Corneal endothelium imaging device

Abstract

This corneal endothelium imaging device comprises: an illumination optical system that emits slit light obliquely with respect to an axis passing through the corneal apex of an eye under examination; and an imaging optical system that images reflected light of the slit light from the corneal endothelium. The imaging optical system is provided with a lens disposed between the eye under examination and an imaging surface. The lens is disposed so as to be inclined such that the principal plane of the lens faces the intersection point between the imaging surface and an object surface, which is the surface of the corneal endothelium of the eye under examination, when viewed in a plane including the optical axis of the illumination optical system and the optical axis of the imaging optical system. The imaging optical system is further provided with an optical mechanism for cancelling astigmatism generated when the corneal endothelium is imaged by the imaging optical system.

Description

Corneal endothelium imaging apparatus

[0001] The technology disclosed in the present specification relates to a corneal endothelium imaging apparatus.

[0002] Corneal endothelium imaging apparatuses that image the corneal endothelium have been developed. The corneal endothelium is located on the back side of the corneal surface. In order to avoid imaging reflected light from the corneal surface, the corneal endothelium imaging apparatus obliquely irradiates an eye to be examined with slit light, and images reflected light of the slit light from the corneal endothelium. Since the eye to be examined is obliquely irradiated with the slit light, the focal plane of the slit light (that is, a plane orthogonal to the optical axis of the slit light) and the corneal endothelial plane are inclined with each other. As a result, the entire corneal endothelial plane cannot be focused, and a clear corneal endothelial image of the entire area cannot be captured. To solve this problem, for example, International Publication No. WO 2020 / 066810 discloses a technique for reducing an angular deviation between the corneal endothelial plane and the focal plane using the Scheimpflug principle.

[0003] In the corneal endothelium imaging apparatus of International Publication No. WO 2020 / 066810, the angular deviation between the corneal endothelial plane and the focal plane is reduced by using the Scheimpflug principle. However, when the eye to be examined is obliquely irradiated with slit light, the slit light is refracted at the corneal surface and reflected by the corneal endothelium. Astigmatism occurs when this reflected light is imaged. Therefore, even if the angular deviation between the corneal endothelial plane and the focal plane is corrected using the Scheimpflug principle, there is a problem that a clear corneal endothelial image cannot be generated due to the occurrence of astigmatism.

[0004] The present specification discloses a technique for capturing a high-quality corneal endothelial image.

[0005] In a first aspect of the technology disclosed herein, a corneal endothelial imaging apparatus comprises an illumination optical system that illuminates a slit beam obliquely with respect to an axis passing through the corneal apex of the eye under examination, and an imaging optical system that images the reflected light from the corneal endothelium of the slit beam. The imaging optical system includes a lens positioned between the eye under examination and the imaging plane. The lens is positioned at an inclination such that, when viewed in a plane containing the optical axes of the illumination optical system and the optical axes of the imaging optical system, the principal plane of the lens faces the intersection of the object plane, which is the surface of the corneal endothelium of the eye under examination, and the imaging plane. The imaging optical system further includes an optical mechanism for compensating for astigmatism that occurs when the corneal endothelium is imaged by the imaging optical system.

[0006] In the corneal endothelial imaging device described above, the lens positioned between the eye under examination and the imaging plane is tilted so that its principal plane is directed toward the intersection of the object plane and the imaging plane. Therefore, similar to the case using the Scheinproof principle, the angular misalignment between the corneal endothelial surface and the focal plane can be reduced. Furthermore, astigmatism can be reduced by incorporating an optical mechanism in the imaging optical system that cancels out astigmatism. As a result, even when the slit light is shone obliquely with respect to the axis passing through the corneal apex of the eye under examination, a higher quality corneal endothelial image can be produced compared to conventional methods.

[0007] A diagram showing the schematic configuration of the optical system of the corneal endothelial imaging device according to Example 1. A block diagram showing the control system of the corneal endothelial imaging device according to Example 1. A diagram for explaining the principle of Scheinproof. A diagram showing the relationship between the corneal endothelial surface and the focal plane of the imaging optical system; (a) shows a schematic diagram of the relationship between the corneal endothelium and the focal plane of the imaging optical system, and (b) shows the corneal endothelial image when the objective lens is not tilted. A diagram showing the meridional and sagittal planes. A diagram showing astigmatism occurring in the virtual image of the corneal endothelial surface. A diagram showing optical simulation using a Grustrand model eye. A diagram showing multiple lenses constituting the objective lens. A diagram showing the relationship between the change in distance between lenses L2 and L3 and astigmatism. A diagram showing a support member that supports multiple lenses constituting the objective lens and multiple lenses. A diagram showing a modified example of the support member that supports multiple lenses constituting the objective lens and multiple lenses. This figure shows corneal endothelial images acquired with the corneal endothelial imaging device according to the example, and corneal endothelial images acquired with the corneal endothelial imaging devices of Comparative Examples 1 and 2. This figure shows a schematic configuration of the optical system of the corneal endothelial imaging device according to Example 2.

