JPS6219145A - Cornea meter - 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 the Invention The present invention relates to a keratometer for automatically measuring the radius of curvature of the cornea.

Problems with the Prior Art Various measuring methods and measuring devices have been proposed and put into practical use as keratometers. However, conventional methods and devices have complex configurations and are not suitable for automation.

In addition, the complicated configuration increases the size of the device, and other ophthalmologic devices, such as autorefractometers, fundus cameras,
The idea was to create an integrated multifunctional machine that could be combined with a surgical microscope. ``Object of the Invention It is an object of the present invention to solve the conventional problems and provide a new and useful keratometer that is simple in construction and suitable for combination with other ophthalmological machines.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is an optical layout diagram and a block diagram of an electrical system showing the present invention. An annular slit 11 having a center on the optical axis Δ of the device is formed in the index plate 10 . Behind this slit 11 is an annular light source 12 and a reflecting mirror 13.
There is an index illumination section consisting of. The light from slit 11 is
As shown in FIG. 2, it is reflected by the cornea C of the eye to be examined, creating a toric virtual image 11'. The light from this virtual image 11' passes through lenses 16 and 17 provided on the index plate 10 to the detector 1.
4.15, respectively.

In this embodiment, the detector 14.15 is composed of an area type CCD, and its detection signal is sent to the video signal processing circuit 21.22 of the alignment detection system 20 and the detection signal counting circuit 31.32 of the corneal topography measurement system 30. Output.

[Alignment detection]

The alignment detection system 30 in this embodiment is used for coarse alignment adjustment to capture the eye to be examined within the field of view of the apparatus. The detection signals from each detector 14.15 are converted into video signals by video processing circuits 21.22, and the video signals from both detectors are combined by a video signal synthesis circuit 23, and then displayed on a CRT or liquid crystal display. For example, an image is displayed on the device 24 as shown in FIG.

In FIG. 5, lla' indicates the index image obtained by the detector 14, and llb" indicates the index image obtained by the detector 15. When the alignment is incomplete, that is, the working distance between the eye to be examined and the device is the normal distance. If not, as shown in FIG. 5, both images 113'' and llb' are displayed out of alignment. Further, if there is a shift in the horizontal, vertical, and vertical directions within a plane perpendicular to the optical axis to be examined, the center of the image will be displayed shifted from the intersection Q of the reticle lines 40 formed on the display surface. The measurer views the images 11a' and ll on the display device 24.
While looking at b', move the device casing back and forth, left and right, and up and down so that both images match as shown by the dotted line ``R'' and their centers approximately coincide with the intersection Q.

FIG. 6 shows another example of the display format, in which a signal corresponding to the upper half screen frame of the detector 14 is inputted from the video signal processing circuit 21 to the video synthesis circuit 23. on the other hand,
A signal corresponding to the lower half screen frame of the detector 15 is inputted from the video signal processing circuit 22 . Both human power signals are combined in a video signal combining circuit 23 and displayed simultaneously on a display device 24. In this display, when the working distance is inappropriate, the images 11a' and 11b' are shifted from each other in the left and right directions. Furthermore, the alignment deviation in the horizontal and vertical directions is displayed as a difference in the division ratio of the index images 11a' and 11b'. The measurer places the separation index image 1 as indicated by the dotted line
The device is moved back and forth, left and right, and up and down so that 1a' and llb' match and the center thereof substantially coincides with the intersection Q.

[Cornea shape detection]

When the rough alignment described above is completed, the detectors 14 and 15
The detection signals from the counters are input to counting circuits 31 and 32. The counting circuit 31, as shown in FIG.
is scanned to obtain a binarized signal for each pixel based on a predetermined threshold level. Pixels on which the projection index image is projected output a signal "1", and pixels on which the projection index image is not projected output a signal -"O". Further, address information E (xSy) of the pixel that outputs the signal "1" is detected.

Similarly, the counting circuit 32 detects address information of the pixel onto which the projection index image is projected based on the detection output of the detector 15. The address information detected by the counting circuits 31 and 32 are both input to the arithmetic circuit 33.

The arithmetic circuit 33 calculates each address information E of the index image 11'.
For (x, y), perform the following calculation to find the center point G of the index image. That is, from the address information E (x, y), y, S of the pixel pair EISE2 having the same address Xa
Find y, +yb/2-+'lp from address yb and calculate P+(
Find the address of xa%+yp). Similar calculations are performed for other pairs of pixels having the same X address to find midpoints Pl(]-1, 2, --n), and a straight line P passing through these midpoints P. Next, from address information E (XSV), pixel pair E5 (Xe
% 5'a), select E6 (xfSye), and select Xe +
'Jt/2'' Calculate tXq and find the midpoint Ql(I
Find XQ, ye). Similarly, the midpoint Qi(i
=1.2.3---n) and find a straight page passing through these midpoints Q1. The center G of the index is found from the intersection of these two straight lines ",".

Next, address information E (x
The radial distance Pwt (FIG. 4) of Sy) is determined in at least three directions using the following equation.

P w 1(θ+) −(R, −R2)CO82(θ+
-A)+R+ Here, R,, R2 are the radii of curvature of the cornea in two mutually orthogonal directions, and Δ indicates the main axis angle of the cornea. By solving the simultaneous equations of the three calculated equations, the radius of curvature R, , R2 of the cornea and the main radial axis angle A can be determined. The measurement results R2 and Δ are digitally displayed on the display device 34.

If there is an error in the working distance, the projection magnification of the target projected image onto the detector 14, 15 will change, resulting in a measurement error. However, in the present invention, the center G of the index projection image is determined, and when G takes a predetermined address, that is, a different address from the address at which it should be located at the correct working distance, the amount of deviation is calculated. This amount of deviation and lens 16
, (2) From the magnification of 7, calculate the size of the index image when the device is located at the normal working distance. The address information R1, R2, A of the index image obtained by this calculation is calculated. Therefore, in the apparatus of the present invention, it is not necessary to precisely adjust the working distance. Also,
If the detection surfaces of the detectors 14 and 15 are made sufficiently larger than the projected target image, the alignment in the horizontal and vertical directions can be measured because the shape of the projected target image can be determined even if there is some alignment error. be.

In the present invention, the light source 12 may emit either visible light or invisible light (infrared light). Furthermore, by observing the corneal reflection image 11' of the slit 11 with an anterior segment magnification observation means (not shown), it is possible to determine whether there is irregular astigmatism in the cornea to be examined from the disturbance of the reflection image 11'. It is also possible to determine the amount of irregular astigmatism by detecting this reflected image with the detectors 14 and 15. Furthermore, in the example of FIG. 6, instead of using the anterior segment magnification observation means, the detector 14.1
5 can also be used as an anterior segment observation means.

Effects of the Invention As described above, the present invention detects a circular index projected on the examined cornea from two directions, and calculates the radius of curvature of the cornea from this detection output. It has the advantage of being easy to combine with machinery.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the optical device and electrical system of the device according to the present invention, Fig. 2 is an optical path diagram showing the optical path of light from the index entering the detector, and Fig. 3 is a diagram showing the optical path of the detected index image. A schematic diagram showing the method of determining the center, FIG. 4 is a schematic diagram showing the principle of determining the corneal shape, FIG. 5 is an explanatory diagram showing an example of a display method, and FIG. 6 is an explanatory diagram showing another example of the display method. It is. 11... Slit index, 16.17... Lens, 14.25... Detector, 20... Alignment system, 30... Corneal shape detection system. Figure 5 Figure 6

Claims (1)

[Scope of Claims] An index projecting means for projecting one circular index onto the cornea to be examined; and two different opposite images of the circular index by the cornea.
An appropriate projection position and projection index shape are determined based on two detection means that detect from two directions and the amount of deviation of the projection position of the index image onto the detection means from a predetermined position. and calculation means for determining the radius of curvature of the cornea based on the index projection image.