JPS6232934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ophthalmological instruments, and more particularly to keratometers. A keratometer that measures the shape of the cornea is generally used to measure the three elements of corneal curvature, degree of astigmatism, and astigmatic axis direction, but it can also be used to inspect the base curve of contact lenses.

Conventionally, a keratometer, usually called an ophthalmometer or keratometer, projects an inspection mark onto the cornea, observes the reflected image with a microscope, and measures the amount of adjustment until the reflected image reaches a predetermined state.
Alternatively, it is known to project concentric marks onto the cornea and measure from the distortion of the reflected image.

However, with well-known methods, it is not possible to measure the above three elements at the same time, so errors may occur due to the subject's eye movement during measurement, leading to a decrease in accuracy, or even if the test time is short, test data collection The problem was that the subsequent analysis required a long time.

The present invention has the object of enabling short-time testing, shortening the time it takes to obtain results, and achieving high measurement accuracy. Therefore, in the embodiment described later, a two-dimensional position detection element that has been put into practical use recently is used, and multiple signal sequences indicating a light spot on a plane (x ₀ , y ₀ on xy coordinates) output from this element are The shape of the cornea is determined from a curve, which is generally an ellipse, and is a series of light spots. In this case, the shape of the curve will be a circle for a normal cornea, and a circle for a toric surface with corneal astigmatism. Further, it is possible to determine the radius of curvature of the cornea from the size of the circle or ellipse, the degree of corneal astigmatism from the radial ratio, and the direction of the axis of astigmatism from the inclination of the axis of the eclipse. For example, even if it is a circle, there are three variables: the major axis, minor axis, and rotation angle from the reference coordinate axis, so the shape can be determined by pressing three points on the coordinates, and if the center moves The oval shape is determined by hitting at least 6 points.

An embodiment will be described below with reference to the drawings. 1st
The figure shows a longitudinal section, and FIG. 2 shows a front view seen from the cornea side, and in the figure, E is the cornea of the eye to be examined. Reference numeral 1 denotes an analog two-dimensional position detection element, which obtains the incident position of the light beam as an output corresponding to the position on the x and y coordinates, and is sensitive to, for example, an infrared wavelength region. 2 is the imaging lens of the projection system,
L is the optical axis of the projection system. Next, 30 to 37 are minute light sources in the form of points, which are arranged at equal intervals on a circumference centered on the optical axis L, and are sequentially blinked by a control circuit (not shown). Infrared light emitting diodes are suitable as these light sources, but for example, one end of the optical fiber may be placed opposite the lamp, and the other end may be placed in this position, or the light sources may be arranged on a circumference with different radii. You can also add more to retrieve multiple curves and improve accuracy.

Further, the position of the light source in the optical axis direction, the imaging lens, and the arrangement of the two-dimensional position detection element are determined as follows. First, consider the corneal surface as a mirror surface, and assume that a convex mirror with an average radius of the cornea is located at a predetermined position.For example, if the light source 3
4 forms a virtual image 34' on this mirror surface. Therefore, the surface on which the virtual image of the light source is formed and the light-receiving surface of the two-dimensional position detection element are conjugately connected by the imaging lens 2, and the imaging magnification is determined according to the dimensions of the detection element. Note that if the radius of the cornea differs from the predetermined amount, the position where the virtual image of the light source is formed may shift, but it will almost never exceed the depth of field. With the above configuration, when the light sources 30 to 37 blink at intervals commensurate with the response speed of the two-dimensional position detection element, the light beam emitted from the light source 30 is specularly reflected by the cornea Ec, and the two-dimensional position detection element is detected by the imaging lens 2. The light is focused on the light receiving surface of 1. This light focusing position is determined by the light source that emits light and the shape of the subject's cornea.
For example, 30' in FIGS. 3, 4, and 5 indicates the focusing position.

When a light beam is incident on the two-dimensional position detection element 1, an electric signal corresponding to the position (x coordinate, y coordinate) is outputted, and this signal is appropriately processed and stored in the storage circuit. Next, when the light source 31 is turned on,
Since light enters the position 31' and there is a corresponding output, this is stored. When the light source is sequentially blinked in this manner, the light source images are arranged on the closed curve 38 of a circle or a circle on the light receiving surface of the two-dimensional position detection element 1, as shown in FIGS. 3 to 5. Become,
Also, that signal will be stored. A radial curve ax ² that connects each of the stored index image positions
+bxy+cy ² =1 or ax ² +bxy+cy ² +dx+ey
= 1 (when the major axis and minor axis are equal, it becomes a circle), the major axis, minor axis, and rotation angle are calculated.

In Figure 3, the curved line of light source images forms a circle,
Therefore, it can be seen that the cornea is normal. On the other hand, 3
Since the diameter and position of the light source formed by 0 to 37 and the imaging magnification of the lens 2 are fixed, the radius of the cornea can be calculated from the radius of the closed curve. It is assumed that these calculation processes are executed by a microprocessor.

It can be seen that the closed curve 38 in FIG. 4 is an elliptic circle, and is a toric surface with corneal astigmatism, the major axis being horizontal and the minor axis being vertical.

The closed curve 38 in FIG. 5 is also an ellipse, and the cornea is a toric surface with the astigmatic axis tilted from the horizontal axis.

Note that moving the light source or secondary light source along the circumference,
It can also be made to resemble a fixed light source by lighting up at a predetermined position.

The present invention described above has high accuracy because the necessary measurements are completed instantaneously, and the results can be obtained through simple processing, so they can be submitted to the doctor's judgment immediately after the measurements. Furthermore, because of its simple structure, it is inexpensive and can be widely used by ophthalmologists in towns, so it has the effect of increasing the accuracy of disease diagnosis and prescription prescriptions for glasses. In addition, since an analog two-dimensional position detection element is used to detect the center of gravity of the light beam, even if the two-dimensional position detection element deviates from a predetermined position in the optical axis direction and the target image cannot be clearly formed, the corneal shape can be accurately determined. can be measured. That is, the tolerance of the set position of the two-dimensional position detection element in the optical axis direction increases. Furthermore, even if tears adhere to the cornea and the corneal reflection image becomes blurred on the two-dimensional position detection element, accurate measurements can be made.

[Brief explanation of the drawing]

FIG. 1 is an optical sectional view showing the embodiment, FIG. 2 is a front view as seen from the cornea side, and FIGS. 3, 4, and 5 are plan views of the position detection element. In the figure, 1 is a two-dimensional position detection element, 2 is an imaging lens, and 30 to 37 are light sources.

Claims (1)

[Claims] 1. A plurality of point-like indicators sequentially projected onto the cornea in at least three meridian directions on the same circumference, and an imaging optical system that forms corneal reflected images of the indicators on a predetermined image plane. , an analog two-dimensional position detection element located on the predetermined image plane of the imaging optical system, and a mechanism for storing index image position coordinates sequentially detected by the two-dimensional position detection element and connecting each index image position. A keratometer characterized by having means for measuring the corneal shape from a circular curve.