JP7714897B2 - Ophthalmic equipment and programs - Google Patents

Description

This disclosure relates to an ophthalmic device and ophthalmic program for acquiring the axial length of a subject's eye.

An ophthalmic device is known that illuminates the optic body of the anterior segment of the subject's eye in a light-section manner and captures a cross-sectional image of the anterior segment.

Japanese Patent Application Laid-Open No. 2019-134907

In recent years, there has been a significant increase in the prevalence of myopia, particularly among young people, and evaluation of myopia progression based on axial length has attracted attention. The inventors investigated a device configuration that acquires both the ocular refractive power of the subject's eye and a cross-sectional image of the anterior segment, and then obtains axial length based on these. In such a device, they found that light projected onto the subject's eye is reflected by the cornea and appears as an artifact in the cross-sectional image of the anterior segment. For example, the artifact can affect the derivation of axial length.

This disclosure has been made in consideration of the above circumstances, and its technical objective is to provide an ophthalmic apparatus and ophthalmic program that can accurately obtain the axial length of a subject's eye.

(1) An ophthalmologic apparatus according to a first aspect of the present disclosure includes an eye refractive power measurement optical system that projects a first measurement light onto a fundus of an eye to obtain an eye refractive power of the eye based on light reflected from the fundus of the eye from the first measurement light, and a cross-sectional image capturing optical system that projects a second measurement light onto an anterior segment of the eye to form a light section passing through an optical axis of the eye refractive power measurement optical system on the anterior segment, and obtains a cross-sectional image of the anterior segment of the eye based on return light from the light section of the second measurement light, thereby obtaining an axial length of the eye to be examined. The ophthalmologic device is characterized by comprising: a setting means for setting an analysis region in the anterior segment cross-sectional image that does not include at least a reflected image generated by reflection of the second measurement light on the cornea of the test eye; a shape information acquisition means for analyzing the analysis region set by the setting means and acquiring anterior segment shape information relating to the shape of the anterior segment; and an axial length acquisition means for acquiring the axial length based on the ocular refractive power acquired using the ocular refractive power measurement optical system and the anterior segment shape information acquired by the shape information acquisition means.
(2) An ophthalmic device according to a second aspect of the present disclosure is an ophthalmic device for acquiring the axial length of a subject's eye, comprising: an ophthalmic refractive power acquisition means for acquiring the ocular refractive power of the subject's eye; an anterior ocular segment cross-sectional image acquisition means for acquiring a cross-sectional image of an anterior ocular segment of the subject's eye; a setting means for setting an analysis region in the anterior ocular segment cross-sectional image that does not include a reflection image generated when measurement light projected onto the subject's eye is reflected by the cornea of the subject's eye; a shape information acquisition means for analyzing the analysis region set by the setting means to acquire anterior ocular segment shape information related to the shape of the anterior ocular segment; and an axial length acquisition means for acquiring the axial length based on the ocular refractive power and the anterior ocular segment shape information acquired by the shape information acquisition means.
(3) An ophthalmologic program according to a third aspect of the present disclosure is an ophthalmologic program used in an ophthalmologic apparatus for acquiring an axial length of the eye to be examined, the ophthalmologic program including: an ophthalmologic apparatus for projecting a first measurement light onto a fundus of the eye to be examined and acquiring an ocular refractive power of the eye to be examined based on light reflected from the fundus of the eye from the first measurement light; and an ophthalmologic apparatus for projecting a second measurement light onto an anterior segment of the eye to be examined and forming a light section passing through an optical axis of the ocular refractive power measurement optical system on the anterior segment of the eye to be examined, and acquiring a cross-sectional image of the anterior segment of the eye to be examined based on return light from the light section of the second measurement light, the ophthalmologic program including: an ophthalmologic apparatus for projecting a first measurement light onto a fundus of the eye to be examined and acquiring an ocular refractive power of the eye to be examined based on light reflected from the fundus of the eye from the first measurement light; When executed by a processor of the device, the method causes the ophthalmic device to perform the following steps: a setting step of setting an analysis area in the anterior segment cross-sectional image that does not include a reflected image caused by at least the second measurement light being reflected by the cornea of the test eye; a shape information acquisition step of analyzing the analysis area set in the setting step to acquire anterior segment shape information related to the shape of the anterior segment; and an axial length acquisition step of acquiring the axial length based on the ocular refractive power acquired using the ocular refractive power measurement optical system and the anterior segment shape information acquired in the shape information acquisition step.

FIG. 1 is an external view of an ophthalmic apparatus. FIG. 1 is a schematic diagram illustrating an optical system of an ophthalmic apparatus. FIG. 2 is a schematic diagram showing the relationship between the luminosity of the subject's eye and wavelength. FIG. 2 is a schematic diagram illustrating the relationship between the light sensitivity of an image sensor and wavelength. FIG. 2 is a simplified schematic diagram of a fixation target presenting optical system. FIG. 2 is a simplified schematic diagram of a visual target projection optical system. 10 is a flowchart showing a control operation of the ophthalmologic apparatus. 10 is an example of a cross-sectional image of the anterior segment of the eye. FIG. 2 is a diagram illustrating an analysis region of a cross-sectional image. FIG. 10 is a schematic diagram for explaining a method for deriving the axial length. FIG. 10 is a diagram showing refractive power in the meridian direction. 10 is an example of a cross-sectional image of the anterior segment of the eye.

"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 also includes "substantially conjugate." In other words, "conjugate" in this embodiment also includes cases where the positions are shifted from a perfect conjugate position within a range allowable in relation to the technical significance of each part.

The ophthalmic apparatus of this embodiment is an apparatus capable of acquiring the axial length of the subject's eye. For example, the ophthalmic apparatus may have an optical system used to measure the axial length, an axial length acquisition means, etc. Furthermore, for example, the ophthalmic apparatus may have a shape information acquisition means, an anterior segment information acquisition means, an identification means, a setting means, etc.

<Fixation target presentation optical system>
The ophthalmologic apparatus of this embodiment may include a fixation target presenting optical system (e.g., a fixation target presenting optical system 150). The fixation target presenting optical system may project fixation light onto the subject's eye to present a fixation target to the subject's eye. The fixation target presenting optical system may be capable of changing the presentation distance of the fixation target. For example, this allows the fixation target presenting optical system to be used to fogging the subject's eye when the ocular refractive power of the subject's eye is acquired by the first optical system. The fixation target presenting optical system may also be used to add accommodation to the subject's eye. That is, for example, the fixation target may be used to fogging the subject's eye.

<Ocular refractive power measurement optical system>
The ophthalmologic apparatus of this embodiment may include an eye refractive power measurement optical system (e.g., measurement optical system 100). The eye refractive power measurement optical system is an optical system for acquiring the eye refractive power of the subject's eye. For example, the apparatus may include a configuration for projecting measurement light (first measurement light) onto the fundus of the subject's eye and acquiring the eye refractive power based on light reflected from the fundus. The first measurement light may be visible light or infrared light.

The eye refraction measurement optical system may be a measurement optical system used in an objective eye refraction measurement device (such as an autorefractometer or wavefront sensor). The projection optical axis of the first measurement light in the eye refraction measurement optical system may be positioned on the plane of the light section formed by the cross-sectional image capturing optical system described below. For this reason, the eye refraction measurement optical system is used to obtain the eye refraction on the light section of the anterior eye segment (on-plane eye refraction). Of course, the eye refraction measurement optical system may also be capable of obtaining the eye refraction on other planes.

<Cross-sectional image capturing optical system>
The ophthalmologic apparatus of this embodiment may include a cross-sectional image capturing optical system (e.g., 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 the anterior segment of the subject's eye. For example, the apparatus may include a configuration for projecting measurement light toward the anterior segment of the subject's eye and detecting return light (scattered light) due to scattering of the measurement light from an oblique direction relative to the optical axis of the projected measurement light to acquire a cross-sectional image of the anterior segment. Furthermore, the apparatus may include a configuration for projecting measurement light (second measurement light) toward the anterior segment of the subject's eye, forming a light section passing through the optical axis of the eye refractive power measurement optical system at the anterior segment, and acquiring a cross-sectional image of the anterior segment based on scattered light from the light section of the second measurement light. The measurement light (second measurement light) may be visible light or infrared light.

