JPS6343091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for automatically measuring the radius of curvature of a subject having curvature, such as a cornea or a contact lens.

Conventionally, various types of off-salmometers are known as devices for measuring the radius of curvature of the cornea. These devices calculate the radius of curvature from the radius of the corneal reflected image of an annular marker or the interval between the corneal reflected images of two point markers.
In both cases, the image interval of the reflected image of the index projected onto the subject from a direction symmetrical to the observation optical axis (the annular index is considered to be a circular arrangement of point indexes, and therefore the image interval is equal to the radius) is the angle of the cornea. Since it is based on the principle that it changes according to the curvature, it is possible to perform accurate measurements even in an unstable state due to slight fixation movements of the eye to be examined.

A Littmann-type ophthalmometer is known as one such ophthalmometer.

This objective lens system consists of a front lens and a rear lens whose front focal position matches the rear focal position of the front lens, which are symmetrical to each other with respect to the optical axis of the objective lens system. An illumination system is installed that projects two bright spots using a parallel beam from the front lens. A deflection concave lens for measurement is placed at the rear focal position. At this time, in order to prevent the influence of visual fixation micromovement, the objective optical path is divided into two optical paths by an optical path splitter, and the interval between the bright spot images is determined by determining the relative interval between the doubled images. In addition, if the cornea to be tested has an astigmatic surface, the two bright spots and the double image will be arranged in a straight line in the radial direction. I am measuring the same. Such a Littmann-type off-salmometer is configured to project a bright spot onto the cornea to be examined using a parallel beam of light, so there is no need to align the cornea and the bright spot in principle; Although there is an advantage that the error caused by positioning does not become an error factor and all that is required is focusing,
In order to find the distance between the two bright spot images, the optical path is divided into two in the telecentric optical system, a double image is obtained, and when the two bright spot images match, the two This method determines the distance between bright spot images and, in turn, the curvature of the cornea, and the configuration and measurement procedure are extremely complicated.

On the other hand, a method using a position sensor to automatically measure the distance between two bright spot images is known as JP-A-54-160271, but in this method, the bright spot projections are parallel. Since measurements are not performed using a luminous flux, not only is it necessary to precisely align the cornea and the bright spot in order to perform highly accurate measurements, but also
Since a position sensor is used, it is necessary to alternately blink bright spots arranged symmetrically with respect to the optical axis of the objective lens, which has the disadvantage of complicating the configuration.

An object of the present invention is to provide a radius of curvature measuring device that takes advantage of the optical system of a Littmann-type off-salmometer and automates the measurement.

The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the present invention. The objective lens system is composed of a front lens 1, a rear lens 2, and an aperture 3.The rear focal position of the front lens 1 and the front focal position of the rear lens 2 are arranged so as to coincide with each other. It forms a telecentric optical system. A diaphragm 3 for limiting the luminous flux is arranged at a focal position common to the front lens 1 and the rear lens 2. Naturally, the center of the aperture 3 coincides with the optical axis. A bright spot 1 is directed toward the object 100 with a parallel light beam from a direction symmetrical to the optical axis of the objective lens system.
A pair of projection lenses 11a and 11b for projecting images 0a and 10b are provided. That is,
A bright spot 10 is located at the focal position of the projection lenses 11a and 11b.
a and 10b are respectively arranged. Therefore,
Optical axis of objective lens system and projection lenses 11a, 11b
The optical axes of are in the same plane, and the angle between the optical axis of the objective lens system and the optical axis of the projection lens 11a and the angle between the optical axis of the objective lens system and the optical axis of the projection lens 11b are both equal angles. It is θ. An optical path splitter 1 is provided between the rear lens 2 and the rear focal plane of the lens 2.
2 are provided and form mutually conjugate rear focal planes. At one rear focal position, a reticle 13 having a crosshair or the like is arranged, and the eyepiece 1
3', and a one-dimensional image sensor 14 is arranged in the other rear focal plane so as to receive reflected images of the bright spots 10a and 10b from the subject 100. Each element of the image sensor 14 is scanned by the clock and sequentially outputs the signals of the elements driven by the clock.
When the element receiving the bright spot image is driven, it produces a pulse-like output. That is, since two bright spot images are received, two pulses are obtained during one scan. A calculation display device 15 is connected to the image sensor 14 . The calculation display device 15 includes a waveform shaping circuit 16, a computer 17, a display device 18, etc., and converts the input signal into the curvature of the subject 100 and displays it.

