JPH0444736A - Cornea form measuring device - Google Patents

Abstract

PURPOSE:To project a concentric circular pattern with a uniform light quantity all over the wider area of the cornea front surface by using a reflective lighting system, and regulating the optical configuration between a platide plate and a reflecting means disposed between the platide plate and a light source. CONSTITUTION:The emitted light from a light source 7 enters to a platide plate 4 rear surface directly, or after it is once reflected by the inner side wall surface and inner rear wall surface of a housing 2 subjected to matte aluminium coating 13 as a reflecting means. At this time, the light directly radiated to a cornea front surface 9 through the channels 11, 12 of the platide plate 4 from the light source 7 is shielded by a light shielding plate 8, and the optical pass length from the light source 7 to the cornea front surface 9 of a testee is made constant. Consequently, the pattern projected on the cornea front surface 9 has an uniform brightness over the whole area. Also, the angle entering the curvature center of the cornea of the light radiated to the cornea front surface 9 from the channels 11, 12 of the platide plate 4 can be increased from the center part of the platide plate 4 toward the peripheral part, so that the above pattern is projected over a wider area of the cornea front surface 9.

Description

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

Conventional technology A conventional corneal topography 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 subject's cornea through a Placido plate on which a concentric pattern is formed. , forming a reflected image from the anterior surface of the cornea on a photographic film or a projection surface of a display;
A type of device that measures the curvature of the cornea by analyzing this pattern is generally known.

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 projected as uniformly as possible from the center to the periphery of the anterior corneal surface. It is important to.

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 peripheral wall (
20a) and a rear end wall (20a) continuous to the peripheral wall (20a).
A silk-like light source housing housing (20) consisting of (b) is provided, and a circular front end opening of this housing (20) is sealed by a disk-shaped Placido plate (22). Further, a cylindrical partition wall (29) passing through the housing (20) is provided on the optical axis line (28) of the measurement unit, and a central optical path (27) is formed inside the partition wall (29). A light source accommodating space (21) is formed outside the partition wall (29) in the housing (20), and the light source accommodating space (21) is
Inside 21), a 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 plate-like body having translucency,
A ring-shaped groove (19) of a predetermined width is formed on the front surface of the optical axis (2).
8) are formed concentrically at predetermined intervals, and the area other than the ring-shaped groove (19) on the front surface is coated with a light-shielding coating. Further, a diffuse transmission plate (24) is disposed between the light source (23) and the Placido plate (22) in the light source housing space (21), and a diffuse transmission plate (24) is arranged between the light source (23) and the Placido plate (22).
22) Light should be irradiated as uniformly as possible over the entire area of the rear surface. As a result, a concentric pattern is projected onto the anterior surface of the cornea (26) with uniform brightness. In addition, in front of the periphery of the Placido plate (22),
A plurality of ring-shaped diffuse reflection plates (25) are connected to the device main body (20).
By concentrating the light emitted from the Placido plate (22) radially with respect to the optical axis (28) on the peripheral part of the anterior corneal surface (26), the peripheral part of the anterior corneal surface (26) is connected to It is now possible to project concentric patterns onto the image.

In the irradiation system of the corneal topography measurement device shown in Fig. 4,
A conical Placido plate (32), which has a circular opening at its apex through which the partition wall (37) of the central optical path can pass, is formed in the circular front end opening of the light source housing (30) so that the front side thereof is concave. A single ring-shaped light source (33) is installed in the light source housing space (3I)! has been done.

A light-shielding coating is applied to the front surface of the Placido plate (32) so that ring-shaped slits (35) of a predetermined width are formed concentrically around the optical axis at predetermined intervals. On the other hand, the rear surface of the Placido plate (32) is processed and 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, the light that enters the Placido plate (32) from each ring-shaped rear surface (34b) perpendicular to the optical axis of the Placido plate (32) is totally reflected on the inner circumferential wall surface (34a) of each disc. By irradiating light that would normally be radiated outward from the optical axis toward the front surface of the cornea, the number of light sources can be reduced and a concentric pattern can be projected onto a wider area of the front 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 that images the concentric circular pattern on the front surface of the cornea onto the film surface, display surface, etc. of the measuring section, and the imaging operation is At this time, the entire illumination system is moved back and forth with respect to the main body of the device. Therefore, when the weight of the illumination system is large, the mechanism 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 produce a concentric pattern over a larger area of the anterior corneal surface and with a uniform light intensity over the entire area, while reducing the number of light sources and avoiding complicating the structure of the Placido plate. An object of the present invention is to provide a corneal topography measurement device with an improved illumination system capable of projecting images.

