JPS6266830A - Apparatus for measuring shape of cornea - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a corneal shape measuring device that can accurately measure the shape of a cornea without being affected by differences in reflectance of the cornea of an eye to be examined.

[Prior Art] Generally, in order to obtain false information about the eye to be examined, a predetermined index is projected onto the eye to be examined, the reflected image is detected by a detection element, and the measured value is obtained by analyzing the output. ing.

However, at that time, the light transmittance, fundus reflectance, corneal reflectance, etc. of the eye to be examined vary greatly depending on the individual, so the light intensity of the index reflected image by the eye to be examined is 3 to 4 times higher depending on the individual eye to be examined. It will make a huge difference.

By the way, as a detection element for detecting the reflected image of the eye to be examined,
In recent years, light accumulation type one-dimensional line sensors have been mainly used due to their small size, light weight, and high reliability.However, the dynamic range of this light accumulation type sensor with respect to the input light is quite narrow, so it may be difficult to Therefore, various methods have been used in the past, mainly methods that vary the light amount of the illumination light source that projects the index onto the eye being examined. , and a method in which the sensitivity of the photodetector element is variable.

However, since the eye to be examined is a living organism that is particularly sensitive to light, the index projection light is required to be as weak as possible so as not to affect the eye.
It is not possible to vary the amount of light over a wide range, and the former method of varying the amount of light from the illumination light source is not very effective in practice.
Therefore, the latter method in which the sensitivity of the photodetector is made variable is usually adopted, and the light accumulation time of the photodetector is made variable, and the light accumulation time is lengthened appropriately to ensure that the input light level of the photodetector is sufficient. The light receiving sensitivity is made variable by obtaining a detection signal at a certain point in time.

However, when the light accumulation time is increased in this way, the influence of the movement of the subject's eye is mixed in, resulting in the problem that accurate data cannot be obtained. Also.

Among ophthalmological measuring devices, especially corneal topography measuring devices, in order to receive the reflected light from the specular cornea, it is necessary to use a light source with a very short emission time, such as a strobe flash, and the light accumulation time is very short. It is unsuitable for measuring methods that require long periods of time. Therefore, in a normal corneal shape measuring device, the illumination light source emits light so that the amount of light incident on the one-dimensional line sensor, etc. at an average corneal reflectance has a dynamic range that is about half that of the -dimensional line sensor, etc. I am trying to set the amount of light. For this reason, not only the subject's eye having an average reflectance but also the subject's eye having a reflectance deviating from the average in any direction.

The probability of being covered by the dynamic range of the -dimensional line sensor becomes considerably large, and differences in the reflectance of the cornea of the subject's eye due to individual differences can be absorbed to a certain extent.

However, although this method can detect reflected light over a fairly wide range, it does not always detect it at the appropriate level, so the difference between the highest and lowest levels is
This has the disadvantage that a difference in /N ratio occurs, and measurement accuracy is not uniform.

[Object of the Invention] The object of the present invention is to grasp the corneal reflection image of a projection index for observation and optical axis adjustment by a light receiving means, compare and process the output signal level, and detect the corneal reflection state of the eye to be examined. The object of the present invention is to provide a corneal shape measuring device that enables highly accurate measurement by controlling the light intensity of the measurement light source to the optimum state for each eye to be examined.

[Summary of the invention] The gist of the present invention is to achieve the above objects.

a first projection and imaging means including a first illumination light source that projects an index onto the cornea of the eye to be examined and forms a first reflected image of the index; a second projection imaging means including a second illumination light source for projecting an indicator onto the cornea of the eye to be examined and forming a second corneal reflection image of the indicator; a light receiving means for receiving the corneal reflected image of No. 2, a comparing means for comparing an output signal obtained by the light receiving means with a predetermined value, and controlling an amount of light emitted from the first illumination light source according to an output result of the comparing means. This is a corneal shape measuring device characterized by comprising a light emission amount control means.

