reference position may be set, for example, at a position approximately 250 μm away from the lower end position of the boundary between the choroid and the sclera.

[0105] In the above embodiment, the case where the shooting mode is automatically selected based on the result of the determination process has been described, but this is not necessarily limited to this. For example, the method of setting the shooting mode according to the determination result may be the following method. For example, the determination result may be displayed, and a selection operation of the shooting mode according to the determination result may be accepted via the operation unit 75, and the shooting mode according to the selection operation may be set.

[0106] Alternatively, for example, either the RETINAL mode or the CHOROIDAL mode may be selectable in advance based on a user setting and an operation input during shooting. In this case, the user setting and the operation input during shooting may be given priority, and the determination process in the above embodiment may not be performed, or the shooting mode selected by the operation input during shooting may be set regardless of the determination process.

[0107] For example, in the determination process in the above embodiment, the imaging mode suitable for detecting foveal tissue was determined based on a tomographic image. However, this is not necessarily limited to this, and the determination process may also determine the imaging mode suitable for detecting foveal tissue based on axial length information of the subject's eye. The axial length of the subject's eye may be a value measured in advance using an axial length measurement device separate from the OCT device. It may also be a value measured by the OCT device. Measurement can be performed using any of various known methods for measuring the axial length using an OCT device. For example, the axial length of the subject's eye is calculated and acquired by the control unit 70 based on the working distance and depth position information of the retinal surface acquired via the OCT optical system. At this time, the axial length can be obtained as the distance between the irradiation position of the measurement light on the cornea and the irradiation position on the retina. The working distance is the distance between the device and the subject's eye in the anterior-posterior direction. The working distance may be a fixed value predetermined for each device or an actual measurement value. For example, the actual measurement value may be obtained based on at least one of the detection result of the alignment target image detected in the observation image of the anterior segment and the drive amount of the drive unit 5 .

[0108] Furthermore, for example, in region G1 or region G2, regardless of whether the depth region where real image R exists is above or below the threshold, if the evaluation value of a portion of the region away from the zero delay position is sufficiently high, imaging may be performed in RETINAL mode.

[0109] Also, for example, in the case of follow-up imaging, the imaging mode may be selected to be the same as that of the previous imaging (e.g., baseline) without determining the imaging mode, or even if a determination is made, regardless of the determination result, and imaging may be performed.

[0110] In this case, the imaging conditions, including the imaging mode used in the previous imaging, may be stored in advance in the memory 72. In the case of a follow-up imaging, the same imaging mode as used in the previous imaging (e.g., baseline imaging) may be selected by referring to the imaging conditions. Furthermore, imaging conditions related to at least one of the scan pattern, OPL, focus state, and polarization state may be stored as imaging conditions, and these imaging conditions may also be reproduced. This facilitates appropriate comparison of imaging results and analysis results obtained on different days for the same subject's eye.

[0111] For example, in the above embodiment, the analysis process is described as being related to tissue thickness, but this is not necessarily limited to this, and analysis may be performed on measurement values ​​(actual measurements) based on 3D OCT data other than tissue thickness, or may show the results of comparing the measurement values ​​with normal eye data. The measurement values ​​based on 3D OCT data may relate to at least one of tissue thickness, density, shape, etc.

[0112] Furthermore, when an analysis map is output as a result of the analysis process, the analysis map may be a tissue thickness map of the subject's eye E (specific examples include a fundus layer thickness map, a corneal thickness map, etc.), a density map (specific examples include a blood vessel density map, a cell density map, etc.), a curvature map (topography), a height map (elevation map), or a two-dimensional distribution of layer thickness information or blood vessel information other than those listed here. The normal eye data may be statistical data of a normal eye compared to measurement values ​​(actual measurements) based on three-dimensional OCT data. The comparison result may be information indicating the degree of deviation between the measurement values ​​and the normal eye data, and may be expressed, for example, by a difference, a percentage (e.g., percentile), a standard deviation, etc. The analysis map may also indicate a two-dimensional distribution of changes over time in the measurement values ​​or the above comparison results. In the above embodiment, the three-dimensional OCT data that forms the basis of the analysis map indicates the reflection intensity in a three-dimensional area of ​​the subject's eye E (a two-dimensional area in the XY directions plus the depth direction), but this is not necessarily limited to this and may also be three-dimensional motion contrast data.

Claims

1. An OCT system comprising: an OCT optical system having a light splitter that splits light from an OCT light source into a measurement light path and a reference light path; and a spectrometer that detects a spectral interference signal between the measurement light guided to the fundus of the test eye via the measurement light path and the reference light from the reference light path; an image processor that processes the spectral interference signal to acquire OCT data of the fundus; an imaging control unit that controls the capture of the OCT data; and an analysis processing unit that analyzes the captured OCT data, wherein the imaging control unit performs a determination process when capturing the OCT data to determine whether the imaging mode suitable for detecting a predetermined tissue present in the retina is a first mode in which the retinal surface of the test eye is formed behind the zero delay position, or a second mode in which the posterior choroidal surface of the test eye is formed anterior to the zero delay position; and either the first mode or the second mode is selected based on the result of the determination process, and then the OCT data is captured after adjusting the optical path length of either the measurement light path or the reference light path according to the selected imaging mode; The analysis processing unit detects the predetermined tissue from the OCT data captured in the selected imaging mode, and further performs analysis processing on the OCT data based on the position of the predetermined tissue.

2. An OCT system according to claim 1, wherein the determination means makes the determination based on a tomographic image acquired with the optical path length adjusted so that the retinal surface is located behind the zero delay position or the choroidal posterior surface is located in front of the zero delay position.

3. An OCT system as described in claim 1 or 2, further comprising a scanning pattern selection means for selecting one of two or more mutually different scanning patterns, wherein the imaging control means sets the imaging mode based on the determination process when a scanning pattern in which a scan line is set for a specified tissue is selected from the two or more scanning patterns.

4. An OCT system as described in claim 3, which sets the shooting mode based on the judgment process when a wide-area scanning pattern is selected whose shooting range is a first analysis area in the center of the fundus and a second analysis area that is at least partially different from the first analysis area.

5. An OCT system according to any one of claims 1 to 3, wherein in the case of follow-up imaging, an imaging mode used in previous imaging of the subject's eye is selected.

Images