JP2008264516A - Ophthalmologic examination apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ophthalmologic examination apparatus capable of quantitatively measuring the shape of an iris. <P>SOLUTION: The ophthalmologic examination apparatus comprises a slit light projecting optical system 70 for projecting a slit light to the anterior ocular part of the eye to be examined from the pupil to the periphery of the iris, a driving device 44 for moving and controlling the slit light projecting optical system so as to perform scanning with the slit light to be projected by the slit light projecting optical system 70, a photographing optical system 80 for photographing, a plurality of times, a cross-sectional image of the anterior ocular part resulting from reflected light of the slit light projected by the slit light projecting optical system 70, in response to the movement of the slit light, and a data analyzing section 45 for performing: a step for analyzing the cross-sectional image photographed by the photographing optical system 80 so as to calculate depth of the anterior chamber at the plurality of positions of the eye to be examined; a step for calculating plurality of position coordinates on the surface of the iris, based on the plurality of calculated depth of the anterior chamber; and a step for calculating the curvature radius of the iris, based on the plurality of calculated position coordinates. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ophthalmic examination apparatus used for examination of ophthalmic diseases such as glaucoma.

Glaucoma is a disease in which the optic nerve is affected mainly due to an increase in intraocular pressure, resulting in abnormal visual field and decreased visual acuity, and is a disease that is one of the top causes of blindness in ophthalmology.
FIG. 27 shows the cross-sectional structure of the eye. Reference numeral 10 is a cornea, which is a transparent film in front of the eyeball, reference numeral 12 is located in front of the crystalline lens, and an iris whose main function is to adjust the amount of input light, reference numeral 14 is a crystalline lens, and reference numeral 16 is It is a vitreous body consisting of a jelly-like transparent tissue. The crystalline lens 14 is supported so as to be suspended from the ciliary body 17 via a chin band.
A region surrounded by the cornea 10, the lens 14, and the iris 12 is called an anterior chamber 18, and a portion surrounded by the iris 12 and the vitreous body 16 is called a posterior chamber. Anterior chamber 18 and posterior chamber 19 are filled with transparent aqueous humor. Aqueous humor carries oxygen and nutrients to each tissue in the eye and carries waste from each tissue in the eye to the outside of the eye. After being circulated toward the center, the blood is discharged into the vein from a corner portion (A portion in the figure: called a corner angle) sandwiched between the cornea 10 and the iris 12.

  Intraocular pressure indicates the pressure in the eyeball and is determined by the balance between production and excretion of aqueous humor. That is, when the aqueous humor discharge capacity decreases or the production capacity increases, the intraocular pressure increases. Conversely, when the discharge capacity increases or the production capacity decreases, the intraocular pressure decreases. Glaucoma is most often caused by a decrease in the amount of aqueous humor that drains out of the eye, thereby increasing intraocular pressure, rather than by increasing the amount of aqueous humor. . Since the amount of aqueous humor produced is almost constant in the ciliary body regardless of the amount discharged outside the eye, the intraocular pressure increases when the amount of aqueous humor discharged from the corner is suppressed.

  The reason why the amount of aqueous humor discharged outside the eye decreases and the intraocular pressure increases can be attributed to the aqueous humor in the mesh tissue, trabecular meshwork formed at the corner where the aqueous humor is discharged. When the aqueous humor is difficult to be discharged (open-angle glaucoma), the corner itself is inherently narrow, and for some reason when the pressure difference between the anterior chamber 18 and the posterior chamber 19 occurs, There is a case where the iris 12 is pushed from the back side toward the cornea 10 and the aqueous humor is not discharged because the root of the iris 12 blocks the corner (a closed angle glaucoma).

Open-angle glaucoma has a slow increase in intraocular pressure, and the symptoms progress slowly, whereas closed-angle glaucoma suddenly increases intraocular pressure by closing the outlet of the aqueous humor, and the symptoms progress rapidly. There is a difference that blindness may occur within a few days. Both open-angle glaucoma and pre-attack angle glaucoma have no subjective symptoms, and in particular, closed-angle glaucoma has the property that the symptoms progress rapidly when onset. Pre-diagnosis is extremely important.
Of these open-angle glaucoma and closed-angle glaucoma, open-angle glaucoma is very difficult to diagnose from the corner findings because the shape of the corner part is very similar to that of healthy subjects. The angle of the anterior chamber and the depth of the anterior chamber are examined, and if the interval is narrow, glaucoma can be prevented from occurring by treating it with the possibility that angle-closure glaucoma may develop. Is possible.

In order to prevent the onset of glaucoma, an ophthalmologist examines the distance (anterior chamber depth) between the corneal endothelial surface and the iris. In this method, an ophthalmologist applies an examination lens (angle mirror) to the cornea to visually confirm the shape of the anterior chamber part. An inspection must be done.
Therefore, the method of inspecting using the lens for inspection in this way is actually the extent that an ophthalmologist performs when there is a risk of glaucoma.

There is also a method for inspecting the interval between the cornea and the iris by using slit light (slit lamp) without using an inspection lens.
This method is merely a visual assessment of the distance between the cornea and the iris, and qualitatively evaluates the distance between the cornea and the iris, and is far less accurate than a method of diagnosis using an inspection lens. As for the base (corner angle) of the iris, it is difficult to see the interval clearly, and there is a problem that accurate diagnosis is difficult.

  Therefore, the present inventors are capable of examining ophthalmic diseases in the closed angle glaucoma or the anterior chamber portion without operation that must be a specialist such as using a lens for examination in ophthalmic practice. An inspection apparatus that can inspect a subject without imposing a burden has been proposed (Patent Document 1).

JP 2006-87614 A

With the above-described conventional inspection apparatus, it has become possible to easily measure the anterior chamber depth, which is the distance between the iris and the corneal endothelium surface.
However, even if only the anterior chamber depth can be measured, the position of the iris is known, but in order to grasp the eye physiological function and the disease state of the eye more accurately, it is necessary to know the shape of the iris.
If the shape of the iris is known, it is possible to ascertain whether it is easy to develop angle-closure glaucoma and whether the anterior chamber pressure or posterior chamber pressure is higher. For example, if the surface shape of the iris is a circular arc with a small radius of curvature, it is possible to grasp the pathological condition such that the outlet of the aqueous humor at the corner is compressed and a closed angle glaucoma is likely to develop.