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a configuration diagram of an optical system and an electric system showing an embodiment of the present invention, in which a collimator ring lens l, a ring-shaped strobe 2, a ring-shaped fluorescent tube 3 are arranged in sequence facing the eye E to be examined.
are arranged, and a ring-shaped slit 4 is provided on the opposite side of the eye E of the ring lens 1. Further, on the optical axis of the eye E to be examined, objective lenses 5. A guichroic mirror 6, a multi-hole diaphragm 7, and a prism 8 are arranged, and a one-dimensional position detection element 9 is provided at a position corresponding to the multi-hole diaphragm 7. A relay lens 10 and a TV right camera 1 are sequentially arranged opposite to the guichroic mirror 6.
The output of the V right camera 1 is connected to a TV monitor 12 and a video signal processing circuit 13.
The output of is connected to interface 14. The output of the interface 14 is connected to a strobe trigger circuit 15, a strobe light amount control circuit 16, a display 17, and further connected to a microcomputer path 18 so as to transmit and receive signals. Further, the output of the strobe light amount control circuit 16 is connected to a strobe trigger circuit 15, and the output of this strobe trigger circuit 15 is connected to the ring-shaped strobe 2. The microcomputer pass 18 includes an analog processing circuit 19. C.P.
U20, ROM21, and RAM22 are connected to each other, the output of the detection element 9 is connected to the analog processing circuit 19, and the output of the power supply circuit 23 is connected to the ring-shaped fluorescent tube 3.

When observing the corneal shape and adjusting the optical axis between the cornea Ec and the device, the light beam emitted from the ring-shaped fluorescent tube 3 driven by the power supply circuit 23 passes through the ring-shaped strobe 2 and illuminates the ring-shaped slit 4. It has become. This slit 4 is located on the focal plane of the ring lens l when viewed in a cross section including the optical axis, and the slit 4 is optically positioned at an infinity point, and the light projected from that infinity point is illuminated. The cornea Ec of the optometrist E is illuminated. The surface of the cornea Ec is like a convex mirror, so the slit 4
A ring-shaped corneal reflection image Sa is formed. This corneal reflected image Sa is reflected by the gicroic mirror 6 via the objective lens 5, is imaged by the TV right camera 1 via the relay lens 10, and is projected on the TV monitor 12. . In addition, the video signal obtained by the TV right camera 1 is transmitted to the video signal processing circuit 1.
3, and in this video signal processing circuit 13, the corneal reflection image Sa of the slit 4 illuminated by the fluorescent tube 3
The signal levels are compared and determined, and the results are input to the interface 14.

On the other hand, when measuring the corneal shape, the ring-shaped strobe 2 is driven by the strobe trigger circuit 15, and the visible light emitted from the strobe 2 illuminates the slit 4 in the same way as when observing the corneal shape, and is converted into parallel light by the lens l. As a result, a corneal reflection image Sa is formed on the cornea Ha of the eye E to be examined.

This corneal reflected image Sa passes through an objective lens 5, a visible light-transmissive gicchroic mirror 6, passes through a multi-hole aperture 7, is further deflected by a prism 8, and is re-imaged on a -dimensional position detection element 9. It is now possible to do so.

As shown in FIG. 2(a), the multi-hole diaphragm 7 has, for example, five openings 7a to 7e, and the prism 8 also has openings 7a to 7e.
5 as divided by the dotted line in Fig. 2(a) corresponding to 7e.
Each of these elements 8a to 8e has a cross-sectional shape as shown in FIG. 2(b). Only one detection element 9 is shown in the figure, but it is actually used in the apertures 7a to 7e of the multi-hole diaphragm 7 and the prism element 8.
The coordinates of the five corneal reflection images separated by the multi-hole diaphragm 7 and the prism 8 are 5, which are arranged at 72° intervals around the measurement optical axis in correspondence to a to 8e. It is detected by the detection elements 9. The analog signal output from each detection element 9 is A/D converted by an analog processing circuit 19, and then sent to the R
Transferred to AM22.

The system control system centered on the CPU20 includes ROM2.
A program for controlling the system is written in the RAM 22, and the RAM 22 is used as a work area for the system. Then, the strobe light amount control circuit 16 is controlled by the data obtained by the video signal processing circuit 13 via the TV right camera 1, and the strobe light amount control circuit 16 is controlled by the strobe light amount control circuit 16 with an appropriate light amount via the strobe trigger circuit 15. The indicator corneal reflection image Sa with the optimum light intensity is obtained, and the data obtained through the detection element 9 is calculated by the system control system and displayed on the display 1.
7 is now displayed.

3(a) is a timing chart of the operation of the video signal processing circuit 13, and FIG. 3(b) is a configuration diagram of the video signal processing circuit 13. In (a), the signal AO is the TV of FIG.
It is the same as the signal AO shown on the monitor 12, and shows one scanning line of the video signal that passes approximately through the center of the external eye part of the eye E to be examined. The signal AI is a horizontal synchronization signal of the scanning line signal AO, and the signal A2 is the signal of the iris of the eye E to be examined, and the signal A
3 indicates a signal from the pupil. 0 Normally, the signal level increases in the order of pupil signal A3, iris signal A2, and signals from the sclera and skin outside the iris.

