JP3103314B2 - Corneal shape measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corneal shape for projecting a plurality of indices on a cornea of an eye to be examined and measuring a corneal shape based on a reflection image of the cornea. It relates to a measuring device. 2. Description of the Related Art A conventional corneal shape measuring apparatus of this type projects a ring-shaped index image, that is, a Myer image, on a cornea of an eye to be examined.
Measurements are made based on the size and distortion of the reflected image formed by corneal reflection. [0003] However, in this conventional corneal shape measuring apparatus, there is a possibility that a measurement error may occur due to a variation in the working distance between the apparatus and the eye to be examined. [0004] It is an object of the present invention to provide a corneal shape measuring apparatus capable of performing accurate measurement so that an error due to a variation in working distance does not occur. A corneal shape measuring apparatus according to the present invention for achieving the above object is a point light source provided on a circumference around an optical axis of an optical system facing an eye to be examined. Light source means for forming two ring indices which differ in distance from the cornea of the subject's eye in the optical axis direction;
Projection means including the optical system for projecting the images of the two ring indices onto the photoelectric detector, and measuring the radius of curvature of the cornea from the respective sizes of the images of the two ring indices projected on the photoelectric detector. Means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 shows an embodiment of a corneal shape measuring apparatus according to the present invention, wherein E is an eye to be examined, and C is the cornea. In the present embodiment, two ring-shaped light sources composed of a group of point light sources, that is, a first ring light source 1 and a second ring light source 2 are used as the ring-shaped indices projected toward the cornea C of the eye E. Have been. Although these two ring light sources 1 and 2 are concentric, they are arranged so that the distances S1 and S2 from the cornea C are different from each other. The projection lens 3, the aperture stop 4, and the area-type CCD 5 are sequentially arranged to face the subject's eye E, and the aperture stop 4 is arranged at the rear focal position of the projection lens 3. In FIG. 1, light from a first ring light source 1 is reflected by a cornea C to form a first ring reflection image R1 by a group of point light sources, and this image passes through a projection lens 3, an aperture stop 4, and a CCD 5 Is imaged. On the other hand, light from the second ring light source 2 is also reflected by the cornea C to form a second ring reflected image R2, and is formed on the CCD 5 via the projection lens 3 and the aperture stop 4. Now, the radii of the first ring light source 1 and the second ring light source 2 are respectively A1 and A2, the radii of the first ring reflection image R1 and the second ring reflection image R2 are B1 and B2, and the radii of curvature of the cornea C, respectively. Is r, and if the cornea C is further moved away from the first ring light source 1 and the second ring light source 2 by the moving distance ΔS, the following equation is established. r = 2 (S1 + ΔS) · B1 / (A1−B1) (1) r = 2 (S2 + ΔS) · B2 / (A2−B2) (2) That is, these expressions represent two reflected images R1. , R2 are formed on the cornea C at substantially the same radius of curvature r. From equations (1) and (2), ΔS = {B2 (A1-B1) .S2-B1 (A2-B2) .S1} / {B1 (A2-B2) -B2 (A1-B1)} (3) By substituting this into equation (1), r = {2B1 / (A1-B1)} [S1 + {B2 · S2 (A1-B1) −B1 · S1 (A2-B2)} / {B1 (A2−B2) −B2 (A1−B1)}] = 2B2 · B1 (S2−S1) / {A2 · B1−A1 · B2} (4) It is clear that the movement distance ΔS is a factor completely unrelated to the measurement. Now, when the first ring light source 1 and the second ring light source 2 are integrated and approached in the direction of the cornea C, the first and second ring reflection images R1 and R2 obtained by corneal reflection become large. 2 and 3 show the situation, and FIG.
The first ring reflection image R1 and the second ring reflection image R2 when the distances from the ring light source 1 and the second ring light source 2 to the cornea C are S1 and S2, respectively. Further, when the ring light sources 1 and 2 approach the cornea C direction more than that, the first
The ring reflection image R1 and the second ring reflection image R2 become large as shown in FIG. This means that a wide range of measurement from the central part to the peripheral part of the cornea C can be performed by changing the distance to the cornea C. As the corneal reflection image projection optical system used in the above embodiments, not only the object side telecentric optical system but also an image side telecentric optical system can be used. FIG. 4 shows an embodiment in which a telecentric optical system is formed before and after.
The aperture stop 4 is disposed at the rear focal position of the projection lens 3 and at the front focal position of the relay lens 6. According to this, even when the position of the cornea C is displaced to the position indicated by Ca due to the alignment error, or when there is an error in the mounting position of the CCD 5, the first and second rings projected on the CCD 5 are also provided. The sizes of the reflection images R1 and R2 do not change. FIG. 5 shows the first and second ring reflection images R1 and R2 as C
In order to increase the depth of focus when projecting onto a CD 5, a variable aperture stop 4a capable of changing the size of an aperture is used in place of the aperture stop 4 in FIG. Thus, even when an alignment error occurs in the optical axis direction, the image can be projected with a small blur, so that accurate measurement can be performed. At this time, it is also effective to link the brightness of the ring light sources 1 and 2 so as to follow the size of the aperture stop 4a as the light amount decreases. As described above, the corneal shape measuring apparatus according to the present invention can perform accurate measurement without errors due to the working distance.

[Brief description of the drawings] FIG. 1 is an optical layout diagram of a first embodiment. FIG. 2 is an explanatory diagram of a ring reflection image. FIG. 3 is an explanatory diagram of a ring reflection image. FIG. 4 is an optical layout diagram of a second embodiment. FIG. 5 is an optical layout diagram of a third embodiment. [Explanation of symbols] 1 First ring light source 2 Second ring light source 3 Projection lens 4 Aperture stop 4a Variable aperture stop 5 Area CCD 6 relay lens

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Claims (1)

(57) [Claims] A light source means including a point light source provided on a circumference around the optical axis of the optical system facing the eye to be examined, forming two ring indices having different distances from the cornea of the eye in the optical axis direction , and light reflected by the cornea Projection means including the optical system for projecting the images of the two ring indices onto a photoelectric detector , respectively, and those of the images of the two ring indices projected on the photoelectric detector
Means for measuring the radius of curvature of the cornea from the respective sizes.
A corneal shape measuring device.