  If it is sufficient if the iris shape can be grasped as an image, a detailed photograph can be taken with an ultrasonic biomicroscope as shown in FIG. However, even an ultrasonic biomicroscope cannot quantitatively grasp the shape of the iris.

  As described above, since the conventional apparatus cannot quantitatively grasp the shape of the iris, it cannot accurately grasp the eye physiology function or the disease state of the eye, and the eye shape is measured quantitatively. There has been a problem that an apparatus capable of more easily and accurately grasping a function and a disease state of an eye disease is desired.

  Therefore, the present invention has been made to solve the above-mentioned problems, and an object thereof is an ophthalmic examination capable of quantitatively measuring the shape of an iris so that an eye physiological function and an eye disease pathology can be grasped easily and accurately. To provide an apparatus.

In order to solve the above problems, the present invention has the following configuration.
That is, according to the ophthalmic examination apparatus according to the present invention, in the ophthalmic examination apparatus for examining the anterior segment of the eye to be examined, the slit light is directed from the pupil region to the periphery of the iris toward the anterior segment of the subject eye. Are projected by the slit light projection optical system, a drive device that controls the movement of the slit light projection optical system so as to scan the slit light projected by the slit light projection optical system, and the slit light projection optical system. The cross-sectional image of the anterior segment obtained by the reflected light of the slit light is photographed a plurality of times in accordance with the movement of the slit light, and the cross-sectional image photographed by the photographing optical system is subjected to image analysis and subjected to image analysis. Calculating anterior chamber depth at a plurality of positions of the optometry, calculating a plurality of position coordinates of the iris surface based on the calculated anterior chamber depths, and Based on the position coordinates of a few, it is characterized by comprising a data analyzing unit for executing a step of calculating a curvature radius of the iris.
By adopting this configuration, the radius of curvature of the iris can be calculated based on the measured anterior chamber depth, so that the quantitative shape of the iris can be known.

Further, the data analysis unit may calculate a first radius of curvature on the center side of the iris and a second radius of curvature on the peripheral side of the iris.
According to this configuration, the curvature radii of the center side and the peripheral side can be compared. For this reason, various cases can be determined.

Further, the data analysis unit, when calculating the radius of curvature of the iris, approximating the surface curve of the iris with a quadratic curve based on the least square method of the calculated plurality of position coordinates, Approximating a quadratic curve to a circle equation based on the linear least square method, calculating the circle center and circle radius, and using the calculated circle center and circle radius as initial values, the nonlinear least square method The radius of curvature of the iris may be calculated by executing the step of approximating the surface curve of the iris to a circle equation based on this.
According to this configuration, an approximation is first made to a quadratic curve, and then the initial value of the circle equation is calculated by the linear least square method, and the initial value is used to approximate the circle using the nonlinear least square method. The surface shape can be accurately applied to the circle, and the iris shape can be easily grasped quantitatively.

Furthermore, the data analysis unit may detect whether the center position of the approximate circle obtained by the nonlinear least square method is on the corneal side or the posterior chamber side with respect to the iris.
In other words, when the center position of the circle is on the posterior chamber side of the iris, it can be understood that the iris is formed in a direction projecting to the cornea side, and when the center position of the circle is on the cornea side of the iris Can grasp that the iris is deformed due to trauma or the like.

  Note that a display unit that displays the calculated radius of curvature may be provided.

  According to the ophthalmic examination apparatus according to the present invention, the iris shape of the eye to be examined can be detected as quantitative measurement data, which may cause the development of ophthalmic diseases of the subject, for example, closed angle glaucoma. It becomes possible to carry out an accurate inspection for the above.

Hereinafter, specific examples of the ophthalmic examination apparatus according to the present invention will be described in detail with reference to the drawings.
An ophthalmic examination apparatus according to the present invention projects slit light onto a subject's eye and takes a cross-sectional image of the cornea and iris of the subject's eye to obtain a cross-sectional shape of the anterior segment, an inspection lens, and the like. It is possible to measure quantitatively without using it, and in particular, the radius of curvature can be calculated after approximating the shape of the iris to a circle.

FIG. 1 is a perspective view showing the overall configuration of an embodiment of an ophthalmic examination apparatus 20 according to the present invention. FIG. 2 is a block diagram showing the internal configuration of the entire ophthalmic examination apparatus 20.
The ophthalmic examination apparatus 20 of the present embodiment includes a measurement unit 30 that houses a measurement optical system including slit light projection optical systems 70a and 70b, a photographing optical system 80, and the like, and a drive that controls the position of the measurement unit 30 by three-axis driving. The apparatus 44 and the measurement part 30 have the data analysis part 45 which analyzes the measurement data, the gantry part 40 which accommodates the operation control part 46, and the operation panel 50 for performing measurement operation.
The ophthalmic examination apparatus 20 includes a measurement unit 30 disposed above the gantry 40 and an operation panel 50 disposed above the measurement unit 30.

The operation panel 50 is for a measurer or the like to operate the inspection apparatus, and is supported at a position above the measurement unit 30 by a monitor arm 52 erected on the rear part of the gantry unit 40.
The operation panel 50 is provided with a monitor unit 53 for displaying inspection results and the like on the front surface, and operation buttons 54 are arranged on the periphery of the monitor unit 53. The operation panel 50 is provided by the monitor arm 52 so as to be able to swing in the horizontal direction above the measurement unit 30. In this embodiment, the operation panel 50 has an angle range of about 45 ° to the left and right (total rotation angle) on the front side of the apparatus. Can be swung at 90 °. In addition, a small printer 55 is installed on the rear surface of the operation panel 50, and the measurement result can be printed and output.
The operation button 54 is connected to the operation control unit 46 and can be controlled so that the operation control unit 46 executes the corresponding operation based on an operation signal output from the operation button 54 when operated. The monitor unit 53 is connected to the data analysis unit 45 and displays the analyzed inspection result. Similarly, the printer 55 is also connected to the data analysis unit 45 and controlled to output an analysis result in accordance with the measurement person's operation.

  Slit light projection optical systems 70a and 70b that project slit light for measuring the depth of the anterior chamber toward the right or left eye of the subject, the eye to be examined, and the measurement optical system. An alignment optical system 90 for projecting alignment light for accurately aligning the image and an imaging optical system 80 for detecting reflected light from the eye to be inspected are provided in a casing 32 provided to cover the outer surface of the measurement unit 30. It is stored.