Means for Solving the Problems To achieve the above object, the length of the optical path from the light source to the anterior surface of the cornea is 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, in the present invention, the front end opening of a light source housing housing, which is formed of a peripheral wall and a rear end wall continuous to the peripheral wall, which is provided at the front end of a main body including an optical measurement part, is sealed with a Placido plate, and the measurement part is A central optical path passing through the housing is formed on the optical axis of the housing, a light source accommodating space is formed outside the central optical path in the housing, and at least one light source is disposed in the light source accommodating space, and at least one light source is connected to the light source. 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 on the optical axis, and a light shielding means is disposed on the inner peripheral wall surface and the inner rear end wall surface of the housing. A reflecting means is provided for causing the light emitted from the light source to enter the rear surface of the Placido plate, and the Placido plate is a translucent plate having a concave front surface, A large number of ring-shaped grooves having a predetermined width are formed concentrically at predetermined intervals around the optical axis on the front surface, 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 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 plurality 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 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 front surface of the corner M of the subject is constant. The present invention constitutes a corneal shape measuring device characterized in that

Effect In the configuration described above, 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, but at this time, the light shielding plate prevents the light from passing directly from the light source to the front surface of the cornea through the groove of the Placido plate. The irradiated light 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 corneal surface.

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

As shown in FIG. 1, the corneal shape measuring device according to the present invention has a main body (not shown) equipped with an optical measurement section (not shown).
1), a peripheral wall (10a) and the peripheral wall (10
A silk-like light source housing housing (10) consisting of a rear end wall (10b) continuous to a) is provided, and a Placido plate having a shape that becomes a part of a spherical surface is provided in the circular front end opening of the housing. (4) is mounted such that its front side is concave and its center of curvature is located on the optical axis line (3) of the optical measuring section extending in the direction of the central axis of the housing (10).

Further, a substantially cylindrical partition wall (6) penetrating the housing (10) is provided on the optical axis &1 (3), and the partition wall (
A central optical path (5) is formed through the inner space of 6) to the central circular opening (5a) of the Placido plate (4).

A light source accommodating space (2) is formed outside the partition wall (6) in the housing (10), and this light source accommodating space (2)
Inside, a single ring-shaped light source (7) is arranged with its center located on the optical axis (3) and surrounding the outer periphery of the partition wall 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 space between the light source (7) and the optical axis m.
(3) Placido plate at the top (4) A light shielding plate (8) on a ring for blocking direct light reaching the front surface of the cornea (9) of the subject located at a predetermined position in front of the septum is spaced apart from the outer periphery of the septum. It is placed so as to surround the area.

In addition, a satin-like aluminum coating (13) is applied to the inner side wall surface and rear wall surface of the housing (2), and the light emitted from the light source (7) is incident on the rear surface of the Placido plate (4). It functions as a reflective means to 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). Become.

A light source housing space (2) is provided approximately in the middle of the central optical path (5).
A condensing lens (14) is disposed to guide the reflected light from the front surface of the cornea to the imaging optical system of the optical measurement unit disposed behind the cornea.

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. It is formed concentrically with the optical axis (3) as the center, and is coated with a light-shielding coating on the area other than the ring-shaped groove on the front surface. In this case, the width of the grooves and the spacing of the grooves are determined by theoretical methods known in the art for patterning Placido plates.

Furthermore, the front surface of the Placido plate (4) has two ring-shaped regions centered on the optical axis (3) and extending radially from the optical axis (3), that is, as shown in FIG.
4) The first ring-shaped region (A 6N region) located in the center and the second ring-shaped region (Bfil
area).

As shown in FIG. 1a, the ring-shaped groove (11) in the first region (A) has a substantially V-shaped cross section in the radial direction, and two slopes (11a) forming the cross section, (
1 and 1a) are mutually 45@ in the direction parallel to the optical axis.
It has a bottom wall formed to intersect at an acute angle. On the other hand, the ring-shaped groove (12) in the second region (B)
has its bottom wall (12a) aligned with the optical axis (3) in the radial direction.
) is formed to have a substantially U-shaped cross section making an acute angle of 55° towards the front of the Placido plate (4).

In this case, the inner side wall surface and the inner rear wall surface of the housing (2) are coated with a matte aluminum coating (13) that functions as a reflective means, and the groove (1) of the Placido plate (4).
1) and (12), the optical path length from the light source (7) to the anterior surface of the cornea (9) through the reflecting means is approximately constant;
In addition, as you go from the center of the Placido plate (4) to the periphery, 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, more precisely, the front surface of the cornea approximately changes. When considered as a spherical mirror, it is designed to have an optical arrangement such that the angle of incidence at the focal point gradually increases.

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

In the above configuration, the light emitted from the ring-shaped light source (7) is directly incident on the periphery of the rear surface of the Placido plate (4), or the light emitted from the ring-shaped light source (7) is directly incident on the periphery of the rear surface of the Placido plate (4), or the light emitted from the ring-shaped light source (7) is directly incident on the peripheral part of the rear surface of the Placido plate (4), or the light that is emitted from the ring-shaped light source (7) is directly incident on the peripheral part of the rear surface of the Placido plate (4), or the light that is emitted from the ring-shaped light source (7) is directly incident on the peripheral part of the rear surface of the Placido plate (4), or the light that is emitted from the ring-shaped light source (7) is directly incident on the peripheral part of the rear surface of the Placido plate (4), or the light that is emitted from the ring-shaped light source (7) is directly incident on the peripheral part of the rear surface of the Placido plate (4).
After being reflected at 3), it enters the rear surface of the Placido plate (4). At this time, the light irradiated directly from the light source (7) to the anterior surface of the cornea (9) through the groove of the Placido plate (4) is blocked by the light shielding plate (8).

In this way, the optical path length from the light source (7) to the anterior surface of the cornea (9) becomes approximately constant, and a concentric pattern of uniform brightness is projected onto the anterior surface of the cornea (9).

Furthermore, from the optical arrangement of the inner side wall surface and inner rear wall surface of the housing (2) coated with a satin-like aluminum coating (13), and the bottom walls of the grooves (11) and (12), the first plate of the Placido plate is The irradiated light from the groove (11) of the ring-shaped area (A) is directed to a predetermined position in the central area of the anterior surface of the cornea (9), and the irradiated light from the groove of the second ring-shaped area CB) of the Placido plate (4) is Irradiation is applied to predetermined positions in the peripheral area of the anterior surface of the cornea (9), and from the groove of the Placido plate (4) to the anterior surface of the cornea (9) as it goes from the center to the peripheral area of the Placido plate (4).
It is possible to increase the angle of the light irradiated to the effective center of curvature of the cornea, and as a result, the light is projected over a wider area of the anterior surface of the cornea (9), and with almost uniform brightness over the entire area. be done.

Furthermore, the reflected image from the anterior surface of the cornea (6) is reflected from the central optical path (5).
is guided to the measuring section of the main body (1) through the. In this way, corneal topography measurements can be made more accurately and more quickly than with 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 peripheral area portion (16) in the shape of a spherical surface with a concave front side attached to the peripheral edge of the circular front end opening of the housing, and a disk shape, with its front surface The inner circular opening of the peripheral area part (16) is sealed so as to be smoothly continuous with the front surface of the peripheral area part (16), and a circular opening (5a) for the central optical path (5) is provided in the center.
) is formed in the central region portion (15).

