WO2021199772A1

WO2021199772A1 - Device for estimating state of eyeball internal tissue and method therefor

Info

Publication number: WO2021199772A1
Application number: PCT/JP2021/006219
Authority: WO
Inventors: ニーラムコーシック; 佳那竹山; 羽根　一博; 敬佐々木; 中澤　徹
Original assignee: 国立大学法人東北大学
Priority date: 2020-03-31
Filing date: 2021-02-18
Publication date: 2021-10-07
Also published as: JPWO2021199772A1; JP7214270B2

Abstract

The present invention estimates the state of an eyeball internal tissue with high accuracy and in a simple manner. A device 1 for estimating the state of an eyeball internal tissue is provided with a first light irradiation unit LU, an imaging unit 20, and a processing unit. The first light irradiation unit LU is disposed at a first position P1 outside an eyeball 40 of a living body, and irradiates a target tissue 44 inside 45 of the eyeball 40 with light. The imaging unit 20 captures an image of light reflected on the inside 45 of the eyeball 40. The processing unit acquires shadow information about the target tissue 44 from first imaging information obtained by the imaging unit 20, and estimates the state of the target tissue 44 from the shadow information.

Description

State estimation device for internal tissue of the eyeball and its method

The present invention relates to an apparatus for estimating the state of the internal tissue of the eyeball and a method thereof.

A method of irradiating the internal tissue of the eyeball with light to image the target tissue is known. For example, an imaging system for eye tissue has been proposed in which an irradiation beam is emitted from different illumination points toward the eye tissue, and light backscattered from at least one of the retina and the iris is collected from the pupil to acquire an image of the fundus. There is. According to this system, it is possible to process an image of the fundus to obtain a phase contrast image and extract information on eyeball tissue from the phase contrast image (see Patent Document 1).

Special Table 2019-518511 Gazette

However, in the above-mentioned imaging system for eye tissue, at least two images captured from two different illumination points are required in order to acquire a phase contrast image. Furthermore, in order to extract information on the eye tissue, a phase contrast image is calculated from the intensities of the two images, and this phase contrast image is reconstructed using an algorithm of a predetermined function to obtain only the phase and absorption information of light. It is necessary to acquire the including image. As described above, in order to extract the information of the eyeball tissue, it is necessary to perform a plurality of processes on the images of the plurality of fundus, which is complicated.

One of the objects of the present invention is to estimate the state of the internal tissue of the eyeball easily and with high accuracy.

Not limited to this purpose, it is also possible that the actions and effects derived from each configuration shown in the “mode for carrying out the invention” described later and which cannot be obtained by the conventional technique are exhibited. It can be positioned as another purpose.

In one aspect, the state estimation device for the internal tissue of the eyeball is arranged at a first position outside the eyeball of the living body, and a first light irradiation unit that irradiates light toward the target tissue inside the eyeball. It includes an imaging unit that captures the light reflected inside the eyeball, acquires shadow information about the target tissue from the first imaging information obtained by the imaging unit, and obtains shadow information about the target tissue from the shadow information of the target tissue. It is provided with a processing unit that estimates the state.

On the other side, the method of estimating the state of the internal tissue of the eyeball irradiates light from the first position outside the eyeball of the living body toward the target tissue inside the eyeball, and the light reflected inside the eyeball. To image. Further, the shadow information about the target tissue is acquired from the first imaged information captured, and the state of the target tissue is estimated from the shadow information.

According to the present invention, the state of the internal tissue of the eyeball can be estimated easily and with high accuracy.

FIG. 1 is a diagram showing a configuration of a state estimation device for an internal tissue of the eyeball according to the first embodiment. FIG. 2 is a cross-sectional view schematically showing the internal structure of the main body of FIG. FIG. 3 is a diagram showing an optical system used by the light irradiation unit and the imaging unit of FIG. FIG. 4 is a block diagram showing the configuration of the control device of FIG. 1 and the function of each device. FIG. 5 is a diagram showing an image captured in the first embodiment, and FIG. 5A shows an example of a marked image with a shadow extracted. FIG. 5B shows a method of acquiring the size of the shadow from the image of FIG. 5A. FIG. 6 is a cross-sectional view schematically showing the internal structure of the main body in the second embodiment. FIG. 7 is a diagram showing an optical system used by the light irradiation unit and the imaging unit of the second embodiment. FIG. 8 is a diagram showing an image captured in the second embodiment. FIG. 9 is a diagram showing the verification results using the model eye. FIG. 9A shows an example of a marked image in which a shadow is extracted, and FIG. 9B shows a method of obtaining the size of a shadow from the image of FIG. 9A. FIG. 10 shows the result of comparing the measurement results by the present state estimation device and the optical coherence tomography (OCT). FIG. 10A shows an image of an enucleated pig eye taken by using a fundus camera, and FIG. 10B shows an intensity-normalized image of the image of FIG. 10A. Further, FIG. 10C shows an image obtained by applying a clustering algorithm using the K-means method to the image of FIG. 10B, and FIG. 10D shows an image obtained by differentiating the image of FIG. 10C.

