JPH031835A - Apparatus for measuring shape of cornea - Google Patents

Abstract

PURPOSE:To reduce measuring errors regardless of a change in a distance between a cornea and an indicator by detecting a blurring to use the results for correction of the shape of the cornea. CONSTITUTION:For example, a specified one is used among a plurality of indicators and a shape of a cornea is measured from a reflected image on an image sensor 3. First, a distance between an eye E to be inspected and an indicator 4 are adjusted so that the reflected image on the image sensor 3 becomes small and the most clear and the condition thus obtained is defined as condition 0. When the indicator 4 is moved before and after the condition 0 with respect to the eye E to be inspected at an equal interval, the reflected image is blurred larger than that in the condition 0. The reflected image on the image sensor 3 in various conditions undergoes a horizontal scanning in a fixed direction to check a size of the reflected image and a degree of blur. Then, a table is prepared for (n) model eyes in which curvature radii of the cornea are already found to be R1, R2... and Rn to improve a measuring accuracy by correction of a measured regardless of a change in a distance between the eye E to be inspected and the indicator 4. This table is used to correct an actual measured value of the eye to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a corneal shape measuring device that projects an index onto the cornea of an eye to be examined and measures the corneal shape based on the reflected corneal image.

[Prior Art] Conventionally, in this type of corneal shape measuring device, an index such as a ring-shaped slit is projected onto the cornea of the eye to be examined, and the reflected image is received by a two-dimensional photodetector, and the received image is detected. size,
The corneal shape is measured by analyzing the amount of distortion contained in the received light image.

However, if the distance between the cornea and the index changes due to an attenuation error in the anteroposterior direction of the optical system, the size of the corneal reflection image also changes, making it difficult to accurately measure the corneal shape. Therefore, Japanese Patent Laid-Open No. 61249432 discloses a means for correcting the size of the corneal reflection image using an aperture to reduce the measurement error of the corneal shape measurement value.

[Problem 8 to be solved by the invention] However, in the conventional example, if the distance between the cornea and the index changes as described above, it is not possible to accurately measure the corneal shape. The disclosed proposal also has the disadvantage that it is difficult to manufacture because precise positional accuracy of the diaphragm is required in order to obtain a constant luminous flux as a corneal reflection image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a corneal shape measuring device that eliminates the above-described drawbacks of the conventional example and can reduce measurement errors even when the distance between the cornea and the index changes.

[Means for Solving the Problems] In order to achieve the above object, the corneal shape measuring device according to the present invention includes a projection means for projecting an indicator onto the cornea of the eye to be examined, and a corneal reflection image of the indicator. a light receiving means for receiving light; a first detecting means for detecting the shape of a corneal reflected image on the light receiving means; a second detecting means for detecting a blur state of the corneal reflected image on the light receiving means; and a correction means for correcting the corneal shape obtained by the first detection means based on the result of the first detection means.

[Operation] The corneal shape measuring device having the above configuration detects the blur state and uses the result to correct the corneal shape, thereby accurately measuring the corneal shape.

[Example] The present invention will be explained in detail based on illustrated embodiments.

In the configuration diagram of FIG. 1, an objective lens 1 is arranged facing the cornea Ec of an eye E to be examined, and an aperture 2. Further, an image sensor 3 is arranged at the rear. As shown in FIG. 2, indicators 4a to 4d are arranged on two orthogonal meridians around the objective lens 1, and light sources 5a to 5d consisting of LEDs or incandescent lamps are provided behind the indicators 4a to 4d, respectively. There is.

The indicators 4a to 4d are illuminated by light sources 5a to 5d, projecting dotted light spots h4A to 4D onto the cornea Ec of the eye E to be examined, and projecting the cornea E onto the imaging device 3 through the objective lens 1 and the aperture 2.
A reflected image of the point light spots 4A to 4D is formed by c. When the distance between the eye E and the indicators 4a to 4d is changed, the size of the reflected image on the image sensor 3 changes, and when the reflected image becomes larger, the reflected image becomes blurred, and when it becomes smaller, it becomes clearer. However, since the aperture 2 is placed at the focal point of the objective lens 1, even if the distance between the cornea Ec and the indicators 4a to 4d changes significantly, the size of the reflected image on the image sensor 3 will not change much. For example, it is already known in Japanese Patent Laid-Open No. 62-21 that it is possible to measure the corneal shape from a plurality of corneal reflection images on the image sensor 3.
This is disclosed in Japanese Patent No. 6528.

Prior to measurement, for example, only a specific index out of a plurality of indexes is used, and the corneal shape is measured from the reflected image on the image sensor 3. First, the distance between the eye E and the index 4 is adjusted so that the reflected image on the image sensor 3 is the clearest and smallest, and this state is defined as state 0. When the index 4 is moved at equal intervals before and after the state O with respect to the eye E, the reflected image becomes blurred and larger than in the state 0. Tested eye E and index 4 than state 0
The state with a large distance to the state O is defined as a state child, the state closest to state 0 is state 1, state 2, etc., the state with a small distance is defined as state -, and the state closest to state O is state -1, state -2, etc.・・・
shall be.

The reflected image on the image sensor 3 in each state is horizontally scanned in a fixed direction to examine the size and degree of blur of the reflected image. FIG. 3 shows an output waveform diagram of the horizontal scanning output on the image sensor 3 after A/D conversion, where the horizontal axis shows the scanning position and the vertical axis shows the A/D conversion value, that is, the density of the reflected image. In order to express the blurring of the reflected image, the intensity of the reflected image is determined by A/
Let d be the scanning line spacing when the D conversion value is greater than a certain value, and let the scanning line spacing in states -3, ..., Ol..., 3 be d-3,..., dOl... , d3, then 1. For example, in state 0 where the reflected image is the clearest, 1. Since the state of blur is small, the scan line interval d of the waveform after A/D conversion is small, and the height h of the A/D conversion value output waveform, which indicates the density of the reflected image, is large. Since the image is blurred compared to state 0, the scanning line interval d is large and the density of the reflected image h
is getting smaller.