[0008] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0009] In a second aspect of the technology disclosed herein, in the first embodiment described above, the lens may be positioned at an inclination such that the principal plane of the lens intersects the intersection of the object plane and the image plane.

[0010] With this configuration, the lenses are positioned according to the Scheinproof principle. This effectively reduces the angular misalignment between the corneal endothelial surface and the focal plane.

[0011] In a third aspect of the technology disclosed herein, in the first or second embodiment described above, the lens may consist of a plurality of lenses arranged along the direction through which the reflected light passes. The optical mechanism may compensate for astigmatism by adjusting the distance between at least two of the plurality of lenses.

[0012] With this configuration, astigmatism can be accurately reduced by adjusting the distance between multiple lenses.

[0013] In a fourth aspect of the technology disclosed herein, the optical mechanism in the first or second embodiment described above may be a cylindrical lens or a toric lens configured to cancel out astigmatism.

[0014] With this configuration, astigmatism can be accurately reduced by using a cylindrical lens or a toric lens.

[0015] (Example 1) An embodiment of the corneal endothelial imaging device 10 will be described with reference to the drawings. As shown in Figure 1, the corneal endothelial imaging device 10 includes an observation optical system 12, an imaging illumination optical system 14, an imaging optical system 16, a position detection illumination optical system 18, a position detection optical system 20, a fixation target optical system 64, an alignment optical system 66, an alignment detection optical system 84, and a calculation unit 90 (see Figure 2).

[0016] The observation optical system 12 includes two illumination light sources 30, a half mirror 22, an objective lens 24, a half mirror 26, a cold mirror 27, and a CCD camera 28. The two illumination light sources 30 emit infrared light in front of the eye under examination E. The reflected light from the eye under examination E passes through the half mirror 22, objective lens 24, half mirror 26, and cold mirror 27, which are arranged on the optical axis O1, and is input to the CCD camera 28. The optical axis O1 is arranged approximately parallel to the axis passing through the corneal apex of the eye under examination E. The cold mirror 27 transmits infrared light and reflects visible light. Therefore, the CCD camera 28 receives infrared light that has passed through the cold mirror 27. As a result, a frontal image of the anterior segment of the eye under examination E is captured.

[0017] The imaging and illumination optical system 14 irradiates the eye E with illumination light for imaging the corneal endothelium of the eye E under examination. The imaging and illumination optical system 14 includes a projection lens 32, a cold mirror 34, a slit 36, a focusing lens 38, and a light source 40. The light source 40 emits visible light. The light emitted from the light source 40 passes through the focusing lens 38 and the slit 36 ​​and irradiates the cold mirror 34. The cold mirror 34 transmits infrared light and reflects visible light. The visible light reflected by the cold mirror 34 passes through the projection lens 32, which is positioned on the optical axis O2, and irradiates the eye E under examination. The optical axis O2 is positioned obliquely to the axis passing through the corneal apex of the eye E under examination. In this embodiment, the optical axis O2 is tilted at 30 degrees with respect to the optical axis O1.

[0018] The corneal endothelium is located on the back side (retinal side) of the cornea C. In the imaging illumination optical system 14, slit light is shone obliquely to the axis passing through the corneal apex in order to avoid reflected light from the corneal surface. The slit light is shone obliquely to the axis passing through the corneal apex, passes through the cornea C, and is reflected by the corneal endothelium. Here, the slit light is refracted by the cornea C and shines on the corneal endothelium. For this reason, the corneal endothelium imaging device 10 captures a virtual image of the corneal endothelium, rather than a real image of the corneal endothelium.

