JPS5928945A - 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 relates to a corneal shape measuring device for measuring the radius of curvature, refractive power, degree of astigmatism, pace curve of a contact lens, etc. of the cornea.

Conventional keratometers include devices such as the so-called Sacliff type and IJ) Mann type, but these all project a projection index for measurement onto the cornea of the eye to be examined from the circumferential direction of the objective lens, and calculate the reflected corneal image. The size is observed using a measuring optical system equipped with a matching system, and the radius of corneal curvature and corneal refractive power are determined from the amount of movement of the prism, etc. of the matching system. Each of these methods has the following advantages and disadvantages.

In other words, the Sacliff-type keratometer is easy to use because a circular slit-shaped projection index is projected onto the cornea, so corneal astigmatism and disturbances in the reflected image due to tears can be seen from the appearance of the corneal reflection image.
There is a drawback that if the distance between the projection index and the eye to be examined deviates from the proper position, an error occurs in the measured value.

On the other hand, with the Stoman type keratometer, it is possible to obtain accurate measurement values with little error even if the distance between the projection index and the eye to be examined deviates slightly from the proper position, but the index only measures a specific meridian direction relative to the cornea of the eye to be examined. However, since it only projects images, it has the disadvantage that it is difficult to grasp the state of corneal astigmatism.

An object of the present invention is to integrally form a circular slit-shaped projection index and a projection lens consisting of a toric cylindrical lens for optically projecting the projection index onto the cornea from an infinite distance, thereby changing the optical axis of the projection lens. The objective is to create an accurate keratometer that matches the projection index with high accuracy, can be produced at low cost, and does not cause measurement errors even if the distance between the cornea of the eye being examined and the index deviates slightly from the optimal position. Some 0
The present invention will be described in detail below according to the drawings.
Ec indicates the cornea of the eye to be examined. Reference numeral 1 denotes an index projection lens, and the projection light exit side of the front surface is an annular cylindrical lens surface, and a circular slit projection index 2 as shown in FIG. It is drawn and integrated directly onto the projection lens 1 by vapor deposition, painting, or the like. The light source for illuminating the projection index 2 may be, for example, an annular strobe, an annular fluorescent lamp, or a plurality of minute light sources (for example, light emitting diodes) arranged on the circumference.

Here, the projection lens 10 is a toric cylindrical lens that has refractive power in each meridian direction and has no refractive power in the direction perpendicular to this, that is, in the circumferential direction. It has an aperture of 5 and constitutes a telescopic link optical system.

A position detection element 6 is provided at the imaging position of the objective lens 4. As the position detection collector 6, a one-dimensional image sensor such as a CCD, a one-dimensional photodiode array, a two-dimensional image sensor, etc. is used. light source 3
are arranged concentrically around the optical axis X of the objective lens 4.

As a result, within a cross section including the optical axis X as shown in FIG. It is converted into a parallel light beam and projected onto the cornea EcK.

Due to the convex mirror action of the angle JiEc, a corneal reflection image 2' (virtual image) of the projection index 20 is formed, but since the index projection optical system illuminates the subject's eye with a light beam from infinity as described above, the projection index and Even if the distance to the cornea Ec deviates slightly from the optimum distance, the size of the corneal reflection image 2' does not change.

Furthermore, since the imaging optical system that forms the corneal reflection image 2' on the position detection element B is a telescopic link system, the size of the projected image 7 of the membrane reflection image 2' does not change. Due to the cooperative action of the imaging optical system, even if the subject's eye moves slightly in the optical axis direction, the size of the corneal reflection image 2' does not change, and no measurement error occurs.If the cornea Ec is a perfect sphere at zero, The corneal reflection image 2' is a perfect circle, but since the cornea Ec is generally a toric surface, the corneal reflection image 2' is often an ellipse.

Therefore, in order to measure the shape of the corneal reflection image 2', a measurement system for determining an elliptical shape is generally required. FIG. 6 is a diagram of an embodiment of this measurement system.

This uses a one-dimensional photodiode array as the position detection confectionery 6, and rotates and scans it around the measurement optical axis It is detected and calculated electrically.

If this elliptical shape is converted, the radius of curvature of the cornea, the degree of astigmatism,
The astigmatism axis direction can be calculated.

Note that the measurement system is not limited to this, and may have a configuration in which a plurality of, for example, three one-dimensional photodiode arrays are arranged in a predetermined positional relationship, or a two-dimensional image element may be used for instantaneous automatic measurement. .

In addition, in order to observe the external appearance and the corneal reflection image when aligning the cornea Ec and the measurement system, a light splitting mirror 7 (for example, a half mirror) is installed in the measurement optical path.