The cross-sectional image capturing 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 measurement optical system and the projection optical axis of the second measurement light in the cross-sectional image capturing optical system may be arranged coaxially. In this case, the second measurement light may be projected as slit light in the cross-sectional image capturing optical system. For example, the irradiation area of the slit light is set as a light section plane of the anterior segment. In this case, the cross-sectional image capturing optical system may have a lens system and a photodetector arranged in a Scheimpflug relationship with the light section plane formed in the anterior segment. For example, the photodetector may be a two-dimensional image sensor. The receiving optical axis of the second measurement light is arranged so as to be inclined with respect to the light section plane.

It is preferable that the range of anterior ocular segment cross-sectional images captured by the cross-sectional image capturing optical system includes from the anterior cornea of the subject's eye to at least the anterior surface of the lens. Needless to say, it is even more preferable if it includes from the anterior cornea to the posterior surface of the lens. In this case, the corneal thickness, anterior corneal radius of curvature, posterior corneal radius of curvature, anterior chamber depth, lens thickness, anterior lens radius of curvature, and posterior lens radius of curvature can all be obtained, allowing for more accurate determination of axial length.

<Front image capturing optical system>
The ophthalmologic apparatus of this embodiment includes a front image capturing optical system (e.g., a target projection optical system 400, an alignment target projection optical system). The front image capturing optical system may project a third measurement light onto the cornea of the subject's eye and capture a front image of the anterior segment including a projected image of the third measurement light projected onto the cornea, thereby acquiring corneal shape information related to the shape of the cornea. The front image capturing optical system may be a measurement optical system used in a corneal shape measuring device (autokeratometer). Note that the third measurement light in the front image capturing optical system is infrared light, but may also be visible light.

<Common use of the fixation target presentation optical system and the cross-sectional image capturing optical system>
In this embodiment, the fixation target presenting optical system and the cross-sectional image capturing optical system may share a common optical path. That is, a part of the fixation optical path of the fixation light in the fixation target presenting optical system and a part of the measurement optical path (projection optical path) of the second measurement light in the cross-sectional image capturing optical system may be a common optical path. For example, an optical path combining member may be provided to combine the respective optical paths of these optical systems. Note that the fixation light projected from the fixation target presenting optical system is focused on the fundus, and the second measurement light projected from the cross-sectional image capturing optical system is focused on the anterior segment. While this results in a complex configuration due to the shared optical system, the optical path combining member can be easily configured. For example, if both the fixation light and the second measurement light are visible light, the optical path combining member can be more easily configured.

By using an optical path coupling member to share the fixation target presenting optical system and the cross-sectional image capturing optical system, astigmatism may occur in at least one of the fixation light and the second measurement light. Therefore, each optical system may be configured to take into account the effects of astigmatism.

The optical path coupling member may be composed of at least one optical element, such as a beam splitter, a dichroic mirror, or a half mirror. In this case, the optical path coupling member may be either a prism-type element or a flat-type element.

Examples of prism-type components that can be used include cube half mirrors made by bonding together right-angle prisms, dichroic prisms, etc. Such prism-type components suppress the occurrence of astigmatism, allowing for the capture of good anterior segment cross-sectional images. When a prism-type component is used for the optical path combining component, one of the fixation target presenting optical system and the cross-sectional image capturing optical system can be arranged on the transmission side of the optical path combining component, and the other of the fixation target presenting optical system and the cross-sectional image capturing optical system can be arranged on the reflection side of the optical path combining component.

Examples of planar components include a plate half mirror and a dichroic mirror. Because either the fixation light or the second measurement light passes through such planar components at a large angle of incidence, astigmatism is likely to occur on the transmission side. Therefore, when a planar component is used for the optical path combining component, it is preferable to place the fixation target presenting optical system on the transmission side of the optical path combining component and the cross-sectional image capturing optical system on the reflection side of the optical path combining component. By placing the fixation optical path on the transmission side, priority is given to the imaging performance of the illumination light, allowing for good capture of cross-sectional images of the anterior segment. Note that, although placing the measurement optical path on the reflection side reduces the imaging performance of the fixation light, performance sufficient to allow fixation on the fixation target is still ensured, minimizing the impact on visibility.

In this embodiment, a common lens may be arranged in the common optical path between the fixation target presenting optical system and the cross-sectional image capturing optical system. More specifically, a common lens with a different function for each optical system may be arranged in the common optical path between the fixation optical path of the fixation light in the fixation target presenting optical system and the measurement optical path of the second measurement light in the cross-sectional image capturing optical system.

In this embodiment, the common lens may function as a length-shortening lens for shortening the overall length of the fixation target presenting optical system. This shortens the focal length of a portion of the fixation target presenting optical system, including the length-shortening lens, without changing the overall focal length (composite focal length) of the fixation target presenting optical system. In addition, in this embodiment, the common lens may function as a field lens for changing the direction of travel of the second measurement light in the cross-sectional image capturing optical system. More specifically, it may function as a field lens for changing the direction of travel of the second measurement light that passes outside the optical axis of the cross-sectional image capturing optical system. In other words, it may function as a field lens that approximately coincides with the image plane of the cross-sectional image capturing optical system and transmits the second measurement light without eclipse.

For example, the fixation target presenting optical system includes a total length shortening lens in its configuration, and by sharing the fixation optical path and the measurement optical path, the total length shortening lens can be used as a field lens in the cross-sectional image capturing optical system, making it possible to install optical components (e.g., objective lenses) located downstream of the field lens without increasing their diameter. The placement of a common lens with these functions saves space for the entire optical system, resulting in a more compact ophthalmic device.

<Shape information acquisition means>
The ophthalmologic apparatus of this embodiment may include a shape information acquisition means (e.g., a control unit 50). The shape information acquisition means may acquire anterior eye segment shape information relating to the shape of the anterior eye segment by analyzing an anterior eye segment cross-sectional image. The multiple parameters include at least parameters of the cornea and the crystalline lens. For example, the shape information may be information capable of identifying the shape of a translucent body included in the anterior eye segment. As an example, the shape information may include coordinates where each translucent body is located, an equation representing the shape of each translucent body, and a value calculated from the equation (e.g., curvature, thickness, depth, etc.), etc.

The multiple parameters included in the shape information may include parameters related to the shape of the cornea. For example, the radius of curvature of the anterior surface of the cornea, the radius of curvature of the posterior surface of the cornea, and the corneal thickness. The multiple parameters may also include parameters related to the shape of the crystalline lens. For example, the radius of curvature of the anterior surface of the crystalline lens, the radius of curvature of the posterior surface of the crystalline lens, and the crystalline lens thickness. The multiple parameters may also include parameters related to the depth of the anterior segment of the eye. For example, the anterior chamber depth.

The shape information acquisition means may perform analysis of the anterior segment cross-sectional image using points on the optical axis of the second measurement light in the cross-sectional image capturing optical system. The shape information acquisition means may also perform analysis of the anterior segment cross-sectional image using points on the optical axis of the first measurement light in the eye refractive power measuring optical system. Note that because the optical axis of the first measurement light passes through the center of the pupil (i.e., the center of each optical body), it is easy to capture the vertices of the optical bodies, thereby enabling accurate acquisition of anterior segment shape information.

The shape information acquisition means may acquire anterior eye shape information by analyzing an analysis region set by the setting means that does not include a reflected image in the anterior eye cross-sectional image. In this case, anterior eye shape information may be acquired by changing whether or not points on the optical axis of the second measurement light are used in the analysis depending on the position of the set analysis region. Furthermore, in this case, anterior eye shape information may be acquired by changing whether or not points on the optical axis of the first measurement light are used in the analysis depending on the position of the set analysis region. More specifically, for example, if the analysis region is located overlapping the center of each optical body, analysis may be performed using points on the optical axis of the first measurement light. For example, if the analysis region is located without overlapping the center of each optical body, analysis may be performed without using points on the optical axis of the first measurement light. For example, if the analysis region is located close to but does not overlap the center of each optical body, analysis may be performed without using points on the optical axis of the first measurement light. By appropriately changing the points used in analyzing the anterior eye cross-sectional image, anterior eye shape information can be acquired with high accuracy.