[0019] The imaging optical system 16 images the reflected light from the corneal endothelium of the slit light irradiated onto the eye E by the imaging illumination optical system 14. The imaging optical system 16 includes an objective lens 46, a cold mirror 48, a slit 56, a magnification lens 58, a focusing lens 60, a cold mirror 27, and a CCD camera 28. The reflected light from the corneal endothelium of the slit light irradiated onto the eye E by the imaging illumination optical system 14 passes through the objective lens 46, which is positioned on the optical axis O3, and is irradiated onto the cold mirror 48. The cold mirror 48 transmits infrared light and reflects visible light. The visible light reflected by the cold mirror 48 passes through the slit 56, the magnification lens 58, and the focusing lens 60, and is reflected by the cold mirror 27. The visible light reflected by the cold mirror 27 is input to the CCD camera 28. As a result, the corneal endothelium is imaged. The optical axis O3 is positioned obliquely to the axis passing through the corneal apex of the eye E under examination. Specifically, optical axis O3 is positioned symmetrically to optical axis O2 with respect to optical axis O1. In this embodiment, optical axis O2 is tilted at 30 degrees with respect to optical axis O1. That is, the angle between optical axis O3 and optical axis O2 is 60 degrees.

[0020] The objective lens 46 is composed of a plurality of lenses L1 to L4 (see Figure 8) arranged along the direction in which the reflected light passes. In this embodiment, the objective lens 46 is configured to form an image in the slit 56 at a magnification of 3x. Furthermore, the objective lens 46 is positioned at an inclination with respect to the optical axis O3. The objective lens 46 will be described in detail later.

[0021] The position detection illumination optical system 18 includes an objective lens 46, a cold mirror 48, a focusing lens 52, and a light source 54. The light source 54 emits infrared light. The objective lens 46 and the cold mirror 48 are used in conjunction with the imaging optical system 16. The light emitted from the light source 54 passes through the focusing lens 52, the cold mirror 48, and the objective lens 46, which are arranged on the optical axis O3, and is obliquely irradiated onto the cornea C of the eye E under examination. Specifically, the light emitted from the light source 54 is tilted 30 degrees with respect to the optical axis O1 and irradiates onto the cornea C of the eye E under examination.

[0022] The position detection optical system 20 includes a light-emitting lens 32, a cold mirror 34, and a line sensor 44. The light-emitting lens 32 and the cold mirror 34 are used in conjunction with the imaging illumination optical system 14. The reflected light from the cornea C of the eye E examined by the position detection illumination optical system 18 passes through the light-emitting lens 32 and the cold mirror 34, which are positioned on the optical axis O2, and is input to the line sensor 44. The incident position of the reflected light incident on the line sensor 44 differs depending on the anterior-posterior position (Z direction) of the eye E examined relative to the corneal endothelial imaging device 10. Therefore, by detecting the incident position of the reflected light, the Z-direction position of the eye E examined relative to the corneal endothelial imaging device 10 can be detected.

[0023] The fixation target optical system 64 comprises a half mirror 22, a projection lens 68, a half mirror 70, a pinhole plate 72, and a fixation target light source 74. The fixation target light source 74 emits visible light. The half mirror 22 is used in conjunction with the observation optical system 12. Light emitted from the fixation target light source 74 passes through the pinhole plate 72, the half mirror 70, and the projection lens 68, and is irradiated onto the half mirror 22. The light reflected by the half mirror 22 is irradiated onto the eye under examination E along the optical axis O1. By having the subject fixate on the light from the fixation target light source 74, the eyeball (i.e., the eye under examination E) can be kept as still as possible.

[0024] The alignment optical system 66 comprises a half mirror 22, a projection lens 68, a half mirror 70, an aperture 76, a pinhole plate 78, a focusing lens 80, and a light source 82. The light source 82 emits infrared light. The projection lens 68 and the half mirror 70 are used in conjunction with the fixation target optical system 64. Light emitted from the light source 82 passes through the focusing lens 80, the pinhole plate 78, and the aperture 76 and is irradiated onto the half mirror 70. The light reflected by the half mirror 70 passes through the projection lens 68 and is irradiated onto the half mirror 22. The light reflected by the half mirror 22 is irradiated onto the eye under examination E along the optical axis O1.

[0025] The alignment detection optical system 84 includes a half mirror 22, an objective lens 24, a half mirror 26, and a sensor 88. The half mirror 22, objective lens 24, and half mirror 26 are used in common with the observation optical system 12. The reflected light from the eye E, illuminated by the alignment optical system 66, passes through the half mirror 22 and objective lens 24, which are positioned on the optical axis O1, and illuminates the half mirror 26. The light reflected by the half mirror 26 is input to the sensor 88. By detecting the position of the bright spot with the sensor 88, the position of the corneal apex (i.e., the position in the X and Y directions) is detected.

[0026] Next, the control system of the corneal endothelial imaging device 10 will be described. As shown in Figure 2, the corneal endothelial imaging device 10 is controlled by a calculation unit 90. The calculation unit 90 is composed of a microcomputer (microprocessor) consisting of a CPU, ROM, RAM, etc. The calculation unit 90 is connected to an illumination light source 30, a light source 40, a light source 54, a fixation target light source 74, a light source 82, a CCD camera 28, a line sensor 44, and a sensor 88.

