JP2001212083A - Analytical method of platide ring pattern with high resolution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To project a pattern with a high resolution without an adhesion of the adjacent ring in case of projecting pattern on the ring to get a radius of a curvature on the cornea. SOLUTION: Set the space of the pattern without adhesion of the adjacent ring and project its pattern. When it is re-projected, the pattern is calculated at intervals of 1/2 in discontinuous order and finally, get a double resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing high-resolution analysis on a corneal shape analyzer.

[0002]

2. Description of the Related Art Corneal image capturing and analysis by projecting a concentric ring pattern onto the cornea is a general corneal shape analysis technique. Normally, about 20 to 40 concentric ring patterns are projected, and in analysis, each ring is separated and extracted from the image, and the positional relationship is analyzed to determine the radius of curvature of the cornea at an arbitrary position of the cornea. Alternatively, the diopter value is displayed as a color map corresponding to the color. The resolution, that is, the resolution of the color-mapped position calculation, is determined by the number of rings projected onto the corneal surface. Therefore, in order to increase the resolution, the ring interval is reduced. In the prior art, the projection and analysis are performed by setting the ring interval at a fine granularity at which each ring position can be separated and analyzed at the time of analysis. As a pattern projection method, a placid plate method in which a pattern is projected from a position relatively far from the cornea, and a cone method in which a pattern is projected close to the cornea with a cone including the pattern are known. In the cone method, the ring interval is very narrow, and the eye interval with a small corneal curvature is such that the ring interval is more likely to be dense.

[0003]

In both the Placid plate method and the cone method, the projection of a concentric ring pattern onto a minute area on the corneal surface results in an apparent proximity ring when the number of rings is increased to increase the resolution. It becomes difficult to separate each other by crossing over or coalescing. This depends on the resolution of the CCD camera in the observation system, and it is difficult to separate and specify each ring. This is because the ring interval is relatively small with respect to the cell size constituting the light receiving surface of the CCD camera. In these systems, in principle, the difficulty of separating each ring becomes more remarkable for an eyeball having a small corneal curvature radius.

[0004]

SUMMARY OF THE INVENTION To solve these problems,
In order to create a color map with high resolution, the present invention projects a concentric discontinuous pattern instead of the conventionally used concentric continuous pattern. FIG. 1 shows the discontinuous pattern. A discontinuous pattern that is parallel to the horizontal direction is set, and the discontinuous interval is at a position that complements the preceding and following discontinuous positions. In this pattern, the trajectory of each ring position is discontinuous, and the distance to an adjacent ring position inside or outside an arbitrary ring pattern is twice as large as that of a continuous pattern, and the resolution is half that in the meridian direction. The non-continuous portion is restored by performing a Fourier transform process on, and the same resolution as in the case of a continuous pattern is obtained. In addition, since the distance is doubled as described above, the adhesion of the proximity ring does not occur by using the minimum pattern that can be separated and analyzed by projecting the conventional concentric continuous pattern as a reference. This utilizes the property that the radius of curvature of the cornea changes slowly in the meridian direction.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical system for projecting a pattern and an optical system for observing the pattern are arranged as shown in FIG. The cone (01) located in front of the cornea (C) is illuminated from inside by a fluorescent tube (02) placed on its back,
The pattern on the film is projected onto the cornea through the included film. The light of the LED (06) is
The light is reflected by the half mirror (04) by 5), and further projected on the cornea (C) through a hole formed in the center of the cone (01) by the lens (03), thereby forming a fixation lamp for observation. The pattern projected on the cornea (01) passes through the lens (03), the half mirror (04), and the lens (07).
After the focus adjustment, the image is recognized by the CCD (08), and the image is processed by a computer positioned at the subsequent stage to obtain a corneal curvature radius.

The pattern projected onto the corneal surface is one in which discontinuous line segments as shown in FIG. 1 are periodically arranged regularly. When the discontinuous line drawn in the lateral direction is projected onto the cornea, it forms a discontinuous concentric ring pattern centered on the corneal vertex.

