JPS628170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the anterior radius of curvature of the cornea.

Conventionally, keratometers are called ophthalmometers, keratometers, and the like, and are widely used as test instruments for contact lens wear and for detecting corneal inflection abnormalities.

However, in both cases, the measurements are manual and time consuming, and it is extremely difficult to keep the eyeballs from moving during the measurements, resulting in a lack of accuracy.

There are also some that require photographing, which requires extremely troublesome post-processing.

The keratometer of the present invention has been developed in view of the above points, and is designed so that the rear focal position of the main lens almost coincides with the front focal position of the sub-lens, and the diaphragm is placed at that position, facing the cornea. A projection system consisting of a collimator lens, a slit, and a light source is provided at a plurality of positions at different angles with respect to the optical axis of the main lens, and the projection system is configured such that the main lens and the sub-lens are conjugate with the reflected image of the slit of the projection system by the cornea. The present invention is characterized in that an image sensor or the like is disposed at a position, the distance between the reflected images of the slit is read by the image sensor or the like, and the radius of curvature of the anterior surface of the cornea is calculated from this value.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic optical path diagram showing an embodiment of the present invention, FIG. 2 is a perspective view of the embodiment of the present invention, and FIGS.
FIG. 5 is a diagram showing the principle of the present invention.

In the figure, 1 is the main lens, 3 is the sub-lens, 2 is the rear focal position of the main lens 1 and the sub-lens 3
A diaphragm 5 consisting of a perforated reflector placed near the front focal point of the eye is placed at a position conjugate with the reflected image of the cornea 4 of the eye to be measured, with the diaphragm 2, the main lens 1, and the sub-lens 3 in between. It is an image sensor.

Similarly, reference numeral 8 denotes a focus plate 9 placed at a position conjugate with the reflected image of the cornea 4 of the eye to be measured, sandwiching the diaphragm 2 and the main lens 1 and sub-lens 3.
is the eyepiece.

7 is a half mirror for dividing the optical path into the image sensor 5 side and the finder focus plate 8 side, and is placed in front of the sub-lens 3 as shown in FIG. This may be between the sub-lens 3 and the image sensor 5 shown in FIG.

Reference numerals 6 and 6' designate light projecting systems, which face the cornea 4 and are positioned at angles of θ ₁ and θ 2, respectively, with respect to the focal point F on the optical axis A of the cornea ₄ , as shown in FIG.
6a, 6a' are projection lenses; 6b, 6b' are slits placed at the focal points of the projection lenses 6a, 6a'; 6c,
6c' is a light source.

In FIG. 2, reference numeral 10 denotes an illumination system, which includes an illumination lens 10a, an index or diffuser plate 10b, and an illumination light source 10c.

The operation of the keratometer in the present invention will be explained below.

First, a method of determining the distance between the cornea 4 of the eye to be measured and the main lens 1 will be explained.

The light from the illumination system 10 is transmitted from the illumination light source 10c,
The illumination lens 10 passes through the index or diffuser plate 10b.
a to reach an aperture 2 consisting of a perforated reflector. Then, the reflected light from the aperture 2 passes through the main lens 1 and is projected onto the cornea 4, and the reflected light passes through the main lens 1 again, passes through the aperture 2, and reaches the half mirror 7. Here, the optical path is divided into two, one passing through the finder focus plate 8 and the other passing through the sub-lens 3 and reaching the image sensor 5.

At this time, in the focus plate 8, the aperture 2
When the image is in focus, the reflected image of the cornea 4, the image pickup device 5 and the focus plate 8 become conjugate, and the slits 6b and 6b' of the light projection system 6 also become conjugate.

In this state, the light from the light projection systems 6 and 6' is reflected by the cornea 4, passes through the main lens 1 and the diaphragm 2, and is divided by the half mirror 7. One side is sent to the focus plate 8 and the other is sent to the sub lens. 3 through the image sensor 5
reach. At this time, it goes without saying that the projection system 6,
The images of the slits 2b and 2b' of 6' are formed on the image sensor 5.

By the way, the distance h between the points where the light from the light projection systems 6 and 6' is reflected by the cornea 4 is h= _h1 + _h2 =R(where the distances from the optical axis A are _h1 and _h2 , respectively). sinθ ₁ /2 + sinθ ₂ /2)...

Here, R is the radius of curvature of the front surface of the cornea 4.

Further, if the power ratio of the main lens 1 and the sub-lens 3 is M, then H=Mh, and the equation is obtained.

Here, H is the distance between the reflected images of the slits 6b, 6b' of the light projection systems 6, 6' appearing on the image pickup device 5.

Further, if the bit pitch of the image sensor 5 is P and the number of bits is N, then H=PN, and the equation is obtained.

Since P, M, θ ₁ and θ ₂ are known constants,
By counting the number of bits N on the image sensor 5, the radius of curvature R of the anterior surface of the cornea can be measured.

Figure 4 shows the case where the cornea 4 is deviated perpendicularly to the optical axis A, as shown by the dotted line, but in this case, the chief ray after corneal reflection is parallel to the optical axis A, so h = h' and the measurement is made. There is no error.

FIG. 5 shows a case where the cornea 4 is displaced in the optical axis direction as shown by the dotted line, but in this case, the chief ray after corneal reflection remains unchanged, and the center of the blur of the image on the image sensor 5 cannot be taken. There is no measurement error.

As described above, in the present invention, there is no measurement error even if the focusing is slightly shifted in the direction of the optical axis and in the direction perpendicular thereto (the plane where the light projection system is located).

The explanation so far has been based on the case where there are two light emitting systems on both sides, but the same applies if there are multiple light emitting systems, and in that case, the curvature of each part of the corneal cross section can be measured. , it is also possible to know the shape of the corneal cross section. In addition, by rotating this device 90 degrees, the vertical curvature of the cornea can also be measured.
By combining it with a mechanism that detects the rotation angle, it is also possible to measure the degree of astigmatism and the axis of astigmatism.

[Brief explanation of the drawing]

FIG. 1 is a schematic optical path diagram showing an embodiment of the present invention, FIG. 2 is a perspective view of the embodiment of the present invention, FIGS.
FIG. 5 is a diagram showing the principle of the present invention. 1...Main lens, 2...Aperture, 3...Sub lens, 4...Cornea, 5...Image sensor, 6, 6'...Light projection system, 6a, 6a'...Light projection lens, 6b, 6b'...Slit, 6c, 6c'...Light source, 7...Half mirror, 8
...Finder focus plate, 9...Eyepiece lens, 10...Illumination system, 10a...Illumination lens, 10b... Index or diffuser plate, 10c...Illumination light source.

Claims (1)

[Claims] 1 The rear focal position of the main lens and the front focal position of the sub-lens are approximately aligned, and an aperture is placed at that position, and collimator lenses and slits are placed at multiple positions facing the cornea at different angles to the optical axis of the main lens. and a light source, and an imaging device or the like is disposed at a position conjugate with the reflected image of the slit of the projection system by the cornea with respect to the main lens and the sub-lens, and the imaging device or the like is used to capture the reflected image of the slit by the cornea. A keratometer characterized in that the radius of curvature of the anterior surface of the cornea is calculated from this value by reading the distance between the corneal and corneal surfaces.