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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for examining for the presence or
absence of ophthalmic diseases in a patient's eye, and more particularly
to an apparatus for 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 the ciliary body, the 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, the inner surface of the
ciliary body, and the front surface of the crystalline lens. The camera
oculi is filled with transparent humor aqueous, which has chemical and
physical characteristics that are different from those of lymphatic liquid
and has a close relation with the metabolism of the cornea or crystalline
lens. The humor aqueous contains proteins the increase of which causes
turbidity in the camera oculi 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
functions 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
the naked eye. This is, however, disadvantageous because the judgment
depends upon 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, highly complicated to analyze, and is thus 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.
Such use of a laser beam to focus on a selected spot in the camera oculi of
an eye for ophthalmic measurement by detecting light scattered from the
eye conventionally has been accompanied by such problems as an increased
intensity of the laser beam imposing major discomfort on the patient as
well as a high risk. If, in order to avoid this, a small-output laser
light source is employed, the intensity of the laser beam impinging on the
camera oculi is reduced, and as a consequence it is necessary to raise the
sensitivity of the light detection system, raising the cost of the overall
apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide an ophthalmic
disease detection apparatus which, with respect to the patient, imposes as
little discomfort as possible and involves little risk, in addition to
which the output of the laser light source can be small, enabling the
overall apparatus to be made compact in size.
An apparatus for detecting ophthalmic diseases in a patient's eye according
to the present invention comprises a light transmitting means which
comprises a laser source for producing a laser beam, a laser beam
projector for projecting the laser beam along a first optical axis, means
for focusing the laser beam at a selected spot in the patient's eye, light
receiving means including visual observing means or observation equipment
for observing light scattered from the spot in the patient's eye and a
photoelectric converting means photoelectrical converter for
photoelectrically converting the scattered light into an electrical
signal, and means for processing the electrical signal to evaluate the
ophthalmic diseases in the patent's eye. The laser beam projector and
light receiving means are arranged so that their optical axes cross
substantially at right angles with each other An optical element or light
guiding means lying along a second optical axis is further provided in the
light receiving means to divide the scattered light on to the
photoelectrical converter and observation equipment. The optical element
is arranged so that the optical axis of the scattered light directed
towards the photoelectrical converter lies in a plane that includes the
optical axes of the laser beam projector and the light receiving means.
Because in accordance with the said arrangement the laser beam projector
and the light receiving means are arranged at a set angle or 90 degrees to
each other, light scattered laterally is received from an angle of 90
degrees. Therefore, the scattered laser light is formed almost entirely of
polarized (S-polarized) components perpendicular to the plane of
incidence, that is, a plane that includes the incident laser beam and the
reflected beam. An optical element such as a semi-transparent mirror or a
beam splitter for guiding the scattered laser light along a third optical
axis to a photoelectric converter is positioned so that the optical axis
of the laser light scattered towards the photoelectric converter is in a
plane that includes the optical axes of the laser beam projector and laser
light receiving means, so that laser light scattered from the camera oculi
impinges on the said semi-transparent mirror or beam splitter as
S-polarized light, therefore facilitating the reflection thereof,
S-polarized light generally being readily reflected. Thus, it becomes
possible to efficiently guide the scattered light to the photoelectric
converter.
Thus, as in accordance with this invention, a semitransparent mirror is
disposed so that the optical axis of the laser light scattered towards the
photoelectrical converter is positioned in a plane that includes the
optical axes of the laser beam projector and the laser light receiving
means, thereby enabling the scattered light to be guided efficiently to
the photoelectric converter, making it is possible to decrease the output
of the projected laser beam by a corresponding amount. Not only does this
reduce the amount of discomfort on the patient by enabling the laser light
source to be made smaller, but it also makes it possible to reduce the
cost of the overall apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the present invention will become more apparent
from a consideration of the following detailed description taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a general perspective view of an apparatus according to the
present invention.
FIG. 2 (A) is a drawing showing the arrangement of the optical system of
the apparatus viewed along a horizontal cross-section.
FIG. 2 (B) is a drawing showing the arrangement of the optical system of
the apparatus viewed along a perpendicular cross-section.
FIG. 3 is an explanatory drawing illustrating the effect of the apparatus
of the invention.
FIG. 4 is a drawing showing the arrangement of the optical system of
another embodiment of the apparatus.
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 arranged to pass along the optical
axis L1 of first optical axis of a laser beam projector, through a lens
2', a beam splitter 5 and a condenser lens 6 to converge on the eye under
examination at a spot P in the anterior aqueous humor 11c on the inner
side of the cornea 11b and to the front of the crystalline lens 11a.
The laser beam projector is provided with a slit light source 12. As shown
in FIG. 2 (A), light from the slit light source 12 passes via a slit 14, a
shutter 13 and a lens 15' to the beam splitter 5 and passes along the
optical axis L1 to form a slit image in the region of the aqueous humor
11c. Because the light from the laser light source converges to form a
spot, this slit image can be used to illuminate the surrounding area
thereof to facilitate confirmation of the position of the spot of
converged light.