The waveform shaping circuit 16 outputs a pulse having a width equal to the interval between two pulses included in the time-series input signal. The computer 17 calculates the bright spot image interval from the width of the pulse output by the waveform shaping circuit 16, the frequency f of the clock that drives the image sensor 14, and the interval between the elements of the image sensor 14, and then The curvature of the subject 100 is calculated from the correspondence between the curvature of and the bright spot image interval. Computer 17 has printer 1
8 is connected, and is controlled by a computer 17 so as to project the curvature of the subject.

With this configuration, the examiner looks through the eyepiece 13' and moves the apparatus to align and focus so that a clear bright spot image is symmetrical to the intersection of the crosshairs. In this way, a bright spot image will be formed on the image sensor 14.
However, according to the optical system shown in Fig. 1, because of the aperture 3 in the telecentric optical system, the central ray of the imaging light beam is always parallel to the optical axis even if the positions of the front lens 1 and the eye 100 to be examined are misaligned. become. To explain using FIG. 2, FIG. 2a shows a state in which the front focal position of the front lens 1 exactly matches the position of the virtual image of the bright spots 10a and 10b and is in focus. b shows the front pin state, and FIG. 2 c shows the rear pin state.
Therefore, in any case, the maximum position of the light intensity distribution on the reticle 13 and image sensor 14 is located at a certain distance r from the optical axis, so strict alignment is not necessary. The signal output from the image sensor 14 in time series generates pulses at positions corresponding to the elements receiving the bright spot image, so two pulses are generated in one scan of the image sensor 14 ( Figure 3 a). The waveform shaping circuit 16 generates pulses having a pulse width corresponding to between these pulses (FIG. 3b). Waveform shaping circuit 16
Since the bright spot image interval can be determined as t, f, and d from the pulse width (t seconds) of the pulse generated, the clock frequency (f), and the element interval (d) of the image sensor 14, the computer 17 inputs the pulses from the waveform shaping circuit 16 and calculates the bright spot image interval. Thereafter, the curvature of the subject 100 is calculated from the correspondence between the curvature of the subject 100 and the bright spot image interval, which is known in advance. The examiner is printer 18
The curvature of the object can be instantly known from the numerical value displayed.

Since the curvature obtained in this way is only in the direction of one radial line, if the subject 100 has a toric-like astigmatic surface, it is necessary to measure the astigmatic axis even if the subject 100 is a lens. For example, it can be rotated around the optical axis. Since different curvatures are sequentially printed on the printer 18, the directions to be measured (directions represented on the plane of the paper in FIG. 1) at the time of the maximum curvature and the time of the minimum curvature respectively become astigmatism axes.

When the subject 100 is a cornea, the apparatus may be rotated around the optical axis. In addition, bright spots 10a, 10
The same result can be obtained by rotating the image sensor 14 and the projection lenses 11a and 11b around the optical axis of the objective lens system, while synchronizing the rotation of the image sensor 14 around the optical axis.

The diaphragm 3 described above may be any member that limits the luminous flux between the lenses 1 and 2, and a concave lens may be placed at the diaphragm 3 position. In this case, the maximum diameter of the concave lens acts as a diaphragm member that limits the luminous flux.

