JPS63300739A - Cornea measuring apparatus - Google Patents

Abstract

PURPOSE:To quantitatively measure even a complicated shape having sharp unevenness, by calculating said shape by utilizing scattering beam. CONSTITUTION:The slit beam formed by the slit plate 2 illuminated by a beam source 1 is projected on the cornea Ec of an eye E to be examined by a projection lens 3. The reflected image of the cornea Ec passes through the imaging lens 4 and iris 5 on an optical axis L2 to project a cornea image on an image pickup apparatus 7 having an image pickup element 6. The signal from the image pickup apparatus 7 is sent to a signal processor 8 and the intersecting points of the scanning line of the image pickup element 6 and the cornea image are calculated at a signal level and, from the average position of these intersecting points, the position of the surface of the cornea is measured. When the beam is projected on the cornea Ec, the cornea Ec scatters slit beam and, therefore, a beam cutting surface is viewed when the cornea is viewed in an oblique direction and the image thereof is picked up by the image pickup apparatus 7 to calculate the positions of the front and rear surfaces of the cornea.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a keratometry device that can simultaneously measure the curvature and thickness of the cornea in ophthalmology, and is particularly useful for use in corneal plastic surgery and cataract surgery. It is related to.

[Prior Art] Until now, no keratometry device has been known that can simultaneously measure the curvature and thickness of the cornea. A keratometer is a device that measures corneal curvature, but since this keratometer uses corneal reflection to determine corneal curvature, quantitative measurements are difficult when the cornea forms a complex curved surface. It has the disadvantage of On the other hand, there are known methods for determining corneal thickness, such as an optical method using a pachometer and an ultrasonic method, but both are contact-type and measure each area one point at a time, so they cover the entire corneal surface. It has the disadvantage that it is difficult to grasp the thickness distribution over the area.

In general, after corneal surgery or in patients with diseases such as keratoconus, the cornea has a very complex shape with uneven parts, so it is difficult to accurately understand this shape when diagnosing treatment. extremely important.

Furthermore, in cases such as radial corneal incision surgery for refractive correction, it is necessary to know the thickness of the cornea and its local changes, and if possible, it is preferable to perform this measurement in a non-contact manner.

[Object of the Invention] In order to satisfy such requirements, the object of the present invention is to provide a method for measuring the curvature and thickness of the cornea with one device, and also to be able to accurately measure these measurements using a non-contact method. An object of the present invention is to provide a keratometry device that has the following features.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to provide an imaging optical system that projects an image of a light beam scattered by the cornea onto an imaging device from a direction having an angle with the projection optical axis; The apparatus includes a signal processing means for processing an output signal, and a signal processing means for determining an intersection between a scanning line of the imaging device and the scattering image from a signal level, and determining keratometry information from an average position of the intersection of each scanning line. This is a keratometry device characterized by the following.

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows an embodiment of a keratometry device according to the present invention,
In order to facilitate analysis, a projection optical system consisting of a light source 1, a slit plate 2, and a projection lens 3 is provided on the projection optical axis B1, which is preferably arranged to pass through the center of curvature O of the corneal surface of the eye E to be examined. It is being The slit plate 2 has a slit 2a as illustrated in FIG. 2, and the direction of the slit 2a is perpendicular to the plane of the paper in FIG.

Further, an imaging optical system including an imaging lens 4, an aperture 5, and an imaging element 6 is disposed on an optical axis B2 that preferably has an angle in the width direction of the slit 2a with respect to the projection optical axes 1, 1. The imaging device 6 is provided in an imaging device 7 consisting of a television camera, and the output of this imaging device 7 is connected to a signal processing device 8 .

It is desirable to use a solid-state image sensor such as a COD as the image sensor 6. Further, the aperture 5 is located at the focal point of the imaging lens 4 and constitutes a telecentric optical system, so that dimensional errors do not occur even when objects have depth.

The slit light beam illuminated by the light source 1 and formed by the slit plate 2 is projected onto the cornea E of the eye E by the projection lens 3.
projected onto c. The reflected image of the cornea Ec passes through the imaging lens 4 and the aperture 5 on the optical axis B2, and then is transferred to the imaging device 7 having the imaging element 6.
Take a corneal image. The signal from the imaging device 7 is sent to the signal processing device 8, where the intersection between the scanning line of the imaging device 6 and the corneal image is determined based on the signal level, and the position of the corneal surface can be measured from the average position of these intersections.