To project the discontinuous pattern of FIG. 1, a conical cone as shown in FIG. 2 is used. The inside of the cone is hollow and is a conical cylinder made of transparent resin. A transparent film with a printed pattern is attached to the inner wall. Alternatively, the pattern is arranged by directly cutting the discontinuous pattern on the inner wall surface and applying a coating. For projection onto the cornea, the tip of the cone is brought close to the corneal surface, and the ring wall surface is molded of thick transparent resin. Illumination light from the fluorescent tube (02) is scattered within the resin and partially blocked by a pattern attached or cut inside, thereby forming a concentric discontinuous pattern in the cornea. Projected onto

In order to observe correctly, it is necessary to project a discontinuous pattern concentrically around the apex of the cornea. Therefore, the point light source (06) is replaced by a lens (05), a half mirror (04), and a lens (03). ) To irradiate as a fixation lamp to fixate its bright spot. On the observed image, a bright spot is observed at the center of the concentric discontinuous pattern.

The concentric discontinuous pattern projected on the cornea passes through a lens (02) and a half mirror (07),
The focus is adjusted by the lens (07), collected by the CCD camera (08), and observed as an image as shown in FIG.

In the image analysis, after this image is digitized, the radius of curvature in a subdivided area on the cornea is calculated by specifying the position of each concentric discontinuous pattern. In this calculation, it is obtained as the amount of displacement from the reference position at the time of calibration. As can be seen from FIG.
In this embodiment, since the ring pattern is discontinuous every 30 degrees, a ring position corresponding to each discontinuous ring position needs to be obtained from the pattern by calculation of the adjacent discontinuity. Therefore, the obtained image is temporarily expanded in the music coordinate space, and Fourier-transformed in the distance direction from the center. Although the interval between the ring patterns is slightly displaced according to the corneal shape, the amount of the change is small, so that the peak position in the frequency space after the Fourier transform exhibits the frequency position corresponding to each ring position and the projection It is divided into two types, one having a peak at 0 frequency due to the background luminance distributed over the entire image. Therefore, when a new peak position is set at a portion corresponding to a half position of the frequency corresponding to the ring position, and the image is reconverted to the real space by performing an inverse Fourier transform, a concentric circle as shown in FIG. The continuous pattern can be reconstructed. Further, at the time of reconstruction, it is not necessary to return to a space having the same resolution as the observation system, and it is possible to perform reconstruction in a space with a higher resolution. This makes it possible to obtain a higher resolution of the ring recognition position, which has become relatively large with respect to the CCD cell.

In this embodiment, the intervals between the discontinuous patterns in the horizontal direction of the discontinuous patterns shown in FIG. 1 need not be equal, but complement the discontinuous positions of adjacent discontinuous patterns before and after. When viewed in the meridian direction,
They are arranged at substantially equal intervals with respect to a true spherical surface. The shape of the inner surface of the cone is adjusted so as to reflect concentrically at substantially equal intervals when projected onto the cornea. The best interval can be selected as appropriate according to the magnification of the optical system.

[0012]

According to the present method, even if a discontinuous pattern is projected, a reconstructed image of the same kind as that of the continuous pattern can be obtained. However, in the projection of the discontinuous pattern, the proximity ring position in each meridian direction is twice as large as that in the case of the continuous pattern projection, so that the ring position can be specified in the image before the reconstruction. It can be said that it is easy. This is because, by increasing the ring interval, adhesion of the adjacent ring is eliminated. However, since the image is analyzed as a double ring density by reconstructing an image, it is observed as data having a measurement density four times higher on the corneal surface than in the case where a continuous pattern is used.

[0013]

[Brief description of the drawings]

FIG. 1 shows a pattern for cutting on or on a transparent film fixed to the hollow inner surface of a hollow conical member.

FIG. 2 is a hollow conical member that projects concentric light beams.

FIG. 3 is a reflected light beam projected on a simulated eye.

FIG. 4 is a schematic diagram of an optical system of a corneal shape measuring apparatus.

FIG. 5 is an image reconstructed from a pattern projected on a simulated eye.

[Explanation of symbols]

 C. . . Cornea 01. . . Corn 02. . . Fluorescent tube 03. . . Lens 04. . . Half mirror 05. . . Lens 06. . . Fixation point light source 07. . . Lens 08. . . CCD camera

Claims (1)

[Claims] A projection unit configured to project a pattern light beam formed by a light source of a light source through an irradiation unit and a light shielding unit of a pattern light beam forming member onto a cornea of an eye to be inspected; A corneal shape measuring device having an imaging means for imaging a reflected light beam from the cornea, wherein the pattern light beam projected onto the cornea is a concentric light beam and at least one
The luminous flux on adjacent concentric circles of the set is a combined luminous flux composed of a luminous flux having an illuminated portion and a light-shielding portion arrayed in the meridian direction, in which irradiation portions are regularly arranged on the circumference. Is a projection pattern of the corneal shape measuring device.