A window 110 for the photographing optical system 80 is provided on the front surface of the casing 32. On each of the left and right sides of the window 110, there are provided three transmission windows 111, 112, 113 arranged in the vertical direction.
The transmission windows 111 and 113 are transmission windows for projecting projection light from the light source 95 for miosis to the eye to be examined in order to perform a pupil reduction operation when examining a subject having a large pupil diameter.
The middle transmission window 112 is a transmission window of a light source used for alignment in the horizontal direction and the vertical direction (XY direction).

  A chin rest 61 and a forehead support 62 for supporting the head of the subject are disposed on the front side of the gantry 40. The chin rest 61 is supported by the chin rest 63, and by rotating a handle 64 extending from the chin rest 63 to both sides, the chin rest 61 moves up and down to raise the eye position of the subject. Is adjustable.

FIG. 3 shows a block diagram of the operation control unit.
The operation control unit 46 includes a CPU 47 and a memory composed of a ROM 49 and a RAM 48. The ROM 49 stores a control program for causing the CPU 47 to execute a predetermined operation in advance to perform operation control. The CPU 47 outputs a control signal so that the drive device 44, the slit light projection optical systems 70a and 70b, the alignment optical system 90, and the photographing optical system 80 perform predetermined operations by reading and executing the control program in the ROM 49. To do.

FIG. 4 shows a block diagram of the data analysis unit.
The data analysis unit 45 has a function of executing data analysis based on photographed image data, and is provided in the gantry 40.
The data analysis unit 45 includes a CPU 100, a memory including a ROM 103 and a RAM 102, and a storage device 104 such as a hard disk. The ROM 103 or the hard disk 104 stores a data analysis program for performing data analysis by causing the CPU 100 to execute a predetermined operation in advance. When the CPU 100 reads and executes a data analysis program in the ROM 103 or the hard disk 104, data analysis in the inspection apparatus can be realized. The data analysis program can be easily realized by the macro function of the spreadsheet application software.

  In the above-described embodiment, the CPUs that are different between the operation control unit 46 and the data analysis unit 45 have been described to execute the functions of the operation control and the data analysis. One CPU may be used in common by the data analysis unit 45, and this one CPU may execute both functions of operation control and data analysis.

Next, the configuration of the measurement optical system provided in the measurement unit 30 will be described.
FIG. 5 shows slit light projection optical systems 70 a and 70 b, a photographing optical system 80, an alignment optical system 90, and a miosis light source 95 provided in the measurement unit 30.
In the present embodiment, the slit light projection optical systems 70a and 70b are made independent for the right eye and the left eye, and according to the examination of the right eye and the left eye, the slit light projection optical system 70a for the right eye and the left The eye slit light projection optical system 70b is used. The slit light projection optical systems 70a and 70b include a halogen lamp 71 as a light source for projecting slit light, optical systems 72a and 72b including a plurality of optical lenses, a slit 73, and a mirror 74. These slit light projection optical systems 70a and 70b are set so that the slit light is projected from a direction inclined at a predetermined angle with respect to the visual axis of the eye to be inspected (angle 60 ° in this embodiment).

The photographing optical system 80 is disposed at a central position between the slit light projection optical systems 70a and 70b disposed on the left and right. The photographing optical system 80 includes a microscope optical system 81 and a CCD camera 82. The CCD camera 82 is controlled to tilt at a predetermined angle with respect to the optical axis. In FIG. 5, the position 1 is the direction of the CCD camera during the auto-alignment operation for aligning the slit light with the eye to be examined, 2 is the direction of the CCD camera when using the left-eye slit light projection optical system 70b, 3 Indicates the direction of the CCD camera when the slit light projection optical system 70a for the right eye is used.
Reference numeral 83 denotes a light source of the fixation lamp, and 84 denotes a mirror that reflects light from the light source 83 toward the eye to be examined. In the present embodiment, a fixation lamp is presented by using a narrow mirror 84 so as not to disturb the received light amount of the photographing optical system as much as possible.

The alignment optical system 90 includes an LED 91 that emits red light or infrared light used as alignment light, a slit 92, and a mirror 93. A mirror 97 for inputting the reflected light of the LED 91 to the photographing optical system 80 is arranged in a symmetrical arrangement in the horizontal plane with respect to the optical axis of the photographing optical system 80 of the alignment optical system 90. A beam splitter 99 is disposed on the optical axis of the photographic optical system 80, and the reflected light of the alignment optical system 90 reflected by the mirror 97 is input to the same optical axis as that of the photographic optical system 80. 82 to enable photographing.
The miosis light source 95 uses a white LED as a light source, and is arranged in the vicinity of the front portion of the measurement unit 30. In the apparatus of the present embodiment, four white LEDs are arranged for miosis.

The measurement optical system including the slit light projection optical systems 70a and 70b and the photographing optical system 80 is fixedly supported by using the bottom plate of the measurement unit 30 as a support stage, and the bottom plate is driven by triaxial control accommodated in the gantry unit 40. It is fixed to the device. The drive device based on the three-axis control is a known mechanism including a guide mechanism such as a slide guide and a drive unit such as a ball screw and a servo motor for rotating the ball screw.
The three-axis control drive device controls the movement of the bottom plate in the XY direction and the Z direction, and moves the measurement optical system including the slit light projection optical systems 70a and 70b and the photographing optical system 80 in the XY direction and the Z direction. Control. The XY direction refers to the moving direction in the vertical plane, and the Z direction refers to the horizontal moving direction. Specifically, the X direction is a lateral direction (horizontal direction) with respect to the eyes, the Y direction is a vertical direction (vertical direction) with respect to the eyes, and the Z direction is a front-rear direction (horizontal direction) with respect to the eyes.
In the present embodiment, the X direction (the direction in which the eye is moved in the left-right direction) is set to move about 100 mm for examination of the right eye and the left eye, the Y direction is ± 15 mm, and the Z direction ( The direction of movement in the front-rear direction with respect to the eye to be examined is provided so as to be movable by ± 15 mm.

