Ophthalmic devices

Abstract

To provide an ophthalmologic apparatus capable of reducing a burden on a subject and accurately acquiring an eye axial length.SOLUTION: An ophthalmologic apparatus includes: an eye refractive power measurement optical system for projecting first measurement light to an eyeground of a subject's eye and acquiring an eye refractive power of the subject's eye based on reflection light of the first measurement light reflected in the eyeground; a cross-sectional image imaging optical system for acquiring an anterior eye part cross-sectional image of the subject's eye by projecting second measurement light to an anterior eye part of the subject's eye and detecting, by a light detector, return light of the second measurement light from an oblique direction to a light projection optical axis of the second measurement light; and eye axial length acquisition means for acquiring an eye axial length of the subject's eye based on the eye refractive power and the anterior eye part cross-sectional image. The first measurement light is an infrared light and the second measurement light is red visible light or infrared light.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an ophthalmic apparatus that acquires the axial length of a subject's eye. [Background technology]

[0002] There is known an ophthalmologic apparatus that illuminates the optic body of the anterior segment of a subject's eye in a light-cut manner and captures a cross-sectional image of the anterior segment. Visible light of blue, green, white, etc. is projected onto the subject's eye. In Patent Document 1, blue visible light is used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-134907 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned ophthalmologic apparatus, the light having a wavelength suitable for photographing opacities in the optical medium is used to illuminate the anterior segment of the subject's eye, so the subject may feel dazzled. In particular, when the subject, such as a young person (including a child), cannot tolerate the glare caused by the illumination, it is difficult to photograph the subject accurately and efficiently.

[0005] On the other hand, in recent years, the prevalence of myopia has increased significantly, especially among young people, and evaluation of myopia progression based on axial length has attracted attention. The inventors have studied a device configuration that acquires both the ocular refractive power and anterior ocular cross-sectional image of the subject's eye and acquires the axial length based on these. However, if the anterior ocular cross-sectional image of the subject's eye is not captured properly due to the influence of glare, it becomes difficult to acquire the axial length.

[0006] The present disclosure has been made in consideration of the above circumstances, and has as its technical object to provide an ophthalmic apparatus that reduces the burden on a subject and can obtain an axial length with high accuracy. [Means for solving the problem]

[0007] The ophthalmic device disclosed herein includes an ophthalmic power measuring optical system for projecting a first measurement light onto the fundus of the test eye and acquiring the ocular refractive power of the test eye based on the light reflected from the fundus of the first measurement light; a cross-sectional image capturing optical system for projecting a second measurement light onto an anterior segment of the test eye and detecting the return light of the second measurement light from an oblique direction with a photodetector with respect to the projection optical axis of the second measurement light, thereby acquiring a cross-sectional image of the anterior segment of the test eye; and an axial length acquiring means for acquiring the axial length of the test eye based on the ocular refractive power and the anterior segment cross-sectional image, wherein the first measurement light is infrared light and the second measurement light is red visible light or infrared light. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an external view of an ophthalmologic apparatus. [Diagram 2] FIG. 2 is a schematic diagram showing an optical system of an ophthalmic apparatus. [Diagram 3] 1 is a schematic diagram showing the relationship between the visibility of a test eye and wavelength. [Figure 4] 2 is a schematic diagram showing the relationship between the light receiving sensitivity of an image sensor and wavelength. FIG. [Diagram 5] FIG. 2 is a simplified schematic diagram of a fixation target presenting optical system. [Figure 6] FIG. 2 is a schematic diagram showing a simplified visual target projection optical system. [Figure 7] 4 is a flowchart showing a control operation of the ophthalmic apparatus. [Figure 8] 1 is an example of a cross-sectional image of the anterior segment. [Figure 9] FIG. 11 is a schematic diagram for explaining a method for deriving the axial length. [Figure 10] FIG. 1 is a diagram showing refractive power in the meridian direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] "overview" An overview of an ophthalmic device according to an embodiment of the present disclosure will be described. The items classified in < > below can be used independently or in association with each other. In this embodiment, "conjugate" is not necessarily limited to a perfect conjugate relationship, but includes "approximate conjugate." In other words, "conjugate" in this embodiment also includes cases where the position is shifted from the perfect conjugate position within a range permitted in relation to the technical significance of each part.

[0010] The ophthalmic device of the present embodiment is a device capable of acquiring the axial length of the subject's eye. For example, the ophthalmic device may be configured to reduce glare caused by illumination of the subject's eye. In other words, the ophthalmic device may be configured to suppress miosis of the subject's eye. This allows the ocular refractive power of the subject's eye to be measured accurately in an ocular refractive power measuring optical system described later. In addition, in a cross-sectional image taking optical system described later, a good cross-sectional image that captures the anterior segment of the subject's eye deeper (for example, up to the posterior surface of the crystalline lens) is easily acquired. As a result, the axial length can be acquired accurately based on the ocular refractive power and the cross-sectional image of the anterior segment. In particular, when the subject has difficulty in enduring glare (for example, young people including children), reducing glare as in the present embodiment is effective.

[0011] The ophthalmologic apparatus of this embodiment may include an optical system used to acquire the axial length, and an axial length acquisition unit.

[0012] <Ocular refractive power measurement optical system> The ophthalmologic apparatus of the present embodiment may have an eye refractive power measuring optical system (e.g., a measuring optical system 100). The eye refractive power measuring optical system is an optical system for acquiring the eye refractive power of the subject's eye. For example, the ophthalmologic apparatus may include a configuration for projecting measuring light (first measuring light) onto the fundus of the subject's eye and acquiring the eye refractive power based on the reflected light of the measuring light reflected by the fundus.

[0013] The eye refraction measuring optical system may be a measuring optical system used in an objective eye refraction measuring device (such as an autorefractometer and a wavefront sensor). The projection optical axis of the first measuring light in the eye refraction measuring optical system may be disposed on the surface of a light section formed by a cross-sectional image capturing optical system described later. For this reason, the eye refraction measuring optical system is used to obtain the eye refraction on the light section of the anterior eye (on-surface eye refraction). Of course, the eye refraction measuring optical system may be capable of obtaining the eye refraction on other surfaces.

[0014] <Cross-sectional image capturing optical system> The ophthalmic apparatus of the present embodiment may have a cross-sectional image capturing optical system (for example, a cross-sectional image capturing optical system). The cross-sectional image capturing optical system is an optical system for acquiring a cross-sectional image of an anterior segment of an eye to be examined. For example, the apparatus may include a configuration for acquiring a cross-sectional image of an anterior segment of an eye by projecting a measurement light toward the anterior segment of an eye to be examined and detecting return light (scattered light) due to scattering of the measurement light from an oblique direction with respect to the projection optical axis of the measurement light. In addition, the apparatus may include a configuration for projecting a measurement light (second measurement light) toward the anterior segment of an eye to be examined, forming a light section passing through the optical axis of the eye refractive power measurement optical system on the anterior segment, and acquiring a cross-sectional image of an anterior segment based on scattered light from the light section of the second measurement light.

[0015] The cross-sectional image photographing optical system may be an optical system based on the Scheimpflug principle. In this case, the projection optical axis of the first measurement light in the eye refractive power measuring optical system and the projection optical axis of the second measurement light in the cross-sectional image photographing optical system may be arranged coaxially. In this case, the second measurement light may be projected as slit light in the cross-sectional image photographing optical system. For example, the irradiation area of ​​the slit light is set as a light section plane of the anterior eye. In this case, the cross-sectional image photographing optical system may have a lens system and a photodetector arranged in a Scheimpflug relationship with the light section plane formed in the anterior eye. For example, the photodetector may be a two-dimensional imaging element. The receiving optical axis of the second measurement light is arranged to be inclined with respect to the light section plane.

[0016] The imaging range of the anterior segment cross-sectional image by the cross-sectional image capturing optical system preferably includes at least the anterior surface of the cornea of ​​the subject's eye to the anterior surface of the crystalline lens. Needless to say, it is even more preferable if it includes the anterior surface of the cornea to the posterior surface of the crystalline lens. In this case, the corneal thickness, the anterior corneal radius of curvature, the posterior corneal radius of curvature, the anterior chamber depth, the crystalline lens thickness, the anterior crystalline lens radius of curvature, and the posterior crystalline lens radius of curvature can be obtained without omission, so that the axial length can be calculated more accurately.

[0017] <First measuring light and second measuring light> In this embodiment, the first measurement light in the eye refractive power measuring optical system may be composed of light having a wavelength that the subject's eye does not feel glare. For example, the first measurement light may be composed of infrared light (near infrared light, mid infrared light, or far infrared light). This allows the subject to not feel glare when the first measurement light is projected, suppresses pupil constriction, and allows the eye refractive power to be accurately determined.

