JPH0314444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the radius of curvature of a curved surface, and more particularly to a curvature measuring device that can be applied to an off-salmometer that measures the radius of curvature of the cornea of a human eye.

In this specification, the principles and embodiments of the present invention will be explained with respect to an ophthalmometer, but the present invention is not limited thereto, and the main diameter of the curved surface of a spherical surface or toric surface that has light reflectivity can be broadly described. The present invention is also applicable to measuring the radius of curvature of a line.

The refractive power of the human cornea itself is approximately 45D, which is approximately 80% of the total refractive power of the entire eye, and approximately 75% of astigmatic eyes have corneal astigmatism, that is, the anterior surface of the cornea is not spherical but has a toric surface shape. This is due to what you are doing. Furthermore, when prescribing a contact lens, the base curve needs to be prescribed based on the radius of curvature of the anterior surface of the cornea of the eye in which the contact lens is to be worn. From these viewpoints, measuring the radius of curvature of the anterior surface of the cornea has important significance. In response to this demand, various types of off-salmometers have been put into practical use as devices for measuring the radius of curvature of the anterior surface of the cornea of the human eye. Both types of off-salmometers project one or more optotypes onto the cornea to be examined, and observe the size of the projected image or the position of its reflected image with the focal plane of an observation telescope. The radius of curvature and axis of corneal astigmatism of the cornea to be examined were measured from the amount of change in size or the amount of relative positional shift of the reflected image of the optotype.

In the ophthalmometer, especially when measuring the cornea of an astigmatic eye where the cornea has a toric surface shape, the first (strong principal meridian) and second principal meridian (weak principal meridian)
It is necessary to measure three measurable quantities: the radius of curvature of there was. However, the human eye is always accompanied by physiological eyeball vibrations, and longer measurement times result in vibrations in the projected image due to eyeball vibrations, which can lead to measurement errors and frequent alignment adjustment operations during measurements. There was a big problem that it was necessary.

As a device that solves the drawbacks of this conventional device,
For example, JP-A-56-18837, JP-A-56-66235
Publication or US Pat. No. 4,159,867 discloses that the reflected image of the projected image from the cornea is detected by a one-dimensional or two-dimensional position sensor, and the radius of curvature and the cornea of the eye to be examined are determined from the detected position. An apparatus for measuring major radius axis angles is illustrated.

However, these devices, like the conventional off-salmometers in practical use, are of the type that uses a telescope to image the reflected image of the projection target from the cornea.
In order to improve measurement accuracy, the focal length of the telescope had to be increased, which had the disadvantage of increasing the size of the Ikioi device. Also, since it is an imaging type, it requires a focusing mechanism. In addition, alignment between the device and the cornea to be examined is performed using this focusing telescope, so the alignment is inaccurate.
Moreover, it did not lead to shortening of measurement time or complete automation.

Using a non-imaging optical system, the refractive properties of the optical system,
U.S. Patent No. 3880525 is a device that mainly measures the spherical refractive power and cylindrical refractive power of eyeglass lenses and their axial angles.
It is disclosed in the specification of No. This device irradiates a parallel light beam onto the eyeglass lens to be examined, selects the light beam deflected by the refractive characteristics of the lens to be examined using a mask means having a point aperture, and is arranged at a distance shorter than the focal length of the lens to be examined. The refractive characteristics of the lens to be tested are determined from the position of the projection point of the light beam passing through the point aperture onto the detector. However, this U.S. patent specification only discloses the measurement of refractive characteristics in a refractive optical system, and does not disclose or suggest anything about the curved surface characteristics of a reflective optical system, especially the measurement of the radius of curvature of the reflective curved surface.

Therefore, it is an object of the present invention to solve the above-mentioned drawbacks of the conventional off-salmometers and provide a curvature measuring device that can be applied to off-salmometers, radius meters, etc., and is capable of automatic measurement using a non-imaging optical system. It is something to do.

Another object of the present invention is that by using a non-imaging optical system, it is smaller than conventional devices, and optical members such as imaging telescopes that need to be observed and manipulated by the examiner can be reduced. It is an object of the present invention to provide a curvature measuring device that can automatically measure the radius of curvature without having to.

Yet another object of the present invention is to provide excellent operability and reduce measurement time by automatically outputting information for alignment between the curved surface to be inspected and the optical axis of the device, which was done by collimation in conventional devices. The objective is to provide an automatic curvature measuring device that can

That is, according to the present invention, an illumination optical system includes a light source and a collimator means for converting the light from the light source into a parallel light beam; a detection optical system having a mask means having a point pattern consisting of at least three points to be selected; and a detection means for detecting the reflected light selected by the mask means; a detection corresponding to the point pattern detected by the detection means; a calculation means for calculating a radius of curvature of a curved surface to be measured from point information, and wherein both the mask means and the detection means are located on a non-conjugate surface that is optically different from the light source. is provided.

