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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ophthalmologic apparatus, and more
particularly to an ophthalmologic apparatus having a projection optical
system for projecting a laser beam onto a prescribed point of an eye under
examination as a spot image.
2. Description of the Prior Art
Ophthalmologic apparatuses of this type include, for example, the laser
beam coagulation apparatus which is used for directing a laser beam onto
living tissue within the eye for raising the tissue to a high temperature
and causing it to thermocoagulate. In using this apparatus, it is
necessary to adjust the diameter of the laser beam spot according to the
size of the portion to be subject to thermocoagulation. Conventionally, a
zoom lens optical system has been used for this adjustment of the spot
diameter.
The zoom lens optical system used in such an ophthalmologic apparatus
comprises first and second lens groups which can be moved with respect to
each other to provide variable power capability. Since the lens groups are
moved so that the surface from which the laser beam is emitted and the
point at which the spot image is formed fall at the conjugate points of
the zoom lens optical system, it is consistently possible to obtain a spot
image that is in good focus and has a sharp edge.
In the case of conducting laser beam coagulation, however, it is not always
desirable to use a sharp-edged image and there are cases in which it is
better to conduct the optical coagulation with a spot image having a fuzzy
edge. For this, it is necessary to form the spot image at a position that
is not at the focal point so as to separate it from the conjugate
position. Where a zoom lens is used to realize variable power capability,
however, the aforesaid movement of the lens groups is controlled so as to
maintain the conjugate relationship. Thus the spot image is always in
focus and it is not possible to obtain a spot image with a fuzzy edge.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore to provide an
ophthalmologic apparatus of simple structure which is able to vary the
size of a laser beam spot image and to provide a spot image with a fuzzy
edge.
For realizing this object, the present invention provides an ophthalmologic
apparatus having a projection optical system for projecting a laser beam
onto a prescribed point of an eye under examination as a spot image,
wherein the projection optical system comprises a zoom lens for varying
the diameter of the spot image and some of the lenses constituting the
zoom lens are movable for enabling projection of a spot image with a fuzzy
edge.
With this arrangement, since the projection optical system for the laser
beam includes a zoom lens, the size of the projected spot image can be
varied. Moreover, since some of the lenses constituting the zoom lens are
movable, it is possible to project a spot image that is out of focus and
has a fuzzy edge. Preferably the movement of the lenses constituting the
zoom lens should be controlled by cam grooves provided in the zoom
lens-barrel so as to enable either variable power projection of a
sharp-edged spot image or of a fuzzy-edged spot.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the present invention will become more apparent
from the following detailed description taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a schematic view showing the overall structure of an embodiment
of the ophthalmologic apparatus according to this invention;
FIG. 2 is an optical diagram showing the arrangement of the lenses of an
optical system constituted mainly of a zoom lens system;
FIG. 3 is a graph showing the relationship between the movement of an
ordinary zoom lens system and the size of a spot image;
FIG. 4 is a graph showing the relationship between the movement of a zoom
lens system according to an embodiment of this invention and the size of a
spot image; and
FIG. 5 is a spreaded view of the configuration of cam grooves formed in a
zoom lens barrel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention will now be explained in detail with reference to the
embodiment illustrated in the drawings.
FIG. 1 shows an embodiment of the invention as applied to a laser beam
coagulation apparatus. The apparatus comprises a laser beam projection
optical system 21, a slit image formation optical system 20 and an
observation optical system 50. The slit image formation optical system 20
is disposed in a cylindrical member 22 so as to be rotatable about its
axis A. Light emitted by a lamp 24 is condensed by condenser lenses 25,
25' and directed onto a slit 26. Between the condenser lens 25 and the
slit 26 are disposed a roof deflection prism 27, a heat cut filter 28 and
a removable blue filter 29. An image 34' of the illuminated slit 26 is
formed at an image focal point 34, located, for example, on the retina of
an eye 33 of a patient under examination, by an imaging lens 30
constituted of lenses 30a, 30b. A mirror 35 is disposed between the lens
30b and the eye 33 of the patient. The mirror 35 is constituted of three
mirror sections 35a to 35c. Among these mirrors, the center one, mirror
35a, is arranged to be rotatable up and down about an axis perpendicular
to the drawing sheet and to be rotatable to the left and right about a
horizontal axis within the drawing sheet.
