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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for detecting ophthalmic diseases in
a patient's eye, and more particularly to an improvement in the alignment
capability of an apparatus used in detecting ophthalmic diseases in which
laser light is radiated via an optical system at one spot in the camera
oculi of the patient's eye, particularly in the anterior chamber thereof,
and the laser light scattered therefrom is analyzed to measure the protein
concentration for ophthalmic disease detection in the camera oculi.
2. Description of the Prior Art
The camera oculi is comprised of the camera oculi anterior (anterior
chamber) and the camera oculi posterior (posterior chamber). The camera
oculi anterior is defined by a space surrounded by the rear surface of the
cornea, a part of ciliary body, iris, and the front surface of the
crystalline lens, while the camera oculi posterior is defined by a space
surrounded by the rear surface of the iris, inner surface of the ciliary
body, and front surface of the crystalline lens. The camera oculi is
filled with transparent humor aqueous, which has chemical and physical
characteristics different from lymphatic liquid and is closely related to
the metabolism of the cornea or crystalline lens. The humor aqueous
contains proteins which increase causing the camera oculi to be turbid
when it becomes inflamed.
In this respect, the measurement of protein concentration in the camera
oculi of the patient's eye is of great importance in determining whether
the camera oculi is inflamed, that is, whether a blood-aqueous barrier is
functioning normally or not.
To measure the protein concentration in the camera oculi, a slit lamp
microscope is very often used to determine the turbidity by grading via
naked eyes. This is, however, disadvantageous because the diagnosis
depends upon the judgement of the person who performs the measurement.
On the other hand, a photographic measuring method has been developed to
make a quantitative measurement of the protein concentration. This method
is, however, too complicated to analyze, thus making it very difficult to
apply in a clinical examination.
To overcome this problem, an apparatus for detecting ophthalmic diseases
has been proposed which includes means for focusing a laser beam at a
selected spot in the camera oculi of an eye. In the apparatus, the light
scattered from the eye is photoelectrically detected and converted into an
electrical signal which is subsequently used to determine the protein
concentration essential to ophthalmic disease detection in the camera
oculi of the patient's eye. See, for example, Japanese Patent Laying-open
No. 120834/87.
In order to increase the reliability of the measured data obtained using
this type of ophthalmic disease detection apparatus, it is necessary that
the measurements are always precisely made on the same part of the eye,
which in, turn requires prior positional alignment of the patient's eye
with the laser beam projector, and light-receiving means.
To achieve this type of alignment, conventional ophthalmic disease
detection apparatuses have been provided with special index means. This
makes the apparatus complex, however, because such means requires the use
of an optical alignment system and the like, raising the manufacturing
cost of the overall apparatus.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to
provide an ophthalmic disease detection apparatus in which the positional
alignment process is simplified.
Another object of the present invention is to provide an ophthalmic disease
detection apparatus which enables the protein concentration in a patient's
eye to be measured with ease and precision.
In an apparatus for detecting ophthalmic diseases in a patient's eye in
accordance with the present invention, a laser beam is projected at a
selected spot in the patient's eye and light scattered therefrom is
received on a photoelectrical converter for conversion into an electrical
signal. The apparatus comprises a laser source for producing a laser beam,
a laser beam projector for projecting the laser beam, means for focusing
the laser beam at a selected spot in the patient's eye, and means provided
in the laser beam projector for monitoring light scattered from the cornea
of the patient's eye on which the laser beam is projected and a virtual
image which is formed by the cornea surface from light scattered at the
exit window of the laser beam. The apparatus is positionally aligned
relative to the patient in such a manner that the virtual image and the
scattered light from the cornea take predetermined positions on the
monitoring means.
In the apparatus according to the present invention, light scattered from
the cornea of a patient's eye on which a laser beam is projected by a
laser beam projector, and a virtual image which is formed by the cornea
surface from light scattered at the exit window of the laser beam, can be
monitored by monitoring means provided in the laser beam projector. Since
the virtual image moves in accordance with the movement of the laser beam
projector but the scattered light image does not move, by monitoring these
images it is possible to positionally align the apparatus with respect to
the eye being examined.
In a preferred embodiment, a polarizing beam splitter or semitransparent
mirror is provided behind the exit window to guide the light scattered
from the cornea of the patient's eye and the virtual image formed by the
cornea surface to the monitoring means.
Preferably, the monitoring means includes a CCD camera for picking up the
light scattered from the cornea of the patient's eye and the virtual image
formed by the cornea surface and a monitor screen with markings therefor.
Alternatively, the monitoring means includes a monitor screen provided with
line sensors to detect the light scattered from the cornea of the
patient's eye and the virtual image formed by the cornea surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the present invention will become more apparent
from the accompanying drawings and the following detailed description of
the invention.
FIG. 1 is a perspective view of an apparatus according to the present
invention;
FIG. 2 is a drawing showing the arrangement of the optical system of the
apparatus;
FIGS. 3 and 4 are drawings showing the arrangement of embodiments of the
optical system of the apparatus with another optical alignment system;
FIG. 5 is an explanatory drawing illustrating the image on a
light-receiving screen; and
FIG. 6 is an explanatory drawing illustrating the image on a monitor
screen.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will now be described in detail with reference to the
drawings.
In FIGS. 1 and 2 which show an arrangement of the ophthalmic disease
detection apparatus according to the present invention, reference numeral
1 denotes a laser light source such as, for example, a helium-neon or
argon laser source. The laser light source 1 is disposed on a stand 2.
Light from the laser light source 1 is passed through a laser beam filter
3, a prism 4, a swingable mirror 5, a prism 6, a lens 7, a beam splitter
8, a semitransparent mirror (or a polarized light beam splitter) 61, a
lens 9 and a prism 10 and converges on an eye under examination 11 at a
spot in the anterior chamber 11a thereof.
The laser beam projector is provided with a slit light source 12. Light
from the slit light source 12 passes via a slit light shutter 13 and a
slit 14 and goes via the beam splitter 8, the prism 6, the lens 9 and the
prism 10 to form a slit image in the anterior chamber 11a. With the light
from the laser light source being converged to a spot, this slit image is
for illuminating the surrounding area to confirm the position of the spot
of converged light.
The width of the slit 14 can be adjusted by an adjusting knob 15 and the
length of the slit 14 can be switched by a switching knob 16.
A portion of the laser light scattered from the measuring spot in the
anterior chamber 11a passes through an objective lens 20 of a
light-receiving means 29 and is split by a semitransparent mirror or a
beam splitter 21. One part of the light thus split passes through a lens
22, a mask 26 provided with a slit 26a, and a shutter 26' and impinges on
a photomultiplier 27 used as the photoelectric converter. The other part
of the scattered light split by the beam splitter 21 passes via a lens 30
and prisms 31 and 34 to an eyepiece 32 by means of which an examiner 33
can carry out observations.
The output from the photomultiplier 27 is passed through an amplifier 28,
and is then input to a counter 40 which counts the intensity of the
scattered light detected by the photomultiplier as numbers of pulses per
unit time period. The output of the counter 40, i.e., the number of
samplings or the total pulse count, is stored in a memory 25 allocated for
each unit time period. The data stored in the memory 25 is processed by an
evaluating device 41 which, as explained below, computes the protein
concentration in the anterior chamber.
Under the control of the evaluating device 41, the mirror 5 is caused to
swing by means of a mirror drive circuit 60, causing the laser beam to
scan, thereby moving a spot of laser light within the anterior chamber.
The light-receiving means 29 is affixed to a support 70. The support 70 and
the laser beam projector are affixed so that they can rotate, with respect
to each other, about a shaft 71 so as to allow the angle between the
optical axes of the laser beam projector and the light-receiving means to
be adjusted to a required setting. In this preferred embodiment this angle
is set to be approximately 90 degrees.
Also, the laser beam projector is provided with a light-receiving screen or
visual indicating means 63, a lens 62 and the semitransparent mirror
(polarized light beam splitter) 61. The screen 63 serves to monitor
scattered light A from the cornea of the eye at the point of entry of the
projected laser beam, and a virtual image B' (see FIG. 3) which is formed
by the corneal surface 11b from light scattered at the movable exit window
B of the laser beam, for positional alignment of the apparatus relative to
the patient's eye.
In accordance with this invention, an eye fixation light 90 comprising a
light-emitting diode or the like powered by electricity supplied from a
power source 91 is disposed at a position that permits the examiner to fix
the patient's eye. The light selected for the eye fixation light 90 is of
a different color than the light of the laser light source 1. For example,
when the light from the laser light source is red, a green light is
selected. The eye fixation light 90 can be turned in the direction
indicated by the arrow by means of a link mechanism 92 to enable it to be
adjusted so that it is always optimally positioned with respect to the eye
being examined.
Provided on the base 2 is an input means, such as a joystick 45 equipped
with a push-button 46, and this can be operated to insert the laser filter
3, the slit light shutter 13 and the photomultiplier shutter 26' into, or
out of, the optical system concerned.
The operation of the apparatus will now be described. In conducting the
measurement, the slit light source 12 is first activated and, via the beam
splitter 8, the semitransparent mirror 61, the lens 9 and the prism 10, an
image of the slit 14 is formed on a part of the anterior chamber 11a that
includes the measuring point P. Following this, light from the laser light
source 1 is converged on the measuring point P via the said optical
system.
Prior to the measurement the apparatus is first aligned. The scattered
light A from the corneal surface 11b of the eye at the point of entry of
the projected laser beam, and the virtual image B' which is formed by the
corneal surface 11b from light scattered at the exit window B of the laser
beam are simultaneously monitored for positional alignment of the
apparatus.
The laser beam impinging on the eye produces the scattered light A at the
corneal surface 11b. The scattered light is monitored using the same
optical axis L as that of the laser beam projector. The light is passed
through the laser beam exit window B, the semitransparent mirror 61 to
split the optical axis, to the image-formation lens 62 and form an image
at the light-receiving screen 63 for alignment purposes. By fixing the
distance between the image-formation lens 62 and the light-receiving
screen 63, in accordance with image-formation formulae, and by focusing
the scattered light image A' on the surface of the light-receiving screen
63 it becomes possible to determine the distance from the laser beam exit
window B to the corneal surface 11b.
Also, in accordance with curved surface image formation formulae, corneal
reflection of the scattered light from the laser beam exit window B forms
a virtual image B' over a line linking the corneal center of curvature C
with the axis of the laser beam exit window B. The virtual image B' and
the scattered light image A' are monitored on the light-receiving screen,
as illustrated by FIG. 5. As the scattered light image A' is made in
focus, laser beam exit window B is observed as an out-of-focus virtual
image B'. Because image A' is monitored using the same optical axis as
that of the laser beam projector, there is no movement of the image A' on
the light-receiving screen. Therefore, having the center of the virtual
image B' at a predetermined position above the light-receiving screen 63
ensures that the laser beam projection position will be at a plane
perpendicular to the optical axis of the projected beam. Thus, this
determines the three-dimensional components of the measurement location,
enabling ophthalmic measurements to be carried out with a high degree of
precision.
Measurement is started following the above alignment.
A portion of the light from the measuring point P is simultaneously
directed by the beam splitter 21 to the examiner 33 for observation and
through the lens 22, a prism 23 and the mask 26 to impinge on the
photomultiplier 27.
The mirror 5 is driven to swing in the direction indicated by the arrow by
means of the mirror drive circuit 60, causing the part to be measured to
be scanned by the laser beam.
The photomultiplier 27 receives the incident scattered laser light via the
slit 26a, detects the intensity of the light that has been scattered by
protein particles in the anterior chamber 11a and converts this
information into a corresponding series of pulses which are counted by the
counter 40 as numbers of pulses per unit time period. The count values are
then stored in a memory 25 allocated for each unit time period. The data
stored in the memory 25 is processed by the evaluating device 41 to
compute the concentration of protein in the anterior chamber.
FIG. 4 illustrates another embodiment of the present invention. In this
embodiment, a CCD camera 64 replaces the light-receiving screen 63 of the
previous embodiment, which displays on the monitor screen 65 the
scattered-light image A' and the virtual image B' as shown in FIG. 6. For
alignment purposes image A' does not move even when the optical system is
moved, so alignment can be facilitated by adjusting the CCD camera 64 to
display the image A' at a predetermined position on the monitor screen 65
(indicated by first indicating means, 67) and by providing an index or
second indicating means 66 at an image B' as a target value on the monitor
screen. For example, if a joystick or the like is used to move the optical
system to focus the scattered light image A' and with the image A' in
focus the optical system is gradually moved to set the virtual image B' to
the position of the index 66, precise positioning of the projected laser
beam becomes possible.
With this method, although it is not illustrated, positioning can be
carried out automatically by processing image information from the area
sensor of the CCD camera and providing an autofocus mechanism for the
image A' and a moving mechanism for the image B'.
In another embodiment, as shown by the broken line portions in FIG. 5, an
image focusing line sensor or first detecting means 68 and image position
detection line sensors 69, 69' or second detecting means are provided on
the light-receiving screen 63. Image focusing line sensor 68 is positioned
in the vicinity of the positioning detection optical axis, part of which
coincides with the axis of laser beam projection, so that it includes the
image A'. When the peak width of information from the line sensor 68 that
is passed through a differential filter, for example, is the same or less
than a predetermined value, it is considered to be in a state of focus.
As shown in FIG. 5, the line sensors 69, 69' are disposed substantially at
right-angles to each other. When the optical system is moved so that each
of the line sensors at a maximum value moves to its predetermined
position, the center of the image B' is at the predetermined position. As
a result, three-dimensional positioning can be performed.
With this method, while not illustrated, the positioning state can be
indicated by means of LEDs or the like disposed within the visual field of
a microscope provided in the optical observation system for monitoring the
measurement position, or it can be done manually. Positioning can also be
done automatically in the same way as in the above first method, utilizing
information from the line sensors.
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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