[0027] The calculation unit 90 controls the on / off state of the light source 40. The calculation unit 90 receives an image of the corneal endothelium of the eye under examination E captured by the CCD camera 28. The calculation unit 90 also controls the on / off state of the illumination light source 30, light source 54, fixation target light source 74, and light source 82. The calculation unit 90 receives a frontal image of the eye under examination E captured by the CCD camera 28, as well as the position of the corneal apex (bright spot) detected by the sensor 88. Based on the input frontal image of the eye under examination E and the position of the corneal apex (bright spot), the calculation unit 90 calculates the amount of displacement of the corneal apex (bright spot) in the XY direction. The calculation unit 90 receives the detection signal from the line sensor 44 and calculates the amount of displacement of the eye under examination E in the Z direction relative to the corneal endothelium imaging device 10. Based on the amount of positional displacement in the X and Y directions of the corneal apex (bright spot) detected by the alignment detection optical system 84 and the amount of positional displacement in the Z direction of the eye E to be examined detected by the position detection optical system 20, the calculation unit 90 controls the main body drive unit (not shown) to make all of these positional displacement amounts zero, and moves the main body of the corneal endothelial imaging device 10 relative to the holding stand (not shown).

[0028] Next, the objective lens 46 will be described in more detail. As mentioned above, the objective lens 46 is positioned at an inclination with respect to the optical axis O3 (see Figure 1). Specifically, the objective lens 46 is positioned at an inclination based on the Schein-Proof principle. As shown in Figure 3, the surface of the corneal endothelium of the eye under examination E is referred to as the object plane 101. The surface of the slit 56 is referred to as the imaging plane 102. A plane perpendicular to the optical axis O4 of the objective lens 46, consisting of the intersection points of light rays incident on and emitted from the multiple lenses L1 to L4 (see Figure 8) that constitute the objective lens 46, is referred to as the principal plane 103 of the objective lens 46. The objective lens 46 is positioned with its optical axis O4 inclined so that the principal plane 103 of the objective lens 46 intersects with the intersection point 104 of the object plane 101 and the imaging plane 102. In other words, the objective lens 46 is positioned based on the Schein-Proof principle. In this embodiment, the optical axis O4 of the objective lens 46 is tilted at 23.4 degrees with respect to the optical axis O3 of the imaging optical system 16, in the direction in which the principal plane 103 of the objective lens 46 is directed toward the intersection point 104. Furthermore, a model eye commonly used in the field of ophthalmology (for example, a Grustrand model eye) is used as the eye under examination E. Even if the tilt of the objective lens 46 is adjusted using the model eye, the difference between the actual eye under examination E and the model eye is small. Therefore, as will be described later, the same effect can be obtained with the actual eye under examination E.

[0029] As shown in Figure 4, the slit light from the imaging and illumination optical system 14 is irradiated obliquely onto the eye E under examination. Therefore, the focal plane FS of the imaging optical system 16 is tilted with respect to the corneal endothelial surface CE. If the objective lens 46 is positioned along the optical axis O3 of the imaging optical system 16 (i.e., not tilted), the corneal endothelium is imaged with the focal plane FS of the imaging and illumination optical system 14 tilted with respect to the corneal endothelial surface CE. In a corneal endothelial image acquired under these conditions, the central part is in focus, while the parts at both ends are out of focus. For example, if the length of one side of the acquired corneal endothelial image is 250 μm, the corneal endothelial surface CE at both ends of the acquired corneal endothelial image will be 63 μm away from the focal plane FS of the imaging and illumination optical system 14. Therefore, as shown in Figure 4(b), an unclear corneal endothelial image is acquired at both ends.

[0030] In this embodiment, based on the Scheinproof principle, the optical axis O4 of the objective lens 46 is tilted with respect to the optical axis O3 of the imaging optical system 16. This reduces the tilt angle between the focal plane FS of the imaging illumination optical system 14 and the corneal endothelial surface CE. As a result, a clear corneal endothelial image can be captured throughout the entire image.

[0031] In this embodiment, the optical axis O4 of the objective lens 46 was tilted at 23.4 degrees under the conditions that the inclination angle of the optical axis O3 of the imaging optical system 16 with respect to the optical axis O1 was 30 degrees and the imaging magnification at the slit 56 was 3x, but the configuration is not limited to this. The imaging magnification of the imaging optical system 16 and the inclination angle of the optical axis O3 with respect to the optical axis O1 can be set as appropriate. Furthermore, the optical axis O4 of the objective lens 46 only needs to be tilted with respect to the optical axis O3 of the imaging optical system 16 in the direction in which the main plane 103 of the objective lens 46 is directed toward the intersection point 104. For example, the optical axis O4 of the objective lens 46 only needs to be tilted with respect to the optical axis O3 of the imaging optical system 16 in the direction in which the main plane 103 of the objective lens 46 is directed toward the intersection point 104, within a range of 5 degrees or more and 40 degrees or less. Even in this case, the inclination angle between the focal plane FS of the imaging optical system 16 and the corneal endothelial surface CE can be reduced, and a clear corneal endothelial image can be captured in the entire image.

[0032] Furthermore, the objective lens 46 is positioned and adjusted to cancel out astigmatism that occurs when the imaging optical system 16 images the corneal endothelium.

[0033] Now, let's explain astigmatism. As mentioned above, the imaging illumination optical system 14 illuminates the slit light at an oblique angle to the axis passing through the corneal apex. Due to this inclination, the virtual image of the corneal endothelium captured by the imaging optical system 16 exhibits astigmatism.

[0034] As shown in Figure 5, the plane containing the optical axis O3 of the imaging optical system 16, the object point (in this embodiment, the position of the corneal endothelium irradiated by the slit light), and the corneal vertex axis is defined as the meridional plane MS. The plane containing the optical axis O3 of the imaging optical system 16 and perpendicular to the meridional plane MS is defined as the sagittal plane SS. As shown in Figure 6, in the virtual image of the corneal endothelial surface CE, the focal position F1 of the meridional plane MS and the focal position F2 of the sagittal plane SS are misaligned. Note that in Figure 6, for the sake of clarity, only the sagittal plane SS is shown shifted in parallel. That is, the sagittal plane SS is shown shifted in parallel so that the optical axis O3 on the meridional plane MS and the optical axis O3 on the sagittal plane SS appear at different positions. The difference A1 between the focal position F1 of the meridional plane MS and the focal position F2 of the sagittal plane SS is called astigmatism.

[0035] Figure 7 shows an optical simulation using a Grustrand model eye. Note that Figure 7 uses a corneal endothelial imaging device that has not been adjusted for astigmatism. In Figure 7, the horizontal axis of the graph shown above represents the distance from the corneal surface, and the vertical axis represents the MTF (Modulation Transfer Function). Curve 105 represents the meridional plane MS, and curve 106 represents the sagittal plane SS. MTF is an index that represents the contrast characteristics and resolving power at the image plane, and the position with the largest MTF approximately coincides with the focal point. The difference A1 between the position with the highest MTF in the meridional plane MS (i.e., the focal point) and the position with the highest MTF in the sagittal plane SS (i.e., the focal point) is astigmatism. As shown in Figure 7, when using a Grustrand model eye, the astigmatism between the meridional plane MS and the sagittal plane SS is approximately 50 μm. Although Figure 7 shows an example using a Grustrand model eye, even when using the subject eye E, astigmatism is approximately 50 μm in most cases, and there is almost no individual variation.

[0036] In Figure 7, the graph shown below shows a spot diagram where the horizontal axis represents the meridional plane MS and the vertical axis represents the sagittal plane SS. A spot diagram is a figure that shows how multiple light rays emitted from an object point scatter across the image plane, and is used to visually evaluate the imaging state. At the focal position of the meridional plane MS, the sagittal plane SS is spotted over a wide area. At the focal position of the sagittal plane SS, the meridional plane MS is spotted over a wide area. At the position where the curve 105 representing the meridional plane MS and the curve 106 representing the sagittal plane SS intersect, both the meridional plane MS and the sagittal plane SS are spotted over a relatively wide area. Therefore, it is not possible to acquire a good quality image at any position.

[0037] In this embodiment, based on the Scheinproof principle, the objective lens 46 is positioned so that its optical axis O4 is inclined with respect to the optical axis O3 of the imaging optical system 16. Astigmatism can be adjusted by adjusting one of the following: the distance between lenses, the lens thickness, or the lens curvature of the multiple lenses L1 to L4 (see Figure 8) that constitute the objective lens 46. For example, if the optical axis O4 of the objective lens 46 is not inclined with respect to the optical axis O3 of the imaging optical system 16, astigmatism will not change even if the distance between lenses L1 to L4, the lens thickness, or the lens curvature is changed. In other words, in this embodiment, since the optical axis O4 of the objective lens 46 is inclined with respect to the optical axis O3 of the imaging optical system 16, astigmatism can be reduced by adjusting one of the distance between lenses L1 to L4, the lens thickness, or the lens curvature.

