Ocular axial length measuring apparatus

Abstract

To provide an eye axial length measuring device capable of accurately measuring an eye axial length.SOLUTION: The ocular axial length measurement device 100 includes a light source 12 that emits a light beam 50, a variable focus lens 14 on which the light beam 50 emitted from the light source 12 is incident, a polarization beam splitter 16 that guides, in a first direction and a second direction, a reflected light beam 52 obtained by reflecting the light beam 50 transmitted through the variable focus lens 14 by an eye 7 of a subject, a first photodetector 18 that receives the reflected light beam 52 guided in the first direction, a second photodetector 20 that receives the reflected light beam 52 guided in the second direction, and a controller 30 that acquires a focal length of the variable focus lens 14 when the light beam 50 is focused on a cornea of the eye 7 by changing the focal length of the variable focus lens 14 based on an output of the first photodetector 18. An acquisition part 64 for acquiring the focal distance of the variable focus lens 14 when the light beam 50 is focused on the retina of the eye 70 based on the output of the second photodetector 20, and a calculation part 66 for calculating the axial length of the eye 70 by using the focal distance acquired by the acquisition part 64 are provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an axial length measuring device. [Background technology]

[0002] In recent years, the number of children with myopia has been increasing, and evaluation of the progression of myopia based on axial length has attracted attention. Axial length measurement devices using a Fourier domain method that uses a wavelength-swept light source are known. Since wavelength-swept light sources are expensive, axial length measurement devices using a time domain method are also known to reduce costs (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-000257 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to reduce the cost of the axial length measurement device, it is possible to use a confocal optical system. However, even when measuring the axial length using a confocal optical system, it is still necessary to measure the axial length with high accuracy.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to measure the axial length of the eye with high accuracy. [Means for solving the problem]

[0006] The present invention provides an axial length measurement device comprising: a light source that emits light rays; a variable-focus lens onto which the light rays emitted from the light source are incident; a polarizing beam splitter that guides the light rays that are transmitted through the variable-focus lens and reflected by a subject's eye in a first direction and a second direction; a first photodetector that receives the reflected light rays that are guided in the first direction; a second photodetector that receives the reflected light rays that are guided in the second direction; an acquisition unit that changes the focal length of the variable-focus lens and acquires a first focal length of the variable-focus lens when the light rays are focused on the cornea based on the output of the first photodetector and a second focal length of the variable-focus lens when the light rays are focused on the retina of the eye based on the output of the second photodetector; and a calculation unit that calculates the axial length of the eye using the first focal length and second focal length acquired by the acquisition unit.

[0007] In the above configuration, the configuration can include a scanning unit that scans the light beam that has passed through the variable-focus lens, and an optical element that converts multiple light beams emitted in different directions into parallel light beams as a result of the light beam being scanned by the scanning unit, and one of the multiple light beams converted into parallel light beams by the optical element is reflected by the eye to become the reflected light beam and enter the polarizing beam splitter.

[0008] In the above configuration, the area onto which the plurality of light beams converted into parallel light beams by the optical element are projected toward the eye can be configured to be at least twice the diameter of the pupil of the eye.

[0009] In the above configuration, the scanning unit may be an MEMS mirror, and the optical element may be a condenser lens.

[0010] In the above configuration, the optical system may include a first pinhole member having a pinhole for passing the reflected light beam, which is provided at a first focusing point where the light beam is focused on the cornea and the reflected light beam reflected by the cornea is collected, and a second pinhole member having a pinhole for passing the reflected light beam, which is provided at a second focusing point where the light beam is focused on the retina and the reflected light beam reflected by the retina is collected, and which has a pinhole for passing the reflected light beam, wherein the first photodetector receives the reflected light beam that has passed through the first pinhole member, and the second photodetector receives the reflected light beam that has passed through the second pinhole member.

[0011] In the above configuration, the light beam incident on the eye has a polarization direction that results in P polarization with respect to the polarizing beam splitter, and the polarizing beam splitter can be configured to guide the reflected P-polarized light beam in the first direction and guide the reflected S-polarized light beam in the second direction.

[0012] In the above configuration, the acquisition unit can be configured to sweep the focal length of the variable-focus lens, acquire the focal length of the variable-focus lens when the output of the first photodetector is maximized as the first focal length, and acquire the focal length of the variable-focus lens when the output of the second photodetector is maximized as the second focal length.

[0013] In the above configuration, the calculation unit can be configured to calculate the axial length using the first focal length, the second focal length, a third focal length of the anterior segment formed by the cornea and the crystalline lens of the eye, and the refractive index of an intermediate optical body formed by the crystalline lens and the vitreous body of the eye.

[0014] The above configuration may include a beam splitter that guides the light beam emitted by the light source to the variable-focus lens, and guides the reflected light beam that is reflected by the eye and transmitted through the variable-focus lens to the polarizing beam splitter. [Effects of the Invention]

[0015] According to the present invention, the axial length can be measured with high accuracy. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram of an axial length measuring device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the optical path section when the light beam is focused on the cornea in the first embodiment. [Figure 3] FIG. 3 is a diagram showing the optical path section when the light beam is focused on the retina in the first embodiment. [Figure 4] FIG. 4 is a diagram showing the output signal strengths of the first photodetector and the second photodetector relative to the focal length of the variable-focus lens in Example 1. In FIG. [Figure 5] FIG. 5 is a flowchart showing an example of a method for measuring the axial length in the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of a method for calculating the axial length by the calculation unit in the first embodiment. [Figure 7] 7(a) and 7(b) are diagrams showing optical path sections in Modifications 1 and 2 of the first embodiment. [Figure 8] FIG. 8 is a block diagram of an axial length measuring device according to the second embodiment. [Figure 9] 9(a) and 9(b) are diagrams showing the optical path unit in the second embodiment. [Figure 10] 10(a) and 10(b) are diagrams illustrating an example of a method for calculating the axial length by the calculation unit in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0018] FIG. 1 is a block diagram of an axial length measurement device 100 according to a first embodiment. In FIG. 1, electrical connections are indicated by dashed lines. As shown in FIG. 1, the axial length measurement device 100 includes an optical path unit 10, a control unit 60, a display unit 80, and a storage unit 82. The optical path unit 10 includes a light source 12, a variable-focus lens 14, a polarizing beam splitter 16, a first photodetector 18, and a second photodetector 20. The control unit 60 includes an emission control unit 62, an acquisition unit 64, and a calculation unit 66.