When a slit light beam is projected onto the cornea Ec, the cornea Ec scatters the slit light beam, so that when viewed from an angle, a light section is visible. When this is imaged by the imaging device 7 and the video signal is viewed, the signal level is high in the portion where the cornea Ec is present. The positions of the front and back surfaces of the cornea can be determined by binarizing the video signal from the imaging device 7 or by once loading it into a memory and calculating it, and at the same time, the corneal Ec can be determined from the relationship between the positions of the front and back surfaces of the cornea. The thickness of can be found. FIG. 3 shows a corneal image C on the image sensor 6, and shows a corneal image C on the image sensor 6.
Part c appears bright due to scattered light.

FIG. 4 shows scanning lines St on the image sensor 6 of FIG.
A signal obtained by binarizing each of the B2 and B3 signals at an appropriate slice level is shown. In this Figure 4, each A
1, A2, and A3 represent the corneal surface, and B1, B2, and B3 represent the corneal back surface. If these positions are determined for each scanning line and then enlarged and plotted, the result will be as shown in FIG. 5. By finding the points where the corneal image and the scanning line intersect, regression curves Ca and Cb for the front and back surfaces of the cornea can be obtained from these points. Of course, individual values vary due to noise, but the regression curve can be determined with good reproducibility. If this regression curve is obtained for each part, the corneal curvature at that part can be found, and normally, spherical regression is sufficient for the central part. The actual shape can be imaged by photographing from a direction perpendicular to the projection optical axis L1, but since this is practically impossible, the angle may be set to about 45 degrees and the subsequent corrections can be made by calculation. Further, by rotating the slit 2a and the imaging optical system around the projection optical axis L1, it is possible to measure a cross section on another meridian.

Note that instead of binarizing the video signal from the imaging device 7,
The contour of the corneal image C may be calculated with higher accuracy by converting it into a multivalued image using A/D conversion and inputting it into the memory. If the projected slit light beam becomes blurred, the measurement accuracy will decrease, so if the slit plate 2 is bent in advance in the length direction to match the shape of the cornea Ec, the center and periphery of the cornea will be in focus, and the entire surface will be clear. It is possible to project a slit beam of light.

Furthermore, in the same sense, during imaging, projection may be performed using a method based on Scheimpflug's principle so that the center and periphery are in the same focus. If you only want to find the thickness of the cornea Ec,
Rather than once finding a curve representing the contour and calculating the interval between them, it is better to find the interval between the intersections of the front and back surfaces on each scanning line and average them.

[Effects of the Invention] As explained above, the corneal measuring device according to the present invention does not use the surface reflection of the cornea like a conventional keratometer, but uses scattered light to determine the shape. The shape of the cornea can be quantitatively measured even if the shape is complex, and the thickness of the cornea can also be measured using a non-contact method. Even if the value obtained for each scanning line on the image sensor has poor accuracy, the noise is averaged by obtaining the regression curvature, and as a result, the corneal shape can be measured with high precision.

[Brief explanation of drawings]

The drawings show an embodiment of the keratometry device according to the present invention, and the first
The figure shows its configuration, Figure 2 is a front view of the slit plate, Figure 3 is an explanatory diagram of the corneal image on the image sensor, and Figure 4 is a waveform diagram of the signal obtained by binarizing the scanning line that intersects the corneal image. , FIG. 5 shows the intersection points of each scanning line and the corneal image and their regression curves. 1 is a light source, 2 is a slint plate, 3 is a projection lens, 4
5 is an imaging lens, 5 is an aperture, 6 is an imaging element, 7 is an imaging device, and 8 is a signal processing device.

Claims (1)

[Scope of Claims] 1. A projection optical system that projects a slit light beam onto the cornea of the eye to be examined, and an imaging optical system that projects a scattered image of the slit light beam by the cornea onto an image sensor from a direction having an angle with the projection optical axis. , a signal processing means for processing an output signal of the image sensor, and a signal for determining the intersection of the scanning line of the image sensor and the scattering image from the signal level, and obtaining keratometry information from the average position of the intersection of each scanning line. A keratometry device comprising a processing means. 2. The corneal measurement device according to claim 1, wherein the corneal measurement information is a corneal shape obtained by regressing the intersection point to a curve. 3. The keratometry device according to claim 1, wherein the keratometry information is the thickness of the cornea determined from the average value of the interval between two intersections of the scanning lines. 4. The corneal measuring device according to claim 1, wherein the slit light beam of the projection optical system passes through the center of curvature of the cornea.