[0038] In this embodiment, astigmatism of approximately 50 μm is reduced by adjusting the distances between the multiple lenses L1 to L4 that constitute the objective lens 46. As shown in Figure 8, the objective lens 46 is composed of four lenses L1 to L4. Of the distances between the four lenses L1 to L4, the distance between lenses L2 and L3 has the greatest influence on astigmatism. In this embodiment, astigmatism is reduced by adjusting the distance L between lenses L2 and L3. Hereinafter, the amount of change (i.e., adjustment amount) of the distance L between lenses L2 and L3 will be denoted as ΔL. Therefore, the distance between lenses L2 and L3 after adjustment will be L + ΔL.

[0039] Figure 9 shows the relationship between the change in the distance L between lenses L2 and L3 (ΔL) and astigmatism. As shown in Figure 9, there is a proportional relationship between the change in the distance L between lenses L2 and L3 (ΔL) and astigmatism. The astigmatism changes by approximately three times the change in the distance L between lenses L2 and L3. In this embodiment, the distance L between lenses L2 and L3 is adjusted to cancel out an astigmatism of approximately 50 μm. For this reason, the distance L between lenses L2 and L3 is adjusted so that it becomes approximately 20 μm shorter.

[0040] A specific configuration for adjusting the distance L between lenses L2 and L3 will now be described. Figure 10 shows lenses L1 to L4 and a support member 120 that supports lenses L1 to L4. As shown in Figure 10, the support member 120 comprises an inner lens barrel 122 that supports lenses L1 and L2, and an outer lens barrel 124 that supports lenses L3 and L4. The inner lens barrel 122 is fitted inside the outer lens barrel 124 on the side of the eye being examined E (left side in Figure 10). That is, the support member 120 has a double structure consisting of an inner lens barrel 122 and an outer lens barrel 124.

[0041] During the manufacturing of the corneal endothelial imaging device 10, the inner lens barrel 122 is slidable along the optical axis O4 relative to the outer lens barrel 124. By sliding the inner lens barrel 122 relative to the outer lens barrel 124, the distance L + ΔL between lenses L2 and L3 is adjusted. Specifically, the inner lens barrel 122 is slid relative to the outer lens barrel 124 so that the distance L between lenses L2 and L3 is shortened by approximately 20 μm (i.e., ΔL becomes approximately -20 μm). After the distance L + ΔL between lenses L2 and L3 is adjusted, the inner lens barrel 122 is fixed to the outer lens barrel 124. For example, the inner lens barrel 122 may be fixed to the outer lens barrel 124 with screws or with adhesive.

[0042] In this embodiment, the distance L + ΔL between lenses L2 and L3 is adjusted by sliding the inner lens barrel 122 relative to the outer lens barrel 124. Each lens L1 to L4 and the support member 120 have component tolerances. For example, when lenses L1 to L4 are supported by a single lens barrel (i.e., not a double structure of inner lens barrel 122 and outer lens barrel 124), lenses L1 to L4 are fixed at predetermined positions on the lens barrel. In this case, due to component tolerances of lenses L1 to L4 and the lens barrel, the distance L between lenses L2 and L3 may not be the appropriate distance. As described above, astigmatism changes by approximately three times the amount ΔL of change in the distance L between lenses L2 and L3. For example, in order to reduce astigmatism to 10 μm or less, the distance L + ΔL between lenses L2 and L3 must be kept within an error of 3 μm. In this embodiment, even if there are component tolerances in the lenses L1 to L4, the inner lens barrel 122, and the outer lens barrel 124, the distance L + ΔL between lenses L2 and L3 can be accurately adjusted by sliding the inner lens barrel 122 relative to the outer lens barrel 124. As a result, astigmatism can be reduced, and high-quality corneal endothelial images can be captured.

[0043] In this embodiment, the distance L+ΔL between the lenses L2 and L3 is adjusted by sliding the inner lens barrel 122 relative to the outer lens barrel 124, but the configuration is not limited thereto. It is only required that the distance L+ΔL between the lenses L2 and L3 can be adjusted with high accuracy even when there are component tolerances. For example, as shown in FIG. 11, a spacer 226 may be used to adjust the distance L+ΔL between the lenses L2 and L3.

