JP2020049154A - Eyeball imaging apparatus - Google Patents

Abstract

To improve an eyeball imaging apparatus so that the size of an eyeball and a pupil in an image picked up by an imaging element becomes constant even if a distance between the imaging element and the eyeball changes.SOLUTION: The eyeball imaging apparatus includes a lens system 11 and an imaging element. The lens system 11 forms an image of an image ray from an eyeball X located on the front side of the lens system 11 on the imaging surface of the imaging element, the principal ray of the image ray being parallel to an optical axis. In the figure, Y is an image on the imaging surface.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an eyeball imaging device for imaging a subject's eyeball.

Eyeball imaging devices have been known for a long time.
The eyeball imaging apparatus is used, for example, in a subject to determine which of the sympathetic nerve and the parasympathetic nerve is superior.

It has long been known in the medical field that the pupil is subject to dual control of the sympathetic and parasympathetic nerves. Pupil enlargement (mydriasis) is realized by the action of the sympathetic nerve, and pupil reduction (miosis) is realized by the action of the parasympathetic nerve.
Therefore, by irradiating the subject with the stimulating light and observing how the pupil reacts, it is possible to determine which of the sympathetic nerve and the parasympathetic nerve is acting predominantly.
For example, when the sympathetic nerve is dominant, the subject is generally in a nervous state or an excited state, and when the parasympathetic nerve is dominant, the subject is generally in a relaxed state or a sedated state. Therefore, by observing the reaction of the pupil, it is possible to determine which of the sympathetic nerve and the parasympathetic nerve is superior.
In addition, by observing the reaction of the pupil, for example, it is possible to determine the state of mind and body of the subject at the present time, furthermore, it has been found from recent research of the present inventor, From the pupil response, it may be possible to determine whether the subject is under stress, or whether the subject is in a state of lack of sleep.
Moreover, as is well known, both the sympathetic nerve and the parasympathetic nerve belong to the autonomic nerves that work independently of the subject's intention. Therefore, the result of such determination is highly reliable in that it cannot be misled by the subject's will. In view of such a point, the technique for observing the pupil may create a large market in the future.

The method of observing the response of the pupil to the stimulating light as described above is standardized to some extent based on the results of past studies in order to ensure the accuracy or the consistency of the determination result. Generally, the above-described determination is made based on how the size of the pupil changes within 5 to 6 seconds after irradiation with the stimulating light.
However, according to the knowledge of the inventor of the present application, not only the process of changing the size of the pupil, but also the absolute value of the size of the pupil can be accurately measured, so that a judgment that could not be performed conventionally can be performed. Or it may be possible to perform the determination made conventionally with higher accuracy.

However, it is difficult to grasp the absolute value of the size of the pupil with a conventional eyeball imaging apparatus. It is for the following reasons.
An eyeball imaging apparatus has a function of performing imaging, which captures image light from a target eyeball (usually one eyeball, but may be two eyes) which is an eyeball of a subject to be imaged. An imaging device having an imaging surface and a lens system for forming image light from a target eyeball on the imaging surface are provided.
When imaging the pupil, the subject examines the front side of the lens system (in this application, the range located on the optical axis of the image light and opposite to the imaging device with the lens system interposed therebetween is referred to as “the front side of the lens system”. The target eyeball to be imaged is fixedly positioned at a predetermined position. In this state, the target eyeball is imaged by the image sensor, but if a lens system for forming image light on the imaging surface of the image sensor is common, the distance from the image sensor to the target eyeball is large. The size of the target eyeball in the image of the target eyeball captured by the image sensor decreases as the distance increases, or as the optical path of the image light from the target eyeball to the image sensor increases. In this case, it is possible to specify or grasp the relative size of the pupil with respect to the target eyeball and how the pupil size changes after the stimulating light is irradiated from the above-described image. It is difficult to specify or grasp the absolute value of the pupil size.
The conventional eyeball imaging device is provided with a cylindrical hood that can press the periphery of the target eyeball against the tip thereof, and when performing imaging of the pupil, the subject can target the edge of the tip of the hood. In some cases, the target eyeball can be positioned with respect to the image sensor by pressing the eyeball around the eyeball. However, since there are individual differences in the shape of the orbit, the degree of protrusion of the eyeball, and the like, it is difficult to accurately position the target eyeball with respect to the image sensor even with the above-described hood.
This means that it is difficult to specify or grasp the absolute size of the pupil from the image obtained by the image sensor.

Similar problems exist other than when an eyeball imaging device is used to observe a pupil response to a light stimulus. The eyeball imaging device can also be used, for example, for the purpose of iris authentication.
Even in such a field, when the same person's eyeball is imaged, if the size of the iris in the eyeball can always be kept constant in the image, the accuracy of authentication can be increased or the computer required for authentication can be used. Processing may be lighter.

  An object of the present invention is to provide an eyeball imaging apparatus capable of specifying or grasping the absolute size of an object (for example, a pupil) reflected in an image obtained by an imaging element.