Hereinafter, embodiments of the present invention relating to the state estimation device for the internal tissue of the eyeball and the method thereof will be described.
Due to the effects of increased intraocular pressure and the like, progressive optic nerve atrophy accompanied by a change in shape near the optic nerve head occurs, and in the process of progression, there is a disease called glaucoma in which the optic nerve fibers are damaged and visual field loss occurs. Due to the disappearance of the optic nerve fibers during the progression of glaucoma, the optic disc 44, as shown in FIG. 2, is often deepened before the visual field loss occurs. Therefore, glaucoma can be detected by observing the three-dimensional shape of the optic nerve head and its temporal change.
In particular, glaucoma is more likely to develop with aging. When glaucoma develops, the optic nerve is gradually damaged and the visual field becomes narrower. However, the symptoms of glaucoma are less likely to be noticed by the patient in the early stages. For this reason, glaucoma tends to delay the start of treatment.
Three-dimensional image analysis of the fundus using an optical coherence tomography (OCT) is known as a method for measuring the optic nerve head, but it is expensive and is currently provided only in specialized hospitals, etc., on a daily basis. It cannot be used by people for inspection. As mentioned above, since glaucoma is difficult to be aware of, subjective symptoms may appear and it may be too late such as blindness by the time you visit a specialized hospital, and many people routinely examine the onset of glaucoma easily. The development of equipment that can be used is important.
In this embodiment, in order to easily and quickly examine the onset of glaucoma, a method of accurately estimating the state of the optic nerve head will be described as an example of the internal tissue of the eyeball, particularly the target tissue.

In this embodiment, the directions of the drawings used in the description are defined as follows.
The horizontal direction is the front-back direction (in the figure, the front is indicated by "F" and the rear is indicated by "B") and the left-right direction (in the figure, the left is indicated by "L" and the right is indicated by "R". It will be described in detail in (shown). Regarding the left-right direction, the left and right are determined based on the state of facing from the rear to the front. In the vertical direction, the direction of action of gravity is downward (indicated by "D" in the figure), and the opposite direction of downward is upward (indicated by "U" in the figure).

[1. First Embodiment]
[1-1. Configuration of state estimation device for internal tissue of the eyeball]
As shown in FIG. 1, in the present embodiment, the state estimation device 1 of the internal tissue of the eyeball including the main body 2 and the control device 3 will be described.
Here, although the example in which the main body 2 and the control device 3 are connected wirelessly is shown, they may be connected by wire.
The main body 2 transmits the captured image to the control device 3. In this example, an image of the light reflected inside the eyeball is transmitted. The main body 2 includes a light irradiation unit 10 and an imaging unit 20. The light irradiation unit 10 and the image pickup unit 20 have an integral structure.
The main body 2 has a size that can be carried by the subject by hand, and can be used, for example, by attaching it to a camera of a portable device.
The control device 3 receives an image from the main body 2 and estimates the state of the internal tissue of the eyeball from the image.

[1-2. Internal structure of main body 2]
As shown in FIG. 2, the light irradiation unit 10 has a housing 11.
Here, the housing 11 is provided with a hole 12 on the rear surface. Since the left and right eyeballs are measured respectively, one hole 12 is provided here, but if it is desired to measure both eyeballs at the same time, two holes 12 may be provided side by side in the left-right direction. .. The holes 12 have a size sufficient to surround the periphery of the eye 4 of the living body. When the rear surface of the housing 11 is brought into contact with the face of the subject so that the hole 12 is aligned with the position of the eye 4 of the subject, a closed space is formed between the periphery of the eye 4 of the living body and the housing 11. ..
It is preferable to provide a flexible member such as rubber around the hole 12 between the hole 12 and the surface in contact with the face of the subject. The flexible member comes into contact with the face around the eye 4 to reduce stray light from the outside, and the deformation of the flexible member makes the optical axis of the imaging unit 20 easier for the subject's eye 4. Can be matched to.

Lighting is provided inside the housing 11. The lighting is an infrared LED. The wavelength of illumination may be visible light or the like, but infrared light is preferable because it does not make the subject feel dazzling and because the penetration depth of light when irradiating through the skin or the like. In the present embodiment, the illumination light is not incident from the cornea through the lens as is generally performed, but is directly irradiated through the sclera of the eyeball 40 or the skin around the eyeball 40. Therefore, there is no need for a mydriatic drug for pupil dilation as used in eye examinations. Here, for example, an LED having an 850 nm wavelength is used. Illumination, because it is installed in the housing 11 inside the upper position, the illumination is referred to as "upper illumination L _U" (first light irradiation part). Also, the installation position of the upper illumination L _U is referred to as "upper position P1" (first position). The upper position P1 will be described later. Although the description will be given here at the upper position P1, the illumination position is not limited to the upper position P1 as long as the light can enter through the sclera or the skin around the eyeball, and the lower position, the right position, and the like. Any position on the left is possible. In this embodiment, oblique / off-axis illumination is mainly used through the sclera and the skin around the eyeball 40. Further, the lighting is not limited to the fixed one, and for example, the lighting can be installed on a rotating member around the outer periphery of the hole 12 in the housing and can be moved so that the irradiation position becomes an appropriate position. You may.

The imaging unit 20 includes a tubular body 21. Inside the tubular body 21, a first lens R1, a second lens R2, a camera 22, and an image sensor 23 are provided.
Here, the first lens R1 and the second lens R2 are existing ophthalmic objective lenses. The first lens R1 is provided at a boundary where the front surface of the housing 11 and the rear surface of the tubular body 21 are connected. The second lens R2 is provided in the central region of the tubular body 21 in the front-rear direction. The first lens R1 and the second lens R2 are for collecting the light reflected inside the eyeball 40 and relaying it to the camera 22.

A camera 22 is provided in front of the second lens R2. The camera 22 captures the light from the second lens R2 and acquires the captured image. The camera 22 includes an image sensor 23. The image sensor 23 forms an image of an image pickup target and converts the light and darkness of the imaged light into an electric signal. The image converted into an electric signal is transmitted to the control device 3. The image pickup unit 20 is an example of an image pickup unit.

[1-3. Optical system]
The optical system used by the light irradiation unit 10 and the image pickup unit 20 will be described with reference to FIGS. 2 and 3.
First, the structure of the eye 4 will be briefly described with reference to FIG. The eyeball 40 is protected by a plurality of membranes. The membranes are arranged in the order of sclera, choroid, and retina 41 from the outside of the eyeball. The light that enters the eyeball 40 from the pupil 42 is sensed by the photoreceptor cells of the retina 41, transmitted to the brain through the optic nerve 43 stretched around the retina 41, and becomes an image. The optic nerve 43, which covers the retina, converges into a single thick bundle at the back of the eyeball. The place where the optic nerve 43 converges into one bundle is called the optic nerve head 44. The optic disc 44 is often recessed. In other words, the shape of the optic nerve head 44 can be regarded as crater-like.

Upper illumination L _U includes, in the casing 11, the optical axis O _L of illumination, the optical axis passing through the pupil 42 of the eye 40 horizontally (eyeball optical axis) against O _E, the predetermined upward It is installed so as to incline at an inclination angle θ1. The predetermined inclination angle θ1 is, the light from the upper illumination L _U, enters the portion other than the pupil 42 of the eye 40 is set to to illuminate the fundus 45, for example 45 °. In other words, the upper position P1 above the illumination L _U is installed is a position 45 ° inclined upward with respect to the hole 12 of the housing 11.

As shown in FIG. 3, the upper illumination L _U emits light toward the upper position P1 in the interior of the eye 40. Here, the light emitted from the upper illumination L _U, directly sclera of the eye 40, and / or through the skin around the eye 40, reaches the retina 41, the interior of the optic disc 44 of the eye 40 The fundus 45 including the fundus 45 is irradiated. The light incident on the eyeball 40 is scattered to some extent inside the eyeball 40, but most of the light is reflected by the fundus 45 and emitted from the pupil 42 to the outside of the eyeball 40.

The first lens R1 (aberration correction lens) of the image pickup unit 20 collects the light emitted from the pupil 42 to the outside of the eyeball 40. The second lens R2 (aberration correction lens) relays the light from the first lens R1 to the image sensor 23.
Imaging range of the fundus 45 is determined by the angle θ2 and the focal length F _L. The angle of view θ2 represents the width of the imaging range in terms of angles. As shown in FIG. 2, the focal length F _L, here, refers to the distance between the center of the focal point F _P and the first lens R1 which light reflected from the fundus 45 gather. To image the fundus 45 in a wide range, it is necessary to set short focal length F _L. _{In the present embodiment, the focal length FL} is set so that the angle of view θ2 is 60 °.
The central axis of the optical axis of the first lens R1 and the second lens R2 coincides with the central axis of the tubular body 21.

As shown in FIG. 3, the camera 22 collects the light relayed from the second lens R2 by a lens (not shown). The focused light is received by the image sensor 23 and is imaged. In the present embodiment, in order to image the fundus 45 is irradiated with light from only the upper lighting L _U, the captured image is referred to as a "single illumination image I _S" (first imaging information).

[1-4. Control device configuration]
The configuration of the control device 3 will be described with reference to FIG.
The control device 3 includes a processing device 30 and a storage device 34. The processing device 30 realizes a function described later by executing a program stored in the storage device 34. In this example, the processing device 30 is a CPU (Central Processing Unit). The processing device 30 may be configured by a DSP (Digital Signal Processor) or a programmable logic circuit device (PLD; Programmable Logic Device). The processing device 30 is an example of a processing unit.

The storage device 34 stores the information readable and writable. For example, the storage device 34 includes at least one of a RAM (Random Access Memory), a ROM (Read Only Memory), an HDD (Hard Disk Drive), an SSD (Solid State Disk), a semiconductor memory, and an organic memory. The storage device 34 may include a recording medium such as a flexible disk, an optical disk, a magneto-optical disk, and a semiconductor memory, and a reading device capable of reading information from the recording medium.
The control device 3 may be realized by an integrated circuit (for example, LSI (Large Scale Integration) or the like).

[1-5. Processing device functions]
As shown in FIG. 4, the function of the processing device 30 includes a shadow information acquisition unit 31, a parameter acquisition unit 32, and a state estimation unit 33.

