Flow velocity measurement method and flow velocity measurement device

Abstract

This flow velocity measurement method comprises: a heating step (S102) for heating a part of a medium; a first optical measurement step (S101) for acquiring a first image of observation illumination light that has passed through the medium, at a first timing; a second optical measurement step (S103) for acquiring a second image of observation illumination light that has passed through the medium, at a second timing which is after the first timing and which is during or after execution of the heating step; a first refractive index distribution change calculation step (S104) for calculating first information pertaining to a change in refractive index distribution based on the heat distribution of the medium on the basis of the first image and the second image; and a flow velocity calculation step (S105) for calculating the flow velocity of the medium on the basis of the first information pertaining to the change in the refractive index distribution.

Description

Flow velocity measurement method and flow velocity measurement device

[0001] The present invention relates to a flow velocity measurement method and a flow velocity measurement device.

[0002] High intraocular pressure (IOP) is one of the causes of glaucoma, which has been increasing in recent years. High intraocular pressure damages the optic nerve and causes visual field loss. Normally, intraocular pressure is maintained by a balance between the production and drainage of aqueous humor produced within the eye. High intraocular pressure is caused by a decrease in the drainage function of Schlemm's canal and trabeculae, which are the drainage channels for aqueous humor.

[0003] For the diagnosis and treatment of glaucoma, it is important to understand the detailed dynamics of aqueous humor, such as evaluating aqueous humor flow rate and identifying areas where flow is blocked. Identifying the affected area will enable the selection of safer, more effective, and customized treatments, such as minimally invasive glaucoma surgery.

[0004] As a technique for understanding the flow of aqueous humor within the eye, for example, Patent Document 1 discloses a technique in which a traceable component such as a dye or fluorescent substance is locally administered to the aqueous humor to visualize and monitor the flow of aqueous humor.

[0005] WO 2003 / 073968

[0006] However, the technique disclosed in Patent Document 1 requires the use of a syringe or the like to administer the traceable component into the aqueous humor, which is undesirable from the viewpoint of invasiveness.

[0007] In addition to the flow of aqueous humor in the eye, there is also a need in various fields to non-invasively grasp very weak fluid flows (microflow rates) or invisible fluid flows. Specific examples include grasping the state of flow of water, oil, gas, etc. in order to detect the presence or absence of water, oil, or gas leaks and their causes, grasping the state of blood flow in the human body, and verifying the processing accuracy of microchannels.

[0008] An object of the present invention is to provide a flow velocity measurement method and a flow velocity measurement device that can estimate the flow state of a fluid non-invasively.

[0009] The flow velocity measurement method according to the present invention includes a heating step of heating a portion of a medium, a first optical measurement step of acquiring a first image of the observation illumination light that has passed through the medium at a first timing, a second optical measurement step of acquiring a second image of the observation illumination light that has passed through the medium at a second timing that is after the first timing and that is during or after the heating step, a first refractive index distribution change calculation step of calculating first information regarding a change in refractive index distribution based on the thermal distribution of the medium based on the first image and the second image, and a flow velocity calculation step of calculating the flow velocity of the medium based on the first information regarding the change in refractive index distribution.

[0010] In this method, a part of the medium is heated in a heating step, images of the medium before and after heating are acquired in a first optical measurement step and a second optical measurement step, and the flow velocity of the medium is calculated based on these images. This method can be performed without using a syringe or the like, and can estimate the flow state of a fluid non-invasively.

[0011] Furthermore, when acquiring the heat distribution of a medium after heating, it is also possible to use, for example, a thermal camera. However, since a thermal camera observes the heat on the surface of the medium, it cannot directly observe the heat inside the medium. As a result, temporal and spatial blurring occurs in the process of the heat propagating to the observation surface, making it difficult to measure flow velocity with high temporal and spatial resolution. Therefore, the flow velocity measurement method according to the present invention calculates information regarding changes in the refractive index distribution based on the heat distribution in the medium, and calculates the flow velocity of the medium based on this information. This makes it possible to achieve flow velocity measurement with high temporal and spatial resolution.

[0012] The flow velocity measuring device according to the present invention includes a heating means for heating a portion of a medium, a light source unit for emitting observation illumination light to the medium, an optical unit for reflecting or scattering the observation illumination light that has passed through the medium, a light detection unit for capturing the observation illumination light reflected or scattered by the optical unit to obtain an image, a refractive index distribution change calculation means for calculating first information regarding a change in the refractive index distribution of the medium based on a first image and a second image obtained at different times by the light detection unit, and a flow velocity calculation means for calculating the flow velocity of the medium based on the first information regarding the change in refractive index distribution.

[0013] The flow velocity measuring device according to the present invention comprises a heating means for heating a portion of the aqueous humor in the eye, a light source unit for emitting observation illumination light to the aqueous humor, a light detection unit for capturing the observation illumination light that passes through the aqueous humor and is reflected or scattered by the iris in the eye to obtain an image, a refractive index distribution change calculation means for calculating first information regarding changes in the refractive index distribution of the aqueous humor based on a first image and a second image obtained at different times by the light detection unit, and a flow velocity calculation means for calculating the flow velocity of the aqueous humor based on the first information regarding changes in the refractive index distribution.

[0014] 1 is a block diagram showing the configuration of a flow velocity measurement device 100 according to a first embodiment. FIG. 2 is a schematic diagram showing an optical arrangement L100 of the flow velocity measurement device 100. FIG. 3 is a schematic diagram for explaining heating of a medium ME and heat distribution. FIG. 4 is a block diagram showing an example of the configuration of an analysis means 130. FIG. 5 is a schematic diagram showing a change in heat distribution according to a flow in the medium ME. FIG. 6 is a block diagram for explaining a flow velocity measurement method according to the present embodiment. FIG. 7 is an example of the timing for acquiring a reference image and a heated image. FIG. 8 is an example of the timing for acquiring a reference image and a heated image. FIG. 9 is an example of the timing for acquiring a reference image and a heated image. FIG. 10 is a schematic graph showing a method for processing a speckle image. FIG. 11 is a schematic graph showing a method for processing a speckle image. FIG. 12 is a schematic graph showing a method for processing a speckle image. FIG. 13 is a schematic diagram for explaining a method for calculating a flow velocity. FIG. 14 is an example of measuring the change over time in a thermal change contrast ratio RC. FIG. 15 is a schematic diagram showing an optical arrangement L200 of a modified example of the first embodiment. FIG. 16 is a block diagram showing the configuration of a flow velocity measurement device 200 according to a second embodiment. FIG. 17 is a schematic diagram for explaining an example of the shape of a heated portion to be generated in the eye to be examined EY. FIG. 22 is a schematic diagram for explaining an analysis method corresponding to FIG. 18. FIG. 23 is a schematic diagram for explaining an analysis method corresponding to FIG. 18. FIG. 24 is a schematic diagram for explaining an example of the shape of a heated portion to be generated in the eye to be examined EY. FIG. 25 is a schematic diagram for explaining an analysis method corresponding to FIG. 22. FIG. 26 is a schematic diagram for explaining an example of the shape of a heated portion to be generated in the eye to be examined EY. FIG. 27 is a block diagram showing the configuration of a flow velocity measurement device 300 according to a third embodiment. FIG. 28 is a schematic diagram showing an optical arrangement L400 of a fourth embodiment.