[0044] The support member 220 includes a first lens barrel 222 that supports the lenses L1 and L2, a second lens barrel 224 that supports the lenses L3 and L4, and a spacer 126. The first lens barrel 222 is arranged along the optical axis O4 closer to the subject's eye side (the left side in FIG. 11) than the second lens barrel 224. A cylindrical spacer 226 is arranged between the first lens barrel 222 and the second lens barrel 224. The spacer 226 is provided with a through hole 226a through which reflected light from the corneal endothelium can pass via the lenses L1 to L4.

[0045] A plurality of spacers 226 with different plate thicknesses are provided. Specifically, the plurality of spacers 226 have different plate thicknesses in increments of 5 μm. When manufacturing the corneal endothelium imaging apparatus 10, the spacer 226 is arranged between the first lens barrel 222 and the second lens barrel 224. At this time, a spacer 226 with an appropriate plate thickness is selected from the plurality of types of spacers 226 with different plate thicknesses such that the distance L between the lenses L2 and L3 is shortened by approximately 20 μm (that is, ΔL is approximately -20 μm). By arranging the spacer 226 with an appropriate plate thickness between the first lens barrel 222 and the second lens barrel 224, the distance L+ΔL between the lenses L2 and L3 can be adjusted with high accuracy. Therefore, even when the support member 220 of FIG. 11 is used, astigmatism can be reduced, and a high-quality corneal endothelium image can be captured. Furthermore, when the support member 220 of FIG. 11 is used, it is not necessary to perform the work of fixing the first lens barrel 222 to the second lens barrel 224 after arranging the spacer 226. Therefore, the number of work steps when manufacturing the corneal endothelium imaging apparatus 10 can be reduced. In addition, axis misalignment of the lenses L1 to L4 can be suppressed when fixing the first lens barrel 222 to the second lens barrel 224.

[0046] FIG. 12 shows a corneal endothelium image captured by the corneal endothelium imaging apparatus 10 of the present example, and corneal endothelium images captured by the corneal endothelium imaging apparatuses of Comparative Examples 1 and 2.

[0047] In the corneal endothelium imaging apparatus of Comparative Example 1, the objective lens 46 is disposed such that the optical axis O4 of the objective lens 46 coincides with the optical axis O3 of the imaging optical system 16. That is, the optical axis O4 of the objective lens 46 is not inclined with respect to the optical axis O3 of the imaging optical system 16 based on the Scheimpflug principle. Since the objective lens 46 is not inclined, the distance L between the plurality of lenses L1 to L4 constituting the objective lens 46 is also not adjusted.

[0048] In the corneal endothelium imaging apparatus of Comparative Example 2, the optical axis O4 of the objective lens 46 is inclined with respect to the optical axis O3 of the imaging optical system 16 based on the Scheimpflug principle. However, the distance L between the plurality of lenses L1 to L4 constituting the objective lens 46 is not adjusted.

[0049] As shown in FIG. 12, in Comparative Example 1, since the objective lens 46 is not inclined, the imaging surface is inclined with respect to the corneal endothelium surface. For this reason, both end portions of the corneal endothelium image (the left and right end portions in FIG. 12) are out of focus. Further, the curve 105 representing the meridional surface MS and the curve 106 representing the sagittal surface SS are misaligned, and astigmatism occurs. Therefore, the corneal endothelium imaging apparatus of Comparative Example 1 cannot capture a high-quality corneal endothelium image.

[0050] In Comparative Example 2, the objective lens 46 is inclined based on the Scheimpflug principle, so the imaging surface and the corneal endothelium surface substantially coincide with each other. For this reason, even at both end portions of the corneal endothelium image (the left and right end portions in FIG. 12), focus is achieved equivalently to the central portion. However, the distance L between the lenses L1 to L4 is not adjusted. Therefore, the curve 105 representing the meridional surface MS and the curve 106 representing the sagittal surface SS are misaligned, and astigmatism occurs. Therefore, the entire corneal endothelium image is not clear, and the corneal endothelium imaging apparatus of Comparative Example 2 also cannot capture a high-quality corneal endothelium image.

[0051] On the other hand, in this embodiment, the objective lens 46 is tilted based on the Scheinproof principle, so the imaging plane and the corneal endothelial surface are approximately in line. As a result, the edges of the corneal endothelial image (the left and right edges in Figure 12) are in focus at the same level as the central portion. Furthermore, the distance L between lenses L1 to L4 is adjusted. As a result, the curve 105 representing the meridional plane MS and the curve 106 representing the sagittal plane SS are approximately in line, and astigmatism is reduced. Therefore, the corneal endothelial imaging device 10 of this embodiment can capture a clear corneal endothelial image across the entire corneal endothelial image.