<Anterior segment information acquisition means>
The ophthalmologic apparatus of this embodiment may include an anterior eye segment information acquiring means (e.g., the control unit 50). The anterior eye segment information acquiring means may acquire anterior eye segment information related to the anterior eye segment of the subject's eye. The anterior eye segment information may include anterior eye segment shape information (described above) of the subject's eye. In this case, the anterior eye segment information may include the corneal radius of curvature, which is one of the parameters in the anterior eye segment shape information. Of course, a parameter other than the corneal radius of curvature may also be acquired. The anterior eye segment information may also include pupil state information related to the pupil state of the subject's eye. For example, the pupil state may be at least one of a miotic state and a dilated state. Note that the pupil state information may include information that can determine the presence or absence of miosis or mydriasis. For example, a value such as the pupil diameter may be used. The pupil state information may also include a determination result of the presence or absence of miosis or mydriasis based on the pupil diameter value.

The anterior segment information acquisition means may acquire the anterior segment information by receiving anterior segment information acquired by a device other than the ophthalmic device. Alternatively, the anterior segment information may be acquired by input by the examiner using an operation means (e.g., monitor 16). Alternatively, the anterior segment information may be acquired by analyzing a cross-sectional image of the anterior segment acquired using a cross-sectional image capturing optical system. Alternatively, the anterior segment information may be acquired by analyzing a frontal image of the anterior segment acquired using a frontal image capturing optical system.

<Identification means>
The ophthalmologic apparatus of this embodiment may include an identifying unit (e.g., the control unit 50). The identifying unit may identify a reflected image included in an anterior segment cross-sectional image acquired using the cross-sectional image capturing optical system. The identifying unit may identify the position (e.g., coordinates) of the reflected image, or may identify a predetermined range including the position of the reflected image.

The identification means may identify the position of the reflected image based on an operation signal input by the examiner operating an operation means (e.g., monitor 16). The identification means may also identify the position of the reflected image based on brightness information (e.g., at least one of brightness, gradation, shade, etc.) of the anterior segment cross-sectional image. The identification means may also identify the position of the reflected image based on at least one of anterior segment information and anterior segment shape information. In this case, the anterior segment information and anterior segment shape information may be associated in advance through experiments or simulations. For example, the position of the reflected image may be identified according to pupil diameter, corneal shape, lens shape, etc.

For example, the reflection image included in the anterior segment cross-sectional image may be a corneal reflection image generated by reflection (specular reflection) of the second measurement light from the cross-sectional image capturing optical system on the cornea. In particular, it may be a slit reflection image generated by projecting slit light as the second measurement light. Furthermore, for example, the reflection image included in the anterior segment cross-sectional image may be a corneal reflection image generated by specular reflection of the third measurement light from the front image capturing optical system. Of course, a corneal reflection image different from the corneal reflection image derived from the second measurement light and the corneal reflection image derived from the third measurement light may be included.

<Setting method>
The ophthalmologic apparatus of this embodiment may include a setting unit (e.g., a control unit 50). The setting unit may set an analysis region in an anterior-segment cross-sectional image acquired using the cross-sectional image capturing optical system that does not include a reflection image generated by at least the second measurement light being reflected (specularly reflected) by the cornea of the subject's eye. Furthermore, an analysis region may be set that does not include a reflection image generated by the third measurement light being reflected (specularly reflected) by the cornea of the subject's eye. For example, such an analysis region is set to acquire anterior-segment shape information (e.g., shape information related to the cornea or the crystalline lens) that includes an area on the optical axis of the second measurement light in the cross-sectional image capturing optical system.

The setting means may set an analysis region to be analyzed from a target region that can be analyzed in the anterior segment cross-sectional image. In this case, an area excluding the position of the reflected image may be set as the analysis region that does not include a reflected image. Alternatively, an area excluding a predetermined range that includes the position of the reflected image may be set as the analysis region that does not include a reflected image. This allows for accurate acquisition of anterior segment shape information based on the anterior segment cross-sectional image. Of course, the setting means may also indirectly set the analysis region by setting a non-analysis region that is not to be analyzed (i.e., the position of the reflected image or a predetermined range that includes the position of the reflected image) from the target region in the anterior segment cross-sectional image.

The setting means may also set the analysis region by excluding the position of the reflected image in the anterior segment cross-sectional image (or a predetermined range including the position of the reflected image) and interpolating using the excluded surrounding data. In other words, the reflected image may be removed from the anterior segment cross-sectional image by image processing, and the analysis region may be set for the resulting anterior segment cross-sectional image that does not include the reflected image. In this case, the entire target region described above can be set as the analysis region that does not include the reflected image. Of course, it is also possible to set a portion of the target region as the analysis region.

The setting means may set the analysis region based on the anterior segment information acquired by the anterior segment information acquisition means. For example, the analysis region may be set based on the pupil state of the subject's eye (for example, pupil diameter, etc.). Alternatively, the analysis region may be set based on the shape of each optic body in the anterior segment of the subject's eye (for example, corneal radius of curvature, etc.). This makes it easy to determine the region suitable for analyzing the anterior segment cross-sectional image. The setting means may set the analysis region by excluding the position of the reflected image identified by the identification means (or a predetermined range including the position of the reflected image).

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

The axial length acquisition means may acquire the ocular refractive power of the subject's eye by controlling the acquisition of ocular refractive power using the ocular refractive power measurement optical system. More specifically, the ocular refractive power of the subject's eye may be acquired by controlling the projection of the first measurement light in the ocular refractive power measurement optical system and the detection by the photodetector of the fundus reflection light of the first measurement light.

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

The axial length acquisition means may acquire the axial length of the subject's eye based on the ocular refractive power and multiple parameters included in the shape information acquired by the shape information acquisition means through analysis of the anterior segment cross-sectional image. For example, the axial length acquisition means may derive the axial length by ray tracing based on the ocular refractive power and multiple parameters. In ray tracing, the axial length is calculated as the distance between the corneal apex and the point where a light ray incident from a far point on a predetermined position in the anterior segment intersects with the optical axis after being refracted by an optic body. In this case, the ocular refractive power at the optical section (on-plane ocular refractive power) may be used instead of the spherical equivalent power commonly used in the field of ophthalmology to determine the far point. This allows for more accurate identification of the far point position of the light ray passing through the section plane. As a result, the axial length can be more accurately determined. In this case, ray tracing may be performed for each of multiple light rays, and the axial length may be calculated as the result of the ray tracing for each light ray. For example, the average value (or weighted average) of the axial lengths obtained by each ray tracing calculation may be calculated as the axial length of the subject's eye.

In the ray tracing calculation, the position of incidence of the light ray on the boundary surface of each optic body and the change in angle at the boundary surface may be determined taking into account the shape of the optic body on the cross-section identified from the anterior segment information. The ray tracing calculation may also take into account the decentration of the optic body in the anterior segment. The decentration is identified based on the anterior segment information. As a result of considering the decentration of the optic body in the cross-section, the axial length can be calculated more accurately. In this case, for example, ray tracing calculation may be performed for each of multiple light rays including at least the first and second light rays to determine the axial length for each light ray, and the final measurement value may be calculated based on the multiple axial lengths. The first and second light rays are light rays that are arranged on either side of the optic axis on the cross-section.

In this embodiment, the axial length acquisition means may adjust the light intensity of the second measurement light in the cross-sectional image capture optical system based on the anterior segment cross-sectional image. More specifically, an anterior segment cross-sectional image (first anterior segment cross-sectional image) of the subject's eye may be acquired, and if this anterior segment cross-sectional image is determined to be inappropriate for analysis, the light intensity of the second measurement light may be adjusted and an anterior segment cross-sectional image (second anterior segment cross-sectional image) may be acquired again. Furthermore, in this embodiment, the axial length acquisition means may adjust the detection conditions of the photodetector in the cross-sectional image capture optical system based on the anterior segment cross-sectional image. More specifically, a first anterior segment cross-sectional image may be acquired, and if the first anterior segment cross-sectional image is determined to be inappropriate for analysis, the detection conditions of the photodetector may be adjusted and a second anterior segment cross-sectional image may be acquired. This increases the likelihood of acquiring appropriate values for multiple parameters based on the anterior segment cross-sectional image, resulting in improved accuracy of the axial length.