[0018] In this embodiment, the second measurement light in the cross-sectional image photographing optical system may be composed of light having a wavelength at which the subject's eye does not feel glare. For example, the second measurement light may be composed of red visible light. The luminosity of red visible light is low, and the subject is unlikely to feel glare. For example, the second measurement light may be composed of infrared light (near infrared light, mid infrared light, or far infrared light). The luminosity of infrared light is approximately 0, and the subject is unlikely to feel glare. Therefore, the subject does not feel (is unlikely to feel) glare when the second measurement light is projected, and the frequency of failure to photograph due to turning away the face or blinking is reduced. As a result, the anterior eye cross-sectional image can be photographed with high accuracy.

[0019] In the eye refractive power measuring optical system and the cross-sectional image photographing optical system, infrared light can be used for the first measuring light and the second measuring light, but the first wavelength of the first measuring light and the second wavelength of the second measuring light may be the same wavelength or may be different from each other. For example, when the first wavelength and the second wavelength are different from each other, the second wavelength may be shorter than the first wavelength, or the second wavelength may be longer than the first wavelength. This suppresses the interference between the infrared lights and improves the measurement accuracy.

[0020] In this embodiment, the second wavelength of the second measurement light may be shorter than the first wavelength of the first measurement light. More specifically, in the wavelength range of red visible light to infrared light corresponding to the first measurement light and the second measurement light, the first wavelength may be set on the long wavelength side where visibility is low, and the second wavelength may be set on the short wavelength side where visibility is high. For example, since the first measurement light is focused on the fundus and the second measurement light is focused on the anterior segment, the first measurement light is more likely to be felt as glare than the second measurement light. By setting the wavelengths in this way, the burden on the subject is further reduced.

[0021] For example, near-infrared light may be used as the first measurement light. As an example, the first wavelength of the first measurement light may have a peak wavelength between 800 nm and 900 nm. In this case, a light source having an emission wavelength of 800 nm at its lower limit and 900 nm at its upper limit may be used in the eye refractive power measurement optical system. Alternatively, a light source having an emission wavelength of shorter than 800 nm at its lower limit and longer than 900 nm at its upper limit may be used, and light having a wavelength shorter than 800 nm and light having a wavelength longer than 900 nm may be cut by an optical member (such as a cut filter, for example) in the optical path.

[0022] For example, red visible light or near infrared light may be used as the second measurement light. As an example, the second wavelength may have a peak wavelength between 650 nm and 800 nm. Preferably, the peak wavelength is between 700 nm and 750 nm, which is less likely to affect miosis. In this case, a light source with a lower limit of the emission wavelength of 700 nm and an upper limit of 750 nm may be used in the cross-sectional image capturing optical system. Alternatively, a light source with a lower limit of the emission wavelength shorter than 700 nm and an upper limit of the emission wavelength longer than 750 nm may be used, and light with a wavelength shorter than 700 nm and light with a wavelength longer than 750 nm may be cut by an optical member in the optical path.

[0023] For example, by using near-infrared light as the first measurement light and red visible light or near-infrared light as the second measurement light, the subject is less likely to feel dazzled and a photodetector with various wavelength sensitivity ranges can be used (details will be described later).

[0024] In this embodiment, at least two types of measurement light may be provided as the second measurement light that can be projected by the cross-sectional image capturing optical system: light having the above-mentioned second wavelength (i.e., red visible light or infrared light) and light having a wavelength different from the second wavelength. For example, the light having a wavelength different from the second wavelength may be light that takes into consideration the wavelength transmittance (scattering component) of the subject's eye. As an example, it may be at least any visible light such as blue visible light, green visible light, white visible light, etc. Note that if the light having the second wavelength is infrared light, red visible light can also be used as the light having a wavelength different from the second wavelength.

[0025] For example, the longer the wavelength of the second measurement light, the more effective it is in reducing glare, but the more difficult it is to scatter, and the darker the anterior-segment cross-sectional image is. For this reason, the second measurement light may include light with a second wavelength (red visible light or infrared light) that prioritizes reducing glare, and light with a wavelength different from the second wavelength that prioritizes brightness of the anterior-segment cross-sectional image. For example, when the subject's eye suffers from cataract disease, the light with the second wavelength is more transmitted than visible light even if there is opacity, and the anterior-segment cross-sectional image is not very bright, which may make it difficult to diagnose cataracts. For this reason, the second measurement light may include light with a wavelength different from the second wavelength that is suitable for photographing opacities, in addition to the light with the second wavelength. For example, the second wavelength light and the light with a wavelength different from the second wavelength may be selectively projected in this way, so that a good anterior-segment cross-sectional image can be obtained.

[0026] <Photodetector> The photodetector of the cross-sectional image capturing optical system may be a detector having a wavelength sensitivity range for the second measurement light (second wavelength), i.e., a detector having a wavelength sensitivity range for red visible light, a detector having a wavelength sensitivity range for infrared light, a detector having a wavelength sensitivity range for red visible light and infrared light, etc.

[0027] The detector may include a semiconductor substrate made of various elements. The semiconductor may be made of a single element. For example, any of silicon (Si), germanium, selenium, etc. may be used as the material. As an example, a photodetector using a semiconductor substrate made of Si (hereinafter, Si image sensor) is sensitive to wavelengths including the ultraviolet to infrared ranges. Although the sensitivity to red visible light and infrared light is reduced, it is possible to detect these lights, and an anterior segment cross-sectional image can be obtained. Of course, a photodetector with improved infrared light sensitivity using a semiconductor substrate made of black Si as a material in addition to normal Si may be used.

[0028] The semiconductor may be a material made of multiple elements (so-called compound semiconductor). In this case, a material made of a combination of iridium, gallium, and arsenic (InGaAs), a material made of indium and antimony (InSb), a material made of mercury, cadmium, and tellurium (HgCdTe), etc. may be used. In addition to these, a material made of multiple elements including silicon may be used. As an example, a photodetector using a semiconductor substrate made of InGaAs (hereinafter, InGaAs image sensor) is sensitive to wavelengths including the visible range (red visible range) to the infrared range. It has high sensitivity to red visible light and infrared light, and can acquire a cross-sectional image of the anterior eye segment.

[0029] In addition, if the ophthalmic device becomes expensive, it may hinder the widespread use of the device, and the axial length may not be obtained at an appropriate time. For example, in response to the global issue of the increase in the prevalence of myopia, mainly among young people, evaluation of the progression of myopia based on the axial length has attracted attention, but if many facilities such as hospitals and schools do not have the device, the opportunity to obtain the axial length will decrease. In this embodiment, a Si image sensor, which has a lower detection sensitivity than an InGaAs image sensor but is inexpensive, is used as the photodetector of the cross-sectional image capturing optical system, thereby realizing a reduction in the cost of the device.

[0030] <Method for acquiring axial length> The ophthalmologic apparatus of this embodiment may include an axial length acquiring means (for example, the control unit 50). For example, the axial length acquiring means may serve as an image processing unit, an axial length acquiring unit, and an arithmetic control unit, etc.

[0031] The axial length acquiring means may acquire the ocular refractive power of the subject's eye by controlling acquisition of the ocular refractive power using the ocular refractive power measuring optical system. More specifically, the axial length acquiring means may acquire the ocular refractive power of the subject's eye by controlling projection of the first measurement light in the ocular refractive power measuring optical system and detection of the fundus reflected light of the first measurement light by the photodetector.

[0032] The axial length acquiring means may acquire the cross-sectional image of the anterior segment of the subject's eye by controlling acquisition of the cross-sectional image of the anterior segment of the subject's eye using the cross-sectional image capturing optical system. More specifically, the cross-sectional image of the anterior segment of the subject's eye may be acquired by controlling projection of the second measurement light in the cross-sectional image capturing optical system and detection of the return light (scattered light) of the second measurement light by the photodetector.

[0033] The axial length acquiring means may acquire the axial length of the subject's eye based on the ocular refractive power acquired by using the ocular refractive power measuring optical system and the anterior ocular segment cross-sectional image acquired by using the cross-sectional image taking optical system. In other words, the axial length of the subject's eye may be acquired in a less burdensome state in which glare caused by projection of the first measurement light and the second measurement light on the subject is reduced.

[0034] The axial length acquiring means may acquire the axial length based on the ocular refractive power of the subject's eye and an anterior ocular cross-sectional image. For example, the axial length may be derived by ray tracing calculation based on the ocular refractive power and the anterior ocular cross-sectional image. In the ray tracing calculation, the distance between the intersection point and the corneal apex when a light ray incident from a far point to a predetermined position of the anterior ocular intersects on the optical axis after being refracted by a transparent body is derived as the axial length. In this case, the ocular refractive power on the light section (on-surface ocular refractive power) may be used instead of the spherical equivalent power that is generally used in the field of ophthalmology when specifying the far point. This allows the position of the far point of the light ray passing through the cross-sectional surface to be specified more appropriately. As a result, the axial length can be obtained more appropriately. In this case, the ray tracing calculation may be performed for each of the multiple light rays, and the axial length may be obtained as a result of the ray tracing calculation for each light ray. For example, the average value (or weighted average) of the axial lengths obtained by each ray tracing calculation may be determined as the axial length of the subject's eye.