The width and length of the slit 14 can be adjusted by an adjusting knob 15
and a switching knob 16, respectively, which are shown in FIG. 1.
The laser light scattered from the measuring spot P in the aqueous humor
11c advances along an optical axis L2 or second optical axis to an
objective lens 20 and is split by a semitransparent mirror or a beam
splitter 21. One part of the light passes along a third optical axis
through a lens 22, a shutter 26' and a mask 26 provided with a slit 26a
and impinges on a photoelectric converter 27 comprised of, for example, a
photomultiplier. The other part of the scattered light split by the beam
splitter 21 passes along a fourth optical axis via a lens 30, a prism 31
and a field-of-vision stop 34 to an eyepiece 32 by means of which an
examiner 33 carries out observations. With this embodiment the beam
splitter 21 is positioned so that, as shown in FIG. 2 (B), the optical
axis of the scattered laser light that goes to the photoelectric converter
27 is in a plane L3 that includes the optical axes L1 and L2 of the laser
beam projector and the light receiving means.
The output from the photoelectric converter 27 is passed through an
amplifier 28 and is input to a counter or counting means 40 and the
intensity of the scattered light detected by the photoelectric converter
is counted as a number of pulses per unit time. The output of the counter,
i.e., the number of samplings or the total pulse count, is stored in a
memory or memory means 41 allocated for each unit time. The data stored in
the memory 41 is processed by an evaluating device 42 which computes the
cell count and the concentration of protein in the anterior chamber.
As shown in FIG. 1, the light receiving means 29 is affixed to a support
70. The support 70 and the laser beam projector are provided so as to be
rotatable, 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 an optimum setting. As shown in FIG. 2
(A), in this embodiment, the optical axis L1 of the laser beam projector
is arranged at an angle of approximately 90 degrees to the optical axis L2
of the light receiving means, so the light receiving means receives the
light laterally, at this angle of 90 degrees.
Also in accordance with this embodiment, an eye fixation light 90
constituted of a light-emitting diode or the like is provided at a
position that permits fixation of the patient's eye by the examiner. 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 to an
optimum position with respect to the examiner. 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 into, or retract from, the optical system
such optical elements as shutters and filters.
The operation of the apparatus arranged thus will now be described. In
conducting the measurement, the slit light source 12 is activated and an
image of the slit 14 is formed on a portion of the anterior aqueous humor
11c that includes the measuring point P. Following this, light from the
laser light source 1 is converged on the measuring point P by means of the
laser light projector system.
A portion of the light scattered from the measuring point P is
simultaneously directed by the beam splitter 21 to the examiner 33 for
observation and through a lens 22, shutter 26' and mask 26 to impinge on
the photoelectric converter 27. Because in accordance with the present
embodiment, as described above, the optical axis L1 of the laser beam
projector and the optical axis L2 of the light receiving means are
arranged at substantially 90 degrees to each other, the photoelectric
converter 27 receives light scattered laterally from an angle of 90
degrees. In this case, as illustrated in FIG. 3, almost all the components
of the light scattered at 90 degrees are polarized (S-polarized)
components perpendicular to the plane that includes the optical axes L1
and L2 (in the drawing this polarized component portion is indicated by
the vertical double-headed arrows). The beam splitter 21 is positioned so
that the S-polarized component impinges thereon, i.e., so that an optical
axis L4 of the scattered laser light is in a plane that includes the
optical axes L1 and L2, which enables the scattered light to be
efficiently guided to the photoelectric converter 27. The photoelectric
converter 27 detects the intensity of the light and converts this into a
corresponding series of pulses which are counted by a counter 40 as
numbers of pulses per unit time and the count values are stored in the
memory 41 allocated for each unit time, and the evaluating device 42
processes the data contained in the memory 41 to evaluate the protein
concentration and blood cell count.
Since the transmittivity (also reflectivity) of the beam splitter 21 can be
set as required, the sensitivity can be raised simply by increasing the
amount of light directed at the photoelectric converter. However, the
light for observation purposes will be reduced by a corresponding amount,
making observation more difficult, and this, in turn, can make positional
alignment more difficult. With this arrangement according to the first
embodiment of the invention, the amount of light for observation purposes
can be maintained unchanged, with only the quantity of scattered laser
light (signal component) being increased.
FIG. 4 shows another embodiment of the present invention. In this
embodiment, the relationship between the observation system and the signal
light receiving means has been reversed. With this arrangement, the
scattered light impinges on the semitransparent mirror (or beam splitter)
as P polarized light, facilitating the transmission there of, and then
impinges on the photoelectric converter 27. With this arrangement the
process of observation of the scattered light by the examiner 33 is
carried out from above.
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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