JPS6083641A - Astigmometer - 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 The present invention relates to an astigmatism measurement device that measures the astigmatism angle and degree of astigmatism of an eye to be examined using a liquid crystal astigmatism chart 1.

As a conventional astigmatism measuring device, a method is widely adopted in which the test subject is shown an astigmatism chart made up of a large number of rods arranged in the radial direction. When such an astigmatism chart is shown to a test subject with astigmatic eyes, the density of the bars, that is, the contrast, appears to differ depending on the direction.
To measure diopter, the cylindrical lenses are replaced one after another, and the degree of astigmatism can be calculated from the refractive power of the cylindrical lens when the line density becomes uniform.

In addition, when this astigmatism chart 1 is built into a measurement product, the refractive power of the cylindrical lens located in the middle is sequentially changed.

Furthermore, the conventional device requires a mechanism for generating an arbitrary degree of astigmatism at an arbitrary angle by relatively rotating two concave and convex cylindrical lenses as means for generating astigmatism. However, two stepping motors are required to rotate this lintorical lens, which makes the mechanism quite complex, and since it has mechanically moving parts, it takes time to measure, and it is difficult to obtain accurate measurement values. There are problems such as separation.

An object of the present invention is to provide an astigmatism measurement device that can perform highly accurate measurements at high speed using a liquid crystal astigmatism chart without using mechanical movable parts. The astigmatism chart is formed by means of liquid crystal elements that operate each bar line independently, and the contrast of the liquid crystal element is adjusted by changing the voltage applied between the electrodes of the liquid crystal element, and the contrast of the liquid crystal element is adjusted from the applied voltage value. It is characterized by setting an astigmatism constant.

EMBODIMENT OF THE INVENTION Below, this invention is demonstrated in detail based on the Example of illustration.

FIG. 1 shows a liquid crystal astigmatism chart 1.1 used in an astigmatism measuring device according to the present invention, in which each rod 2 is arranged in the radial direction.
are formed of independently actuated liquid crystal elements as illustrated in FIG.

When a test subject with astigmatism looks at such an astigmatism chart ■, the density of the bar line 2 appears to be different depending on the direction.
This determines the angle of astigmatism, or axis of astigmatism. As shown in FIG. 2, the bar 2a that appears darkest and the bar 2b that appears thinnest generally form a right angle, and are in the astigmatic angle direction and in the radial direction perpendicular to this astigmatic angle direction, respectively.

Next, to measure the degree of astigmatism, use these two wooden sticks 2a and 2b.
Delete the other bar lines 2, leaving only the bar line 2, so that the state shown in FIG. 2 is obtained. Therefore, the voltage V applied to the liquid crystal 3 in FIG.
When gradually changing relative to bars 2a and 2b,
As shown in the graph in Figure 4, the display contrast of the liquid crystal changes, so if you calibrate this contrast ratio and degree of astigmatism in advance, the two wooden bars 2a and 2b in Figure 3 will have the same density. The degree of astigmatism of the eye to be examined can be measured from the applied voltage value when the eye is visible.

FIG. 5 shows an example of an optical system for measuring astigmatism using the liquid crystal astigmatism chart 1 as shown in FIG. This fifth
In the figure, the eye E to be examined looks at a liquid crystal astigmatism chart 1 having a pattern as shown in FIG. 1 through an objective lens 4, an aperture 5, and an imaging lens 6. The relationship between the degree of astigmatism and contrast of the eye E to be examined differs depending on the pupil diameter,
In this example, the diaphragm 5 is placed at a position that is almost conjugate with the pupil of the eye E to be examined, and the light beam incident on the eye E is always kept constant, thereby providing accurate calibration values for the degree of astigmatism and contrast. It is possible to measure astigmatism with high accuracy.

As described above, the astigmatism measuring device according to the present invention eliminates the need for a plurality of cylindrical lenses and their rotation mechanism, which were required in conventional astigmatism measuring devices. A simple, compact, and inexpensive device can be obtained. In addition, 1. Since no mechanical moving parts are required, it is possible to perform high-speed and accurate measurements.

[Brief explanation of drawings]

The drawings show an embodiment of the astigmatism measuring device according to the present invention, in which Fig. 1 is a top view of a liquid crystal astigmatism chart, Fig. 2 is a cross-sectional view of a liquid crystal element, and Fig. 3 is a pattern during astigmatism measurement. FIG. 4 is a graph showing the relationship between applied voltage and contrast, and FIG. 5 is an optical configuration diagram of the astigmatism measuring optical system. Reference numeral 1 is a liquid crystal astigmatism chart, 2 is a bar line of the liquid crystal astigmatism 2 chart, 3 is a liquid crystal, 4.6 is a lens, and 5 is an aperture. Patent Applicant Canon Co., Ltd. Figure 1 Hanging Figure 5 Figure 2 Figure 4

Claims (1)

[Scope of Claims] 1. An astigmatic chart 1 is formed on each bar line arranged in the radial direction by a liquid crystal element that operates independently, and the voltage applied between the electrodes of the liquid crystal element is changed to control the liquid crystal element. An astigmatism measuring device having a contrast and calculating an astigmatism constant from the applied voltage value. 2. The astigmatism measuring device according to claim 1, wherein the liquid crystal element displays two orthogonal bar lines in a predetermined direction, and the contrast thereof is adjusted.