JPH02220626A - Apparatus for measuring shape of cornea - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to a corneal shape measuring device used in eye clinics, etc. to analyze the shape of the corneal surface before and after corneal surgery, and to prescribe contact lenses. It is.

[Prior Art] Conventional corneal shape analysis means generally examine a corneal reflection image of a distant placido ring. In addition to this,
A method is also known in which a ring image is projected near the cornea and the corneal reflection image is analyzed.

[Problem to be solved by the invention] However, since the projection angle is large in the former method,
The disadvantage is that the light beam is eclipsed by the subject's nose, eyelids, etc., making it difficult to see the shape of the entire cornea. Furthermore, although the latter method reduces the projection angle, it has the disadvantage that the measurement error associated with the error in the working distance is large.

The purpose of the present invention is to provide a corneal shape that enables accurate adjustment of one working distance by projecting an index image such as a Placido ring onto the cornea using a lens whose projection angle is not so large, and enables highly accurate corneal shape analysis. The purpose of this invention is to provide a measuring device.

[Means for Solving the Problems] In order to achieve the above object, the corneal shape measuring device according to the present invention has an aperture disposed approximately conjugately at the center of curvature of the cornea of the eye to be examined, and an index is attached to the cornea. a projection optical system that projects a corneal reflected image of the target, a light receiving optical system that receives a corneal reflected image of the target with a light receiving sensor, and an alignment optical system that receives the corneal reflected light with a thicker beam than during measurement and performs alignment. ,
The present invention is characterized in that the shape of the cornea is determined from the corneal reflection image on the light receiving sensor.

[Operation] The corneal shape measuring device having the above-mentioned configuration performs positioning using a beam of light that is thicker than that used during measurement, and determines the corneal shape from the corneal reflection image of the index on the light receiving sensor.

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

FIG. 1 shows an example of the tsl, in which an objective lens l, a half mirror 2. A dichroic diaphragm 3 shown in FIG. 2, a lens 4, a finger J15 consisting of a placido ring shown in FIG. In addition, a lens 9 and an area sensor array 1 are provided on the reflection side of the half mirror 2.
0 is placed. Index 5 is the angle tl of the eye E to be examined! JE
c, and the dichroic diaphragm 3 is arranged substantially conjugate to the center of curvature O and the midpoint M between the corneal apex. Furthermore, the light beam emitted from the measurement light source 6 and the light beam emitted from the second observation light source 8 have different wavelengths, and only the measurement light passes through the center 3a of the dichroic diaphragm 3, while the observation light passes through the entire surface. It looks like this.

The light flux from the observation light source 8 during positioning illuminates the index 5 via the lens 7 and the measurement light source 6. The image of the optotype 5 is captured by the lens 4. Dichroic aperture 3. half mirror 2,
A corneal reflection image projected onto the cornea Ec through the objective lens L and reflected by the cornea Ec is formed by the objective lens L and the half mirror 2.
, and is projected onto an area sensor array lO arranged conjugately to the rear focus of the objective lens l.

FIG. 4 is an enlarged view of the light beam incident on the cornea Ec.

During alignment during observation, the convergence angle θ is
Therefore, the luminous flux is thick, and the depth of focus of the index image, which is a ring image, is shallow, allowing highly accurate positioning. On the other hand, during measurement, the beam diameter from one point of index 5 is the dichroic aperture 3.
The convergence angle φ is narrower than the convergence angle θ, and the measurement accuracy is improved by narrowing the light beam and reducing the area irradiated from each point of the index 5 onto the angle l11Ec. The dichroic diaphragm 3 may be placed in the projection optical system as in the embodiment, or it may be placed near the lens 9 of the light receiving system, which is approximately conjugate with the center of curvature of the eye E, to obtain the same effect. has.

The area sensor array 10 is an imaging element of a television camera and is capable of video image analysis, but it may also be used for recording instead of a film.The distance between the index 5 and the dichroic aperture 3 is adjusted to match the average corneal curvature. If the cornea Ec has this curvature, the ring-shaped light beam emitted from the center 3a of the dichroic diaphragm 3 will enter the corneal surface from the perpendicular direction.