Dichroic mirror) It is convenient to provide an observation optical system having trirelay lenses 8, 9, a mirror 10, and an eyepiece 11. Note that when a dichroic mirror is used as the light splitting mirror 7, it is preferable to separately provide an illumination light source that emits a light flux to be guided to the m-alignment optical system, that is, a light flux that is reflected by the light splitting mirror 7 in FIG.

FIG. 4 shows a second embodiment of the present invention, which attempts to improve the performance of the target projection optical system.

It is desirable that the light beam that projects the projection index 102 of the circular slit onto the cornea is a completely parallel light beam in the meridian direction including the optical axis X. Therefore, by making the cross-sectional shape in the meridian direction of the cylindrical lens of the projection light exit surface of the target projection lens 101 of the present embodiment a multidimensional curve, that is, by making it a special shape similar to the aspherical lens with respect to the spherical lens, the projection light can be projected. The luminous flux is made to be close to a perfectly parallel luminous flux. The rear surface of the projection lens 101, on which the projection index 102 is formed, is substantially perpendicular to the projection light beam, so that the illumination light from the light source 3 is efficiently incident thereon.

112 is an expansion membrane member, which is made of a transparent circular flat plate as shown in FIG. Protecting. The protective member 112 has a diaphragm function consisting of an annular light transmitting portion that transmits only the effective light beam of the target projection irradiation light beam and blocks other light.

6 shows a sixth embodiment, which is an application example for measuring the shape of not only the central part of the cornea Ec but also the peripheral part, and the index projection lens 201 has a plurality of toric cylindrical lenses arranged concentrically. A projection index 20 of a plurality of circular slits is provided, each corresponding to the rear focal point position of the cylindrical lens.
2 is provided.

As described above, according to the present invention, an index projection optical system for corneal shape measurement that does not change the size of the corneal reflected image even if the distance between the projection index and the cornea of the eye to be examined deviates from the optimum position is produced with high precision and at low cost. It can be provided at a low cost.

By combining the target projection optical system of the present invention with an IJ-type imaging optical system and an automatic measurement system that uses a one-dimensional photodiode array or two-dimensional image confectionery as the detection section, it is possible to accurately measure the working distance. This makes it possible to easily realize an automatic corneal shape measuring device with a wide tolerance for alignment (distance between the device and the cornea of the eye to be examined).

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the first embodiment of the present invention, FIG. 2 is a diagram of a circular slit index, FIG. 3 is an explanatory diagram of a shape detection section of a corneal reflection image, and FIG. 4 is a diagram of a second embodiment of the present invention. Figure 5 is an explanatory diagram of a protective member with an aperture function of the projection optical system, Figure 6 is a diagram of the third embodiment of the present invention, Ec in the figure is the cornea, and 1,101.201 company Index projection lens, 2゜102.202 a Projection index, 2' is a corneal reflection image of the projection index, 2'' is a projected image after corneal reflection, 3 is a light source, 4
5 is an objective lens, 5 is an aperture, and 6 is a detection element. Applicant Canon Co., Ltd. Haku 47 F, 5 (2) Mootoka

Claims (1)

[Scope of Claims] 1. In an apparatus for projecting a predetermined index onto the cornea of a subject's eye and measuring the corneal shape from a corneal reflection image of the index, the means for projecting the index is a means for projecting the index from an infinite distance. ,
A corneal shape measuring device characterized in that the projection means and the index are provided integrally. 2. The corneal shape measuring device according to claim 1, wherein the projection means has a toric cylindrical surface that has refractive power in each meridian direction and has no refractive power in the circumferential direction perpendicular thereto. 3. The corneal shape measuring device according to claim 2, having a plurality of annular cylindrical surfaces arranged concentrically in each meridian direction. 4. Claim 2 in which the same medium has the same refractive index from the toric cylindrical surface to the focal point in each meridian direction
The corneal shape measuring device according to item 1 or 3. 5. A corneal shape measuring device according to claim 4, in which a projection index is provided at a focal position in each meridian direction. 6. Claim 1, in which a transparent protection plate is provided on the exit side of the projection means. The corneal topography measurement device described. 7. The corneal shape measuring device according to claim 6, wherein the protection plate has an aperture function that blocks light other than the effective light beam of the projection means. 8. The corneal shape measuring device according to claim 5, wherein the projection index is annular and is provided at right angles to the projection optical axis in each meridian direction. 9. The projection index is circular and the projection optical axis 1 is aligned in each meridian direction.
The corneal shape measuring device according to claim 5, which is provided at the third point /Cf1Jr.