The axial length acquisition means may determine whether the first anterior segment cross-sectional image is suitable for analysis based on whether the first anterior segment cross-sectional image was obtained satisfactorily. The axial length acquisition means may also determine whether the first anterior segment cross-sectional image is suitable for analysis based on whether multiple parameters based on the first anterior segment cross-sectional image were obtained satisfactorily. This makes it easier to acquire appropriate values even when measurement values for multiple parameters cannot be obtained or the measurement values are inaccurate.

For example, the axial length acquisition means may adjust the light intensity of the second measurement light within a predetermined range in which the luminance information of each optic body detected from the second anterior segment cross-sectional image does not become saturated. In this case, the axial length acquisition means may increase or decrease the output setting value of the light source, or may insert or remove an optical element in the optical path of the second measurement light emitted from the light source. Note that, as an example, the predetermined range may be set in advance based on the detection sensitivity, gain, etc. of the photodetector. Also, for example, the axial length acquisition means may adjust the detection conditions of the photodetector within a predetermined range in which the luminance information of each optic body detected from the second anterior segment cross-sectional image does not become saturated. In this case, the axial length acquisition means may change at least one of the exposure time, gain, etc. of the photodetector.

The ophthalmologic apparatus in this embodiment may be configured to include at least an ocular refractive power acquisition means for acquiring the ocular refractive power of the subject's eye, an anterior ocular segment cross-sectional image acquisition means for acquiring a cross-sectional image of the anterior ocular segment of the subject's eye, a setting means for setting an analysis region that does not include a corneal reflection image in the anterior ocular segment cross-sectional image, a shape information acquisition means for analyzing the analysis region to acquire anterior ocular segment shape information, and an axial length acquisition means for acquiring the axial length based on the ocular refractive power and the anterior ocular segment shape information.

In this case, the ocular refractive power acquisition means may acquire the ocular refractive power by receiving measurement results using a device other than the ophthalmic device, by calling up from an electronic medical record, or by input by the examiner using an operating means, etc. Of course, if the ophthalmic device is equipped with an ocular refractive power measurement optical system, the ocular refractive power may be acquired as a measurement result using this optical system. Similarly, the anterior ocular segment cross-sectional image acquisition means may acquire the ocular refractive power by receiving an image captured using a device other than the ophthalmic device, by calling up from an electronic medical record, etc. If the ophthalmic device is equipped with a cross-sectional image capturing optical system, the anterior ocular segment cross-sectional image may be acquired as a result of capturing using this optical system.

"Example"
An example of the ophthalmologic apparatus according to this embodiment will be described.

<Overall structure>
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, an autorefractometer in this embodiment) 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.

The ophthalmic device 10 has 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 control unit 50.

The measurement unit 11 includes a measurement system and an imaging system used to examine the subject's eye. In this embodiment, the optical system shown in Figure 2 is arranged.

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

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.

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

The calculation control unit 50 (also called a processor; hereinafter simply referred to as the control unit 50) is responsible for overall control of the ophthalmic device 10. It also processes various test results obtained via the measurement unit 11.

<Optical system>
2 is a schematic diagram showing the optical systems 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 imaging optical system 200, a cross-sectional imaging optical system (an irradiation optical system 300a and a light-receiving optical system 300b), a target projection optical system 400, and an alignment target projection optical system. The apparatus 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 defined as the upstream side, and the eye to be examined side is defined as the downstream side.

<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: astigmatic axis angle may be acquired as measurement results of the ocular refractive power.

The measurement optical system 100 has a projection optical system 100a and a light-receiving optical system 100b.

The projection optical system 100a has at least a measurement light source 111, and projects spot-shaped measurement light onto the fundus of the subject's eye E through the center of the pupil or the apex of the cornea. The measurement light source 111 may be an SLD light source, an LED light source, or another light source. In this embodiment, infrared light is used as the measurement light. For example, near-infrared light with a peak wavelength between 800 nm and 900 nm may be used. As an example, near-infrared light with a peak wavelength of 870 nm may be used.

In this embodiment, a prism 115 is placed on the common path of the projection optical system 100a and the light receiving optical system 100b. By rotating the prism 115 around the optical axis, the projection light beam on the pupil is rotated eccentrically at high speed. As an example, in this embodiment, the projection light beam is rotated eccentrically in a region on the pupil between φ2 mm and φ4 mm. This region is the measurement region for the eye refractive power in this embodiment.

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 beam reflected from the fundus in a ring shape through the periphery of the pupil. The ring lens 124 is positioned at a pupil conjugate position, and the image sensor 125 is positioned at a fundus conjugate position. The ocular refractive power is derived by analyzing the ring image formed on the image sensor 125 via the ring lens 124.

As mentioned above, in this embodiment, the measurement light is eccentrically rotated at high speed on the pupil, so analysis is performed on the output image from the image sensor 125 based on an exposure time sufficiently long relative 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: astigmatic axis angle are obtained as results of the analysis.

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

<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.

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 positioned at a conjugate position with the fundus. The fixation light beam from the light source 151 passes through the fixation target plate 155 and lens 156 on the optical axis L2, and then passes through the half mirror 503. It also passes through lens 504, passes through the half mirror 502, and is reflected by the half mirror 501, becoming coaxial with the optical axis L1. The fixation light beam then passes through the objective lens 505 and reaches the fundus.

The measurement light source 111, ring lens 124, and image sensor 125 in the measurement optical system 100, and the light source 151 and 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 a drive unit 160. For example, the focal length within the drive unit 160 in the measurement optical system 100 and the focal length within 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 subject's eye E, the presentation distance of the fixation target plate 155 relative to the subject's eye E (i.e., the presentation position of the fixation target) can be changed, and the measurement light source 111 and 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 ring lens 124 are pupil conjugate at a constant magnification.

<Frontal shooting optical system>
The front imaging optical system 200 is used to capture a front image of the anterior segment of the subject's eye E. For example, the front imaging optical system 200 includes an image sensor 205 and the like. The image sensor 205 may be disposed at a pupil conjugate position. An observation image of the anterior segment may be acquired as the front image. 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 imaging optical system 200.

<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.

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 (illumination light). The irradiation optical system 300a includes a light source 311 and a slit 312. The light source 311 may be an SLD light source, an LED light source, or another light source. 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 specified wavelength may also be used. The slit 312 may be positioned at the pupil conjugate position.

The light source 311 of the irradiation optical system 300a will now be described in detail. Figure 3 is a schematic diagram showing the relationship between luminosity and wavelength of the subject's eye. The subject's eye has luminosity in the visible range, but it is generally greatest 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 less susceptible to dazzling by red visible light. It is said that the subject is not dazzled by infrared light.

Traditionally, when obtaining cross-sectional images of the anterior segment of the eye 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 other conditions tend to show up in cross-sectional images due to the transmittance of the subject's eye, but the illumination light is dazzling and a burden to the subject. On the other hand, with the increase in the prevalence of myopia, particularly among young people, in recent years, there is growing importance in measuring the axial length of young people. However, because young people are less likely to have cataracts, it is possible to use light other than the above as illumination light.

In this embodiment, red visible light to near-infrared light, which is less likely to cause glare to the subject's eyes, is used as illumination light. For example, compared to the visibility of green visible light around 550 nm, the visibility of red visible light around 650 nm is approximately 1/10, and the visibility of red visible light around 700 nm is approximately 1/200. This significantly reduces the burden on the subject. In particular, when targeting young people, including children, this not only reduces the burden but also leads to more efficient measurements.

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

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 the cut surface set in the anterior segment. That is, the optical arrangement is such that the extensions of the cut surface, the principal plane of the lens system 322, and the imaging surface of the image sensor 321 intersect at a single intersection (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 composed of a semiconductor substrate made of silicon as a single element.

The image sensor 321 of the light receiving optical system 300b will now be described in detail. Figure 4 is a schematic diagram showing the relationship between the light receiving sensitivity and wavelength of the image sensor 321. For example, an image sensor made of silicon as a single element has sensitivity to wavelengths around 300 nm to 1000 nm, which includes wavelengths in the ultraviolet, visible, and infrared ranges. However, sensitivity is highest around 550 nm to 650 nm, which includes green visible light, and gradually decreases as the wavelength approaches the infrared range. However, sensitivity above 650 nm, which includes the red visible to near-infrared light used in the irradiation optical system 300a, is sufficient for capturing cross-sectional images of the anterior segment.

