Patent Description:
There is known a scanning laser ophthalmoscope (SLO) that obtains a fundus image by scanning a light beam at high speed to irradiate the retina of a subject with the light beam and detecting reflected light from the retina with a light detector. Conventionally, a combination of a polygon mirror and a galvano mirror has been used for scanning a light beam. In addition, to reduce the size and cost, it has been proposed to use a micro electro mechanical system (MEMS) that biaxially drives to two-dimensionally scan a light beam instead of the polygon mirror and the galvano mirror (for example, Patent Document <NUM>). Patent Document <NUM> discloses a portable MEMS-based scanning laser ophthalmoscope (MSLO).

<CIT> discloses a wide-field SLO for retinal imaging, comprising: laser illumination subassemblies <NUM> that generate optical illumination beams <NUM> for scanning the human eye <NUM>, a 2D MEMS scanning minor <NUM> approximately <NUM> in diameter, a conic front objective <NUM>, and a detector sub-assembly <NUM> detecting light scattered from the retina.

However, it has been found that it is difficult to obtain a high-quality fundus image only by replacing the polygon mirror and the galvano mirror with a scanning unit such as a MEMS that biaxially drives.

The present invention has been made in view of above problems, and an object thereof is to provide a fundus photography device capable of obtaining a high-quality fundus image.

The present invention is a fundus photography device including: a light source; a scanning unit that includes a mirror that biaxially drives in a horizontal direction and a vertical direction to two-dimensionally scan a light beam emitted from the light source; an optical system that causes the light beam that has been reflected by the mirror of the scanning unit to enter an eye of a subject; and a light detector that detects the light beam that has been reflected by a retina of the subject, wherein an external diameter of the mirror of the scanning unit is <NUM> or greater and <NUM> or less.

In the above configuration, a configuration in which an optical magnification of the optical system is <NUM> times or greater and <NUM> times or less is employed.

In the above configuration, a configuration in which a resonant frequency in a horizontal direction of the scanning unit is <NUM> or greater and <NUM> or less is employed.

In the above configuration, a configuration in which a mechanical deflection angle in at least one of a horizontal direction or a vertical direction of the scanning unit is <NUM> degrees or greater and <NUM> degrees or less in half angle may be employed.

In the above configuration, a configuration in which the optical system includes an optical component that converts incident light beams, which have optical axes mutually diffusing and are diffusion lights, to light beams, which have optical axes mutually converging and are substantially parallel lights, and the light beam reflected by the mirror of the scanning unit is condensed between the scanning unit and the optical component, becomes diffusion light, enters the optical component, is converted to substantially parallel light by the optical component, and enters an eye of the subject may be employed.

In the above configuration, a configuration in which the optical system includes a first optical component and a second optical component, where the first optical component converts incident light beams, which have optical axes mutually diffusing and are substantially parallel lights, to light beams, which have optical axes parallel to each other and are convergent lights, and the second optical component converts the light beams emitted from the first optical component to light beams, which have optical axes mutually converging and are substantially parallel lights, and the light beam reflected by the mirror of the scanning unit enters the first optical component as substantially parallel light, is condensed between the first optical component and the second optical component, becomes diffusion light, enters the second optical component, is converted to substantially parallel light by the second optical component, and enters an eye of the subject may be employed.

In the above configuration, a configuration in which a signal processing unit that processes an output signal from the light detector is provided and an image generation unit that generates a fundus image of the subject, based on a signal processed by the signal processing unit may be employed.

The present invention allows a high-quality fundus image to be obtained.

Hereinafter, with reference to the drawings, embodiments of the present invention will be described.

<FIG> is a block diagram of a fundus photography device in accordance with a first embodiment. As illustrated in <FIG>, a fundus photography device <NUM> includes a projection unit <NUM>, a control unit <NUM>, a light detector <NUM>, and a display unit <NUM>. The projection unit <NUM> includes a light source <NUM>, an adjustment mechanism <NUM>, a scanning unit <NUM>, an optical system <NUM>, and a drive circuit <NUM>. The control unit <NUM> includes a drive control unit <NUM>, a signal processing unit <NUM>, and an image generation unit <NUM>.