[0019] The emission control unit 62 controls the light source 12 to emit a light beam 50 (laser light). The light source 12 is, for example, an LD light source that emits the light beam 50 of infrared light (wavelength: approximately 780 nm to 900 nm). The light beam 50 emitted by the light source 12 has a polarization direction that results in P-polarization with respect to the polarizing beam splitter 16. Hereinafter, the P-polarization of the light beam 50 will always refer to the above state. Note that the light source 12 may emit the light beam 50 as monochromatic light such as red light (wavelength: approximately 610 nm to 660 nm), green light (wavelength: approximately 515 nm to 540 nm), or blue light (wavelength: approximately 440 nm to 480 nm), or as a combined light obtained by combining at least two of these. An example of such a light source 12 is a light source that includes at least one laser diode chip of red, green, and blue, and a combining device as needed.

[0020] A light ray 50 emitted from the light source 12 is incident on a variable-focus lens 14. The variable-focus lens 14 is capable of changing its focal length. The variable-focus lens 14 changes its focal length under the control of an acquisition unit 64, thereby changing the focal position of the light ray 50. The light ray 50 passes through the variable-focus lens 14 and enters the eye 70, where it is reflected by the eye 70. The reflected light ray 52 reflected by the eye 70 passes through the variable-focus lens 14 and enters the polarizing beam splitter 16.

[0021] The polarizing beam splitter 16 guides P-polarized light beams and S-polarized light beams in different directions. For example, the polarizing beam splitter 16 transmits P-polarized light beams and guides them in a first direction, and reflects S-polarized light beams and guides them in a second direction. When light 50 entering the eye 70 is P-polarized, the reflected light 52 reflected by the cornea remains P-polarized, while the reflected light 52 reflected by the retina becomes elliptically polarized. Therefore, since the reflected light 52 reflected by the cornea is P-polarized, it passes through the polarizing beam splitter 16 and is received by the first photodetector 18. Since the reflected light 52 reflected by the retina is elliptically polarized, a portion of it passes through the polarizing beam splitter 16, but the remainder is reflected by the polarizing beam splitter 16 and is received by the second photodetector 20. The first photodetector 18 and the second photodetector 20 are, for example, avalanche photodiodes (APDs).

[0022] Based on a control signal from the emission control unit 62, the acquisition unit 64 sweeps (changes) the focal length of the variable-focus lens 14, for example, from a minimum to a maximum, and acquires output signals from the first photodetector 18 and the second photodetector 20. The acquisition unit 64 acquires the focal length of the variable-focus lens 14 when the light beam 50 is focused on the cornea of ​​the eye 70 based on the output signal from the first photodetector 18, and acquires the focal length of the variable-focus lens 14 when the light beam 50 is focused on the retina of the eye 70 based on the output signal from the second photodetector 20. The variable-focus lens 14 includes, for example, a liquid lens and a piezoelectric vibrator. When a voltage is applied to the piezoelectric vibrator of the variable-focus lens 14, the shape of the liquid lens changes, thereby changing the focal length of the variable-focus lens 14. The acquisition unit 64 controls the focal length of the variable-focus lens 14 by controlling the voltage applied to the variable-focus lens 14.

[0023] The memory unit 82 stores information indicating the relationship between the voltage applied to the variable-focus lens 14 and the focal length of the variable-focus lens 14. Current information may be stored instead of voltage, and refractive power information may be stored instead of focal length. The memory unit 82 is a non-volatile memory, such as a semiconductor memory such as a flash memory. The acquisition unit 64 identifies the voltage applied to the variable-focus lens 14 when it determines, based on the output signal of the first photodetector 18, that the light beam 50 is focused on the cornea of ​​the eye 70, and acquires the focal length of the variable-focus lens 14 when the light beam 50 is focused on the cornea of ​​the eye 70 from this voltage and the information stored in the memory unit 82. The acquisition unit 64 also identifies the voltage applied to the variable-focus lens 14 when it determines, based on the output signal of the second photodetector 20, that the light beam 50 is focused on the retina of the eye 70, and acquires the focal length of the variable-focus lens 14 when the light beam 50 is focused on the retina of the eye 70 from this voltage and the information stored in the memory unit 82. The calculation unit 66 calculates the axial length of the eye 70 using the focal length of the variable-focus lens 14 acquired by the acquisition unit 64. The display unit 80 displays the calculation result of the axial length. The display unit 80 is, for example, a liquid crystal display.

[0024] The extraction control unit 62, the acquisition unit 64, and the calculation unit 66 may be processed by a processor such as a CPU (Central Processing Unit) working in cooperation with a program. The extraction control unit 62, the acquisition unit 64, and the calculation unit 66 may be circuits designed specifically for them. The extraction control unit 62, the acquisition unit 64, and the calculation unit 66 may be a single circuit or different circuits.

[0025] FIG. 2 is a diagram showing the optical path section 10 in the first embodiment when the light ray 50 is focused on the cornea 71. FIG. 3 is a diagram showing the optical path section 10 in the first embodiment when the light ray 50 is focused on the retina 72. As shown in FIGS. 2 and 3, the light source 12 emits a P-polarized light ray 50. The light ray 50 emitted by the light source 12 passes through the lens 22. The lens 22 is a condenser lens that converts the light ray 50 from divergent light to parallel light. The parallel light is not limited to completely parallel light, and approximately parallel light that is slightly convergent or divergent is also acceptable (the same applies hereinafter). The light ray 50 that has passed through the lens 22 passes through the beam splitter 24 and enters the variable-focus lens 14. The beam splitter 24 is, for example, a half mirror.

