JPS5867233A - Apparatus for measuring cornea shape - 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 is an apparatus for optically measuring the corneal shape of an eye to be examined, in particular, a device for measuring the corneal curvature, degree of astigmatism, and astigmatism axis direction in a small area of the eye to be examined by projecting an index from the direction of the measurement source axis. This article relates to a corneal topography measuring device that can be used.

Corneal shape 6111 determination devices generally measure corneal curvature, degree of astigmatism,
It is used to measure the three elements along the astigmatism axis, but it is also used to test the pace curve of contact lenses. Conventionally, a corneal shape measuring device called an ophthalmometer or a keratometer has been known, which projects an index obliquely onto the measuring light 111 (7) to measure the relatively large 1.alpha region of the eye to be examined. (about 4 mm in diameter). However, with this method, it is impossible to measure the corneal shape in the vicinity of the measurement source axis.

By measuring the corneal shape in the vicinity of the measurement optical axis in a spot-like manner and performing this at a plurality of different locations, it becomes possible to measure the corneal shape in micro areas, for example, areas with a diameter of about 2 mm, compared to the conventional method.

In view of the above points, an object of the present invention is to provide a novel corneal shape measuring device that can measure the corneal shape in a small region of an eye to be examined.

The purpose of this is to project the index onto the subject's eye from the direction of the measurement optical axis using an imaging lens, move at least one of the index and the imaging lens in the direction of the optical axis, and direct the corneal reflected light onto the image plane of the imaging lens. The corneal curvature is calculated by observing the object and measuring the moving distance of the two points that are in focus. achieved.

Here, the optical receiver output becomes maximum at two positions on the optical axis: an optical position where the corneal surface position is conjugate with the index, and an optical position where the corneal curvature center position is conjugate with the index. Note that the index position and the light receiving position are provided at optically conjugate positions.

By the way, the corneal surface can generally be considered a toric surface,
If the above measurement in one meridian direction is performed in other meridian directions, particularly in the three meridian directions, the corneal curvature, astigmatism degree, and astigmatism axis direction can be determined.

Hereinafter, the present invention will be described in detail using the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. A light source 1 illuminates a slit plate 2 which serves as an index provided on the optical axis, and the light beam from the slit opening of the slit plate 2 as shown in FIG. 2 passes through a light splitting member 3 and is covered by an imaging lens 4. The cornea Ec of the optometrist E is irradiated.

The reflected light from the cornea Ec passes through the imaging lens 4 again, is reflected by the light splitting member 3, and is split into three beams by the light splitting member 5°6, as shown in Figure 3 tA) (B) Ic) The light is received by the light receiving element 10.11.12 provided on the image plane of the imaging lens 4 through the mask plate 7.8.9. The slit openings of the slit plate 2 and the mask openings of the mask plate 7.8.9 correspond in each meridian direction, and each has a narrow opening width in the measurement meridian direction^Here, the imaging lens 4 is directed in the direction of the light 111 as shown by the arrow. When moved, the light receiving element 10 is located at a lens position where the apex positions of the slit plate 2 and the cornea Ec are conjugate.
, 11.12 first shows the maximum value. Imaging lens 4
When further moved in the optical axis direction, the slit image moves by the value of the radius of corneal curvature (7), that is, at the lens position where the slit plate 2 and the center of corneal curvature are conjugate, and the light receiving element 1 is moved again.
The outputs of 0, 11, and 12 show the maximum values.

Therefore, the amount of movement of the imaging lens 4 in the optical axis direction has a certain correlation with the corneal curvature radius in the measurement meridian direction. Point B will be discussed in detail later.

By the way, the eye to be examined generally has astigmatism, and the corneal surface can be regarded as a toric surface rather than a spherical surface.

From this, the movement i of the imaging lens 4 in the optical axis direction at which the output of the light receiving elements 10, 11, 12 becomes maximum is generally different. Here, since the change in the radius of curvature of the toric surface in the meridian direction changes sinusoidally, it is possible to calculate the corneal shape if it is determined in at least three meridian directions. That is, when the radius of curvature k Rs and the angle in the meridian direction are θ, it is generally expressed as R=A sin(2θ0a ) + B. Here, the unknown quantities A, B, and α are determined by measuring the corneal curvature in the three meridian directions. A, B, .

α corresponds to the degree of astigmatism, the average corneal curvature, and the direction of astigmatism, respectively.

First, in the one shown in FIG. 4, the index 2 is fixed and the imaging lens 4 is moved in the optical axis direction. Slit plate 2
and the cornea EC are conjugate, and the imaging lens 4 and the cornea E
c is the optical axis length of a1, the optical axis length of the imaging lens 4 and the slit plate 2 is bo, the corneal curvature radius is R1, the focal length of the imaging lens 4 is f, +, ta, 1'S1 Assume that the image/lens 4 is moved by X in the optical axis direction, that is, at the position 4', the photoreceiver output shows a maximum value.

The following two equations are clear from the imaging-related equations.

a]-R-x ”bo+x=end (2
)By the way. is set to a predetermined amount in advance by the measuring device, and a is also correspondingly calculated as a constant from equation (1). It is understood from this that the radius of corneal curvature R can be determined by detecting the amount of movement z of the imaging lens in the optical axis direction.

In addition, slit 2 and angle jf! When Ec is the same size and has a conjugate relationship, that is. = 2f, equation (3) is simplified as follows from a=2f.

However, the amount of movement x of the imaging lens 4 can be determined accurately using an encoder or the like.

In FIG. 5, the imaging lens 4 is fixed, contrary to the case in FIG.
The indicator 2 moves in the direction of the light beam 1.

When an index image is formed on the cornea Ec, the optical axis length of the eye Ec to be examined and the imaging lens 4 is a. ,fi! 7 If the optical axis length of the image lens 4 and the index 2 is equal to y, and the moving distance of the index 2 at which the light receiver output becomes maximum is y, then the following formula holds true from the image formation formula.

11 ao+hyaku-ryu (5)1
1 1 R+ ao+b y = f (6) Now, in this method, the optical axis length a of the eye Ec and the imaging lens 4. Although it is relatively difficult to measure, for example, it is possible to determine 11411 by detecting that the slit plate 2 and the cornea Ec have a conjugate relationship at the same magnification.

That is, from the same-magnification system, ao=b=2f, and equation (7) becomes as follows.

. This method calculates the curvature of one corner by detecting the extremely large output power, but it requires conversion using equation (3) or equation (7), which is relatively complicated.

The system shown in FIG. 6 is a practical system that eliminates the above-mentioned complications. In this method, the imaging lens 4 and the index 2 are moved integrally in the optical axis direction. If the moving distance in the optical axis direction at which the conjugate position of index 2 becomes the corneal LCH corneal curvature center position is 2, then 11 1100. = Completed (9) From now on R =
Z, and the measured value of the moving distance becomes the radius of curvature, which is convenient.

Although only the relative relationship between the index 2 and the imaging lens 4 has been described in the above principle explanation, the position of the imaging surface, that is, the light receiving surface is always set at a position equivalent to the index 2. That is, when adopting the method shown in FIGS. 5 and 6, the part surrounded by the broken line in FIG. Board 2
are always kept in an optically conjugate relationship.

FIG. 7e shows a second embodiment of the device of the present invention.

This is done by eliminating the light splitting members 5 and 6, and also by preventing blurring in the longitudinal direction of the slit from being picked up.

The slit plate 2 opens slits in three meridian directions, for example, every 120° in the circumferential direction, as shown in Figure 8 CB).
A flat mask plate 13 shown in FIG. Mask board 13
The mask opening is made more difficult in the longitudinal direction than the slit opening in the slit plate 2', so that blurring in the longitudinal direction of the slit is not picked up. This is done in consideration of lens vomiting in the eye to be examined due to slit projection. ft from each mask opening L1 of the mask plate 13, is directed by the ICE light guide 14, 15, 16 to the light receiving element 10, 11, 12 provided on the end face thereof.

FIG. 9 shows a third embodiment of the device of the present invention.

Light emitted from a light source 17 such as an LED is passed through a lens 18. The image of the light source 17 is focused by the movable lens 20 through the light splitting member 19 onto the vertex of the cornea Ec of the eye E to be examined. The light reflected by the cornea Ec is reflected by the light splitting member 19, passes through the light splitting member 21.22, and is passed through the mask plate 26, 27.28 having an elongated opening in the generatrix direction by cylindrical lenses 23, 24.25.
and enter the light receiving elements 29, 30, and 31, respectively.

The mask plates 26, 27, and 28 are provided at positions conjugate with the light source 17 serving as an index, and are viewed from the optical axis direction.
．． The longitudinal direction of the opening of No. 28 forms an angle of 12σ with the circumferential direction.

When the movable lens 20 is moved in the optical axis direction, when the conjugate position of the light source 17 reaches the corneal surface position, the light receiving elements 29 and 3
The output reaches a maximum at 0.31, and when the movable lens 20 is further moved to a position of 20' and the conjugate position of the photoconductor 17 becomes the center of corneal curvature, the output reaches a maximum again.

The corneal curvature is calculated from the moving distance of the movable lens 20. As described above, if the corneal curvature is determined in the three meridian directions, the degree of astigmatism and the astigmatism 'I11 direction can be calculated from this.

By the way, the present invention has been mainly described with reference to photoelectric detection, but optical detection means detecting the focus state of the target image by corneal reflection with the naked eye.

It should be clearly stated that it may be observed and detected using a microscope, etc.

As described above, according to the present invention, the index is projected from the measurement optical axis direction (
7) It is possible to provide a corneal shape measuring device that can measure corneal shapes such as corneal curvature, curvature, and astigmatism axis direction in a small area of the eye to be examined, and can also automate the measurement.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an embodiment of the present invention device a, Fig. 2 is an explanatory diagram of a slit plate, Fig. 3 (A) () 3) (C) is a diagram of each mask plate, and Figs. The figure is a diagram explaining the principle of the present invention, and Figure 7 is a diagram of an embodiment of g2 of the device of the present invention, r'l'': 8
4 181 is a diagram of a slit plate and a mask plate, respectively, and FIG. 9 is a diagram of a third embodiment (1) of the apparatus of the present invention. E in the figure is the eye to be examined.
Ecfd: cornea, lFi light source, 2.2' is slit plate,
3.5.6 u, light splitting member, 4 is imaging lens, 7, 8
．． 9.13 is a mask plate, 10.11.12 is a light receiving element,
14, 15, and 16 are light guides, and 23, 24, and 25 are cylindrical lenses.

Claims (1)

[Scope of Claims] 1. An apparatus for projecting an index onto the cornea of an eye to be examined and measuring the shape of the cornea using corneal reflected light, comprising an imaging optical system for projecting the index onto the eye to be examined; At least one of the optical system and the indicator is movable in the optical axis direction, and a conjugate position of the indicator by the imaging optical system is a first position at the corneal surface and a second position at the center of corneal curvature. A corneal shape measuring device characterized by measuring the shape of the cornea based on the sense of distance traveled. 2. The corneal shape measuring device according to claim 1, wherein a light receiving element is provided at an image plane position of the imaging optical system. 3. Claim 1 or 2, wherein the imaging optical system is movable in the optical axis direction and the index is fixed.
The corneal topography measuring device described in Section 1. 4. The imaging optical system is fixed, and the index is movable in the optical axis direction.
The corneal topography measuring device described in Section 1. 5. The corneal shape measuring device according to claim 1 or 2, wherein the imaging optical system and the index are movable integrally in the optical axis direction. 6. The corneal shape measuring device according to claim 3, 4, or 5, wherein the index is a slit that is located on the optical axis and has a narrow opening width of 1 in the measurement meridian direction. 7. The corneal shape measuring device according to claim 6, wherein a mask having a narrow aperture width in the measurement meridian direction is provided in the optical path in front of the image plane position of the imaging optical system. The corneal shape measuring device according to claim 6, wherein the corneal shape measuring device is provided in three meridian directions. 9. The corneal shape measuring device according to claim 6, wherein the optical path is divided into three by a light splitting member according to the three meridian directions. 10. The corneal shape measuring device according to claim 7, wherein the longitudinal direction of the opening of the mask is shorter than the longitudinal direction of the slit. 11. The corneal shape measuring device 1a according to claim 7, wherein a light guide is provided between the mask and the light receiving element.