JPS6214291B2 - - 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. In conventionally known keratometers, an optotype is projected onto the cornea,
A method of measuring the size of the projected image using a microscope has been used. However, with this method, it is not possible to simultaneously measure the three elements, so errors occur due to eye movement of the subject during measurement, resulting in a decrease in accuracy.

An object of the present invention is to improve accuracy by making it possible to measure corneal shape instantaneously.

An embodiment will be described below with reference to the drawings. In the figure, Ec indicates the subject's cornea. Further, 1 is an annular light source, which may be formed by arranging minute light sources,
The slit may be illuminated. Note that an arrangement in which the light sources are not continuous is also possible. Reference numeral 2 denotes a projection lens, and the optical axis X of the projection lens coincides with the center of the annular light source 1, as shown in the axial configuration in FIG.

11 and 14 are position detectors that use a self-scanning one-dimensional photodiode array, and although only two are shown in Figure 1, in reality, as shown in Figure 3, they are equipped with projection optics. 6 (11
~16) It is arranged. The positional relationship between the light source 1 and the detectors 11 to 16 is such that the light receiving surface of the light source 1 and the detectors 11 to 16 is the surface of the cornea Ec, assuming an average radius of corneal curvature as the cornea Ec and considering this surface as a convex mirror. In other words, the virtual image 1' formed by the cornea Ec and the light-receiving surfaces of the detectors 11 to 16 are related to each other so that they are conjugate with respect to the projection lens 2.

Here, when the light source 1 is turned on, if the cornea Ec is spherical, the light source image 1'' will be a circle at the light-receiving surface position of the detector (Fig. 3), and if it is a toric surface with corneal astigmatism, it will be an ellipse. The radius of curvature of the cornea is determined from the size of the circle or ellipse, and the degree of corneal astigmatism is determined from the ellipticity.
The astigmatism axis direction can be determined from the axis direction of the ellipse. For example, when specifying the center of an ellipse, there are three variables: the long axis, the short axis, and the rotation angle from the reference coordinate axis, so the shape can be specified by selecting three points on the coordinates. Therefore, if there is no movement of the center, it is sufficient to have position information on at least three radial directions that are not located on the same radius.

In the above configuration, a virtual image 1' is formed by the specular action of the cornea Ec by illuminating the cornea Ec with the light source 1, and the virtual image 1' is projected onto the detector 11 through the projection lens 2.
16. When the image of the annular light source 1'' crosses each detector in a circular manner as shown in FIG.
It responds to light at points c, d, e, and f, and outputs signals corresponding to the positions that responded to the light. An electrical processing system (not shown) captures and stores these signals,
Applying these to the formula for an ellipse, the results confirm that it is a circle because the major and minor axes are equal, and the radius of the circle is calculated, which further confirms that it is a spherical surface and the radius of curvature. is shown.

On the other hand, when the light source image 1'' becomes an ellipse and crosses each detector as shown in FIG.
.about.16 respond to light at points a', b', c', d', e', and f' in order, and output signals corresponding to the respective positions that responded to the light. In this case as well, the major axis, minor axis, and rotation angle of the axis of the ellipse are calculated, from which the reference radius of curvature, degree of corneal astigmatism, and axial direction are indicated.

In the embodiment described above, if the detectors are operated simultaneously, the measurement ends instantly, which has the effect of preventing the intervention of errors due to movement of the subject's eye and improving accuracy. It is also possible to measure by rotating the detector around the rotation axis, but the advantage of fixing it radially in advance is that the measurement time is shorter, a rotation mechanism is not required, and the electrical processing circuit is simpler. There is. When fixedly installed radially as in the present invention, the corneal reflection image of the annular index is approximately orthogonal to the one-dimensional optical position detection means arranged radially, so the measurement range can be larger and the measurement accuracy can be increased compared to when the index is obliquely arranged. It is also suitable for automatic measurement. In addition,
It is preferable to use invisible light such as infrared rays as the measurement beam because it does not make the subject nervous.

[Brief explanation of the drawing]

FIG. 1 is an optical cross-sectional view showing one embodiment of the present invention.
Figure 2 is a view seen from the optical axis direction. FIG. 3 and FIG. 4 are diagrams showing a detector and a reflected image. In the figure, 1 is an annular light source, 2 is a projection lens, 11
~14 is a position detector, Ec is a cornea, and X is an optical axis.

Claims (1)

[Scope of Claims] 1. An annular index projected onto the cornea, an imaging optical system that forms a corneal reflected image of the index onto a predetermined image plane, and a A keratometer comprising one-dimensional optical position detectors arranged radially in at least three meridian directions around the optical axis of the imaging optical system. 2. Claim 1, wherein the one-dimensional optical position detector is a self-scanning photodiode array.
Keratometer as described in section.