The drive control unit <NUM> generates a control signal for controlling the light beam with which the retina of a subject is irradiated. The drive circuit <NUM> drives the light source <NUM> and the scanning unit <NUM> on the basis of the control signal of the drive control unit <NUM>.

The light source <NUM> emits an invisible light beam of infrared laser light having a wavelength of about <NUM> to <NUM>, for example. The light source <NUM> may emit a visible light beam of, for example, a red laser light (wavelength: about <NUM> to <NUM>), a green laser light (wavelength: about <NUM> to <NUM>), and/or a blue laser light (wavelength: about <NUM> to <NUM>).

The adjustment mechanism <NUM> includes a collimating lens, a toric lens, an aperture, and/or the like, and shapes a light beam <NUM> emitted by the light source <NUM>. The light beam <NUM> is, for example, an infrared laser light, a red laser light, a green laser light, or a blue laser light.

The scanning unit <NUM> is a scanner having a mirror that biaxially swings and drives to two-dimensionally scan the light beam <NUM>. The light beam <NUM> is scanned by the scanning unit <NUM> in the horizontal direction (a main scanning direction) and the vertical direction (a sub-scanning direction). The scanning unit <NUM> is, for example, a micro electro mechanical system (MEMS).

The optical system <NUM> irradiates an eye <NUM> of the subject with the light beam <NUM> that has been scanned by being reflected by the mirror of the scanning unit <NUM>.

The light detector <NUM> is a photodetector such as, for example, an avalanche photodiode, and detects a reflected light <NUM> that has been reflected by the eye <NUM> of the subject and has passed through the optical system <NUM>, the scanning unit <NUM>, and the adjustment mechanism <NUM>. The light detector <NUM> starts the detection at a timing when the light source <NUM> emits the light beam <NUM> on the basis of the synchronization signal from the drive circuit <NUM>.

The signal processing unit <NUM> processes the output signal of the light detector <NUM>, on the basis of the control signal from the drive control unit <NUM>. The signal processing unit <NUM> starts the process at a timing when the light source <NUM> emits the light beam <NUM> on the basis of the synchronization signal from the drive circuit <NUM>.

The image generation unit <NUM> generates a fundus image on the basis of the signal processed by the signal processing unit <NUM>. The display unit <NUM> is, for example, a liquid crystal display, and displays a fundus image generated by the image generation unit <NUM>.

The drive control unit <NUM>, the signal processing unit <NUM>, and the image generation unit <NUM> may be implemented by a processor such as a central processing unit (CPU) in cooperation with a program. The drive control unit <NUM>, the signal processing unit <NUM>, and the image generation unit <NUM> may be circuits that are specially designed. The drive control unit <NUM>, the signal processing unit <NUM>, and the image generation unit <NUM> may be one circuit or different circuits.

<FIG> illustrates the optical system of the fundus photography device in accordance with the first embodiment. As illustrated in <FIG>, the light beam <NUM> emitted by the light source <NUM> is converted from diffusion light to substantially parallel light by a collimating lens <NUM>, and then passes through a half mirror <NUM>, a diopter adjustment lens <NUM>, and a diopter adjustment lens <NUM> to enter a reflection mirror <NUM>. The light beam <NUM> enters the reflection mirror <NUM> as convergent light. The light beam <NUM> is reflected by the reflection mirror <NUM> to enter the scanning unit <NUM>, and is two-dimensionally scanned by being reflected by the scanning unit <NUM>.