The corneal reflection image Sa by the ring-shaped fluorescent tube 3 is formed on the signal A2 of the iris, and is set at a reference level B.
, C are provided so that the peak on the scanning line signal AO of the corneal reflection image Sa can be compared with these reference levels B and C. At this time, a gate signal p is provided to remove influences outside the iris, and the range of comparison is limited. In this embodiment, the signal of the corneal reflection image Sa is lower than the reference level B, and is lower than the reference level C.
Therefore, in comparison with the reference level C, a signal Ca having a comparison signal consisting of two peaks, which is the difference between the peak signal of the corneal reflection image Sa and the reference level C, is output. In comparison with , a signal Ba having no comparison signal is output. Then, the signal Ca is temporarily held in a flip-flop circuit and then output as a signal cb having a step comparison signal.

As shown in FIG. 2(b), the configuration of the video signal processing circuit 13 that outputs these signals includes a buffer amplifier 30 to which the video signal from the TV camera 11 is input.
The output of the buffer amplifier 30 is connected to a DC regeneration circuit 31, and the output of this DC regeneration circuit 31 is connected to the analog switch 3.
2 and the synchronous separation circuit 33. The synchronization separation circuit 33 outputs a horizontal periodic signal S1 and a vertical synchronization signal S2, the horizontal synchronization signal Sl is input to the counter 34, and the vertical synchronization signal S2 is input to the counter 34, the one-shot multi-circuit 35 . The information is input to the interface 14. From the counter 34, a gate signal S3. S4 is output, gate signal S3 is input to analog switch 32, and gate signal S4 is input to comparators 36a and 36b. Further, the output of the analog switch 32 is connected to one input terminal of each of comparators 36a and 36b, and reference levels B and C are inputted to the other input terminals of the comparators 36a and 36b, respectively. Furthermore, flip-flop circuits 37a and 37b are connected to the output terminals of the comparators 36a and 36b, respectively, and the output of the one-shot multi-circuit 35 is also connected to the flip-flop circuits 37a and 37b.
The outputs of the flip-flop circuits 37a and 37b are connected to the interface 14, respectively.

The video signal is then amplified by a buffer amplifier 30,
After the level is held constant in the DC regeneration circuit 31, it is input to the analog switch 32 and the synchronization separation circuit 33, and the horizontal synchronization signal S1 is counted by the counter 34. When the screen is approximately in the center, the counter 34 outputs the signal to the gate. The signal S3 is output to the analog switch 32 and switches the analog switch 32. At the same time, the counter 34 outputs a gate signal S shown as D in FIG. 3(a).
4 is output to comparators 36a and 36b. In addition,
This counter 34 is reset every frame by inputting the vertical synchronization signal S2.

Further, the video signal input to the analog switch 32 is transferred to the comparator 36 by the operation of the analog switch 32.
a, 36b, where it is compared with reference levels B, C, and the results are input to flip-flop circuits 37a, 37b.
is stored in the memory. Then, by the pulse output S5 of the falling edge of the vertical synchronization signal S2 inputted via the one-shot multi-circuit 35, the interface 14
An interrupt is sent to the CPU 20 via the CPU 20, and the contents stored in the flip-flop circuits 37a and 37b are read. After that, the pulse output S of the one-shot multi-circuit 35 at the rising edge of the vertical synchronization signal S2
5, the flip-flop circuits 37a and 37b are reset.

A series of operations will be completed.

In this way, the CPU 20 captures the video signal level of the corneal reflection image Sa for each frame, sets the light emission amount of the strobe 2 according to it to the strobe light amount control circuit 16 via the interface 14, and sets the strobe light amount control circuit 16 to the strobe trigger circuit. By causing the strobe 2 to emit light with an optimum amount of light via the sensor 15, the coordinates of the five points of the corneal reflection image Sa can be clearly detected on the detection element 9.

Then, by substituting the coordinates of these five points into the general formula of the quadratic curve, AX2 + BXY + CY2 + DX + EY + Fn O, and solving the simultaneous equations, the coefficients A to E are obtained, and the general formula of the ellipse, (x-xo) 2/a ' + (y-yo) 2/
b2=Madashi, xxXcosθ−Y sinθ'! -Xsin
θ+Y Co! The major axis a and the minor axis of the ellipse are thereby deformed to θ.