Next, an operation method when actually inspecting using the ophthalmic inspection apparatus shown in FIG. 1, an analysis method of data obtained by the inspection, and the like will be described with reference to each drawing.
First, the subject is seated in front of the inspection apparatus, the head of the subject is not displaced by the chin rest 61 and the forehead support 62, and then the subject is encouraged to gaze at the fixation lamp. .
In the present embodiment, as shown in FIG. 6, a fixation light source is presented using a mirror 84. When the mirror 84 is used, the optical path of the photographing optical system 80 is blocked. Therefore, in the present embodiment, the mirror 84 is elongated in the vertical direction (1 mm width) so as not to block the optical path widely. A black spot B for fixation is provided at the upper and lower central portions of the mirror 84. Part A in the figure shows a region (viewing angle 10 °) in which the light (red) of the light source 83 is reflected by the mirror 84.

When the mirror 84 is formed in such an elongated shape, the red A portion can be easily visually recognized even when the subject's eye is displaced from the normal position and the black point B cannot be visually recognized by the subject at the time of setting at the start of measurement. It becomes possible to do. When red is visible, the handle 64 can be turned to adjust the height of the head to a position where the black spot B can be seen.
Compared with a method using a half mirror instead of the mirror 84, the method using the mirror 84 can suppress a reduction in the amount of reflected light from the eye to be examined by the imaging optical system 80 and increase the measurement accuracy. There is an advantage that you can.

FIG. 7 is a flowchart illustrating the overall operation of the ophthalmic examination apparatus.
When fixation is possible, right eye examination begins. The measurement start operation is performed when a person such as a measurer presses the operation button 54 of the operation panel 50. Of course, the examination may be started from the left eye.
When the operation button 54 is pressed, the operation control unit 46 and the data analysis unit 45 execute the following operations based on the control program and the data analysis program.
The first operation performed after the start of measurement is an auto-alignment / measurement operation (step S100).

FIG. 8 shows a control flow of the auto alignment / measurement operation.
The operation control unit 46 performs alignment control for accurately aligning the measurement optical system with the position of the eye to be examined at the start of measurement. The alignment control in the inspection apparatus of this embodiment is performed as follows.
FIG. 9 shows a state of the eye to be examined as seen by the CCD camera 82 of the photographing optical system 80. In the left diagram of FIG. 9, it can be confirmed that three lights are shown on the upper right side with respect to the optical axis of the CCD camera 82. Of these three lights, the light on the left and right sides is the reflected light from the alignment light source transmitted from the transmission window 112, and the center light is the reflected light of the fixation lamp 83.
The right diagram in FIG. 9 shows the center of the reflected light from the alignment light source aligned with the optical axis of the imaging optical system 80. Thus, by aligning the center of the reflected light from the light source for alignment with the optical axis of the imaging optical system 80, alignment in the left-right direction and the up-down direction (XY direction) can be performed.
Such alignment is executed by the operation control unit 46 moving and adjusting the measurement unit 30 in the XY direction based on the position of the reflected light for alignment detected by the data analysis unit 45.

  FIG. 10 shows the principle of alignment control in the front-rear direction. In the ophthalmic examination apparatus of the present embodiment, the alignment optical system 90 is disposed at the right position, the alignment light is projected from the alignment optical system 90 toward the eye to be examined, and the alignment light reflected from the cornea is reflected on the left mirror. Alignment is performed by being detected by the CCD camera 82 through 97. Infrared rays are used for alignment light.

FIG. 10 shows the case where the cornea is located in front of the reference position. At this time, since the alignment light incident from the alignment optical system 90 is reflected on the right side of the cornea of the eye to be examined, the reflected light from the cornea is shifted to the left side of the optical axis when viewed from the CCD camera 82 of the photographing optical system 80.
On the other hand, the II diagram of FIG. 10 is a case where the cornea is located behind the position to be the reference. At this time, since the alignment light incident from the alignment optical system 90 is reflected on the left side of the cornea of the eye to be inspected, the reflected light from the cornea is shifted to the right side of the optical axis when viewed from the CCD camera 82 of the photographing optical system 80.
In this way, the data analysis unit 45 detects the deviation of the alignment light with respect to the optical axis as viewed from the CCD camera 82, and the operation control unit 46 adjusts the position of the measurement unit 30 in the front-rear direction to project slit light onto the top of the cornea. The projection positions of the optical systems 70a and 70b can be matched.

  As described above, in the auto alignment operation, the data analysis unit 45 and the operation control unit 46 align the eye to be examined and the measurement optical system in the XY direction (step S200), and detect the corneal apex position (Z direction). Is performed) (step S202).

After alignment, the data analysis unit 45 measures the central film thickness of the cornea (step S204).
Since the center optical axis of the measurement optical system is aligned with the center of the pupil of the eye to be examined (vertex of the eye to be examined) by the alignment operation, slit light is projected from the left and right slit light projection optical systems 70a and 70b at this point. The reflected light from the eye to be examined is visually recognized by the photographing optical system. The slit light is reflected from the front and back surfaces of the cornea, and the thickness of the cornea can be detected. And the data analysis part 45 averages the measured value by the right and left slit light projection optical systems 70a and 70b, and makes it a center angle | corner film thickness. Measurement accuracy can be increased by measuring using the left and right slit light projection optical systems 70a and 70b. The actual thickness of the cornea is obtained in the data analysis unit 45 by converting the detection result data in consideration of the refractive index of the cornea and the like.

When the eye blinks or the eye moves, the value of the corneal thickness cannot be obtained as an appropriate value. Therefore, in step S206, the data analysis unit 45 determines whether or not the value of the corneal thickness is appropriate. If it is determined that the value is not appropriate, the data analysis unit 45 returns to step S200 to execute again from the alignment and determines that it is appropriate If so, the process advances to step S208 to move the operation unit 30 to the scanning start position in order to measure the radius of curvature of the next cornea.
The motion control unit 46 aligns the measurement optical system so as to match the vertex position of the eye to be examined, and moves the measurement optical system from the state as described above (step S208). The data analysis unit 45 detects the curvature of the cornea at this position (step S210).

FIG. 11 shows a method for measuring the radius of curvature of the cornea.
The radius of curvature of the cornea is measured from a state in which the apex position of the cornea of the eye to be inspected and the focus position (intersection position of the optical path) of the optical system of the inspection apparatus coincide with each other at a predetermined distance (3.9 mm in this embodiment). The data analysis unit 45 captures an image at a position where the optical system is moved to the back side of the eye to be examined.
FIG. 11 shows an enlarged view of the state in which the slit light 1 has moved to the back side by D from the apex position of the cornea with respect to the eye to be examined. In the figure, slit light 2 is slit light in a state where the measurement optical system is moved laterally from the vertex position of the eye to be examined.
The data analysis unit 45 virtually extends the slit light 2, the extension line up to intersecting the z-axis is a, the length in the z-axis direction is b, the length of a in the y-axis direction is h, a The angle made with the z-axis is θ. Let z be the length in the z-axis direction from the apex of the cornea until the slit light 2 enters the eye.

z can be obtained from b and the movement amount D of the optical system of the inspection apparatus, and the data analysis unit obtains the curvature radius R of the cornea from D, h, and θ by the following equation.
That is, b = h / tan θ, z = D−b = D−h / tan θ, c = R−z,
^{R 2 -h 2 = c 2 →} R 2 -h 2 = (R-z) 2 → R = (z 2 + h 2) / 2z
= ((D−h / tan θ) ² + h ² ) / 2 (D−h / tan θ)
The value of h is obtained by converting image data.

  Then, the data analysis unit 45 determines whether or not the obtained corneal curvature value is appropriate (step S212), and when it is determined that the corneal curvature value is appropriate, an operation for measuring the anterior chamber depth is performed. (Step S214). When it is determined that the curvature value of the cornea is not appropriate, the measurement is performed again by returning to the alignment operation between the eye to be examined and the measurement optical system.

For measurement of the anterior chamber depth, the operation control unit 46 scans and moves the measurement optical system horizontally with respect to the eye to be examined, and the slit light projected from the slit light projection optical systems 70a and 70b to the eye to be examined is reflected from the eye to be examined. This is done by capturing the light with the photographing optical system 80.
In the present embodiment, the operation control unit 46 moves the slit light projection optical systems 70a and 70b from the center of the pupil toward the periphery of the iris so as to scan the anterior eye part while maintaining a projection angle of 60 °. The data analysis unit 45 acquires data. The time required for the scan movement is about 0.5 seconds. By inspecting in a short time, the measurement accuracy can be improved by preventing shaking and blinking of the fixation.
Since the slit light projection optical systems 70a and 70b project the slit light from the oblique direction to the eye to be examined, the slit light projection direction is changed to the left and right depending on whether the eye to be examined is the right eye or the left eye. The slit light is moved from the center side to the ear side, and measurement is performed so that the slit light is not blocked by the nose or the like.

The data analysis unit 45 analyzes the cross-sectional images of the cornea and iris captured when the measurement optical system scans, displays the analysis result on the monitor unit 53 of the operation panel 50, and outputs the measurement data from the printer 55. To do.
FIG. 12 shows an example of actual measurement data, and shows image data obtained by scanning and moving the measurement optical system. At the time of scanning movement, 21 pieces of image data are acquired at predetermined intervals from the center of the pupil toward the periphery of the iris.

The white portion on the left side in the figure shows the cross section of the cornea. The reason why it gradually shifts to the right side from the center of the pupil to the periphery of the iris is because the cornea is curved. The thickness of the cornea can be analyzed from the cross section (white portion) of the cornea.
The part that glows white behind the cornea is the image of the iris. From the cross-sectional image of the iris, it can be seen that there is an iris behind the cornea at a predetermined interval, and that the interval with the cornea becomes narrower as the periphery of the iris is approached.

Based on the measurement data shown in FIG. 12, the data analysis unit 45 analyzes the anterior chamber depth as numerical data (step S216).
However, when analyzing the anterior chamber depth, it is possible to obtain a more accurate examination result by correcting the measurement data.
FIG. 13 shows a flowchart for correcting the measurement data and quantitatively calculating the iris shape.
As an operation for correcting the measurement data, first, it is corrected that erroneous measurement data may be obtained due to the movement of the subject's head or the fixation of the eye during the measurement. For this reason, the data analysis unit detects a shift (corresponding to a shift in the XY direction) from the position of the fixation lamp captured as an image and the position of the theoretical fixation lamp, and uses the detected value as a detection value. Based on the measurement data, the measurement data is corrected (step S300). As a result, a more accurate anterior chamber depth can be obtained.

Further, it is possible to calculate a fixation failure or misalignment in the Z direction from the deviation between the cornea image captured as an image and the position theoretically obtained from the radius of curvature of the cornea. In step S302, the data analysis unit 45 corrects the measurement data of the anterior chamber depth by correcting the shift in the Z direction.
In anterior chamber depth measurement, data is collected at regular intervals while scanning the measurement optical system, so that the position of the corneal epithelium moves in a state where the amount of change is substantially constant. However, when it reaches the position where it moves from the cornea to the sclera, the amount of change changes (slightly bulges). In step S304, the data analysis unit 45 determines the corneal limbus from the amount of change in the position of the corneal epithelium, and corrects the measurement data of the anterior chamber depth from the corneal thickness and the corneal curvature radius in steps S306 and S308. .

The subject needs to receive the measurement with the measuring unit 30 facing the measurement unit. However, the subject may place the face on the chin rest 61 with the face slightly left or right. There is a case where the forehead is separated from the forehead rest 62. In such a case, there may be an inaccurate measurement such as a difference in measurement results between the right eye and the left eye.
Therefore, as described above, the method of correcting the measurement data by comparing with the position of the fixation lamp or the position of the cornea can obtain an accurate measurement result even when the face is displaced at the time of measurement. Thus, measurement with higher accuracy becomes possible.

FIG. 14 shows an example of the measurement result of the anterior chamber depth measured and corrected by the data analysis unit 45. Here, the measurement position represents the distance (mm) moved from this position in the X direction when the position where the slit light is first projected is 0.
Using the result shown in FIG. 14, the data analysis unit 45 executes Step S310 for quantitatively calculating the shape of the iris based on the corrected anterior chamber depth.

FIG. 15 shows the principle of determining the quantitative shape of the iris.
The data analysis unit 45 takes the corneal apex defined in step S202 as the origin O, takes the posterior chamber side in the Z direction, and moves the slit light in the X direction. Based on the position coordinates of the iris surface, the data surface of the iris is circular. The radius r is calculated based on the equation of the circle. Further, the data analysis unit 45 calculates the center position (x, z) of the circle.