Shadow information obtaining unit 31 obtains the contour and the shadow S of the optic disk 44 (shadow information) from a single illumination image I _S acquired from the imaging unit 20. (In the present invention, "shadow" refers to the dark portion generated when the light beam is interrupted by the object or the like.) Light irradiated from above the illumination L _U strikes obliquely to the optic disc 44. As described above, since the optic nerve head 44 is recessed, a shadow S is formed in the recess from the direction of light irradiation according to the depth of the recess. Therefore, the single lighting image I _S of the captured light reflected from the fundus 45, includes a shadow S of depression of the optic papilla 44. Single illumination image I _S including shadow S, since it can be said that the sterically captured images of the fundus 45, also referred quasi 3D image.

In Figure 5A, showing an example of a single illumination image _{I S.} FIG. 5A is an actual measurement of pig eyes using the device 1 of the present embodiment.
Shadow information obtaining unit 31 extracts the low lightness region within a single illumination image I _S as a shadow S (a specific, acquisition) is. At the same time, the contour of the optic nerve head 44 is extracted. When the shadow S is extracted by the shadow information acquisition unit 31 using a predetermined threshold value or the like, the shadow information acquisition unit 31 marks a range including the shadow S and its peripheral region. As shown in FIG. 5A, here, the marks are marked with break points.

The parameter acquisition unit 32 acquires the shadow size L (first parameter) from the shadow S acquired by the shadow information acquisition unit 31. The size L of the shadow, in particular, from the upper illumination L _U from the direction the light is irradiated shadow formed in a manner extending in the recess (recesses) of the optic disc 44 length L (recessed edge , The longest length of shadow that extends in the direction of light irradiation (advancing).) The length L of the shade may be obtained directly from the image I _S obtained. However, it may be difficult to accurately obtain the shadow edge when the shadow edge is unclear by the direct method. In the present embodiment, a method of calculating (acquiring) the length L of the shadow S will be described with reference to FIG. 5B.

(0) It is assumed that the parameter acquisition unit 32 in advance, part of a single illumination image I _S including a shadow S of the shadow information obtaining unit 31 obtains (area surrounded by a broken line; see FIG. 5A) images Enlarge and use existing software to emphasize the shadow S.

(1) The length L of the shadow S is acquired by using two circles or ellipses (hereinafter, referred to as "first circle C1" and "second circle C2"). The size of the circles C1 and C2 is preferably large enough to include the shadow S.
First, the shadow S is surrounded by the first circle C1 so that one arc of the shadow S (a part of the arc around the circumference) is inscribed in the first circle C1. Specifically, the shadow S is the first circle along the contour of the recess of the optic disc 44 (preferably the inner contour; where the inner contour refers specifically to the inner edge of the crater-shaped recess). It is desirable to enclose it in C1. However, when the shape is unclear, a part of the arc of the first circle C1 follows a part of the contour (periphery) of the shadow S forming a part of the contour of the recess of the optic nerve head 44. The first circle C1 is placed on the shadow S.

(2) Further, the shadow S is surrounded by the second circle C2 so that the other arc of the shadow S (the other part of the circumference is isolated) is inscribed in the second circle C2. Specifically, the second circle C2 is shadowed so that a part of the arc of the second circle C2 follows a part of the contour (periphery) of the shadow S facing the inner contour of the recess of the optic nerve head 44. Place on S. However, when the shape is unclear, the arc of the second circle C2 follows the contour of the shadow S facing a part of the contour (periphery) of the shadow S along which a part of the arc of the first circle C1 follows. The second circle C2 is placed on the shadow S. Here, a part of the contour of the shadow S on which the second circle C2 is overlapped is different from a part of the contour of the shadow S on which the first circle C1 is overlapped. Therefore, the arc of the second circle C2 intersects the arc of the first circle C1 at two points.

(3) Then, the length of the shadow S surrounded by the arc of the first circle C1 and the arc of the second circle C2 is measured. Here, the virtual coordinates (in FIGS. 2 and 3) in which the upward direction U is the Y axis and the left direction L is the X axis, the origin о coincides with or substantially coincides with the center of one circle, and two circles. C1, so that a line of arc connecting each other point of intersection of C2 is parallel to the Y axis, overlaying a single illumination image I _S. Then, the distance between the points on the arcs of the two circles, which is the width of the shadow S in the X-axis direction, that is, the points on the arcs of the second circle C2 and the arcs of the first circle C1 intersecting the X-axis. Measure the distance between the points. In other words, the length of the shadow S is the width of the area surrounded by the first circle C1 and the second circle C2, and is the line connecting the vertices of the arcs of the intersecting circles C1 and C2. It is the length of a line that is almost vertical. As a result, the shadow length L is accurately acquired.

Next, the parameter acquisition unit 32 is a value representing the size of the optic nerve head 44 different from this size D, based on the length L of the shadow and the size D (diameter; second parameter) of the optic nerve head. Acquire (calculate) d (depth; third parameter).

Here, it is assumed that the shape of the recess of the optic nerve head 44 can be modeled as a crater-shaped parabolic surface, an ellipse, or a spherical surface. When oblique light is incident on such a shape, the depth d of the recess is obtained in a two-dimensional plan projection drawing when a shadow of exactly half the diameter D of the recess is obtained. The shadow length L and the inclination angle θ1 are expressed by the following simple equation 1.

However, the above equation cannot be used for very deep recesses or shallow recesses. Further, it is very difficult to obtain a shadow of exactly half the diameter D in the recess of the optic nerve head 44, which is a complicated elliptical (circular) shape. Shadows that are shorter or longer than half the diameter D can be corrected using an arbitrary correction factor, but they are not accurate.
Therefore, in the present embodiment, the recess of the optic disc 44 is a parabolic curved surface, an ellipse, or a spherical surface having the first circle C1 as the diameter D, and the shape formed by the shadow is the second circle C2. Use the result derived from the calculation expressed as an equation.

Here, the size D of the optic nerve head 44 is the diameter D of the optic nerve head 44, and here, a predetermined literature value (in the case of a human, a general diameter is 1.5 mm) is used. The diameter of the optic nerve head 44 may be estimated from the fundus photograph and used. Further, the value d is, in detail, the depth d of the depression of the optic nerve head 44. When the recess of the optic nerve head 44 is a radial curved surface having the first circle C1 as the diameter D or a spherical surface and the shape formed by the shadow is the second circle C2, the length L of the shadow and the optic nerve head The relationship between the diameter D of 44 and the depth d of the depression of the optic disc 44 is expressed by Equation 2.

When the recess of the optic disc 44 is elliptical, the relationship between the length L of the shadow, the diameter D of the optic disc 44, and the depth d of the recess of the optic disc 44 is determined by Equation 3. expressed.

As shown in FIG. 2, the optical axis O _L of the illumination of the upper illumination L _U is because it is incident on the eyeball 40 with the inclination angle θ1 of 45 °, a tan .THETA.1 = 1. Therefore, the depth d of the depression of the optic nerve head 44 can be obtained by inserting the shadow length L, the diameter D of the optic nerve head 44, and the angle θ1 into the above mathematical formula. Of these, since the diameter D and the angle θ1 of the optic nerve head 44 are preset values, the depth d of the depression of the optic nerve head 44 can be substantially obtained only by acquiring the shadow length L. It is possible to get it.

The state estimation unit 33 acquires the depth d of the depression of the optic disc 44 acquired by the parameter acquisition unit 32, and estimates the state of the optic disc 44. For example, the state estimation unit 33 sets the acquired depth d as a general value (for example, a clinically obtained average value) or a value obtained for each eye 4 of the subject at the time of the previous examination. By comparing, it is estimated whether the condition of the optic disc 44 is normal or abnormal.

[1-6. Storage device functions]
As shown in FIG. 4, the function of the storage device 34 includes a storage unit 35.
The storage unit 35 stores various information used for estimating the state of the optic nerve head 44. Storage unit 35, for example, a single illumination image I _S captured by the imaging unit _20, a single illumination image shadow information obtaining unit 31 is marked I _S, using the parameter acquiring unit 32 and the acquired parameters D, Information including d, L, the estimation result in the state estimation unit 33, and the like is stored. Further, information such as the result detected by the irradiation adjusting unit 37, which will be described later, is stored.

[1-7. motion]
The method of estimating the state of the internal tissue of the eyeball will be described.
First, the hole 12 of the main body 2 is aligned with the position of the eyeball 40, and the rear surface of the housing 11 of the main body 2 is brought into contact with the face of the subject.
Next, light is irradiated toward the upper lighting L _U of the housing 11 to the eye 40 inside the optic disc 44. The optical axis _{O L} of the illumination of the upper illumination _{L U} is inclined by 45 ° upwards with respect to the optical axis _{O E} of the eye 40.
Light emitted from the upper illumination L _U is reflected by the fundus 45 of the eye 40, is emitted from the pupil 42 of the eye 40. The emitted light is collected by the first lens R1 and the second lens R2 of the image pickup unit 20, and is imaged by the camera 22.
Single illumination image I _S captured by the camera 22 is converted into an electric signal by the image sensor 23 of the imaging unit 20, it is transmitted to the processor 30.
If the captured fundus image deviates significantly from the desired position, the subject can easily adjust to the desired position by shifting the direction of the main body 2.

Shadow information obtaining unit 31 of the processor 30 obtains a shadow S of the optic papilla 44 from a single illumination image I _S acquired.
The parameter acquisition unit 32 of the processing unit 30 acquires the length L of the shadow S formed in the recess of the optic nerve head 44 acquired by the shadow information acquisition unit 31. The length L of the shadow S is obtained using the two circles C1 and C2.
Parameter acquisition unit 32, and shadow length L, a and the diameter D of the optic nerve head 44, on the basis of the inclination angle θ1 of upper illumination L _U, to obtain the depth d of the recess of the optic nerve head 44.
The state estimation unit 33 of the processing unit 30 estimates the state of the optic nerve head 44 based on the depth d.