By determining the rotation angle θ and performing calculations on it, it is possible to calculate the radius of curvature of the amphipathic meridian of the cornea Ec, the refractive power, the degree of astigmatism, and the axis of astigmatism, which are displayed on the display 17.

In the above-described embodiment, the signal level of the corneal reflection image Sa is determined by inputting the video signal captured by the TV camera 11 to the video signal processing circuit 13, but the video signal processing circuit 13 may be removed. A light-receiving sensor (not shown) is placed at the center of the multi-hole diaphragm 7 toward the subject's eye E, and the signal obtained by this light-receiving sensor is input to the strobe trigger circuit 15 and sent to the strobe light amount control circuit 16 via the interface 14. The signal from the light receiving sensor is integrated by an integrator provided in the strobe light amount control circuit 16, and compared with the set value by a comparator.
Measurement can be performed by controlling the amount of light emitted by the strobe 2 so that the input light level of the corneal reflection image Sa input to the detection element 9 is appropriate. Furthermore, instead of providing an integrator and a comparator in the strobe light amount control circuit 16, an integrator and a comparator are provided in the strobe trigger circuit 15.

The strobe light amount control circuit 16 can also be omitted.

[Effects of the Invention] As explained above, the corneal shape measuring device according to the present invention has the following effects:
In order to observe the shape of the cornea of the eye to be examined and to adjust the optical axis between the cornea of the eye to be examined and the device, the corneal reflection image of the index projected onto the cornea is captured by an image sensor for observing the anterior segment of the eye to be examined. picture,
The difference in corneal reflectance is determined by comparing the difference in the brightness level of the index reflected image due to the difference in corneal reflectance with the set value,
By controlling the amount of strobe flash light within a safe range suitable for the cornea of each eye without unnecessarily increasing the amount of light emitted, it is possible to obtain an input optical signal at the appropriate level at the detection element. While maintaining an appropriate S/N ratio without being affected by individual differences in the eye being examined,
This makes it possible to measure the corneal shape with high precision and safety.

[Brief explanation of the drawing]

The drawings show an embodiment of the corneal shape measuring device according to the present invention, and FIG. 1 is a configuration diagram, FIG. 2(a) is a front view of a multi-hole aperture, FIG. 2(b) is a sectional view of a prism, 3(a) is a timing diagram of the video signal processing circuit, and FIG. 3(b) is a configuration diagram of the video signal processing circuit. Symbol l is a ring lens, 2 is a ring strobe, 3 is a ring-shaped fluorescent tube, 4 is a ring-shaped slit, 5 is an objective lens,
6 is a guichroic mirror, 7 is a multi-hole diaphragm, 8 is a prism, 9 is a one-dimensional position detection element, 11 is a TV camera, 1
2 is a TV monitor, 13 is a video signal processing circuit, 14 is an interface, 15 is a strobe trigger circuit, 16 is a strobe light amount control circuit, 17 is a display, 19 is an analog processing circuit, 20 is a CPU, 21 is a ROM, 22 is RAM, 2
3 is a power supply circuit, 32 is an analog switch, 33 is a synchronous separation circuit, 34 is a counter, 35 is a one-shot multi-circuit, 36 is a comparator, and 37 is a flip-flop circuit. Patent applicant Canon Co., Ltd. Figure 1 Figure 3 (G) (b)

Claims (1)

[Scope of Claims] 1. A first projection imaging means including a first illumination light source that projects an indicator onto the cornea of the eye to be examined and forms a first reflected image of the indicator; a second illumination light source that projects an index onto the cornea of the eye to be examined and forms a second corneal reflection image of the index; projection imaging means; light receiving means for receiving the second corneal reflected image; comparison means for comparing the output signal obtained by the light receiving means with a predetermined value; 1. A corneal shape measuring device comprising: a light emitting light amount control means that controls the amount of light emitted by the comparison means. 2. The light receiving means is used for observing the shape of the cornea and for observing the cornea and the first
2. The corneal shape measuring device according to claim 1, wherein the corneal shape measuring device is an image sensor for performing optical axis adjustment with a projection imaging means. 3. The corneal shape measuring device according to claim 1, wherein the light receiving means is a light receiving sensor that is provided on the measurement optical axis and directly receives the second corneal reflected image.