The light beam <NUM> that has been two-dimensionally scanned by being reflected by the scanning unit <NUM> passes through a projection lens <NUM> and enters the eye <NUM> of the subject. The optical axes of the light beams <NUM> scanned by the scanning unit <NUM> mutually diffuse, and each of the light beams <NUM> is convergent light until it reaches a focal point <NUM>. Each light beam <NUM> enters the projection lens <NUM> as diffusion light. The projection lens <NUM> converts the light beams <NUM> that are reflected in different directions by the scanning unit <NUM> and have optical axes mutually diffusing, to the light beams <NUM> having optical axes mutually converging, and converts each of the light beams <NUM> from diffusion light to substantially parallel light and causes them to enter the eye <NUM> of the subject. The light beam <NUM> passes through a pupil <NUM>, converges in a crystalline lens <NUM> or near the crystalline lens <NUM>, passes through a vitreous body <NUM>, and focuses substantially at a retina <NUM>. That is, the retina <NUM> of the subject is irradiated with the light beam <NUM> using Maxwellian view. The term "substantially parallel" means that the light beam <NUM> is substantially parallel to such an extent that the light beam <NUM> can be focused substantially at the retina <NUM> (the same applies to the following description). The projection lens <NUM> is a convex lens and has an optical magnification of <NUM> times or greater and <NUM> times or less, which will be described later. The optical magnification is a value represented by, for example, a ratio of a distance between the projection lens <NUM> and the mirror of the scanning unit <NUM> to a distance between the projection lens <NUM> and the crystalline lens <NUM> of the subject or a convergence position of the light beam <NUM> near the crystalline lens <NUM>.

The light beam <NUM> is reflected by the retina <NUM> of the subject. The reflected light <NUM> reflected by the retina <NUM> travels back along the optical path along which the light beam <NUM> has advanced toward the retina <NUM>, in the order of the projection lens <NUM>, the scanning unit <NUM>, the reflection mirror <NUM>, the diopter adjustment lens <NUM>, and the diopter adjustment lens <NUM>, is reflected by the half mirror <NUM>, passes through a condenser lens <NUM>, and enters the light detector <NUM>. The light detector <NUM> detects the reflected light <NUM> reflected by the retina <NUM>. The image generation unit <NUM> generates a fundus image on the basis of the signal obtained by processing a detection result such as the luminance variation of the reflected light <NUM> by the light detector <NUM> by the signal processing unit <NUM>.

The collimating lens <NUM>, the diopter adjustment lens <NUM>, and the diopter adjustment lens <NUM> correspond to the adjustment mechanism <NUM> in <FIG>. The projection lens <NUM> corresponds to the optical system <NUM> in <FIG>.

<FIG> is a diagram for describing scanning of the light beam. As illustrated in <FIG>, the scanning unit <NUM> performs raster scanning with the light beam <NUM> from the upper left to the lower right as indicated by arrows <NUM>. In raster scanning, the horizontal direction is the main scanning direction, and the vertical direction is the sub-scanning direction. For example, the number of scanning lines is <NUM>. The retina <NUM> is not irradiated with the light beam <NUM> unless the light source <NUM> emits the light beam <NUM> even when the mirror of the scanning unit <NUM> biaxially swings and drives. For example, in the dotted arrows <NUM> in <FIG>, the light beam <NUM> is not emitted. The drive circuit <NUM> synchronizes the emission of the light beam <NUM> from the light source <NUM> and the biaxial swing drive of the scanning unit <NUM>. This causes the light source <NUM> to emit the light beam <NUM> in the solid line arrows <NUM>.

<FIG> is a perspective view of the scanning unit, and <FIG> is an enlarged perspective view of the vicinity of the mirror of the scanning unit. As illustrated in <FIG>, the scanning unit <NUM> is, for example, a MEMS, and includes an outer frame <NUM>, a suspension <NUM>, an inner frame <NUM>, a piezoelectric unit <NUM>, and a mirror <NUM>. The inner frame <NUM> is fixed to the outer frame <NUM> through the suspension <NUM>. The piezoelectric unit <NUM> has a structure in which a piezoelectric film such as a PZT film is sandwiched between upper and lower electrodes, and is fixed to the inner frame <NUM> by four first torsion bars <NUM> arranged at <NUM>-degree intervals. The mirror <NUM> is fixed to the piezoelectric unit <NUM> by two second torsion bars <NUM> arranged at <NUM>-degree intervals.