For example, there are image sensors whose sensitivity is greatest in the infrared range, but these are expensive. While it would be desirable for these devices to be widely used in hospitals, schools, and other facilities, the high cost of the devices could hinder their widespread use. Using an image sensor made of silicon makes it possible to keep the cost of the device low.

In this type of cross-sectional imaging optical system, the illumination light beam from the light source 311 becomes a slit light beam via a slit 312 on the optical axis L3, passes through the lens 313, and is reflected by the half mirror 503, becoming coaxial with the optical axis L2. The illumination light beam also passes through the lens 504, passes through the half mirror 502, and is reflected by the half mirror 501, becoming coaxial with the optical axis L1. The illumination light beam then passes through the objective lens 505 to reach the anterior segment. Return light from the cut surface formed in the anterior segment reaches the image sensor 321 via the lens 322.

<Indicator projection optical system>
The target projection optical system 400 is used to measure the corneal shape. The target projection optical system 400 projects a target for measuring the corneal shape onto the anterior segment from the front side facing the subject's eye.

The target projection optical system 400 includes multiple point light sources 401. The point light sources 401 project a target at infinity by irradiating the cornea with parallel light. The point light sources 401 emit infrared light. However, visible light may also be used. The point light sources 401 are arranged symmetrically both vertically and horizontally around the optical axis L1. For example, in this embodiment, two point light sources are provided on each side. This allows four point image targets to be projected onto the cornea. Note that the shape of the targets is not limited to this, and linear targets and other targets may be included. Furthermore, the number of targets is not limited to this, and the system may be configured with three or more point image targets.

In this embodiment, the circumferential area onto which these four point images are projected becomes the corneal shape measurement area using the target projection optical system 400 and the front imaging optical system 200. As an example, when a corneal model eye with a predetermined radius of curvature is placed at a predetermined working distance, each point image is projected onto a circumferential area of φ3 mm on the corneal model eye.

<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.

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, visible light may also be used. 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.

<Common optical path for fixation target presentation optical system and cross-sectional imaging optical system>
In this embodiment, visible light is emitted from both the fixation target presenting optical system 150 and the target projection optical system 300a. 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, thereby sharing their respective optical paths. For example, the half mirror 503 is flat, 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 to form a cut surface in the anterior segment and obtain a clear cross-sectional image 70. For this reason, it is preferable to dispose the target projection optical system 300a on the reflection side, where the influence of astigmatism is minimal.

In addition, in this embodiment, lens 504a is positioned on the optical axis of the fixation target presenting optical system 150. Lens 504a functions as an overall length shortening lens for shortening the overall length of the fixation target presenting optical system 150. Lens 504a also serves to reduce the diameter of lens 156, which is located upstream of lens 504a.

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

When the working distance from the subject's eye E to the objective lens is a predetermined value, in Figure 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. Light rays from both 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 Figure 5(b), if lens 504a is placed in the fixation target presenting optical system 150, the distance of the fixation target presenting optical system 150 can be shortened. This is because the combined focal length of lens 156 and lens 504a is shorter than the focal length of lens 156 alone. Each light ray from the fixation target plate 155 reaches the lens 156 with a small diameter.

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

In this way, by placing lens 504a in the fixation target presenting optical system 150, it is possible to design lens 156 with a small diameter. Furthermore, the overall length of the fixation target presenting optical system 150 can be shortened while maintaining the specified working distance of the subject's eye E and the combined focal length of the fixation target presenting optical system 150. As a result, this leads to a more compact ophthalmic device 10.

In addition, in this embodiment, lens 504b is positioned on the optical axis of the visual target projection optical system 300a. Lens 504b serves to reduce the diameter of objective lens 505, which is located downstream of lens 504b.

Figure 6 is a simplified schematic diagram of the visual target projection optical system 300a. Figure 6(a) shows the case where the lens 504b is not provided. Figure 6(b) shows the case where the lens 504b is provided. Here, the optical path from the subject's eye E to the slit 312 is a straight line, and some optical components 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.

In Figures 6(a) and 6(b), light rays from the center of the slit 312 pass through the center of the objective lens 505, regardless of whether lens 504b is present. However, in Figure 6(a), light rays from the periphery of the slit 312 are refracted at a position farther away from the center of the objective lens 505. In order to allow such light rays to reach the subject's eye E, an objective lens 505 with a large diameter is required. On the other hand, in Figure 6(b), light rays from the periphery of the slit 312 are refracted at the center of the objective lens 505. In order to allow such light rays to reach the subject's eye E, an objective lens 505 with a small diameter can be used.

In this way, by placing lens 504b in the visual target projection optical system 300a, the direction of travel of light rays passing outside the optical axis L3 can be changed without changing the direction of travel of light rays passing through the optical axis L3, so the objective lens 155 can be designed with a small diameter. Note that the further light rays from the central and peripheral parts of the slit 312 are refracted in areas away from the center of the objective lens 505, the greater the aberration that can occur. For this reason, an objective lens 155 with an appropriate diameter may be used that suppresses the generation of aberrations while minimizing the size of the ophthalmic device 10.

In this embodiment, a lens 504 is arranged in the fixation target presenting optical system 150 and the visual target projection optical system 300a, which share the lenses 504a and 504b, which have different roles as described above. For example, the lens 504 is arranged downstream of the half mirror 503, which joins the optical axis L2 of the fixation target presenting optical system 150 and the optical axis L3 of the visual target projection optical system 300a. This further reduces the space required inside the optical system.

<Control operation>
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 measures the corneal curvature, measures the eye refractive power, and captures a cross-sectional image of the anterior eye segment, and obtains the axial length based on the results of the measurements and capture.

<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 segment observation image.

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 the observation image of the anterior segment acquired via the front imaging 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. Alignment in the Z direction is also 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 alignment may be adjusted based on the alignment index detected in the observation image.

<Cornea shape 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 astigmatism power, and the astigmatic axis angle are acquired as the corneal shape information.

<Eye refractive power measurement (S3)>
Next, the ocular refractive power of the subject's eye E is measured. Since infrared light is projected onto the subject's eye E as measurement light, the pupil diameter of the subject's eye E becomes a predetermined size with suppressed miosis (for example, φ2 mm or less). As an example, the pupil diameter becomes any diameter included in the measurement region of the subject's eye E (region on the pupil between φ2 mm and φ4 mm). For example, in measuring the ocular refractive power, a preliminary measurement may be performed first, followed by the main measurement.

In the preliminary measurement, the refractive power of the subject's eye E is measured with the fixation target positioned at a predetermined presentation distance. During measurement, the fixation target plate 155 may be positioned at an initial position that is optically far enough from the subject's 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 subjected to image analysis by the control unit 50. As a result of the analysis, the value of the refractive power in each meridian direction is determined. By performing predetermined processing on the refractive power in each meridian direction, at least the spherical power in the preliminary measurement is obtained.

The control unit 50 then moves the fixation target plate 155 to the 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 subject's eye E to clearly observe the fixation target. The control unit 50 then moves the fixation target from the fogging start position to apply fogging to the subject's eye E. This releases the adjustment of the subject's eye E.

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 with fogging applied, thereby obtaining the objective values of the test eye E's SPH: spherical power, CYL: cylindrical power, and AXIS: astigmatic axis angle.

<Capturing an Anterior Segment Cross-Section Image (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 captures the cross-sectional image of the anterior segment upon completion of the main measurement of the eye refractive power. 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. In other words, immediately upon completion of the main measurement, 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 capture a cross-sectional image of the anterior segment. This reduces misalignment between the time of measurement of the eye refractive power and the time of capturing the cross-sectional image.

Figure 8 is an example of a cross-sectional image 70 of the anterior segment. In addition to the cornea, iris, and lens, artifacts may appear in the cross-sectional image 70. For example, the slit light (illumination light) emitted from the irradiation optical system 300a forms a cut surface in the anterior segment, but some of the light may be reflected (specularly reflected) by the cornea. The image sensor 321 of the light receiving optical system 300b captures the corneal reflection of the slit light along with the return light from the cut surface of the slit light, and this image of the corneal reflection appears in the cross-sectional image 70 as an artifact 75. Note that the presence of artifact 75 makes it difficult to accurately obtain anterior segment shape information in the analysis in the subsequent step S5.