[0015] Next, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, the following drawings are schematic, and for the sake of convenience, some configurations may be omitted. Furthermore, parts common to multiple embodiments are given the same reference numerals, and descriptions thereof may be omitted.

[0016] [First embodiment] [Flow velocity measurement device 100] Fig. 1 is a block diagram showing the configuration of a flow velocity measurement device 100 according to the first embodiment. Fig. 2(a) and Fig. 2(b) are schematic diagrams showing an optical arrangement L100 of the flow velocity measurement device 100.

[0017] 1, the flow velocity measurement device 100 according to this embodiment includes a heating means 110 for heating a part of the medium ME to be measured, an optical measurement means 120 for measuring the medium ME, and an analysis means 130 for analyzing the output from the optical measurement means 120. An optical unit 160 is disposed behind the medium ME.

[0018] The flow velocity measurement device 100 generates a heat distribution in the medium ME using the heating means 110, measures the temporal change in the refractive index distribution in the medium ME according to the heat distribution using the optical measurement means 120, and analyzes the change using the analysis means 130, thereby measuring the flow state of the medium ME. The flow state includes information such as the flow velocity in the medium ME and the direction of flow in the medium ME.

[0019] The medium ME is a fluid, such as a liquid or a gas.

[0020] The heating means 110 is a means capable of heating only a portion of the medium ME. The heating means 110 generates, for example, heating light 110a and irradiates and focuses the heating light 110a on a portion of the medium ME. A heated portion ME_H is generated in a portion of the medium ME, centered on the area where the heating light 110a is focused. The heating means 110 has, for example, a first light source that generates the heating light 110a. The first light source may be, for example, a monochromatic light source having an intensity peak at a single wavelength. The first light source may be, for example, a laser or other light source.

[0021] The heating light 110a exhibits an intensity peak at, for example, a first wavelength. The optical absorption coefficient AB1 of the medium ME at the first wavelength is relatively high. As a result, the heating light 110a is strongly absorbed in the heated portion ME_H, causing a local temperature rise. The first wavelength can be appropriately selected depending on the optical absorption characteristics of the medium ME to be measured.

[0022] The heating light 110a may be capable of spatial scanning within the medium ME. For example, in the configurations shown in Figures 2(a) and 2(b), the heating means 110 may have an optical rail, an optical mirror, or the like so that the heating light 110a can be irradiated at specific positions in the X and Y directions within the medium ME. The heating means 110 may also have a focusing means, such as a focusing lens, so that the heating light 110a can be irradiated at specific positions in the Z direction within the medium ME.

[0023] Furthermore, the intensity of the heating light 110a may be modulated over time.

[0024] The optical measuring means 120 is a means for optically measuring a change in the refractive index distribution based on the thermal distribution of the medium ME. The optical measuring means 120 includes, for example, a light source unit 121 and a light detecting unit 122.

[0025] The light source unit 121 generates, for example, observation illumination light 121a and irradiates the observation illumination light 121a onto the medium ME and the optical unit 160. The light source unit 121 includes, for example, a second light source that generates the observation illumination light 121a. The second light source may be, for example, a monochromatic light source having an intensity peak at a single wavelength, a white light source, or another light source. The second light source may be, for example, a coherent light source such as a laser, an incoherent light source such as a monochromatic or white LED, or another light source.

[0026] The observation illumination light 121a exhibits an intensity peak at, for example, the second wavelength. The optical absorption coefficient AB2 of the medium ME at the second wavelength is relatively low. As a result, the observation illumination light 121a is hardly absorbed by the medium ME, and the temperature of the medium ME is not increased by the observation illumination light 121a. The second wavelength can be appropriately selected depending on the optical absorption characteristics of the medium ME to be measured.

[0027] The light absorption coefficient AB1 of the medium ME at the first wavelength is greater than the light absorption coefficient AB2 at the second wavelength, for example, 10 times or more the light absorption coefficient AB2.

[0028] For example, if the medium ME is water, the first wavelength of the heating light 110a may be 1550 nm, and the second wavelength of the observation illumination light 121a, 121b may be approximately 700 nm to 1000 nm. When such wavelengths are selected, the light absorption coefficient AB1 of water at the first wavelength is 100 times or more the light absorption coefficient AB2 of the second wavelength. By selecting such wavelengths according to the medium ME, sufficient heat generation can be induced at a small focal point within the medium ME, while at the same time preventing the medium from heating due to the observation illumination light 121a, 121b.

[0029] The light detection unit 122 detects observation illumination light 121b, which is a component of the observation illumination light 121a that has been reflected or scattered by the optical unit 160. The observation illumination light 121b also has the same wavelength distribution as the observation illumination light 121a. The light detection unit 122 may be, for example, a camera that has a lens, an image sensor, etc., and is capable of capturing an image of the optical unit 160 irradiated with the observation illumination light 121a. Alternatively, the light detection unit 122 may be an image sensor, a photodiode array, etc., instead of a camera.

[0030] The image sensor or photodiode array or the like included in the light detection unit 122 has sufficient sensitivity to the second wavelength of the observation illumination light 121a, 121b. For example, if the second wavelength is in the visible to near-infrared region, the image sensor may be a CMOS sensor, a CCD sensor, or the like containing a material such as Si. For example, if the second wavelength is in the near-infrared to infrared region, the image sensor may be an image sensor containing a material such as InGaAs.

[0031] The light detection unit 122 may have no optical sensitivity or may have a sufficiently low optical sensitivity to the first wavelength of the heating light 110a. The light detection unit 122 may further include an optical filter that cuts off the first wavelength.

[0032] The optical unit 160 is, for example, a screen on which the light detection unit 122 captures an image. The optical unit 160 is, for example, an optical member capable of uniformly reflecting the second wavelength of the observation illumination light 121 a, 121 b at a predetermined viewing angle. The optical unit 160 may have, for example, a minute illuminance distribution pattern (e.g., a concave-convex pattern) on its surface on the medium ME side, which can project an image.

