JPH0435173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a corneal topography device having an improved illumination system.

BACKGROUND TECHNOLOGY A conventional corneal shape measuring device projects a concentric pattern on the front surface of the cornea by irradiating light from a light source onto the front surface of the cornea of the subject through a Placido plate on which a concentric pattern is formed. Generally known is a type that measures the curvature of the cornea by forming a reflected image from the front surface of the cornea on a photographic film or a projection surface of a display, and analyzing this pattern.

Accurate and rapid measurements with this type of device require that a concentric pattern be projected over as wide an area of the anterior cornea as possible, and that the pattern be distributed as uniformly as possible from the center to the periphery of the anterior corneal surface. It is important to project with

For this reason, various improvements have been made to the illumination systems of corneal topography measuring devices. Typical conventional examples are shown in FIGS. 3 and 4.

In the illumination system of the corneal shape measuring device shown in FIG. 3, a pan-shaped light source is provided at the front end of the main body equipped with an optical measurement section (not shown), and includes a peripheral wall 20a and a rear end wall 20b continuous with the peripheral wall 20a. A housing housing 20 is provided, and a circular front end opening of the housing 20 is sealed by a disk-shaped Placido plate 22. Furthermore, a cylindrical partition wall 29 is provided on the axis 28 of the optical axis of the measuring section, passing through the housing 20 , and a central optical path 27 is formed inside the partition wall 29 .
A light source accommodating space 21 is formed outside of the light source accommodating space 9 , and within the light source accommodating space 21 , a large number of light sources 23 and a diffuse transmission plate 24 are arranged between the Placido plate 22 and the light sources 23 .

The Placido plate 22 is a translucent plate-like body, and ring-shaped grooves 19 of a predetermined width are formed concentrically at predetermined intervals around the optical axis 28 on the front surface thereof. Front ring-shaped groove 1
The area other than 9 is coated with a light-shielding coating. Furthermore, a diffuser-transmitting plate 24 is arranged between the light source 23 and the Placido plate 22 in the light source housing space 21, so that light is irradiated from the light source 23 as uniformly as possible over the entire area of the rear surface of the Placido plate 22. There is. As a result, a concentric circular pattern is projected onto the anterior corneal surface 26 with uniform brightness. In addition, in front of the peripheral edge of the Placido plate 22, a plurality of ring-shaped diffuse reflection plates 25 are connected to the device main body 20, and the light emitted from the Placido plate 22 radially with respect to the optical axis 28 is directed to the front surface of the cornea 26. By focusing the light on the periphery, a concentric pattern can be projected onto the periphery of the anterior corneal surface 26.

In the irradiation system of the corneal shape measuring device shown in FIG. 4, the circular front end opening of the light source accommodating housing 30 has a circular opening at the apex through which the partition wall 37 of the central optical path can pass. Board 3
2 is attached so that the front side thereof has a concave surface, and a single ring-shaped light source 33 is disposed within the light source housing space 31.

The front surface of the Placido plate 32 is coated with a light-shielding coating so that ring-shaped slits 35 of a predetermined width are formed concentrically around the optical axis at predetermined intervals. 3
The rear surface of the lens 2 is formed into a stacked shape of disks having a predetermined thickness and a radius that decreases toward the rear along the optical axis.

In this way, by totally reflecting the light incident into the Placido plate 32 from each ring-shaped rear surface 34b perpendicular to the optical axis of the Placido plate 32 on the inner circumferential wall surface 34a of each disc, the optical axis is By irradiating light that is radiated outward toward the front surface of the cornea, the number of light sources is reduced.
The concentric pattern is projected onto a wider area of the anterior surface of the cornea, and a pattern projection image having uniform brightness over the entire area is obtained.

