JP6763457B2 - Optical coherence tomography equipment and optical coherence tomography control program - Google Patents

Description

The present disclosure relates to an optical coherence tomography apparatus for obtaining motion contrast data of a subject, and an optical coherence tomography control program.

Conventionally, as a device for performing angiography, for example, a fundus camera, a scanning laser optometry device, and the like are known. In this case, a contrast medium that emits light by a specific excitation light is injected into the body. The device obtained angiographic images by receiving light from the contrast agent. That is, conventionally, injection of a contrast medium has been required.

In recent years, an apparatus for obtaining motion contrast (angiographic image) without using a contrast agent by applying OCT technology has been proposed (see, for example, Patent Document 1).

International Publication No. 2010/143601

When acquiring motion contrast data using OCT, multiple OCT signals that differ in time with respect to the same part of the subject are acquired, and the acquired multiple OCT signals are processed to acquire motion contrast data in the subject. are doing. However, while acquiring a plurality of OCT signals that differ in time with respect to the same part of the subject, the plurality of acquired OCT signals may be acquired at different positions due to the movement of the subject. is there. In this case, good motion contrast data cannot be obtained.

In view of the above problems, the present disclosure has a technical problem of providing an optical coherence tomography apparatus capable of easily and accurately acquiring a plurality of OCT signals for the same site, and an optical coherence tomography control program. To do.

In order to solve the above problems, the present disclosure is characterized by having the following configurations.

(1)
An optical coherence tomography apparatus that detects an OCT signal from the measurement light and reference light applied to the eye to be inspected and processes the OCT signal to acquire a tomographic image of the eye to be inspected.
A frontal observation optical system that obtains a frontal image of the eye to be inspected,
An OCT optical system that acquires a plurality of OCT signals that differ in time with respect to the same scanning region on the eye to be inspected.
When a plurality of OCT signals are acquired by the OCT optical system in the first scanning region on the eye to be inspected, a first front image is acquired by the front observation optical system, and the plurality of OCT signals are acquired in the first scanning region. After that, the control means for acquiring the second front image by the front observation optical system after the acquisition of the first front image, and
The misalignment between the first front image and the second front image is detected by image processing, and based on the detection result of the misalignment, the quality of the plurality of OCT signals acquired in the first scanning region is good or bad. Judgment means to judge
An arithmetic processing means for processing the plurality of OCT signals determined to be good by the determination means and acquiring motion contrast data in the eye to be inspected.
With
The control means acquires a plurality of OCT signals that are temporally different with respect to at least two or more scanning regions on the eye to be inspected by the OCT optical system.
After the acquisition of the plurality of OCT signals is completed in the entire scanning region, the plurality of OCT signals are reacquired in the scanning region in which the determination means determines that the plurality of OCT signals are not good. ..
(2)
It is executed in the control device that controls the operation of the optical coherence tomography device that detects the OCT signal by the measurement light and the reference light applied to the test eye and processes the OCT signal to acquire the tomographic image of the test eye. Optical coherence tomography control program
By being executed by the processor of the control device,
The front image acquisition step to obtain the front image of the eye to be inspected,
An acquisition step of acquiring a plurality of OCT signals that differ in time with respect to the same scanning area on the eye to be inspected, and
When a plurality of OCT signals are acquired by the acquisition step in the first scanning region on the eye to be inspected, the first front image is acquired by the front image acquisition step, and after the acquisition of the plurality of OCT signals in the first scanning region. The control step of acquiring the second front image by the front image acquisition step after the acquisition of the first front image, and the control step.
The misalignment between the first front image and the second front image is detected by image processing, and based on the detection result of the misalignment, the quality of the plurality of OCT signals acquired in the first scanning region is good or bad. Judgment step to judge
An arithmetic processing step of processing the plurality of OCT signals determined to be good by the determination step and acquiring motion contrast data in the eye to be inspected.
To the optical coherence tomography apparatus
The control step, respectively acquires at least two scanning areas with respect to plurality of temporally different OCT signal on the eye to be examined,
After the acquisition of the plurality of OCT signals is completed in the entire scanning region, the plurality of OCT signals are reacquired in the scanning region where the determination step determines that the plurality of OCT signals are not good. ..

It is a block diagram explaining the structure of the optical coherence tomography apparatus which concerns on this embodiment. It is a figure which shows the outline of the OCT optical system which concerns on this embodiment. It is an image figure of the fundus for explaining the imaging of this embodiment. It is a figure explaining the relationship between the acquisition operation of an OCT signal and the acquisition operation of a front image. The flowchart of the judgment process is shown. It is a figure explaining the transformation example of the relationship between the acquisition operation of an OCT signal and the acquisition operation of a front image.

Hereinafter, one of the typical embodiments will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an optical coherence tomography apparatus according to the present embodiment. FIG. 2 is a schematic view illustrating an OCT optical system.

The optical coherence tomography apparatus (hereinafter referred to as an OCT device) 1 processes the detection signal acquired by the OCT optical system (interference optical system) 100. In the present embodiment, the OCT device 1 observes an image captured by the OCT optical system 100 on a display means (for example, a monitor) 75. For example, the OCT device 1 is composed of an OCT optical system, a CPU (control unit) 70, a mouse (operation unit) 76, a memory (storage unit) 72, and a monitor 75, and each unit is via a bus or the like. Is electrically connected to the CPU 70. In the following description, a case where the fundus of the eye to be inspected is photographed by the OCT device 1 as a subject will be described as an example. Of course, the OCT device 1 can image various living bodies. For example, ears, nose, various organs and the like can be mentioned. Further, for example, the OCT device 1 may capture the anterior segment of the eye to be inspected.

The control unit 70 controls the operation of each unit based on the arithmetic program and various control programs stored in the memory 72 (details will be described later). As the control unit 70, the operation unit 76, the memory 72, and the monitor 75, various programs are installed on the commercially available PC using the arithmetic processing unit, the input unit, the storage unit, and the display unit of the commercially available PC (personal computer). You may do so.

In the present embodiment, the OCT device 1 has been described by taking as an example a device in which the OCT optical system 100 and each part are integrated, but the present invention is not limited to this. For example, the OCT device 1 may be configured not to include the OCT optical system 100. In this case, the OCT device is connected to a separately provided OCT optical system or the like, receives an OCT signal or OCT image data, and performs various arithmetic processes based on the received information.

For example, in this embodiment, the OCT optical system 100 includes a front observation optical system 200. Of course, the OCT optical system and the front observation optical system 200 do not have to be integrated. The OCT optical system 100 irradiates the fundus Ef with the measurement light. The OCT optical system 100 detects the interference state between the measurement light reflected from the fundus Ef and the reference light by the light receiving element (detector 120). The OCT optical system 100 includes an irradiation position changing unit (for example, an optical scanner 108 and a fixation target projection unit 300) that changes the irradiation position of the measurement light on the fundus Ef in order to change the imaging position on the fundus Ef. The control unit 70 controls the operation of the irradiation position changing unit based on the set imaging position information, and acquires a tomographic image based on the received signal from the detector 120.

<OCT optical system>
The OCT optical system 100 will be described. The OCT optical system 100 has a device configuration of a so-called optical coherence tomography (OCT) for ophthalmology, and captures a tomographic image of the eye E to be inspected. The OCT optical system 100 divides the light emitted from the measurement light source 102 into the measurement light (sample light) and the reference light by the coupler (optical divider) 104. Then, the OCT optical system 100 guides the measurement light to the fundus Ef of the eye E by the measurement optical system 106, and guides the reference light to the reference optical system 110. After that, the detector 120 receives the interference light obtained by combining the measurement light reflected by the fundus Ef and the reference light.

The detector 120 detects an interference signal between the measurement light and the reference light. In the case of Fourier domain OCT, the spectral intensity (spectral interference signal) of the interference light is detected by the detector 120, and the complex OCT signal is acquired by the Fourier transform on the spectral intensity data.

For example, in the Fourier domain OCT, the depth profile (A scan signal) in a predetermined range is acquired by calculating the absolute value of the amplitude in the complex OCT signal acquired by the Fourier transform on the spectral intensity data. OCT image data (tomographic image data) is acquired by arranging the depth profiles of the measurement light scanned by the optical scanner 108 at each scanning position. Further, three-dimensional OCT image data (three-dimensional tomographic image data) may be acquired by scanning the measurement light two-dimensionally. Further, from the three-dimensional OCT image data, an OCT front image (for example, an integrated image integrated in the depth direction, an integrated value of spectrum data at each XY position, and at each XY position in a certain depth direction). Brightness data, retinal surface image, etc.) may be acquired.

In addition, motion contrast data is acquired from at least two or more OCT signals at the same position (same part) at different times. That is, motion contrast data is acquired by analyzing at least two or more complex OCT signals. For example, the functional OCT signal is acquired from the complex OCT signal. The functional OCT image data is acquired by arranging the functional OCT signals at each scanning position of the measurement light scanned by the optical scanner 108. Further, the three-dimensional function OCT image data (three-dimensional motion contrast data) is acquired by scanning the measurement light two-dimensionally in the XY directions. Further, from the three-dimensional function OCT image data, an OCT function front image (for example, a Doppler front image, a signal image data speckle variance front image) is acquired. In addition, each image data may be image data or signal data. The details of the motion contrast data will be described later.

For example, examples of the Fourier domain OCT include Spectral-domain OCT (SD-OCT) and Swept-source OCT (SS-OCT). Further, for example, it may be Time-domain OCT (TD-OCT). In the case of SD-OCT, a low coherent light source (broadband light source) is used as the light source 102, and the detector 120 is provided with a spectroscopic optical system (spectrometer) that disperses the interference light into each frequency component (each wavelength component). .. The spectrometer consists of, for example, a diffraction grating and a line sensor. In the case of SS-OCT, a wavelength scanning light source (wavelength variable light source) that changes the emission wavelength at high speed in time is used as the light source 102, and for example, a single light receiving element is provided as the detector 120. The light source 102 is composed of, for example, a light source, a fiber ring resonator, and a wavelength selection filter. Then, as the wavelength selection filter, for example, a combination of a diffraction grating and a polygon mirror, and a filter using Fabry-Perot Etalon can be mentioned.

The light emitted from the light source 102 is divided into a measured luminous flux and a reference luminous flux by the coupler 104. Then, the measured luminous flux is emitted into the air after passing through the optical fiber. The luminous flux is focused on the fundus Ef via the optical scanner 108 and other optical members of the measurement optical system 106. Then, the light reflected by the fundus Ef is returned to the optical fiber through the same optical path.

The optical scanner 108 scans the measurement light two-dimensionally (in the XY direction) on the fundus. The optical scanner 108 is arranged at a position substantially conjugate with the pupil. The optical scanner 108 is, for example, two galvanometer mirrors whose reflection angles are arbitrarily adjusted by the drive mechanism 50.

As a result, the light flux emitted from the light source 102 changes its reflection (traveling) direction and is scanned at an arbitrary position on the fundus. As a result, the imaging position on the fundus Ef is changed. The optical scanner 108 may have a configuration that deflects light. For example, in addition to a reflection mirror (galvano mirror, polygon mirror, resonant scanner), an acoustic optical element (AOM) that changes the traveling (deflection) direction of light is used.

The reference optical system 110 generates a reference light that is combined with the reflected light acquired by the reflection of the measurement light at the fundus Ef. The reference optical system 110 may be of the Michaelson type or the Machzenda type. The reference optical system 110 is formed by, for example, a reflective optical system (for example, a reference mirror), and the light from the coupler 104 is reflected by the reflective optical system to be returned to the coupler 104 again and guided to the detector 120. As another example, the reference optical system 110 is formed by a transmission optical system (for example, an optical fiber) and guides the light from the coupler 104 to the detector 120 by transmitting it without returning it.

The reference optical system 110 has a configuration in which the optical path length difference between the measurement light and the reference light is changed by moving the optical member in the reference optical path. For example, the reference mirror is moved in the optical axis direction. The configuration for changing the optical path length difference may be arranged in the measurement optical path of the measurement optical system 106.

<Front observation optical system>
The front observation optical system 200 acquires front image data of the eye to be inspected. The front image data may be image data or signal data. For example, the front observation optical system 200 is provided to obtain a front image of the fundus Ef. The front observation optical system 200 includes, for example, an optical scanner that scans measurement light (for example, infrared light) emitted from a light source two-dimensionally on the fundus of the eye, and a symfocal aperture arranged at a position substantially conjugate with the fundus of the eye. It includes a second light receiving element that receives the reflected light from the fundus of the eye through the device, and has a so-called scanning laser ophthalmoscope (SLO) for ophthalmology.

The front observation optical system 200 may have a so-called fundus camera type configuration. Further, for example, it may be an infrared photographing optical system for photographing a subject using infrared light. Further, for example, the OCT optical system 100 may also serve as the front observation optical system 200. That is, the front image data (hereinafter, referred to as a front image) may be acquired by using the data forming the two-dimensionally obtained tomographic image (OCT front image).

The front observation optical system 200 does not have to be integrated with an OCT device or the like. In this case, for example, the front image data acquired by the separately provided front observation optical system 200 is received by an OCT device or the like.

<Focus target projection unit>
The fixation target projection unit 300 has an optical system for guiding the line-of-sight direction of the eye E. The fixation target projection unit 300 has an fixation target presented to the eye E, and can guide the eye E in a plurality of directions.

For example, the fixation target projection unit 300 has a visible light source that emits visible light, and changes the presentation position of the target in two dimensions. As a result, the line-of-sight direction is changed, and as a result, the imaging region is changed. For example, when the fixation target is presented from the same direction as the imaging optical axis, the central portion of the fundus is set as the imaging region. Further, when the fixation target is presented above the imaging optical axis, the upper part of the fundus is set as the imaging region. That is, the imaging portion is changed according to the position of the optotype with respect to the imaging optical axis.

The fixation target projection unit 300 has, for example, a configuration in which the fixation position is adjusted according to the lighting positions of LEDs arranged in a matrix, the light from the light source is scanned by an optical scanner, and the fixation position is determined by lighting control of the light source. Various configurations such as an adjustment configuration can be considered. Further, the fixation target projection unit 300 may be an internal fixation lamp type or an external fixation light type.

<Control unit>
The control unit 70 includes a CPU (processor), RAM, ROM, and the like. The CPU of the control unit 70 controls the entire device such as each member of each configuration 100 to 300. The RAM temporarily stores various types of information. The ROM of the control unit 70 stores various programs, initial values, and the like for controlling the operation of the entire device. The control unit 70 may be composed of a plurality of control units (that is, a plurality of processors).

A non-volatile memory (storage means) 72, an operation unit (control unit) 76, a display unit (monitor) 75, and the like are electrically connected to the control unit 70. The non-volatile memory (memory) 72 is a non-transient storage medium capable of retaining the stored contents even when the power supply is cut off. For example, a hard disk drive, a flash ROM, an OCT device 1, a USB memory detachably attached to the OCT optical system 100, and the like can be used as the non-volatile memory 72. The memory 72 stores a photographing control program for controlling the photographing of the front image and the tomographic image by the OCT optical system 100. Further, the memory 72 stores a fundus analysis program that enables the use of the OCT device 1. Further, in the memory 72, information on the tomographic image data (OCT image data), the three-dimensional tomographic image data (three-dimensional OCT image data), the front image data (frontal image data of the fundus), and the tomographic image data in the scanning line Etc., various information related to shooting is stored. Various operation instructions by the inspector are input to the operation unit 76.

The operation unit 76 outputs a signal corresponding to the input operation instruction to the control unit 70. For the operation unit 74, for example, at least one of a mouse, a joystick, a keyboard, a touch panel, and the like may be used.

The monitor 75 may be a display mounted on the main body of the apparatus, or may be a display connected to the main body. A display of a personal computer (hereinafter referred to as "PC") may be used. A plurality of displays may be used together. Further, the monitor 75 may be a touch panel. When the monitor 75 is a touch panel, the monitor 75 functions as an operation unit. Various images including tomographic image data and frontal image data taken by the OCT optical system 100 are displayed on the monitor 75.

<Signal processing method>
In the present embodiment, which describes the arithmetic processing method for acquiring the motion contrast data from the OCT signal in the present embodiment, in order to acquire the motion contrast data, the control unit 70 is at the same position and at least two frames at different times. Interference signal (OCT signal) is acquired.

In the present embodiment, the control unit 70 acquires motion contrast data (for example, functional OCT image data) from a plurality of OCT signals by performing processing related to the Doppler phase difference method and processing related to the vector difference method. As a method of processing the complex OCT signal, for example, a method of calculating the phase difference of the complex OCT signal, a method of calculating the vector difference of the complex OCT signal, a method of multiplying the phase difference and the vector difference of the complex OCT signal, and the like can be considered. Be done. In this embodiment, a method of multiplying the phase difference and the vector difference will be described as an example.

First, the control unit 70 Fourier transforms the OCT signal acquired by the OCT optical system 100. The control unit 70 obtains a complex OCT signal by Fourier transform. The complex OCT signal includes a real number component and an imaginary number component.

To obtain a blood flow signal, it is necessary to compare images at the same position at different times. Therefore, it is preferable that the control unit 70 aligns the image based on the image information. Image registration is the process of aligning and arranging multiple images of the same scene. As a cause of the displacement of the image, for example, the movement of the eye to be inspected during imaging (for example, fixation tremor, adjustment tremor, pulsation, etc.) can be considered. Even if the frames are aligned with each other, a phase shift may occur between the A scan lines in the same image. Therefore, it is preferable to perform phase correction. The registration and phase correction processes are for facilitating the processes of the present embodiment and are not essential.

Next, the control unit 70 calculates the phase difference for the complex OCT signals acquired at at least two or more different times at the same position. The control unit 70 removes a random phase difference existing in a region where the S / N ratio (signal noise ratio) is low.

The control unit 70 removes a portion having a small phase difference. This is to remove the reflected signal from the highly reflective part such as NFL (nerve fiber layer). This makes it easy to distinguish whether the signal is from a high-reflection portion or a blood vessel. In the present embodiment, one frame for which the phase difference is calculated is acquired. When there are a plurality of frames for which the phase difference has been calculated, it is better that the control unit 70 adds and averages the signals of the frames subjected to the above processing to remove noise.

Next, the control unit 70 calculates the vector difference of the complex OCT signal. For example, the vector difference of the complex OCT signal detected by the OCT optical system is calculated. For example, a complex OCT signal can be represented as a vector on the complex plane. Therefore, by detecting two signals at the same position at different times and calculating the vector difference, contrast image data in the eye to be inspected is generated. When the vector difference is imaged, for example, the image may be performed based on the phase information in addition to the magnitude of the difference. In this embodiment, one frame for which the vector difference is calculated is acquired. When there are a plurality of frames for which the vector difference is calculated, it is better that the control unit 70 adds and averages the signals of the frames subjected to the above processing to remove noise.