[0033] [Optical Arrangement L100] Next, the optical arrangement L100 of the flow velocity measurement device according to this embodiment will be described with reference to FIGS. 2(a) and 2(b).

[0034] 2(a) and 2(b), in the optical arrangement L100, the heating means 110, the light source unit 121, and the light detection unit 122 are arranged in front of the medium ME, and the optical unit 160 is arranged behind the medium ME. 2(a) and 2(b) show examples of the optical paths of the observation illumination light 121a and the observation illumination light 121b in the same optical arrangement L100.

[0035] 2A, the observation illumination light 121a is emitted from the light source unit 121, passes through a region of the medium ME that includes the heated portion ME_H, and then reaches the optical unit 160. Of the observation illumination light 121a, a component of the observation illumination light 121b that is reflected or scattered by the optical unit 160 passes through a region of the medium ME that does not include the heated portion ME_H, and enters the light detection unit 122.

[0036] 2B, the observation illumination light 121a is emitted from the light source unit 121, passes through a region of the medium ME that does not include the heated portion ME_H, and then reaches the optical unit 160. A component of the observation illumination light 121a that is reflected or scattered by the optical unit 160 passes through a region of the medium ME that includes the heated portion ME_H, and then enters the light detection unit 122 as observation illumination light 121b.

[0037] In the optical arrangement L100, as shown in FIGS. 2A and 2B, the optical axis AX11 of the light source unit 121, the optical axis AX21 of the light detection unit 122, and the optical axis AX31 of the heating means 110 intersect with each other.

[0038] Fig. 3 is a schematic diagram for explaining heating and heat distribution in the medium ME. Fig. 3 shows the focused spot SP of the heating light 110a irradiated into the medium ME, and the heated portion ME_H in the medium that occurs when the focused spot SP is maintained for a predetermined irradiation time t. The upper part of Fig. 3 shows a surface in the medium ME that is perpendicular to the optical axis AX31 of the heating means 110. The lower part of Fig. 3 shows a surface in the medium ME that is parallel to the optical axis AX31 of the heating means 110.

[0039] 3, immediately after irradiation of the heating light 110a begins, a minute heat source is generated in the focused spot SP due to light absorption. The focused spot SP has, for example, a diameter D10 in a plane perpendicular to the optical axis AX31. This minute heat source quickly expands due to thermal diffusion, generating a heated portion ME_H. The heated portion ME_H has, for example, a diameter D11 in a plane perpendicular to the optical axis AX31. The diameter D11 is determined, for example, by the diameter D10 and a thermal diffusion length LT, which indicates the degree of thermal diffusion.

[0040] The thermal diffusion length LT is calculated, for example, by the following equation 1 when the medium ME has a thermal diffusion coefficient α and the irradiation time t of the heating light 110a has elapsed. As shown in Equation 1, the thermal diffusion length LT is expressed as double the square root of the product of the thermal diffusion coefficient α of the medium ME and the irradiation time t.

[0041] In this embodiment, the diameter D10 of the focused spot SP is set to be sufficiently smaller than the thermal diffusion length LT. In such a case, the thermal diffusion length LT becomes the dominant factor in determining the diameter D11 of the heated portion ME_H, and a heated portion ME_H of a stable size can be formed regardless of the diameter of the focused spot SP. The diameter D10 of the focused spot SP is set to be, for example, 1 / 5 to 1 / 10 or less of the thermal diffusion length LT of the medium ME.

[0042] For example, if the medium ME is water and the irradiation time t is 1.0 second, the thermal diffusion length LT is about 780 μm. In this case, the diameter D10 of the focused spot SP is set to, for example, about 30 to 60 μm.

[0043] Furthermore, for example, as shown in Figure 3, when forming a focused spot SP by focusing the heating light 110a, the width F20 of the focal depth that satisfies the diameter D10 of the focused spot SP is set to be approximately the same as the width F10 of the flow path of the medium ME or smaller than the width F10 of the flow path of the medium ME.

[0044] FIG. 4 is a block diagram showing an example of the configuration of the analysis means 130. As shown in FIG.

[0045] 4, the analysis means 130 includes a CPU 131, a ROM 132, a RAM 133, a storage device 134, a display processing unit 135, a display device 136, an input unit 137, and a communication interface unit 138. The analysis means 130 also includes a bus BS for transmitting control signals, data signals, etc.

[0046] The CPU 131 loads various programs stored in the ROM 132 or the storage device 134 into the RAM 133 and executes them. In this embodiment, the CPU 131 reads out and executes the programs stored in the ROM 132 or the storage device 134, thereby realizing the functions of a refractive index distribution change calculation means 140 and a flow velocity calculation means 150, which will be described later.

[0047] The storage device 134 may be, for example, a non-volatile storage device such as a flash memory, an SSD, a magnetic storage device (e.g., an HDD), an optical disk, or a volatile storage device such as a RAM. The storage device 134 stores programs executed by the CPU 131 and data referenced by the CPU 131.

[0048] The display processing unit 135 displays the display data calculated by the CPU 131 on the display device 136. The display device 136 may be, for example, a liquid crystal display.

[0049] The input unit 137 includes a group of buttons for accepting user operation inputs, and an interface circuit for recognizing operation inputs such as pressing of each button and outputting the inputs to the CPU 131. For example, a touch panel input method may be adopted as the input unit 137.

[0050] For example, the light detection unit 122 of the optical measurement means 120 (FIG. 1) is connected to the communication interface unit 138. When the light detection unit 122 is a camera or the like, the communication interface unit 138 is configured to be able to acquire images transmitted from the light detection unit 122.

[0051] The heating means 110 (FIG. 1) may be connected to the communication interface unit 138. In such a case, the analyzing means 130 may be configured to be able to control the irradiation of the heating light 110a from the heating means 110 to the medium ME, for example, the spatial scanning and temporal intensity modulation of the heating light 110a.

[0052] Furthermore, not all of these means are essential components of the analysis means 130, and the functions of the analysis means 130 can be changed as appropriate, taking into account the type of medium ME, the surrounding environment, weather conditions, the purpose of the flow velocity measuring device 100, the calculation load of the analysis means 130, etc.

[0053] [Flow velocity measurement method] [Measurement of heat distribution] A flow velocity measurement method using the flow velocity measurement device 100 configured as above will be described with reference to Figures 5 to 14. Figure 5 is a schematic diagram showing a change in heat distribution according to the flow in the medium ME.