Next, examples of the measured iris shape will be described with reference to FIGS.
In the example shown in FIG. 16, the radius of curvature of the iris is 8.5 mm, and the projection of the iris toward the cornea side is large. When such an iris is detected, it is generally hyperopia, and the anterior chamber depth is narrow and the risk of developing closed angle glaucoma is high.
The example shown in FIG. 17 shows a case where a lens extraction operation and an artificial lens insertion operation are performed on the subject shown in FIG. By such an operation, the iris surface became almost flat (curvature radius 115 mm). And the anterior chamber depth became very wide, and the risk of developing angle-closure glaucoma was almost eliminated.
In the example shown in FIG. 18, the center of the approximate circle of the iris is centered on the cornea side of the iris, and the curving direction is opposite to that of the normal case (curvature radius—22.3 mm). In this example, it is considered that the corner was damaged by trauma.

Next, a method for quantitatively calculating the shape of the iris will be described based on the flow of FIG.
First, in step S400, the data analysis unit 45 determines the position coordinates (x _i , z _i ) at each point where the slit light is projected onto the iris surface based on the measurement result of the anterior chamber depth as shown in FIG. Is calculated.

The principle of calculating the position coordinates is shown in FIG.
Each position coordinate (x _i , z _i ) is based on the intersection (x _θi , z _θi ) of the slit light on the corneal endothelium surface and the exit angle θ when the slit light exits from the corneal endothelium surface into the anterior chamber. Is calculated.
Specifically, calculation is possible based on the following formula.
x _i = x _θi −Δx = x _θi −ACDsin θ
z _i = z _θi + Δz = z _θi + ACD cos θ
Here, Δx is a distance in the X direction from the position x _i to the position x _θi . Δz is a distance in the Z direction from the position z _i to the position z _θi . ACD is the calculated anterior chamber depth (ACD).
Note that the intersection (x _θi , z _θi ) of the slit light on the corneal endothelium surface and the exit angle θ when the slit light is emitted from the corneal endothelium surface into the anterior chamber follow the ray tracing using a standard eye shape as a model. To calculate.

In the next step S402, the data analysis unit 45 approximates the calculated multiple positions (x _i , z _i ) of the iris surface to a quadratic curve equation by the least square method.
The quadratic curve obtained here can be expressed by z = ax ² + bx + c, and constants a, b, and c of the quadratic equation are calculated in step S402.

In step S404, the data analysis unit 45 approximates the quadratic curve equation obtained by approximation to a circle equation by the linear least square method. Since the linear least square method does not require the initial value setting, the approximation can be easily performed but the accuracy is not so high.
The equation of the circle obtained here can be expressed by (x−x ₀ ) ² + (z−z ₀ ) ² = r ² , and the initial value (x _0, z ₀₎ of the center position of the circle in this step S404. ) And an initial value r of the radius of the circle.

Subsequently, in step S406, the data analysis unit 45 further approximates the equation of the circle by the nonlinear least square method based on the obtained initial value of the equation of the circle. In the nonlinear least square method, the solution may diverge without converging. However, since the initial value calculated in the previous step S404 is used, the solution can be surely converged.
The equation of the circle obtained here is
f (x, z) = (x−x ₀ ) ² + (z−z ₀ ) ² −r ²
In step S406, an equation of a circle approximating the shape of the iris surface is finally calculated.

In step S408, the data analysis unit 45 determines whether the center position of the circle is on the corneal side or the posterior chamber side of the iris. When the center of the circle exists on the cornea side, the data analysis unit 45 attaches a minus (−) sign to the calculated radius r so that the measurement person can easily understand the display.
In step S410, the data analysis unit 45 outputs data based on the calculated circle equation so that the monitor unit 53 displays the center position (x _0, z ₀ ) of the circle and the radius r of the circle. To do.

As described above, in the present embodiment, since the circular approximation is performed after the quadric curve approximation of the iris surface shape, the iris surface shape can be grasped more accurately and quantitatively.
FIG. 21 (a) simply represents the surface shape of the measured iris, and FIG. 21 (b) shows a case where circular approximation is performed without quadratic curve approximation, and FIG. ) Shows a case where circular approximation is performed after quadratic curve approximation. As can be seen by comparing these figures, the original surface shape of the iris does not necessarily match a part of the circle, but by performing the circular approximation after the quadratic curve approximation, the surface shape of the iris is extremely high. Approximate the shape of the iris along the circle, and accurately grasp the iris surface shape.

Hereinafter, the description returns to step S102 in the flowchart of FIG.
The data analysis unit 45 determines the pupil diameter after the auto alignment / measurement operation is completed in step S100 (step S102). The determination of the pupil diameter means that there are individual differences in the pupil diameter, and since the number of measurement points for the anterior chamber depth is small for people with large pupil diameters, the accurate anterior chamber depth cannot be measured. In such a case, the pupil is forcibly reduced (step S103), and the measurement can be performed again by increasing the number of measurement points.

FIG. 22 illustrates the state before miosis and the state after miosis. FIG. 22 (a) shows the state before iris reduction, because the pupil diameter is large, the area of the iris 12 for measuring the anterior chamber depth is narrow, and the number of measurement points when the slit light is scanned is reduced. Indicates that it will end up. On the other hand, FIG. 22 (b) shows that the iris 12 is squeezed and the number of measurement points of the anterior chamber depth increases by reducing the pupil.
The operation of reducing the pupil is performed by turning on the light source 95 of the white LED provided in the measurement unit 30. By turning on the white LED light source, the pupil is forcibly reduced, and the number of measurement points of the anterior chamber depth can be increased for measurement.

  In addition to the purpose of increasing the number of measurement points, the method of measuring the depth of the anterior chamber by miosis operation has a higher risk of developing angle-closure glaucoma than the other eyes. It is said that the shape of the peripheral anterior chamber in the normal pupil is different, and the risk of developing glaucoma can be detected more accurately by comparing the measurement result in the normal pupil and the measurement result in the miosis. It becomes possible. Therefore, when there is a risk of developing glaucoma, the miosis operation can be manually performed.

When it is determined that there is no problem in the determination of the pupil diameter, the measurement is performed a plurality of times in that state (step S104). Then, the measurement data of a plurality of times are averaged (step S106), and the measurement result is displayed on the monitor unit 53 of the operation panel 50 (step S108). When averaging the measurement data, weighting is performed based on the difference between the median and other measurement values. For measurement data close to the median, the measurement value is quadrupled, and the difference from the median increases. Averaged 3 times, 2 times, 1 time, 0 times.
After the measurement of the right eye is completed, it is determined whether the measurement of both eyes is completed (step S110). If the measurement of the left eye is not completed, the measurement optical system is moved to the measurement position of the left eye (step S111). Measured by the same method as described above for the left eye. Thus, measurement can be performed for both eyes.

