JPH06102B2 - Keratometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a keratometer for automatically measuring a radius of curvature of a cornea.

Problems of the Prior Art As a keratometer, various measuring methods and measuring devices have been proposed and put into practical use. However, the conventional methods and devices have a complicated configuration and are not suitable for automation.

Further, the device is large due to the complicated configuration, other ophthalmologic devices, such as an autorefractometer, a fundus camera,
It has been difficult to fabricate an integrated multi-function machine in combination with a surgical microscope.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above conventional problems and provide a new and useful keratometer that has a simple structure and is suitable for combination with other ophthalmologic machines.

Example Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is an optical layout diagram and a block diagram of an electric system showing the present invention. The index plate 10 is formed with an annular slit 11 having a center on the optical axis A of the apparatus. Behind the slit 11, there is an index illuminating section including an annular light source 12 and a reflecting mirror 13. The light from the slit 11 is reflected by the cornea C of the eye to be examined, as shown in FIG. 2, to form a circular virtual image 11 '. The light from the virtual image 11 ′ is the index plate 10
Through the lenses 16 and 17 provided on the detectors 14 and 1,
5, respectively.

In the present embodiment, the detectors 14 and 15 are composed of area CCDs, and the detection signals thereof are sent to the video signal processing circuits 21 and 22 of the alignment detection system 20 and the detection signal counting circuits 31 and 32 of the corneal shape measuring system 30. Is output.

[Alignment detection]

The alignment detection system 30 in this embodiment is used for coarse alignment adjustment for capturing an eye to be inspected in the visual field of the apparatus. The detection signals from the respective detectors 14 and 15 are converted into video signals by the video processing circuits 21 and 22, and the video signals from both detectors are combined by the video signal synthesizing circuit 23, and a display composed of a CRT or a liquid crystal display is displayed. An image is displayed on the device 24, for example, as shown in FIG.

In FIG. 5, 11 a ″ indicates the index image by the detector 14, and 11 b ″ indicates the index image by the detector 15. When the alignment is incomplete, that is, when the working distance between the eye to be inspected and the device is not within the normal distance, both images 11a ″ and 11b ″ are displayed as deviated, as shown in FIG. Further, when there is a deviation in the left-right and up-down directions in a plane perpendicular to the optical axis to be inspected, the center of the image is displayed with a deviation from the intersection Q of the reticle lines 40 formed on the display surface. The measurer views the images 11a ″, 11 on the display device 24.
While looking at b ", the device housing is moved back and forth, left and right, and up and down so that both images are aligned and the center is substantially aligned with the intersection Q, as shown by the dotted line".

FIG. 6 shows another example of the display format. A signal corresponding to the upper half screen frame of the detector 14 is input from the video signal processing circuit 21 to the video synthesizing circuit 23. on the other hand,
A signal corresponding to the screen frame of the lower half of the detector 15 is input from the video signal processing circuit 22. Both input signals are combined in the video signal combining circuit 23 and are simultaneously displayed on the display device 24. In the display, when the working distance is incorrect, the images 11a ″ and 11b ″ are shifted from each other to the left and right. The misalignment in the left-right and up-down directions is displayed as the difference in the division ratio of the index images 11a ″ and 11b ″. The measurer moves the device back and forth, left and right, and up and down so that the separation index images 11a "and 11b" match as indicated by the dotted line "and the center thereof substantially matches the intersection Q".

[Corneal shape detection]

When the above rough alignment is completed, the detectors 14 and 15
The detection signal from is input to the counting circuits 31 and 32. The counting circuit 31, as shown in FIG.
Are scanned, and a binarized signal is obtained for each pixel with reference to a predetermined threshold level. The pixel on which the projection index image is projected outputs the signal “1”, and the pixel which is not projected outputs the signal “0”. Further, the address information E (x, y) of the pixel that outputs the signal "1" is detected.

Similarly, the counting circuit 32 detects the address information of the pixel on 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 determines the address information E of each index image 11 '.
For (x, y), the center point G of the index image is obtained by the following calculation. That is, from the address information E (x, y), the same _{x a} pixel pairs _E 1 having address, _{E 2} of _y a, _y from address _{b y a + y b / 2 =} 1 y p the determined _P 1 _{(x a} ,
₁ y _p ) to find the address. The same calculation is performed for other pixel pairs having the same x address, and the midpoint P _i (i = 1,
2, −−n), and a straight line P passing through these midpoints P _i is obtained. Next, from the address information E (x, y), a pixel pair E ₅ (x _e , y _e ) and E ₆ (x having the same y address, for example, y _e address)
_f , y _e ) is selected and x _e + y _f / 2- _i x _q is calculated to obtain the midpoint Q ₁ ( _i x _q , y _e ). Similarly for midpoint Q
_i (i = 1,2,3−−n) is calculated and a straight line passing through these midpoints Q _i is calculated. The center G of the index is determined from the intersection of these two calculated straight lines.

Next, the address information E (x, with the obtained center G as the center,
The radial radial distance P _i (FIG. 4) of y) is obtained in at least three directions by the following equation.

Pw _i (θ _i ) = (R ₁ −R ₂ ) cos ₂ (θ _i −A) +
R ₁ Here, R ₁ and R _d are the radii of curvature of the cornea in two directions orthogonal to each other, and A is the main radial axis angle of the cornea. The radii of curvature R ₁ , R ₂ of the cornea and the main radial axis angle A can be obtained by solving the simultaneous equations of the three equations produced. The measurement results R ₁ , R ₂ , and A are digitally displayed on the display device 34.

If there is an error in the working distance, the projection magnification of the index projection image on the detectors 14 and 15 changes, which causes a measurement error. However, in the present invention, the center G of the index projection image is obtained, and when G has a predetermined address, that is, an address different from the address that should be located when the working distance is correct, the deviation amount is calculated. This shift amount and the lens 16,
From the magnification of 17, the size of the index image when the device is located at the normal working distance is calculated. The address information R ₁ , R ₂ , and A of the index image obtained by this calculation is calculated. Therefore, the device of the present invention does not require precise adjustment of the working distance. Further, if the detection surfaces of the detectors 14 and 15 are made sufficiently larger than the projected index image, the shape of the projected index image can be obtained even if there is some alignment error in the alignment in the left-right and up-down directions. It is possible.

In the present invention, the light source 12 may emit either visible light or invisible light (infrared light). Also slit 11
By observing the corneal reflection image 11 'of FIG. 2 by an anterior segment magnifying observation means (not shown), it is possible to know from the disturbance of the reflection image 11' whether or not there is irregular astigmatism of the relative cornea. It is also possible to obtain the amount of irregular astigmatism by detecting this reflected image with the detectors 14 and 15. Further, in the example of FIG. 6, instead of using the anterior segment magnifying observation means, the detectors 14, 1 are used.
5 can also be used as an anterior segment observation means.

EFFECTS OF THE INVENTION The present invention detects the circular index projected on the cornea to be inspected from two directions as described above, and obtains the radius of curvature of the cornea from the detected outputs. It has the advantage that it can be easily combined with a machine.

[Brief description of drawings]

FIG. 1 is a diagram showing a block diagram of an optical device and an electric system of an apparatus according to the present invention, FIG. 2 is an optical path diagram showing an optical path through which light from an index enters a detector, and FIG. 3 is a detection index image. FIG. 4 is a schematic diagram showing a method of obtaining a center, FIG. 4 is a schematic diagram showing a principle of obtaining a corneal shape, FIG. 5 is an explanatory diagram showing an example of a display system, and FIG. 6 is an explanatory diagram showing another example of the display system. Is. 11 ... Slit index, 16, 17 ... Lens, 14, 25 ... Detector, 20 ... Alignment system, 30 ... Corneal shape detection system.

Claims (1)

[Claims] 1. An index projection means for projecting an index on a cornea to be examined, a detection means for detecting reflection images of the index by the cornea from at least two different directions, and an index image on the detection means. An appropriate projection position and a projection index shape are calculated based on a deviation amount of the projection position from a predetermined position, and a computing means for calculating the radius of curvature of the cornea based on the index projection image thus obtained. Characteristic keratometer.