[0054] As shown in the left part of Fig. 5, the heated portion ME_H generated in the medium ME by the heating means 110 becomes a point heat source. As shown in the center part of Fig. 5, the point heat source quickly diffuses heat within the medium ME. At this time, as shown in the right part of Fig. 5, if there is a flow within the medium ME, the heat distribution due to thermal diffusion changes depending on the direction of the flow. In this way, the flow state of the medium can be measured from the shape of the heat distribution and its change over time.

[0055] FIG. 6 is a block diagram for explaining the flow velocity measuring method according to this embodiment.

[0056] In step S101 (FIG. 6), at least one frame of a reference image is acquired. The reference image is acquired by the optical measurement means 120, for example, before the heating means 110 heats the medium ME (step S102). Such a reference image is an image captured by the observation illumination light 121b transmitted through the medium ME in which no heated portion ME_H is generated. The reference image is transmitted to the analysis means 130, for example, via the communication interface unit 138 (FIG. 4), as appropriate.

[0057] Next, in step S102 (FIG. 6), heating of a part of the medium ME is started. The heating is performed by the heating means 110.

[0058] Next, in step S103 (FIG. 6), at least one frame of a heated image is acquired. The heated image is acquired by the optical measurement means 120 during or after the heating means 110 is running. The heated image is an image captured by the observation illumination light 121b that has passed through the medium ME in which the heated portion ME_H is generated. The heated image is transmitted to the analysis means 130 as appropriate, for example, via the communication interface unit 138 (FIG. 4).

[0059] Next, in step S104 (FIG. 6), the refractive index distribution change amount is calculated using the reference image and the heated image. The refractive index distribution change amount is calculated by the refractive index distribution change calculation means 140 included in the analysis means 130.

[0060] Next, in step S105 (FIG. 6), the flow velocity of the medium ME is calculated. The flow velocity is calculated by the flow velocity calculation means 150 included in the analysis means 130.

[0061] 6, step S101 for acquiring the reference image may be performed after step S102 and before step S103. Such a reference image is an image obtained by the observation illumination light 121b transmitted through the medium ME in which the heated portion ME_H is generated.

[0062] 7 shows an example of the timing for acquiring the reference image and the heated image, and is a specific example of steps S101 to S103 shown in FIG.

[0063] In the example shown in FIG. 7, step S101 is performed at timing t101 before heating starts, and a reference image is acquired.

[0064] Next, at timing t102 after timing t101, the heating means 110 is turned on to start the execution of step S102, and heating of the medium is started.

[0065] Next, step S103 is performed from timing t103 after timing t102, and a heated image is acquired. Step S103 may be performed multiple times at predetermined intervals from timing t103.

[0066] Next, at timing t104 after timing t103, the heating means 110 is turned off to end the execution of step S102 and terminate the heating of the medium.

[0067] Next, at timing t105 after timing t103, acquisition of the heated image is completed. Timing t105 may be before timing t104 or after timing t104. That is, step S103 (acquisition of the heated image) may be completed before turning off the heating means 110, or may be continued for a predetermined time (between timing t104 and timing t105) after turning off the heating means 110.

[0068] It is to be noted that the time from timing t101 to timing t102 is preferably as short as possible in order to reduce noise such as disturbance of the fluid.

[0069] FIG. 8 shows another example of the timing for acquiring the reference image and the heated image. In the example shown in FIG. 7, the heating means 110 is always ON in step S102. However, for example, in step S102, the intensity of the heating light 110a (FIGS. 2A and 2B) may be temporally modulated. More specifically, for example, in step S102, the heating means 110 may be periodically turned ON / OFF. In the example shown in FIG. 8, a cycle PE1 including turning the heating means 110 ON and OFF is repeatedly performed. Below, one cycle PE1 including timings t111 to t115 will be described.

[0070] In the example shown in FIG. 8, step S101 is performed at timing t111 before the start of heating, and a reference image is acquired.

[0071] Next, at timing t112 after timing t111, the heating means 110 is turned on to start or resume heating of the medium ME. In the first cycle PE1, timing t112 is the timing at which step S102 starts to be executed.

[0072] Next, step S103 is performed from timing t113 after timing t112, and a heated image is acquired. The heated image may be acquired multiple times at predetermined intervals from timing t113.

[0073] Next, at timing t114, the heating means 110 is turned off to interrupt or terminate heating of the medium. In the final cycle PE1, timing t114 is the timing at which execution of step S102 ends.

[0074] Incidentally, step S103 (acquisition of a heated image) may be performed within a predetermined time after the heating means 110 is turned off, as shown at timing t115.

[0075] 9 shows another example of the timing of acquiring a reference image and a heated image. In the example shown in FIG. 9, multiple image sets including image sets IS1 to IS3 are acquired. Each of these multiple image sets includes one frame of a reference image and one frame of a heated image acquired after a waiting time t2 from the time the reference image is acquired.

[0076] In the example shown in FIG. 9, step S101 is performed at timing t301 before the start of heating, and a reference image included in image set IS1 is acquired.

[0077] Next, at timing t302 after timing t301 and before the start of heating, step S101 is performed to acquire a reference image included in image set IS2.

[0078] Next, at timing t303 after timing t302, the heating means 110 is turned ON to start the execution of step S102, and heating of the medium is started.

[0079] Next, at timing t304 after timing t303, when the waiting time t2 has elapsed since timing t301, step S103 is performed to acquire the heated images included in the image set IS1.

[0080] Next, at timing t305, which is after timing t303 and after the waiting time t2 has elapsed since timing t302, step S103 is performed to acquire heated images included in image set IS2.

[0081] 9, step S101 is executed multiple times at regular intervals from timings t301 and t302 before the start of step S102 until timing t307 (described later) after the end of step S102, thereby acquiring a reference image. Similarly, step S103 is executed multiple times at regular intervals from timings t304 and t305 after the start of step S102 until timing t308 (described later) after the end of step S102, thereby acquiring heated images. In this way, another image set (not shown) is acquired.

[0082] Next, at timing t306 after timing t305, the heating means 110 is turned off, the execution of step S102 is completed, and heating of the medium is completed.

[0083] In order to measure the process of heat dissipation after heating is completed, an image set IS3 as shown in FIG. 9 may be acquired after timing t306 when heating of the medium is completed.

[0084] In such a case, for example, at timing t307 after timing t306 when heating of the medium is completed, step S101 is performed to acquire a reference image included in image set IS3.

[0085] Next, after timing t307, at timing t308 when the waiting time t2 has elapsed since timing t307, step S103 is performed to acquire the heated images included in image set IS3.

[0086] As in the example shown in FIG. 8, in the example shown in FIG. 9, the heating means 110 may be repeatedly turned on and off, and a set of images corresponding to the cyclic heating may be periodically acquired.