[0035] In the ray tracing calculation, the incident position of the light beam on the boundary surface of each transparent body and the angle change at the boundary surface may be determined taking into consideration the shape of the transparent body on the cross section specified from the anterior eye information. In addition, in the ray tracing calculation, the decentering of the transparent body of the anterior eye may be taken into consideration. The decentering is specified based on the anterior eye information. As a result of taking into consideration the decentering of the transparent body in the cross section, the axial length can be calculated more appropriately. In this case, for example, the ray tracing calculation may be performed for each of a plurality of light beams including at least the first light beam and the second light beam to calculate the axial length for each light beam, and the final measurement value may be calculated based on the plurality of axial lengths. The first light beam and the second light beam are light beams arranged on either side of the axis of the eye on the cross section.

[0036] The axial length acquiring means may control switching between at least two types of measurement light in the cross-sectional image capturing optical system, namely, light of the second wavelength (red visible light or infrared light) as the second measurement light and light having a wavelength different from the second wavelength. For example, when the cross-sectional image capturing optical system has one light source capable of projecting measurement light including each wavelength (for example, a light source projecting white visible light), a wavelength converter for converting the wavelength of the light source may be controlled, or an optical member disposed in the optical path of the measurement light may be controlled to be inserted or removed. The optical member may be a cut filter, a dichroic mirror, or the like. Also, for example, when the cross-sectional image capturing optical system has a plurality of light sources capable of projecting measurement light of each wavelength, the light source may be controlled to be turned on and off. For example, this allows the two types of measurement light to be selectively used according to the state of the subject's eye, and the axial length can be efficiently acquired.

[0037] The axial length acquisition means may continuously project the second measurement light and continuously detect the return light of the second measurement light in the cross-sectional image capturing optical system to acquire a plurality of anterior segment cross-sectional images. In this case, the axial length acquisition means may execute the projection of the second measurement light and the detection of the return light in real time, and acquire a plurality of anterior segment cross-sectional images by capturing the anterior segment cross-sectional images as moving images. In this case, the axial length acquisition means may execute the projection of the second measurement light and the detection of the return light at a predetermined time interval (for example, at one second intervals) and acquire a plurality of anterior segment cross-sectional images by capturing the anterior segment cross-sectional images as still images.

[0038] In this embodiment, since the second measurement light has a wavelength that reduces glare, it is possible to easily obtain multiple anterior ocular cross-sectional images in succession. Note that, since the pupil state (miosis and mydriasis) and accommodation state of the subject's eye change over time, if a configuration is used to obtain multiple anterior ocular cross-sectional images, it is possible to select an appropriate anterior ocular cross-sectional image that takes into account the state of the subject's eye, and obtain the axial length based on the selected image.

[0039] The axial length acquisition means may execute a calculation process based on a plurality of anterior ocular segment cross-sectional images. For example, the calculation process may be a process for obtaining a representative value (for example, an average value, a median value, a mode value, a maximum value, a minimum value, etc.). For example, the calculation process may be a process for obtaining a variation (for example, a variance, a standard deviation, a standard error, a coefficient of variation, etc.). Of course, various types of processing may be executed in combination, or different processing may be executed.

[0040] The axial length acquisition means may perform arithmetic processing on the multiple anterior segment cross-sectional images. For example, the axial length acquisition means may perform averaging processing on the multiple anterior segment cross-sectional images to obtain a single composite anterior segment cross-sectional image (synthetic cross-sectional image). At this time, the variations (e.g., variations in luminance information, etc.) of the multiple anterior segment cross-sectional images may be analyzed to eliminate those that are inappropriate for the averaging processing. In this way, the axial length based on the ocular refractive power of the subject eye and the composite cross-sectional image may be acquired.

[0041] The axial length acquisition means may also perform arithmetic processing on shape information relating to the shape of the anterior segment, which can be obtained by analyzing each of a plurality of anterior segment cross-sectional images. The shape information may be information capable of identifying the shape of the optic body included in the anterior segment. For example, the shape information may be parameters representing the shape of each optic body (e.g., curvature, thickness, depth, etc.). The shape information may also include a plurality of parameters. That is, one or more parameters may be acquired for each anterior segment cross-sectional image.

[0042] In this case, the axial length acquisition means may obtain parameters for each anterior segment cross-sectional image and calculate a representative value of the parameters. Variations in the parameters may be obtained and parameters that are inappropriate for calculating the representative value may be excluded. It is not necessary to calculate representative values ​​for all parameters that can be analyzed from the anterior segment cross-sectional image, and representative values ​​may be calculated for only some of the parameters. In this way, the axial length may be acquired based on the ocular refractive power of the subject eye and one or more parameters obtained from the anterior segment cross-sectional image.

[0043] The axial length acquiring means may also perform a calculation process on the axial length based on the ocular refractive power of the subject eye and a plurality of anterior segment cross-sectional images. In other words, the axial length may be calculated for each anterior segment cross-sectional image using each parameter. In this case, the axial length acquiring means may calculate a representative value from each axial length. Of course, the axial length variation may be calculated and those that are inappropriate for calculating the representative value may be excluded.

[0044] The axial length acquisition means may be configured to perform at least one of arithmetic processing on a plurality of anterior segment cross-sectional images, arithmetic processing on shape information, arithmetic processing on the axial length, etc. By performing these arithmetic processing, the axial length can be acquired with high accuracy. For example, the arithmetic processing reduces the influence of the subject's facial movement, the pupil state and accommodation state of the subject's eye, the resolution of the detector, etc., and therefore improves the accuracy of the axial length. Note that arithmetic processing on the anterior segment cross-sectional images tends to be complicated, so that the axial length can be acquired efficiently by performing arithmetic processing on the shape information and the axial length.

[0045] In addition, for these calculation processes, it is not necessary to use the ocular refractive power obtained by infrared light, the anterior ocular cross-sectional image obtained by red visible light or infrared light, etc. That is, for example, the ocular refractive power obtained by light with a wavelength different from that of infrared light may be used, or the anterior ocular cross-sectional image obtained by red visible light or light with a wavelength different from that of infrared light may be used. However, with light with these different wavelengths, pupil constriction and blinking caused by the subject feeling dazzled by the light are likely to affect the accuracy of the axial length. For this reason, it is preferable to use infrared light or red visible light as in this embodiment.

[0046] The axial length acquisition means may execute the acquisition of the ocular refractive power using the ocular refractive power measurement optical system and the acquisition of the anterior ocular segment cross-sectional image using the cross-sectional image taking optical system in parallel. For example, the axial length acquisition means may set the detection timing of the photodetector of the ocular refractive power measurement optical system and the detection timing of the photodetector of the cross-sectional image taking optical system to be the same (parallel) when the measurement light is projected from both optical systems to the subject's eye. Note that the term "same" does not necessarily require that the respective detection timings are completely simultaneous. For example, there may be a time difference between the respective detection timings to such an extent that no significant difference occurs in the state (pupil state or accommodation state) of the subject's eye.

[0047] In this embodiment, the first measurement light in the eye refractive power measuring optical system and the second measurement light in the cross-sectional image taking optical system are both wavelengths that reduce glare, so even if both measurement lights are projected, the burden on the subject is small. In addition, by making the detection timing of the photodetector of the eye refractive power measuring optical system and the photodetector of the cross-sectional image taking optical system the same, there is no deviation in the state of the subject's eye between the acquired eye refractive power and the anterior eye cross-sectional image. For example, by using such eye refractive power and the anterior eye cross-sectional image, the accuracy of the axial length can be improved.

[0048] "Example" An example of an ophthalmic apparatus according to the present embodiment will be described.

[0049] <Overall composition> 1 is an external view of an ophthalmic apparatus 10. The ophthalmic apparatus 10 is a combination device of an objective eye refractive power measuring device (particularly, in this embodiment, an autorefractometer) and a Scheimpflug camera. In this embodiment, the ophthalmic apparatus 10 is a stationary examination device, but is not necessarily limited to this and may be a handheld type.

[0050] The ophthalmologic apparatus 10 includes at least a measurement unit 11, a base 12, an alignment drive unit 13, a face support unit 15, a monitor 16, and an arithmetic and control unit 50.

[0051] The measurement unit 11 includes a measurement system and an imaging system that are used to examine the subject's eye. In this embodiment, the optical system shown in FIG.

[0052] The alignment drive unit 13 may be capable of moving the measurement unit 11 three-dimensionally relative to the base 12 .

[0053] The face support unit 15 is used to fix the subject's face in front of the measurement unit 11. The face support unit 15 is fixed to the base 12 and supports the subject's face.

[0054] The monitor 16 functions as a touch panel that also serves as an operation unit. The monitor 16 also displays the ocular refractive power, an anterior ocular segment cross-sectional image, axial length, and the like of the subject's eye E on the screen.

[0055] The arithmetic control unit 50 (also called a processor; hereinafter, simply referred to as the control unit 50) is responsible for the overall control of the ophthalmic apparatus 10. In addition, it processes various examination results acquired via the measurement unit 11.

[0056] <Optical system> 2 is a schematic diagram showing the optical system of the ophthalmic apparatus 10. As an example, the ophthalmic apparatus 10 includes a measurement optical system 100, a fixation target presenting optical system 150, a front photographing optical system 200, a cross-sectional photographing optical system (an irradiation optical system 300a and a light receiving optical system 300b), an index projecting optical system 400, and an alignment index projecting optical system. The ophthalmic apparatus 10 also includes half mirrors 501, 502, and 503 that branch and combine the optical paths of each optical system, an objective lens 505, and the like. In each optical system, the light source side is upstream and the examined eye side is downstream.

[0057] <Measurement optical system> The measurement optical system 100 is used to objectively measure the ocular refractive power of the subject's eye E. For example, the values ​​of SPH: spherical power, CYL: cylindrical power, and AXIS: cylindrical axis angle may be acquired as the measurement results of the ocular refractive power.

[0058] The measurement optical system 100 includes a projection optical system 100a and a receiving optical system 100b.

[0059] The projection optical system 100a has at least a measurement light source 111, and projects a spot-shaped measurement light onto the fundus of the test eye E through the center of the pupil or the corneal apex of the test eye E. The measurement light source 111 may be an SLD light source, an LED light source, or other light sources. In this embodiment, infrared light is used as the measurement light. For example, near-infrared light having a peak wavelength between 800 nm and 900 nm may be used. As an example, near-infrared light having a peak wavelength of 870 nm may be used.

[0060] In this embodiment, a prism 115 is disposed on a common path of the projection optical system 100a and the light receiving optical system 100b. The prism 115 is rotated about the optical axis, so that the projection light beam on the pupil is eccentrically rotated at high speed. As an example, in this embodiment, the projection light beam is eccentrically rotated in an area on the pupil of φ2 mm to φ4 mm. This area is the measurement area for the eye refractive power in this embodiment.

[0061] The light receiving optical system 100b has at least a ring lens 124 and an image sensor 125. The light receiving optical system 100b extracts the measurement light reflected from the fundus in a ring shape through the periphery of the pupil. The ring lens 124 is disposed at a pupil conjugate position, and the image sensor 125 is disposed at a fundus conjugate position. The eye refractive power is derived by analyzing the ring image formed on the image sensor 125 via the ring lens 124.

[0062] As described above, in this embodiment, since the measurement light is eccentrically rotated at high speed on the pupil, analysis processing is performed on the output image from the image sensor 125 based on an exposure time that is sufficiently long with respect to the rotation period, or on an additive image of image data sequentially output from the image sensor 125, to derive the ocular refractive power. In this embodiment, at least the values ​​of SPH: spherical power, CYL: cylindrical power, and AXIS: cylindrical axis angle are acquired as the results of analysis processing.

[0063] The measurement optical system 100 may have optical elements such as lenses and diaphragms in addition to the measurement light source 111, the prism 115, the ring lens 124, and the image sensor 125. The measurement light beam from the measurement light source 111 passes through the hole of the hole mirror 113 and the prism 115, and is reflected by the half mirror 502 and the half mirror 501, respectively, to become coaxial with the optical axis L1, and then reaches the fundus via the objective lens 505. The reflected light beam of the measurement light beam reflected by the fundus passes through the optical path that the measurement light beam passed through, is reflected by the mirror of the hole mirror 123, and reaches the image sensor 125 via the ring lens 124.

[0064] <Fixation target presentation optical system> The fixation target presenting optical system 150 presents a fixation target to the subject's eye E. The fixation target is presented on the optical axis of the measurement optical system 100. The fixation target presenting optical system 150 is used to fixate the subject's eye E. It is also used to apply fogging and accommodation load to the subject's eye.

[0065] For example, the fixation target presenting optical system 150 includes at least a light source 151 and a fixation target plate 155. The fixation target plate 155 may be disposed at a position conjugate with the fundus. A fixation light beam from the light source 151 passes through the fixation target plate 155 and the lens 156 on the optical axis L2, and then passes through a half mirror 503. The fixation light beam also passes through a lens 504, passes through a half mirror 502, and is reflected by a half mirror 501, becoming coaxial with the optical axis L1. The fixation light beam further passes through an objective lens 505 to reach the fundus.

[0066] The measurement light source 111, the ring lens 124, and the image sensor 125 in the measurement optical system 100, and the light source 151 and the fixation target plate 155 in the fixation target presenting optical system 150 can be moved integrally along the optical axis by the drive unit 161 as the drive unit 160. For example, the focal length in the drive unit 160 in the measurement optical system 100 and the focal length in the drive unit 160 in the fixation target presenting optical system 150 have a predetermined relationship. For example, by moving the drive unit according to the ocular refractive power of the test eye E, the presentation distance of the fixation target plate 155 relative to the test eye E (i.e., the presentation position of the fixation target) can be changed, and further, the measurement light source 111 and the image sensor 125 are optically conjugated with the fundus. At this time, regardless of the movement of the drive unit, the hole mirror 113 and the ring lens 124 are pupil conjugated at a constant magnification.

[0067] <Frontal shooting optical system> The front photographing optical system 200 is used to capture a front image of the anterior segment of the subject's eye E. For example, the front photographing optical system 200 includes an image sensor 205 and the like. The image sensor 205 may be disposed at a pupil conjugate position. As the front image, an observation image of the anterior segment may be acquired. The observation image is used for alignment and the like. In addition, an index image (point image) projected onto the cornea from the index projection optical system 400, and an index image (Mayer ring image) projected onto the cornea from the alignment index projection optical system 600 are captured by the front photographing optical system 200.

[0068] <Cross-section imaging optical system> The cross-section photographing optical system is used to photograph a cross-sectional image of the anterior segment of the eye, and includes an irradiation optical system 300a and a light receiving optical system 300b.

[0069] The irradiation optical system 300a is coaxial with the projection optical axis (optical axis L1) of the measurement light in the measurement optical system 100, and irradiates the anterior segment with slit light. The irradiation optical system 300a has a light source 311 and a slit 312. The light source 311 may be an SLD light source, an LED light source, or other light sources. In this embodiment, red visible light or near infrared light is used as the illumination light. For example, red visible light or near infrared light having a peak wavelength between 650 nm and 800 nm may be used. As an example, red visible light having a peak wavelength of 730 nm may be used. Of course, near infrared light having a peak wavelength of a predetermined wavelength may be used. The slit 312 may be disposed at a pupil conjugate position.

[0070] The light source 311 of the irradiation optical system 300a will be described in detail. Fig. 3 is a schematic diagram showing the relationship between the luminosity of the subject's eye and wavelength. The subject's eye has luminosity in the visible range, which is generally maximum at around 550 nm, which is green visible light, and gradually decreases as the wavelength becomes longer (approaching the infrared range). In other words, the subject's eye is easily dazzled by green visible light, but is not easily dazzled by red visible light. It is said that the subject is not dazzled by infrared light.

[0071] Conventionally, when a cross-sectional image of the anterior eye is obtained based on the Scheimpflug principle, blue visible light, green visible light, white visible light, etc. have been used as illumination light. This is because cataracts and the like tend to appear in cross-sectional images due to the influence of the transmittance of the subject's eye, but the illumination light is dazzling and burdensome to the subject. On the other hand, with the increase in the prevalence of myopia, mainly among young people, in recent years, it is important to measure the axial length of young people, but since young people are less likely to have cataracts, it is possible to use light other than the above as illumination light.

[0072] Therefore, in this embodiment, red visible light to near infrared light, which is less likely to cause glare to the subject's eye, is used as the illumination light. For example, compared with the visibility of green visible light at around 550 nm, the visibility of red visible light at around 650 nm is approximately 1 / 10, and the visibility of red visible light at around 700 nm is approximately 1 / 200. This significantly reduces the burden on the subject. In particular, when the subject is a young person, including a child, this not only reduces the burden but also leads to more efficient measurement.

[0073] In this embodiment, the cross section through which the slit light passes in the anterior segment is referred to as a "cutting surface." The cutting surface is the object surface of the cross-sectional imaging optical system. In FIG. 2, the opening of the slit 312 has a horizontal direction (depth direction into the paper) as its longitudinal direction. Therefore, in this embodiment, a horizontal plane (XZ cross section) including the optical axis L1 is set as the cutting surface. In this embodiment, the cutting surface is formed at least between the anterior surface of the cornea and the posterior surface of the lens.