Problems to be Solved by the Invention However, the conventional example shown in FIG. 3 uses a diffused illumination system to project a concentric pattern, and because it uses a large number of light sources, the weight of the illumination system increases. increase On the other hand, the illumination system of a corneal topography measuring device is generally linked to an imaging system for imaging a concentric circular pattern on the front surface of the cornea onto a film surface, display surface, etc. of the measuring section.
During imaging operations, the entire illumination system moves back and forth with respect to the main body of the apparatus. Therefore,
When the weight of the illumination system is large, the structure for smoothly moving the illumination system and the imaging system becomes complicated, and the manufacturing cost becomes high. In addition, there are inherent limitations when attempting to form concentric patterns over a larger area of the anterior corneal surface.

In the conventional example shown in Fig. 4, the number of light sources to be used is small and the lighting system can be made lightweight, which is advantageous, but the structure of the Placido plate is complicated, so the design and It has the disadvantage that it is not easy to process and the manufacturing cost is high.

It is therefore an object of the present invention to reduce the number of light sources and to avoid complicating the structure of the Placido plate, while providing uniform light over a wider area of the anterior surface of the cornea. It is an object of the present invention to provide a corneal topography measuring device having an improved illumination system capable of projecting a concentric circular pattern with a certain amount of light.

Means for Solving the Problems In order to achieve the above object, the optical path length from the light source to the anterior surface of the cornea is made constant, and the light irradiated from the Placido plate to the anterior surface of the cornea is Although the light may be incident at a larger angle to the center of curvature of the cornea, the present inventor used a reflective illumination system and developed an optical arrangement of a Placido plate and a reflecting means disposed between the Placido plate and the light source. It has been discovered that this problem can be easily solved by adjusting the .

Therefore, the present invention seals the front end opening of a light source housing, which is provided at the front end of a main body provided with an optical measuring section and includes a peripheral wall and a rear end wall continuous with the peripheral wall, with a Placido plate. A central optical path passing through the housing is formed on the optical axis of the measuring section, a light source housing space is formed outside the central optical path within the housing, and at least one light source is disposed within the light source housing space; a light shielding means for blocking direct light from the light source to the front surface of the cornea of the subject located at a predetermined position in front of the Placido plate on the optical axis; A wall surface is provided with a reflecting means for making the light emitted from the light source enter the rear surface of the Placido plate, and the Placido plate is a translucent plate with a concave front surface. A large number of ring-shaped grooves having a predetermined width are formed concentrically at a predetermined interval around the optical axis on the front surface, and a light-shielding area is formed on the front surface excluding the ring-shaped grooves. Each of the plurality of ring-shaped grooves of the Placido plate has an acute angle bottom facing toward the front side of the Placido plate with respect to the optical axis in at least a part of the radial cross section. The plurality of ring-shaped grooves include a plurality of types of grooves each having a bottom wall with an acute angle of different size with respect to the optical axis, and the groove having a bottom wall with a large acute angle has a bottom wall with a small acute angle. The reflecting means and the bottom wall of the groove of the Placido plate are arranged and formed so that the optical path length from the light source to the anterior surface of the cornea of the subject is constant. The present invention constitutes a corneal shape measuring device characterized by the following.

Effect In the above configuration, the irradiated light from the light source enters the posterior surface of the Placido plate either directly or after being reflected by the reflecting means. Light shining directly onto the front is blocked. In this way, the optical path length from the light source to the anterior surface of the subject's cornea becomes constant. As a result, the pattern projected onto the anterior surface of the cornea will have uniform brightness over its entire area. At the same time, as we move from the center of the Placido plate toward the periphery, we considered the angle at which the light irradiated from the grooves of the Placido plate to the front surface of the cornea enters the center of curvature of the cornea.More precisely, we considered the front surface of the cornea to be approximately a spherical mirror. The angle of incidence at the focal position of the case can be increased, so that the pattern is projected over a wider area of the anterior surface of the cornea.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, in the corneal shape measuring device according to the present invention, a peripheral wall 10a and a rear end wall 10b continuous with the peripheral wall 10a are connected to the front end of a main body 1 equipped with an optical measurement section (not shown). A pot-shaped light source housing housing 10 is provided, and a placido plate 4 having a shape that is a part of a spherical surface is installed in the circular front end opening of the housing.
However, the front side is a concave surface and the center of curvature thereof is mounted on the optical axis 3 of the optical measuring section extending in the direction of the central axis of the housing 10.

Further, a substantially cylindrical partition 6 is provided on the optical axis 3 and passes through the housing 10, and the central circular opening 5 of the Placido plate 4 is passed through the inner space of the partition 6 from the central circular opening 5b of the rear end wall 10b of the housing.
A central optical path 5 is formed leading to point a.

A light source housing space 2 is formed outside the partition wall 6 in the housing 10, and within this light source housing space 2, a single ring-shaped light source 7 is located with its center on the optical axis 3, and are arranged so as to surround the outer periphery of the area at predetermined intervals.

Between the ring-shaped light source 7 and the Placido plate 4 in the light source housing space 2, there is a line between the light source 7 and the optical axis 3.
A ring-shaped light-shielding plate 8 for blocking direct light reaching the front surface 9 of the cornea of the subject located at a predetermined position in front of the Placido's plate 4 above is arranged so as to surround the outer periphery of the septum at intervals. .

Furthermore, a satin-like aluminum coating 13 is applied to the inner side wall surface and rear wall surface of the housing 2, and functions as a reflection means for making the light irradiated from the light source 7 enter the rear surface of the Placido plate 4. . In this case, the satin-like aluminum coating surface 13 is designed to reflect light while scattering it appropriately, making it possible to make the light more uniformly incident over the entire area of the rear surface of the Placido plate 4.

A light source housing space 2 is provided approximately in the middle of the central optical path 5.
a condenser lens 1 for guiding reflected light from the front surface of the cornea to an imaging optical system of an optical measurement unit disposed behind the
4 is placed.

The Placido plate 4 is a translucent acrylic plate, and as shown in FIG. 1a, ring-shaped grooves 11 and 12 having a predetermined width are formed on the front surface at a predetermined interval with the optical axis 3 as the center. It is formed concentrically and has a light-shielding coating applied to the area other than the ring-shaped groove on the front surface. In this case, the width of the grooves and the spacing between each groove are determined by logical methods known in the art for patterning Placido plates.

Furthermore, the front surface of the Placido plate 4 has two ring-shaped areas centered on the optical axis 3 and extending radially from the optical axis 3, that is, as shown in FIG. The area is divided into a first ring-shaped area (area A) and a second ring-shaped area (area B) located outside of the first ring-shaped area (area A).

Then, as shown in FIG. 1a, the first area A
The ring-shaped groove 11 has a substantially V-shaped cross section in the radial direction, and has two sloped surfaces 1 forming the cross section.
1a and 11a have bottom walls formed to intersect with each other at an acute angle of 45° with respect to a direction parallel to the optical axis. On the other hand, the bottom wall 12a of the ring-shaped groove 12 in the second region B faces toward the front of the Placido plate 4 with respect to the optical axis 3 in the radial direction.
It is formed with a substantially U-shaped stepped surface forming an acute angle of 55°.

In this case, the inner side wall surface and inner rear wall surface of the housing 2 are coated with a matte aluminum coating 13 that functions as a reflecting means, and the Placido plate 4
The bottom walls of the grooves 11 and 12 have a substantially constant optical path length from the light source 7 to the anterior corneal surface 9 through the reflecting means,
In addition, the angle at which the light irradiated from the groove of the Placido plate 4 to the front surface of the cornea enters the center of curvature of the cornea as it goes from the center to the peripheral part of the Placido plate 4, or more precisely, the front surface of the cornea is considered to be approximately a spherical mirror. It is designed to have an optical arrangement such that the angle of incidence at the focal point position of the case becomes progressively larger.

These grooves 11 and 12 can be easily formed by a generally known cutting technique using a cutting tool.