Even if the distance between the eye E and the index 4 changes, the measurement accuracy can be improved by correcting the measured value.
A table as shown in Table 1 is created for n model eyes whose corneal radii of curvature are already known to be R1, R2°, ..., Rn, and this table is used to calculate the actual Correct the measured value of the eye to be examined.

First, for all model eyes, measure the radius of corneal curvature RIO to RnO and the total number of bits 010 to DnO recognized in the reflected image on the image sensor 3 when using the measuring device in state O. For each state from -3 to state 3, the corneal curvature radius R and the total number of bits are measured and the table is filled in. However, it is not necessary to measure the R and D values for all states, because index 4 When moving back and forth, the reflected image on the image sensor 3 becomes clearer or blurred and the scanning line interval d changes, but as shown in FIG. 4(c), the reflected image is the clearest in state O. If the scanning line interval d is directly proportional to the distance between the eye E and the index 4, there is no problem in approximation. This is because it is assumed that it is directly proportional to the distance, and the corneal curvature radius R can be calculated from this proportional relationship. Furthermore, since a similar proportional relationship holds true for the value of the total number of bits, this is utilized.

In the measurement, the actual corneal curvature radius R of the eye E to be examined, which is the distance from the index 5, and the total number of recognized bits are also measured, and corrected using the table shown in Table 1. As shown in FIG. 4, the size of the reflected image on the image sensor 3 is minimum in the unblurred state O, and do<di< d2, do <
As the distance from state 0 increases, such as d-1 < d-2, the reflected images in both state + and state - become blurred and larger, so the scanning line interval d also increases, and the measured value of the corneal radius of curvature R also increases. Therefore, the measurement state of the eye E to be examined is state + and state - compared to state 0 where the reflected image is not blurred.
It is necessary to determine whether the for that,
It is necessary to change the distance between the eye E and the index 4 at least twice and measure and compare the R and D values respectively. For example, the measured values measured twice are R1 and Di, R.
2 and D2, it is possible to determine whether the condition is positive or negative by comparing the measured values as shown in Table 2. This is derived from the fact that the smaller the working distance is, the larger the photographic magnification is, and the larger the measured value R is detected, and the farther away from the appropriate working distance, the greater the blurring and the larger the measured value R.

Table 2 DI>D2 D2>DI D2
=DIR1>R2 R1 is in state - R2 is in state + R1 is in state - or R2 is in state , Do, and correct this measured value R' using the table shown in Table 1 prepared in advance.

The correction method is to first compare only the values of Do, and then select a pair (R, D,) with a value of D that is the same as or close to Do from one of the + and - determined states in Table 1. Select all. Now compare R from this set of (R, D),
Let R'' be the closest R to the measured value R'', and let the radius of corneal curvature of the model eye where R'' is located in Table 1 be the final corrected radius of curvature of the measured value R'. . Note that this correction is performed by calculation by a computer, and an example of the program is shown in the flowchart of FIG.

In this embodiment, the correction is made using a table created from the direct proportional relationship shown in FIG. 5, but the relationship shown in FIG.
A table may be created based on that relationship.

In addition, in the blur detection for correction in the above-described embodiment, measurement is performed using only a specific target image, but in reality, eyelashes or the like hang before the light guiding means and obstruct the light flux, so that the light beam cannot be detected on the image sensor 3. In some cases, the exact size of the reflected image cannot be measured, so a single reflected image alone may not be reliable. Therefore, if correction is performed by measuring the average value of the total number of recognition bits for a plurality of index images, more accurate measurement becomes possible.

As another embodiment, even if the index, which was a point in the first embodiment, is changed to a ring index, the same measurement as the point index can be performed. In addition, as another example, if it is possible to measure the density of blur, that is, the height h of the output of the corneal reflection image shown in FIG. This allows you to determine whether the cause is a difference in corneal radius of curvature or defocus.

Even if the aperture 2 in FIG. 1 is omitted, highly accurate measurement is possible.

[Effects of the Invention] As explained above, the corneal shape measuring device according to the present invention has the following effects:
Since the corneal shape measurement value is corrected based on the state of the reflected image on the image sensor, measurement errors can be reduced even if the distance between the cornea and the index changes and the size of the corneal reflected image changes.
Therefore, the influence of alignment errors between the index and the cornea is reduced, so that measurements can be carried out efficiently and easily.

[Brief explanation of the drawing]

The drawings show an embodiment of the corneal shape measuring device according to the present invention,
Figure 1 is a configuration diagram, Figure 2 is a layout diagram of the light source, Figure 3 is a waveform diagram of an output signal, Figure 4 is a blurred code 1 is the objective lens, 2
is an aperture, 3 is an image sensor, 4a to 4d are indicators, 5a to 5d
is a light source. m1 Figure 114 Figure is +fnf S-shaped convergence 1IIL @ Figure 2

Claims (1)

[Claims] 1. a projection means for projecting an index onto the cornea of the eye to be examined; a light receiving means for receiving the corneal reflected image of the index; a first detecting means for detecting the shape of the corneal reflected image on the light receiving means; A second detection means for detecting a blurred state of a corneal reflected image on the light receiving means, and a correction means for correcting the corneal shape obtained by the first detection means based on the result of the second detection means. A corneal shape measuring device characterized by: