SD-OCT device

Abstract

To suppress deterioration of accuracy in measurement in SD-OCT.SOLUTION: An SD-OCT apparatus includes: a light source for outputting light including a plurality of wavelength components; a branching part for branching the light output from the light source at least into a reference light that travels in a light path for reference and a measurement light radiated to a measurement object; a transmission part for transmitting an interference light between the reference light and the measurement light returning from the measurement object; a light reception part in which a plurality of light receiving elements are arranged linearly; and an optical system for dispersing the interference light output from the transmission part and condensing the interference light on the light reception part for each of the wavelength components. The diameter of the wavelength component of a prescribed wavelength condensed on the light reception part by the optical system is equal to or smaller than an average wavelength of a wave-like signal detected through the light reception part by the reception of the interference light.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an SD-OCT device. [Background technology]

[0002] Optical Coherence Tomography (OCT) is a technology that uses the coherence of light to measure the position of an object. In OCT, the structure of an object is measured by utilizing the interference between light returning from the object after the object is irradiated with light and reference light that passes through a reference optical path. OCT includes a method called Spectral Domain OCT (SD-OCT), which disperses the interference light between the light returning from the object and the reference light according to wavelength components, and measures the position of the object by using the dispersed interference light. Patent Document 1 describes a technology that can be applied to SD-OCT. Patent Document 1 discloses a configuration in which the optical path length of the reference light is changed by moving the position of a mirror that reflects the reference light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-32578 Summary of the Invention [Problem to be solved by the invention]

[0004] SD-OCT has the problem that measurement accuracy is insufficient depending on the design of the optical components. The present invention has been made in consideration of such problems, and aims to suppress a decrease in accuracy in measurements using SD-OCT. [Means for solving the problem]

[0005] In order to achieve the above object, the SD-OCT device comprises a light source that outputs light containing multiple wavelength components, a branching section that branches the light output from the light source into at least reference light that follows a reference optical path and measurement light that is irradiated onto the object to be measured, a transmission section that transmits interference light between the reference light and the measurement light that returns from the object to be measured, a light receiving section in which multiple light receiving elements are arranged in a line, and an optical system that disperses the interference light output from the transmission section and focuses it on the light receiving section for each wavelength component, wherein the diameter of the wavelength components of a predetermined wavelength that are focused on the light receiving section by the optical system is less than or equal to the average wavelength of a wave-like signal detected via the light receiving section by receiving the interference light.

[0006] That is, in an SD-OCT device, the diameter of the wavelength component of a predetermined wavelength focused on the light receiving unit is equal to or less than the average wavelength of the wave-like signal detected through the light receiving unit. This reduces the overlap of light between wavelength components on the light receiving unit. When overlapping wavelength components occurs, the signals of the wavelength components cannot be distinguished in the overlapping area, resulting in a decrease in the accuracy of the signal detected through the light receiving unit. By preventing this situation, the SD-OCT device can suppress a decrease in accuracy in SD-OCT measurements. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing the configuration of an SD-OCT device according to one embodiment of the present invention. [Figure 2] 1 is a diagram showing the configuration of an SD-OCT device according to one embodiment of the present invention. [Figure 3] 10A and 10B are diagrams illustrating reception of interference light by a light receiving section. [Figure 4] 5A and 5B are diagrams illustrating a detection signal detected by a light receiving unit. [Figure 5] 4A and 4B are diagrams illustrating the spot diameter of wavelength components received by a light receiving unit. [Figure 6] FIG. 10 is a diagram illustrating overlapping of wavelength components. [Figure 7] 10 is a flowchart illustrating an example of an axial length measurement process. DETAILED DESCRIPTION OF THE INVENTION

[0008] Here, an example of an embodiment of the present invention will be described in the following order. (1) SD-OCT device configuration: (2) Axial length measurement process: (3) Other embodiments:

[0009] (1) SD-OCT device configuration: The SD-OCT device 1 according to this embodiment will be described below. The SD-OCT device 1 of this embodiment uses the corneal apex and fundus (retina) of a subject's eyeball (hereinafter referred to as the eye under examination) as measurement objects, measures the position of the measurement object using the SD-OCT method, and measures the axial length of the eye under examination. FIGS. 1 and 2 are diagrams schematically showing the configuration of the SD-OCT device 1 according to this embodiment. The SD-OCT device 1 includes a control unit 10, an adjustment mechanism 11, a mirror 12, an alignment mechanism 13, a light source 14, and a light receiving unit 15. The SD-OCT device 1 also includes optical members (branching unit 30, transmission units 41a, 42a, 43a, 44a, collimators 42b, 43b, and an optical system 44b) that form optical paths 41 to 44 of light output from the light source 14.

[0010] The control unit 10 includes a processor, RAM, ROM, etc., and controls the SD-OCT device 1 by executing a program stored in the ROM, etc. The adjustment mechanism 11 is a mechanism capable of moving the mirror 12 linearly along the optical path 42. In this embodiment, the adjustment mechanism 11 is a ball-screw mechanism that moves the mirror 12, but it may also be another mechanism, such as a slider-crank mechanism or a power transmission mechanism such as a cam. The mirror 12 reflects incident light. The control unit 10 adjusts the position of the mirror 12 via the adjustment mechanism 11. The alignment mechanism 13 is a mechanism used to adjust the positional relationship between the SD-OCT device 1 and the measurement object. Before measuring the measurement object using SD-OCT, the control unit 10 detects the position of the corneal apex of the subject's eye, which is located at a predetermined position, via the alignment mechanism 13, and adjusts the position of the SD-OCT device 1 so that the detected corneal apex position and the SD-OCT device 1 are in a predetermined positional relationship. The light source 14 outputs light in a predetermined wavelength band in response to instructions from the control unit 10. In this embodiment, the light source 14 outputs light in a wavelength band centered at 840 nm and having a full width at half maximum of 60 nm. Hereinafter, the central wavelength will be defined as the wavelength component, among the wavelength components contained in the light output from the light source 14, that is defined as the wavelength component that primarily contributes to measurement in SD-OCT. In this embodiment, the central wavelength is 840 nm, which is the central wavelength of the wavelength band of the light output from the light source 14. Hereinafter, the central wavelength will be referred to as λ0. The light receiving unit 15 is a plurality of light receiving elements arranged in a line. In this embodiment, the light receiving unit 15 is a sensor in which 2048 light receiving elements, each 7 μm wide, are arranged, and the width is 7 μm × 2048 = 14.336 mm.

[0011] The branching unit 30 is an optical component that branches the light output from the light source 14 into reference light that travels along a reference optical path and measurement light that is irradiated onto the measurement object, and can be configured, for example, by a filter coupler. The transmitting unit 41a is used to form the optical path 41, and in this embodiment, is an optical fiber that transmits the light from the light source 14 to the branching unit 30. The optical path 41 is an optical path that transmits the light output from the light source 14 to the branching unit 30. The transmitting unit 42a and the collimator 42b are used to form the optical path 42. The optical path 42 is an optical path along which the reference light branched by the branching unit 30 travels toward the mirror 12, and an optical path along which the reference light reflected by the mirror 12 and traveling in the reverse direction travels toward the branching unit 30. The transmitting unit 42a is an optical fiber that transmits the reference light branched by the branching unit 30. The collimator 42b converts the light output from the transmitting unit 42a into parallel light. The transmitting unit 43a and the collimator 43b are used to form the optical path 43. The optical path 43 is an optical path along which the measurement light branched by the branching unit 30 travels toward the measurement object, and also an optical path along which the measurement light returning from the measurement object travels toward the branching unit 30. The transmitting unit 43a is an optical fiber that transmits the measurement light branched by the branching unit 30. The collimator 43b converts the light output from the transmitting unit 43a into parallel light.

[0012] The transmitting unit 44a and the optical system 44b are used to form the optical path 44. The optical path 44 is an optical path along which the interference light between the measurement light and the reference light generated by the branching unit 30 travels toward the light-receiving unit 15. The transmitting unit 44a is an optical fiber that transmits the interference light generated by the branching unit 30. The optical system 44b disperses the interference light output from the transmitting unit 44a and focuses it onto the light-receiving unit 15 for each wavelength component. The optical system 44b includes a lens 44c, a dispersing member 44d, a dispersing member 44e, and a lens 44f. The lens 44c is disposed on the optical path 44 at a position spaced a focal length f1 from the output end of the transmitting unit 44a. Therefore, the lens 44c converts the interference light output from the transmitting unit 44a, which travels while diverging radially around the optical axis, into parallel light. The dispersing members 44d and 44e each disperse the incident light. In this embodiment, the dispersing members 44d and 44e are each a diffraction grating, but may be other optical members such as a prism. In this embodiment, the dispersing members 44d and 44e are a diffraction grating with 1,800 slits per mm, but may be a diffraction grating with other numbers of slits per mm (e.g., 2,400 slits per mm). Dispersion by the dispersing members 44d and 44e causes the interference light to change its direction of travel for each wavelength component. The lens 44f is disposed on the optical path 44 at a position spaced a focal length f2 from the light receiving unit 15. The light receiving unit 15 is disposed opposite the lens 44f, and the multiple light receiving elements of the light receiving unit 15 are disposed so as to be aligned perpendicular to the optical axis of the lens 44f and perpendicular to the slits of the dispersing members 44d and 44e.

[0013] In this embodiment, the SD-OCT device 1 generates interference light by a Michelson interferometer from light output from a light source 14. The optical path of the light output from the light source 14 in the SD-OCT device 1 will be described with reference to FIG. Light output from light source 14 propagates through transmission section 41a of optical path 41 and reaches branching section 30. Branching section 30 branches the light into reference light and measurement light. Branching section 30 then causes the reference light to travel along optical path 42 and the measurement light to travel along optical path 43.

[0014] The reference light that travels to the optical path 42 travels through the transmission unit 42a, is output from the transmission unit 42a, and reaches the mirror 12 via the collimator 42b. The reference light reflected by the mirror 12 travels again along the optical path 42, passes through the collimator 42b, and reaches the branching unit 30. The measurement light that travels from the branching unit 30 to the optical path 43 travels through the transmission unit 43a, is output from the transmission unit 43a, and reaches the measurement object via the collimator 43b. The measurement light is then reflected or scattered by the measurement object. As a result, at least a portion of the reflected or scattered measurement light travels in the opposite direction to the incident direction and returns from the measurement object. The measurement light that returns from the measurement object travels again along the optical path 43, passes through the collimator 43b, and reaches the branching unit 30. The branching unit 30 combines the reference light and measurement light that have reached the branching unit 30 to generate interference light between the reference light and measurement light, and causes the generated interference light to travel along an optical path 44.

[0015] As described above, in this embodiment, the reference light split by the splitter 30 travels through the optical path 42, mirror 12, optical path 42, splitter 30, and optical path 44 in this order, before reaching the light-receiving unit 50. Therefore, the optical path of the reference light is formed by the optical path 42, mirror 12, and optical path 44. Hereinafter, the optical path of the reference light is referred to as the reference arm. The controller 10 adjusts the optical path length of the reference arm by moving the mirror 12 via the adjustment mechanism 11. Here, the optical path length refers to the length of the optical path after conversion into an optical path in air. For example, the optical path length of a 1-meter-long optical path in a medium whose refractive index relative to air is 1.2 is 1.2 m = the refractive index of the medium (1.2) × the actual length (1 m). Furthermore, the measurement light branched by the branching unit travels in the order of optical path 43, the measurement object, optical path 43, branching unit 30, and optical path 44, and reaches the light receiving unit 15. Therefore, in this embodiment, the optical path of the measurement light is formed by optical path 43, the measurement object, and optical path 44. Hereinafter, this optical path of the measurement light is referred to as a measurement arm.

[0016] In this embodiment, the control unit 10 switches between a reference arm for measuring the corneal apex of the subject's eye and a reference arm for measuring the retina of the subject's eye by moving the mirror 12 via the adjustment mechanism 11. Hereinafter, the reference arm for measuring the corneal apex of the subject's eye will be referred to as the corneal reference arm. Also, the reference arm for measuring the retina of the subject's eye will be referred to as the retina reference arm. In this embodiment, when the corneal reference arm is used, the zero point of the measurement arm is adjusted to a position near the corneal apex of the subject's eye aligned in the optical path 43 and in front of the corneal apex. Herein, "front" refers to the front as seen from the subject's perspective. Hereinafter, "front" also refers to the front as seen from the subject's perspective. Herein, the zero point refers to a position on the measurement arm where the optical path length of the measurement light reflected in the opposite direction at that position is the same as the optical path length of the reference arm. Also, when the retina reference arm is used, the zero point of the measurement arm is adjusted to a position on the optical path 43 at a predetermined distance behind the cornea of ​​the subject's eye. In this embodiment, this predetermined distance is the minimum value among the lengths assumed as the axial length of the eyeball.

[0017] The interference light traveling along the optical path 44 passes through lens 44c to become parallel light and reaches dispersing member 44d. The interference light that reaches dispersing member 44d is dispersed and split into individual wavelength components before reaching dispersing member 44e. The interference light that reaches dispersing member 44e is dispersed again and reaches lens 44f. The interference light that reaches lens 44f for each wavelength component is split into individual wavelength components, travels along different optical paths for each wavelength component, and is focused onto the light receiving unit 15. Therefore, the interference light is focused at different positions on the light receiving unit 15 for each wavelength component. This allows the control unit 10 to detect the intensity of each wavelength component of the dispersed interference light via the multiple light receiving elements of the light receiving unit 15. The wavelength of light that can be received by the light receiving unit 15 is determined in advance from the positional relationship between the light receiving unit 15 and the dispersion member 44e. Hereinafter, the smallest wavelength of light that can be received by the light receiving unit 15 will be referred to as λ1. Furthermore, the largest wavelength of light that can be received by the light receiving unit 15 will be referred to as λ2.

[0018] Here, a situation in which the light output from the transmitting portion 44a in the optical path 44 is collected on the light receiving portion 15 will be described with reference to FIG. When the interference light is output from the transmitting unit 44a, it spreads radially around the optical axis and enters the lens 44c. The lens 44c converts the incident interference light into parallel light. The interference light converted into parallel light by the lens 44c enters the dispersion member 44d. In this embodiment, the optical system 44b is designed so that the interference light converted into parallel light by the lens 44c enters the dispersion member 44d at an incident angle of 60°. However, the optical system 44b may be designed so that the interference light converted into parallel light by the lens 44c enters the dispersion member 44d at a different incident angle. The dispersion member 44d disperses the interference light into components with different wavelengths. In FIG. 3, the optical paths of the wavelength components of three wavelengths are shown by dashed lines, dashed lines, and dashed two-dot lines, respectively, as an example. The interference light dispersed by the dispersion member 44d is parallel light when viewed in terms of each wavelength component.

[0019] The interference light dispersed by the dispersing member 44d enters the dispersing member 44e. The interference light is further dispersed by the dispersing member 44e. The interference light dispersed by the dispersing member 44e becomes parallel light when viewed for each wavelength component. The interference light dispersed by the dispersing member 44e enters the lens 44f. The interference light dispersed by the dispersing member 44e becomes parallel light for each wavelength component, and parallel light for each wavelength component enters the lens 44f. Therefore, each wavelength component of the interference light is focused at a different position on the light receiving unit 15, which is located at a focal length f2 away from the lens 44f.

[0020] Here, the signal detected via the light receiving section 15 will be described with reference to FIG. A wavelength component of wavelength λ1 in the interference light is collected at one end (hereinafter referred to as the first end) of the light receiving unit 15. A wavelength component of wavelength λ2 in the interference light is collected at the other end (hereinafter referred to as the second end) of the light receiving unit 15. The wavelength of the collected light continuously varies from the first end to the second end of the light receiving unit 15, with shorter wavelength components being collected closer to the first end and longer wavelength components being collected closer to the second end. The control unit 10 detects a signal that associates the position of each light receiving element of the light receiving unit 15 on the light receiving unit 15 (the distance from the first end) with a signal indicating the intensity of light detected via each light receiving element of the light receiving unit 15. Hereinafter, the signal detected here (a signal that associates the position of each light receiving element of the light receiving unit 15 on the light receiving unit 15 with a signal indicating the intensity of light detected via each light receiving element of the light receiving unit 15) will be referred to as a detection signal.

[0021] The intensity of the wavelength component of the interference light with wavelength λ is expressed by the following equation 1:

[0022]

number

[0023] In Equation 1, A represents a constant. x represents the optical path length of the optical path from the zero point in the measurement arm to the object to be measured. Therefore, 2x represents the difference in the optical path length between the reference light and the measurement light (the difference in the optical path length between the reference arm and the measurement arm). Since the wavelength component of wavelength λ1 is collected at the first end of the light receiving unit 15, a signal with a phase of (4πx / λ1) is detected at the first end. In addition, 2At the end, the wavelength component of wavelength λ2 is collected, and therefore a signal with a phase of (4πx / λ2) is detected at the second end. In the light-receiving unit 15, the wavelength of the collected light continuously varies from the first end to the second end. Therefore, the detection signal detected by the light-receiving unit 15 becomes a wavy signal whose phase continuously varies from (4π|x| / λ1) to (4π|x| / λ2) from the first end to the second end, as shown in FIG. 4. The number of waves contained in this wavy detection signal can be calculated by dividing the value of the phase variation from the first end to the second end by 2π, as shown in Equation (2) below.

[0024]

number

[0025] Therefore, when the length of the light receiving section 15 is L, the average wavelength wl of this detection signal can be calculated as shown in equation (3) by dividing L by the number calculated by equation (2).

[0026]

number

[0027] As shown in equations (2) and (3), the larger the optical path length x from the zero point in the measurement arm to the object to be measured (the larger the difference 2x in the optical path length between the reference arm and the measurement arm), the more waves there are in the detection signal, and the shorter the average wavelength wl of the detection signal becomes.

[0028] Next, the size of the focused portion of each wavelength component of the interference light focused on the light-receiving unit 15 will be described using Figure 5. No matter what lens is used, it is impossible to focus light onto a perfect point. Therefore, each wavelength component of the interference light is focused into a spot of finite size on the light-receiving unit 15. Hereinafter, the spot diameter will be defined as the diameter of the focused portion of the wavelength component of the interference light on the light-receiving unit 15, which is the diameter in the direction parallel to the arrangement direction of the multiple light-receiving elements of the light-receiving unit 15.

[0029] The diameter of the wavelength component of the wavelength λ of the interference light output from the optical fiber transmitting unit 44a is the mode field diameter (MFD) when the light of wavelength λ is output from the transmitting unit 44a. The MFD is a value defined as the diameter of the light output from the optical fiber. The light output from the optical fiber spreads circularly with a Gaussian distribution centered on the optical axis. The MFD is the diameter of a circular region of this Gaussian distribution that contains 86.5% of the total energy of the light, centered on the optical axis. The MFD when the light of wavelength λ is output from the transmitting unit 44a is calculated in advance from the wavelength λ of the transmitted light, the diameter of the core of the transmitting unit 44a, and the refractive index of the core and cladding of the transmitting unit 44a. Hereinafter, the diameter of the wavelength component of wavelength λ in the interference light output from the transmitting unit 44a is defined as ω1. ω1 is the MFD when the light of wavelength λ is output from the transmitting unit 44a. As light travels, its diameter expands due to the phenomenon of diffraction. When light with a diameter of ω0 travels a distance z, the diameter of the light is as shown in the following equation (4).

[0030]

number

[0031] Therefore, when light with a diameter ω1 and wavelength λ output from transmitter 44a travels the focal length f1 and reaches lens 44c, the diameter is λf1 / (πω1). In the following, the diameter when light with a diameter ω1 and wavelength λ travels the focal length f1 and reaches lens 44c is defined as ω2. In other words, ω2=λf1 / (πω1). The light transmitted through the lens 44c becomes parallel light, and is incident on the dispersion member 44d with a constant diameter. Here, the case where light is incident on the diffraction grating will be described. When light is incident on the diffraction grating at an incident angle α and exits at a diffraction angle β, the relationship shown in the following equation (5) is satisfied. In equation (5), d is the slit spacing in each of the dispersion members 44d and 44e. Furthermore, in equation (5), m is the diffraction order and is an arbitrary integer.

[0032]

number

[0033] Furthermore, the diameter of light that passes through the diffraction grating changes in a direction perpendicular to the slits of the diffraction grating through which it has passed. The diameter of the light in a direction perpendicular to the slits of the diffraction grating after passing through the diffraction grating becomes cos(β) / cos(α) times the diameter before passing through the diffraction grating. Hereinafter, the diameter of the light traveling along the optical path 44 in a direction perpendicular to the slits of the diffraction gratings of the dispersing members 44d and 44e is referred to as the beam diameter. Therefore, if the angle of incidence of light with wavelength λ when it enters the dispersing member 44d is α1 and the angle of diffraction is β1, when this light passes through the dispersing member 44d, the beam diameter ω3 of this light is expressed by the following equation (6). As described above, in this embodiment, the optical system 44b is designed so that the angle of incidence of the light that has passed through the lens 44c and become parallel light when it enters the dispersing member 44d is 60°.

[0034]

number

[0035] The light of wavelength λ that has passed through the dispersive member 44d is incident on the dispersive member 44e as parallel light. If the incident angle of the light of wavelength λ when it enters the dispersive member 44e is α2 and the diffraction angle is β2, then when this light passes through the dispersive member 44e, the beam diameter ω4 of this light is expressed by the following equation (7):

[0036]

number

[0037] The light of wavelength λ that has passed through the dispersion member 44e is parallel light, and therefore enters the lens 44f with a constant diameter. Here, in the optical system 44b, the number of diffraction gratings included between the lens 44c and the lens 44f is n, and the angle of incidence and the angle of diffraction of light of wavelength λ at the ith diffraction grating are defined as α i , β iThen, the diameter of the light of wavelength λ incident on the lens 44f can be generalized as shown in the following equation (8).

[0038]

number

[0039] Light of wavelength λ incident on lens 44f is focused on light receiving unit 15. The spot diameter of light of wavelength λ focused on light receiving unit 15 is defined as ω5. The beam diameter ω4 of light of wavelength λ incident on lens 44f is expressed by equation (8). In this case, n in equation (8) is 2. This beam diameter is also equal to λf2 / (πω5), which is the diameter when light of diameter ω5 travels the focal length f2 from light receiving unit 15 to lens 44f. Therefore, the relationship of the following equation (9) holds.

[0040]

number

[0041] From equation (9), the spot diameter ω5 when light of wavelength λ is focused on the light receiving unit 15 is expressed by the following equation (10). Power in equation (10) is the magnification of optical system 44b. The magnification Power of optical system 44b is expressed as (focal length f2 of lens 44f) / (focal length f1 of lens 44c). Furthermore, n in equation (10) is 2 because in this embodiment, optical system 44b includes two dispersion members 44d and 44e.

[0042]

number

[0043] In this way, the wavelength component of the interference light having the wavelength λ is condensed on the light receiving section 15 with a spot diameter ω5.

[0044] The SD-OCT device 1 of this embodiment is designed so that the spot diameter of the wavelength component of a predetermined wavelength in the interference light focused on the light receiving unit 15 is equal to or less than the average wavelength of the detection signal detected via the light receiving unit 15. This will be explained in more detail below. In this embodiment, this predetermined wavelength is the central wavelength λ0. The reason for this design will be explained later.

[0045] The spot diameter of the wavelength component with a center wavelength λ0 in the interference light focused on the light receiving unit 15 is calculated as follows. The MFD when light with a center wavelength λ0 is output from the transmitting unit 44a, which is an optical fiber, is calculated in advance from the center wavelength λ0, the diameter of the core of the transmitting unit 44a, and the refractive index of the core and cladding of the transmitting unit 44a. As described above, the angle of incidence when the wavelength component with a center wavelength λ0, which has been collimated by the lens 44c, enters the dispersive member 44d is predetermined to be 60°. The diffraction angle when the wavelength component with a center wavelength λ0 enters the dispersive member 44d at an angle of incidence of 60° is calculated as follows. That is, in equation (5), an equation for the diffraction angle β is obtained by substituting the incident angle of 60° for α, the slit spacing of the dispersive member 44d for d, the center wavelength λ0 for λ, and a predetermined order for m. By solving this equation, the diffraction angle β is obtained when the wavelength component with the central wavelength λ0 is incident on the dispersive member 44d at an incident angle of 60°.

[0046] Furthermore, the angle of incidence when the wavelength component with the central wavelength λ0 is incident on the dispersion member 44e can be calculated from the diffraction angle calculated here and the positional relationship between the dispersion member 44d and the dispersion member 44e. The diffraction angle when the wavelength component with the central wavelength λ0 is incident on the dispersion member 44e at this calculated angle of incidence can be calculated as follows. That is, in equation (5), an equation for the diffraction angle β can be obtained by substituting this angle of incidence for α, the slit spacing of the dispersion member 44e for d, the center wavelength λ0 for λ, and a predetermined order for m. By solving this equation, the diffraction angle β when the wavelength component with the central wavelength λ0 is incident on the dispersion member 44e at this angle of incidence can be calculated.

[0047] Next, the MFD found here, the angle of incidence at dispersive member 44d, the angle of incidence at dispersive member 44e, the angle of diffraction at dispersive member 44d, and the angle of diffraction at dispersive member 44e are substituted for ω1, α1, α2, β1, and β2 in equation (10), respectively. Furthermore, f2 / f1 is substituted for Power in equation (10). As a result, the spot diameter of the wavelength component with the center wavelength λ0 in the interference light focused on the light receiving unit 15 is found in advance as ω5.

[0048] As described above, the mean wavelength wl of the detection signal detected via the light receiving unit 15 decreases as the optical path length x from the zero point in the measurement arm to the object to be measured (the difference in optical path length between the reference arm and the measurement arm) increases. Therefore, when the optical path length x from the zero point in the measurement arm to the object to be measured is the maximum possible value, the mean wavelength wl takes the minimum possible value. In this embodiment, the measurement objects are the corneal apex and retina of the subject's eye. In this embodiment, before measurement, the position of the corneal apex relative to the SD-OCT device 1 is approximately set to a predetermined position by alignment via the alignment mechanism 13. Therefore, individual differences in the position of the corneal apex relative to the SD-OCT device 1 are minimal.

[0049] Furthermore, when the measurement object is a retina, the control unit 10 drives the mirror via the adjustment mechanism 11 to adjust the zero point position of the measurement arm to a predetermined distance behind the cornea. The axial length of the eye (the distance between the corneal apex and the retina) varies from person to person and varies from eye to eye. Therefore, the position of the retina relative to the SD-OCT device 1 may vary from person to person. That is, the assumed position of the retina of the subject's eye on the optical path 43 varies from person to person, resulting in variation in the optical path length x from the zero point of the measurement arm to the measurement object. The magnitude of variation in the optical path length x is calculated by multiplying the value defined as the individual difference in axial length (the difference between the maximum and minimum assumed axial lengths) by the refractive index of the vitreous body.

[0050] In this embodiment, the individual difference in axial length is found from Reference 1 below. Reference 1: C McAlinden, Axial Length Measurement Failure Rates With Biometers Using Swept-Source Optical Coherence Tomography Compared to Partial-Coherence Interferometry and Optical Low-Coherence Interferometry ” AMERICAN JOURNAL OF OPHTHALMOLOGY Elsevier 2017 In Reference 1, the maximum assumed value of axial length is 26.56 mm, and the minimum assumed value of axial length is 20.36 mm. Therefore, the individual difference in axial length is defined as 26.56 mm - 20.36 mm = 6.2 mm. The magnitude of variation that can occur in the optical path length x due to this individual difference in axial length is 8.2832 mm, which is the value obtained by multiplying this value (6.2 mm) by the refractive index of the vitreous body (1.336). From the above, it is assumed that in the SD-OCT device 1 that measures the corneal apex and retina, the optical path length x may vary by 8.2832 mm depending on individual differences in axial length. Therefore, in this embodiment, the optical path length x is assumed to vary within a range of 8.2832 mm, and the range of optical path length x is assumed to be 0 mm to 8.2832 mm. Therefore, in this embodiment, the expected maximum value of optical path length x is 8.2832 mm, which is the magnitude of variation corresponding to individual differences in axial length. Assuming that the optical path length x is 8.2832 mm, the expected minimum value wl of the average wavelength of the detection signal is calculated in advance using Equation (3) from the optical path length x, the minimum wavelength λ1 and the maximum wavelength λ2 of the wavelengths of light that can be received by the light receiving unit 15, and the length L of the light receiving unit 15.

[0051] The SD-OCT device 1 of this embodiment is designed so that the spot diameter ω5 of the wavelength component with a predetermined center wavelength λ0 is equal to or smaller than the minimum value wl assumed as the average wavelength of the predetermined detection signal, i.e., so as to satisfy the relationship of the following equation (11).

[0052]

number

[0053] In this embodiment, the transmitter 44a, dispersing member 44d, dispersing member 44e, lens 44f, and light-receiving unit 15 used in the SD-OCT device 1 are predetermined. The positional relationship between the dispersing member 44d, dispersing member 44e, lens 44f, and light-receiving unit 15 is also predetermined. Therefore, parameters other than f1 in equation (11) can be determined from the transmitter 44a, dispersing member 44d, dispersing member 44e, lens 44f, light-receiving unit 15, and their positional relationship. Therefore, when designing the SD-OCT device 1 of this embodiment, a lens with a focal length f1 that satisfies equation (11) is selected as the lens 44c. This allows the spot diameter ω5 of the wavelength component with the center wavelength λ0 in the SD-OCT device 1 to be equal to or less than the minimum value wl assumed as the average wavelength of the detection signal.

[0054] Here, the intention behind designing the spot diameter ω5 of the wavelength component with the central wavelength λ0 to be equal to or smaller than the minimum value wl assumed as the average wavelength of the detection signal will be described with reference to FIG. Each wavelength component of the interference light is focused to a finite size on the light-receiving unit 15. Therefore, wavelength components corresponding to peaks in the detection signal detected via the light-receiving unit 15 and wavelength components corresponding to adjacent peaks (for example, the wavelength components corresponding to peaks P1 and P2 in FIG. 6) are also focused to a finite size on the light-receiving unit 15. The circles around peaks P1 and P2 in FIG. 6 indicate the spot diameters of the wavelength components in this case. As in the example of FIG. 6, these wavelength components may at least partially overlap on the light-receiving unit 15. In particular, as the optical path length x from the zero point in the measurement arm to the object to be measured increases, the average wavelength of the detection signal becomes shorter and the distance between peaks in the detection signal becomes shorter, increasing the likelihood that wavelength components corresponding to adjacent peaks will overlap on the light-receiving unit 15. In this way, when different wavelength components corresponding to adjacent peaks in the detection signal overlap, it becomes difficult to distinguish between the wavelength components in the overlapping portion, and the accuracy of detecting the intensity of each wavelength component via the light-receiving unit 15 decreases. As a result, the accuracy of measuring the position of the measurement object in SD-OCT also decreases. Therefore, in this embodiment, the spot diameter of the wavelength component of a predetermined wavelength (center wavelength λ0) focused on the light receiving unit 15 is set to be equal to or less than the minimum value assumed as the average wavelength of the detection signal detected through the light receiving unit 15, thereby reducing the overlap between wavelength components corresponding to the peaks of the detection signal.

[0055] As described above, the configuration of the SD-OCT device 1 of this embodiment makes it possible to make the spot diameter of the wavelength component of a predetermined wavelength in the interference light focused on the light receiving unit 15 equal to or less than the average wavelength of the detection signal. This reduces the overlap between signals corresponding to adjacent peaks in the detection signal, and makes it possible to suppress a decrease in accuracy in SD-OCT measurements. In this embodiment, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component with the central wavelength λ0 as the predetermined wavelength is equal to or less than the average wavelength of the detection signal. This reduces the overlap of the wavelength component that mainly contributes to the measurement with other wavelength components, and further suppresses the deterioration of the accuracy of the SD-OCT measurement.

[0056] Furthermore, in this embodiment, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component of a predetermined wavelength in the interference light focused on the light-receiving unit 15 is equal to or smaller than the minimum value expected as the average wavelength of the detection signal. In this embodiment, the measurement object includes the retina of the eyeball. When the measurement object is a retina, the position of the retina varies due to individual differences. In SD-OCT, if the measurement object is not present within a range where good measurement is possible, the reference arm may be adjusted, the zero point of the measurement arm may be moved, and the range where good measurement is possible may be shifted. In other words, adjusting the reference arm may be time-consuming. As such, SD-OCT can be time-consuming for measurement objects whose position varies from individual to individual. In this embodiment, if the position of the measurement object is within the expected range of variation, the spot diameter of the wavelength component of a predetermined wavelength in the interference light focused on the light-receiving unit 15 is equal to or smaller than the average wavelength of the detection signal. Therefore, if the position of the measurement object is within the expected range of variation, overlap between wavelength components corresponding to peaks in the detection signal is reduced, thereby suppressing a decrease in the accuracy of SD-OCT measurements. As a result, the SD-OCT device 1 is more likely to be able to perform accurate measurements within the range of expected variations in the position of the measurement object, and can reduce the likelihood of having to adjust the reference arm.

[0057] (2) Axial length measurement process: The axial length measurement process executed by the SD-OCT device 1 of this embodiment will be described with reference to Fig. 7. The control unit 10 starts the process of Fig. 7 at a specified timing after the subject's eye to be examined is placed at a predetermined position. In step S100, the control unit 10 detects the position of the corneal apex of the examinee's eye, which is located at a predetermined position, via the alignment mechanism 13, and adjusts the position of the SD-OCT device 1 so that the detected corneal apex position has a predetermined positional relationship with the SD-OCT device 1. After completing the processing of step S100, the control unit 10 proceeds to step S105.

[0058] In step S105, the control unit 10 adjusts the reference arm to the corneal reference arm by moving the mirror 12 via the adjustment mechanism 11. After completing the process of step S105, the control unit 10 advances the process to step S110. In step S110, the control unit 10 causes the light source 14 to output light and detects the intensity of the interference light for each wavelength component via the light receiving unit 15. Based on the intensity of the interference light detected for each wavelength component, the control unit 10 identifies the position of the corneal apex of the subject's eye in the optical path 43. After completing the process of step S110, the control unit 10 advances the process to step S115.

[0059] In step S115, the control unit 10 adjusts the reference arm to the retina reference arm by moving the mirror 12 via the adjustment mechanism 11. In this embodiment, as described above, if the position of the measurement object is within the expected range of variation, the spot diameter of the wavelength component of a predetermined wavelength in the interference light focused on the light receiving unit 15 is equal to or less than the average wavelength of the detection signal. Therefore, if the position of the measurement object is within the expected range of variation, overlap between wavelength components corresponding to peaks in the detection signal is reduced. In other words, since the measurement object can be measured with sufficient accuracy within the expected range of variation, adjustment of the reference arm is not required. Therefore, in this embodiment, after adjusting the reference arm to the retina reference arm via the adjustment mechanism 11, the control unit 10 controls the adjustment mechanism 11 not to adjust the reference arm, i.e., adjust the optical path length of the reference light, until the position of the retina is identified. This allows the control unit 10 to reduce the processing load by not performing unnecessary processing via the adjustment mechanism 11. After completing the process of step S115, the control unit 10 advances the process to step S120.

[0060] In step S120, the control unit 10 causes the light source 14 to emit light, and detects the intensity of the interference light for each wavelength component via the light receiving unit 15. The control unit 10 identifies the position of the retina of the subject's eye in the optical path 43 based on the intensity of the interference light detected for each wavelength component. In step S125, the control unit 10 acquires the difference between the position of the retina identified in step S120 and the position of the corneal apex identified in step S115 as the axial length.

[0061] (3) Other embodiments: The above-described embodiment is an example of how the present invention can be implemented, and various other embodiments are possible. Therefore, at least a portion of the configuration of the above-described embodiment may be omitted or replaced.

[0062] In the above-described embodiment, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component with a central wavelength λ0 as a predetermined wavelength component in the interference light on the light receiving unit 15 is equal to or less than the average wavelength of the detection signal. However, the predetermined wavelength here may be a wavelength different from the central wavelength λ0.

[0063] For example, the predetermined wavelength may be λ2, the longest wavelength of light that can be received by the light receiving unit 15. In this case, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component of the wavelength λ2 in the interference light on the light receiving unit 15 is equal to or smaller than the average wavelength of the detection signal. This spot diameter is calculated, for example, as follows. The MFD of the wavelength component of wavelength λ2 output from the transmitting unit 44a is calculated from the wavelength λ2, the core diameter of the transmitting unit 44a, and the refractive index of the core and cladding of the transmitting unit 44a. Furthermore, the angle of incidence and diffraction angle of the wavelength component of wavelength λ2 incident on the dispersive member 44d are calculated using a method similar to that of the above-described embodiment. Similarly, the angle of incidence and diffraction angle of the wavelength component of wavelength λ2 incident on the dispersive member 44e are calculated. The calculated MFD, angle of incidence at the dispersive member 44d, angle of incidence at the dispersive member 44e, angle of diffraction at the dispersive member 44d, and angle of diffraction at the dispersive member 44e are substituted for ω1, α1, α2, β1, and β2 in equation (10), respectively. Furthermore, f2 / f1 is substituted for Power in equation (10). As a result, the spot diameter of the wavelength component of wavelength λ2 in the interference light focused on the light receiving unit 15 is calculated as ω5.

[0064] The longer the wavelength of light incident on the diffraction grating, the larger the diffraction angle β. Therefore, the longer the wavelength of light, the smaller the cos(β i ) becomes smaller, and (cos(α i ) / cos(β i Therefore, (cos(α i ) / cos(β i )) is largest for wavelength λ2.

[0065] The MFD is also defined by the following equation (12): In equation (12), λ represents the wavelength of light propagating through the optical fiber, θ represents the radiation angle of the light relative to the propagation axis of the optical fiber, and F(θ) represents the electric field distribution of the far field pattern (FFP).

[0066]

number

[0067] As shown in equation (12), the MFD increases as the wavelength (λ) of light increases. That is, the MFD for the wavelength component of wavelength λ2 is greater than the MFD for wavelength components of wavelengths shorter than λ2. Therefore, ω1 in equation (10) is greatest for wavelength λ2. As a result, of the spot diameters of the wavelength components focused on the light receiving section 15, the spot diameter for the wavelength λ2 is the largest. Therefore, by designing the spot diameter of the wavelength component of wavelength λ2 on the light receiving unit 15 to be equal to or less than the average wavelength of the detection signal, the spot diameters of the wavelength components corresponding to all peaks in the detection signal will be equal to or less than the average wavelength of the detection signal. In other words, wavelength components corresponding to all adjacent peaks in the detection signal will not overlap on the light receiving unit 15. This allows the SD-OCT device 1 to further suppress a decrease in the accuracy of SD-OCT measurements.

[0068] The predetermined wavelength may also be the smallest wavelength λ1 among the wavelengths of light that can be received by the light receiving unit 15. In this case, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component of the wavelength λ1 in the interference light on the light receiving unit 15 is equal to or smaller than the average wavelength of the detection signal.

[0069] In the above-described embodiment, the central wavelength λ0 is the central wavelength of the wavelength band of the light output from the light source 14. However, the central wavelength λ0 may be another wavelength. For example, the central wavelength λ0 may be a wavelength near the center of the wavelength band of the light output from the light source 14, but different from the central wavelength of this wavelength band. For example, the central wavelength λ0 may be any wavelength within a predetermined width (e.g., 5% of the entire wavelength band) at the center of the wavelength band of the light output from the light source 14, but different from the central wavelength of this wavelength band. The central wavelength λ0 may be the wavelength of light received by a central light-receiving element among multiple light-receiving elements arranged in a line in the light-receiving unit 15. The central wavelength λ0 may also be the average value of the maximum value λ2 and the minimum value λ1 of the wavelength of the light received by the light-receiving unit 15.

[0070] In the above-described embodiment, the expected individual difference in axial length is 6.2 mm, which is the value determined from Reference 1. However, the expected individual difference in axial length may be other values. For example, the expected individual difference in axial length may be a value obtained from Reference 2 below. Reference 2: JB. Jonas, “Retinal Thickness and Axial Length” IOVS the Association for Research in Vision and Ophthalmology (ARVO) 2016

[0071] In Reference 2, the assumed maximum value of axial length is 28.68 mm, and the assumed minimum value of axial length is 20.29 mm. Therefore, the individual variability in axial length determined from Reference 2 is 28.68 mm - 20.29 mm = 8.39 mm. In the measurement arm, this individual variability in axial length can result in a variation in the optical path length of 11.20904 mm, which is the value obtained by multiplying this individual variability (8.39 mm) by the refractive index of the vitreous body (1.336). Therefore, the range of variation in optical path length x is assumed to be 0 mm to 11.20904 mm. The assumed maximum value of the optical path length x from the zero point in the measurement arm to the measurement object is 11.20904 mm. Therefore, assuming that the optical path length x is 11.20904 mm, the minimum value wl expected as the average wavelength of the detection signal is calculated in advance using equation (3) from the optical path length x, the minimum wavelength λ1 and the maximum wavelength λ2 of the wavelengths of light that can be received by the light receiving unit 15, and the length L of the light receiving unit 15. The SD-OCT device 1 may be designed so that the spot diameter of the wavelength component of the predetermined wavelength in the interference light is equal to or smaller than the wl calculated here.

[0072] The estimated individual difference in axial length may be a value obtained from Reference 3 below. Reference 3: Markus Kohlhaas, “Effect of Central Corneal Thickness, Corneal Curvature, and Axial Length on Applanation Tonometry” American Medical Association 2006 In Reference 3, the estimated maximum axial length is 32.93 mm, and the estimated minimum axial length is 18.84 mm. Therefore, the individual variability in axial length calculated from Reference 2 is 32.93 mm - 18.84 mm = 14.09 mm. In this case, multiplying this value by the refractive index of the vitreous body (1.336) yields 18.82424 mm, which is the magnitude of variation in the optical path length from the zero point in the measurement arm to the object being measured. Here, it is assumed that the optical path length x varies within a range of 0 mm to 18.82424 mm. In this case, assuming that the optical path length x = 18.82424 mm, the estimated minimum value wl of the average wavelength of the detection signal can be calculated in advance using Equation (3) based on the optical path length x, the minimum and maximum wavelengths λ1 and λ2 of the wavelengths of light that can be received by the light receiving unit 15, and the length L of the light receiving unit 15. The SD-OCT device 1 may be designed so that the spot diameter of the wavelength component of the predetermined wavelength in the interference light is equal to or smaller than the wl calculated here.

[0073] In the above-described embodiment, the SD-OCT device 1 is designed so that the spot diameter of the wavelength component of the predetermined wavelength in the interference light is equal to or less than the mean wavelength wl of the detection signal when the optical path length x is at the maximum expected value. However, the SD-OCT device 1 may also be designed so that the spot diameter of the wavelength component of the predetermined wavelength in the interference light is equal to or less than the mean wavelength wl calculated from equation (3) when the optical path length x is a value different from the maximum expected value (for example, the median of the expected variation in the optical path length x, or any value within the range of the expected variation in the optical path length x).

[0074] In the above-described embodiment, the control unit 10 adjusts the reference arm by moving the mirror 12 via the adjustment mechanism 11. However, the control unit 10 may adjust the reference arm using other methods. For example, assume that multiple optical systems forming multiple optical paths with different optical path lengths are provided as optical paths in the optical path 42 following the output end of the transmission unit 42a. A rotary mirror is provided to change the direction of travel of light traveling along the optical path 42 to one of these optical systems. In this case, for example, the adjustment mechanism 11 is a mechanism that rotates the rotary mirror. The control unit 10 may adjust the reference arm by adjusting the angle of the rotary mirror provided on the optical path 42 via the adjustment mechanism 11 to direct the reference light to one of these optical systems.

[0075] In the above embodiment, the spot diameter of the wavelength component of the predetermined wavelength focused on the light receiving unit 15 is calculated using equation (10). However, the spot diameter of the wavelength component of the predetermined wavelength focused on the light receiving unit 15 may be calculated using other methods. For example, an optical filter may be applied to the interference light output from the transmitting unit 44a to block wavelength components other than the predetermined wavelength, thereby focusing only the wavelength component of the predetermined wavelength on the light receiving unit 15. Then, the diameter of the wavelength component focused on the light receiving unit 15 may be measured to determine the spot diameter of the wavelength component of the predetermined wavelength focused on the light receiving unit 15. In this case, the SD-OCT device 1 may be designed so that the measured spot diameter is equal to or smaller than the average wavelength of the detection signal.

[0076] In the above-described embodiment, the SD-OCT device 1 is designed by selecting the lens 44c so that the spot diameter of a predetermined wavelength component of the interference light is equal to or smaller than the average wavelength of the detection signal. However, the SD-OCT device 1 may be designed by selecting a member other than the lens 44c. For example, if each element constituting the optical system 44b is predetermined, parameters other than ω1 in equation (11) are predefined. In this case, the optical fiber constituting the transmission unit 44a may be selected so that the MFD for the predetermined wavelength becomes ω1 that satisfies equation (11). The SD-OCT device 1 may also be designed by selecting multiple elements from among the elements constituting the optical path 44.

[0077] In the above-described embodiment, the measurement object is the corneal apex and the retina of the subject's eye. However, the measurement object may be another object such as another part of the subject's eye (a part of the cornea other than the corneal apex, the iris, the conjunctiva, etc.). In the above embodiment, the number n of dispersion members included in the optical system 44b is set to 2. However, n may be set to 1, or may be set to 3 or more. In the above-described embodiment, the SD-OCT device 1 is configured as a Michelson interferometer as an interferometer that generates interference light. However, the SD-OCT device 1 may be configured as another interferometer such as a balanced Michelson interferometer or a Mach-Zehnder interferometer.

[0078] The value defined as the possible individual difference in the axial length of an eyeball may be a value defined as the individual difference in axial length based on the results of measuring the axial lengths of a plurality of eyeballs, for example, the value may be the difference between the minimum and maximum values ​​of the actual measurements of the axial lengths of the eyeballs of a plurality of people. [Explanation of symbols]

[0079] 1...SD-OCT device, 10...control unit, 11...adjustment mechanism, 12...mirror, 13...alignment mechanism, 14...light source, 15...light receiving unit, 30...branching unit, 41...optical path, 41a...transmission unit, 42...optical path, 42a...transmission unit, 42b...collimator, 43...optical path, 43a...transmission unit, 43b...collimator, 44...optical path, 44a...transmission unit, 44b...optical system, 44c...lens, 44d...dispersion member, 44e...dispersion member, 44f...lens

Claims

1. a light source that outputs light containing a plurality of wavelength components; a branching unit that branches the light output from the light source into at least a reference light that follows a reference optical path and a measurement light that is irradiated onto a measurement object; a transmitting unit that transmits interference light between the reference light and the measurement light returned from the measurement object; a light receiving section in which a plurality of light receiving elements are arranged in a line; an optical system that disperses the interference light output from the transmitting unit and collects the light on the light receiving unit for each wavelength component; Equipped with An SD-OCT device in which the diameter of the wavelength component of a predetermined wavelength that is focused on the light receiving unit by the optical system is equal to or less than the minimum value of the average wavelength of a wave-like signal detected through the light receiving unit by receiving the interference light.

2. 2. The SD-OCT apparatus according to claim 1, wherein the predetermined wavelength is a central wavelength of the light.

3. 2. The SD-OCT apparatus according to claim 1, wherein the predetermined wavelength is the maximum wavelength among the wavelength components that can be received by the light receiving unit.

4. the transmission unit is an optical fiber, the optical system comprises one or more dispersive elements; The diameter of the wavelength component of the predetermined wavelength that is condensed onto the light receiving unit by the optical system is determined by the following: a mode field diameter (MFD) when the wavelength component of the predetermined wavelength is output from the transmitting unit; a magnification power of the optical system; the number n of the dispersive members included in the optical system; and an incident angle α when the wavelength component of the predetermined wavelength passes through each of the n dispersive members. １ ~α ｎ and the diffraction angle β １ ~β ｎ The SD-OCT apparatus according to any one of claims 1 to 3, wherein the value is calculated from equation (1) based on the above. [Equation 1]

5. 5. The SD-OCT apparatus according to claim 4, wherein the interference light incident on the dispersion member is parallel light.

6. the measurement object is a retina, The minimum value of the average wavelength is determined by dividing the optical path length x, which is the difference between the maximum and minimum values ​​defined as individual differences that may occur in the axial length of the eyeball, by the minimum wavelength λ among the plurality of wavelengths corresponding to the plurality of wavelength components received by the light receiving unit. １ and maximum wavelength λ ２ and the length L of the light receiving portion, based on the value calculated from equation (2). [Equation 2]

7. 7. The SD-OCT apparatus according to claim 6, wherein the optical path length x is any one of 8.2832 mm, 11.20904 mm, and 18.82424 mm.

8. an adjustment mechanism used to adjust the optical path length of the reference light; a control unit that, when a predetermined object is measured as the measurement target, adjusts the optical path length of the reference light using the adjustment mechanism for measuring the predetermined object, and controls so as not to adjust the optical path length of the reference light using the adjustment mechanism while the measurement of the predetermined object is being performed; The SD-OCT apparatus according to any one of claims 1 to 7, further comprising:

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