Horn II! 1IEC to form a corneal reflection image on the focal plane of the objective lens 1. If the corneal curvature differs, the reflection angle will differ, so the size of the corneal reflection image will also change. To determine the shape of the cornea from a ring-shaped corneal reflection image, first, the radius of curvature is determined by regarding the area near the center of the cornea as a spherical surface, but the periphery generally has a different curvature from the center of the cornea. Each ring image size gives the differential value of the curvature of the part where the light beam hits the cornea Ec, so by integrating these, the corneal curvature can be found. In this example, the center of curvature of the cornea Ec and the distance between the apex and the midpoint M is always held constant during measurement.

FIG. 5 shows a second embodiment, in which the light detecting source 11 is conjugated with the index 5 via a light splitting member 12 consisting of a guichroic mirror or the like. Note that a diaphragm 13 having a small aperture is arranged between the index 5 and the light splitting member 12. Other parts are similar to the embodiment shown in FIG. 1, and positioning is performed using the image of the observation light source 11.

Furthermore, instead of the dichroic diaphragm 3 used in the embodiment shown in FIG. 1, a variable diaphragm 3b that can be narrowed only during measurement may be used as shown in FIG.
In this case, it is also possible to use both the observation light source 8 and the measurement light source 6.

FIG. 7 shows a third embodiment, in which a light splitting member 14 made of a guichroic mirror is provided behind the half mirror 2. A diaphragm 3c, an index 5a, and a measurement light source 15 are arranged, a half mirror 16 and an alignment light source 17 are provided in the reflection direction of the light splitting member 14, and a photoelectric sensor 18 is provided on the reflection side of the half mirror 16. . The photoelectric sensor 18 is conjugated with the positioning light source 17, and the aperture 3C
is substantially conjugate to the center of curvature 0 of the cornea Ec.

The light beam indicated by the four-dot line is for positioning, and a point light source such as a light emitting diode is used as the positioning light source 17, and is arranged conjugately at the corneal vertex. Further, the light splitting member 14 is a guichroic mirror having a property of transmitting the light from the measurement light source 15 and reflecting the light from the 1-positioning light source 17. The alignment light reflected by the cornea Ec is reflected by the half mirror 16 and enters the photoelectric sensor 18 for one alignment, and the output of the photoelectric sensor 18 becomes maximum when the alignment is the longest. Therefore, when the magnitude of the input signal to the photoelectric sensor 18 is above a certain level, the corneal reflection image by the index 5a on the area sensor array 10 is captured.
In this embodiment, the distance to the corneal vertex is always kept constant during measurement.

[Effects of the Invention] As explained above, the corneal shape measuring device according to the present invention has the following effects:
This has the advantage that highly accurate positioning is possible and measurement errors associated with this positioning can be eliminated.

[Brief explanation of the drawing]

The drawings show an embodiment of the corneal shape measuring device according to the present invention,
Fig. 1 is a configuration diagram of the first embodiment, Fig. 2 is a front view of the diaphragm, Fig. 3 is a front view of the index, Fig. 4 is an enlarged explanatory diagram of the luminous flux,
FIG. 5 is a block diagram of the light source section of the second embodiment, FIG. 6 is a front view of another aperture, and FIG. 7 is a block diagram of the third embodiment. 2 and 14 are half mirrors, 13 and 13 are apertures, 5 is an index, 6.15 is a measurement light source, 8.11 is an observation light source, 10 is an area sensor array, 12.14 is a light splitting member, and 17 is a positioning light source , 18 are photoelectric sensors.

Claims (1)

[Claims] 1. A projection optical system that has an aperture that is arranged approximately conjugate to the center of curvature of the cornea of the eye to be examined, and that projects an index onto the cornea; a light receiving optical system that receives the corneal reflected image of the index with a light receiving sensor; A corneal shape measuring device comprising: a positioning optical system that receives corneal reflected light using a relatively thick beam of light for positioning, and determines the corneal shape from a corneal reflected image on the light receiving sensor.