[0026] The variable-focus lens 14 sweeps the focal length, for example, from a minimum to a maximum, under the control of the acquisition unit 64 (see FIG. 1 ). As the focal length of the variable-focus lens 14 changes, the light ray 50 may be focused on the cornea 71 or on the retina 72.

[0027] As shown in Figure 2, when light ray 50 is focused on cornea 71, reflected light ray 52 reflected by cornea 71 is converted into parallel light by variable-focus lens 14, reflected by beam splitter 24, and enters polarizing beam splitter 16. Hereinafter, reflected light ray 52 focused on and reflected by cornea 71 will be referred to as reflected light ray 52a. Polarizing beam splitter 16 has the property of transmitting P-polarized light rays and guiding them in a first direction, and reflecting S-polarized light rays and guiding them in a second direction. Reflected light ray 52a, which is P-polarized light ray 50 reflected by cornea 71, is transmitted through polarizing beam splitter 16 and guided in the first direction, because it is P-polarized.

[0028] The reflected light ray 52a that has passed through the polarizing beam splitter 16 is incident on the lens 26. The lens 26 is a condensing lens. The reflected light ray 52a is converted from parallel light into convergent light by the lens 26 and is converged at the convergence point 30. A first pinhole member 28 is provided at the convergence point 30. The first pinhole member 28 is provided in advance at the convergence point where the parallel light ray is converted into convergent light by the lens 26 and is converged. The first pinhole member 28 has a pinhole 29 that passes the reflected light ray 52a. The reflected light ray 52a that has passed through the first pinhole member 28 is detected by the first photodetector 18.

[0029] In this way, P-polarized light ray 50 is focused on cornea 71, and reflected light ray 52a reflected by cornea 71 remains P-polarized and therefore passes through polarizing beam splitter 16 and is focused at focusing point 30 by lens 26. Even if first pinhole member 28 is provided at focusing point 30, most of reflected light ray 52a passes through pinhole 29 of first pinhole member 28 and is detected by first photodetector 18, resulting in a large output signal from first photodetector 18. On the other hand, reflected light rays other than reflected light ray 52a have portions blocked by first pinhole member 28, so the output signal from first photodetector 18 remains small. This improves the detection accuracy of reflected light ray 52a by first photodetector 18.

[0030] 3, when light ray 50 passes through pupil 73, lens 74, and vitreous body 75 and is focused on retina 72, reflected light ray 52 reflected by retina 72 is converted into parallel light by variable-focus lens 14, reflected by beam splitter 24, and enters polarizing beam splitter 16. Hereinafter, reflected light ray 52 focused on and reflected by retina 72 will be referred to as reflected light ray 52b. Reflected light ray 52b, which is P-polarized light ray 50 reflected by retina 72, becomes elliptically polarized due to birefringence within eye 70. Therefore, part of reflected light ray 52b passes through polarizing beam splitter 16 and is directed in a first direction, while the remainder is reflected by polarizing beam splitter 16 and is directed in a second direction.

[0031] The reflected light ray 52b reflected by the polarizing beam splitter 16 is incident on the lens 32. The lens 32 is a condenser lens. The reflected light ray 52b is converted from parallel light into convergent light by the lens 32 and is converged at the convergence point 36. A second pinhole member 34 is provided at the convergence point 36. The second pinhole member 34 is provided in advance at the convergence point where the parallel light ray is converted into convergent light by the lens 32 and is converged. The second pinhole member 34 has a pinhole 35 that passes the reflected light ray 52b. The reflected light ray 52b that passes through the second pinhole member 34 is detected by the second photodetector 20.

[0032] In this way, P-polarized light ray 50 is focused on retina 72, and reflected light ray 52b from retina 72 becomes elliptically polarized light, is reflected by polarizing beam splitter 16, and is focused at focal point 36 by lens 32. Even if second pinhole member 34 is provided at focal point 36, most of reflected light ray 52b passes through pinhole 35 of second pinhole member 34 and is detected by second photodetector 20, resulting in a large output signal from second photodetector 20. On the other hand, reflected light rays other than reflected light ray 52b are partially blocked by second pinhole member 34, and therefore the output signal from second photodetector 20 remains small. This improves the detection accuracy of reflected light ray 52b by second photodetector 20. Reflected light ray 52b that has passed through polarizing beam splitter 16 passes through first pinhole member 28 and is detected by first photodetector 18, similar to reflected light ray 52a.

[0033] 2 and 3, the reflected light ray 52a reflected by the cornea 71 and the reflected light ray 52b reflected by the retina 72 are guided in different directions by the polarizing beam splitter 16 in order to improve the detection accuracy of the reflected light ray 52a by the first photodetector 18 and the detection accuracy of the reflected light ray 52b by the second photodetector 20. That is, because the cornea 71 and the retina 72 are separated by the axial length of the eye, a difference occurs in the focal length of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 and when it is focused on the retina 72. In this case, by guiding the reflected light ray 52a and the reflected light ray 52b in different directions by the polarizing beam splitter 16, the first pinhole member 28 can be placed at the focal point 30 of the reflected light ray 52a, and the second pinhole member 34 can be placed at the focal point 36 of the reflected light ray 52b. This improves the detection accuracy of the reflected light ray 52a by the first photodetector 18 and the detection accuracy of the reflected light ray 52b by the second photodetector 20. Furthermore, the reflected light ray 52a reflected by the cornea 71 and the reflected light ray 52b reflected by the retina 72 are detected by different photodetectors (the first photodetector 18 and the second photodetector 20), which also improves the detection accuracy. For example, as will be described later, although the intensity of the reflected light ray 52b is small, the reflected light ray 52b is received by the second photodetector 20, which is different from the first photodetector 18 that receives the reflected light ray 52a, thereby improving the detection accuracy.