In the scanning unit <NUM>, warpage behavior caused by applying a voltage to the piezoelectric unit <NUM> is transmitted to the mirror <NUM> through the second torsion bar <NUM>, so that the mirror <NUM> biaxially swings and drives. Accordingly, when the light beam <NUM> enters the mirror <NUM>, the light beam <NUM> is scanned in two-dimensional directions. In <FIG>, the piezoelectric MEMS is illustrated as an example, but the scanning unit <NUM> may be a capacitive MEMS or other elements.

The outer peripheral region of the mirror <NUM> is curved (sagged) for manufacturing reasons. Therefore, when the light beam <NUM> is reflected by the entire region including the outer peripheral region of the mirror <NUM>, it is difficult to reflect the light beam <NUM> only in a desired direction. Therefore, to reflect the light beam <NUM> satisfactory, the light beam <NUM> is made to be reflected by a region further inward than the outer peripheral region where the mirror <NUM> curves. That is, the region excluding the outer peripheral region where curvature occurs of the mirror <NUM> is an effective region capable of reflecting the light beam <NUM> satisfactory. Therefore, the effective diameter, which is the length of the effective region of the mirror <NUM>, is equal to the value obtained by subtracting the length of the outer peripheral region where curvature occurs from the length of the mirror <NUM>. For example, in the case that the mirror <NUM> is circular and curvature occurs in the area within <NUM> from the edge of the mirror <NUM>, the effective diameter of the mirror <NUM> is equal to the value obtained by subtracting <NUM> from the diameter, which is the external diameter of the mirror <NUM>. In addition, in the case that the mirror <NUM> is elliptic, the effective diameter of the mirror <NUM> is equal to the value obtained by subtracting the length of the outer peripheral region where curvature occurs from the minor diameter, which is the external diameter. The external diameter of the mirror <NUM> is <NUM> or greater and <NUM> or less, and the effective diameter is <NUM> or greater and <NUM> or less, which will be described later.

<FIG> is an optical system of a fundus photography device in accordance with a comparative example. As illustrated in <FIG>, in a fundus photography device <NUM> of the comparative example, the light beam <NUM> is two-dimensionally scanned using a combination of a polygon mirror 513a and a galvano mirror 513b. The polygon mirror 513a scans the light beam <NUM> in the horizontal direction (the main scanning direction), for example, and the galvano mirror 513b scans the light beam <NUM> in the vertical direction (the sub-scanning direction), for example. In the fundus photography device <NUM>, the optical magnification of the projection lens <NUM> is <NUM> times. The optical magnification is a value represented by a ratio of the distances between the projection lens <NUM> and the polygon mirror 513a and the galvano mirror 513b to the distance between the projection lens <NUM> and the crystalline lens <NUM> of the subject or a convergence position of the light beam <NUM> near the crystalline lens <NUM>. Other structures are the same as those of the fundus photography device <NUM> of the first embodiment, and the description thereof is thus omitted.

In the fundus photography device <NUM> of the comparative example, the optical magnification of the projection lens <NUM> is <NUM> times for the following reason. When a fundus image is obtained by irradiating the retina <NUM> with the light beam <NUM>, a viewing angle of <NUM> degrees or greater in full angle is required to find a peripheral disease part. That is, the angle θ at which the light beams <NUM> converge at the convergence point in the eye <NUM> is required to be <NUM> degrees or greater. However, when the polygon mirror 513a and the galvano mirror 513b are used, it is difficult particularly for the galvano mirror 513b to scan the light beam <NUM> at a wide angle. For this reason, in the fundus photography device <NUM> of the comparative example using the polygon mirror 513a and the galvano mirror 513b, the optical magnification of the projection lens <NUM> is set to <NUM> times so that the viewing angle at the time of obtaining a fundus image is about <NUM> degrees.