[0074] The light receiving optical system 300b includes a lens system 322 and an image sensor 321. In the light receiving optical system 300b, the lens system 322 and the image sensor 321 are arranged in a Scheimpflug relationship with a cut surface set in the anterior segment. That is, the optical arrangement is such that the extension planes of the cut surface, the principal plane of the lens system 322, and the imaging surface of the image sensor 321 intersect at one intersection line (single axis). A cross-sectional image of the anterior segment is acquired based on a signal from the image sensor 321. The image sensor 321 may be formed of a semiconductor substrate made of silicon as a single element.

[0075] The imaging element 321 of the light receiving optical system 300b will be described in detail. Fig. 4 is a schematic diagram showing the relationship between the light receiving sensitivity and wavelength of the imaging element 321. For example, an imaging element using silicon as a material as a single element has sensitivity to wavelengths around 300 nm to 1000 nm, including wavelengths in the ultraviolet, visible, and infrared regions, but has a maximum sensitivity around 550 nm to 650 nm, including green visible light, and gradually decreases as it approaches the infrared region. However, the sensitivity of 650 nm or more, including red visible light to near-infrared light used in the irradiation optical system 300a, is sufficient for acquiring a cross-sectional image of the anterior eye.

[0076] For example, there are imaging elements whose sensitivity is greatest in the infrared region, but they are expensive. While it is desirable for the device to be used in many facilities such as hospitals and schools, the high cost of the device can hinder its widespread use. If an imaging element made of silicon is used, the device can be made inexpensively.

[0077] In such a cross-section photographing optical system, the measurement light beam from the light source 311 becomes a slit light beam via a slit 312 on the optical axis L3, passes through a lens 313, and is reflected by a half mirror 503 to become coaxial with the optical axis L2. The measurement light beam also passes through a lens 504, transmits through a half mirror 502, and is reflected by a half mirror 501 to become coaxial with the optical axis L1. The measurement light beam further passes through an objective lens 505 to reach the anterior segment. Return light from a cut surface formed in the anterior segment reaches the image sensor 321 via a lens 322.

[0078] <Indicator projection optical system> The index projection optical system 400 is used to measure the corneal shape. The index projection optical system 400 projects an index for measuring the corneal shape from the front surface facing the subject's eye to the anterior segment.

[0079] The index projection optical system 400 includes a plurality of point light sources 401. The point light sources 401 project an index at infinity by irradiating the cornea with parallel light. The point light sources 401 emit infrared light. However, visible light may be used. The point light sources 401 are arranged symmetrically in the vertical direction and the horizontal direction with respect to the optical axis L1. For example, in this embodiment, two point light sources are provided on each side. This allows four point image indices to be projected onto the cornea. The shape of the indices is not limited to this, and may include linear indices. The number of indices is not limited to this, and may be three or more point image indices.

[0080] In this embodiment, the circumferential region onto which these four point images are projected becomes the measurement region of the corneal shape by the target projecting optical system 400 and the front photographing optical system 200. As an example, when a corneal model eye having a predetermined radius of curvature is placed at a predetermined working distance, each point image is projected onto a circumferential region of φ3 mm of the corneal model eye.

[0081] <Alignment target projection optical system> The alignment target projection optical system is used to align (position) the measurement unit 11 with respect to the subject's eye E. In this embodiment, the alignment target projection optical system is formed by the alignment light source 601 and the target projection optical system 400. For example, the working distance may be adjusted by moving the measurement unit 11 in the forward / backward direction so that the Purkinje image by the alignment light source 601 and the Purkinje image by the target projection optical system 400 are captured at a predetermined ratio.

[0082] The alignment light source 601 projects a finite index by irradiating the cornea with diffused light. The alignment light source 601 emits infrared light. However, it may also emit visible light. The alignment light source 601 is arranged in a ring shape centered on the optical axis L1. As a result, in this embodiment, a ring index (so-called Mayer ring) is projected onto the cornea.

[0083] <Common optical path for fixation target presentation optical system and cross-sectional imaging optical system> In this embodiment, both the fixation target presenting optical system 150 and the target projection optical system 300a are irradiated with visible light. The optical axis L2 of the fixation target presenting optical system 150 and the optical axis L3 of the target projection optical system 300a are made coaxial by the half mirror 503. The fixation target presenting optical system 150 is disposed on the transmission side of the half mirror 503, and the target projection optical system 300a is disposed on the reflection side of the half mirror 503, so that the optical paths of the fixation target presenting optical system 150 and the target projection optical system 300a are common. For example, the half mirror 503 is a flat type, and astigmatism is likely to occur on the transmission side of the half mirror 503. The target projection optical system 300a requires a certain level of imaging performance in order to form a cut surface in the anterior eye to obtain a clear cross-sectional image 70. For this reason, it is preferable that the target projection optical system 300a is disposed on the reflection side where the influence of astigmatism is small.

[0084] In this embodiment, a lens 504a is disposed on the optical axis of the fixation target presenting optical system 150. The lens 504a functions as a lens for shortening the overall length of the fixation target presenting optical system 150. The lens 504a also serves to reduce the diameter of the lens 156 located upstream of the lens 504a.

[0085] Fig. 5 is a schematic diagram of a simplified fixation target presenting optical system 150. Fig. 5(a) shows a case where the lens 504a is not arranged. Fig. 5(b) shows a case where the lens 504a is arranged. Here, the optical path from the subject's eye E to the fixation target plate 155 is a straight line, and some optical members are omitted. The fundus imaging light rays from the center and peripheral parts of the fixation target plate 155 are represented by solid lines and dotted lines, respectively.

[0086] When the working distance from the subject's eye E to the objective lens is a predetermined value, in FIG. 5(a), the distance of the fixation target presenting optical system 150 (particularly, the distance from the fixation target plate 155 to the lens 156) is long. Both light rays from the center and periphery of the fixation target plate 155 reach the lens 156 with a large diameter. On the other hand, as shown in FIG. 5(b), by arranging a lens 504a in the fixation target presenting optical system 150, the distance of the fixation target presenting optical system 150 can be shortened. Both light rays from the fixation target plate 155 reach the lens 156 with a small diameter.

[0087] For example, the fixation target presenting optical system 150 may be a target-side telecentric optical system, and the lens 504a may be disposed at a pupil conjugate position. In this case, since light rays from the center and periphery of the fixation target plate 155 pass through the center of the lens 504a, the entire focal length (composite focal length) of the fixation target presenting optical system 150 does not change. Therefore, the relationship between the focal length of the fixation target presenting optical system 150 and that of the drive unit 160 of the measurement optical system 100 is maintained.

[0088] In this way, by arranging the lens 504a in the fixation target presenting optical system 150, the lens 156 can be designed with a small diameter. Also, while maintaining a predetermined working distance of the subject's eye E and a composite focal length of the fixation target presenting optical system 150, the overall length of the fixation target presenting optical system 150 can be shortened. As a result, the ophthalmic apparatus 10 can be made more compact.

[0089] In this embodiment, a lens 504b is disposed on the optical axis of the visual target projection optical system 300a. The lens 504b serves to reduce the diameter of the objective lens 505 located downstream of the lens 504b.

[0090] Fig. 6 is a schematic diagram of a simplified target projection optical system 300a. Fig. 6(a) shows a case where the lens 504b is not arranged. Fig. 6(b) shows a case where the lens 504b is arranged. Here, the optical path from the subject's eye E to the slit 312 is a straight line, and some optical members are omitted. The pupil imaging light rays from the center and periphery of the slit 312 are represented by solid lines and dotted lines, respectively.

[0091] In Fig. 6(a) and Fig. 6(b), the light beam from the center of the slit 312 passes through the center of the objective lens 505 regardless of the presence or absence of the lens 504b. However, in Fig. 6(a), the light beam from the peripheral part of the slit 312 is refracted at a position farther away from the center of the objective lens 505. In order to allow such a light beam to reach the subject's eye E, an objective lens 505 with a large diameter is required. On the other hand, in Fig. 6(b), the light beam from the peripheral part of the slit 312 is refracted at the center position of the objective lens 505. In order to allow such a light beam to reach the subject's eye E, an objective lens 505 with a small diameter can be used.

[0092] In this way, by arranging the lens 504b in the visual target projection optical system 300a, the objective lens 155 can be designed with a small diameter. Note that the light rays from the central and peripheral parts of the slit 312 may generate larger aberrations as they are refracted in an area farther from the center of the objective lens 505. For this reason, the objective lens 155 may have an appropriate diameter that suppresses the generation of aberrations while miniaturizing the ophthalmic apparatus 10.

[0093] In this embodiment, the lens 504 is arranged in the fixation target presenting optical system 150 and the target projection optical system 300a, sharing the lenses 504a and 504b having different roles. For example, the lens 504 is arranged downstream of the half mirror 503 where the optical axis L2 of the fixation target presenting optical system 150 and the optical axis L3 of the target projection optical system 300a are joined. This further reduces the space inside the optical system.