In the above configuration, the light irradiated from the ring-shaped light source 7 is either directly incident on the periphery of the rear surface of the Placido plate 4, or is reflected on the satin-like aluminum coating surface 13 and then applied to the rear surface of the Placido plate 4. incident. At this time, the light irradiated directly from the light source 7 to the front surface of the cornea 9 through the groove of the Placido plate 4 is blocked by the light shielding plate 8 . In this way, light source 7
The optical path length from to the anterior surface of the cornea 9 is approximately constant, and a concentric circular pattern of uniform brightness is projected onto the anterior surface of the cornea.

Furthermore, from the optical arrangement of the inner side wall surface and the inner rear wall surface of the housing 2 coated with the satin-like aluminum coating 13 and the bottom walls of the grooves 11 and 12, the groove 11 of the first ring-shaped area A of the Placido plate
The irradiated light from the groove of the second ring-shaped region B of the Placido plate 4 is irradiated to a predetermined position in the central region of the anterior corneal surface 9, and the irradiated light from the groove of the second ring-shaped region B of the Placido plate 4 is irradiated to a predetermined position in the peripheral region of the anterior corneal surface 9. 4, the angle of the light irradiated from the groove of the Placido plate 4 to the anterior corneal surface 9 with respect to the effective center of curvature of the cornea becomes larger, and as a result, the anterior corneal surface 9 The image is projected over a wider area, and with substantially uniform brightness over the entire area.

Furthermore, the reflected image from the anterior surface of the cornea 6 is reflected from the central optical path 5.
is guided to the measurement section of the main body 1 through. thus,
Corneal topography can be measured more accurately and quickly than when using conventional corneal topography devices.

Further, it is also possible to modify the shape of the Placido plate and the structure of the groove formed in the Placido plate, as shown in FIG. 2, for example.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 only in the configuration of the Placido plate and the grooves in the Placido plate. Therefore, description of the same components will be omitted.

In FIG. 2, the Placido plate has a spherical peripheral region portion 16 with a concave front side attached to the peripheral edge of the circular front end opening of the housing, and a disk-shaped peripheral region portion 16 whose front surface is the peripheral region. The inner circular opening of the peripheral area portion 16 is sealed so as to be smoothly continuous with the front surface of the portion 16, and a central optical path 5 is provided in the center.
and a central region portion 15 in which a circular opening 5a is formed.

The central region portion 15 is made of a translucent acrylic plate, and has a front surface shown in FIGS. 1 and 1.
A ring-shaped groove 11 having a bottom wall having a V-shaped cross section in the radial direction, similar to the ring-shaped groove in the central region of the Placido plate shown in FIG. Coating 15 having light-shielding properties in the area excluding the ring-shaped groove on the front surface
It has been decorated with On the other hand, the peripheral area portion 16 is an acrylic plate having light-transmitting properties, and has a light-blocking property so that a ring-shaped surface area 18 is left on the front surface in a predetermined concentric pattern centered on the optical axis. It is made of coating 15.

In this embodiment as well, substantially the same effects as in the embodiment shown in FIG. 1 can be obtained. In addition,
There is no need to cut grooves in the peripheral area where the front surface is curved, and only a coating with light-shielding properties is applied, and grooves only need to be formed in the flat central area where grooves can be easily formed by cutting. , the manufacturing process of the Placido plate is easier than in the case of the embodiment shown in FIG.

Note that the shape of the Placido plate and the radial cross-sectional shape of the bottom wall of the ring-shaped groove formed in the Placido plate are not limited to the case of this example, and the Placido plate has a shape with a concave front surface. Regarding the cross-sectional shape of the bottom wall of the groove, each of the ring-shaped grooves has a bottom wall that is at an acute angle toward the front side of the Placido plate with respect to the optical axis in at least a part of the radial cross section. and the ring-shaped groove is composed of a plurality of types of grooves each having a bottom wall having an acute angle of different size with respect to the optical axis, and the bottom wall of the adjacent groove has a size of the acute angle with respect to the optical axis. are different, it is sufficient that the groove having a larger acute-angled bottom wall is located outside the groove having a smaller acute-angled bottom wall. Therefore, for example, the size of the acute angle of the bottom wall of each groove with respect to the optical axis is
It may be configured such that it gradually increases in size as it moves away from the optical axis, or the front surface of the Placido plate is a first ring-shaped area in the center, a second ring-shaped area outside of the first ring-shaped area, a third ring-shaped area outside of the first ring-shaped area, etc. ... divided into three or more regions, and in two adjacent regions, the size of the acute angle that the bottom wall of the groove in the outer region makes with respect to the optical axis in at least a part of the radial cross section. However, the bottom wall of the groove in the inner region may be configured to be larger than the acute angle formed with the optical axis in at least a portion of the radial cross section.

