JPH06311965A - Cornea shape measuring instrument - Google Patents

Abstract

PURPOSE:To easily derive an imperfect shere's radius of curvature being orthogonal to a principal meridian by allowing a reflected light obtained by projecting light from source of two sets or more provided with an optical axis in the center to transmit through a lens and a telecentric diaphragm, dividing it into two by a beam splitter and detecting it by a one-dimensional detecting element. CONSTITUTION:From one set of light sources 1a, 1b consisting of plural symmetrical light emission diodes set centering around an optical axis consisting of a chain line, the cornea 3 of an eye to be examined is irradiated obliquely with light beams made parallel by lenses 2a, 2b, and point light source images 1a', 1b' are formed. The reflected light from the light source images 1a,' 1b' is allowed to form an image on a telecentric diaphragm 6 by a lens 4. The light beam which passes through the diaphragm 6 is divided into two by a beam splitter 7, allowed to transmit through convex lenses 8a, 8b, and the light beam is detected by one-dimensional detecting elements 5a, 5b at a position being conjugate to the diaphragm 6. Subsequently, the similar measurement is executed by the light source from a direction different from the sources 1a, 1b. In such a way, an imperfect shere's radius of curvature being orthogonal to a principal meridian is derived easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corneal shape measuring apparatus for measuring a radius of curvature of a cornea.

[0002]

2. Description of the Related Art As a device for measuring the shape of the cornea, a device for measuring the radius of curvature of the cornea in the meridian direction is known.
However, when determining the base curve of the contact lens, it is sometimes necessary to measure not only the radius of curvature of the cornea in the radial direction but also the spherical radius of curvature. The conventional manual measuring device measures the radius of curvature in the meridian direction of the central part of the cornea, rotates the optical system in the measured meridian direction, and then uses the fixation lamp to measure the position where measurement is required. There is also proposed an apparatus that can measure the spherical radius of curvature by guiding the optical axis.

[0003]

The conventional apparatus for measuring a spherical radius of curvature requires a mechanism for rotating an optical system, which is extremely complicated to operate and takes a long time to measure. There is.

Further, since the fixation lamp is placed near the eye to be inspected, there is a drawback that an extremely large adjusting force is required to fix the eye. The present invention has been devised in view of the above drawbacks, and an object thereof is to provide a corneal shape measuring apparatus capable of measuring a spherical curvature radius perpendicular to the main meridian direction of the cornea of the eye to be inspected. .

[0005]

In order to achieve the above object, the present invention has the following features. (1) The first projection optical system projects a predetermined index centering on the corneal apex of the eye to be examined, and the first detection optical system detects the corneal reflection image of the index to measure the corneal shape in the vicinity of the corneal apex. In the corneal shape measuring device capable of performing the above, a mode switching means for switching the mode for measuring the corneal shape in the vicinity of the apex of the cornea to the mode for measuring the spherical radius of curvature, and guiding the fixation of the eye to be examined. A plurality of fixation guiding means for guiding the corneal peripheral portion on the optical axis of the first detection optical system and a plurality of meridians sandwiching a meridian in a direction orthogonal to the meridian of the eye passing through the optical axis of the first detection optical system. Second projection of the point index to the cornea periphery
The projection means, the second detection optical system for detecting the corneal reflection image projected by the second projection means, and the astigmatic axis direction of the eye to be inspected based on the detection results by the first detection optical system and the second detection optical system. And a calculation means for calculating a spherical radius of curvature.

(2) The first projection optical system of (1) is
At least two index sets are provided for projecting the index at positions symmetrical with respect to the optical axis of the detection optical system, and the fixation guiding means fixes the fixation in a direction orthogonal to the direction connecting the indices of each index set. It is characterized in that it is arranged so as to guide the direction and shares the first projection optical system and the second projection optical system.

(3) The first projection optical system of (2) is characterized in that a certain index set and another one index set are arranged in a direction orthogonal to each other, and the index light flux is constituted by a visible light flux. To do.

(4) The first projection optical system of (3) is characterized in that it has four point light sources arranged at 90-degree intervals of the eye to be inspected.