The control unit 70 uses the calculation result of the phase difference as a filter for the calculation result of the vector difference. In the description of the present embodiment, "filtering" means, for example, weighting a certain numerical value. For example, the control unit 70 weights the calculation result of the vector difference by multiplying the calculation result of the phase difference. That is, the vector difference of the portion having a small phase difference is weakened, and the vector difference of the portion having a large phase difference is strengthened. As a result, the calculation result of the vector difference is weighted by the calculation result of the phase difference.

In the processing of the present embodiment, the control unit 70 multiplies, for example, the calculation result of the vector difference and the calculation result of the phase difference. As a result, the control unit 70 generates the functional OCT image data weighted by the calculation result of the phase difference.

By multiplying the calculation result of the vector difference and the calculation result of the phase difference, the demerits of each measurement method can be canceled out, and the image data of the blood vessel portion can be acquired well.

The control unit 70 performs the above arithmetic processing for each scanning line, and acquires functional OCT image data for each scanning line. Then, by acquiring the functional OCT image data at these a plurality of positions, it is possible to acquire the three-dimensional functional OCT frontal image data used as a pseudo angiographic image.

In the present embodiment, the control unit 70 has described a configuration in which the calculation result of the vector difference and the calculation result of the phase difference are multiplied in order to acquire the motion contrast data, but the present invention is limited to this. Not done. For example, the motion contrast data may be acquired using the calculation result of the vector difference. Further, for example, the motion contrast data may be acquired by using the calculation result of the phase difference. Further, for example, the motion contrast data may be acquired by the difference result of amplitude, Amplitude-decorrelation, Speckle variance, Phase variance, or the like.

In the present embodiment, the control unit 70 has described a configuration in which motion contrast data is acquired using two OCT signals as an example, but the present invention is not limited to this. The motion contrast data may be configured to be acquired by two or more OCT signals.

<Shooting operation>
Hereinafter, a series of shooting operations using the OCT device 1 will be described. The following description will be given by taking the case of acquiring the three-dimensional function OCT image data as an example. Of course, the technique disclosed in the present invention can be applied when acquiring motion contrast data. For example, it can be applied when acquiring a functional OCT signal or when acquiring functional OCT image data.

First, the examiner instructs the subject to gaze at the fixation target of the fixation target projection unit 300, and then monitors the front eye observation image taken by the front eye observation camera (not shown) 75. The alignment operation is performed by using the operation unit 76 (for example, a joystick (not shown)) so that the measurement optical axis comes to the center of the pupil of the eye to be inspected.

For example, when the alignment operation is completed, the control unit 70 controls the OCT optical system 100, acquires the three-dimensional OCT image data corresponding to the set region, controls the front observation optical system 200, and controls the fundus image data. (Ocular fundus front image data) is acquired. Then, the control unit 70 acquires three-dimensional OCT image data by the OCT optical system 100 and fundus image data by the front observation optical system 200 at any time. The three-dimensional OCT image data includes image data in which A scan signals are arranged two-dimensionally in the XY directions, a three-dimensional graphic image, and the like.

The examiner sets the scanning position using the front view of the fundus of the front observation optical system 200. Then, when a signal for starting imaging is output from the operation unit 76, the control unit 70 controls the operation of the optical scanner 108 and causes the measurement light to be two-dimensionally scanned in the XY directions in the scanning range corresponding to the imaging region. As a result, acquisition of the three-dimensional function OCT image data is started. As the scanning pattern, for example, a raster scan, a plurality of line scans, a circle shape, a shape having a refraction, a shape having a bend, and the like can be considered.

Hereinafter, the photographing operation using the OCT device 1 will be described. FIG. 3 is a schematic diagram for explaining the photographing of the present embodiment. In the present embodiment, for example, when a signal for starting imaging is output, the control unit 70 acquires a plurality of OCT signals by the OCT optical system 100 in the first scanning region on the fundus of the eye to be inspected. Further, the control unit 70 acquires the first front image by the front observation optical system 200 when the OCT optical system 100 acquires a plurality of OCT signals in the first scanning region. Then, the control unit 70 acquires the second front image by the front observation optical system 200 after the acquisition of the plurality of OCT signals in the first scanning region by the OCT optical system 100. Next, the control unit 70 detects the positional deviation between the first front image and the second front image by image processing, and based on the detection result of the positional deviation, a plurality of OCT signals acquired in the first scanning region. Judge the quality of. The control unit 70 processes a plurality of OCT signals determined to be good and acquires motion contrast data in the fundus of the eye to be inspected.

<OCT signal acquisition>
It will be described in more detail. For example, when a signal for starting imaging is output, the control unit 70 controls the drive of the optical scanner 108 in order to acquire the three-dimensional function OCT image data, and scans the measurement light on the fundus. For example, the control unit 70 controls the OCT optical system 100 in order to acquire the OCT signal at a set frame rate in response to the output of the imaging start signal. The frame rate for obtaining the OCT signal may or may not be changed before and after the start of acquisition of the OCT signal.

The control unit 70 acquires a plurality of OCT signals in the same scanning area. The same scanning area does not have to be exactly the same scanning area, and may be scanned in substantially the same scanning area. Therefore, the control unit 70 repeats scanning in the same scanning area on the fundus. Through such a plurality of scans, the control unit 70 can acquire a plurality of OCT signals in the same scan region.

For example, the control unit 70 scans the measurement light a plurality of times using the optical scanner 108 with respect to the set first scanning region. In this embodiment, a case where one scanning position (first scanning position) is set as the first scanning region will be described as an example. Of course, a plurality of scanning positions (for example, two scanning positions of a first scanning position and a second scanning position) may be set as the scanning area (details will be described later).

As shown in FIG. 3, for example, the control unit 70 scans the measurement light in the X direction along the first scanning position (scanning line) S1. Scanning the measurement light in any of the XY directions (for example, the X direction) in this way is called "B scan". Hereinafter, the interference signal of one frame will be described as an OCT signal obtained by one B scan. The control unit 70 acquires the OCT signal detected by the detector 120 during scanning. In FIG. 3, the direction of the Z axis is the direction of the optical axis of the measurement light. The direction of the X-axis is perpendicular to the Z-axis and to the left and right. The direction of the Y-axis is perpendicular to the Z-axis and up and down.