<Analysis of anterior segment cross-sectional image (S5)>
The control unit 50 acquires anterior eye segment shape information relating to the shape of the anterior eye segment based on the cross-sectional image 70 of the anterior eye segment of the subject's eye E. For example, the anterior eye segment shape information may include a plurality of parameter information that are measurement values 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, the radius of curvature (rp) of the posterior crystalline lens, and the crystalline lens thickness (LT). Note that the corneal shape information acquired in step S2 may also be used as the anterior eye segment shape information.

The control unit 50 performs image processing on the cross-sectional image 70 to detect each optic body (for example, the cornea, aqueous humor, and lens) and acquire anterior segment shape information. For example, the brightness information of the cross-sectional image 70 may be used to detect pixel positions corresponding to tissue boundaries (the anterior and posterior surfaces of the cornea, the anterior and posterior surfaces of the lens, the iris, etc.) and acquire information such as the radius of curvature. Furthermore, for example, the distance to the pixel positions corresponding to the tissue boundaries may be calculated to acquire information such as the thickness and depth of the tissue.

In this embodiment, the control unit 50 sets an analysis region that does not include the artifact 75 when processing the cross-sectional image 70. This is because the artifact 75 may cause the boundaries of each tissue to be erroneously detected or may reduce the accuracy of detecting the boundaries of each tissue. In particular, if at least a portion of the artifact 75 is close to or overlaps with the boundary of a tissue, it has a significant impact on detection. For this reason, the pixel position of the artifact 75 is identified, and the artifact 75 is excluded from the analysis region before image processing is performed.

Figure 9 is a diagram illustrating the analysis region of the cross-sectional image 70. The control unit 50 may identify the pixel position of the artifact 75 using brightness information of the cross-sectional image 70. For example, the corneal reflected light of the slit light is light that does not pass through the cornea or lens and is not attenuated. On the other hand, the returned light from the cross section of the slit light is light that is attenuated by passing through the cornea or lens, and is also part of the light scattered by the cornea or lens. Therefore, the corneal reflected light and the returned light (scattered light) appear as images in the cross-sectional image 70 with different brightnesses. As an example, the control unit 50 may identify the pixel position of the artifact 75 by detecting whether the brightness value of each pixel position in the cross-sectional image 70 exceeds a predetermined threshold.

The control unit 50 then excludes at least the pixel position of the artifact 75 from the target region Q for analysis in the cross-sectional image 70 (i.e., the target region Q including all pixel positions). In this embodiment, a range having a predetermined number of pixels in the vertical and horizontal directions based on the pixel position of the artifact 75 is set as a non-analysis region Q1 (solid line portion in Figure 9) to be excluded from the target region Q. This sets an analysis region Q2 (dotted line portion in Figure 9) that is the target of image processing of the cross-sectional image 70 and is obtained by excluding the non-analysis region Q1 from the target region Q.

The control unit 50 may detect pixel positions corresponding to tissue boundaries based on the brightness information of the analysis region Q2 and specify at least three pixel positions for each boundary. If the tissue boundary detected in the analysis region Q2 includes a pixel position on the optical axis L1, at least three pixel positions may be specified so as to include the intersection of the tissue boundary and the optical axis L1. The control unit 50 can determine a circle that passes through the at least three specified points, as well as the center point and radius of this circle, and acquire information such as the radius of curvature. It can also determine the distance to the pixel positions corresponding to the tissue boundaries and acquire information such as the thickness and depth of the tissue.

Note that when the brightness value of a portion of the cross-sectional image 70 is low (for example, due to reflections of the subject's eyelids or eyelashes), or when the non-analysis region Q1 is set inappropriately, errors may be large when fitting a circle using at least three pixel positions. In this case, the control unit 50 may change the point specified on the cross-sectional image 70. For example, this may be based on the similarity between the cross-sectional image 70 and the anterior eye structure predicted by image processing of the cross-sectional image 70. If the specified point is in an area with low similarity, the point may be deleted and a new point may be selected from an area with high similarity. Furthermore, when four or more pixel positions are specified on the cross-sectional image 70, the control unit 50 may delete certain points so that at least three pixel positions remain. In other words, if a point is specified on the cross-sectional image 70 that does not follow the curved surface of the cornea or lens, it may be deleted as appropriate.

<Eye axis length calculation (S6)>
Next, the control unit 50 calculates the axial length of the subject's eye E. The control unit 50 calculates the axial length based on the ocular refractive power of the subject's eye E and a plurality of parameter information in the anterior segment shape information of the subject's eye E.

First, the control unit 50 determines the position of the far point FP (see Figure 10) 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 = 12 mm, then the distance from the corneal apex C to the far point FP is 12 + 1000/5 = 212 mm. It is believed that light rays from the far point FP form an image on the fundus. Note that VD = 12 mm is a fixed value indicating the distance between the corneal vertices assuming the wearer of eyeglass lenses. VD may vary depending on the device.

Figure 10 is a schematic diagram illustrating a method for deriving the axial length. In this embodiment, the axial length may be derived based on ray tracing calculations on a cross section of the anterior segment. For example, the control unit 50 performs ray tracing calculations based on the position of the far point FP, the refractive index of each optical body, and parameter information in the anterior segment shape information.

The control unit 50 tracks a light ray (for example, ray Lx in Figure 10) incident from a far point FP toward the subject's eye E, and determines the position of the intersection 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 ray tracing calculations will be described later. For example, the position of the fundus Ef can be determined by such ray tracing calculations. The control unit 50 derives the distance between the corneal apex C and the fundus Ef as the axial length AL.

<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. If previous axial length measurement results for the subject's eye E exist, the current measurement results may be displayed together with the previous measurement results. For example, the measurement results may be displayed using a trend graph with age (measurement date) on the horizontal axis and axial length AL on the vertical axis. Of course, the display manner of the measurement results is not limited to these.

<Ray tracing calculation>
Ray tracing calculation for deriving the axial length will be described. In this embodiment, for the sake of convenience, it is assumed that the refractive index of each optically transparent body of the subject's eye E is constant and that 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 changes in the refractive index inside the optically transparent body (for example, changes in the refractive index between the inside and outside of the crystalline lens).

In the widely used expression of ocular refractive power using SPH, CYL, and AXIS, SPH indicates the refractive power related to the principal meridian (or the principal meridian), so it does not necessarily result in an appropriate value when tracing rays on a cross section of the anterior segment. For example, consider a case where SPH = -5D, CYL = -2D, and AXIS = 30°. In this case, if a horizontal cross section were to be obtained using the example optical system above, the refractive power on this cross section would be neither -5D nor -7D with CYL added.

In contrast, in this embodiment, the on-surface ocular power, which is the ocular power on the cross section, is calculated, and the position of the far point FP is set based on the on-surface ocular power. Here, the refractive power P at any surface is expressed by the following formula. However, θ is the angle with respect to the horizontal plane, with the horizontal direction being 0°.

P(θ)=SPH+CYL×[sin2(θ-A)]

Figure 11 shows 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°, the calculation is P(0°) = -5.5D. In this case, if VD = 12 mm, the distance from the corneal vertex C to the far point FP on the cutting plane is 12 + 1000/5.5 = 194 mm.

The control unit 50 tracks the light ray from the far point FP set in this way. For example, it guides a light ray (e.g., light ray Lx in Figure 10) from the far point FP toward a fixed position (e.g., a position of φ6 mm at the position of the pupil of the test eye (approximately 3 mm behind the cornea)). Note that setting the fixed position as the position of the pupil of the test eye at φ6 mm is merely an example and can be changed as appropriate.

This ray first undergoes initial refraction at the anterior surface of the cornea. The intersection of the ray with the anterior surface of the cornea is calculated based on the radius of curvature Ra of the anterior surface of the cornea, the position of the far point FP, and the ray angle at the far point FP. The angle of incidence of the ray at this intersection is then calculated. Upon reaching the anterior surface of the cornea, the ray changes direction at a refraction angle determined relative to the angle of incidence based on Snell's law. In this manner, the ray is sequentially tracked at each optically transparent boundary surface. In this process, anterior segment shape information (Ra, Rp, CT, ACD, ra, rp, LT) obtained based on corneal shape information and cross-sectional image 70 (Scheimpflug image) is appropriately used to determine the intersection of the ray with each boundary surface. In this embodiment, the intersection point (i.e., the position of the fundus Ef) where the ray intersects with the axis of the eye (here, the visual axis) after exiting the posterior surface of the lens is finally determined. The distance from the intersection point to the corneal vertex C (here, the origin) is used as the axial length AL.