In order to solve the above-mentioned problem, the present inventor proposes the following invention.
The present invention is directed to an image pickup device having an image pickup surface having a function of performing image pickup, which picks up image light from a target eyeball which is an eyeball of a subject to be imaged, and the image light from the target eyeball on the image pickup surface An eyeball imaging apparatus including a lens system that forms an image.
The lens system in the eyeball imaging apparatus is configured to form, among image light from the target eyeball, parallel light incident on the lens system along an optical axis on the imaging surface of the imaging device. ing.
In the conventional eyeball imaging device, as described above, the farther the distance from the imaging device to the target eyeball, or the longer the optical path of image light from the target eyeball to the imaging device, the longer the image was captured by the imaging device. The size of the target eyeball in the image of the target eyeball becomes small. As a result of analyzing the cause by the present inventor, the lens system in the conventional eyeball imaging apparatus captures an image light whose diameter increases toward the optical axis among image light coming from the target eyeball toward the lens system. It has been found that this is because an image is formed on the imaging surface of the element. If such image light forms an image on the imaging surface of the image sensor, that is, if it is a target to be imaged by the image sensor, the further away the target eyeball is from the imaging surface, the smaller the range of the starting point of the image light becomes. Therefore, the size of the target eyeball reflected in the image based on the image data generated by the image sensor becomes small. That is, it is difficult to specify or grasp the absolute size of an object (eyeball, pupil, iris, etc.) reflected in an image obtained by the imaging element of the conventional eyeball imaging apparatus from the above-described image. .
The farther the distance from the image sensor to the target eyeball, or the longer the optical path of the image light from the target eyeball to the image sensor, the longer the target eyeball reflected in the image based on the image data generated by the image sensor. In the present invention, the above-described cause of reducing the size of the lens system is to adopt a lens system that forms parallel light incident on the lens system along the optical axis out of image light from the target eyeball on the image sensor. It was solved by. According to such a lens system, the range that is the starting point of the image light that forms an image on the imaging surface of the imaging element is, even if the starting point moves back and forth on the front side of the lens system, that is, the range of the image light from the target eyeball to the imaging element. Even if the optical path length changes, the size does not change as long as the target eyeball is located on the front side of the lens system. Therefore, by adopting such a lens system, even if the position of the target eyeball slightly fluctuates on the front side of the lens system, the size of the object (eyeball, pupil, iris, etc.) reflected in the image obtained by the image sensor is reduced. No change will occur. Of course, it is necessary to set in advance how the size of the pupil in the image is related to the size of the pupil in the actual target eyeball. The size of the pupil in the actual target eyeball can be specified or grasped from the size of the pupil reflected in the image obtained by the eyeball imaging apparatus according to the present invention. In fact, in the eyeball imaging apparatus prototyped by the inventor of the present application, even if a width of ± 5 mm occurs with respect to a reference point in the optical path from the target eyeball to the imaging element, the image based on the image data generated by the imaging element The size of the object (eyeball, pupil, iris, etc.) at the time indicated only about 1% change.
As described above, the lens system in the present invention forms parallel light incident on the lens system along the optical axis out of image light from the target eyeball on the image sensor. In such a lens system, image light that is parallel light on the object side (object side) is formed on the image plane side, or image light whose principal ray is parallel to the optical axis on the object side (object side) is generated. A known or well-known telecentric lens system that forms an image on the image plane side can be applied. A known or well-known telecentric lens system generally includes a plurality of lenses, but the lens system according to the present invention can follow that. However, the lens system in the present invention is not necessarily required to be plural, and may include other optical elements in addition to other lenses. For example, it is also possible to provide a diaphragm between a lens constituting the lens system (for example, when there are a plurality of lenses, for example, the one closest to the image sensor) and the image sensor.
The target eyeball in the present invention may be both eyes of the subject, or may be one eye.
Although not limited thereto, the lens system according to the present invention includes a subject-side lens that converges the image light, which is parallel light, to generate an intermediate image, and the image sensor that generates the intermediate image. And an image-side lens for forming an image on the imaging surface. In that case, at least one of the subject side lens and the image plane side lens may be configured by a plurality of lenses having positive power. Since the subject-side lens allows image light, which is parallel light from the subject's eyes, to pass through, it requires a relatively large aperture of at least about 30 mm, preferably about 40 mm, for example. In this case, the f-number of the subject-side lens having a large aperture becomes extremely large, and unless special measures are taken, the distance from the subject-side lens to the imaging surface of the image sensor tends to be as long as about 200 mm or more. It is. If left unchecked, the size of the eyeball imaging device will increase. If the object side lens is composed of a plurality of lenses having positive power, the f-number can be reduced, so that the distance from the object side lens to the imaging surface of the image sensor can be reduced. . The same effect can be obtained even if the image-side lens is composed of a plurality of lenses having positive power. Both the object side lens and the image plane side lens can be composed of a plurality of lenses having positive power. It is advantageous to reduce the size of the eyeball imaging apparatus by making a plurality of lenses having a positive power that make up the subject-side lens abut on or very close to each other on the optical axis. It is advantageous to reduce the size of the eyeball imaging apparatus by bringing a plurality of lenses having a positive power, which constitute the image-side lens, into contact with or extremely close to each other on the optical axis. Further, the surface of the image-side lens (when the image-side lens is composed of a plurality of lenses having positive power, the one closest to the objective-side lens) is located immediately after the intermediate image. This arrangement is advantageous in reducing the size of the eyeball imaging device. In order to reduce the size of the eyeball imaging device, it is preferable that at least one of the subject-side lens and the image-side lens is made of glass.
The image plane side lens may have an autofocus function. In the eyeball imaging device of the present application, even if the distance between the eyeball and the lens system, or the distance between the eyeball and the imaging surface of the imaging device changes, the size of the eyeball reflected in the image captured by the imaging device does not change, If the distance changes too much, the image may be out of focus. If the image-side lens has an autofocus function (known or incorporated in the autofocus mechanism as a part of a well-known autofocus mechanism), for example, the eyeball may slightly move in the optical axis direction due to individual differences between subjects. Therefore, even if the camera moves back and forth, the range of focus is widened, so that the image captured by the image sensor is in focus.
The subject side lens may be an aspheric lens. Thereby, the aberration occurring in the image can be suppressed. This effect is particularly noticeable when the image-side lens is provided with an autofocus function.

Although not limited to this, the eyeball imaging apparatus of the present invention is configured such that the subject abuts around the target eyeball on the front side of the lens system to position the target eyeball relative to the lens system. It may have a positioning member that enables it. The positioning member may have any configuration as long as the positioning of the target eyeball relative to the lens system is possible.
For example, the positioning member may be a cylindrical member capable of pressing around the periphery of the target eyeball and shielding external light. When the number of target eyeballs is one, the cylinder constituting the positioning member is pressed around one eye, and when the number of target eyeballs is two, the cylinder constituting the positioning member is such that the edge thereof surrounds both eyes. You will be pressed. When the positioning member is a cylindrical member as described above, the imaging element may capture the image light in a state where external light is not included. By blocking external light, imaging can be performed under certain conditions, so that the image of the target eyeball obtained by the imaging device is stable.

The imaging device in the eyeball imaging device according to the present invention may capture the image light having a wavelength in an invisible light region. In that case, the eyeball imaging device of the present invention may include an illumination light source that emits illumination light that is emitted to the target eyeball to generate the image light. This makes it possible to prevent the illumination light from affecting the size of the pupil.
The eyeball imaging device according to the present invention may include a stimulus light source that irradiates the target eyeball with stimulus light that is light in a visible light region. The stimulating light from the stimulating light source can be used as a trigger for causing a pupil expansion / contraction reaction.
An eyeball imaging device provided with a stimulating light source can be applied as a device for observing a pupil response to stimulating light. In that case, the image data generated by the image sensor needs to be for a moving image. On the other hand, for example, if the eyeball imaging device is intended for iris authentication, the image data generated by the imaging device may be for a moving image, or may be for a still image. Good.

FIG. 1 is a perspective view schematically illustrating an appearance of an eyeball imaging apparatus according to an embodiment. FIG. 2 is a horizontal sectional view of the head of the eyeball imaging apparatus shown in FIG. 1. FIG. 2 is a vertical sectional view of the eyeball imaging apparatus shown in FIG. 1. FIG. 2 is a diagram for explaining the behavior of illumination light and reflected light when imaging is performed by the eyeball imaging apparatus illustrated in FIG. 1. FIG. 2 is a side view for explaining the behavior of image light captured by the imaging device of the eyeball imaging apparatus illustrated in FIG. 1. FIG. 10 is a side view for explaining the configuration of another lens system that can be employed in the eyeball imaging apparatus and the behavior of image light captured by the imaging element in that case.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing the appearance of an eyeball imaging apparatus according to this embodiment.
In the eyeball imaging apparatus according to this embodiment, the subject to be imaged is the subject's eyeball. If the eyeball to be imaged is referred to as a target eyeball, the target eyeball may be both eyes of the subject or one eye. Although not limited to this, the target eyeball in this embodiment is assumed to be one eye of the subject. Further, although not limited to this, the eyeball imaging apparatus according to this embodiment is intended to observe the response of the pupil to the stimulating light.
A target eyeball of a subject (hereinafter, the target eyeball may be simply referred to as an “eyeball”) is imaged by an imaging device described later, and image data of an image in which the subject's eyeball is captured by the imaging device is used as a function of the imaging device. Generated by Since the purpose of use of the eyeball imaging apparatus in this embodiment is as described above, the image based on the image data obtained by the imaging device is a moving image in this embodiment. Further, since the purpose of use of the eyeball imaging apparatus in this embodiment is as described above, the image of the moving image based on the image data obtained by the imaging device is, for example, a pupil based on the stimulating light when a doctor or the like views it. The reaction can be observed.

The eyeball imaging apparatus according to this embodiment includes a gripper 10 that can be held by hand, and a head 20 that is provided, for example, on the front side of the upper end of the gripper 10.
The grip 10 and the head 20 are made of, for example, but not limited to, opaque resin. At least the head 20 must be made of an opaque material. Their interiors are hollow, and various components are built in or attached to them as described below. Since the grip 10 and the head 20 have built-in components, they function as a practical case in which components are built.
The grip portion 10 has a shape that can be held by one hand, and is not limited to this, and has a rod shape or a column shape in this embodiment.
The head 20 is a tube whose cross section is, for example, substantially rectangular, which is slightly widened toward the tip, and is made of an opaque material such as an opaque resin. An opening 21 is provided at the tip of the head 20 (the side facing the face of the subject during use, the near side in FIG. 1). Although not limited to this, the opening 21 in this embodiment is a horizontally long substantially rectangular shape whose four corners are rounded. In this eyeball imaging apparatus, the subject itself or a doctor or the like other than the subject grips the gripper 10 and abuts the edge of the opening 21 at the tip of the head 20 around the eyeball, which is one of the eyes of the subject. It is used in the state where it was made. By pressing the edge of the opening 21 around the eyeball without any gap, the resin constituting the head 20 may be opaque, so that a state in which external light does not enter the inside of the head 20 can be created.
In this embodiment, the number of the eyeballs is one. However, when the number of the eyeballs is two, the opening 21 is further elongated horizontally, so that the opening 21 can be pressed around the eyes. .

FIG. 2 is a horizontal sectional view of the head 20 of the eyeball imaging device, and FIG. 3 is a vertical sectional view of the entire eyeball imaging device.
1, the lens system 11, the illumination light source 31A, the stimulating light source 31B, and the first polarizing plate 32 are provided inside the head 20 in FIG. The second polarizing plate 33 and the imaging device 12 are provided on the inner side of the head 20 in FIG.

In this embodiment, there are a plurality of illumination light sources 31A. The illumination light source 31A emits natural light as illumination light. As long as it is possible, the illumination light source 31A can be composed of an appropriate one such as a light bulb or an LED. The illumination light source 31A in this embodiment is an LED, although not limited thereto. The illuminating light source 31A emits light toward the surface of the target eyeball with a certain degree of directivity, although not limited thereto. As will be described later, at the time of imaging, the eyeball is located substantially at the center of the opening 21. Therefore, the optical axis of the light emitted from each of the illumination light sources 31A generally faces the center of the opening 21. I have. As a result, a certain range in which the eyeball is expected to be located at the time of imaging is illuminated with the illumination light from the illumination light source 31A with a somewhat uniform brightness. The illumination light source 31A is fixed to a substrate fixed to the head 20, but illustration of the substrate is omitted.
The wavelength of the illumination light emitted from the illumination light source 31A is not particularly limited. The illumination light source 31A may emit general white light. However, if emphasis is placed on not having a physiological effect on the subject's eyes, the wavelength of the illumination light should be in the invisible light range, and is not limited to this. Is illumination light having a wavelength in the invisible light region, more specifically, light having a wavelength in the infrared region. The illumination light source 31A of this embodiment is configured by an LED that selectively generates light having a wavelength in a specific wavelength range in the infrared region. The wavelength of the light emitted from the illumination light source 31A of this embodiment is, for example, 900 nm or longer. Even if the wavelength of the illumination light is increased, the linear polarizers (more specifically, wire grid polarizers, which will be described later) used for the first polarizer 32 and the second polarizer 33 in this embodiment are used. There is no effect on obtaining a matte image. However, if the wavelength is excessively long, it becomes difficult to perform imaging by a general imaging device 12. In consideration of such points, the wavelength of the illumination light should be appropriately selected in a range longer than 900 nm.
On the other hand, the stimulating light source 31B emits stimulating light for causing a reaction in the pupil. The stimulating light from the stimulating light source 31B is applied to a predetermined range where the eyeball is to be located (at least a range where the pupil is to be located) when the eyeball is imaged by the eyeball imaging device. . Since the stimulating light is for causing pupil reflection, there is light whose wavelength region is in the visible light region. The stimulating light or the stimulating light source 31B may be of any type as long as the condition is satisfied. As described later, there are a plurality of stimulation light sources 31B. The stimulus light source 31B is configured by, for example, an LED.
As described above, the number of the illumination light sources 31A in this embodiment is not limited to this, but is plural. Each illumination light source 31A is located near the opening 21 of the head 20, and in this embodiment, is located slightly inside the wall of the head 20 on both outer sides in the horizontal direction of the opening 21 in FIG. . In this embodiment, a plurality of illumination light sources 31A located on the right and left sides of the opening 21 are arranged linearly, more precisely, in the vertical direction in FIG. The illumination light sources 31A located on the right and left sides of the opening 21 are arranged linearly with the optical path (optical axis) of the illumination light interposed therebetween and perpendicular to the optical path (optical axis) of the illumination light. As shown in FIG. 3, the number of the illumination light sources 31 </ b> A vertically arranged on the right side of the opening 21 is five, and the same applies to the left side of the opening 21. Of course, the number of the illumination light sources 31A arranged in the vertical direction on the right side and the left side of the opening 21 does not need to be five, and more specifically, does not need to be plural.
On the other hand, the stimulating light sources 31B are provided one by one further on the uppermost one of the above-mentioned illumination light sources 31A in a set of five. However, the stimulating light source 31B need not be present at this position, and need not be plural.
Although not limited to this, the illumination light source 31A in this embodiment is always turned on. On the other hand, the stimulating light source 31B is turned on at a suitable timing for a short time, for example, for about 0.5 to 0.6 seconds. It is assumed that the stimulating light source 31B is turned on by operating a switch (not shown) provided on the grip portion 10.

A first polarizing plate, which is a polarizing plate that linearly polarizes the illumination light, which is natural light passing through, in front of each of a set of five illumination light sources 31A vertically arranged near both outer sides of the opening 21. 32 are arranged one by one. The first polarizing plate 32 in this embodiment is a vertically long rectangle as shown in FIGS. 1 and 3, and is not limited to this. In this embodiment, the first polarizing plate 32 extends from the lower end to the upper end of the opening 21. It is arranged near the tip of the opening 21. In this embodiment, of the light emitted from the illumination light source 31A, all of the illumination light that contributes to imaging performed by the image sensor 12 as described later passes through the first polarizing plate 32. The width of one polarizing plate 32 is designed from that viewpoint. Note that, in order to allow all the illumination light contributing to the image pickup by the image pickup device 12 to pass through the first polarizing plate 32, the present invention is not limited to this, but in this embodiment, the lens system 11 (more specifically, A partition wall 19 which is a donut-shaped light-impermeable wall whose inner edge is in contact with the periphery of a first lens and a second lens (to be described later) without gap and whose outer edge is in contact with the inner peripheral surface of the head 20 without gap. , Provided in the head 20. The partition wall 19 divides the space inside the head 20 into a space on the front side of the lens system 11 and a space on the rear side. Due to the presence of the partition wall 19, of the light emitted from each of the illumination light sources 31A, the light that has not passed through the first polarizing plate 32 does not reach the space where the imaging element 12 behind the lens system 11 exists. become.
In this embodiment, the stimulating light emitted from the stimulating light source 31B also passes through the first polarizing plate 32. However, it does not matter whether the stimulating light always passes through the first polarizing plate 32.
The first polarizing plate 32 in this embodiment functions as a polarizing plate for light having a wavelength in the infrared region. Although not necessarily limited to this, the first polarizer 32 in this embodiment is a wire grid polarizer. A wire grid polarizer is a resin plate in which extremely thin metal wires are arranged in parallel at a predetermined interval.The wire polarizer polarizes even light in the infrared region where a normal polarizer does not function as a polarizer. Functions as a board. As an example of the wire grid polarizer, "Asahi Kasei WGF (trademark)" manufactured and sold by Asahi Kasei E-materials Co., Ltd. can be mentioned. Note that the same applies to the second polarizing plate 33.
As described above, the illumination light that has passed through the first polarizing plate 32 becomes linearly polarized light. Here, the polarization plane of the illumination light that is linearly polarized light that has passed through the first polarizing plate 32 is, for example, horizontal in FIG.

The lens system 11 is for imaging reflected light (image light) generated by reflecting illumination light on an object such as an eyeball on the image sensor 12. More specifically, the lens system 11 forms parallel light incident on the lens system 11 along the optical axis out of the image light coming from the eyeball on the imaging surface 12A of the imaging element 12. As far as it is possible, the configuration of the lens system 11 is free. As the lens system 11 of this embodiment, a known or well-known configuration of a telecentric lens system can be applied.
The lens system 11 in this embodiment includes two lenses, a first lens 11A located on the front side and a second lens 11B located on the rear side. Both the first lens 11A and the second lens 11B can be made of glass, and both can be aspherical lenses. Although not limited to this, in this embodiment, the first lens 11A and the second lens 11B are both made of glass, and both are aspheric lenses. However, the lens system 11 does not need to be constituted by two lenses, that is, the first lens 11A and the second lens 11B, and may be constituted by one or three or more lenses. Further, the lens system 11 may include other optical elements other than the lens. The lens system 11 may have a function of enlarging an image, or may have other functions. By controlling the lens system 11 by the first lens 11A and the second lens 11B, it is easy to reduce the combined focal length while maintaining the aperture.
The imaging element 12 captures reflected light and performs imaging. The imaging device 12 of this embodiment may be any device as long as it can perform imaging with light having a wavelength in the infrared region. More specifically, the image sensor 12 in this embodiment can only image light having a wavelength in the infrared region. The image pickup device 12 is, for example, a CCD or can be constituted by CMOS. The surface of the imaging element 12 facing the lens system 11 is the imaging surface 12A. The image light passing through the lens system 11 forms an image on the imaging surface 12A. The image sensor 12 generates image data that is data of an image obtained by imaging, more specifically, an image obtained by image light focused on the imaging surface 12A. The image captured by the image sensor 12 may be a still image or a moving image in nature, but the purpose of use of the eyeball imaging apparatus of this embodiment is based on the stimulus light as described above. Since the reaction of the pupil is observed, the image captured by the image sensor 12 of this embodiment is a moving image, and the image data generated by the image sensor 12 is a video signal.
The imaging device 12 is connected to the processing circuit 13 via a connection line 12a. The processing circuit 13 receives the image data generated by the image sensor 12 from the image sensor 12 via the connection line 12a. The processing circuit 13 performs appropriate processing as required before outputting the video signal to the outside, for example, amplification of a signal, adjustment of brightness, and analog / digital conversion if necessary.
The processing circuit 13 is connected to an output terminal 14 via a connection line 13a. The output terminal 14 connects to an external device via a cable (not shown). The external device is typically a display or a recording device. The display displays a moving image based on the video signal received from the output terminal 14 via the cable. The recording device records the video signal received from the output terminal 14 via the cable, and makes the video signal later viewable on a predetermined display. In this embodiment, the output terminal 14 is connected to a display (not shown) via a cable. Note that the output of the video signal generated by the eyeball imaging device to an external device does not need to be performed by wire as in this embodiment. In the case where the video signal is output wirelessly, the eyeball imaging apparatus includes, in place of the output terminal 14, a known or well-known communication mechanism for performing, for example, Bluetooth (trademark) communication with an external device. . Of course, it is also possible to enable connection to an external device both by wire and wirelessly. Further, the above-described external devices such as a display and a recording device can be provided in the eyeball imaging device. In that case, the output terminal 14 for outputting the video signal to the external device becomes unnecessary.

Although the second polarizing plate 33 is made of the same material as the first polarizing plate 32 as described above, its function is different from that of the first polarizing plate 32. The second polarizing plate 33 is included in surface reflected light (described later) of the reflected light generated by reflecting the illumination light, which has been linearly polarized by the first polarizing plate 32, on the surface of the object, which is an eyeball. Has the function of blocking the linearly polarized light component.
When viewed with the optical axes of the illumination light and the reflected light as axes, the first polarizing plate 32 and the second polarizing plate 33 are oriented such that the polarization planes of the linearly polarized light of the light passing therethrough are orthogonal to each other. ing. In this embodiment, when natural light passes through the second polarizing plate 33 in the same direction as the reflected light, the polarization plane of linearly polarized light generated by passing through the second polarizing plate 33 is aligned with the vertical direction in FIG. It is becoming.
The reflected light from the eyeball passes through the lens system 11 and further passes through the second polarizing plate 33 and is imaged by the image sensor 12. Therefore, the light that contributes to imaging by the imaging element 12 is only a component of the reflected light that can pass through the second polarizing plate 33. The second polarizing plate 33 may be provided on the optical path of the reflected light between the imaging device 12 and the target, and may be provided, for example, on the eyeball side of the lens system 11 or, for example, on the lens system. If the system 11 includes a plurality of lenses, it may be located between the plurality of lenses.

Next, a method of using the eyeball imaging device will be described.
When using the eyeball imaging device, the subject or a doctor or the like grips the grip 10 and places the periphery of the opening 21 in the head 20 around the eye of the subject to observe the reaction of the pupil by the stimulating light. Press. At this time, care should be taken so that external light does not enter the inside of the head 20 from around the opening 21.
In this state, the doctor observes the subject's eyeball. Illumination light from the illumination light source 31A, which is always lit, passes through the first polarizer 32, is reflected by the eyeball located substantially at the center of the opening 21, and passes through the lens system 11 and the second polarizer 33. To reach the image sensor 12. The imaging element 12 captures reflected light from the eyeball and performs imaging. At an appropriate timing, a doctor or the like presses a switch provided on the grip 10. Then, the stimulus light emitted from the sedge climate light source 31B passes through the first polarizing plate 32 and is applied to the eyeball of the subject. The image sensor 12 generates a video signal, which is image data of a moving image, at least for a time necessary for observing a pupil reflex reaction caused by stimulation light. The video signal of the moving image generated by the image sensor 12 is subjected to necessary processing by the processing circuit 13 and then reaches the output terminal 14 via the connection line 13a. As described above, the eyeball observation device of this embodiment is connected to a display (not shown) via the cable connected to the output terminal 14. Therefore, the doctor can perform, for example, an observation for judging which of the sympathetic nerve and the parasympathetic nerve is superior in the subject, while watching the moving image of the eyeball of the subject enlarged and displayed on the display.

The following describes what the moving image of the eyeball displayed on the display looks like.
FIG. 4 conceptually shows what reflected light is imaged by the image sensor 12 when the illumination light source 31A is turned on.
FIG. 4A shows surface reflected light reflected on the outermost surface of the eyeball (for example, the surface of a tear covering the eyeball), and FIG. 4B shows internal reflected light reflected slightly from the surface of the eyeball into the eyeball. Demonstrates behavior. Also, the straight line drawn in the bold circle indicates the direction of the polarization plane of the illumination light or reflected light in the part, and the line drawn radially in the circle is the part in the part. This indicates that the linear polarization of the illumination light or the reflected light is disturbed (for example, natural light is generated).
The illumination light emitted from the illumination light source 31A passes through the first polarizing plate 32. The illumination light passing through the first polarizing plate 32 becomes linearly polarized light. The polarization plane of the linearly polarized light that is the illumination light in that case is in the horizontal direction in FIG. The steps up to here are common to FIGS. 4A and 4B.
The illumination light that is linearly polarized light that has passed through the first polarizing plate 32 hits the eye X and becomes reflected light from the eye X. Of the reflected light reflected on the surface of the eyeball X, the surface reflected light ideally maintains its polarization state. The surface reflected light that is linearly polarized light is blocked by the second polarizing plate 33 in which the direction of the plane of polarization of the linearly polarized light generated when natural light passes is made to be orthogonal to the first polarizing plate 32, and (Fig. 4 (A)).
On the other hand, the polarization state of the internally reflected light is disturbed. Of the light contained in the internally reflected light, the light that vibrates in the direction orthogonal to the plane of polarization of the linearly polarized light contained in the surface reflected light passes through the second polarizing plate 33, so that about half of the light is imaged. The light reaches the element 12 (FIG. 4B).
As a result, the light used for the imaging device 12 to capture an image using the illumination light from the illumination light source 31A is only internal reflection light. Therefore, an image generated by the imaging element 12 performing imaging is an image of an eyeball in a state where no tears exist, and is a so-called matte image. Of course, the image displayed on the display is also a matte image.
In this embodiment, the stimulating light emitted from the stimulating light source 31A and having a wavelength in the visible light range reaches the image sensor 12 in the same manner as the illumination light after causing a reflection reaction in the pupil. Since the element 12 can capture only light having a wavelength in the infrared region, the image is not captured by the imaging element 12 regardless of the polarization state of the stimulating light. Therefore, when considering an image captured by the image sensor 12, the effect of the stimulating light can be ignored.

Further, among the reflected light (image light) from the eyeball, the light that reaches the imaging surface 12A of the imaging element 12 via the lens system 11 will be described with reference to FIG.
In FIG. 5, X is an eyeball, a broken line is an optical axis of image light, 11 is a lens system expressed as a combination of a first lens 11A and a second lens 12B, and Y is an image formed on an imaging surface 12A. is there. The thin line is image light generated from the upper and lower ends of the eyeball X.
In this embodiment, of the image light emitted from the eyeball X, the image light parallel to the optical axis is imaged on the imaging surface 12A of the imaging element 12 via the lens system 11. In other words, the lens system 11 of this embodiment is configured to form image light having a principal ray parallel to the optical axis on the image plane side in front of the lens system 11. Thereby, even if the distance between the eyeball X and the lens system 11 changes, the size of the eyeball in the image formed by the imaging device 12 that has captured the image light, or the pupil reflected in the image. The size is constant. The diameter of the lens system 11 centered on the optical axis, more specifically, the diameter of at least the first lens 11A of the first lens 11A and the second lens 12B is set so that the image sensor 12 can image the entire eyeball. Shape and size. For example, if it is necessary to guide parallel light having a diameter of, for example, 30 mm including the subject's eyeball to the imaging device 12 in order to image the entire eyeball with image light that is parallel light coming out of the subject's eyeball, a circular shape is used. The diameter of the first lens 11A is 30 mm or more, preferably 40 mm or more. If the distance between the eyeball X and the lens system 11 is excessively changed, the image based on the image data obtained by the image sensor of this embodiment may not be in focus. Nevertheless, in this embodiment, the above-described effects can be obtained within a range where focus is achieved.
In this embodiment, the image light having passed through the first lens 11A and the second lens 12B is once converged to generate an intermediate image Z. The position where the intermediate image Z is generated is equal to the position of the focal point of the virtual lens which is conceived when the first lens 11A and the second lens 12B are combined, and in this embodiment, at the position substantially in the optical axis direction, A small stop is arranged on the image pickup surface 12A of the image pickup device 12 within a range in which an amount of image light required for image pickup can be guided. Due to the presence of the stop, only the parallel light from the eyeball is selectively guided to the imaging surface M of the imaging element 12.