In addition, in order to minimize the number of moving parts,
An optical system as shown in FIG. 4 can also be considered. That is, the one in FIG. 1 projects two bright spots, but in FIG.
Projection systems 10a, 10b for astigmatism measurement by projecting a parallel light beam onto the subject 100 using the lens 21, the perforated reflector 22, and the front lens 1.
11a and 11b, the ring image on the image sensor 14 is removed by the image rotator 21 provided between the optical path splitter 12 and the image sensor 14. This eliminates the inconvenience of rotating the image sensor 14.

Therefore, the signals sequentially output from the image sensor 14 according to the rotational position of the image rotator 21 become signals indicating the curvature corresponding to each meridian of the cornea of the eye 100 to be examined.

FIG. 5 shows an apparatus for measuring the astigmatic axis and calculating the curvature in the optical system shown in FIG. 4.

In FIG. 5, a holding member 40 holding the image rotator 21 has a gear 41 formed on its outer periphery, and the gear 41 meshes with a gear 42 fixed to the shaft of a pulse motor 43. The rotation of the pulse motor 43 is controlled by pulses from a drive device 44. The signal from the image sensor 14 is sent to the waveform shaping circuit 16
The data is input to the computer 17 via the . Pulses from the drive device 44 are also input to the computer 17 . That is, when the image rotator 21 rotates 180 degrees, an image of the entire radial line is formed on the image sensor 14, so there is a one-to-one correspondence between the rotation angle of the image rotator 21 and the number of pulses. The computer 17 determines the direction of the meridian corresponding to the signal input from the image sensor 14 based on the number of pulses. The computer 17 controls the printer 18 so that the printer 18 sequentially displays the direction of the radius line and the curvature in correspondence with each other. The direction of the radial line corresponding to the maximum and minimum curvature values printed on the printer 18 is the main radial direction of astigmatism. Of course, the computer 17 may be provided with a function of selecting only the maximum value and minimum value.

In the above explanation, the direction of the radial line is detected by the number of pulses from the initial position, but a rotary encoder type rotation angle reading device or the like may be used to read the rotation angle of the image sensor 14. Of course.

In addition to one-dimensional image sensors, two-dimensional ones can also be used as image sensors. However, in this case, when projecting a bright spot as shown in Figure 1, the information of each pixel in a certain meridian direction is memorized, and the information of each pixel is sequentially mapped to the direction of the meridian along all the meridian lines. Need to remember information. By combining the stored values in each radial direction obtained in this way, an ellipse (in the case of astigmatism) is obtained. On the other hand, when a ring-shaped index as shown in FIG. 4 is used, an ellipse (circle if there is no astigmatism) is directly imaged on the two-dimensional image sensor, so an image rotator is unnecessary. By image-analyzing the ellipse thus obtained to determine the long axis and short axis, it is possible to obtain the main axis direction of the astigmatism and the curvature in that direction.

As described above, according to the present invention, not only is strict alignment between the subject and the device unnecessary, but also measurement values can be obtained instantly, making it possible to obtain an automatic radius of curvature measuring device with good operability. .

[Brief explanation of the drawing]

Fig. 1 shows the optical system of the first embodiment of the present invention, Fig. 2 is an explanatory diagram, and Fig. 2a shows the in-focus state.
FIG. 2b shows the front pin state, and FIG. 2c shows the rear pin state. 3 shows a pulse state, FIG. 4 shows an optical system of the second embodiment, and FIG. 5 shows an apparatus for measuring the astigmatic axis and calculating the curvature of FIG. 4. [Explanation of symbols of main parts], Front lens...1,
Rear lens...2, aperture...3, one-dimensional image sensor...14, calculation display device...15.

Claims (1)

[Claims] 1. Align the rear focal position of the front lens with the front focal position of the rear lens, place the diaphragm at that position, and expose the index with a parallel beam of light across the optical axis of the front lens, facing the subject. An illumination system for projecting onto the specimen is provided, an image sensor is arranged at a position conjugate with the reflected image of the index by the specimen with respect to the front lens and the rear lens, and the distance between the reflected images of the index is determined by the image sensor. An automatic radius of curvature measuring device, characterized in that the radius of curvature of the subject is calculated from this value.