In the present invention, due to the above-mentioned structural features, the device is smaller than conventional curvature radius measurement devices, and the measurement time is short and the radius of curvature of the curved surface to be inspected can be automatically measured with high measurement accuracy. . Furthermore, since alignment information can be automatically output, measurement accuracy can be further increased.

These advantages of the present invention are that, especially when the present invention is applied to an off-salmometer, it is not affected by eye vibration, has high measurement accuracy, is small in measurement time, has a simple configuration, and can perform automatic measurements. A salmometer can be provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The measurement principle and embodiments in which the present invention is applied to an off-salmometer for measuring the radius of curvature of the cornea will be described below with reference to the drawings.

FIGS. 1 and 2 are diagrams explaining the measurement principle of the present invention.

X ₀ with the origin O ₀ at a distance l forward from the apex O _c of the cornea C to be examined along the optical axis O ₁ of the device and the optical axis O ₁
Assuming a -Y ₀ orthogonal coordinate system, there are three point apertures on this X ₀ -Y ₀ coordinate plane: I ₀ ( ₀ X ₁ , ₀ Y ₁ ), J ₀ ( ₀ X ₁ , ₀ Y ₁ ), K ₀
A mask M having ( ₀ X ₃ , ₀ Y ₃ ) is arranged.
A detection surface D is arranged a distance d further forward from the mask M along the optical axis _O1 . This detection surface D
Assume an X-Y orthogonal coordinate system in which the origin O coincides with the optical axis _O1 .

The cornea C has its optical center O _c shifted E _H in a direction parallel to the X ₀ axis, E _v in a direction parallel to the Y ₀ axis, and shifted along the first principal axis (strong principal axis) with the minimum radius of curvature γ ₁ . line) is
Assume that it is arranged at an angle θ with respect to an axis parallel to the X ₀ axis. Also, the radius of curvature of the second principal radius line (weak principal radius line) having the maximum radius of curvature is γ ₂
shall be. Note that the angle of the second principal meridian with respect to the axis parallel to the X ₀ axis is θ+90°.

Now, the optical axis O ₁ including the rays I ₁ , I ₂ , I ₃ of the cornea C to be examined
When a parallel beam of light parallel to is irradiated, this parallel beam of light is reflected by the cornea C and directed toward the mask M. Then, the reflected rays I _{1 ′} , I _{2 ′} , of the rays I ₁ , I ₂ , I 3 ,
I ₃ ' is selectively passed through the point apertures I ₀ , J ₀ , K ₀ and the detection plane D
Upper positions I (X ₁ , Y ₁ ), J (X ₁ , Y ₂ ), J (X ₃ ,
Y ₃ ), the point openings I ₀ , J ₀ , K ₀ of the mask M and the reaching points I, J, K of the detection surface D
The following coefficient equations are defined for the six points.

A ₁₂ = ( _{0 X 1} , _{X 1} ) - ( ₀ X ₂ , X ₂ ) A ₁₃ = _{( 0} X _{1 , X 1 )} - _{( 0} ) − ( ₀ Y ₂ , Y ₂ ) B ₁₃ = ( ₀ Y ₁ , Y ₁ ) − ( ₀ Y ₃ , Y ₃ C ₁₂ = ₀ X ₁ − ₀ X ₂ C ₁₃ = ₀ X ₁ − ₀ X ₃ D ₁₂ = ₀ Y ₁ − ₀ Y ₂ D ₁₃ = ₀ Y ₁ − ₀ Y ₃ ...(1) Formula [P, q]≡P ₁₂ q ₁₃ −q ₁₂ −P ₁₃ [P, q]≡−[q , P] ...Equation (1') Here, P and q are A, B, and B in Equation (1) above, respectively.
If either C or D is taken, [C, D] (d/Z) ₂ + {[A, D] - [B, C]
} (d/Z)+[A,B]=0...Equation (2) holds true. The second roots Z ₁ and Z ₂ of this quadratic equation are the focal point of the first principal axis of the cornea C from the mask M, respectively.
Since Fγ ₁ indicates the distance to the focal point Fγ ₂ of the second principal meridian, the focal length of the spherical reflective optical system is the distance between its radius of curvature R and the theorem = R/2, so this 2 1st and 2nd cornea C from roots Z ₁ , Z ₂
The radii of curvature γ ₁ and γ ₂ of the main radial line can be determined by the following formulas: γ ₁ =2(Z ₁ −l) γ ₂ =2(Z ₂ −l), respectively.

Here, the distance l may be a constant determined by a known working distance detection means, or the mask M may be set using a relay optical system so that l=0.

The angle θ between the first principal meridian γ ₁ and the axis parallel to the X ₀ axis
is θ=/2tan ^-1 {[B, D] - [A, C]/[A, D]
−[B, C]}...obtained as equation (4). The angle of the second principal meridian γ ₂ is θ+90°.

Regarding the alignment adjustment between the corneal apex O _c and the optical axis O ₁ of the device, the respective coordinates of the point apertures I ₀ , J ₀ , and K ₀ ( ₀ X ₁ , ₀ Y ₁ ), ( ₀ X ₂ , ₀ Y ₂ ) _{, ( 0} X ₃ , _{0 Y 3} ) _{, 0 X 1 + 0} X _{2 + 0} If the arrangement of the point aperture M is determined in advance, the points I, J, and K that reach the detection surface D can be set in advance.
The respective coordinate values of (X ₁ , Y ₁ ), (X ₂ , Y ₂ ),
From (X ₃ , Y ₃ ) When calculating, α and β are respectively determined when the vertex of the cornea C (optical axis O _c ) is in the direction parallel to the X ₀ axis in Figure 1.
E _H , Y It expresses the amount of deviation caused by being shifted in the direction E _v parallel to _{the 0} axis, and this allows the optical axis O ₁ to be ₀
You can adjust the alignment by moving it in the Y ₀ direction.

FIG. 3 is an optical layout diagram showing an example in which the embodiment based on the measurement principle of the present invention described above is applied to an ophthalmometer.

In the illumination optical system 1, a light beam from a light source 20 passes through an infrared transmission filter 21 and a diffusion plate 22, passes through a pinhole 7 by a condenser lens 24, and is focused by a collimator lens 30 having a focus at the position of the pinhole 7. The cornea C to be examined is illuminated as a parallel light beam.

On the other hand, a mask 31 in which at least three point openings are formed is arranged between the position sensor 9 and the relay lens 10 of the measurement optical system 2. Then, by means of the relay lens 100, the optical conjugate image M of the mask 31 is placed at a distance l from the vertex of the cornea C to be examined, and the virtual detection surface D, which is the optical conjugate image of the position sensor 9, is placed at the optical position of the mask 31. They are each created at a distance d from the conjugate image M.

The point openings of this mask 31 include a large number of point openings 23a, 23 like the aperture plate 23 shown in FIG.
b, ...23j, 23k, 23l ...23t are arranged in intersecting straight lines, which improves measurement accuracy and is more preferable. However, in this example, in order to simplify the explanation, Point openings J ₀ , N ₀ on the X ₀ axis, point openings I ₀ , K ₀ on the Y ₀ axis, and their origin O ₀
This will be explained using an example of a mask arranged symmetrically around .

The parallel light beam illuminated on the cornea C is reflected by the cornea, selectively transmitted through the point openings I ₀ , J ₀ , K ₀ , and N ₀ of the mask 31 and reaches the position sensor 9 . The _detection points obtained by scanning _{the position} sensor 9 are as shown _in FIG _.
Y ₃ ), N (X ₄ , Y ₄ ), then the coordinates of the point aperture of the mask are I ₀ ( ₀ X ₁ , ₀ Y ₁ ), J ₀ ( ₀ X ₂ , ₀ Y ₂ ), K ₀ ( ₀ X ₃ , ₀ Y ₃ )
,
_{From N 0 ( 0 _ _}

FIG. 6 is a block diagram showing a detection drive and arithmetic processing circuit for performing the above detection and arithmetic processing.

A scan drive circuit 102 scans the flat position sensor 9 under the control of a clock pulse 201 from a clock pulse oscillator 101 of the microprocessor 100. The output signal 201 from each light-receiving unit element of the position sensor 9 is converted into a digital signal with a predetermined resolution, for example, 8 bits (1/256), by the A/D converter 103, and then sent to the microprocessor. 100 is input.

The microprocessor 100 calculates the coordinate values of the destination points I, J, K, and N from the input signal, compares them with the predetermined origin _O0 , and calculates α,
Calculate β. Based on these values, the alignment deviation amounts α and β are graphically displayed on the CRT display 106 via the interface circuit 105 to notify the measuring person of the deviation direction and amount. Alternatively, the alignment may be automatically adjusted by driving the main body of the apparatus horizontally and vertically using a known electromechanical drive system 107 based on the calculated α and β values.

After completing alignment adjustment, position sensor 9
The coordinate information of the new arrival points I, J, K, and N (see FIG. 5) of the corneal reflected light beams that have passed through the point aperture of the mask 31 is obtained from the scanning output 202 of the position sensor 9.
A/D converter 103, microprocessor 100, random access memory
The data are sequentially stored in memory addresses corresponding to the respective light receiving elements of the position sensor 9 in the memory circuit 104 configured with a RAM or the like. _The arithmetic circuit ₁₀₉ in _the microprocessor ₁₀₀ calculates the The calculation results are displayed on the CRT display 106 via the interface circuit 105 as the radius of curvature γ ₁ , γ ₂ and the main meridian angle θ of the cornea to be examined. indicate. Further, it may be printed by the printer circuit 110 if necessary. These series of detection calculation processes are executed by a processing program stored in the program memory 111 in advance.

In the above embodiment, a planar position sensor was used as the position sensor 9, but instead, as shown in FIG. It may be rotated by a pulse motor 113 connected to the circuit 112 to detect the arrival point of the reflected light from the cornea C.

In addition, instead of predetermining the reference origin O ₀ in design, for example, as shown in Fig. 8, the illumination optical axis
A mirror 12 having a reflective surface is inserted in a plane perpendicular to O ₂ , and the illumination light flux reflected by this mirror 12 is made to travel backwards along the same optical path as the illumination optical path in parallel to the illumination optical axis O ₂ , and is connected to the position sensor 9 . The reflected light is detected at this detection point U ₀ ( ₀ X ₁ , ₀ Y ₁ ), V ₀ ( ₀ X ₂ , ₀ Y ₂ ),
The origin O may be determined based on W ₀ ( ₀ X ₃ , ₀ Y ₃ ) and O ₀ ( ₀ X ₄ , ₀ Y ₄ ) (see FIG. 5). According to this method,
There is an advantage that the accuracy of creating the point openings of the mask 31 and the accuracy of positioning the mask 31 when assembling the device can be made rough.

Furthermore, in the explanation of the measurement principle and the embodiments described above, the aperture plate 23 and mask 31 were explained as point apertures that transmit light, but the present invention is not limited to this, and the aperture plate and mask are It may also have a dotted reflective surface that reflects.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams for explaining the measurement principle of the present invention, FIG. 3 is an optical layout diagram showing an embodiment of the present invention, and FIG. 4 is a plan view showing another embodiment of the mask plate. , FIG. 5 is a diagram showing the relationship between the point aperture and the arrival point in the embodiment, FIG. 6 is a block diagram of the detection and arithmetic processing circuit in the embodiment, and FIG. 7 is another embodiment of the detection means in the embodiment. and FIG. 8 are partially omitted optical layout diagrams for determining the reference origin. 1...Illumination light source, 2...Measurement optical system, 7...
Pinhole, 9, 32...Position sensor, 1
0...Relay lens, 12...Reflection mirror, 23
...Aperture plate, 30...Condensing lens, 31...Mask.

Claims (1)

[Scope of Claims] 1. An illumination optical system having a light source and a collimator means for converting light from the light source into a parallel light beam; Selecting a light beam reflected by a curved surface to be inspected from the light beam from the illumination optical system. a detection optical system having a mask means having at least three point patterns, and a detection means for detecting the reflected light selected by the mask means; from detection point information corresponding to the point pattern detected by the detection means; calculation means for calculating the radius of curvature of the curved surface to be inspected, and both of the mask means and the detection means are arranged on non-conjugate surfaces optically different from the light source. Curvature measuring device. 2. The curvature measuring device according to claim 1, wherein the collimator means has a pinhole disposed at its front focal position through which the light beam from the light source passes. 3. The curvature measuring device according to claim 1 or 2, wherein the illumination light beam is infrared light. 4. The curvature measuring device according to any one of claims 1 to 3, wherein the point pattern consists of an opening. 5. Claims 1 to 4, characterized in that the detection optical system includes relay optical means for imaging both the mask means and the detection means on the respective non-conjugate planes. The curvature measuring device according to any one of paragraphs. 6. The detection optical system includes a reflective member having a reflective surface perpendicular to the optical axis of the illumination optical system that can be inserted between the curved surface to be detected and the mask means. The curvature measuring device according to any one of the ranges 1 to 5. 7. The curvature measuring device according to claim 5 or 6, characterized in that the optical axis of the relay optical means and the optical axis of the illumination optical system are at least partially common. 8. The curvature measuring device according to any one of claims 1 to 7, wherein the detection means is a planar position sensor in which a large number of light receiving elements are arranged in a planar manner. 9. Any one of claims 1 to 7, wherein the detection means is a linear position sensor formed by linearly arranging a large number of light-receiving elements and rotating on the non-conjugate plane. The curvature measuring device described in .