Next, instead of the above-described embodiment for calculating the radius of curvature of the entire iris, an embodiment in which the radius of curvature at the center side and the peripheral side of the iris is calculated by dividing the iris surface into two parts will be described.
In this embodiment, the data analysis unit 45 calculates the position coordinates (x _i , z _i ) at each point where the slit light is projected onto the iris surface, and then sets the iris surface as the center side based on the position coordinates. Dividing into two on the peripheral side, each radius of curvature is calculated.
Note that the calculation of the position to divide the iris surface into two is done by dividing the number of all measurement points by the slit light by 2 and dividing it into the center side and the peripheral side when the number of measurement points is halved. ing.

As shown in the flow of FIG. 19, the data analysis unit 45 approximates a plurality of positions (x _i , z _i ) of the iris surface on the center side to an equation of a quadratic curve by the least square method, and obtains the obtained two A quadratic equation is approximated to a circle equation by a linear least square method, and further, based on an initial value of the obtained circle equation, a circle equation is approximated by a nonlinear least square method.

Similarly, the data analysis unit 45 approximates a plurality of positions (x _i , z _i ) of the peripheral iris surface to a quadratic curve equation by the least square method, and the obtained quadratic curve equation is linearly minimized. The circle equation is approximated by the square method, and further, the circle equation is approximated by the nonlinear least square method based on the initial value of the obtained circle equation.

  Then, the data analysis unit 45 determines whether the center position of each circle on the center side and the peripheral side is on the corneal side or on the posterior chamber side with respect to the iris. When the center of the circle exists on the cornea side, the data analysis unit 45 attaches a minus (−) sign to the calculated radius r.

As described above, by calculating the curvature radius that approximates the circle of the iris surface on the center side and the peripheral side, it can be used for examination of the following cases.
FIG. 23 shows an example of a healthy person. The left side of the drawing shows the radius of curvature approximated by a circle for the entire iris, and the right side of the drawing shows the radius of curvature approximated by a circle at two locations on the center side and the peripheral side.
In this example of a healthy person, the radius of curvature on the center side is small and the radius of curvature on the peripheral side is large.

FIG. 24 shows an example of closed angle glaucoma. The left side of the drawing shows the radius of curvature approximated by a circle for the entire iris, and the right side of the drawing shows the radius of curvature approximated by a circle at two locations on the center side and the peripheral side.
In this case, there is no significant difference in the radius of curvature of the entire iris compared to a healthy person. However, by comparing the center side and the peripheral side at two locations, the radius of curvature on the center side and the radius of curvature on the peripheral side are almost the same, and the respective curvature radii are smaller than those of healthy subjects. This case can be detected.

FIG. 25 shows an example of a plateau iris. The left side of the drawing shows the radius of curvature approximated by a circle for the entire iris, and the right side of the drawing shows the radius of curvature approximated by a circle at two locations on the center side and the peripheral side.
In this case, it can be detected that the radius of curvature of the iris is smaller than that of a healthy person in terms of the radius of curvature of the entire iris. Furthermore, by comparing the center side and the peripheral side, the center of the circle is located on the cornea side and is convex downward, and the radius of curvature is extremely small on the peripheral side. This case can be detected.

FIG. 26 shows an example of traumatic corner damage. The left side of the drawing shows the radius of curvature approximated by a circle for the entire iris, and the right side of the drawing shows the radius of curvature approximated by a circle at two locations on the center side and the peripheral side.
In this case, it can be detected that the radius of curvature of the entire iris is larger than that of a healthy person, but the radius of curvature is slightly larger at the center side by comparing the center side and the peripheral side. This case can be detected by the fact that the center of the circle is located on the cornea side on the peripheral side and is convex downward with a very small radius of curvature.

  In addition to the above example, by calculating the radius of curvature that approximates the iris surface in a circle on the center side and the periphery side, in addition to the examples described above, the pupil block that tends to have a smaller radius of curvature on the center side, It is also possible to examine cases such as iris dispersion syndrome, which tend to be located on the corneal side.

  In addition, when measuring using the ophthalmic examination apparatus 20 of each embodiment described above, the measurer assists the subject in the lateral position of the subject or explains to the subject. taking measurement. Since the subject is located on the front side of the gantry 40, it is convenient in terms of operability that the measurer can be operated near the subject. Since the operation panel 50 is disposed above the measurement unit 30 and can be swung left and right, the operation panel 50 can be moved and used in a direction that is easy for the measurer to operate. It is also effective to be able to move the operation panel 50 when the measurement result displayed on the monitor unit 53 is shown to the subject for explanation.

Further, since the operation panel 50 can be swung in an angle range of about 45 ° in the left-right direction, the measurer can operate on either the right side or the left side of the subject. In addition, since the subject and the measurer are located on the front side of the gantry 40, it is possible to use the apparatus by installing an inspection apparatus on the wall and measuring it, and the apparatus can be provided as a space-saving apparatus.
In addition, the measurement operation is fully automated by simply pressing the operation button on the operation panel 50, and the operation panel 50 is arranged toward the subject, so that the subject himself / herself operates the operation panel 50. It is possible to perform inspection even if the measurer is not attached by operating.

In the ophthalmic examination apparatus of the present invention, the iris shape is quantitatively measured, which is very effective for grasping a physiological or pathological state.
For example, it can be applied as follows.

  In many closed-angle eyes, the iris shape protrudes toward the cornea, and the higher the degree of protrusion, the higher the possibility of developing. For this reason, by utilizing the ophthalmic examination apparatus of the present invention, a closed angle eye can be detected with higher accuracy.

  When the projection of the iris shape toward the cornea progresses over time, the pressure on the posterior chamber side is higher than that on the anterior chamber side, indicating that the possibility of developing angle-closure glaucoma is increased. Therefore, quantitative evaluation of the iris shape over time is important for risk determination.

  An increase in the protrusion of the iris shape toward the cornea may deteriorate the outflow efficiency of aqueous humor, and correlates with an increase in intraocular pressure and instability. Therefore, determining the iris shape makes it easy to determine the risk of increased intraocular pressure and to predict instability.

  In the case of blunt eye trauma, the iris shape differs between the injured eye and the normal eye. In the case of a slight difference, it is often overlooked and may cause an inappropriate response. However, an injured eye can be easily detected by the ophthalmic examination apparatus of the present invention.