The laser beam projection optical system 21 is disposed within the same
cylindrical member 22 as houses the slit image formation optical system
20. A laser beam introduced through an optical fiber 41 is deflected
90.degree. by a mirror 42, passed through a lens 43 and a zoom lens
constituted of lenses 44, 45 and reflected by a mirror 31 so as to advance
along the same optical axis as that of the slit image formation optical
system 20, whereafter it passes through the lens 30 and is reflected by
the mirror section 35a to form a spot image 34 on the retina of the eye 33
and coagulate the tissue at this point. The diameter of the laser spot can
be varied between approximately 50 micrometers and 1 mm by movement of the
zoom lenses 44, 45.
The observation optical system 50 is constituted of an object lens 55, a
variable power lens 56, a safety filter 61, an imaging lens 57, erect
prisms 58, and an eyepiece 51. The operator is able to observe both the
slit image and the laser spot image formed within the eye 33 through the
observation optical system 50.
FIG. 2 schematically illustrates the portion of the optical system
centering on the zoom lenses 44, 45 housed within cylindrical member 22
for the laser beam projection optical system 21. The lenses or lens groups
44, 45, which together constitute a zoom lens and may themselves each be
constituted of a plurality of lenses, are disposed so as to be movable
along the optical axis in accordance with the curves shown in FIGS. 3 and
4.
When the zoom lens operates in the manner of an ordinary zoom lens, the
lens 44 moves in the manner indicated by curve 44a in FIG. 3, while the
lens 45 moves in the manner indicated by the curve 45a in the same figure.
In view of the characteristics shown in FIG. 3, the size of the spot image
34 at the point P becomes S1 when the lenses 44, 45 are at the positions X
and Y in FIG. 2. A well-focused, sharp-edged image 34 is consistently
obtained at the spot P irrespective of the positions of the lenses 44
since the point P is always at the image focal point having the end
surface 41a of the optical fiber 41 as its object focal point, i.e., since
the end surface 41a and the point P are the conjugate points. The size of
the spot image 34 at this time is determined by which positional
relationship shown in FIG. 3 the lenses 44, 45 assume.
So as to enable this embodiment of the invention to produce not only a spot
image that is always in sharp focus but also a blurred or fuzzy spot image
that is out of focus, the lens 45 is stopped when it is in the position Y,
as is shown by curve 45c in FIG. 4. As shown by curve 44c in FIG. 4, the
lens 44 is at this time moved between X and X' i.e., moved sequentially
away from and then toward the lens 45. As a result, the spot image 34 is
not formed at the point P but at the point P'. Therefore, the spot image
appearing at point P is blurred and its edge is fuzzy. The length of the
zone over which a blurred spot image is formed is indicated by L.
In all other zones, since the lenses 44, 45 move along curves 44b, 45b
similar to the curves 44a, 44b of FIG. 3, the spot image 34 is formed at
the point P, whereby there is obtained a sharp spot 34 of variable
magnification.
The configuration of cam grooves provided in a rotatable zoom lens barrel
46 for realizing the aforesaid lens movement is shown in FIG. 5.
Specifically, the lens 44 moves along the optical axis of the zoom lens in
accordance with a cam groove 44d, while the lens 45 moves along the
potical axis in accordance with a cam groove 45d. The configuration of the
cam groove for keeping the lens 45 stopped or immovable along the optical
axis at Y is indicated by reference symbol 45e.
As explained in the foregoing, the ophthalmologic apparatus according to
the present invention is provided in its laser beam projection optical
system with a zoom lens which enables the size of the projected spot image
to be varied. Moreover, since some of the lenses constituting the zoom
lens are made movable, it becomes possible to project an out-of-focus,
fuzzy-edged spot image using an apparatus of simple arrangement.
While the invention has been described with reference to a preferred
embodiment, it will be understood by those skilled in the art that various
changes may be made and equivalents may be substituted for elements
thereof without departing from the scope of the invention. In addition,
many modifications may be made to adapt a particular situation or material
to the teachings of the invention without departing from the essential
scope thereof. Therefore, it is intended that the invention should not be
limited to the particular embodiment disclosed as the best mode
contemplated for carrying out the invention, but that the invention will
include all embodiments falling within the scope of the appended claims.
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