When the above-mentioned anterior segment shape information (Ra, Rp, CT, ACD, ra, rp, LT) is used in the ray tracing calculation, in this embodiment, at least the value based on the corneal Purkinje image of the point image index is used for the radius of curvature Ra of the anterior corneal surface, and values based on the cross-sectional image 70 (Scheimpflug image) are used for the remaining values. This is because, for anterior corneal shape, measurement accuracy based on the corneal Purkinje image is generally higher than measurement accuracy based on the Scheimpflug image. As mentioned above, in this embodiment, at least the values of corneal curvature, astigmatism power, and astigmatic axis angle are acquired as corneal shape information. The corneal curvature (curvature of the anterior corneal surface) at the cross section can be calculated from these values using a method similar to that used to calculate the refractive power for the cross section. The reciprocal of the calculated value may be used as Ra.

The axial length AL of the subject's eye E can be determined by tracing rays directed toward such a fixed position. However, the ray tracing method is not limited to the above method. For example, the point at which the image is formed from the far point FP may be determined by paraxial calculation. Alternatively, the point at which the image is formed from the far point FP may be determined by taking into account multiple rays that enter the subject's eye E at different positions. For example, ray tracing for paraxial rays and rays directed toward a fixed position other than the paraxial may be combined. When ray tracing for multiple rays is performed, the final measured value (calculated value) of the axial length may be the average value (or a weighted average value) of the axial lengths obtained by each ray tracing.

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

Note that a predetermined offset value may be added to the axial length value obtained in this embodiment. The offset value corrects for errors between the calculated value and the actual measured value.

Ray tracing may also be performed by tracing rays that are emitted from the far point FP and pass through the circumferential region onto which a point image index for corneal shape measurement is projected. This further optimizes the conditions for ray tracing, making it easier to obtain the axial length with greater accuracy.

As explained above, for example, the ophthalmologic device in this embodiment is equipped with an optical path combining member that combines the fixation optical path of the fixation light in the fixation target presenting optical system and the measurement optical path (light projection optical path) of the measurement light (illumination light) in the cross-sectional image capturing optical system. This allows the fixation target to be appropriately presented to the subject's eye, cross-sectional images of the anterior segment to be captured satisfactorily, and the axial length to be obtained with high accuracy. Note that because the fixation light is focused on the fundus and the illumination light is focused on the anterior segment, the configuration of each optical system becomes complex due to the sharing of these components, but the optical path combining member can be easily constructed. If both the fixation light and the illumination light are visible light, the optical path combining member can be constructed even more easily.

Furthermore, for example, the ophthalmic device in this embodiment has a common lens disposed in the common optical path between the fixation optical path and the measurement optical path. The common lens functions as a length-reducing lens to reduce the overall length of the fixation target presenting optical system, and also functions as a field lens to change the direction of travel of the measurement light (illumination light) in the cross-sectional image capturing optical system. For example, the fixation target presenting optical system includes a length-reducing lens in its configuration, but by sharing the fixation optical path and the measurement optical path, the length-reducing lens can be used as a field lens in the cross-sectional image capturing optical system, allowing for a design without enlarging the objective lens. This results in a space-saving optical system configuration, and a more compact ophthalmic device.

Furthermore, for example, the ophthalmic apparatus in this embodiment uses a flat member as the optical path coupling member. With flat members, astigmatism is more likely to occur on the transmission side and less likely to occur on the reflection side. Therefore, the imaging performance of light arranged on the transmission side is lower than that of light arranged on the reflection side. In this embodiment, by arranging the fixation optical path on the transmission side, priority is given to the imaging performance of the illumination light, allowing for good cross-sectional images of the anterior segment to be captured. Although the imaging performance of the fixation light is reduced by arranging the measurement optical path on the reflection side, the performance is still sufficient to allow fixation on the fixation target, so the impact on visibility is kept to a minimum.

Furthermore, for example, the ophthalmologic apparatus in this embodiment identifies artifacts contained in the anterior segment cross-sectional image and sets an analysis region that excludes the artifacts. This makes it possible to accurately obtain anterior segment shape information by using only the region suitable for analyzing the anterior segment cross-sectional image.

Furthermore, for example, the ophthalmic device in this embodiment changes whether or not to use points on the optical axis of the measurement light in the eye refractive power measurement optical system for analysis, depending on the position of the analysis region relative to the anterior segment cross-sectional image. For example, if an artifact is detected near the curved surface of each tissue, or if an artifact is detected overlapping with the curved surface of each tissue, the accuracy of the anterior segment shape information may decrease. By appropriately changing the points used in analyzing the anterior segment cross-sectional image, it is possible to obtain accurate anterior segment shape information.

<Example of transformation>
In this embodiment, the optical axes of the fixation target presenting optical system 150 and the target projection optical system 300a are branched or combined by a planar half mirror 503. However, this is not limiting. In this embodiment, a prism-type half mirror may be used to branch or combine the optical axes. Prism-type mirrors are less likely to produce astigmatism on either the transmission side or the reflection side. Therefore, regardless of the relationship between the fixation target presenting optical system 150 and the target projection optical system 300a and the half mirror, the imaging performance of the target projection optical system 300a can be maintained. As a result, a cross-sectional image of the anterior segment is captured satisfactorily.

In this embodiment, a configuration in which a shared lens 504 is arranged on the common optical axis of the fixation target presenting optical system 150 and the target projection optical system 300a has been described as an example, but this is not limiting. In this embodiment, lenses with different functions (lenses 504a and 504b) may be arranged on the optical axis of each optical system. In other words, lenses 504a and 504b may be arranged upstream of a half mirror 503 that branches or combines the optical axes of each optical system. However, in order to reduce the size of the ophthalmic device 10, it is preferable to use a lens 504 in which lenses 504a and 504b are shared.

In this embodiment, a configuration has been described in which the pixel position of the artifact 75 is identified using a threshold value for the brightness value in the cross-sectional image 70 of the anterior segment, but this is not limiting. In this embodiment, the pixel position of the artifact 75 may be identified by calculating the similarity between the cross-sectional image 70 and the template image based on the brightness values. As an example, in this case, the control unit 50 may move the template image to be superimposed on the cross-sectional image 70 by one pixel at a time (performing so-called pattern matching) and detect a combination in which the similarity based on the difference in each brightness value is zero (or a value closest to zero). Note that the storage unit (memory) of the ophthalmologic device 1 may store the template image.

For example, because the shape, size, brightness value, etc. of the artifact 75 reflected in the cross-sectional image 70 can be predicted from a design perspective, a template image may be used to detect the artifact 75. In this case, the control unit 50 may identify the pixel position of the template image corresponding to the cross-sectional image 70 as the pixel position of the artifact 75. The control unit 50 may also set the non-analysis region Q1 based on the pixel position of the artifact 75 in the cross-sectional image 70.

Also, for example, a template image representing a standard cross-sectional image of the eye, modeled after the general structure of the eye, may be used. The control unit 50 identifies pixel positions of the template image that correspond to the cross-sectional image 70, but if the cross-sectional image 70 contains artifacts 75 or the like, differences in the respective brightness values will occur, resulting in partial mismatches. Therefore, the control unit 50 may set pixel positions in the cross-sectional image 70 that match the template image as the analysis region Q2 of the cross-sectional image 70. Alternatively, the control unit 50 may identify pixel positions in the cross-sectional image 70 that do not match the template image as pixel positions of artifacts 75, and set the non-analysis region Q1 of the cross-sectional image 70 based on this. In other words, the template image may be used to indirectly detect artifacts 75.

In this embodiment, a configuration has been described in which the non-analysis region Q1 and the analysis region Q2 are set using brightness information in the anterior segment cross-sectional image 70, but this is not limiting. In this embodiment, each region may be set using anterior segment information related to the anterior segment of the subject's eye E. The anterior segment information may include anterior segment shape information (corneal shape information, lens shape information, etc.), information regarding the pupil state (e.g., miosis or mydriasis), etc. This makes it possible to easily determine the region suitable for analysis of the anterior segment cross-sectional image and accurately obtain anterior segment shape information.