  The shape of the iris is greatly changed by miosis or mydriasis. In the case of a closed angle eye, the shape protrudes more toward the cornea due to the mydriasis, but in the case of an open eye, there is often no protrusion. In general examination, it is almost impossible to capture such a change in iris shape due to pupil reaction, but the ophthalmic examination apparatus of the present invention can do so. For this reason, the ophthalmic examination apparatus of the present invention is useful for distinguishing between closed angle glaucoma eyes and open angle glaucoma eyes.

  Aging increases the thickness of the lens, causing changes in accommodation and light refraction. Such age-related refractive changes are due to loosening of the chin ligaments that fix the lens, due to ciliary muscles, or due to thickening of the lens. Although the countermeasures differ depending on surely distinguishing these reasons, it has been difficult in the past. However, it is known that the iris shape protrudes toward the cornea when the lens is thickened, and that the entire anterior chamber depth becomes shallow due to the change in the iris shape when the chin band is loosened. . For this reason, by using the ophthalmic examination apparatus of the present invention, it becomes possible to reliably identify the cause of age-related refraction change.

  If there is a cyst on the back of the iris, if the iris sphincter or dilator is damaged, or if it is a light reaction or a pupil reaction due to drugs, the iris shape is affected. Since the ophthalmic examination apparatus of the present invention can sense these states in detail, appropriate treatment can be performed.

  While the present invention has been described in detail with reference to a preferred embodiment, the present invention is not limited to this embodiment, and it goes without saying that many modifications can be made without departing from the spirit of the invention. .

It is a perspective view showing the whole ophthalmic examination device composition. It is a block diagram which shows the internal structure of the ophthalmic examination apparatus. It is a block diagram which shows the internal structure of an operation control part. It is a block diagram which shows the internal structure of a data analysis part. It is explanatory drawing which shows the structure of a measurement optical system. It is explanatory drawing which shows a fixation method. It is a flowchart explaining operation | movement of the whole ophthalmic test | inspection apparatus. It is a flowchart explaining auto alignment and measurement operation. It is explanatory drawing explaining the method of alignment. It is explanatory drawing which shows the method to align with the top part of the eye to be examined. It is explanatory drawing which shows the method of measuring the curvature radius of a cornea. It is explanatory drawing which shows the measurement data in anterior chamber depth measurement. It is a flowchart explaining data analysis operation | movement. It is a table | surface which shows an example of the measurement result of anterior chamber depth. It is explanatory drawing explaining the principle which measures the surface shape of an iris quantitatively. It is explanatory drawing which shows the example in case the curvature radius of the surface shape of an iris is comparatively small. It is explanatory drawing which shows the example in case the curvature radius of the surface shape of an iris is comparatively large. It is explanatory drawing which shows the example in case the curved direction of the surface shape of an iris is reverse. It is a flowchart explaining the calculation operation | movement of the shape of an iris. It is explanatory drawing explaining the principle which calculates the position of the iris surface. It is explanatory drawing about a circle approximation. It is explanatory drawing which shows the measurement before a miosis and after a miosis. It is explanatory drawing when a curvature radius is measured in two places, a center side and a peripheral side, in the case of a healthy person. In the case of closed angle glaucoma, it is explanatory drawing when a curvature radius is measured in two places, a center side and a peripheral side. In the case of a plateau iris, it is explanatory drawing when a curvature radius is measured in two places, a center side and a peripheral side. It is explanatory drawing when a curvature radius is measured in two places, a center side and a peripheral side, in the case of traumatic corner angle damage. It is explanatory drawing which shows the cross-section of an eye. It is the photograph of the anterior eye part image | photographed with the ultrasonic biomicroscope.

Explanation of symbols

20 Ophthalmic Examination Device 30 Measuring Unit 32 Casing 40 Mounting Unit 44 Drive Device 45 Data Analysis Unit 46 Operation Control Unit 47 CPU
48 RAM
49 ROM
50 Operation panel 52 Monitor arm 53 Monitor unit 54 Operation button 55 Printer 61 Jaw holder 62 Forehead 63 Chin rest 64 Handle 70a, 70b Slit light projection optical system 71 Halogen lamp 73 Slit 74 Mirror 80 Imaging optical system 81 Microscope optical system 82 CCD camera 83 Light source 84 Mirror 90 Alignment optical system 92 Slit 93 Mirror 95 Light source 97 Mirror 99 Beam splitter 100 CPU
102 RAM
103 ROM
104 Storage device 110 Window 111, 112, 113 Transmission window

Claims (5)

In an ophthalmic examination apparatus for examining the anterior segment of the eye to be examined,
A slit light projection optical system that projects slit light from the pupil region to the periphery of the iris toward the anterior segment of the eye to be examined;
A drive device for moving and controlling the slit light projection optical system so as to scan the slit light projected by the slit light projection optical system;
An imaging optical system that captures a cross-sectional image of the anterior segment obtained by reflected light of the slit light projected by the slit light projection optical system a plurality of times in accordance with the movement of the slit light,
Analyzing a cross-sectional image photographed by the photographing optical system to calculate an anterior chamber depth at a plurality of positions of the eye to be examined, and a plurality of position coordinates on the iris surface based on the calculated plural anterior chamber depths An ophthalmic examination apparatus comprising: a data analysis unit that executes a step of calculating a curvature radius of an iris based on a plurality of calculated position coordinates. The data analysis unit
2. The ophthalmic examination apparatus according to claim 1, wherein a first radius of curvature on the center side of the iris and a second radius of curvature on the peripheral side of the iris are calculated. The data analysis unit
When calculating the radius of curvature of the iris,
Approximating the surface curve of the iris with a quadratic curve based on the least squares method for the calculated plurality of position coordinates;
Approximating the calculated quadratic curve to a circle equation based on the linear least squares method to calculate the center of the circle and the radius of the circle;
The radius of curvature of the iris is calculated by executing the step of approximating the surface curve of the iris to the equation of the circle based on the nonlinear least square method with the calculated center of the circle and the radius of the circle as initial values. The ophthalmic examination apparatus according to claim 1 or 2. The data analysis unit
4. The ophthalmic examination apparatus according to claim 3, wherein it is detected whether the center position of the approximate circle obtained by the nonlinear least square method is on the corneal side or the posterior chamber side with respect to the iris.   The ophthalmic examination apparatus according to any one of claims 1 to 4, further comprising a display unit that displays the calculated curvature radius.