[0034] Fig. 4 is a diagram showing the output signal strength of the first photodetector 18 and the second photodetector 20 versus the focal length of the variable-focus lens 14 in Example 1. The lower diagram in Fig. 4 shows the first photodetector 18, and the upper diagram shows the second photodetector 20. In Fig. 4, the horizontal axis represents the focal length of the variable-focus lens 14, and the vertical axis represents the output signal strength of the first photodetector 18 and the second photodetector 20. As shown in Fig. 4, when the focal length of the variable-focus lens 14 changes, the focal position of the light beam 50 changes, and therefore the output signal strength of the first photodetector 18 and the second photodetector 20 changes.

[0035] For example, assume that light ray 50 is focused on cornea 71 when the focal length of variable-focus lens 14 is X. In this case, as shown in Fig. 2, reflected light ray 52a reflected by cornea 71 passes through first pinhole member 28 and is detected by first photodetector 18, and therefore the output signal strength of first photodetector 18 increases, as shown in Fig. 4. Because reflected light ray 52a does not enter second photodetector 20, the output signal strength of second photodetector 20 remains small.

[0036] For example, assume that light ray 50 is focused on retina 72 when the focal length of variable-focus lens 14 is Y. In this case, as shown in FIG. 3, reflected light ray 52b from retina 72 passes through second pinhole member 34 and is detected by second photodetector 20, resulting in an increased output signal intensity from second photodetector 20, as shown in FIG. 4. Reflected light ray 52b is also incident on first photodetector 18, resulting in an increased output signal intensity from first photodetector 18. In this case, because retina 72 is less likely to reflect light than cornea 71, the output signal intensity of first photodetector 18 and second photodetector 20, which receive reflected light ray 52b from retina 72, is smaller than the output signal intensity from first photodetector 18, which receives reflected light ray 52a from cornea 71. Therefore, the first photodetector 18 receives both the reflected light beam 52a and the reflected light beam 52b, but can determine whether it has received the reflected light beam 52a or the reflected light beam 52b from the magnitude of the output signal strength. In other words, if the output signal strength is equal to or greater than a predetermined value, it can be determined that it has received the reflected light beam 52a.

[0037] 4, in order to make it easier to understand that the light intensity of reflected light ray 52b is smaller than the light intensity of reflected light ray 52a, the output signal intensities (output signal intensity at focal length Y) of the first photodetector 18 and the second photodetector 20 that detect reflected light ray 52b are shown to be the same. However, it is preferable to use a highly sensitive photodetector as the second photodetector 20 that outputs a large signal intensity when it detects reflected light ray 52b.

[0038] The output signals of the first photodetector 18 and the second photodetector 20 are input to the acquisition unit 64. Therefore, the acquisition unit 64 can acquire the focal length of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 based on the output signal acquired from the first photodetector 18 when the focal length of the variable-focus lens 14 is swept. That is, the acquisition unit 64 determines that the light ray 50 is focused on the cornea 71 when the output signal acquired from the first photodetector 18 is maximum when the focal length of the variable-focus lens 14 is swept, and can acquire the focal length of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 from the voltage applied to the variable-focus lens 14 at that time. Similarly, the acquisition unit 64 can acquire the focal length of the variable-focus lens 14 when the light ray 50 is focused on the retina 72 based on the output signal acquired from the second photodetector 20 when the focal length of the variable-focus lens 14 is swept. In other words, the acquisition unit 64 determines that the time when the output signal acquired from the second photodetector 20 is maximum when the focal length of the variable-focus lens 14 is swept is the time when the light ray 50 is focused on the retina 72, and can acquire the focal length of the variable-focus lens 14 when the light ray 50 is focused on the retina 72 from the voltage applied to the variable-focus lens 14 at that time.

[0039] [Method for measuring axial length] Fig. 5 is a flowchart showing an example of a method for measuring the axial length in Example 1. As shown in Fig. 5, the emission control unit 62 causes the light source 12 to emit a light beam 50 (step S10). The light beam 50 emitted by the light source 12 is P-polarized.

[0040] Next, the acquisition unit 64 sweeps the focal length of the variable-focus lens 14, for example, from maximum to minimum, and acquires output signals from the first photodetector 18 and the second photodetector 20 (step S12). Next, the acquisition unit 64 acquires the focal length f1c of the variable-focus lens 14 based on the voltage applied to the variable-focus lens 14 when the output signal of the first photodetector 18 was maximum and information indicating the relationship between voltage and focal length stored in the memory unit 82 (step S14). Because the output signal of the first photodetector 18 is maximum when the light ray 50 is focused on the cornea 71, the acquisition unit 64 acquires the focal length f1c of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71.

[0041] Next, the acquisition unit 64 acquires the focal length f1r of the variable-focus lens 14 based on the voltage applied to the variable-focus lens 14 when the output signal of the second photodetector 20 was at its maximum and the information indicating the relationship between voltage and focal length stored in the memory unit 82 (step S16). Since the output signal of the second photodetector 20 is at its maximum when the light ray 50 is focused on the retina 72, the acquisition unit 64 acquires the focal length f1r of the variable-focus lens 14 when the light ray 50 is focused on the retina 72.

[0042] Next, the calculation unit 66 calculates the axial length using the focal lengths f1c and f1r acquired by the acquisition unit 64 (step S18).

[0043] Fig. 6 is a diagram illustrating an example of a method for calculating the axial length by the calculation unit 66 in Example 1. As shown in Fig. 6, the variable-focus lens 14 and the anterior segment of the eye including the cornea 71 can be considered as a composite optical system in which multiple lenses are combined. Here, the distance between the variable-focus lens 14 and the cornea 71 is d, the focal length of the variable-focus lens 14 when the light ray 50 is focused on the retina 72 is f1r, the focal length of the anterior segment formed by the cornea 71 and the crystalline lens 74 is f2, and the refractive index of the optical intermediate body formed by the crystalline lens 74 and the vitreous body 75 is n.

[0044] In this case, the composite focal length f can be calculated by f = (f1r × f2) / (f1r + f2 - d). Since the distance d is equal to the focal length f1c of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71, the composite focal length f can be calculated by f = (f1r + f2) / (f1r + f2 - f1c).

[0045] The distance δ between the principal point of the composite optical system and the principal point of the cornea 71 can be calculated by δ=(f×d) / f1r. Therefore, the distance δ can be calculated by δ=(f×f1c) / f1r.