When the first scan is completed, the control unit 70 performs the second scan at the same position as the first scan. For example, the control unit 70 scans the measurement light along the first scanning line S1 shown in FIG. 3, and then scans the measurement light again. The control unit 70 acquires the OCT signal detected by the detector 120 during the second scan. As a result, the control unit 70 can acquire two frames of OCT signals having different times at the same scanning position. For example, the control unit 70 repeatedly acquires the OCT signal at the same scanning position, and acquires the OCT signal of 4 frames. In this embodiment, a configuration in which four frames of OCT signals are acquired at the same scanning position will be described as an example, but the present invention is not limited thereto. The configuration may be such that at least two frames of OCT signals are acquired at the same position. For example, scanning at the same position may be repeated eight times to acquire consecutive eight frames of OCT signals at different times, or scanning at the same position may be repeated twice to obtain two frames of OCT signals at different times. May be obtained.

If the OCT signals at the same positions at different times can be acquired in one scan, the second scan may not be performed. For example, when two measurement lights whose optical axes are deviated by a predetermined interval are scanned at one time, it is not necessary to scan them a plurality of times, and it is sufficient that OCT signals having different times at the same position in the subject can be obtained. That is, the same position does not have to be exactly the same position, and may be scanned at substantially the same position. When two measurement lights are scanned at one time, an arbitrary blood flow velocity can be detected as a target by the interval between the two measurement lights.

<Get front image>
On the other hand, the control unit 70 controls the front observation optical system 200 in order to be able to repeat the front image at a set frame rate in response to the output of the imaging start signal. The frame rate for obtaining the front image may or may not be changed before and after the start of capture. In the embodiment, the frame rate for obtaining the OCT signal is four times the frame rate for obtaining the front image. That is, it is possible to acquire the OCT signal of 4 frames in the time for acquiring the front image of 1 frame. In the present embodiment, the frame rate for acquiring the OCT signal and the frame rate for acquiring the front image are set so that at least two OCT signals are acquired while the front image of one frame is acquired. Just do it.

Further, for example, in the present embodiment, the relationship between the frame rate when obtaining the OCT signal and the frame rate when obtaining the front image is until the acquisition of a plurality of OCT signals in at least one scanning region is completed. It may be set so that the time required for the process is less than or equal to the time required to complete the acquisition of one front image. For example, a frame rate for obtaining an OCT signal and a frame for obtaining a front image so that a preset number of frames of OCT signals are acquired in order to acquire motion contrast data in at least one scanning region. It suffices if the rate is set.

The control unit 70 repeats the front image acquisition operation while a plurality of OCT signals are acquired. By such control, the control unit 70 monitors the movement (movement) of the eye while the OCT signal is being acquired. For example, the control unit 70 receives the reflected light from the front of the fundus by the operation of the front observation optical system 200. The control unit 70 acquires a front image by processing the received reflected light. The control unit 70 stores the acquired plurality of front images in the memory 72 at any time. As described above, the control unit 70 simultaneously acquires the front image and the OCT signal.

<Parallel acquisition of OCT signal acquisition and front image acquisition>
FIG. 4 is a diagram for explaining the relationship between the OCT signal acquisition operation and the front image acquisition operation. In FIG. 4, the horizontal axis is the time axis (T). For example, the control unit 70 starts acquiring the first front image F1 in response to the output of the signal for starting imaging. When the acquisition of the first front image F1 is completed, the control unit 70 stores the first front image F1 in the memory 72. In the present embodiment, it is assumed that the acquisition of the first front image (front image of one frame) F1 is completed when the time T1 elapses from the output timing (at the time of acquisition start) T0 of the shooting start signal. To do. That is, it shows that the time T1 has elapsed until the first front image F1 is acquired.

Next, the control unit 70 starts acquiring the second front image F2. Further, in parallel with the acquisition of the second front image F2, a plurality of OCT signals on the first scanning line S1 are acquired. In the present embodiment, the frame rate at the time of acquiring the OCT signal is four times the frame rate at the time of acquiring the front image, so that 4 before the front image of one frame is acquired. The OCT signal for a frame can be acquired. For example, the control unit 70 may perform a plurality of OCT signals O1, O2, O3, O4 in the first scanning line S1 during the time T2 for acquiring the second front image F2 (time between the time T1 and the time T2). Can be obtained. When the acquisition of the second front image F2 is completed, the control unit 70 stores it in the memory 72.

<Judgment of quality of OCT signal>
Next, the control unit 70 determines the quality (adequacy) of the plurality of OCT signals O1, O2, O3, O4 acquired in the first scanning line S1. FIG. 5 shows a flowchart of the determination process. In the present embodiment, the quality of the OCT signal is determined in real time. The determination result is used to process a plurality of OCT signals and acquire motion contrast data.

For example, the control unit 70 performs a determination process each time a front image and a plurality of OCT signals are acquired (A1). For example, the control unit 70 detects the positional deviation between the acquired front images (A2). For example, in the misalignment detection, front images at the time of acquiring a plurality of OCT signals and after the acquisition of a plurality of OCT signals are used. In the present embodiment, as the front image at the time of acquiring the plurality of OCT signals, the front image acquired before the acquisition of the plurality of OCT signals is used. Of course, the front image at the time of acquiring a plurality of OCT signals is not limited to the front image acquired before the acquisition of the plurality of OCTs. For example, the front image at the time of acquiring a plurality of OCT signals may be a front image acquired during the acquisition of a plurality of OCTs. In the present embodiment, the front image after the acquisition of the plurality of OCT signals is obtained, and the acquisition of the plurality of OCT signals is completed as the front image after the acquisition of the plurality of OCT signals. At the same time, the front image that has been acquired is used. Of course, the front image after the acquisition of the plurality of OCT signals is not limited to the front image whose acquisition is completed at the same time as the acquisition of the plurality of OCT signals is completed. For example, the front image after the acquisition of the plurality of OCT signals may be a front image acquired after the acquisition of the plurality of OCT signals (preferably immediately after the acquisition of the OCT signals is completed).

For example, when the control unit 70 determines the quality of the plurality of OCT signals O1, O2, O3, O4 acquired in the first scanning line S1, the control unit 70 determines the quality of the plurality of OCT signals O1, O2, O3, O4 acquired in the first scanning line S1. The first front image F1 before the acquisition of O3 and O4 and the second front image F2 whose acquisition is completed at the same time as the acquisition of the plurality of OCT signals O1, O2, O3 and O4 is completed are used. The control unit 70 detects the positional deviation between the first front image F1 and the second front image F2 by image processing. Thereby, in the first scanning line S1, it is possible to detect the movement of the eye while the plurality of OCT signals O1, O2, O3, O4 are acquired. That is, it is possible to detect whether or not a deviation has occurred in the scanning position when a plurality of OCT signals O1, O2, O3, O4 are acquired.