[0052] In this embodiment, the distance L between lenses L2 and L3 was adjusted to reduce astigmatism, but the configuration is not limited to this. For example, the distance between lenses L1 and L2 may be adjusted, or the distance between lenses L3 and L4 may be adjusted. When adjusting the distance between lenses L1 and L2, lens L1 may be supported by the inner barrel or the first barrel, and lenses L2 to L4 may be supported by the outer barrel or the second barrel. Similarly, when adjusting the distance between lenses L3 and L4, lenses L1 to L3 may be supported by the inner barrel or the first barrel, and lens L4 may be supported by the outer barrel or the second barrel.

[0053] Furthermore, although the objective lens 46 in this embodiment was composed of four lenses L1 to L4, it is not limited to this configuration. The objective lens 46 only needs to be composed of two or more lenses, and the number of lenses constituting the objective lens 46 can be appropriately selected according to the magnification to be imaged into the slit 56. If the objective lens 46 is composed of two or more lenses, the distance between the lenses constituting the objective lens 46 can be adjusted by applying the configuration of this embodiment. This makes it possible to reduce astigmatism.

[0054] In this embodiment, astigmatism was reduced by adjusting the distance L between lenses L1 to L4, but astigmatism may also be reduced by adjusting the lens thickness or lens curvature of lenses L1 to L4.

[0055] (Example 2) In Example 1 described above, astigmatism was compensated for by the objective lens 46 (more specifically, by adjusting the distance L between lenses L1 to L4), but the configuration is not limited to this. For example, as shown in Figure 13, astigmatism may be compensated for by the cylindrical lens 130.

[0056] The cylindrical lens 130 is positioned between the objective lens 46 and the cold mirror 48 of the imaging optical system 16. The power and position of the cylindrical lens 130 are set such that the focal position of the virtual image of the meridional surface MS is shifted away from the objective lens 46 relative to the sagittal surface SS. The amount of shift of the meridional surface MS relative to the sagittal surface SS is designed to cancel out astigmatism of approximately 50 μm. The astigmatism of the virtual image of the corneal endothelium on the object side and the astigmatism of the real image on the image side are proportional to the square of the magnification used to image into the slit 56. For example, if the magnification used to image into the slit 56 is 6x, the focal position of the virtual image of the meridional surface MS is 1.8 mm (i.e., 50 μm × 6) greater than the focal position of the real image of the meridional surface MS. 2 The power and arrangement of the cylindrical lens 130 are set to increase the length of the image. In this embodiment as well, astigmatism can be reduced by arranging the cylindrical lens 130. Therefore, high-quality corneal endothelial images can be acquired.

[0057] In this embodiment, the cylindrical lens 130 was positioned between the objective lens 46 and the cold mirror 48, but the configuration is not limited to this. For example, the cylindrical lens 130 may be positioned anywhere between the objective lens 46 and the cold mirror 27 of the imaging optical system 16, as long as it is not in the vicinity of the slit 56, which is the image plane. Also, in this embodiment, astigmatism was compensated for using the cylindrical lens 130, but astigmatism may be compensated for by using a toric lens instead of the cylindrical lens 130.

[0058] The specific examples of the technology disclosed herein have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples described above. Furthermore, the technical elements described herein or in the drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated herein or in the drawings achieves multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness.

Claims

1. A corneal endothelial imaging device comprising: an illumination optical system that irradiates slit light obliquely with respect to an axis passing through the corneal apex of the eye under examination; and an imaging optical system that images the reflected light from the corneal endothelium of the slit light, wherein the imaging optical system comprises a lens positioned between the eye under examination and the imaging plane, the lens being inclined such that, when viewed in a plane including the optical axis of the illumination optical system and the optical axis of the imaging optical system, the principal plane of the lens faces the intersection of the object plane, which is the surface of the corneal endothelium of the eye under examination, and the imaging plane, and the imaging optical system further comprises an optical mechanism for canceling out astigmatism that occurs when imaging the corneal endothelium with the imaging optical system.

2. The corneal endothelial imaging apparatus according to claim 1, wherein the lens is arranged at an inclination such that the main plane of the lens intersects the intersection point between the object plane and the image plane.

3. The corneal endothelial imaging apparatus according to claim 1 or 2, wherein the lens is composed of a plurality of lenses arranged along the direction through which the reflected light passes, and the optical mechanism cancels out the astigmatism by adjusting the distance between at least two of the plurality of lenses.

4. The corneal endothelial imaging apparatus according to claim 1 or 2, wherein the optical mechanism is a cylindrical lens or a toric lens configured to cancel out the astigmatism.

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