[0087] In the example shown in FIG. 9, the time (waiting time t2) that elapses between acquiring the reference image and the heated image can be shortened, so that changes in heat distribution can be detected with low noise.

[0088] [Calculation of Refractive Index Distribution Change Amount] The refractive index distribution change calculation means 140 calculates information regarding the change in refractive index distribution of the medium ME using the reference image and the heated image.

[0089] [Speckle Method] An example of using the speckle method as a refractive index distribution change calculation means will be described below with reference to Fig. 10 to Fig. 13. Fig. 10 is an example of a speckle image. Fig. 11 to Fig. 13 are schematic graphs showing a method of processing a speckle image.

[0090] In the speckle method, observation illumination light 121a is irradiated onto a medium ME, and an optical unit 160 such as a screen is photographed by a light detection unit 122 to obtain a speckle image such as that shown in FIG.

[0091] When the speckle method is used, the second light source that generates the observation illumination light 121a may be, for example, a laser with high coherence.

[0092] The speckle image is an image resulting from interference with an irregular phase relationship when the observation illumination light 121a is scattered by the optical unit 160 and reaches the light detection unit 122. The speckle image also changes as the wavefront changes depending on the refractive index distribution inside the medium ME through which the observation illumination light 121a and 121b pass before reaching the light detection unit 122. For example, if the temperature of the heated portion ME_H ( FIG. 1 ) rises due to the heating light 110a and the refractive index changes accordingly, the brightness distribution of the corresponding portion of the speckle image also changes.

[0093] The amount of change in the luminance distribution of the speckle image can be calculated from the difference between the heated image and the reference image described with reference to Figures 6 to 9. The amount of change in the luminance distribution of the speckle image corresponds to the amount of change in the heat distribution.

[0094] First, the luminance distributions of the reference image and the heated image are obtained. In Fig. 11, the luminance Iref of the reference image at the pixel position in the speckle image is shown by a solid line, and the luminance In of the heated image is shown by a dashed line. In the example shown in Fig. 11, the luminance In of the heated image changes in the direction away from the heating center position relative to the luminance Iref of the reference image.

[0095] Next, the difference between the luminance In and the luminance Iref as shown in FIG. 11 is calculated, and the absolute value of the difference as shown in FIG. 12 is calculated.

[0096] Next, various filter processes are performed on the absolute values ​​of the differences as shown in Fig. 12 to obtain evaluation values ​​as shown in Fig. 13. The peak position of the evaluation value corresponds to, for example, the center position of the heated portion ME_H (Fig. 1), and the width of the evaluation value corresponds to, for example, the width of the heat distribution that changes depending on the flow inside the medium ME, centered on the heated portion ME_H. For the filtering process, for example, a Gaussian filter or the like may be used.

[0097] By performing the processing shown in FIGS. 11 to 13 on the entire image, the heat distribution of the medium ME can be calculated.

[0098] 11 to 13, the absolute value of the difference between the luminance In and the luminance Iref may be normalized by the sum of the luminance In and the luminance Iref, thereby eliminating the influence of the luminance distribution that occurs within the image.

[0099] In the medium ME, speckles fluctuate due to disturbances even in unheated areas. Therefore, when performing the processing described above, for example, accuracy can be improved by updating the reference image, which is used to calculate the difference from the heated image, at regular intervals or by shortening the intervals, as described with reference to Figures 8 and 9.

[0100] Additionally, multiple summing measurements may be performed to remove background noise and increase SNR, eliminating any remaining speckle patterns.

[0101] In addition to the above-described method of calculating the absolute value of the difference in brightness values, a projected speckle method may be used in which a speckle pattern is projected onto the optical unit 160 and a change in refractive index distribution is analyzed based on the displacement of the speckle pattern detected by the light detection unit 122.

[0102] Next, a method for measuring the direction and speed of a fluid flow using the flow velocity calculation means 150 will be described. When a fluid in the medium ME is moving, the heat distribution obtained by a speckle method or the like changes over time. FIG. 14 is a schematic diagram for explaining a method for calculating the flow velocity. The image shown in FIG. 14 is a heat distribution image obtained from a differential image between a reference image and a heated image in the speckle method, for example.

[0103] In the method for calculating the flow velocity, for example, as shown in Figure 14, regions 1 and 2 are set in the difference image along the direction of the flow for which the flow velocity is to be calculated. Next, the average luminance values ​​calculated for regions 1 and 2 are obtained as evaluation values ​​I_R1 and I_R2, respectively. Next, the thermal change contrast ratio RC is calculated, for example, using the following evaluation formula: The evaluation formula shown in Equation 2 can determine the flow direction based on the sign of the thermal change contrast ratio R. Furthermore, since an increase in the absolute value of the thermal change contrast ratio R corresponds to an increase in the flow speed, Equation 2 can be used to calculate the flow velocity.

[0104] [Example] Figure 15 shows an example of measuring the change over time in the thermal change contrast ratio RC. In this measurement example, water enclosed between a glass plate and a scattering plate was irradiated with laser light from the glass plate side, thereby partially heating the water. Speckle images were obtained by irradiating the scattering plate with observation illumination light from the glass plate side and photographing the scattering plate. Furthermore, the change over time in the thermal change contrast ratio RC was measured when the enclosed water flowed upward or downward, and the flow rates between the glass plate and the scattering plate were 0.18 mL / min, 0.36 mL / min, and 0.9 mL / min, respectively.

[0105] As shown in Figure 15, when the flow direction of the medium ME was upward, the sign of the thermal change contrast ratio RC was positive, and when it was downward, the sign of the thermal change contrast ratio RC was negative. In this way, the sign of the thermal change contrast ratio RC was reversed depending on the flow direction. Furthermore, the faster the flow, the larger the absolute value of the thermal change contrast ratio RC. As described above, the flow speed and flow direction can be calculated by evaluating the sign and absolute value of the thermal change contrast ratio RC.

[0106] [Effects] In the flow velocity measurement method according to this embodiment, a part of a medium is heated in a heating step, and images of the medium before and after heating are acquired in a first optical measurement step and a second optical measurement step, and the flow velocity of the medium is calculated based on these images. This method can be performed without using a syringe or the like to inject a traceable component, and it is possible to estimate the flow state of a fluid non-invasively.

[0107] Furthermore, when acquiring the thermal distribution of the medium after heating, for example, a thermal camera or the like can be used. However, with a thermal camera, temporal and spatial blurring occurs during the heat propagation process, making it difficult to measure flow velocity with high temporal and spatial resolution. Therefore, the flow velocity measurement method according to this embodiment can achieve high temporal and spatial resolution flow velocity measurement by observing changes in the refractive index distribution based on the thermal distribution in the medium ME.

[0108] 16(a) and 16(b) are schematic diagrams showing an optical arrangement L200 according to a modification of the first embodiment. In this modification, an example will be described in which the flow velocity measurement device 100 according to the first embodiment includes an optical arrangement L200 (FIGS. 16(a) and 16(b)) instead of the optical arrangement L100 (FIGS. 2(a) and 2(b)).

[0109] As shown in Figures 16(a) and 16(b), the optical arrangement L200 (Figures 16(a) and 16(b)) is basically configured in the same way as the optical arrangement L100 (Figures 2(a) and 2(b)). However, in the optical arrangement L200, the light source unit 121 has an optical axis AX12, the light detection unit 122 has an optical axis AX22, and the heating means 110 has an optical axis AX32.

[0110] 16(a) and 16(b), the optical axis AX12 of the light source unit 121 and the optical axis AX32 of the heating unit 110 are parallel to each other. On the other hand, the optical axis AX22 of the light detection unit 122 intersects with the optical axis AX12 of the light source unit 121 and the optical axis AX32 of the heating unit 110.

[0111] In this modified example, the optical axes of the light source unit 121 and the heating means 110 are parallel to each other, but the optical axes of the heating means 110, the light source unit 121, and the light detection unit 122 may all be arranged to be parallel to each other, or any two of the heating means 110, the light source unit 121, and the light detection unit 122 may be arranged to be parallel to each other and the other may be arranged to intersect.

[0112] [Second Embodiment] [Flow Velocity Measurement Device 200] Fig. 17 is a block diagram showing the configuration of a flow velocity measurement device 200 according to the second embodiment. In this embodiment, an example will be described in which the flow state of aqueous humor in an eye to be examined EY is measured using the flow velocity measurement device 200. As shown in Fig. 17, the eye to be examined EY includes a cornea, a crystalline lens, and aqueous humor ME2 filled between the cornea and the crystalline lens.

[0113] The flow velocity measurement device 200 ( FIG. 17 ) according to this embodiment has basically the same configuration as the flow velocity measurement device 100 ( FIG. 1 ) according to the first embodiment. Furthermore, the flow velocity measurement method according to this embodiment is basically the same as the flow velocity measurement method according to the first embodiment. However, the measurement target of the flow velocity measurement device 200 according to this embodiment is aqueous humor ME2 contained in the subject's eye EY. The iris 161 is located behind a portion of the aqueous humor ME2. The light detection unit 122 of the flow velocity measurement device 200 photographs the iris 161 ( FIG. 17 ) rather than the optical unit 160 ( FIG. 1 ).

[0114] The flow velocity measuring device 200 generates a heat distribution including a heated portion ME2_H in the aqueous humor ME2 using the heating means 110, measures the temporal change in the refractive index distribution in the aqueous humor ME2 corresponding to the heat distribution using the optical measuring means 120, and analyzes the change using the analyzing means 130, thereby measuring the flow state of the aqueous humor ME2. The flow state of the aqueous humor includes information such as the speed and direction of the aqueous humor flow.

[0115] The aqueous humor ME2 is a transparent liquid present in the front part of the eye EY. The aqueous humor ME2 has a flow direction FL as shown in FIG.

[0116] The iris 161 basically has the same function as the optical unit 160. The iris 161 reflects, for example, the observation illumination light 121a and functions as a screen for the light detection unit 122 to capture an image.

[0117] 17 , when measuring the aqueous humor ME2, the observation illumination light 121a is emitted from the light source unit 121, passes through a portion of the aqueous humor ME2 including the heated portion ME2_H, and then reaches the iris 161. Of the observation illumination light 121a, a component of the observation illumination light 121b that is reflected or scattered by the iris 161 passes through a portion of the aqueous humor ME2 that does not include the heated portion ME2_H, and enters the light detection unit 122.

[0118] Unlike the example shown in Figure 17, the observation illumination light 121a when measuring the aqueous humor ME2 is emitted from the light source unit 121, passes through a portion of the aqueous humor ME2 that does not include the heated portion ME2_H, and then reaches the iris 161.The observation illumination light 121b, which is a component reflected or scattered by the iris 161, may pass through a portion of the aqueous humor ME2 that includes the heated portion ME2_H and enter the light detection unit 122.

[0119] 3 in the aqueous humor ME2, the focal depth width F20 that satisfies the diameter D10 of the focal spot SP is set equal to or smaller than the distance from the cornea to the iris 161. The distance from the cornea to the iris 161 is, for example, about 1.5 mm.

[0120] [Flow Velocity Measurement Method] The flow velocity measurement method using the flow velocity measurement device 200 is basically the same as the flow velocity measurement method using the flow velocity measurement device 100. However, the flow velocity measurement device 200 may also apply flow velocity measurement methods as described with reference to FIGS. 18 to 24. FIGS. 18, 22, and 24 are schematic diagrams for explaining examples of the shapes of heated portions generated in the subject's eye EY. FIGS. 19 and 23 are schematic diagrams for explaining heat distributions corresponding to FIGS. 18 and 22, respectively. FIGS. 20 and 21 are schematic diagrams for explaining an analysis method.

[0121] In the example shown in Fig. 18, a heated area ME2_Ha is generated in the measurement target portion of the eye EY. The heated area ME2_Ha is a point-like heat source. The heat distribution including the heated area ME2_Ha is expanded into polar coordinates from the center of the heated area ME2_Ha according to the angle RA_sp, and the heat distribution TD1(RA_sp) at the angle RA_sp is obtained, as shown in the upper right part of Fig. 19. In the example shown in Fig. 19, the heat distribution corresponding to the reference angle of 0 degrees is represented by the heat distribution TD1(0). The angle RA_sp corresponds to the flow direction FL for which the flow speed is to be obtained. The deformation amount of the heat distribution TD1(RA_sp) corresponds to the flow speed at the angle RA_sp.

[0122] To determine the deformation of the thermal distribution TD1(RA_sp), for example, as shown in Fig. 20, a rectangular region corresponding to the angle RA_sp may be defined as Region 1 (Fig. 14), and a rectangular region corresponding to the diagonal position of the angle RA_sp (angle RA_sp + 180°) may be defined as Region 2 (Fig. 14), and the thermal change contrast ratio RC may be calculated. This allows the flow speed in each flow direction (angle RA_sp) to be analyzed, as shown in the lower right part of Fig. 19.

[0123] Note that, for example, two diagonally positioned fan-shaped regions may be set as region 1 and region 2, as shown in Fig. 21. In such a case, the fan-shaped region within a certain angle range centered on angle RA_sp may be set as region 1 (Fig. 14), and the fan-shaped region within a certain angle range centered on the diagonal position of angle RA_sp (angle RA_sp + 180°) may be set as region 2 (Fig. 14), and the thermal change contrast ratio RC may be calculated. This method also makes it possible to analyze the flow speed in each flow direction (angle RA_sp), as shown in Fig. 19.

[0124] In the example shown in FIG. 22 , a heated area ME2_Hb is generated in the measurement target portion of the eye EY. The heated area ME2_Hb is, for example, a ring-shaped heat source surrounding the pupil. As shown in FIG. 23 , the heat distribution including the heated area ME2_Hb is expanded into polar coordinates from the center of the heated area ME2_Hb (e.g., the center of the pupil) according to the angle RA_rg to determine the heat distribution TD2(RA_rg) at the angle RA_rg. In the example shown in FIG. 23 , the value corresponding to the reference angle of 0 degrees is represented by the value TD2(0). The angle RA_rg corresponds to each direction of flow from the center of the pupil outward. The deformation amount of the heat distribution TD2(RA_rg) corresponds to the flow speed at the angle RA_rg. For example, regions 1 and 2 described with reference to Figures 20 and 21 are set in the direction along each angle RA_rg, and the speed of the flow from the center of the pupil toward the outside can be analyzed using the thermal change contrast ratio RC.

[0125] In the example shown in Fig. 24, multiple heated portions ME2_Ha similar to those shown in Fig. 18 are generated in the measurement portion of the subject's eye EY. The multiple heated portions ME2_Ha are arranged, for example, in a ring-shaped region surrounding the pupil. As in the examples shown in Figs. 18 and 19, each heated portion ME2_Ha may be expanded in polar coordinates according to the angle from the center of the heated portion ME2_Ha to determine the heat distribution at each angle. Furthermore, as in the examples shown in Figs. 22 and 23, the multiple heated portions ME2_Ha arranged in the ring-shaped region may be expanded in polar coordinates according to the angle corresponding to each direction of flow from the center of the pupil outward to determine the flow speed at each angle.

[0126] Third Embodiment Fig. 25 is a block diagram showing the configuration of a flow velocity measurement device 300 according to a third embodiment. The flow velocity measurement device 300 is basically configured in the same manner as the flow velocity measurement device 100 (Fig. 1) and the flow velocity measurement device 200 (Fig. 17). The flow velocity measurement method according to this embodiment is basically the same as the flow velocity measurement method according to the first or second embodiment. However, in this embodiment, an optical unit 162 is used instead of the optical unit 160. In this embodiment, the thermal distribution and the corresponding refractive index distribution are measured using the principle of the BOS (Background Oriented Schlieren) method, rather than the speckle method.

[0127] When the BOS method is used, the second light source that generates the observation illumination light 121a may be an incoherent light source such as a monochromatic or white LED that does not generate speckles.

[0128] The optical section 162 has a luminance distribution pattern PTref that can be imaged by the light detection section 122 on the surface on the side where the observation illumination light 121a is incident.

[0129] The pattern PTref is a pattern, concavities, convexities, etc. on the surface of the optical unit 162 that can be imaged by the light detection unit 122. The pattern PTref may be projected onto the surface of the optical unit 162 from an external projector or the like, or from the light source unit 121. The projector or the like that projects the pattern PTref may have an incoherent light source, such as a monochromatic or white LED that does not generate speckles.

[0130] 25 is the aqueous humor ME2 contained in the subject's eye EY similar to that in the second embodiment, the optical unit 162 may be the iris 161. When the optical unit 162 is the iris 161, the light detection unit 122 captures an image of the unevenness and wrinkles on the surface of the iris 161 as a luminance distribution pattern PTref.

[0131] 25, the image captured by the light detection unit 122 is a luminance distribution pattern PTn. The pattern PTn is a variation of the pattern PTref due to a change in the refractive index distribution in the medium ME. By calculating the difference between the pattern PTref and the pattern Ptn, the change in the refractive index distribution of the medium ME can be analyzed.

[0132] 2(a), the example shown in Fig. 25 is an example in which the observation illumination light 121a passes through a region of the medium ME that does not include the heated portion ME_H, is reflected or scattered by the optical unit 160, and the observation illumination light 121b passes through a region of the medium ME that does not include the heated portion ME_H, and the observation illumination light 121b enters the light detection unit 122. However, the flow velocity measurement device 300 may be configured in a manner similar to the example shown in Fig. 2(b), in which the observation illumination light 121a passes through a region of the medium ME that does not include the heated portion ME_H, is reflected or scattered by the optical unit 160, and the observation illumination light 121b passes through a region of the medium ME that does not include the heated portion ME_H, and the observation illumination light 121b enters the light detection unit 122.

[0133] [Fourth Embodiment] Fig. 26 is a schematic diagram showing an optical arrangement L400 of a fourth embodiment. The flow velocity measurement device 400 according to the fourth embodiment is basically configured in the same manner as the flow velocity measurement device 100 (Fig. 1) and performs measurements in the same manner. However, the flow velocity measurement device 400 according to this embodiment has an optical arrangement L400 (Fig. 26) that is different from the optical arrangement L100 (Figs. 2(a) and 2(b)) according to the first embodiment. Furthermore, in this embodiment, the heat distribution and the corresponding refractive index distribution are measured using the principles of shadowgraphy rather than the speckle method.

[0134] The optical arrangement L400 is basically configured in the same manner as the optical arrangement L100. However, in the optical arrangement L400 ( FIG. 26 ), the heating means 110 and the light source unit 121 are arranged in front of the medium ME, the optical unit 160 is arranged behind the medium ME, and the light detection unit 122 is arranged between the optical unit 160 and the medium ME. In the optical arrangement L400, the medium ME and the optical unit 160 are arranged at a distance from each other.

[0135] In the optical arrangement L400, the observation illumination light 121a is emitted from the light source unit 121, passes through a region including the heated portion ME_H of the medium ME, and then reaches the optical unit 160. Of the observation illumination light 121a, observation illumination light 121b is reflected or scattered by the optical unit 160 and enters the light detection unit 122.

[0136] When the thermal distribution of the medium ME and the corresponding refractive index distribution are uniform, the observation illumination light 121a passing through the medium ME is refracted uniformly, and the luminance distribution when the light detection unit 122 captures an image of the optical unit 160 is uniform. On the other hand, when a gradient occurs in the thermal distribution of the medium ME and the corresponding refractive index distribution, the refraction angles of the multiple light rays contained in the observation illumination light 121a differ, and a luminance distribution of bright areas where the light rays are dense and dark areas where the light rays are sparse occurs in the optical unit 160. By capturing an image of this luminance distribution generated in the optical unit 160 with the light detection unit 122, it is possible to analyze changes in the refractive index distribution of the medium ME.