Next, for example, the control unit 70 determines the quality of the plurality of OCT signals O1, O2, O3, O4 acquired in the first scanning line S1 based on the detection result of the misalignment. For example, the control unit 70 determines whether or not the misalignment (displacement amount) satisfies an allowable range (for example, a predetermined threshold value) (A3). For example, when the deviation amount satisfies the allowable range (YES in FIG. 5), the control unit 70 determines that the plurality of OCT signals are good. Further, for example, when the deviation amount does not satisfy the allowable range (NO in FIG. 5), the control unit 70 determines that the plurality of OCT signals are not good.

For example, when it is determined that the plurality of OCT signals are good, the control unit 70 stores the plurality of OCT signals O1, O2, O3, O4 acquired in the first scanning line S1 in the memory 72 (A5). ). Next, the control unit 70 determines whether or not the imaging is completed up to the final scanning line Sn. That is, the control unit 70 determines whether or not the imaging in the entire scanning region (in the present embodiment, the entire scanning line) is completed (A6). When it is determined that the shooting at all the scanning lines (all scanning positions) is completed, the control unit 70 ends the shooting (A9). If it is determined that shooting on all scanning lines has not been completed, shooting is continued. For example, the control unit 70 sets a region for acquiring a plurality of OCT signals O1, O2, O3, O4 as a second scanning region (this is different from the first scanning region (in the present embodiment, the first scanning line S1)). In the embodiment, it is changed to the second scanning line S2) (A7). That is, the control unit 70 finishes the acquisition of the plurality of OCT signals O1, O2, O3, O4 in the first scanning line S1, and the control unit 70 completes the acquisition of the plurality of OCT signals O1, O2, O3 acquired in the first scanning line S1. , O4 is stored in the memory 72. Then, the control unit 70 starts acquiring a plurality of OCT signals O1, O2, O3, O4 (see, for example, FIG. 4) at the second scanning line (second scanning position) S2 (A8).

For example, the control unit 70 changes the sub-scanning position (position in the Y direction) by controlling the optical scanner 108, and scans the measurement light a plurality of times in the main scanning direction (X direction) on the second scanning line S2. To do. The change of the scanning position is not limited to the Y direction. You may change it in the X direction. This makes it possible to take a wide-angle shot in the X direction. Of course, the configuration may be such that the direction is changed to both the X direction and the Y direction. As shown in FIG. 4, even when a plurality of OCT signals O1, O2, O3, and O4 are acquired in the second scanning line S2, the control unit 70 is in the same manner as in the case of the first scanning line S1. 3 Acquire the front image F3. Then, the control unit 70 determines the quality of the plurality of OCT signals O1, O2, O3, O4 acquired in the second scanning line S2. In this case, in the determination, the acquisition of the second front image F2 and the plurality of OCT signals O1, O2, O3, O4 before the acquisition of the plurality of OCT signals O1, O2, O3, O4 in the second scanning line S2 is completed ( The third front image F3 whose acquisition is completed at the same time as (time T3 o'clock) is used. The control unit 70 detects the positional deviation between the second front image F2 and the third front image F3 by image processing, and based on the detection result of the positional deviation, the plurality of OCT signals O1 acquired in the second scanning line S2. , O2, O3, O4 are judged.

In the present embodiment, when determining the quality of a plurality of OCT signals, continuously acquired front images (for example, the first front image F1 and the second front image F2) are used in the determination process. The configuration has been described as an example, but the present invention is not limited to this. The front image for performing the OCT determination process includes a front image before acquisition of a plurality of OCT signals in the scanning line and a plurality of front images acquired after the front image before acquisition of the plurality of OCT signals. The configuration may be such that the front image acquired after the acquisition of the OCT signal of is used. For example, the first front image acquired at the start of shooting is set as the reference image. Then, at each scanning position, the determination process may be performed based on the positional deviation between the acquired front image and the reference image when a plurality of OCT signals are acquired. More specifically, for example, there is a configuration in which the first front image F1 and the third front image F3 are used when determining a plurality of OCT signals O1, O2, O3, O4 in the second scanning line S2. ..

Similar to the operation after the determination in the first scanning line S1, the control unit 70 acquires a plurality of OCT signals O1, O2, O3, O4 when it is determined that the plurality of OCT signals are good. To the next scanning position (scanning line). Similarly, the control unit 70 performs determination processing while acquiring the OCT signal and the front image, and scans the measurement light a plurality of times in each scanning line up to the final scanning line Sn, thereby scanning each scanning line. Acquire a plurality of OCT signals in. That is, as shown in FIG. 3, the control unit 70 performs a raster scan (scan at a transverse position) of the measurement light, and at least two frames or more (in the present embodiment) having different times at each scanning line (S1 to Sn). 4 frames) OCT signal is acquired. This makes it possible to acquire three-dimensional information on the fundus. Even if the shooting is not completed up to the final scanning position, if the examiner performs an operation to stop the shooting, the shooting operation may be terminated at that point. In this way, by determining the quality of the acquired plurality of OCT signals and changing the scanning area based on the determination result, it is possible to acquire the plurality of OCT signals in each scanning area more quickly.

On the other hand, for example, when it is determined that the plurality of OCT signals are not good, the control unit 70 reacquires the plurality of OCT signals in the first scanning line S1. For example, the control unit 70 deletes the plurality of OCT signals O1, O2, O3, O4 and the first front image F1 acquired in the first scanning line S1 (A11), and starts reacquisition. The control unit 70 controls the optical scanner 108 based on the amount of deviation between the first front image F1 and the second front image F2, and corrects the scanning position (A12). For example, the control unit 70 appropriately drives and controls the two galvano mirrors of the optical scanner 108 so that the deviation of the scanning position is corrected. After correcting the scanning position, the control unit 70 starts acquiring a plurality of OCT signals again on the first scanning line S1 (A13).