[0009]

EXAMPLES Examples of the present invention will be described below.
FIG. 1 is a diagram showing a measurement optical system of the corneal shape measuring apparatus.
Reference numerals 1a, 1b, 1c and 1d (1c and 1d are not shown) are point light sources composed of a light emitting diode, and are used as measurement light projected on the cornea of the eye to be inspected, and are also fixed to the eye to be inspected. It emits a light flux in the near-infrared region so as to function as a target. Light emitted from the point light sources 1a and 1b is converted into a parallel light flux by the collimating lenses 2a and 2b, and the cornea 3 of the eye to be inspected.
Are projected at an angle of α onto the point light source images 1a ′, 1b ′.
Are formed on the eye to be examined. Similarly, the point light sources 1c, 1 (not shown) located at a position rotated by 90 degrees with respect to the optical axis O of the point light source 1a.
The light emitted from d is collimated by unillustrated collimating lenses 2c and 2d to be a parallel light beam, which is projected on the cornea 3 of the eye to be examined at an angle α, and unillustrated point light source images 3c ′ and 3d ′.
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The imaging lens 4 includes a one-dimensional position detecting element 5
a, 5b detection surfaces and point light source images 1a ', 1b', 1c ',
1d ′ is arranged at a conjugate position, and a telecentric diaphragm 6 is arranged at the image-side focal position thereof. The beam splitter 7 divides the optical path into two. Further, between the telecentric diaphragm 6 and the one-dimensional position detecting elements 5a and 5b, convex cylindrical lenses 8a and 8b are arranged so that their axes (bus lines) coincide with the detection direction of the one-dimensional position detecting element. The focal lengths of the convex cylindrical lenses 8a and 8b are infinite in the cross section in the cylinder axis direction, and the telecentric diaphragm 6 and the one-dimensional position detecting element 5 are in the cross section in the direction orthogonal to the cylinder axis direction.
It is designed so that a and 5b are almost conjugate. Further, the one-dimensional position detecting elements 5a and 5b are orthogonal to each other.

FIG. 2 is a block diagram of the electric system of the apparatus. 1
0 is an LED driver for turning on the four point light sources (1a, 1b, 1c, 1d), 11 is a drive circuit for capturing signals on the detection elements 5a, 5b, 12 is a clock counter, and 13 is a clock generation circuit. , 14 is a peak-hold circuit for holding the peak voltage of the signal sent from 11, and 15 is a peak-hold circuit with the signal from 11
From the computer through the computer 17 to compare the voltage with the signal converted to ½ of the peak voltage to output a strobe signal, and 16 is a comparator for outputting a strobe signal. Latch for holding counter value, 18 is A / D
The converter 19 is a D / A converter.

Reference numeral 20 denotes a switch for switching the measurement mode, which switches from the mode for measuring the radius of curvature in the meridian direction near the apex to the mode for measuring the spherical radius of curvature in the peripheral portion of the cornea. Reference numeral 21 is a display circuit, and 22 is a television monitor. The television monitor 22 displays an anterior ocular segment image captured by a television camera (not shown) and also displays measurement data and the like.

The signal obtained by the detection element 5 is transmitted to the drive circuit 11. The signal from the drive circuit 11 is transmitted to the comparator 15 and the peak-hold circuit 14.
The peak voltage detected by the peak hold circuit 14 is converted into a digital signal by the A / D converter 18 and then input to the computer 17. The digital signal of the peak voltage output at 17 is converted into a voltage signal of 1/2 of the peak voltage at the D / A converter 19 and input to the comparator 15. This signal is compared with the signal directly input to the comparator 15 to output a strobe signal.
The signal of ½ of the input voltage is compared with the signal input one time before. The strobe signal causes the signal of the counter 12 to enter the latch 16, and the position of the bright and dark edges is read from the waveform at that time.

Next, the operation of the apparatus having the above-mentioned structure will be described. The method of measuring and calculating the radius of curvature of the central portion of the cornea in the radial direction is described in detail in Japanese Patent Laid-Open No. 61-85920, and the description thereof is incorporated herein by reference. The eye to be inspected and the device are placed in a predetermined positional relationship by a known alignment mechanism (not shown). The measurement mode when the power is turned on is a mode for measuring the radius of curvature in the meridian direction near the apex of the cornea and the axial angle of the main meridian, and the point light sources 1a to 1d are sequentially or simultaneously (image separation when simultaneously lit). It is better to use a prism or the like), and the radius of curvature and the axial angle of the strong and weak main meridians are calculated by detecting the image position.

When the switch 20 is pressed, the mode is switched to the mode for measuring the spherical radius of curvature of the peripheral portion of the cornea. Mode
When the mode is switched, the point light source 1a lights up (blinks for attention). The light emitted from the point light source 1a is made into a parallel light flux by the collimating lens, and the eye to be examined can see the point light source 1a at infinity. Point light source 1a
When is fixed, the subject's eye 3 rotates by an angle α with respect to the measurement optical axis. The measurement optical axis is aligned with the lower part of the cornea, and a measurement switch (not shown) is pressed to turn on the point light sources 1c and 1d.
The interval between the corneal reflection images 1c and 1d is detected by the one-dimensional position detecting element 5b, and the spherical curvature radius in the lower cornea is calculated based on the detection result.

Next, the point light source 1b is fixed and the point light sources 1c and 1d are turned on in other states to measure the spherical radius of curvature of the upper part of the cornea. Similarly, by turning on the point light sources 1a and 1b by using the point light source 1c as a fixation lamp, the spherical radius of curvature around the right part of the cornea can be obtained, and by using the point light source 1d as a fixation lamp, The spherical radius of curvature at the periphery is measured. If the cornea of the eye to be inspected is an accurate toric surface, only one measurement data is required, but in consideration of the fact that the eye to be inspected is not exactly the toric surface in general, it is aspherical in each meridian direction. The four spherical radii of curvature are measured in order to obtain the best data for calculating the various radii of curvature. In the modification of the fixation direction in this embodiment, the fixation lamps are switched in a predetermined order based on the measurement signal from the measurement switch, but a fixation specification switch may be provided for selective specification.

Based on the thus obtained spherical radius of curvature of the peripheral portion, the peripheral spherical radius of curvature orthogonal to the strong and weak main meridian directions can be calculated by the following method. Let R _s1 (weak main meridian direction) and R _s2 (strong main meridian direction) be the spherical curvature radii on the main meridian to be obtained, and let R _m1 (weak main meridian) be the radius of curvature obtained by measuring the central part. Direction) and R _m2 (direction of strong main meridian), the following equation holds.

[Equation 1] h is the distance from the center of the cornea to the Sagittal R measurement point. Since (R _m1 ) ² is sufficiently larger than h ² , _Formula 1 can be approximated to Formula 2 below.

[Equation 2] Furthermore, by plotting the spherical curvature radius at a position at a predetermined distance from the center of the cornea of the eye to be examined, the locus can be approximated to an ellipse. The following equation is obtained from the locus of this spherical radius of curvature and Equation 1.

[Equation 3] For x and y in Equation 3, the data obtained by adding the coordinate transformation for rotating the axis by the astigmatic axis angle θ obtained in the corneal center measurement to the spherical radius of curvature around the cornea obtained in the above measurement is used. To do. The conversion formula is shown in Formula 4.

[Equation 4] By substituting the converted x and y into the equation 3 and using the equation 1, the spherical radius of curvature on the main meridian near the measurement position of the spherical radius of curvature used as data is obtained. be able to. In this way, a total of four spherical radiuses of curvature can be calculated for the upper and lower main meridians. Regarding the data selection for calculating the spherical radius of curvature on the main meridian, the measurement data at the position closest to the main meridian is taken, and the average of the two closest data points is taken. You can also use it. Further, as shown in FIG. 3, the number of point light sources is increased, and the point light sources near the weak main line direction obtained by the center measurement are used as a fixation lamp.
A more accurate spherical radius of curvature can be measured by using one point light source as the measurement light.

[0018]

According to the present invention, the spherical radius of curvature perpendicular to the main meridian direction of the cornea can be measured very easily.

[Brief description of drawings]

FIG. 1 is a diagram showing a measurement optical system of a corneal shape measuring apparatus.

FIG. 2 is a block diagram of an electric system of the apparatus.

FIG. 3 is a diagram showing a case where the number of point light sources is increased.

[Explanation of symbols]

 1 Light emitting diode 2 Collimating lens 3 Eye cornea 4 Imaging lens 5 Detection element

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[Procedure amendment]

[Submission date] February 28, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Based on the thus obtained spherical radius of curvature of the peripheral portion, the peripheral spherical radius of curvature orthogonal to the strong and weak main meridian directions can be calculated by the following method. Let R _s1 (weak main meridian direction) and R _s2 (strong main meridian direction) be the spherical curvature radii on the main meridian to be obtained, and let R _m1 (weak main meridian) be the radius of curvature obtained by measuring the central part. Direction) and R _m2 (direction of strong main meridian), the following equation holds.

[Equation 1] h is the distance from the center of the cornea to the Sagittal R measurement point. Since (R _m1 ) ² is sufficiently larger than h ² , _Formula 1 can be approximated to Formula 2 below.

[Equation 2] Furthermore, by plotting the spherical curvature radius at a position at a predetermined distance from the center of the cornea of the eye to be examined, the locus can be approximated to an ellipse. The following equation is obtained from the locus of this spherical radius of curvature and Equation 1.

[Equation 3] X and y in Equation 3 are the corneal deficiencies around the cornea obtained in the above measurement.
Astigmatic axis angle θ obtained by measuring the center of the cornea
The data with coordinate transformation to rotate the axis is used. Strange
The substitution formula is shown in Equation 4.

[Equation 4] By substituting the converted x and y into the equation 3 and using the equation 1, the spherical radius of curvature on the main meridian near the measurement position of the spherical radius of curvature used as data is obtained. be able to. In this way, a total of four spherical radiuses of curvature can be calculated for the upper and lower main meridians. Regarding the data selection for calculating the spherical radius of curvature on the main meridian, the measurement data at the position closest to the main meridian is taken, and the average of the two closest data points is taken. You can also use it. Furthermore, arranged to increase the number of point light sources as shown in FIG. 3, the point source close to Yowanushi via line direction obtained at the center measured using a fixation lamp, the direction perpendicular to the meridian 2
A more accurate spherical radius of curvature can be measured by using one point light source as the measurement light.

Claims (4)

[Claims] 1. A corneal shape in the vicinity of a corneal apex is formed by projecting a predetermined index around the corneal apex of an eye by the first projection optical system and detecting a corneal reflection image of the index by the first detection optical system. In a corneal shape measuring device capable of measuring, a mode switching means for switching from a mode for measuring a corneal shape in the vicinity of a corneal apex to a mode for measuring a spherical radius of curvature, and a fixation of an eye to be examined. Fixation guidance means for guiding and guiding the peripheral portion of the cornea on the optical axis of the first detection optical system;
Second projection means for projecting a plurality of point indices on the corneal peripheral portion with a meridian in a direction orthogonal to the meridian of the eye to be inspected that passes through the optical axis of the detection optical system, and the cornea projected by the second projection means A second detection optical system for detecting a reflected image and a calculation means for calculating a spherical radius of curvature of the eye to be inspected in the astigmatic axis direction based on the detection results of the first detection optical system and the second detection optical system. A corneal shape measuring device characterized by the above. 2. The first projection optical system according to claim 1, further comprising at least two index sets for projecting indices at positions symmetrical with respect to the optical axis of the first detection optical system, and the fixation system. The guiding means is arranged so as to guide the fixation direction in a direction orthogonal to the direction connecting the indexes of each index set, and includes the first projection optical system and the second projection optical system.
A corneal shape measuring apparatus that shares a projection optical system. 3. The first projection optical system according to claim 2, wherein a certain index set and another one index set are arranged in a direction orthogonal to each other, and the index light flux is constituted by a visible light flux. A corneal shape measuring apparatus characterized in that a fixation guiding means is shared. 4. The first projection optical system according to claim 3,
A corneal shape measuring apparatus having four point light sources arranged at 0 degree intervals.