[0137] In the optical arrangement L400, the longer the distance from the medium ME to the optical unit 160, the more accurately the change in the refractive index distribution of the medium ME can be analyzed.

[0138] In the optical arrangement L400, an example has been shown in which the optical axis AX14 of the light source unit 121, the optical axis AX24 of the light detection unit 122, and the optical axis AX34 of the heating means 110 all intersect with one another. However, the optical axes of these heating means 110, light source unit 121, and light detection unit 122 may all be arranged to be parallel, or any two of these heating means 110, light source unit 121, and light detection unit 122 may be arranged to be parallel and the other optical axis may be arranged to intersect.

[0139] Other Embodiments The flow velocity measurement device and the flow velocity measurement method according to the embodiments have been described above, but these are merely examples, and the specific configurations and the like can be adjusted as appropriate.

[0140] 100...flow velocity measuring device, 110...heating means, 120...optical measuring means, 140...refractive index distribution change calculating means, 150...flow velocity calculating means, 160...optical section

Claims

1. A flow velocity measurement method comprising: a heating step of heating a portion of a medium; a first optical measurement step of acquiring a first image of observation illumination light that has passed through the medium at a first timing; a second optical measurement step of acquiring a second image of the observation illumination light that has passed through the medium at a second timing that is after the first timing and is during or after the heating step; a first refractive index distribution change calculation step of calculating first information regarding a change in refractive index distribution based on the thermal distribution of the medium based on the first image and the second image; and a flow velocity calculation step of calculating the flow velocity of the medium based on the first information regarding the change in refractive index distribution.

2. A flow velocity measurement method according to claim 1, wherein the observation illumination light is emitted from a light source unit, passes through the medium, and is reflected or scattered by an optical unit, and the first image and the second image are obtained by capturing the observation illumination light reflected or scattered by the optical unit with a light detection unit.

3. The flow velocity measurement method according to claim 2, wherein the light source unit and the light detection unit are disposed in front of the medium, and the optical unit is disposed behind the medium.

4. The flow velocity measuring method according to claim 2, wherein the medium is aqueous humor in the eye, and the optical part is the iris in the eye.

5. A flow velocity measurement method according to claim 2, wherein the heating step is performed using a heating light source, and at least two of the optical axes of the heating light source, the light source unit, and the light detection unit are approximately parallel.

6. A flow velocity measuring method according to claim 2, wherein the heating step is performed using a heating light source, and the optical axis of the heating light source, the optical axis of the light source unit, and the optical axis of the light detection unit all intersect.

7. A flow velocity measuring method according to claim 2, wherein the light detecting section acquires a speckle image resulting from interference of the observation illumination light whose wavefront has been changed by the refractive index distribution inside the medium.

8. A flow velocity measuring method according to claim 2, wherein the optical detection unit acquires a light-dark image corresponding to the refractive index distribution of the medium caused by the thermal distribution of the medium.

9. A flow velocity measurement method according to claim 2, wherein the optical unit has a luminance distribution pattern on its surface that can be imaged by the light detection unit, and the light detection unit images a change in the image of the luminance distribution pattern caused by a change in the refractive index distribution of the medium.

10. A flow velocity measuring method according to claim 1, wherein the heating step is performed using a monochromatic light source, and the intensity of the light incident on the medium from the monochromatic light source is modulated over time during the heating step.

11. The flow velocity measuring method according to claim 1, wherein the heating step is performed using a monochromatic light source, and the light incident on the medium from the monochromatic light source is spatially scanned within the medium.

12. A flow velocity measurement method according to claim 1, wherein the heating step is performed using a monochromatic light source that generates light of a first wavelength, the observation illumination light is light of a second wavelength, the light absorption coefficient of the medium at the first wavelength is a first coefficient, the light absorption coefficient of the medium at the second wavelength is a second coefficient, and the first coefficient is 10 times or more the second coefficient.

13. A flow velocity measurement method according to claim 1, wherein the heating step is performed by focusing a monochromatic light source within the medium to a first diameter for a time t, and when the thermal diffusion length in the medium is defined as twice the square root of the value obtained by multiplying the thermal diffusion coefficient of the medium by the time t, the first diameter is 1 / 5 to 1 / 10 or less of the thermal diffusion length.

14. A flow velocity measuring method according to claim 1, wherein an image showing the change in refractive index distribution is obtained as the first information regarding the change in refractive index distribution, and the flow velocity of the medium is calculated based on the brightness of a first region in the image showing the change in refractive index distribution, the first region including a part of the region heated in the heating step, and the brightness of a second region including another part of the region heated in the heating step.

15. A flow velocity measurement method according to claim 1, further comprising: a third optical measurement step of acquiring a third image of the observation illumination light that has passed through the medium at a third timing during or after the heating step and that is later than the second timing; and a second refractive index distribution change calculation step of calculating second information regarding a change in refractive index distribution of the medium based on the first image and the third image, wherein the flow velocity of the medium is calculated based on the first information and the second information regarding the change in refractive index distribution of the medium.

16. A flow velocity measurement method according to claim 15, further comprising the steps of: acquiring an image showing the change in refractive index distribution as the second information relating to the change in refractive index distribution; and calculating the flow velocity of the medium based on the brightness of a first region in the image showing the change in refractive index distribution, the first region including a part of the region heated in the heating step, and the brightness of a second region including another part of the region heated in the heating step.

17. A flow velocity measuring device comprising: a heating means for heating a part of a medium; a light source unit for emitting observation illumination light to the medium; an optical unit for reflecting or scattering the observation illumination light that has passed through the medium; a light detection unit for capturing the observation illumination light reflected or scattered by the optical unit to obtain an image; a refractive index distribution change calculation means for calculating first information regarding a change in refractive index distribution of the medium based on a first image and a second image obtained at different times by the light detection unit; and a flow velocity calculation means for calculating the flow velocity of the medium based on the first information regarding the change in refractive index distribution.

18. A flow velocity measuring device comprising: a heating means for heating a portion of the aqueous humor in the eye; a light source unit for emitting observation illumination light to the aqueous humor; a light detection unit for capturing the observation illumination light that passes through the aqueous humor and is reflected or scattered by the iris in the eye to obtain an image; a refractive index distribution change calculation means for calculating first information regarding changes in the refractive index distribution of the aqueous humor based on a first image and a second image obtained at different times by the light detection unit; and a flow velocity calculation means for calculating the flow velocity of the aqueous humor based on the first information regarding the changes in the refractive index distribution.

Images