[0046] The distance b from the principal point of the cornea 71 to the retina 72 can be calculated by b=f-δ. Taking into account the refractive index n of the optical intermediate body, the axial length A can be calculated by A=b×n.

[0047] The focal lengths f1c and f1r are obtained in steps S14 and S16 in Figure 5. The focal length f2 of the anterior segment and the refractive index n of the intermediate body have been proposed in various publications, and appropriate values ​​can be adopted by referring to these publications. For example, the following publications are known. Publication 1: "Refractive index distribution, wavelength dispersion, and its temperature change in the crystalline lens," Fujimitsu Morioka, Nara Medical University Institutional Repository, June 2, 1999, pp. 287-293. Publication 2: "Human model eye with a gradient-index crystalline lens," Longhui Liu et al., Optics, Vol. 30, No. 6, 2001, pp. 407-413. Publication 3: "Study on refractive index distribution and wavelength dispersion of the cornea," Chihiro Watanabe, Nara Medical University Institutional Repository, April 16, 1999, pp. 241-251.

[0048] 5, the calculation unit 66 calculates the axial length from the above formula using the focal lengths f1c and f1r acquired by the acquisition unit 64, the appropriately set focal length f2 of the anterior segment, and the refractive index n of the intermediate body. Next, the calculation unit 66 displays the calculated axial length on the display unit 80 (step S20).

[0049] 1, 2, and 3, a light beam 50 emitted from a light source 12 passes through a variable-focus lens 14 and enters an eye 70 of a subject. A reflected light beam 52 reflected by the eye 70 enters a polarizing beam splitter 16 and is guided in a first direction to pass through the polarizing beam splitter 16 and a second direction to be reflected by the polarizing beam splitter 16. The reflected light beam 52 guided in the first direction is detected by a first photodetector 18, and the reflected light beam 52 guided in the second direction is detected by a second photodetector 20. The acquisition unit 64 changes the focal length of the variable-focus lens 14, and acquires the focal length f1c (first focal length) of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 based on the output of the first photodetector 18, and acquires the focal length f1r (second focal length) of the variable-focus lens 14 when the light ray 50 is focused on the retina 72 based on the output of the second photodetector 20.

[0050] Because the variable-focus lens 14 can change the focal length at high speed, it is possible to quickly obtain the focal length f1c when the light ray 50 is focused on the cornea 71 and the focal length f1r when the light ray 50 is focused on the retina 72. This prevents the position of the eye 70 from moving while the focal lengths f1c and f1r are being obtained, improving the accuracy with which the first photodetector 18 and the second photodetector 20 detect the reflected light ray 52. ​​In addition, by using the polarizing beam splitter 16 to guide the reflected light ray 52 in the first and second directions, as described above, the accuracy with which the first photodetector 18 and the second photodetector 20 detect the reflected light ray 52 is improved. The obtaining unit 64 obtains the focal lengths f1c and f1r when the light ray 50 is focused on the cornea 71 or the retina 72 based on the outputs of the first photodetector 18 and the second photodetector 20, thereby improving the detection accuracy of the first photodetector 18 and the second photodetector 20, and thereby enabling the focal lengths f1c and f1r to be obtained with high accuracy. The calculation unit 66 calculates the axial length using the focal lengths f1c and f1r, and therefore the axial length can be measured with high accuracy.

[0051] In the first embodiment, as shown in FIG. 2, a first pinhole member 28 having a pinhole 29 for passing reflected light 52a is provided at a focal point 30 where reflected light 52a transmitted through the polarizing beam splitter 16 is focused. The first photodetector 18 receives the reflected light 52a that has passed through the first pinhole member 28. As shown in FIG. 3, a second pinhole member 34 having a pinhole 35 for passing reflected light 52b is provided at a focal point 36 where reflected light 52b reflected by the polarizing beam splitter 16 is focused. The second photodetector 20 receives reflected light 52b that has passed through the second pinhole member 34. This makes it easier to detect the peak of the output signal due to reflected light 52a from the first photodetector 18, and also makes it easier to detect the peak of the output signal due to reflected light 52b from the second photodetector 20. Therefore, the detection accuracy of the reflected light beam 52a by the first photodetector 18 and the detection accuracy of the reflected light beam 52b by the second photodetector 20 are improved.

[0052] In Example 1, the light ray 50 incident on the eye 70 has a polarization direction that results in P-polarized light relative to the polarizing beam splitter 16. In this case, the reflected light ray 52a reflected by the cornea 71 remains P-polarized, while the reflected light ray 52b reflected by the retina 72 becomes elliptically polarized. The polarizing beam splitter 16 transmits the P-polarized reflected light ray 52a and guides it in a first direction, and reflects the S-polarized reflected light ray 52b and guides it in a second direction. As a result, the first photodetector 18 detects the reflected light ray 52a reflected by the cornea 71, and the focal length f1c of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 can be obtained based on the output of the first photodetector 18. The second photodetector 20 receives the reflected light ray 52b reflected by the retina 72, and the focal length f1r of the variable-focus lens 14 when the light ray 50 is focused on the retina 72 can be obtained based on the output of the second photodetector 20. The light beam 50 may have a polarization direction that results in S-polarized light relative to the polarizing beam splitter 16 .

[0053] Furthermore, in the first embodiment, the acquisition unit 64 sweeps the focal length of the variable-focus lens 14, and acquires the focal length f1c of the variable-focus lens 14 when the output of the first photodetector 18 is maximized as the focal length (first focal length) when the light ray 50 is focused on the cornea 71. The acquisition unit 64 acquires the focal length f1r of the variable-focus lens 14 when the output of the second photodetector 20 is maximized as the focal length (second focal length) when the light ray 50 is focused on the retina 72. This makes it possible to easily and quickly acquire the focal lengths f1c and f1r.