The control unit 70 acquires a front image after scanning position correction before acquiring a plurality of OCT signals. That is, for example, a front image at the time of reacquisition of a plurality of OCT signals is acquired. The control unit 70 is based on a front image at the time of reacquisition of a plurality of OCT signals after reacquisition of a plurality of OCT signals, a front image whose acquisition is completed at the same time as the reacquisition of a plurality of OCT signals is completed, and a positional deviation. The quality of the reacquired plurality of OCT signals is determined. Then, the control unit 70 determines, based on the determination result, whether to shift to scanning at the next scanning position or to perform scanning at the same scanning position again. If the OCT signal is not acquired satisfactorily a plurality of times, the control unit 70 displays an error (for example, a display prompting the resetting of the shooting position, a display prompting the readjustment of the shooting conditions), and the like, and ends the shooting. You may let it. As described above, when the plurality of OCT signals cannot be acquired satisfactorily, the plurality of OCT signals in each scanning region can be acquired with high accuracy by acquiring the plurality of OCT signals again.

<Acquisition of motion contrast data>
The control unit 70 processes a plurality of OCT signals determined to be good to acquire motion contrast data (acquiring three-dimensional function OCT image data in the present embodiment) in the fundus of the eye to be inspected. For example, when the control unit 70 shifts to the acquisition of a plurality of OCT signals in the next scanning line, the control unit 70 performs arithmetic processing of the plurality of OCT signals in each scanning line acquired before that.

For example, the control unit 70 acquires a plurality of OCT signals in the first scanning line S1, and then scan positions (acquisition positions) of the plurality of OCT signals from the first scanning line S1 to the second scanning line S2. To move. When the control unit 70 starts acquiring a plurality of OCT signals in the second scanning line S2, the control unit 70 starts arithmetic processing of the acquired plurality of OCT signals in the first scanning line S1. That is, the control unit 70 starts arithmetic processing of a plurality of OCT signals corresponding to the first scanning line S1 while acquiring the OCT signal on the second scanning line S2, and performs the first scanning. The function OCT image data in the line S1 is acquired. The control unit 70 performs the above processing for each scanning line, acquires a plurality of OCT signals for each scanning line, and acquires functional OCT image data for each scanning line. Then, by acquiring the functional OCT image data at these plurality of positions (scanning lines), a three-dimensional functional OCT front image which is a pseudo angiographic image (an image that can be used as an angiographic image for the purpose). You can get the data. In this way, the motion contrast data can be acquired more quickly by performing the operation of acquiring the motion contrast data during the acquisition of the plurality of OCT signals. In the present embodiment, when the acquisition of a plurality of OCT signals at the next scanning line is performed, the calculation processing of the plurality of OCT signals at each scanning line acquired before that is performed. However, it is not limited to this. For example, the control unit 70 may be configured to start arithmetic processing of a plurality of OCT signals in each scanning line after acquiring a plurality of OCT signals in each scanning line.

As described above, the front image at the time of acquiring the plurality of OCT signals and the front image after the acquisition of the plurality of OCT signals in the predetermined scanning region are acquired in the predetermined scanning region based on the detection result of the positional deviation. By determining the quality of the plurality of OCT signals, it is possible to collectively determine the quality of the plurality of OCT signals acquired in the same portion (same scanning area). Therefore, it is possible to easily confirm whether or not the acquired plurality of OCT signals are satisfactorily photographed. As a result, a plurality of OCT signals in the same scanning region can be easily and accurately acquired.

<Example of transformation>
In the present embodiment, after the acquisition of the first front image F1 is completed, the acquisition of a plurality of OCT signals on the first scanning line S1 is started, but the present invention is not limited to this. The acquisition of a plurality of OCT signals may be started in parallel with the acquisition of the first front image F1 according to the output of the imaging start signal. In this case, when determining the quality of the plurality of OCT signals, the plurality of OCT signals acquired in parallel with the acquisition of the first front image F1 (acquired at the start of imaging) are deleted, and the second front image is deleted. The determination process for the plurality of OCT signals is started from the plurality of OCT signals acquired in parallel at the time of acquisition of F2. For example, in the first scanning line S1, eight frames of OCT signals (OCT signals for four frames when the first front image F1 is acquired and OCT signals for four frames when the second front image F2 is acquired) are acquired. The OCT signals for 4 frames at the time of acquiring the first front image F1 are deleted.

In the present embodiment, the configuration in which the timing of starting the front image acquisition and the timing of starting the acquisition of a plurality of OCT signals in a predetermined scanning region are synchronized is given as an example, but the present invention is not limited to this. The acquisition start operation of a plurality of OCT signals and the acquisition start operation of the front image in a predetermined scanning region may be asynchronous. For example, as shown in FIG. 6, acquisition of a plurality of OCT signals on the first scanning line S1 is started during acquisition of the first front image F1 (for example, after half of the time T1 has elapsed). In this case, the first front image F1 and the second front image F2 are acquired when a plurality of OCT signals O1, O2, O3, and O4 are acquired on the first scanning line S1. That is, the determination process for the plurality of OCT signals O1, O2, O3, O4 in the first scanning line S1 is performed using the positional deviation of the first front image F1 and the second front image F2. Further, the acquisition of the plurality of OCT signals O1, O2, O3, O4 on the second scanning line S2 is started during the acquisition of the second front image F2 (for example, after half of the time T2 has elapsed). The plurality of OCT signals O1, O2, O3, and O4 in the second scanning line S2 are subjected to determination processing based on the second front image F2 and the third front image F3.

In the present embodiment, it is determined based on the detection result of the positional deviation between the front image of one frame when a plurality of OCT signals are acquired in the predetermined scanning region and the front image of one frame after the acquisition of the plurality of OCT signals. The configuration is such that the quality of a plurality of OCT signals acquired in the scanning region of is determined, but the present invention is not limited to this. For example, when a front observation optical system (for example, an infrared observation optical system) that can acquire a plurality of front images while acquiring a plurality of OCT signals is used, one front of the plurality of front images is used. An image (for example, the latest front image) may be selected to perform the determination process. Further, for example, a plurality of OCT signal determination processes may be performed using all the plurality of front images.