[0094] <Control action> The control operation of the ophthalmic apparatus 10 will be described with reference to the flowchart shown in Fig. 7. In this embodiment, the ophthalmic apparatus 10 sequentially performs corneal curvature measurement, ocular refractive power measurement, and photographing of an anterior segment cross-sectional image, and obtains the axial length based on the results of the measurement and photographing.

[0095] <Alignment (S1)> First, the measurement unit 11 is aligned with the subject's eye E. The examiner instructs the subject to place his or her face on the face support unit 15. The control unit 50 starts presenting a fixation target and acquiring an anterior eye observation image.

[0096] For example, the control unit 50 adjusts the subject's eye E and the ophthalmic device 10 to a predetermined positional relationship based at least on an observation image of the anterior eye acquired via the front photographing optical system 200. More specifically, alignment in the XY directions is performed so that the optical axis L1 coincides with the corneal apex of the subject's eye E. Also, alignment in the Z direction is performed so that the distance between the subject's eye E and the ophthalmic device 10 is a predetermined working distance. At this time, an alignment index may be projected onto the cornea, and the alignment may be adjusted based on the alignment index detected in the observation image.

[0097] <Cornea topography measurement (S2)> Next, the corneal shape of the subject's eye E is measured. The control unit 50 projects a point image index from the index projection optical system 400, and captures a corneal Purkinje image of the point image index using the frontal imaging optical system 200. The control unit 50 also acquires corneal shape information based on the corneal Purkinje image. For example, the corneal shape information is derived based on the image height of the corneal Purkinje image. In this embodiment, at least the values ​​of the corneal curvature, the degree of astigmatism, and the astigmatism axis angle are acquired as the corneal shape information.

[0098] <Eye Refractive Index Measurement (S3)> Next, the eye refractive power of the subject's eye E is measured. For example, in measuring the eye refractive power, a preliminary measurement may be performed first, and then a main measurement may be performed.

[0099] In the preliminary measurement, the eye refractive power of the test eye E is measured with the fixation target positioned at a predetermined presentation distance. During the measurement, the fixation target plate 155 may be positioned at an initial position that is optically far enough away from the test eye E and corresponds to the far point of the 0D eye. A ring image captured by the image sensor 125 based on the measurement light irradiated in this state is image-analyzed by the control unit 50. As a result of the analysis, the value of the refractive power in each meridian direction is obtained. At least the spherical power in the preliminary measurement is obtained by performing a predetermined process on the refractive power in each meridian direction.

[0100] Next, the control unit 50 moves the fixation target plate 155 to a fogging start position where the subject's eye E is in focus according to the spherical power of the preliminary measurement of the subject's eye E. This allows the fixation target to be clearly observed by the subject's eye E. Thereafter, the control unit 50 adds fogging to the subject's eye E by moving the fixation target from the fogging start position. This releases the adjustment of the subject's eye E.

[0101] This measurement is performed with fogging applied to the test eye E. A predetermined analysis process is performed on the ring image captured of the test eye E to which fogging has been applied, thereby obtaining the objective values ​​of the test eye E's SPH: spherical power, CYL: cylindrical power, and AXIS: astigmatism axis angle.

[0102] <Capturing cross-sectional images of the anterior segment (S4)> Next, a cross-sectional image (Scheimpflug image) of the anterior segment of the subject's eye E is captured. The control unit 50 immediately executes the capture of the cross-sectional image of the anterior segment after the main measurement of the eye refractive power is completed. For example, the operation of capturing the cross-sectional image may be triggered by the completion of the main measurement of the eye refractive power. That is, immediately after the main measurement is completed, illumination light is emitted from the irradiation optical system 300a, and the illumination light is scattered by the cornea and the crystalline lens, and the scattered light is focused on the image sensor 321 to obtain a cross-sectional image of the anterior segment. This reduces alignment deviation between the time of measuring the eye refractive power and the time of capturing the cross-sectional image.

[0103] <Eye axis length calculation (S5)> Next, the axial length of the subject's eye E is calculated. The control unit 50 calculates the axial length based on the information or images acquired in steps S2 to S4.

[0104] First, the control unit 50 determines the position of the far point FP (see FIG. 9) relative to the corneal apex C based on the measurement results of the ocular refractive power of the subject's eye E. For example, if the subject's eye E has no astigmatism, SPH=-5D, and VD=12mm, then the distance from the corneal apex C to the far point FP is 12+1000 / 5=212mm. It is considered that a light ray from the far point FP forms an image on the fundus. Note that VD=12mm is a fixed value indicating the corneal apex distance assuming the wearing of spectacle lenses. VD may vary depending on the device.

[0105] 8 is an example of a cross-sectional image 70 of the anterior eye. Next, the control unit 50 acquires anterior eye shape information related to the shape of the anterior eye based on the cross-sectional image 70 of the anterior eye of the subject's eye E. For example, the anterior eye shape information may include information such as the radius of curvature (Ra) of the anterior corneal surface, the radius of curvature (Rp) of the posterior corneal surface, the corneal thickness (CT), the anterior chamber depth (ACD), the radius of curvature (ra) of the anterior crystalline lens surface, the radius of curvature (rp) of the posterior crystalline lens surface, and the crystalline lens thickness (LT). Note that the information acquired in step S2 may be used as the anterior eye shape information.

[0106] The control unit 50 detects each optical body (for example, the cornea, aqueous humor, crystalline lens, etc.) by performing image processing on the cross-sectional image 70, and acquires anterior eye shape information. For example, the control unit 50 may use the luminance information of the cross-sectional image 70 to detect pixel positions corresponding to tissue boundaries (the anterior and posterior surfaces of the cornea, the anterior and posterior surfaces of the crystalline lens, the iris, etc.) and acquire information such as the radius of curvature. In addition, for example, the control unit 50 may obtain the distance of the pixel positions corresponding to the tissue boundaries and acquire information such as the thickness and depth of the tissue.

[0107] 9 is a schematic diagram for explaining a method for deriving the axial length. In this embodiment, the axial length may be derived based on a ray tracing calculation on a cut surface of the anterior segment. For example, the control unit 50 performs the ray tracing calculation based on the position of the far point FP, the refractive index of each light-transmitting body, and the anterior segment shape information.

[0108] The control unit 50 tracks a light ray (e.g., light ray Lx in FIG. 9) incident from a far point FP toward the subject's eye E, and determines the position of the intersection point where the light ray is refracted by each optically transparent body of the subject's eye E and intersects with the optical axis. Details of the ray tracing calculation will be described later. For example, the position of the fundus Ef is determined by such ray tracing calculation. The control unit 50 derives the distance between the corneal apex C and the fundus Ef as the axial length AL.

[0109] <Display output (S6)> Finally, the axial length AL is displayed on the monitor 16. In this embodiment, the axial length AL is displayed together with at least one of the corneal shape information and the ocular refractive power (SPH, CYL, AXIS) of the subject's eye E. Note that, for example, if there are previous axial length measurement results for the subject's eye E, the current measurement result may be displayed together with the previous measurement results.

[0110] <Ray tracing calculation> Ray tracing calculation for deriving the axial length will be described. In this embodiment, for convenience of explanation, it is assumed that the refractive index in each transparent body of the subject's eye E is constant and there is no change in refraction inside each body. However, this is not necessarily limited to this, and the axial length may be derived taking into account the change in the refractive index inside the transparent body (for example, the change in the refractive index between the inside and outside of the crystalline lens).

[0111] Incidentally, in the widely used expression format of ocular refractive power by SPH, CYL, and AXIS, SPH indicates the refractive power related to the strong meridian (or weak meridian), so it is not necessarily an appropriate value in ray tracing on a cut surface of the anterior eye. For example, consider a case where SPH=-5D, CYL=-2D, and AXIS=30°. In this case, if a horizontal cross section is obtained in the above optical system example, the refractive power on this cross section is neither -5D nor -7D with CYL added.

[0112] In contrast, in this embodiment, the on-surface ocular power, which is the ocular power on the cut surface, is calculated, and the position of the far point FP is set based on the on-surface ocular power. Here, the refractive power P on an arbitrary surface is expressed by the following formula. Here, θ is an angle with respect to the horizontal plane, and the horizontal direction is set to 0°.

[0113] P(θ)=SPH+CYL×[sin2(θ-A)]

[0114] 10 is a diagram showing the refractive power in each meridian direction when the subject's eye E has SPH=-5D, CYL=-2D, and AXIS=30°. For example, the cutting plane in this embodiment is a horizontal plane (θ=0°). Therefore, if the subject's eye E has SPH=-5D, CYL=-2D, and AXIS=30°, P(0°)=-5.5D is calculated. In this case, if VD=12mm, the distance from the corneal apex C to the far point FP on the cutting plane is 12+1000 / 5.5=194mm.

