Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-03-30
2001-05-01
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06224213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a corneal-shape measuring apparatus for measuring the shape of a cornea of an eye to be examined.
2. Description of the Related Art
An apparatus for measuring a corneal shape is known in which a multiplicity of ring pattern targets (indexes) are projected onto a cornea to be examined, a target (index) image formed on the cornea is picked up, and the corneal shape is measured on the basis of the picked-up image.
Conventionally, the projection of ring pattern targets (indexes) onto the cornea is effected by illuminating from behind a Placido plate having a target (index) portion on which annular light-transmitting portions and light-shielding portions (masking portions) are alternately formed concentrically, and its illuminating methods include those shown in
FIGS. 7A
to
7
C.
In a method shown in
FIG. 7A
, an annular light source
101
constituted by a fluorescent lamp, a cold cathode-ray tube, a stroboscope tube, a neon tube, or the like is disposed in the rear of a Placido plate
100
, an illumination space is provided in such a manner as to envelop the light source
101
by a reflecting member
102
and the Placido plate
100
, and the light emitted from the light source
101
is reflected by the reflecting member
102
, thereby making it possible to illuminate the Placido plate
100
efficiently.
In a method shown in
FIG. 7B
, instead of the annular light source
101
in
FIG. 7A
, a multiplicity of light-emitting diodes (LEDs)
103
are arranged annularly around an outer rim portion of the Placido plate
100
, and the Placido plate
100
is illuminated by the reflection of the reflecting member
102
.
In a method shown in
FIG. 7C
, a multiplicity of LEDs
111
are arranged annularly immediately behind the light-transmitting portions of a Placido plate
110
so as to effect illumination.
However, these illuminating methods have the following problems. In the case of the method shown in
FIG. 7A
, to illuminate the entire region of the Placido plate
100
uniformly, it is necessary to provide a relatively large illuminating space between the Placido plate
100
and the reflecting member
102
, so that the apparatus becomes large in size. In addition, the Placido plate
100
formed of a resin can expand and deform due to heat generated from the annular light source
101
, possibly reducing measurement accuracy. Although it is possible to form the Placido plate
100
of glass so as to prevent the deformation due to the thermal expansion, the apparatus becomes very expensive.
In the case of the method shown in
FIG. 7B
, the generation of heat can be suppressed by using the LEDs
103
, but it is still necessary to provide a sufficiently large illuminating space between the Placido plate
100
and the reflecting member
102
in order to illuminate the entire region of the Placido plate
100
, making the apparatus large in size. In addition, if the LEDs
103
are provided around the outer rim portion of the Placido plate
100
as shown in the drawing, the illumination of ring pattern targets (indexes) on the outer side of the Placido plate
100
is shaded, so that a large apparatus is required to project the ring pattern targets (indexes) over a wide range, and the clearance between the apparatus and the eye to be examined becomes short. Further, since a difference in the quantity of light occurs in correspondence with the distance from each LED
103
, it is difficult to illuminate the Placido plate
100
uniformly, and hence it becomes difficult to detect edges of the ring pattern targets (indexes) projected onto the cornea, leading to a decline in the measurement accuracy.
In the case of
FIG. 7C
, since the LEDs
111
must be arranged annularly for the respective light-transmitting portions of the Placido plate
110
, the LEDs
111
are required in a large quantity, and these LEDs
111
, combined with a power source therefor, make the apparatus very expensive.
SUMMARY OF THE INVENTION
In view of the above-described problems of the conventional art, it is an object of the present invention to provide a corneal-shape measuring apparatus which can be made compact without requiring a large illuminating space and which is capable of uniformly projecting ring pattern targets (indexes) with a simple arrangement at low cost.
The present invention provides the followings:
(1) A corneal-shape measuring apparatus for measuring the shape of a cornea of an eye to be examined, comprising:
a target plate formed of a transparent resin as material thereof and for projecting a target formed by a light-transmitting portion and a light-shielding portion onto a wide range of the cornea;
a surface emitting plate for illuminating the target from behind;
an imaging optical system for picking up a target image formed on the cornea; and
processing means for analyzing the picked-up target image to determine the corneal shape.
(2) The corneal-shape measuring apparatus according to (1), further comprising:
an illuminating light source disposed to allow rays of light to be incident upon an end face of said target plate,
wherein said target plate has the target formed on its front surface facing the cornea, is provided with matte treatment in a color of high reflectivity on a rear surface thereof, and is used jointly with said surface emitting plate.
(3) The corneal-shape measuring apparatus according to (2), wherein said illuminating light source includes a light-emitting diode.
(4) The corneal-shape measuring apparatus according to (2), wherein the matte treatment includes a white matte coating.
(5) The corneal-shape measuring apparatus according to (2), wherein the matte treatment includes a white diffusing film.
(6) The corneal-shape measuring apparatus according to (5), wherein said white diffusing film has dot-shaped regions which have reflectivity different from that of white diffusing regions thereof and whose density differs relative to a distance from said illuminating light source.
(7) The corneal-shape measuring apparatus according to (1), wherein said surface emitting plate comprises:
a plurality of plate members formed of a transparent resin as material thereof and provided with matte treatment in a color of high reflectivity on rear surfaces thereof; and
illuminating light sources arranged so as to cause the rays of light to be incident upon end faces of said plate members.
(8) The corneal-shape measuring apparatus according to (7), wherein said illuminating light sources include light-emitting diodes.
(9) The corneal-shape measuring apparatus according to (7), wherein the matte treatment includes a white matte coating.
(10) The corneal-shape measuring apparatus according to (7), wherein the matte treatment includes a white diffusing film.
(11) The corneal-shape measuring apparatus according to (10), wherein said white diffusing film has dot-shaped regions which have reflectivity different from that of white diffusing regions thereof and whose density differs relative to a distance from said illuminating light source.
(12) The corneal-shape measuring apparatus according to (7), wherein said plurality of plate members include at least conical plate members.
(13) The corneal-shape measuring apparatus according to (7), wherein said plurality of plate members include a plurality of flat, annular plate members of different diameters.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 11-88060 (filed on Mar. 30, 1999), which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 5300965 (1994-04-01), Kitajima
patent: 5500697 (1996-03-01), Fujieda
patent: 5907388 (1999-05-01), Fujieda
patent: 4-44736 (1992-02-01), None
patent: 7-194551 (1995-08-01), None
patent: 11-513580 (1999-11-01), None
patent: 97/14351 (1997-04-01), None
Manuel George
Nidek Co. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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