The central area portion (15) is a translucent acrylic plate, and has a ring-shaped groove on the front surface in the radial direction similar to the ring-shaped groove in the central area of the Placido plate shown in FIGS. 1 and 1a. A ring-shaped groove (11) having a bottom wall with a ■-shaped cross section is formed concentrically around the optical axis,
A light-shielding coating (15) is applied to the area other than the ring-shaped groove on the front surface. On the other hand, the peripheral area portion (16) is a translucent acrylic plate, with a ring-shaped surface area (18) left on the front surface in a predetermined concentric pattern centered on the optical axis. It is coated with a light-shielding coating (15).

In this embodiment as well, substantially the same effects as in the embodiment shown in FIG. 1 can be obtained. In addition, it is only necessary to apply a light-shielding coating to the peripheral area where the front surface is curved without cutting grooves, and grooves can be formed only in the flat central area where grooves can be easily formed by cutting. Therefore, 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 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. The ring-shaped groove includes a plurality of types of grooves each having a bottom wall having an acute angle with respect to the optical axis, and the bottom wall of the adjacent groove has an acute angle with respect to the optical axis. When the sizes are different, it is only necessary that the groove having a larger acute-angled bottom wall is located on the outside than the groove having a smaller acute-angled bottom wall.
For example, the size of the acute angle of the bottom wall of the guide with respect to the optical axis may be configured to gradually increase as it moves away from the optical axis, or the front surface of the Placido plate may be in the first ring-shaped area in the center, and the outside of the first ring-shaped area may be It is divided into three or more regions, such as a second ring-shaped region, a third ring-shaped region outside it, and so on, 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 portion of the radial cross section is such that the bottom wall of the groove in the inner region makes an optical axis in at least a portion of the radial cross section. The angle may be larger than the acute angle formed with respect to the axis.

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 reflective means and the groove bottom wall of the Placido plate extend from the light source to the anterior surface of the subject's cornea. The optical path length is constant, and the light irradiated 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 Placido plate to the periphery. This reduces the number of light sources and avoids complicating the structure of the Placido plate, while projecting a concentric pattern onto a wider area of the anterior surface of the cornea, and making the concentric pattern uniform in 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 the drawing]

FIG. 1 is a schematic side sectional view 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; FIG. FIG. 2 is an enlarged sectional view showing the structure of the groove of 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.・・・・・・・・・・Main body・・・Light source housing space・・・Optical axis・・・・・・・・・・Platido plate・・・・・・・・・・Central optical path (7)・・・・・・・・・Light source (8)・・・・・・・・・ Light shielding plate (9)・・・・・・・・・...Anterior cornea (lO) ...Housing (II),
(12)... Groove (13)... Satin-like aluminum coating (15)... Coating layer with light-shielding properties

Claims (1)

[Claims] (1) The front end opening of the light source housing, which is provided at the front end of the main body equipped with the optical measuring section and consists of a peripheral wall and a rear end wall continuous with the peripheral wall, is sealed with a Placido plate, and the optical axis of the measuring section is sealed. A central optical path passing through the housing on an axis is formed, a light source accommodating space is formed outside the central optical path in the housing, and at least one light source is disposed in the light source accommodating space, and a line from the light source to the optical axis 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 on the top;
Reflection means is provided on the inner peripheral wall surface and the inner rear end wall surface of the housing for making the light irradiated from the light source enter the rear surface of the Placido plate, and the Placido plate has a concave front surface. A light-transmitting plate-like body, on the front surface of which a large number of ring-shaped grooves having a predetermined width are formed concentrically at predetermined intervals around the optical axis; A light-shielding coating is applied to a region other than the ring-shaped groove, and each of the plurality of ring-shaped grooves of the Placido plate is arranged so that the Placido plate is formed with respect to the optical axis in at least a part of the radial cross section. The plate has a bottom wall with an acute angle toward the front side, and the plurality 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. The groove having a smaller bottom wall is located outside the groove having a smaller acute-angled bottom wall, and the bottom wall of the groove of the reflecting means and the Placido plate extends from the light source to the anterior surface of the cornea of the subject. A corneal shape measuring device characterized in that the device is arranged and formed so that the optical path length is constant.