[0115] The control unit 50 tracks a ray from the far point FP thus set. For example, it guides a ray (e.g., a ray Lx in FIG. 9) from the far point FP toward a fixed position (as an example, a position of φ6 mm at the position of the pupil of the subject's eye (approximately 3 mm behind the cornea)). Note that setting the fixed position to φ6 mm at the position of the pupil of the subject's eye is merely an example and can be changed as appropriate.

[0116] This light ray is first refracted at the front surface of the cornea. The intersection of the light ray and the front surface of the cornea is calculated based on the radius of curvature Ra of the front surface of the cornea, the position of the far point FP, and the light ray angle at the far point FP. Furthermore, the angle of incidence of the light ray at the intersection is calculated. The light ray that reaches the front surface of the cornea changes its direction at a refraction angle determined with respect to the angle of incidence based on Snell's law. In this manner, the light ray is tracked successively at each transparent body boundary surface. At that time, the anterior eye shape information (Ra, Rp, CT, ACD, ra, rp, LT) acquired based on the corneal shape information and the cross-sectional image 70 (Scheimpflug image) is appropriately used to give the intersection of each boundary surface and the light ray. In this embodiment, the intersection (i.e., the position of the fundus Ef) where the light ray intersects with the axis of the eye (here, the visual axis) after leaving the rear surface of the crystalline lens is finally obtained. The distance from the intersection to the corneal apex C (here, the origin) is used as the axial length AL.

[0117] In addition, when the above-mentioned anterior eye shape information (Ra, Rp, CT, ACD, ra, rp, LT) is used in the ray tracing calculation, in this embodiment, for at least the radius of curvature Ra of the corneal anterior surface, a value based on the corneal Purkinje image of the point image index is used, and for the remaining values, values ​​based on the cross-sectional image 70 (Scheimpflug image) are used. This is because, for the corneal anterior surface shape, the measurement accuracy based on the corneal Purkinje image is generally higher than that based on the Scheimpflug image. As described above, in this embodiment, at least the values ​​of the corneal curvature, the astigmatism degree, and the astigmatism axis angle are obtained as the corneal shape information. The corneal curvature (curvature of the corneal anterior surface) at the cut surface can be obtained from these values ​​using a method similar to the method of obtaining the refractive power for the cut surface. The reciprocal of the obtained value may be used as Ra.

[0118] The axial length AL of the subject's eye E can be obtained by tracing rays directed toward such a fixed position. However, the method of ray tracing is not limited to the above method. For example, the point at which an image is formed from the far point FP may be obtained by paraxial calculation. Also, the point at which an image is formed from the far point FP may be obtained by considering a plurality of rays that are incident on the subject's eye E at different positions. For example, ray tracing for each of a paraxial ray and a ray directed toward a fixed position other than the paraxial ray may be combined. When ray tracing for a plurality of rays is performed, the final measurement value (calculated value) of the axial length may be the average value (weighted average value) of the axial lengths obtained by each ray tracing.

[0119] The axial length AL may also be obtained by tracing rays directed toward a measurement region (φ2 mm to φ4 mm on the pupil) by the measurement optical system 100. For example, ray tracing may be performed for each of a plurality of rays directed toward a region on the pupil of φ2 mm to φ4 mm, and the average value of the axial length obtained by each ray tracing may be obtained as the calculation result. Since ray tracing is performed under more appropriate conditions, the axial length can be obtained more accurately.

[0120] A predetermined offset value may be added to the axial length value obtained in this embodiment, which corrects the error between the calculated value and the actual measured value.

[0121] Ray tracing may also be performed by tracing a ray that is emitted from the far point FP and passes through a circumferential region onto which a point image index for corneal shape measurement is projected. This makes the conditions for ray tracing more appropriate, making it easier to obtain the axial length with higher accuracy.

[0122] As described above, for example, in the ophthalmic apparatus of this embodiment, in the ocular refractive power measuring optical system for acquiring the ocular refractive power of the subject's eye, infrared light is used as the measurement light, and in the cross-sectional photographing optical system for acquiring a cross-sectional image of the anterior segment of the subject's eye, red visible light or infrared light is used as the illumination light. This reduces the glare of the illumination light on the subject, and allows the axial length to be acquired under a condition where the burden when capturing a cross-sectional image of the anterior segment is reduced. In particular, for young people including children, the effect of glare is large, so the use of red visible light or infrared light is more effective.

[0123] In addition, for example, the ophthalmologic apparatus of this embodiment configures the measurement light (infrared light) of the eye refractive power measurement optical system and the illumination light (red visible light or infrared light) of the cross-section photographing optical system with different wavelengths, which makes it easier to configure each optical system to reduce the glare of the illumination light on the subject.

[0124] In addition, for example, the ophthalmic apparatus of this embodiment configures the wavelength of the illumination light in the cross-sectional photographing optical system to be shorter than the wavelength of the measurement light in the eye refractive power measurement optical system. For example, since the measurement light from the eye refractive power measurement optical system is focused on the fundus and the illumination light from the cross-sectional photographing optical system is focused on the anterior eye, if they have the same wavelength, the measurement light is more likely to be felt as glare. For this reason, in the wavelength range from red visible light to infrared light, the measurement light that is more likely to be felt as glare for the above-mentioned reason is set on the long wavelength side with low visibility, and the illumination light that is less likely to be felt as glare is set on the short wavelength side with high visibility, thereby reducing the burden on the subject.

[0125] In addition, for example, the ophthalmologic apparatus of this embodiment uses near-infrared light with a peak wavelength between 650 nm and 800 nm as illumination light in the cross-section photographing optical system. This makes it difficult for the subject to feel glare, and allows the use of photodetectors with various wavelength sensitivity ranges. For example, a Si image sensor that is sensitive to wavelengths from the ultraviolet range to the near-infrared range, an InGaAs image sensor that is sensitive to wavelengths in the near-infrared range, etc. can be used.

[0126] Also, for example, in the ophthalmologic apparatus of this embodiment, the cross-sectional photographing optical system is configured with a photodetector having a semiconductor substrate made of silicon. For example, a Si image sensor has lower sensitivity to near-infrared wavelengths (especially wavelengths longer than 800 nm) than an InGaAs image sensor, but can obtain a sufficient anterior eye cross-sectional image. Furthermore, since a Si image sensor is cheaper than an InGaAs image sensor, it is possible to reduce the cost of the apparatus.

[0127] <Example of transformation> In this embodiment, the projection optical system 100a of the measurement optical system 100 has been described as an example in which the measurement light source 111 emits near-infrared light as the measurement light, but the present invention is not limited thereto. For example, an optical member for limiting the wavelength of the measurement light may be arranged in the optical path of the measurement light from the measurement light source 111. Similarly, in this embodiment, the irradiation optical system 300a of the cross-section photographing optical system has been described as an example in which the light source 311 emits red visible light or near-infrared light as the illumination light, but the present invention is not limited thereto. For example, an optical member for limiting the wavelength of the illumination light from the light source 311 may be arranged in the optical path of the illumination light. For example, such an optical member for limiting the wavelength of the measurement light and the illumination light may be a cut filter.

[0128] In this embodiment, the irradiation optical system 300a of the cross-section imaging optical system is described as projecting red visible light or near-infrared illumination light, but the present invention is not limited to this. For example, in addition to the illumination light having a wavelength of red visible light or near-infrared light, the configuration may be such that illumination light having a wavelength different from the wavelength of red visible light or near-infrared light can be selectively projected. As an example, the configuration may be such that at least one of visible light such as blue visible light, green visible light, and white visible light can be projected.

[0129] In this case, the control unit 50 may control a plurality of light sources and switch each of them on and off to project either illumination light having a wavelength of red visible light (or near infrared light) or illumination light having a wavelength different from red visible light (or near infrared light) toward the subject's eye. Alternatively, the control unit 50 may control and switch optical members arranged in the optical path of the illumination light from the light source to project either illumination light having a wavelength of red visible light (or near infrared light) or illumination light having a wavelength different from red visible light (or near infrared light) toward the subject's eye. This allows selective use of illumination light that takes into account glare to the subject's eye and illumination light that takes into account the condition of the subject's eye (cataracts, etc.) depending on the situation. For example, even if the subject's eye has cataracts, etc., the cross-sectional image 70 can be appropriately acquired and the axial length can be measured.

[0130] In this embodiment, the configuration for acquiring one cross-sectional image 70 using the cross-sectional imaging optical system has been described as an example, but the present invention is not limited thereto. For example, the cross-sectional imaging optical system may be configured to acquire multiple cross-sectional images. In the cross-sectional imaging optical system, the illumination optical system 300a projects red visible light or near infrared light, thereby reducing glare on the subject's eye, and therefore, multiple cross-sectional images can be acquired continuously.