The fundus photography device <NUM> using the polygon mirror 513a and the galvano mirror 513b is large and expensive. Therefore, instead of the polygon mirror 513a and the galvano mirror 513b, it is conceivable to use the scanning unit <NUM> that biaxially swings and drives to biaxially scan the light beam <NUM>. However, the inventor has found that it is difficult to obtain a high-quality fundus image only by arranging the scanning unit <NUM> at the positions of the polygon mirror 513a and the galvano mirror 513b. This will be described below.

To ensure the resolutions on the retina and the SN ratio of the fundus image, the fundus photography device is required to irradiate the entire width of approximately <NUM> on the retina corresponding to a viewing angle of <NUM> degrees (full angle) with about <NUM> light beams <NUM> without interference. That is, the spot size (the diameter) of the light beam <NUM> on the retina <NUM> is required to be <NUM> or less. <FIG> illustrates a relationship between the diameter of the light beam at the time of entering the cornea and the diameter of the light beam on the retina. As illustrated in <FIG>, as the diameter of the light beam <NUM> at the time of entering the cornea increases, the diameter of the light beam <NUM> on the retina <NUM> decreases. It is revealed that the diameter (the spot size) of the light beam <NUM> on the retina <NUM> can be made to be <NUM> or less by adjusting the diameter of the light beam <NUM> at the time of entering the cornea to be <NUM> or greater. The reason why the diameter of the light beam <NUM> on the retina <NUM> decreases as the diameter of the light beam <NUM> at the time of entering the cornea increases is as follows. The crystalline lens <NUM> exists on the retina side of the cornea, and the cornea and the crystalline lens <NUM> have optical characteristics having a positive light condensing power as a convex lens. When the diameter of the light beam <NUM> incident on it is large, the light condensing power becomes large and the spot size of the retina <NUM> becomes small. By contrast, when the diameter of the incident light beam <NUM> is small, the light condensing power is small and it is difficult to condense the light beam <NUM>, and the spot size of the retina <NUM> does not become sufficiently small.

In the fundus photography device <NUM> of the comparative example, the optical magnification of the projection lens <NUM> is <NUM> times. Therefore, when the scanning unit <NUM> is arranged at the positions of the polygon mirror 513a and the galvano mirror 513b without change, it is required to adjust the effective diameter of the mirror <NUM> of the scanning unit <NUM> to be <NUM> or greater to make the diameter of the light beam <NUM> at the time of entering the cornea <NUM> or greater. However, it is not practical to adjust the effective diameter of the mirror <NUM> of the scanning unit <NUM> to be <NUM> or greater. This is because of the following reasons.

<FIG> illustrates a relationship between the external diameter of the mirror of the scanning unit and the horizontal resonant frequency of the scanning unit. As illustrated in <FIG>, as the external diameter of the mirror <NUM> of the scanning unit <NUM> increases, the horizontal resonant frequency of the scanning unit <NUM> decreases. This is because as the external diameter of the mirror <NUM> of the scanning unit <NUM> increases, the inertia increases and the deformation of the mirror <NUM> increases, and thus, the horizontal resonant frequency cannot be increased. In the case that the difference between the external diameter and the effective diameter of the mirror <NUM> is <NUM>, the horizontal resonant frequency can be about <NUM> when the external diameter of the mirror <NUM> is <NUM>, can be about <NUM> when <NUM>, can be about <NUM> when <NUM>, and can be about <NUM> when <NUM>. Here, under the condition that the scanning unit <NUM> is a circular MEMS, the value of the difference between the external diameter and the effective diameter of the mirror <NUM> is adjusted to be <NUM>, but this value may differ depending on the characteristics of the MEMS.