Effects of the Invention As described above, according to the present invention, a reflective illumination system is used to project a concentric pattern, and the reflecting means and the groove bottom wall of the Placido plate are used to define the optical path length from the light source to the front surface of the subject's cornea. is constant, and the light emitted from the groove of the Placido plate toward the front surface of the cornea is incident on the center of curvature of the cornea at a larger angle as it goes from the center of the plate to the periphery. By reducing the number of light sources and avoiding complicating the structure of the Placido plate, a concentric pattern can be projected onto a wider area of the anterior surface of the cornea, and the concentric pattern can have uniform brightness over the entire area. It is possible to provide a corneal topography measuring device capable of projecting images. Accordingly, the corneal shape can be measured accurately and quickly, and an inexpensive corneal shape measuring device can be easily manufactured.

[Brief explanation of drawings]

FIG. 1 is a schematic side sectional view taken along a direction parallel to the optical axis, showing a first embodiment of the illumination system of the corneal topography measuring device according to the present invention, and FIG. 1a is the same as that shown in FIG. 1. FIG. 2 is an enlarged cross-sectional view showing the structure of the grooves in the Placido plate of the illumination system; FIG. 3 is a schematic side sectional view taken along a direction parallel to the optical axis, showing the illumination system of a conventional corneal topography measurement device; FIG. 4 is a schematic side sectional view showing the illumination system of a conventional corneal topography measurement device. FIG. 2 is a side cross-sectional view of the system along a direction parallel to the optical axis. DESCRIPTION OF SYMBOLS 1... Main body, 2... Light source housing space, 3... Optical axis line, 4... Placido plate, 5... Central optical path, 7...
...Light source, 8... Light shielding plate, 9... Front surface of the cornea, 10...
... Housing, 11, 12 ... Groove, 13 ... Satin-like aluminum coating, 15 ... Coating layer having light-shielding properties.

Claims (1)

[Claims] 1. The front end opening of a light source housing housing, which is provided at the front end of a main body including an optical measurement section and is composed of a peripheral wall and a rear end wall continuous with the peripheral wall, is sealed with a Placido plate, and the front end opening of the light source housing housing is provided on the optical axis of the measurement section. a central optical path passing through the housing is formed, a light source housing space is formed outside the central optical path in the housing, and at least one light source is disposed in the light source housing space, and a light source on the optical axis from the light source is formed. A light shielding means for blocking direct light reaching the front surface of the cornea of the subject located at a predetermined position in front of the Placido plate, and the light source illuminates the inner peripheral wall surface and the inner rear end wall surface of the housing. The Placido plate is a translucent plate with a concave front surface and has a predetermined shape on the front surface. A large number of wide ring-shaped grooves are formed concentrically at predetermined intervals around the optical axis, and a light-shielding coating is applied to an area of the front surface other than the ring-shaped grooves. each of the plurality of ring-shaped grooves of the Placido plate has a bottom wall having an acute angle toward the front side of the Placido plate with respect to the optical axis in at least a part of the radial cross section, and A large number of ring-shaped grooves are composed of a plurality of types of grooves each having a bottom wall with an acute angle of different size with respect to the optical axis, and the groove with a bottom wall with a large acute angle is larger than the groove with a bottom wall with a small acute angle. is also located on the outside, and the reflecting means and the bottom wall of the groove of the Placido plate are arranged and formed so that the optical path length from the light source to the anterior surface of the cornea of the subject is constant. A corneal shape measuring device featuring: