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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a surface examining apparatus capable of
examining a surface including depth information, for example, a surface
examining apparatus which can be used for ophthalmic examination such as
the examination of glaucoma.
2. Related Background Art
In the heretofore known ophthalmic examining apparatus, an eye fundus
camera has been widely used as the means for recording information of an
eye to be examined, for example, the information of the eye fundus. To
gather the uneven state of the eye fundus, there have been practiced a
method simply stereo-photographing the eye fundus and gathering the uneven
state of the eye fundus from the image of the eye fundus and a method of
projecting a striped pattern onto the eye fundus and gathering the uneven
state of the eye fundus from the shape ofthe image of the striped pattern.
However, in the former method, it is difficult to transform the depth of
the unevenness into the form of a numerical value. In the latter method,
it is necessary to accurately superpose and project a striped pattern. In
a case where, for example, the state of the depth profile of an optic
disc, which is information for judgment of glaucoma is to be examined, the
depth profile is wiped out by an illuminating light for the observation of
the eye fundus image. This leads to the disadvantage that measurement
becomes impossible or discontinuity occurs due to the measurement
conforming to the interval between the stripes.
In the field of eye fundus cameras U.S. Pat. No. 4,213,678 discloses a
known technique of scanning and illuminating the eye fundus by a light,
but this patent only discloses the detection of the eye fundus image and
does not disclose the detection of the depth distribution information of
the eye fundus.
Also, in Japanese Laid-Open Patent Application No. 16103/1981, there is
disclosed as an eye refractometer, the technique of projecting a
predetermined index mark onto a predetermined portion of the eye fundus,
providing light beam separating means in the optical path for receiving
the reflected light from the eye funduds, and finding the refractive power
of the eye from the position of the image of the index mark onlight
position detecting means. However, this publication of course does not
disclose the technical idea of detecting the depth distribution
informaiton of the eye fundus. Further, an eye refractometer and an eye
fundus camera differ fundamentally from each other, and this disclosure
simply cannot be combined with U.S. Pat. No. 4,213,678.
SUMMARY OF THE INVENTION
It is an object of the present inventin to provide a surface examining
apparatus which is capable of quantitatively detecting the depth
distribution information of a surface to be examined.
It is a further object of the present invention to provide a surface
examining apparatus which is capable of displaying the corrected image of
a surface to be examined on the basis of the depth distribution
informaiton of the surface to be examined.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the general construction of an embodiment of the present
invention.
FIG. 2 is a perspective view of a light-receiving stop.
FIG. 3 illustrates the positions of light spots projected onto a planar
image pick-up element.
FIG. 4 illustrates stereo images.
FIG. 5 shows a modification of a light-receiving mask.
FIG. 6 shows the image of a surface to be examined corrected on the basis
of the depth distribution information of the surface to be examined.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinafter be described in detail with respect
to an embodiment applied to an ophthalmic examining apparatus.
Referring to FIG. 1, reference numeral 1 designates a point source of light
comprising a coalescence point, for example, a scanning light source on the
lightemitting surface of a cathode ray tube scanner 1'. The scanning light
source may be one provided by scanning of a polygon mirror or the like. On
an optic axis passing through the point source of light 1 and an eye E to
be examined, there are disposed, in succession from the point source of
light 1 side, a projection lens 2, an apertured mirror 4 having an
aperture stop 3 at the center thereof and provided obliquely, and an
objective lens 5. On the reflection side of the apertured mirror 4 which
reflects the light beam from the objective lens 5, there are disposed a
light-receiving stop 8 comprising a combination of a liquid crystal plate
block 6 shown in FIG. 2 and a light-receiving mask 7 having two stop
apertures 7a and 7b also shown in FIG. 2, a beam splitter 9, a projection
lens 10, and a planar image pick-up element 11 comprising a
two-dimensional solid state image pick-up element which is a light
position detecting sensor substantially conjugate with the eye fundus Ef,
such as a two-dimensional CCD. Also, in the direction of reflection of the
beam splitter 9, there are provided a projection lens 12 and a
light-receiving element 13 which serves as a light amount detecting sensor
disposed at a position substantially conjugate with the pupil of the eye E
to be examined. The outputs of the planar image pick-up element 11 and the
light-receiving element 13 are connected to an electrical processing unit
14, the output of which is connected to the point source of light 1, the
liquid crystal plate block 6 and image display means 15 comprising a Braun
tube or the like.
The light beam from the point source of light 1 passes through the
projection lens 2, the aperture stop 3 disposed near the aperture in the
apertured mirror 4 and the objective lens 5 to the interior of the eye E
to be examined, and irradiates a point on the eye fundus Ef. The light
reflected by the eye fundus Ef passes through the objective lens 5 again
and is reflected by the mirror portion of the apertured mirror 4,
whereafter it passes through the light-receiving stop 8 comprising a
combination of the liquid crystal plate block 6 and the light-receiving
mask 7 as shown in FIG. 2 and further through the beam splitter 9 and is
projected onto the planar image pick-up element 11 by the projection lens
10.
The aforementioned light-receiving stop 8 is for taking out depth
information, and is comprised of a combination of the light-receiving mask
7 having two stop apertures 7a and 7b provided point-symmetrically with
respect to the optic axis as shown, for example, in FIG. 2 and the liquid
crystal plate block 6 comprising two liquid crystal plates 6a and 6b
independently covering the step apertures 7a and 7b, respectively, and is
adapted to alternately shield the stop apertures 7a and 7b from the light
by means of the two liquid crystal plates 6a and 6b. Accordingly, if it is
out of focus, the light beam projected onto the planar image pick-up
element 11 becomes light spots in which the lights passing through the
stop apertures 7a and 7b (which are the pupils of the light-receiving
optical system) are separated from eachother as indicated by P1 and P2 as
shown in FIG. 1 and if it is in focus, the light beam becomes a single
light spot in which the light spots are coincident with each other as
indicated by P0. Further, depending on whether the focal plane lies before
or behind the planar image pick-up element 11, the coordinates of the light
spots alternately projected are replaced with each other and thus, it
becomes possible to gather that information as well.
FIG. 3 shows this state, and represents the positions of the light spots on
the x, y coordinates. THe coordinates of the two light spots P1 and P2 are
(x1, y1) and (x2, y2), respectively (where y1=y2=y0), and the coordinates
of the centers thereof are detectable as (x0, y0). From this, the light
spot on the eye fundus Ef has the coordinates (x0, y0) on the planar image
pick-up element 11, and the depth .DELTA. thereof can be calculated as a
value proportional to (x1-x2). By plotting .DELTA. at each scanning
position, the depth distribution can be grasped. When the number of the
stop apertures is not two but one, the depth .DELTA. can likewise be
calculated by finding the absolute position of a single light beam or the
planar image pick-up element 11. On the other hand, as regards the image
information, measurement is effected with the reflected light beam from
the eye fundus Ef being separated, and for this purpose, the light beam
reflected by the apertured mirror 4 and passed through the light-receiving
stop 8 is divided by the beam splitter 9 and the divided light beams are
projected onto the light-receiving element 13 by the projection lens 12.
In this case, the light-receiving stop 8 is so disposed as to be imaged on
the light-receiving element 13, and since the size of the pupil will not
vary, this is convenient for measurement. The concentration of the light
sopot on the coordinates (x0, y0) can be determined by the output signal
of the light-receiving element 13 and therefore, if the point source of
light 1 is scanned in the area of the eye fundus Ef, the map of the eye
fundus surface and the information in the direction of depth thereof will
be obtained. The information of the light-receiving element 13 and the
information of the planar image pick-up element 11 are displayed on the
image display means 15 via the electrical processing unit 14.
With respect to the forms of the images displayed on the image display
means 15, the eye fundus image F and the depression figure D on any
cross-section S are conceivable as shown, for example, in FIG. 1, and in
this case, the designation of the cross-section can be selected
arbitrarily by inputting it from a terminal 16 to a microprocessor and the
depth information can be displayed as by a horizontal line together with
that portion of the image information it corresponds to. As a further
display method, it is also conceivable to depict the eye fundus image and
a contour figure superposed thereon or a monochromatic or colored
concentration figure corresponding to the depression. Also, by using the
liquid crystal shutters 6a and 6b alternately, respective eye fundus
images F1 and F2 can be depicted side by side on the same screen of the
image display means 15 in conformity with the light beams passing through
the two stop apertures 7a and 7b substantially outside the axis, as shown
in FIG. 4, and stereoscopic observation will also become possible of the
observing these images by left and right eyes, respectively.
In the above-described embodiment, the stop apertures 7a and 7b have been
shown as being fixedly provided, but alternatively, as shown in FIG. 5, a
light-receiving mask 7' having a single off-axis stop aperture 7c may be
rotated about the optic axis and the light spot image may be measured at
two points symmetric with the optic axis.
Further, besides the above-described embodiment, it is of course possible
to make the forms of the projection side and the light-receiving side
converse, that is, to make the position of the aperture stop converse so
as to pass the light beam through the off-axis aperture during projection
and pass the light beam through the central aperture during light
reception.
Also, as regards the coordinates P0 of the image, it is possible to
determine it by the coordinates on the projection side, i.e., at the
scanning position of the cathode ray tube scanner 1', instead of
determining it on the image receiving side, i.e., at the light beam
position on the planar image pick-up element 11.
Also, in the foregoing description, discrete light-receiving means have
been used for the determination of the XY coordinates of the image and the
determination of the concentration, but the concentrationcan also be
determined directly from the output of the planar image pick-up element.
Now, if there is a difference in the depth when the concentration is
measured at the received light amount level, even if the reflected light
is one from the same point on the eye fundus, the light-receiving level
varies and therefore, in roder to eliminate this, it is desirable that the
received light amount level be corrected on the basis of the depth
information. This may be accomplished as by setting a complete diffusing
surface as the surface to be examined, defining the light amount level
when the spacing between P1 and P2 is zero as a reference light amount
level, causing the microprocessor 14 to memorize the light amount level
when the complete diffusing surface has been shifted by a predetermined
amount in the direction of the optic axis and preparing a correction
coefficient in advance.
Further, in order to prevent the width ofthe scanning light beam on the
planar image pick-up element 11 from being varied by the depth position to
thereby cause defocus, the spacing between P1 and P2 when the complete
diffusing surface has been shifted by a predetermined amount in the
direction of the optic axis with the state in which the spacing between P1
and P2 is approximately zero as the reference can also be memorized by the
microprocessor 14. In this case, when the eye fundus surface which is
actually an uneven surface to be examined is to be imaged, the uneven
portion is defocused, but the uneven portion can be electrically
eliminated and the corrected image as a flat sharp eye fundus surface is
possible. Thus, in this case, the blurred depression in the eye fundus
image F in FIG. 1 is displayed as a blurfree corrected eye fundus image F'
(FIG. 6).
As described above, according to the present invention, the depth
information can be obtained and thus, it becomes possible, for example, to
display as an image the degree of depression, i.e., the C/D ratio, of the
optic disc which plays an important role in the judgment of glaucoma, and
to precisely measure the area portion thereof, and accuracy can be brought
about particularly in the diagnosis of glaucoma.
While the embodiment of the present invention has been described
withrespect to an ophthalmic examining apparatus, the present invention is
also applicable to other medical examining apparatus or industrial
examinations.
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