When a fundus image is obtained by irradiating the retina <NUM> with the light beam <NUM> by raster scanning, it is required to set the number of scanning lines to <NUM> or greater and a frame rate to <NUM> fps or greater to obtain a high-quality fundus image. To achieve a frame rate of <NUM> fps in raster scanning with <NUM> scanning lines, the horizontal resonant frequency of the scanning unit <NUM> is required to be <NUM> or greater. From <FIG>, to set the horizontal resonant frequency of the scanning unit <NUM> to <NUM> or greater, the external diameter of the mirror <NUM> of the scanning unit <NUM> is required to be <NUM> or less (<NUM> or less as the effective diameter of the mirror <NUM>). For this reason, it is not practical to adjust the effective diameter of the mirror <NUM> of the scanning unit <NUM> to be <NUM> or greater to obtain the resonant frequencies required in the fundus photography device.

The deformation of the mirror <NUM> of the scanning unit <NUM> was simulated for the case in which the external diameter of the mirror <NUM> of the scanning unit <NUM> is <NUM>, the mechanical deflection angle is <NUM> degrees in half angle, and the horizontal resonant frequency is <NUM>. <FIG> present simulation results of the deformation of the mirror of the scanning unit. <FIG> illustrates the mirror <NUM> as viewed from above, <FIG> illustrates the mirror <NUM> as viewed from the front, and <FIG> illustrates the mirror <NUM> as viewed from an angle. <FIG> is a graph presenting the deformation along line A-A in <FIG>. In <FIG>, a part in which the deformation amount is small is indicated by coarse hatching, and a part in which the deformation amount in the positive direction and the negative direction is large is indicated by dense hatching.

As presented in <FIG>, in the case that the external diameter of the mirror <NUM> was <NUM>, the mechanical deflection angle was <NUM> degrees, and the horizontal resonant frequency was <NUM>, a high-order deformation mode was generated in the mirror <NUM>, and the largest deformation amount was about ±<NUM>. It is considered that such a high-order deformation mode becomes larger as the external diameter of the mirror <NUM> becomes larger. Therefore, when the effective diameter of the mirror <NUM> is adjusted to be <NUM> or greater, it is considered that the high-order deformation mode generated in the mirror <NUM> interferes with the optical performance, and it is not practical to adjust the effective diameter of the mirror <NUM> to be <NUM> or greater. In addition, in the case that the effective diameter of the mirror <NUM> is adjusted to be <NUM> or greater, it is considered that a large deflection angle cannot be obtained because of an increase in air resistance, and in this respect, it is not practical to adjust the effective diameter of the mirror <NUM> to <NUM> or greater.

In the case that the scanning unit <NUM> that biaxially swings and drives to two-dimensionally scan the light beam <NUM> is used as in the fundus photography device <NUM> of the first embodiment, the scanning angle θ1 (see <FIG>) of the light beam <NUM> can be made to be large compared with that in the case in which the polygon mirror 513a and the galvano mirror 513b are used. In this case, even when the optical magnification of the projection lens <NUM> is set to <NUM> times or greater and <NUM> times or less, the convergence angle θ2 (see <FIG>) of the light beam <NUM> at the convergence point in the eye <NUM> becomes large, and it is possible to achieve that the viewing angle at the time of obtaining the fundus image becomes about <NUM> degrees. In this case, the spot size of the light beam <NUM> on the retina <NUM> can be made to be <NUM> or less by adjusting the effective diameter of the mirror <NUM> of the scanning unit <NUM> to be <NUM> or greater (adjusting the external diameter to be <NUM> or greater).

In the first embodiment, the external diameter of the mirror <NUM> of the scanning unit <NUM> is <NUM> or greater and <NUM> or less. When the external diameter of the mirror <NUM> is <NUM> or greater (the effective diameter is, for example, <NUM> or greater), the spot size of the light beam <NUM> on the retina <NUM> can be made to be <NUM> or less, and the resolutions on the retina <NUM> and the SN ratio of the fundus image can be ensured. By adjusting the external diameter of the mirror <NUM> to be <NUM> or less (the effective diameter is, for example, <NUM> or less), raster scanning with <NUM> or more scanning lines and a frame rate of 15fps or greater can be performed. Thus, a high-quality fundus image can be obtained. In addition, since the diameter of the light beam <NUM> at the time of entering the cornea becomes <NUM> or less, even non-mydriasis is hardly blocked by the iris because the diameter of the human pupil is generally about <NUM> to <NUM>, and a fundus image can be obtained. The external diameter of the mirror <NUM> may be <NUM> or greater and <NUM> or less, may be <NUM> or greater and <NUM> or less, or may be <NUM> or greater and <NUM> or less. That is, the effective diameter of the mirror <NUM> may be <NUM> or greater and <NUM> or less, may be <NUM> or greater and <NUM> or less, or may be <NUM> or greater and <NUM> or less.