Note that the lens system 11 in the eyeball imaging apparatus according to the present embodiment can be, for example, as shown in FIG. The lens system 11 is housed in the head 20 of the eyeball imaging device as in the case described above.
In this case, the lens system 11 couples the image light, which is parallel light, to the subject side lenses 11C and 11D for generating an intermediate image and the image light after generating the intermediate image to the imaging surface 12A of the image sensor 12. Image-side lenses 11E and 11F for imaging.
Of the subject-side lenses 11C and 11D, the subject-side lens 11C located at least on the front side has a diameter of at least the first lens 11A of 30 mm or more, preferably 40 mm, for the same reason as in the above-described example. Is 30 mm or more, preferably 40 mm or more. Although not limited to this, the diameters of the subject-side lenses 11C and 11D in this embodiment are the same, so that both diameters are 30 mm or more, preferably 40 mm or more. Both the subject-side lenses 11C and 11D can be made of glass, and both can be aspherical lenses. Although not limited to this, in this embodiment, both the subject-side lenses 11C and 11D are made of glass, and both are aspheric lenses.
Each of the subject-side lenses 11C and 11D is a lens having a positive power in this example. It is possible to replace the subject-side lenses 11C and 11D with a single lens equivalent to the combination thereof, but if the subject-side lenses 11C and 11D are made of two lenses, the diameter of Since the f-number can be reduced even if the value is increased, the size of the eyeball imaging device can be reduced. In this example, the subject-side lenses 11C and 11D are two lenses, but may be a larger number of lenses. The subject-side lenses 11C and 11D are extremely close in this example, and the distance between them is, for example, about 1 to 5 mm. Both may be in contact with each other.
Both the image-side lenses 11E and 11F are lenses having positive power in this example. The image-side lenses 11E and 11F are not limited to these, but both are made of glass, and both are aspheric lenses. It is possible to replace the image-side lenses 11E and 11F with a single lens equivalent to the combination thereof, but if the image-side lenses 11E and 11F are composed of two lenses, Since the f-number can be reduced even when the diameter is increased, the size of the eyeball imaging apparatus can be reduced. In this example, the image-side lenses 11E and 11F are two lenses, but may be a larger number of lenses. In this example, the image-side lenses 11E and 11F are extremely close to each other, and the distance between them is, for example, about 1 to 5 mm. Both may be in contact with each other. The front surface of the image plane side lens 11E is located immediately after an intermediate image described later. The distance from the intermediate image to the image plane side lens 11E is, for example, about 1 to 5 mm.
As shown in FIG. 6, when the lens system 11 is employed, the image light, which is parallel light from the eyeball X, passes through the subject-side lenses 11C and 11D and converges to form an intermediate image Z. To form After forming the intermediate image Z, the image light passes through the image-side lenses 11E and 11F located immediately after that, and forms an image Y on the imaging surface 12A of the imaging device 12. As in the case of the lens system 11 described above, a stop is provided at or near the position where the intermediate image Z in the optical axis direction is generated, so that only parallel light from the eyeball is selectively provided. An image Y is formed on an imaging surface 12A of the imaging element 12.
The image-side lenses 11E and 11F may have an autofocus function. In other words, the image-side lenses 11E and 11F may be incorporated in a known or well-known autofocus mechanism to form a part of the autofocus mechanism. Is also good. In that case, the image-side lenses 11E and 11F automatically move according to the position of the eyeball in the optical axis direction. This makes it easier to focus on the image of the eyeball generated by the image sensor 12 capturing the image light, even if the eyeball moves slightly in the optical axis direction.

DESCRIPTION OF SYMBOLS 10 Grasping part 11 Lens system 12 Image sensor 12A Imaging surface 20 Head 31A Illumination light source 32 First polarizing plate 33 Second polarizing plate X Eyeball

Claims (9)

An imaging element having an imaging surface having a function of performing imaging, which captures image light from a target eyeball that is an eyeball of a subject to be imaged; and forming the image light from the target eyeball on the imaging surface. An eyeball imaging device comprising a lens system,
The lens system, of the image light from the target eyeball, the parallel light incident on the lens system along the optical axis to form an image on the imaging surface of the imaging device,
Eyeball imaging device. On the front side of the lens system, the subject is provided with a positioning member that enables relative positioning of the target eyeball with respect to the lens system by contacting the periphery of the target eyeball,
The eyeball imaging device according to claim 1. The positioning member is a cylindrical member that can press around the circumference of the target eyeball, and can shield external light,
The imaging device is configured to capture the image light in a state that does not include external light,
The eyeball imaging device according to claim 2. The imaging device is configured to capture the image light having a wavelength in an invisible light region,
Having an illumination light source that irradiates illumination light that is radiated to the target eyeball to generate the image light,
An eyeball imaging device according to claim 1. The target eye has a stimulating light source that irradiates stimulating light that is light in a visible light region,
An eyeball imaging device according to claim 1. The lens system includes a subject-side lens that converges the image light, which is parallel light, to generate an intermediate image, and an image plane that forms the image light after generating the intermediate image on the imaging surface of the image sensor. A side lens,
Has,
The eyeball imaging device according to claim 1. At least one of the subject side lens and the image plane side lens is configured by a plurality of lenses having a positive power,
An eyeball imaging apparatus according to claim 6. The image side lens has an autofocus function,
An eyeball imaging apparatus according to claim 6. The subject side lens is an aspheric lens,
The lens according to claim 6.

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