JPS6248496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ophthalmological measuring device, particularly a corneal topography measuring device.

A keratometer that measures the shape of the cornea is generally used to measure corneal curvature, corneal refractive power, corneal astigmatism, and corneal astigmatism axis direction, but it can also be used for tests such as measuring the curvature of the surface of contact lenses. There is.
Conventional keratometers include devices based on the principles of the so-called Sacliff method and Litman method, but all of them project a measurement projection index onto the cornea of the eye to be examined from the circumferential direction of an objective lens, and measure the size of the corneal reflection image. It was viewed using a measuring optical system equipped with a matching system, and the corneal curvature semi-longitudinal and corneal refractive power were determined from the amount of movement of the prism, etc. of the matching system. With these methods, measurement takes time, and if the subject's eye moves rapidly, it is difficult to measure and errors occur.

In addition, since the Sacliff-type keratometer projects a circular slit-shaped projection index onto the cornea, it is easy to use because it allows you to see corneal astigmatism and disturbances in the reflected image due to tears from the appearance of the corneal reflection image. There was a drawback that if the position of the optometrist deviated from the proper position, errors would occur in the measured values.

On the other hand, with the Litman type keratometer, even if the distance between the projection index and the eye to be examined deviates slightly from the proper position, accurate measurement values can be obtained with few errors. Since only the index is projected, it has the disadvantage that it is difficult to understand the state of corneal astigmatism.

SUMMARY OF THE INVENTION An object of the present invention is to provide a corneal shape measuring device that takes a short measurement time, is less prone to measurement errors, and is easy to operate.

In other words, even if the distance between the measuring device and the eye to be examined deviates from the optimal distance, the measurement error is small, and
This corneal shape measuring device is less likely to cause errors due to movement of the subject's eye and can accurately measure corneal curvature, astigmatism, etc. Moreover, the external image of the subject's eye and the corneal reflection image of the measurement projection index are always displayed on the same screen. By making it possible to observe, alignment operations are made easier.
The present invention aims to provide a corneal shape measuring device that can monitor whether a corneal reflection image is disturbed by lachrymal fluid, irregular astigmatism, or the like.

The purpose of this is to illuminate the measurement index with a continuously lit observation light source and a measurement light source that momentarily lights up at high intensity only during measurement, and to project the index onto the cornea of the eye to be examined. A corneal reflection image is created by projecting an infinite beam onto the object, and the corneal reflection image is focused on the light-receiving surface of the measurement detection element using a telecentric optical system.The signal of the detection element is electrically processed to obtain a measurement value. This is realized by the apparatus of the present invention, which includes a measurement system and an observation system for observing the test site.

According to the present invention, during measurement, the amount of irradiation is small because it passes through a small-diameter aperture in a telecentric system, and therefore a high-intensity light source is used instantaneously to provide a sufficient amount of light to the measurement system in a short time. On the other hand, the observation system uses a continuously lit light source and is constantly observed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of one embodiment. E indicates the eye to be examined and E _C indicates the cornea. 1 is a projection lens that has refractive power in each meridian direction, and has refractive power in the direction perpendicular to the meridian, that is,
It is an annular cylindrical lens that has no refractive power in the circumferential direction. Reference numeral 2 denotes a circular slit projection index, which is arranged near the rear focal point of the projection lens 1. Reference numeral 3 denotes a measurement light source that instantaneously emits high-intensity light to illuminate the projection index 2 only when measuring, and is, for example, an annular strobe. Reference numeral 4 denotes an observation light source, which is made of, for example, an annular fluorescent lamp, and illuminates the measurement index 2 through the control of the measurement light source 3 in a continuous lighting state.

Here, the projection lens 1 is fixed to the outer periphery of a lens barrel 6 that holds an objective lens 5, and the measurement light source 3 and the light source 4 for sightseeing are attached to a light source attachment ring 9 using attachment pieces 7 and 8. Reference numeral 9 has a structure that allows for slight adjustment of movement in the axial direction, and is attached to the outer periphery of the lens barrel 6, forming a concentric circle with the optical axis a of the objective lens 5. Note that the projection index 2 may be attached to and integrated with the projection lens 1.

By the way, in such an index projection system, it goes without saying that the optical axis b of the projection lens 1 and the projection index 2 must match exactly, but the measurement light source 3
It is also desirable that the observation light source 4 also coincide with the optical axis b of the projection lens 1. In particular, when an annular strobe is used as the measurement light source 3, the light emitting part of the annular strobe is a thin circular bright line, so it precisely coincides with the optical axis b of the projection lens 1 along the entire circumference in the meridian direction. Otherwise, the illuminance of the index projection light beam will drop sharply. Therefore, in this embodiment, the screw holes of the mounting pieces 7 and 8 for fixing the measurement light source 3 and the observation light source 4 are made into oval-shaped elongated holes, and the light sources are fixed in a structure that allows eccentric adjustment. Furthermore, by slightly moving the light source mounting ring 9 in the direction of the measuring optical axis, it can be fixed to the lens barrel 6 while being adjusted so that the optical axis b of the projection lens 1 and the light emitting part of the annular strobe coincide. .

Further, the measurement light source 3 and the observation light source 4 are fixed by mounting pieces 7 and 8 shown in FIGS. 2 and 3 in such a manner that the illumination light beam is not kicked. For example, the observation light source 4 has a mounting piece 8 as shown in FIG.
Since the rear tube wall of the observation light source 4 is held at several places and fixed to the light source mounting ring 9 with mounting screws, the light beam illuminating the projection index 2 will not be kicked.

On the other hand, the measurement light source 3 is held by a mounting piece 7 as shown in FIG. 2 in such a way that the inner wall of the inner circumference can be pushed open at several places, and the mounting piece 7 does not kick the measurement light beam. Furthermore, the illumination light beam of the observation light source 4 is also fixed to the light source attachment ring 9 so as not to be kicked.

Another method is to hold and fix the measurement light source 3 and the observation light source 4 with a mounting piece made of a transparent material as shown in FIG. 4, which can also fix the illumination light beam without kicking it. According to the above-mentioned index projection means, the projection index 2 illuminated by the observation light source 4 and the measurement light source 3
is optically turned into a beam of light from an infinite distance by the projection lens 1 and projected onto the cornea E _C .

This target projection light beam forms a corneal reflection image 2' (virtual image) of the projection target 2 by the convex mirror action of the cornea E _C and is projected onto the cornea E _C as a light beam from an infinite distance by the aforementioned target projection system. Therefore, projection index 2 and cornea E _C
Even if the distance from the corneal reflection image 2' deviates slightly from the optimum distance, the size of the corneal reflection image 2' does not change.

Corneal reflection image 2′ of the projection index 2 obtained in this way
detection element 1 using a telecentric imaging optical system.
If the measurement image 2'' is formed by projecting onto the light-receiving surface of 0, due to the cooperative action of the target projection optical system and the imaging optical system, even if the cornea _E of the eye E to be examined moves slightly in the optical axis direction. The size of the measurement image 2'' of the corneal reflection image 2' does not change, and no measurement error occurs.

By the way, if the cornea E _C is a perfect spherical surface, the corneal reflection image 2' will be a perfect circle, but since the cornea E _C is generally a toric surface due to astigmatism, the corneal reflection image 2' may become an ellipse. many. Therefore, in order to measure the shape of the corneal reflection image 2', a measurement system that obtains an elliptical shape is required.

An embodiment of the measurement system will now be described with reference to FIG.

In FIG. 1, reference numeral 5 denotes an objective lens, and a diaphragm plate 11 is disposed near the focal point on the rear side, and a polarizing prism 12 is fixed close to the rear side. The aperture plate 11 has a shape with five small hole openings in the center, as shown in FIG. 5, and the polarizing prism 12 has five wedge-shaped prism pieces as shown in FIG. They are assembled into an integrated shape, and the small hole opening of the diaphragm plate 11 and the center of the wedge-shaped prism piece of the polarizing prism 12 match.