Since the scanning unit <NUM> can increase the scanning angle θ1, even when the optical magnification of the projection lens <NUM> (the optical system) is adjusted to be <NUM> times or greater and <NUM> times or less, it is possible to achieve that the viewing angle at the time of obtaining the fundus image is about <NUM> degrees. In this case, by adjusting the external diameter of the mirror <NUM> of the scanning unit <NUM> to be <NUM> or greater (adjusting the effective diameter to be, for example, <NUM> or greater), the spot size of the light beam <NUM> of the retina <NUM> can be made to be <NUM> or less. The optical magnification of the projection lens <NUM> (the optical system) may be <NUM> times or greater and <NUM> times or less, may be <NUM> times or greater and <NUM> times or less, and may be <NUM> times or greater and <NUM> times or less, and may be <NUM> time.

When a fundus image is obtained by irradiating the retina <NUM> with the light beam <NUM> that is two-dimensionally scanned by the scanning unit <NUM>, to obtain a high-quality fundus image, the resonant frequency in the horizontal direction (the resonant frequency in the main scanning direction) of the mirror <NUM> of the scanning unit <NUM> is preferably <NUM> or greater, more preferably <NUM> or greater, further preferably <NUM> or greater. To prevent the high-order deformation mode generated in the mirror <NUM> from increasing and interfering with the optical performance, the resonant frequency in the horizontal direction of the mirror <NUM> of the scanning unit <NUM> is preferably <NUM> or less, more preferably <NUM> or less, further preferably <NUM> or less.

To achieve a viewing angle of about <NUM> degrees at the time of obtaining a fundus image, the mechanical deflection angle in either one of the horizontal direction and the vertical direction, preferably the mechanical deflection angles in both the horizontal direction and the vertical direction of the mirror <NUM> of the scanning unit <NUM> are preferably <NUM> degrees or greater in half angle, more preferably <NUM> degrees or greater in half angle, further preferably <NUM> degrees or greater in half angle. In consideration of air resistance, the deformation of the mirror <NUM>, and the like, the mechanical deflection angle in either one of the horizontal direction and the vertical direction, preferably the mechanical deflection angles in both the horizontal direction and the vertical direction of the mirror <NUM> of the scanning unit <NUM> are preferably <NUM> degrees or less in half angle, more preferably <NUM> degrees or less in half angle, further preferably <NUM> degrees or less in half angle.

The projection lens <NUM> (an optical component) converts the light beams <NUM> that are reflected in different directions by the scanning unit <NUM> and have optical axes mutually diffusing, to the light beams <NUM> having optical axes mutually converging, and converts each light beam <NUM> from diffusion light to substantially parallel light. The light beam <NUM> is condensed between the scanning unit <NUM> and the projection lens <NUM>, then becomes diffusion light, enters the projection lens <NUM>, is converted to substantially parallel light by the projection lens <NUM>, and enters the eye <NUM> of the subject. Use of such a projection lens <NUM> to constitute the optical system <NUM> allows the fundus photography device <NUM> to be miniaturized.