[1-8. Action and effect]
Since the state estimation device for the internal tissue of the eyeball of the present embodiment has the above-described configuration, the following actions and effects can be obtained.
(1) According to this, while the subject is looking straight, it can be acquired that contains the shadow S formed recess of the optic disc 44 by the irradiation light single illumination image I _S. As a result, the state of the optic nerve head 44 can be estimated easily and with high accuracy.
(2) Further, the depth d of the depression of the optic nerve head 44 can be obtained from the length L of the shadow S and the diameter D of the optic nerve head 44. In particular, in the present embodiment, since the diameter D of the optic nerve head 44 adopts the literature value, it is only necessary to obtain the shadow length L. Therefore, the number of parameters required to estimate the state of the optic nerve head 44 is small.
(3) The length L of the shadow S can be extracted using two circles, and does not require specialized knowledge (particularly knowledge of mathematics). Therefore, the parameters necessary for estimating the state of the optic nerve head 44 can be obtained by a simple method.
(4) by irradiating light obliquely against the upper illumination L eye 40 from _U, forcibly without increasing significantly the pupil 42 can image the fundus 45 of the eye 40. Therefore, the burden on the subject is small.

[2. Second embodiment]
The state estimation device for the internal tissue of the eyeball and the method thereof according to the second embodiment will be described with reference to FIGS. 4, 6 and 7. The state estimation device according to the present embodiment is different from the state estimation device according to the first embodiment in that a plurality of lights are provided. Hereinafter, the same reference numerals are given to the configurations common to those of the first embodiment, and the description thereof will be omitted.

[2-1. Internal structure of main body 2]
As shown in FIG. 6, the housing 11 has, in its interior, in addition to the above illumination L _U, comprising a lower illumination is installed in the lower position L _{D (second} light irradiator). The illuminations L _U and L _D are both infrared LEDs.
Lower illumination L _D, similar to the above illumination L _U, the optical axis O _L of illumination, with respect to the optical axis passing through the pupil 42 of the eye 40 horizontally (eyeball optical axis) O _E, a predetermined downward It is installed so as to incline at the inclination angle θ1 of. The predetermined inclination angle θ1 is set similarly to the above illumination L _U, for example to 45 °.

[2-2. Optical system]
The optical system used by the light irradiation unit 10 and the image pickup unit 20 will be described with reference to FIG. 7.
Upper illumination L _U has a light irradiated from the upper position P1, at the same time, the lower the illumination L _D irradiates light from the lower position P2 (second position). Light irradiated upward illumination L _U and lower illumination L eyeball from _D 40 inside the optic disc 44 is directly sclera of the eye 40, and / or through the skin around the eye 40, retina 41 Is reflected by the fundus 45, and is emitted from the pupil 42 to the outside of the eyeball 40. The emitted light is collected by the imaging unit 20 and imaged. Since the image captured by the imaging unit 20 captures two lights, it is referred to as "plural illumination image _IP " (second imaging information). The plurality of illumination images _IP are transmitted from the imaging unit 20 to the processing device 30.

[2-3. Control device configuration]
As shown in FIG. 4, the control device 3 further includes a lighting control device 36 (adjustment unit). The function of the lighting control device 36 includes an irradiation adjusting unit 37. Radiation adjusting section 37 obtains the plurality of illumination images _{I P} from the imaging unit 20, based on the plurality of illumination image _{I P,} adjust the illumination _L U, _{L D.}

Figure 8 shows an example of multiple illumination image I _P.
Radiation adjusting section 37 detects the irradiation state of the illumination _L U, _{L D} lightness of the plurality illumination image _{I P.} Here, plural illumination image I _P, it is seen that light is hitting strong on the left side of the image. Although the optic disc 44 is imaged (region surrounded by a broken line), point low brightness there are a plurality in the plurality of illumination image I _P.

Radiation adjusting section 37, the illumination _L U, from the irradiation condition of the _{L D,} adjusting the direction and the irradiation intensity of the illumination _L U, _{L D.} _{Therefore, the inclination angle θ1 of the illuminations L U} and L _D described in the first embodiment may be changed from 45 °. By changing the tilt angle θ1, the brightness of the image can be further emphasized.
Furthermore, radiation adjusting section 37, any upward illumination L _U and lower illumination L _D may determine whether to get a single illumination image I _S using.

[2-4. Action and effect]
(5) by irradiating the same time upward illumination L _U and the lower lighting L _D, it is possible to obtain a plurality of illumination images I _P of the wide-angle fundus 45. Therefore, the position and angle of the optic nerve head 44 to be imaged can be accurately grasped.
(6) based on the plurality of illumination image I _P, in order to adjust the upper illumination L _U and the lower lighting L _D, it is possible to obtain a single illumination image I _S that includes the clearer shadow S. Therefore, the state of the optic nerve head 44 inside the eyeball 40 can be estimated with even higher accuracy.

[3. Modification example]
[3-1. Modification 1]
The above-described embodiment is merely an example, and there is no intention of excluding the application of various modifications and techniques not specified in this embodiment. Each configuration of the present embodiment can be variously modified and implemented without departing from the gist thereof. In addition, it can be selected as needed and can be combined as appropriate.

For example, two illumination L _U, light is irradiated to the eyeball 40 and different in time from each L _D, may respectively be obtained a single illumination image I _S. In this case, radiation adjusting section 37, by comparing the to do single illumination image I _S acquired, the illumination L _U, may be adjusted L _D. Furthermore, radiation adjusting section 37 may determine whether to obtain more single lighting image I _S using any of the illumination L. Each two illumination L _U, respectively determine the length L of the shade from a single illumination image I _S obtained in L _D, comparison, or, by, for example, taking an average value, it is increased more measurement precision good.

Alternatively, the number of lights may be three or more. In this case, different images can be obtained for the entire fundus 45. Further, the position of the illumination is not limited to the upper side and the lower side, and may be the left side and the right side.

The lighting may be a visible light LED instead of an infrared LED. Visible light can be used to estimate the state of arteries in the fundus 45, including the retina 41. If a shadow is visible in the lower part of the retina 41, an abnormality of the artery in the fundus 45 is presumed. The length of the shadow can be used to determine the presence or absence of arterial bleeding or blood clots.

[3-2. Modification 2]
Here, it may be difficult to accurately identify the shadow of the image from the black-and-white images as shown in FIGS. 5A, 5B, and 8. As the cause, for example, the position of the recess and the shape of the recess can be considered. An example in which the position of the recess is the cause is that there is almost no recess near the center of the optic disc and there is a recess in a portion other than the center of the optic disc. In this case, it is difficult to accurately determine the position (contour) of the recess only by the shade of the shadow on the inner edge of the optic nerve head. Further, an example caused by the shape of the recess is a case where the shadow region formed in the recess is not clear. The shadows formed by an object irradiated with light from a light source are mainly shadows formed when the object completely blocks the light rays (main shadow) and shadows formed when the object partially blocks the light rays (penumbra). The penumbra is not as clear as the main shadow. Since the surface of the recess of the optic nerve head 44 is not flat, a penumbra is often formed in the recess depending on the surface shape of the recess. Therefore, in order to accurately detect shadows from an image with penumbra, it is recommended to apply a method using a clustering-based algorithm that divides the pixels of the image into a specific number of similar or dissimilar groups. preferable. For example, it is preferable to use the K-means clustering, which is the most common clustering algorithm. Further, the image subjected to the processing such as the K-means method may be further differentiated. By processing the image in this way, the shadow region can be specified more clearly.

[4. inspection result]
[4-1. Verification 1]
It was verified whether the depth was accurately calculated from the length of the shadow of the recess of the optic nerve head. The analysis results are evaluated with reference to FIGS. 9A and 9B.
[Optical design of the state estimation device for the internal tissue of the eyeball]
The state estimation device 1 in this demonstration has the same structure as that shown in FIGS. 6 and 7. Specifically, two IR-LEDs (wavelength 850 nm) were used as light sources, and each was arranged so as to be at an angle of 45 ° with respect to the optical axis. The illumination light from the LED has an intensity that does not cause heat damage, and when it passes through the sclera, it diffuses and can uniformly illuminate the internal region of the eyeball 40. A 78D ophthalmic lens (outer angle field of view 60 °, focal length 8 mm) (Righton, Japan) was used as the first lens R1 (objective lens). An aberration correction lens was used as the second lens R2. As the camera 22, the color filter of the camera sensor of the Web camera (Logitech HD Pro Web camera C920) was changed for IR imaging by replacing it with an IR filter. The designed state estimation device was a palm-sized, portable and lightweight size, and had excellent ability to capture a fundus image as shown in FIGS. 9A and 9B.

[Calculation of depth by shadow length]
In the verification, a model eye was created using a 3D printer. The dimensions of the optic disc of the model eye were 3 mm in diameter and 1.5 mm in depth. An aberration-correcting lens with a focal length of 24 mm was used as the eye lens that functions as the pupil of the eye. The eyes of the model eye are filled with water. The model eye was measured using the state estimation device 1.
As shown in FIGS. 9A and 9B, the image of the model eye was able to capture the shadow of light as in the fundus image. The obtained shadow image was analyzed using the method described in this embodiment. Since the model eye has a spherical shape, Equation 2 is used. The depth calculated by the analysis was 1.50 mm, which is consistent with the designed depth.
Therefore, it was confirmed that the actual depth of the optic disc can be obtained from the length of the shadow by using the method described in the present embodiment, and the state of the optic disc can be estimated from this depth.

[4-2. Verification 2]
[Comparison of measurement results of optic disc depth]
Regarding the depth of the optic nerve head, the measurement result using the state estimation device 1 of the present embodiment and the measurement result using the existing OCT were compared.
As a sample, the eyeballs of three excised pigs were prepared.
When the cross-sectional image of the optic nerve head measured by the OCT image was analyzed, the depth at the measured cross-sectional point of these samples varied in the range of 183 μm to 490 μm.
Next, the eyeball of the pig was measured using the state estimation device 1 of the present embodiment. FIG. 10A is a monochrome image of a pig's eyeball obtained by using the state estimation device 1 of the present embodiment. The shadow of the optic nerve head was obtained by tilted light illumination. The shape of the optic nerve head of the porcine eyeball is known to be elliptical. Therefore, the depth of the optic nerve head was calculated using Equation 3.
Further, image processing was performed to obtain an accurate shadow. FIG. 10B is an intensity image in which one pixel is normalized with an intensity of 8 bits (256 levels). FIG. 10C is an image obtained by repeating the K-means method 1000 times. By the K-means method, it was possible to clearly separate the shadowed part from the non-shadowed part.
The image of FIG. 10C was differentiated in order to obtain the shadow length more accurately. FIG. 10D is an image obtained by the differential K-means method obtained by the differential process. The shadow area identified by the differential processing was the area surrounded by the broken line. The diameter of the optic nerve head was about 2.1 mm. The angle of oblique illumination in this image was 45 °. When the depth of the optic disc in various shadow cross sections was calculated using Equation 3, the depth of the optic disc varied from 179 μm to 350 μm. The range of this value was in good agreement (overlap) with the range of the depth value of the optic disc of the porcine eyeball obtained by OCT.
From the above, by using the state estimation device 1 of the present embodiment, the depth of the optic nerve head equivalent to that of the OCT can be easily obtained without using an expensive device such as the OCT. It was proved that the state estimation device 1 of the above is excellent as a simple inspection device.
It is also possible to calculate the volume and area of the optic nerve head from the values obtained by the state estimation device 1 of the present embodiment. In addition, the shape obtained from the shadow can be used to reconstruct the shape of the optic nerve head in 3D, and there is a possibility that the progression of various eye diseases including glaucoma can be easily detected by daily diagnosis.

1 State estimation device for internal tissue of the eyeball 2 Main body 3 Control device 4 Eye 10 Light irradiation unit 11 Housing 12 Hole 20 Imaging unit (imaging unit)
21 Cylinder 22 Camera 23 Image sensor 30 Processing device (processing unit)
31 Shadow information acquisition unit 32 Parameter acquisition unit 33 State estimation unit 34 Storage device 35 Storage unit 36 Lighting control device (adjustment unit)
37 Irradiation adjustment unit 40 Eyeball 41 Retina 42 Pupil 43 Optic nerve 44 Optic nerve papilla 45 Fundus P1 upper position (first position)
P2 lower position (second position)
L _U upper illumination (first illumination unit)
L _D lower illumination (second illumination unit)
O _L illumination optical axis _{O E} eyeball optical axis _{F P} focus _{F L} focal length θ1 inclination angle θ2 angle R1 first lens R2 second lens _{I S} single lighting image (first sensing information)
_IP multiple illumination image (second imaging information)
C1 First circle C2 Second circle S Shadow (shadow information)
L Shadow length (first parameter)
D Diameter of optic disc (second parameter)
d Depth of optic disc depression (third parameter)

Claims

A first light irradiation unit that is placed at a first position outside the eyeball of a living body and irradiates light toward a target tissue inside the eyeball.
It also includes an imaging unit that captures the light reflected inside the eyeball.
The processing unit includes a processing unit that acquires shadow information about the target tissue from the first imaging information obtained by the imaging unit and estimates the state of the target tissue from the shadow information.
A device for estimating the state of internal tissues of the eyeball.
The processing unit
The first parameter representing the magnitude of the shadow information is acquired from the first imaging information, and the shadow information is obtained.
Based on the first parameter and the second parameter representing the size of the target tissue, a third parameter representing the size of the target tissue different from the second parameter is acquired.
The state of the target tissue is estimated from the third parameter.
The state estimation device for an internal tissue of the eyeball according to claim 1.
The acquisition of the first parameter is
Including obtaining the magnitude of the shadow information using at least two circles,
The state estimation device for an internal tissue of the eyeball according to claim 2.
The first position is a position where the optical axis of the light emitted by the first light irradiation unit is inclined at a predetermined angle with respect to the optical axis of the eyeball.
The state estimation device for an internal tissue of the eyeball according to any one of claims 1 to 3.
In addition to the first light irradiation unit,
It is arranged at a second position different from the first position, and includes a second light irradiation unit that irradiates light toward the target tissue inside the eyeball.
The first light irradiation unit and the adjustment unit for adjusting the irradiation of the second light irradiation unit are provided.
The state estimation device for an internal tissue of the eyeball according to any one of claims 1 to 4.
The imaging unit
The second imaging information obtained by imaging the light that is simultaneously irradiated from the first light irradiation unit and the second light irradiation unit toward the target tissue inside the eyeball and reflected inside the eyeball is acquired.
The adjusting unit adjusts the irradiation of the first light irradiation unit and the second light irradiation unit based on the second imaging information.
The state estimation device for an internal tissue of the eyeball according to claim 5.
The shadow information is shadow information in the recess of the optic nerve head.
The state estimation device for an internal tissue of the eyeball according to any one of claims 1 to 6.
The shadow information is obtained by separating a shadow portion and a non-shadow portion by an image processing means using a clustering algorithm.
The state estimation device for an internal tissue of the eyeball according to any one of claims 1 to 7.
Light is irradiated from the first position outside the eyeball of the living body toward the target tissue inside the eyeball.
In addition to imaging the light reflected inside the eyeball
The shadow information about the target tissue is acquired from the first imaged information captured, and the shadow information is obtained.
The state of the target tissue is estimated from the shadow information.
A method for estimating the state of internal tissues of the eyeball.