The corneal reflection image 2' incident from the objective lens 5 passes through the small hole opening of the diaphragm plate 11 and the polarizing prism 12, and is divided into five light beams, which are focused on the light receiving surface of each detection element (for example, a one-dimensional photo-double array). For example, as shown in FIG. 7, a detection element 10 is placed at a position where a reconstructed image 2'' of the corneal reflection image 2' is generated.

In an actual keratometer, the detection signal of the detection element 10 is electrically calculated by a signal processing circuit (not shown) to determine the major axis, minor axis, and elliptical axis of the ellipse of the corneal reflection image 2'. The radius of curvature, degree of astigmatism, and axis angle of the cornea can be calculated by converting.

In the measurement system of this embodiment, the corneal reflection image 2' is detected in five meridian directions, but the detection is not limited to this, and may be detected in three meridian directions, or may be detected using a two-dimensional image element.

By the way, the observation optical system is composed of a light splitting mirror 13 (for example, a half mirror or a dichroic mirror) and an imaging lens 14, and uses a TV camera to monitor the appearance of the eye E and the corneal reflection image 2' of the projection index 2. 1
The image is formed on the imaging plane No. 5. This image is always reproduced on a TV monitor (not shown) so that it can be observed.

As described above, according to the present invention, there is almost no error even when the distance between the measuring device and the eye to be examined is slightly deviated from the optimum position. Since the measurement information can be detected within 30 minutes, accurate measurements can be made even when measuring subjects who are easily mobile, such as infants, which is very useful.

Furthermore, since the corneal reflection image of the measurement projection index illuminated by a continuous light source different from the measurement light source can be observed at the same time as the external image of the eye to be examined, alignment is easy.
In addition, we provide an extremely easy-to-operate corneal shape measurement device that can constantly monitor the measurement area even if it is not kicked by eyelids or eyelashes, and can also confirm that the corneal reflection image is not disturbed by lachrymal fluid or irregular astigmatism. can. Further, according to the present invention, regarding the toric cylindrical lens, a toric measurement light source and a toric observation light source are sequentially provided so that their projection optical axes coincide with each other on the side opposite to the eye to be examined, thereby providing a common circular index during observation and measurement. A common toric cylindrical lens that projects the index from infinity in each meridian direction can be used, allowing for observation and measurement with good illumination efficiency and sufficient light intensity.

[Brief explanation of the drawing]

Figure 1 is a sectional view of an embodiment of the present invention, Figures 2 to 4 are explanatory diagrams of the mounting piece of the light source, Figure 5 is a diagram of the aperture, Figure 6 is a diagram of the polarizing prism, and Figure 7 is a diagram of the polarizing prism. FIG. 3 is an explanatory diagram of a detection element surface. In the figure, E _C is the cornea, 1 is the projection lens for the index, 2 is the projection index, 3 is the measurement light source, 4 is the observation light source, 5
1 is an objective lens, 7 and 8 are light source mounting pieces, 10 is a detection element, 11 is an aperture, and 12 is a polarizing prism.

Claims (1)

[Scope of Claims] 1. A corneal shape measuring device that projects a predetermined index onto the cornea of a subject's eye, observes the shape of the corneal reflection image of the index with an observation system, and measures it with a measurement system, wherein the index is a circular index. and the means for projecting the index is a toric cylindrical lens having refractive power in each meridian direction and no refractive power in the circumferential direction orthogonal thereto, and the circular index is projected in each meridian direction of the lens. A toroidal light source for measurement, whose tube is transparent and emits instantaneous light, and a circular light source for observation are installed at the focal position of the lens, and the projection optical axis thereof coincides with the opposite side of the eye to be examined with respect to the lens. A corneal shape measuring device characterized by having an annular light source arranged therein. 2. The corneal shape measuring device according to claim 1, wherein the measurement system includes a telecentric optical system. 3. The corneal shape measuring device according to claim 1, wherein the circular index is integrated with the annular cylindrical lens. 4. The index, the annular cylindrical lens, the annular light source for measurement, and the annular light source for observation are mounted using the outer peripheral surface of the lens barrel member of the measurement system as a mounting guide. Corneal topography measurement device. 5. The corneal shape measuring device according to claim 1, wherein the annular light source for measurement is held and fixed so as to be adjustable in the meridian direction.