[0054] Furthermore, in the first embodiment, the calculation unit 66 calculates the axial length using the focal lengths f1c and f1r of the variable-focus lens 14 when the light ray 50 is focused on the cornea 71 or the retina 72, the focal length f2 of the anterior segment formed by the cornea 71 and the crystalline lens 74, and the refractive index n of the optical intermediate body formed by the crystalline lens 74 and the vitreous body 75. This allows the axial length to be calculated with high accuracy.

[0055] 2 and 3, the first embodiment is provided with a beam splitter 24 that guides the light ray 50 emitted by the light source 12 to the variable-focus lens 14 and guides the reflected light ray 52 that is reflected by the eye 70 and transmitted through the variable-focus lens 14 to the polarizing beam splitter 16. This improves the detection accuracy of the reflected light ray 52a by the first photodetector 18 and the detection accuracy of the reflected light ray 52b by the second photodetector 20.

[0056] In the first embodiment, the acquiring unit 64 may acquire the focal length f1c of the varifocal lens 14 when the light ray 50 is focused on the cornea 71 and the focal length f1r of the varifocal lens 14 when the light ray 50 is focused on the retina 72 by the following method. That is, the acquiring unit 64 adjusts the focal length of the varifocal lens 14 so that the output signal of the first photodetector 18 reaches a maximum value equal to or greater than a predetermined value. Alternatively, the acquiring unit 64 adjusts the focal length of the varifocal lens 14 so that the output signal of the first photodetector 18 reaches a maximum value while preventing the output signal of the second photodetector 20 from increasing. The acquiring unit 64 may then acquire the focal length f1c of the varifocal lens 14 based on the voltage applied to the varifocal lens 14 when the output signal of the first photodetector 18 reached a maximum value and on information stored in the memory unit 82 indicating the relationship between voltage and focal length. Similarly, the acquiring unit 64 adjusts the focal length of the varifocal lens 14 so that the output signal of the second photodetector 20 reaches a maximum value. The acquisition unit 64 may then acquire the focal length f1r of the variable-focus lens 14 based on the voltage applied to the variable-focus lens 14 when the output signal of the second photodetector 20 reached its maximum value and information indicating the relationship between the voltage and the focal length stored in the memory unit 82.

[0057] [Variations] Fig. 7(a) is a diagram showing an optical path section in Modification 1 of Example 1, and Fig. 7(b) is a diagram showing an optical path section in Modification 2 of Example 1. Figs. 7(a) and 7(b) illustrate the optical path section subsequent to the polarizing beam splitter 16. Also shown are stray light 54, which is reflected light other than reflected light rays 52a and 52b that are formed when light ray 50 is focused on and reflected by the cornea 71 or retina 72.

[0058] 7(a), in Modification 1 of Example 1, an aperture member 38 is provided between the polarizing beam splitter 16 and the lens 26, and an aperture member 40 is provided between the polarizing beam splitter 16 and the lens 32. The aperture members 38 and 40 have openings 39 and 41 that allow light to pass through. By providing the aperture members 38 and 40 between the polarizing beam splitter 16 and the lenses 26 and 32, most of the stray light 54 is blocked by the aperture members 38 and 40. Therefore, the incidence of stray light 54 on the first photodetector 18 and the second photodetector 20 is reduced, and the detection accuracy of the reflected light rays 52a and 52b by the first photodetector 18 and the second photodetector 20 is improved.

[0059] As shown in FIG. 7( b), in Modification 2 of Example 1, light-blocking aperture members 42 and 45 are provided instead of the aperture members 38 and 40. The light-blocking aperture member 42 has an opening 44 around a light-blocking center portion 43 that allows light to pass through. Similarly, the light-blocking aperture member 45 has an opening 47 around a light-blocking center portion 46 that allows light to pass through. By providing the light-blocking aperture members 42 and 45, the central portion of stray light 54 is blocked by the light-blocking aperture members 42 and 45, thereby preventing stray light 54 from entering the first photodetector 18 and the second photodetector 20. This improves the detection accuracy of reflected light rays 52a and 52b by the first photodetector 18 and the second photodetector 20.

[0060] The aperture member and the light-blocking aperture member do not necessarily have to be provided both between the polarizing beam splitter 16 and the first photodetector 18 and between the polarizing beam splitter 16 and the second photodetector 20, but may be provided only on one side. Since the light intensity of the reflected light ray 52b reflected by the retina 72 is smaller than the light intensity of the reflected light ray 52a reflected by the cornea 71, it is preferable that the aperture member and the light-blocking aperture member be provided at least between the polarizing beam splitter 16 and the second photodetector 20. [Example]

[0061] FIG. 8 is a block diagram of an axial length measurement device 200 according to a second embodiment. As shown in FIG. 8, in the second embodiment, the optical path unit 10a has a scanning unit 90 (scanner) between the variable-focus lens 14 and the eye 70. The scanning unit 90 is, for example, a MEMS (Micro Electro Mechanical Systems) mirror. Under the control of the emission control unit 62, the scanning unit 90 scans the light beam 50 transmitted through the variable-focus lens 14 in two-dimensional directions. The light beam 50 scanned by the scanning unit 90 is projected toward the eye 70. The reflected light beam 52 reflected by the eye 70 passes through the scanning unit 90 and the variable-focus lens 14 and enters the polarizing beam splitter 16. The other configurations are the same as those shown in FIG. 1 of the first embodiment, and therefore will not be described further.

[0062] 9(a) and 9(b) are diagrams showing the optical path section in Example 2. In Figures 9(a) and 9(b), the optical path section between the variable-focus lens 14 and the eye 70 is shown. The other configurations are the same as those in Figures 2 and 3 of Example 1, and therefore are not shown. Figure 9(a) shows the case where light ray 50 is focused on the cornea 71, and Figure 9(b) shows the case where light ray 50 is focused on the retina 72.

[0063] As shown in Figures 9(a) and 9(b), light ray 50 transmitted through variable-focus lens 14 is reflected by mirror 92 and enters scanning unit 90. Mirror 92 is, for example, a plane mirror. Scanning unit 90 scans light ray 50 in two dimensions, horizontally and vertically. Scanned in two dimensions by scanning unit 90, multiple light ray 50 emitted from scanning unit 90 in different directions at different times enters optical element 94. As shown in Figure 9(a), when light ray 50 is focused on cornea 71, light ray 50 is collected near mirror 92 and enters optical element 94 as diffused light. As shown in Figure 9(b), when light ray 50 is focused on retina 72, light ray 50 is collected near scanning unit 90 and enters optical element 94 as diffused light.

[0064] The optical element 94 is, for example, a condenser lens. The optical axis direction of the optical element 94 is approximately parallel to the line of sight when the eye 70 is facing forward. The multiple light beams 50 emitted in different directions from the scanning unit 90 are converted into parallel light beams by the optical element 94. As shown in FIG. 9( a), when the light beam 50 is focused on the cornea 71, the light beam 50 is converted from a diffused light beam into a convergent light beam by the optical element 94. As shown in FIG. 9( b), when the light beam 50 is focused on the retina 72, the light beam 50 is converted from a diffused light beam into a slightly diffused light beam by the optical element 94. The optical axis direction of the optical element 94 and the line of sight when the eye 70 is facing forward are parallel to each other, and the light rays 50 are parallel to each other, but are not limited to being completely parallel. As will be described later, it is acceptable for the light rays 52a and 52b reflected by the eye 70 to be tilted to such an extent that they can enter the polarizing beam splitter 16 via the optical element 94, the scanning unit 90, and the variable-focus lens 14.

[0065] The multiple light rays 50 converted into parallel light rays by the optical element 94 are projected toward the eye 70. The area 96 onto which the multiple light rays 50 are projected toward the eye 70 is at least twice the diameter 76 of the pupil 73 of the eye 70. Note that although FIGS. 9(a) and 9(b) illustrate the vertical direction of the eye 70, the same applies to the horizontal direction of the eye 70, etc. One of the multiple light rays 50 is reflected by the cornea 71 or the retina 72. The reflected light ray 52a reflected by the cornea 71 and the reflected light ray 52b reflected by the retina 72 are incident on the variable-focus lens 14 via the optical element 94 and the scanning unit 90. The reflected light rays 52a and 52b are converted into parallel light by the variable-focus lens 14, reflected by the beam splitter 24, and incident on the polarizing beam splitter 16 (see also FIGS. 2 and 3).

[0066] The method for measuring the axial length in Example 2 is the same as the method for measuring the axial length in Example 1 shown in Fig. 5, except for the method for calculating the axial length by the calculation unit 66. Figs. 10(a) and 10(b) are diagrams illustrating an example of the method for calculating the axial length by the calculation unit 66 in Example 2. Figs. 10(a) and 10(b) mainly illustrate the variable-focus lens 14, optical element 94, and eye 70. A mirror 92 and a scanning unit 90 are disposed between the variable-focus lens 14 and the optical element 94.

[0067] Figure 10(a) shows the case where light ray 50 is focused on the cornea 71. As shown in Figure 10(a), light ray 50 converted into converging light by variable-focus lens 14 is focused in front of optical element 94, and then becomes diverging light and enters optical element 94. Light ray 50 is converted into converging light by optical element 94 and is focused on the cornea 71. When light ray 50 is focused on the cornea 71, the focal length of variable-focus lens 14 is f1c, the focal length of optical element 94 is f3, the distance between variable-focus lens 14 and optical element 94 is d2, and the distance between optical element 94 and cornea 71 is d3.

[0068] In this case, since 1 / (d2-f1c)+1 / d3=1 / f3 is satisfied, d3=f3(d2-f1c) / (d2-f1c-f3), where d2 is a value obtained from the arrangement of the optical system, f3 is a value obtained from the focal length of the selected optical element 94, and f1c is a value obtained based on the output signal of the first photodetector 18. In this way, since d2, f3, and f1c are all known values, the value of d3 can be obtained.

[0069] 10(b) shows the case where light ray 50 is focused on retina 72. As shown in FIG. 10(b), light ray 50 converted into converging light by variable-focus lens 14 is focused just before optical element 94, then becomes divergent light and enters optical element 94. Light ray 50 is converted into slightly divergent light by optical element 94, passes through the anterior segment of the eye and the optical intermediate body, and is focused on retina 72. When light ray 50 is focused on retina 72, the focal length of variable-focus lens 14 is f1r, the focal length of optical element 94 is f3, the focal length of the anterior segment of the eye 70 is f2, the refractive index of the optical intermediate body is n, the distance between variable-focus lens 14 and optical element 94 is d2, and the distance between optical element 94 and cornea 71 is d3.

[0070] The composite focal length f4 of the composite optical system (hereinafter referred to as the first composite optical system) of the variable-focal-length lens 14 and optical element 94 can be calculated by f4 = (f1r × f3) / (f1r + f3 - d2). As described above, d2 and f3 are known values, and f1r is also a known value because it is a value obtained based on the output signal of the second photodetector 20. Therefore, the value of f4 can be calculated.

[0071] Here, the radius of the light ray 50 incident on the variable-focus lens 14 is defined as R. In this case, the NA of the light ray 50 after passing through the first combining optical system can be calculated by NA = R / f4. Furthermore, the radius R' of the light ray 50 at the optical element 94 can be calculated by R' = (R × (d2 - f1r)) / f1r. The distance X1 between the optical element 94 and the focal point 99 of the first combining optical system can be calculated by X1 = (f4 × R') / R. The distance X2 between the optical element 94 and the principal point 98 of the first combining optical system can be calculated by X2 = X1 + f4. The distance d4 between the principal point 98 of the first combining optical system and the cornea can be calculated by d4 = X2 + d3.

[0072] The composite focal length f5 of the composite optical system (hereinafter referred to as the second composite optical system) combining the first composite optical system and the anterior segment can be calculated by f5 = (f4 × f2) / (f4 + f2 - d4). Since the anterior segment satisfies 1 / f2 = 1 / (d3 + X1) + 1 / b, b = {f2 × (d3 + X1) / (d3 + X1 - f2). Taking into account the refractive index n of the intermediate body, the axial length A can be calculated by A = b × n.

[0073] 9(a) and 9(b), the second embodiment includes a scanning unit 90 that scans a light beam 50 that has passed through the variable-focus lens 14, and an optical element 94 that converts the multiple light beams 50 that are emitted in different directions as a result of scanning by the scanning unit 90 into parallel light beams. As a result, even if the position of the eye 70 is displaced from the reference position, one of the multiple light beams 50 is reflected by the cornea 71 or retina 72, becomes reflected light beam 52a or 52b, and enters the polarizing beam splitter 16. This increases the tolerance for the position of the eye 70, making it possible to easily measure the axial length while ensuring measurement accuracy.

[0074] 9(a) and 9(b), in Example 2, the area 96 onto which the plurality of light beams 50 converted into parallel light beams by the optical element 94 are projected toward the eye 70 is at least twice the diameter 76 of the pupil 73 of the eye 70. This increases the tolerance for the position of the eye 70, making it possible to easily measure the axial length while ensuring measurement accuracy. From the viewpoint of easily measuring the axial length while ensuring measurement accuracy, the area 96 is preferably at least three times the diameter 76 of the pupil 73, more preferably four times or more, and even more preferably five times or more. From the viewpoint of preventing the device from becoming too large, the area 96 is preferably at most eight times the diameter 76, more preferably seven times or less, and even more preferably six times or less.

[0075] In the second embodiment, the scanning unit 90 is a MEMS mirror, and the optical element 94 is a condenser lens, which can prevent the device from becoming too large.

[0076] Although the first embodiment, its modifications, and the second embodiment have been described with reference to the case where only one light source is provided, multiple light sources emitting light beams of different wavelengths may be provided. In this case, the axial length may be measured for each of the multiple wavelengths of light beams and the average value may be calculated. This allows the axial length to be calculated more accurately.

[0077] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0078] DESCRIPTION OF SYMBOLS 10, 10a...optical path section, 12...light source, 14...variable focus lens, 16...polarized beam splitter, 18...first photodetector, 20...second photodetector, 22...lens, 24...beam splitter, 26...lens, 28...first pinhole member, 29...pinhole, 30...focusing point, 32...lens, 34...second pinhole member, 35...pinhole, 36...focusing point, 38...aperture member, 39...opening, 40...aperture member, 41...opening, 42...light-shielding aperture a light-shielding aperture member, 43...center portion, 44...aperture, 45...light-shielding aperture member, 46...center portion, 47...aperture, 50...light ray, 52, 52a, 52b...reflected light ray, 54...stray light, 60...control unit, 62...emission control unit, 64...acquisition unit, 66...calculation unit, 70...eye, 71...cornea, 72...retina, 73...pupil, 74...crystalline lens, 76...pupil diameter, 80...display unit, 82...storage unit, 90...scanning unit, 92...mirror, 94...optical element, 96...area, 100, 200...axial length measuring device

Claims

1. a light source that emits a light beam; a variable focus lens onto which the light beam emitted from the light source is incident; a polarizing beam splitter that guides the light beam, which is transmitted through the variable-focus lens and reflected by the subject's eye, in a first direction and a second direction; a first photodetector that receives the reflected light beam directed in the first direction; a second photodetector that receives the reflected light beam directed in the second direction; an acquisition unit that changes a focal length of the variable-focus lens, and acquires a first focal length of the variable-focus lens when the light beam is focused on the cornea of ​​the eye based on the output of the first photodetector, and acquires a second focal length of the variable-focus lens when the light beam is focused on the retina of the eye based on the output of the second photodetector; a calculation unit that calculates the axial length of the eye using the first focal length and the second focal length acquired by the acquisition unit.

2. a scanning unit that scans the light beam that has passed through the variable-focus lens; an optical element that converts a plurality of light beams emitted in different directions into parallel light beams as a result of the light beam being scanned by the scanning unit, 2. The axial length measuring device according to claim 1, wherein one of the plurality of light beams converted into parallel light beams by the optical element is reflected by the eye to become the reflected light beam and enter the polarizing beam splitter.

3. 3. The axial length measuring device according to claim 2, wherein an area onto which the plurality of light beams converted into parallel light beams by the optical element are projected toward the eye is at least twice the diameter of the pupil of the eye.

4. the scanning unit is a MEMS mirror, 4. The axial length measuring device according to claim 2, wherein the optical element is a condenser lens.

5. a first pinhole member provided at a first focusing point where the light beam is focused on the cornea and the reflected light beam reflected by the cornea is focused, the first pinhole member having a pinhole for passing the reflected light beam; a second pinhole member provided at a second light-focusing point where the light beam is focused on the retina and the reflected light beam reflected by the retina is focused, the second pinhole member having a pinhole for passing the reflected light beam; the first photodetector receives the reflected light beam that has passed through the first pinhole member; 3. The axial length measuring device according to claim 1, wherein the second photodetector receives the reflected light beam that has passed through the second pinhole member.

6. the light beam incident on the eye has a polarization direction that is P-polarized with respect to the polarizing beam splitter, 3. The axial length measurement device according to claim 1, wherein the polarizing beam splitter guides the reflected light beam of P-polarized light in the first direction and guides the reflected light beam of S-polarized light in the second direction.

7. 3. The axial length measurement device according to claim 1, wherein the acquisition unit sweeps the focal length of the variable-focus lens, acquires the focal length of the variable-focus lens when the output of the first photodetector is maximized as the first focal length, and acquires the focal length of the variable-focus lens when the output of the second photodetector is maximized as the second focal length.

8. 3. The axial length measurement device according to claim 1, wherein the calculation unit calculates the axial length using the first focal length, the second focal length, a third focal length of an anterior segment formed by the cornea and the crystalline lens of the eye, and a refractive index of an intermediate body formed by the crystalline lens and the vitreous body of the eye.

9. 3. The axial length measurement device according to claim 1, further comprising a beam splitter that guides the light beam emitted by the light source to the variable-focus lens and guides the reflected light beam that is reflected by the eye and transmitted through the variable-focus lens to the polarizing beam splitter.

Images