In the present embodiment, a case where one scanning position (first scanning position) is set as the first scanning region is given as an example, but the present invention is not limited to this. A plurality of scanning positions may be set as the scanning area. For example, the measurement light may be set to be scanned at two scanning positions, a first scanning position and a second scanning position, as the first scanning region. In this case, for example, when the frame rate for acquiring the front image and the OCT signal is the frame rate mentioned in the present embodiment (when the frame rate for acquiring the OCT signal is four times the frame rate for acquiring the front image), 1 While acquiring the front image of the frame, the OCT signal of 2 frames is acquired at the first scanning position, and the OCT signal of 2 frames is acquired at the second scanning position. That is, based on the detection result of the positional deviation between the front image of one frame when a plurality of OCT signals are acquired in a predetermined scanning region (for example, the first scanning region) and the front image of one frame after the acquisition of the plurality of OCT signals. When making a determination, the quality of a plurality of OCT signals at the two scanning positions can be collectively determined. Then, the control unit 70 processes each of the plurality of OCT signals acquired with respect to at least two or more (two in the present embodiment) scanning positions, and the motion contrast data at each scanning position on the fundus of the eye to be inspected. To get each. In this way, the motion contrast data at the plurality of scanning positions is acquired at the time of acquiring the plurality of OCT signals and during the detection of one positional deviation between the front images acquired after the acquisition of the plurality of OCT signals. Therefore, the shooting can be completed more quickly.

When a plurality of scanning positions are set as the scanning area, an arbitrary order can be used as the order of acquiring a plurality of OCT signals at each scanning position. For example, when the measurement light is set to be scanned at two scanning positions, a first scanning position and a second scanning position, as the first scanning region, one frame is set at the first scanning position. After acquiring the OCT signal, one frame of OCT signal is acquired at the second scanning position. After that, the OCT signal of one frame is acquired at the first scanning position, and the OCT signal of one frame is acquired at the second scanning position. That is, by alternately acquiring the OCT signals at the first scanning position and the second scanning position, the OCT signals of two frames are acquired at the respective scanning positions. Further, for example, when one frame of OCT signal is acquired at the first scanning position and the second scanning position, the OCT signal and the second scanning position at the first scanning position are obtained in one scanning. The OCT signals in the above may be acquired at the same time.

In the present embodiment, when it is determined that the OCT signal is not good, the image is taken again in the same scanning area, but the present invention is not limited to this. After all the scanning positions are completed, the OCT signal in the scanning region determined that the OCT signal is not good may be re-photographed. Further, the examiner may be notified of the scanning area where the OCT signal is not satisfactorily acquired. In this case, the examiner may perform re-shooting or the like based on the notified information.

In the present embodiment, the case of acquiring a frontal image of the fundus in order to detect the displacement of the fundus of the eye to be inspected is described as an example, but the present invention is not limited to this. For example, the front image of the anterior segment of the eye to be inspected may be captured, and the image may be taken at the fundus based on the positional deviation between the front images of the anterior segment.

It should be noted that the present embodiment is not limited to the optical coherence tomography apparatus that acquires the OCT signal, which has been described as an example. The technique of the present disclosure can be applied to any device that acquires motion contrast data from a plurality of signals (for example, an imaging signal acquired by a fundus imaging device with a wave surface compensation function).

The present invention is not limited to the device described in the present embodiment. For example, optical coherence tomography calculation software (program) that performs the functions of the above-described embodiment is supplied to a system or an apparatus via a network or various storage media. Then, a computer of the system or device (for example, a CPU or the like) can read and execute the program.

1 Optical coherence tomography device 70 Control unit 72 Memory 75 Monitor 76 Operation unit 100 Interference optical system (OCT optical system)
108 Optical scanner 120 Detector 200 Front observation optical system 300 Fixed target projection unit

Claims (4)

An optical coherence tomography apparatus that detects an OCT signal from the measurement light and reference light applied to the eye to be inspected and processes the OCT signal to acquire a tomographic image of the eye to be inspected.
A frontal observation optical system that obtains a frontal image of the eye to be inspected,
An OCT optical system that acquires a plurality of OCT signals that differ in time with respect to the same scanning region on the eye to be inspected.
When a plurality of OCT signals are acquired by the OCT optical system in the first scanning region on the eye to be inspected, a first front image is acquired by the front observation optical system, and the plurality of OCT signals are acquired in the first scanning region. After that, the control means for acquiring the second front image by the front observation optical system after the acquisition of the first front image, and
The misalignment between the first front image and the second front image is detected by image processing, and based on the detection result of the misalignment, the quality of the plurality of OCT signals acquired in the first scanning region is good or bad. Judgment means to judge
An arithmetic processing means for processing the plurality of OCT signals determined to be good by the determination means and acquiring motion contrast data in the eye to be inspected.
With
The control means acquires a plurality of OCT signals that are temporally different with respect to at least two or more scanning regions on the eye to be inspected by the OCT optical system.
After the acquisition of the plurality of OCT signals is completed in the entire scanning region, the plurality of OCT signals are reacquired in the scanning region in which the determination means determines that the plurality of OCT signals are not good. Optical coherence tomography equipment. The optical coherence tomography apparatus according to claim 1, wherein the first scanning region includes at least two or more scanning positions on the eye to be inspected. It is executed in the control device that controls the operation of the optical coherence tomography device that detects the OCT signal by the measurement light and the reference light applied to the test eye and processes the OCT signal to acquire the tomographic image of the test eye. Optical coherence tomography control program
By being executed by the processor of the control device,
The front image acquisition step to obtain the front image of the eye to be inspected,
An acquisition step of acquiring a plurality of OCT signals that differ in time with respect to the same scanning area on the eye to be inspected, and
When a plurality of OCT signals are acquired by the acquisition step in the first scanning region on the eye to be inspected, the first front image is acquired by the front image acquisition step, and after the acquisition of the plurality of OCT signals in the first scanning region. The control step of acquiring the second front image by the front image acquisition step after the acquisition of the first front image, and the control step.
The misalignment between the first front image and the second front image is detected by image processing, and based on the detection result of the misalignment, the quality of the plurality of OCT signals acquired in the first scanning region is good or bad. Judgment step to judge
An arithmetic processing step of processing the plurality of OCT signals determined to be good by the determination step and acquiring motion contrast data in the eye to be inspected.
To the optical coherence tomography apparatus
The control step, respectively acquires at least two scanning areas with respect to plurality of temporally different OCT signal on the eye to be examined,
After the acquisition of the plurality of OCT signals is completed in the entire scanning region, the plurality of OCT signals are reacquired in the scanning region in which the determination step determines that the plurality of OCT signals are not good. Optical coherence tomography control program. The optical coherence tomography control program according to claim 3, wherein the first scanning region includes at least two or more scanning positions on the eye to be inspected.

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