[0131] In this case, the control unit 50 may constantly project illumination light from the light source 311 and constantly capture the return light of the illumination light by the image sensor 321 to obtain a cross-sectional image of the subject's eye as a moving image. In this case, the control unit 50 may also project illumination light from the light source 311 every time a predetermined time elapses (for example, every second) to obtain a cross-sectional image of the subject's eye as a still image. Note that the image sensor 321 may capture the return light every time a predetermined time elapses in accordance with the projection timing of the illumination light, or may constantly capture the return light. In this case, the control unit 50 may also project the return light of the illumination light by the image sensor 321 every time a predetermined time elapses to obtain a cross-sectional image of the subject's eye as a still image. Note that the light source 311 may project illumination light every time a predetermined time elapses in accordance with the image capture timing of the image sensor 321, or may constantly project illumination light. For example, by continuously acquiring cross-sectional images of the subject's eye, it is possible to grasp the pupil state (miosis and mydriasis) and the accommodation state of the subject's eye. By selecting an appropriate one from multiple cross-sectional images, the axial length can be measured with high accuracy.

[0132] When the cross-sectional images of the subject's eye are continuously obtained, a calculation process may be performed. For example, the axial length can be measured with high accuracy by synthesizing the cross-sectional images of the subject's eye by averaging. Of course, a representative value (e.g., average, median, mode, etc.) may be calculated for the anterior eye shape information that can be obtained based on the cross-sectional images of the subject's eye. A representative value may be calculated for the axial length obtained by ray tracing calculation using the ocular refractive power of the subject's eye and the anterior eye shape information. Note that the representative value may be calculated using the remaining values ​​after excluding the maximum and minimum values ​​for the anterior eye shape information and the axial length. The axial length can be measured with high accuracy by these methods as well. Furthermore, in such a calculation process, outliers may be excluded based on the variance of each data.

[0133] The cross-sectional photographing optical system may include a rotation mechanism for rotating the slit 312 of the irradiation optical system 300a and a movement mechanism for moving the image sensor 321 of the light receiving optical system 300b. For example, when continuously acquiring cross-sectional images of the subject's eye, the rotation mechanism and the movement mechanism may be controlled to change their positions while maintaining the Scheimpflug relationship between the slit 312 and the image sensor 321. For example, this may result in obtaining multiple cross-sectional images each having a different angle of the light section with respect to the anterior segment. Also, such multiple cross-sectional images may be synthesized to obtain a three-dimensional cross-sectional image.

[0134] In this embodiment, the configuration in which the ocular refractive power of the test eye is measured using the measurement optical system 100, and then the cross-sectional image 70 of the test eye is obtained using the cross-sectional photographing optical system is described as an example, but is not limited thereto. For example, the ocular refractive power of the test eye and the cross-sectional image 70 of the test eye may be obtained at the same timing (in parallel). This can improve the accuracy of the axial length.

[0135] In this case, the control unit 50 controls both the measurement light from the measurement light source 111 in the projection optical system 100a and the illumination light from the light source 311 in the irradiation optical system 300a to project both lights toward the subject's eye. The projection of the lights does not necessarily have to start at the same time. The control unit 50 also controls both the image sensor 125 in the light receiving optical system 100b and the image sensor 321 in the light receiving optical system 300b to capture the ring image and the cross-sectional image 70 at the same timing.

[0136] For example, in measuring the refractive power of the subject's eye, accommodation is released by fog, but when a cross-sectional image of the anterior eye is subsequently acquired, accommodation may occur again, and the state of the subject's eye may be different. In addition, for example, in measuring the refractive power of the subject's eye, near-infrared light is used, resulting in a pupil state without miosis. In acquiring a cross-sectional image of the anterior eye, visible red light or near-infrared light having a wavelength that does not cause glare to the subject's eye is used, resulting in a pupil state without miosis, but the respective states may be different. However, if the measurement of the refractive power of the eye and the acquisition of the cross-sectional image are performed at the same time, the axial length can be calculated with the pupil state and the accommodation state of the subject's eye being matched, and the accuracy is improved. In addition, by suppressing the miosis of the subject's eye, it becomes easier to acquire a good cross-sectional image in which a deeper portion of the anterior eye is captured.

[0137] In this embodiment, the alignment between the subject eye and the ophthalmic device 10 is performed as the first step S1 of the flowchart shown in Fig. 7, but the present invention is not limited to this. For example, the alignment between the subject eye and the ophthalmic device 10 may be performed as appropriate while the flowchart progresses. For example, the alignment may be performed before the measurement of the ocular refractive power of the subject eye (between step S2 and step S3) or before the acquisition of a cross-sectional image of the anterior eye segment (between step S3 and step S4).

[0138] As an example, a case where alignment is performed again before a cross-sectional image of the anterior eye is acquired will be described. For example, the control unit 50 may detect the corneal apex position from the cross-sectional images sequentially generated by the image sensor 321. Also, for example, the control unit 50 may move the measurement unit 11 with respect to the subject's eye E so as to match the corneal apex position with a predetermined position set in advance in the cross-sectional image. For example, depending on the corneal curvature of the subject's eye E, a slight deviation may occur in the working distance between the subject's eye E and the ophthalmic device 10. However, by performing alignment again using the corneal apex position in this way, a cross-sectional image (captured image) can be acquired while maintaining an appropriate working distance. As a result, the focus of the cross-sectional image is stabilized, and the axial length can be calculated with high accuracy.

[0139] In this embodiment, the actual axial length of the subject eye may differ from the axial length derived by ray tracing calculation based on the ocular refractive power and anterior eye shape information of the subject eye. That is, there may be a discrepancy between the actual axial length and the axial length calculated by calculation. This may occur, for example, when the refractive index of each transparent body of the subject eye is set to be constant. This is because the refractive index adopted from a model eye or literature values ​​does not necessarily match that of each individual eye.

[0140] For this reason, the refractive index may be changed by the examiner arbitrarily selecting a model eye or a literature value. The refractive index may be changed by the examiner directly inputting a numerical value. The axial length calculated by ray tracing may be multiplied by a coefficient preset based on an experiment or simulation. The number of such coefficients is not limited to one, and multiple coefficients may be prepared according to at least one of country, region, age, and the like. With these, the axial length is derived with high accuracy at a value closer to the actual axial length.

[0141] Also, for example, refractive index information on the refractive index of the transparent body may be acquired separately from the cross-sectional image 70 of the anterior eye segment, and the refractive index information may be used to derive the axial length AL. That is, in acquiring the axial length AL, the refractive index of the transparent body based on the refractive index information may be further considered. As an example, the refractive index information may include the refractive index of the crystalline lens. It is known that the refractive index of the crystalline lens changes with age. Therefore, the storage unit of the ophthalmic device 10 may have a calculation formula or a look-up table in which the refractive index of the crystalline lens is associated with each age. In this case, the age of the subject is input, and the refractive index according to the age can be acquired. The control unit 50 may perform a ray tracing calculation using such a refractive index of the crystalline lens. This also allows the axial length to be derived with high accuracy at a value closer to the actual axial length. [Explanation of symbols]

[0142] 10 Ophthalmology equipment 50 Control section 100 Measurement optical system 150 Fixation target presentation optical system 200 Frontal Shooting Optical System 300a Irradiation optical system 300b Receiving optical system 400 Index projection optical system

Claims

1. an eye refractive power measuring optical system for projecting a first measurement light onto a fundus of a subject's eye and acquiring an eye refractive power of the subject's eye based on a reflected light of the first measurement light reflected by the fundus; a cross-sectional image photographing optical system for projecting a second measurement light onto an anterior segment of the subject's eye and detecting a return light of the second measurement light from an oblique direction with respect to an optical axis of the second measurement light, thereby acquiring a cross-sectional image of the anterior segment of the subject's eye; an axial length acquiring means for acquiring an axial length of the subject's eye based on the ocular refractive power and the anterior ocular segment cross-sectional image; An ophthalmic device comprising:

1. An ophthalmic apparatus comprising: a first measuring light source configured to measure a focal length of an object; a second measuring light source configured to measure a focal length of an object;

2. 2. The ophthalmic apparatus of claim 1, An ophthalmic apparatus, wherein a first wavelength of the first measurement light and a second wavelength of the second measurement light are different from each other.

3. 3. The ophthalmic apparatus according to claim 2, 1. An ophthalmic apparatus comprising: a first measuring light source configured to receive a first beam from a first measuring light source;

4. In the ophthalmic apparatus according to claim 2 or 3, An ophthalmic apparatus, wherein the infrared light of the second measuring light is near-infrared light, and the second wavelength has a peak wavelength between 650 nm and 800 nm.

5. In the ophthalmic apparatus according to any one of claims 2 to 4, The cross-sectional image capturing optical system is capable of selectively projecting light having a wavelength different from the second wavelength as the second measurement light, An ophthalmologic apparatus, characterized in that the axial length acquisition means controls switching between projecting light having the second wavelength and projecting light having a wavelength different from the second wavelength.

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