<FIG> illustrates an optical system of a fundus photography device in accordance with a second embodiment. As illustrated in <FIG>, in a fundus photography device <NUM> of the second embodiment, the optical system <NUM> that irradiates the eye <NUM> of the subject with the light beam <NUM> reflected by the scanning unit <NUM> includes a projection lens 27a (a first optical component) and a projection lens 27b (a second optical component). The projection lens 27a converts the light beams <NUM> that are reflected in different directions by the scanning unit <NUM> and have optical axes mutually diffusing, to the light beams <NUM> having optical axes substantially parallel to each other, and converts each light beam <NUM> from substantially parallel light to convergent light. That is, the light beams <NUM> that have been reflected in different directions by the scanning unit <NUM> becomes parallel to each other by the projection lens 27a. The projection lens 27b converts the light beams <NUM> emitted from the projection lens 27a to the light beams <NUM> having optical axes mutually converging, and converts each light beam <NUM> from diffusion light to substantially parallel light. The light beam <NUM> enters the projection lens 27a as substantially parallel light, is condensed between the projection lens 27a and the projection lens 27b, then becomes diffusion light, enters the projection lens 27b, is converted to substantially parallel light by the projection lens 27b, and enters the eye <NUM> of the subject. Other configurations are the same as those of the fundus photography device <NUM> of the first embodiment, and the description thereof is thus omitted.

In the case that the optical system <NUM> includes the projection lens 27a (a first optical component) and the projection lens 27b (a second optical component) as in the fundus photography device <NUM> of the second embodiment, it is easy to achieve an optical magnification of <NUM> times or greater and <NUM> times or less for the optical system <NUM>.

accordance with a third embodiment. As illustrated in <FIG>, in a fundus photography device <NUM> of the third embodiment, the optical system <NUM> that irradiates the eye <NUM> of the subject with the light beam <NUM> reflected by the scanning unit <NUM> includes a converter lens <NUM> between the scanning unit <NUM> and a projection lens <NUM>, in addition to the projection lens <NUM>, and uses the scanning unit <NUM> that is a MEMS instead of the polygon mirror 513a and the galvano mirror 513b in <FIG>. Other configurations are the same as those of the fundus photography device <NUM> of the comparative example, and the description thereof is thus omitted.

In the configuration of the third embodiment, by providing the converter lens <NUM> between the scanning unit <NUM> and the projection lens <NUM>, even when the polygon mirror 513a and the galvano mirror 513b are replaced with the scanning unit <NUM> that is a MEMS, the fundus photography device can be structured without replacing the projection lens <NUM>. The projection lens <NUM> is the projection lens used in the comparative example of <FIG>, and is used in scanning by the polygon mirror and the galvano mirror.

In the first to third embodiments, the case in which a MEMS is used as the scanning unit <NUM> that biaxially drives to two-dimensionally scan the light beam <NUM> has been described as an example, but the scanning unit <NUM> may be other than the MEMS.

Claim 1:
A fundus photography device comprising:
a light source (<NUM>);
a scanning unit (<NUM>) that includes a mirror configured to biaxially drive in a horizontal direction and a vertical direction to two-dimensionally scan a light beam (<NUM>) emitted from the light source;
an optical system (<NUM>) configured to cause the light beam that has been reflected by the mirror of the scanning unit to enter an eye (<NUM>) of a subject; and
a light detector (<NUM>) configured to detect the light beam that has been reflected by a retina (<NUM>) of the subject,
wherein an external diameter of the mirror of the scanning unit is <NUM> or greater and <NUM> or less, wherein the mirror of the scanning unit is circular or elliptic, and wherein the external diameter is a diameter of the mirror of the scanning unit when the mirror of the scanning unit is circular, and is a minor diameter of the mirror of the scanning unit when the mirror of the scanning unit is elliptic,
wherein an effective diameter of the mirror of the scanning unit is <NUM> or greater and <NUM> or less wherein the effective diameter of the mirror of the scanning unit is equal to a value obtained by subtracting <NUM> from the external diameter of the mirror of the scanning unit,
wherein an optical magnification of the optical system is <NUM> times or greater and <NUM> times or less,
wherein a resonant frequency in the horizontal direction of the scanning unit is <NUM> or greater and <NUM> or less.