For example, the control unit 50 may set at least the non-analysis region Q1 in the cross-sectional image 70 based on the radius of curvature of the anterior corneal surface, which is one piece of anterior eye shape information of the subject's eye E. In this case, the control unit 50 acquires the radius of curvature of the anterior corneal surface of the subject's eye E and acquires the pixel position of the artifact 75 corresponding to the radius of curvature. For example, the approximate pixel position where the artifact 75 is reflected can be predicted from the radius of curvature of the anterior corneal surface. The storage unit of the ophthalmologic apparatus 1 may have a correspondence table in which pixel positions that change for each radius of curvature are previously associated. This makes it possible to determine the non-analysis region Q1 without using brightness information of the cross-sectional image 70.

Furthermore, for example, the control unit 50 may set at least the analysis region Q2 in the cross-sectional image 70 based on the pupil diameter, which is one piece of pupil state information of the subject's eye E. In this case, the control unit 50 may obtain the pupil diameter PDM (see FIG. 8) by detecting the iris of the subject's eye E, and set the region inside the pupil diameter PDM as the analysis region Q2. Note that the region inside the pupil diameter PDM may be limited to the same region as the measurement region of the eye refractive power by the measurement optical system 100 (for example, φ2 mm to φ4 mm on the pupil).

Of course, the cross-sectional image 70 may be configured such that the non-analysis region Q1 and analysis region Q2 are set by combining brightness information and anterior segment information.

In this embodiment, an example has been described in which an artifact 75 is reflected in the cross-sectional image 70 of the anterior segment due to the slit light emitted from the irradiation optical system 300a, but this is not limiting. For example, an artifact can also be reflected when the measurement light emitted from the target projection optical system 400 or the measurement light emitted from the alignment target projection optical system is reflected by the cornea and captured by the image sensor 321.

Figure 12 is an example of a cross-sectional image 70 of the anterior segment. For example, the cross-sectional image 70 may contain a point-shaped artifact 76 caused by the light source 401, a ring-shaped artifact 77 caused by the alignment light source 601, etc. (The shapes of the artifacts are not limited to these). For this reason, the control unit 50 may exclude artifacts 76 and 77 from the target region Q as a non-analysis region Q1, as with artifact 75, and perform image processing on an analysis region Q2 that does not include these artifacts. This allows for more accurate acquisition of anterior segment shape information of the subject's eye, and enables the appropriate axial length to be obtained.

When capturing a cross-sectional image of the anterior segment, turning off the light source 401 can suppress the appearance of artifacts 76 in the cross-sectional image 70. Furthermore, turning off the alignment light source 601 can suppress the appearance of artifacts 77 in the cross-sectional image 70.

In this embodiment, an example has been described in which artifacts are excluded from the analysis region of the cross-sectional image 70 in order to properly acquire anterior eye shape information, but this is not limiting. For example, an optical element may be placed in the optical path of the optical system provided in the ophthalmic device 10 to block at least some of the corneal reflected light, such as the slit light from the irradiation optical system 300a, the measurement light from the target projection optical system 400, and the measurement light from the alignment target projection optical system. This suppresses artifacts from appearing in the cross-sectional image 70, allowing for proper acquisition of anterior eye shape information based on the cross-sectional image 70.

While the present embodiment has been described with reference to an example in which the refractive index of each optical body of the subject's eye E is constant, this is not limiting. For example, refractive index information regarding the refractive index of the optical bodies may be acquired separately from the cross-sectional image 70 of the anterior segment, and the refractive index information may be used to derive the axial length AL. In other words, the refractive index of the optical bodies based on the refractive index information may also be taken into consideration when acquiring the axial length AL. 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 lookup table that associates the refractive index of the crystalline lens with each age. In this case, by inputting the subject's age, the refractive index according to age can be acquired. The control unit 50 may perform ray tracing calculations using this refractive index of the crystalline lens.

In this embodiment, a configuration has been described in which measured values are applied to all of the anterior segment shape information (Ra, Rp, CT, ACD, ra, rp, LT) used in the ray tracing calculation of the axial length AL, but this is not limiting. In this embodiment, an assumed value may be applied to part of the anterior segment shape information. Note that the assumed value may be selected from at least one of standard values based on an eye model, average values based on statistical data, etc., past measurements of the subject eye, estimated values that can be obtained by taking into account the measured values of valid parameters and the general ratios of each tissue, etc.

10 Ophthalmic apparatus 50 Control unit 100 Measurement optical system 150 Fixation target presenting optical system 200 Front imaging optical system 300a Irradiation optical system 300b Light receiving optical system 400 Target projection optical system

Claims (5)

an eye refractive power measuring optical system for projecting a first measurement light onto a fundus of the eye to be examined and acquiring an eye refractive power of the eye to be examined based on light reflected from the fundus of the eye by the first measurement light;
a cross-sectional image capturing optical system for projecting a second measurement light onto an anterior segment of the subject's eye to form a light section passing through the optical axis of the eye refractive power measuring optical system on the anterior segment of the subject's eye, and for acquiring a cross-sectional image of the anterior segment of the subject's eye based on return light from the light section of the second measurement light;
and
An ophthalmologic apparatus for acquiring an axial length of the subject's eye,
a setting means for setting an analysis region in the anterior ocular segment cross-sectional image that does not include a reflection image generated by at least the second measurement light being reflected by a cornea of the subject's eye;
a shape information acquiring means for analyzing the analysis region set by the setting means and acquiring anterior eye segment shape information relating to the shape of the anterior eye segment;
an axial length acquiring means for acquiring the axial length based on the ocular refractive power acquired by using the ocular refractive power measuring optical system and the anterior ocular segment shape information acquired by the shape information acquiring means;
An ophthalmic apparatus comprising: The ophthalmic apparatus of claim 1,
a front image photographing optical system for projecting a third measurement light onto the cornea of the subject's eye and photographing a front image of an anterior segment including a projected image of the third measurement light onto the cornea, thereby acquiring corneal shape information relating to a shape of the cornea;
The ophthalmologic apparatus is characterized in that the setting means further sets the analysis region in the anterior segment cross-sectional image so as not to include a reflected image generated by the third measurement light being reflected by the cornea. The ophthalmic apparatus according to claim 1 or 2,
an identification means for identifying the reflected image included in the anterior segment cross-sectional image,
The ophthalmologic apparatus according to claim 1, wherein the setting means sets the analysis region by excluding the reflected image identified by the identifying means from the anterior segment cross-sectional image. An ophthalmologic apparatus for acquiring an axial length of a subject's eye,
an eye refractive power acquiring means for acquiring the eye refractive power of the subject's eye;
an anterior ocular segment cross-sectional image acquisition means for acquiring a cross-sectional image of an anterior ocular segment of the subject's eye;
a setting means for setting an analysis region in the anterior ocular segment cross-sectional image that does not include a reflection image generated when measurement light projected onto the subject's eye is reflected by the cornea of the subject's eye;
a shape information acquiring means for analyzing the analysis region set by the setting means and acquiring anterior eye segment shape information relating to the shape of the anterior eye segment;
an axial length acquiring means for acquiring the axial length based on the ocular refractive power and the anterior eye segment shape information acquired by the shape information acquiring means;
An ophthalmic apparatus comprising: an eye refractive power measuring optical system for projecting a first measurement light onto a fundus of the eye to be examined and acquiring an eye refractive power of the eye to be examined based on light reflected from the fundus of the eye by the first measurement light;
a cross-sectional image capturing optical system for projecting a second measurement light onto an anterior segment of the subject's eye to form a light section passing through the optical axis of the eye refractive power measuring optical system on the anterior segment of the subject's eye, and for acquiring a cross-sectional image of the anterior segment of the subject's eye based on return light from the light section of the second measurement light;
and
An ophthalmic program used in an ophthalmic apparatus for acquiring an axial length of the subject's eye,
When executed by a processor of the ophthalmic device,
a setting step of setting an analysis region in the anterior ocular segment cross-sectional image that does not include a reflection image generated by at least the second measurement light being reflected by a cornea of the subject's eye;
a shape information acquiring step of analyzing the analysis region set in the setting step and acquiring anterior eye segment shape information relating to the shape of the anterior eye segment;
an axial length acquiring step of acquiring the axial length based on the ocular refractive power acquired using the ocular refractive power measuring optical system and the anterior ocular segment shape information acquired in the shape information acquiring step;
an ophthalmic program causing the ophthalmic device to execute the above steps.