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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser scanning type eye fundus camera for scan
projecting a laser beam onto the retina of an eye to be tested and
receiving a reflected beam from the retina through a light receiving
element and then color photographing the retina in accordance with a
signal coming from the light receiving element.
2. Description of the Related Art
Heretofore, an illuminating light of somewhat strong (or intensified)
energy has been used for projecting the same to the retina of an eye to be
tested in order to photograph a retina using a conventional eye fundus
camera.
The test according to this conventional method was painful to the patient
both physically and mentally.
In recent years, in order to diminish this burden or pain and enhance the
safety of the testing, there was proposed a laser scanning type eye fundus
camera in which a laser beam is scan projected to the retina so that a
strong (or intensified) energy would not be irradiated to a particular
part for a long period of time. Moreover, as a color photograph obtained
by illuminating the retina with a white light is useful in ordinary eye
fundus testing, there has been contemplated a laser scanning type eye
fundus camera by which a color photograph can be taken.
As such a laser scanning type eye fundus camera which is capable of color
photographing, there is one disclosed, for example, in U.S. Pat. No.
4,781,453. In this laser scanning type eye fundus camera, the retina is
photographed for each frame using a laser beam of various wavelengths in
the four colors of R, G, B and Y, and retina images obtained by respective
wavelengths are combined to obtain one color retina image.
However, when the retina is to be photographed for each frame in sequence
using four kinds of laser beams which have different wavelengths, it takes
a long period of time to obtain one color retina image. In such a long
period of time, there is a problem that the retina image may be changed
due to movement of the eye to be tested. Therefore, it becomes difficult
to obtain a clear retina image because there occurs a slippage of the
respective images when such images of various wavelengths are combined.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a laser
scanning type eye fundus camera which is capable of color photographing in
a shorter period of time than the above-mentioned conventional eye fundus
camera.
In order to achieve the above-mentioned object, the present invention
includes laser beam generating means for generating laser beams having
wavelengths of three primary colors;
a scanning optical system for scan projecting the laser beams to the retina
of an eye to be tested;
switch means for selectively switching laser beams of various wavelengths
coming from said laser beam generating means and guiding the same to said
scanning optical system;
control means for controlling said switch means so as to selectively switch
at least two laser beams among said three laser beams and permitting said
scanning optical system to scan project one frame portion of such selected
laser beams to the retina of the eye and also permitting said scanning
optical system to scan project one frame portion of two laser beams or
less including the remaining one among said three laser beams to the
retina of the eye; a light receiving optical system for taking out a
reflected light from the retina of the eye;
first light receiving means for receiving reflected light having two
wavelengths among said wavelengths of said three primary colors which are
guided by said light receiving optical system; second light receiving
means for receiving a reflected light having the remaining one wavelength
among said wavelengths of said three primary colors which is guided by
said light receiving optical system; and
image processing means for composing said various primary colors in
accordance with output from said light receiving means in order to form a
single color retina image.
These and other objects, features and advantages of the present invention
will be well appreciated upon reading of the following description of the
invention when taken in conjunction with the attached drawings with the
understanding that some modifications, variations and changes of the same
could be made by the skilled person in the art to which the invention
pertains without departing from the spirit of the invention or the scope
of claims appended hereto.
BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS
FIG. 1 is a plan view showing an arrangement of an optical systems of a
laser scanning type eye fundus camera according to the present invention;
FIG. 2 is a schematic side view showing the arrangement of FIG. 1;
FIG. 3 is a control circuit diagram of a laser scanning type eye fundus
camera shown in FIG. 2;
FIG. 4 is a detailed view of a synchronous control circuit shown in FIG. 3;
FIG. 5 is an explanatory view showing photographing patterns of the laser
scanning type eye fundus camera shown in FIGS. 1 through 4;
FIG. 6 is an explanatory view showing another example of photographing
patterns of the laser scanning type eye fundus camera shown in FIGS. 1
through 4; and
FIGS. 7 and 8 are arrangements showing another example of an optical path
switch means shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The embodiment of the present invention will be described hereinafter with
reference to the drawings. FIGS. 1 through 5 show a first embodiment of
the present invention.
In FIG. 1, a laser scanning type eye fundus camera has first, second and
third lasers 1, 2 and 3 (laser generating means) for generating laser
beams having wavelengths of three primary colors, i.e., B (Blue), G
(Green) and R (Red). The lasers 1, 2 and 3 may include a laser emitting
diode or the like. Laser beams generated by the lasers 1, 2, 3 are made
incident to the scanning optical system 4. In this case, a blue laser beam
generated by the laser 1 is made incident to a scanning optical system 4
through a lens 5 and a half mirror 6 as a beam splitting means. Similarly,
a green laser beam generated by the laser 2 is made incident to the
scanning optical system 4 through a dichroic mirror 7, a rotating mirror
8a of an optical path switch device 8 (optical path switch means), the
lens 5, and the half mirror 6. Likewise, a red laser beam generated by the
laser 3 is made incident to the scanning type optical system through the
rotating mirror 8a of the optical path switch device 8 (optical path
switch means), the lens 5, and the half mirror 6 after transmitting
through the dichroic mirror 7.
The dichroic mirror 7 is provided with a coating material so that a laser
beam of a green wavelength is reflected and a laser beam of a red
wavelength is permitted to transmit. Accordingly, the rotating mirror 8a
can be removably inserted into the optical path as will be described
afterward. When the rotating mirror 8a is removed from the optical path,
the blue laser beam is guided to the scanning optical system 4. On the
other hand, when the rotating mirror 8a is inserted into the optical path
4, the green and red laser beams are guided to the scanning optical system
4.
This scanning optical system 4, as shown in FIGS. 1 and 2, includes a
polygonal scanner 9 for horizontally scanning a laser beam, relay lenses
10, 11 commonly used as a variable lens, a galvano scanner 12 for changing
the horizontal scanning position of the polygonal scanner 9 to a vertical
direction, a relay lens 13, a focus lens, a reflecting mirror 15, an
objective lens 16, etc. Such scanning optical system 4 scan projects the
laser beams from the lasers 1, 2 and 3 to the retina Ef of the eye to be
tested in accordance with the operation of the scanners 9 and 12 to
illuminate the retina Ef. The scanning range of the retina by the scanning
optical system 4 can be changed to 20.degree..about.60.degree. by the
relay lens.
The reflected light from this retina Ef can be recieved through the light
receiving optical system 4. This light receiving optical system includes
the scanning optical system 4, the half mirror 6, a lens 17 and a dichroic
mirror 18. The dichroic mirror 18 has such characteristics as to reflect
the red light and permit the green and blue light to transmit. The
reflected light received by this light receiving optical system and
permitted to transmit through the dichroic mirror 18 is made incident to a
light receiving device 19, such as P.M.T. (photomultiplier). The light
reflected by this dichroic mirror 18 is made incident to a light receiving
device 20 such as P.M.T. (photomultiplier), etc. Accordingly, when the
reflected laser beams of blue, green and red colors reflected by the
retina Ef are recieved through the light receiving optical system, the
reflected laser beams of blue and green colors are permitted to transmit
through the dichroic mirror 18 and input into the light receiving device
19. On the other hand, the reflected laser beam of the red wavelength is
reflected by the dichroic mirror 18 and input into the light receiving
device 20.
Also, a portion of the laser beams coming from the lasers 1, 2 and 3, is
permitted to transmit through the half mirror 16 and made incident to a
light receiving element 21 as a reference light receiving device.
The mirror 8a, the polygonal scanner 9 and the galvano scanner 12 are drive
controlled by a control circuit shown in FIG. 3. This control circuit 22
and its operation will now be described with reference to FIGS. 1 through
5.
Upon actuation of the control circuit 22, the polygonal scanner 9 is
rotated at a high speed rate in accordance with a signal from a clock
oscillator 24 of a synchronous control circuit 23 through a driver 25.
When the laser beams are generated from the lasers 1, 2 and 3, in the
foregoing state, the polygonal scanner 9 of the scanning optical system 4
horizontally scans the laser beams to the retina Ef by the number of
reflecting surfaces every time the polygonal scanner 9 makes one rotation.
On the other hand, the polygonal scanner 9 outputs a horizontal
synchronous signal every time the laser beam has made one horizontal
scanning to the retina Ef as described. This horizontal synchronous signal
is input into a scanning signal counter 26, a sampling control portion 27,
and a synchronous signal generating portion 28. A clock signal is input
into the sampling control portion 27 and the synchronous signal generating
portion 28 from the clock oscillator 24.
The scanning signal counter 26 counts the horizontal synchronous signal
coming from the polygonal scanner 9 and inputs a scanning position change
signal into a vertical synchronous control portion 29 every time the
horizontal synchronous signal is input. The vertical synchronous control
portion 29 outputs a vertical synchronous signal upon input of this
scanning position change signal in order to cause a driver 30 to rotate
the galvano scanner 12 by a predetermined angle to displace the horizontal
scanning position downward by a predetermined pitch. Also, when all of the
lines for one frame portion are scanned, a one frame scanning end signal
is input into the vertical synchronous signal control portion 29 from the
scanning signal counter 26 and an optical path switch signal is input into
a mirror pivot driving means, such as a solenoid, of the optical path
switch device 8.
By this, the vertical synchronous control portion 29 returns the galvano
scanner 12 to the original scanning portion. On the other hand, the
optical path switch device 8 is actuated by the optical path switch
signal. When the mirror 8a of this optical path switch device 8 is
inserted into the optical path, the mirror 8a is taken out of the optical
path, whereas when the mirror 8a is removed out of the optical path, the
mirror 8a is inserted into the optical path. A switching state of this
mirror 8a is maintained until the next signal is input.
This scanning number is different depending on the switching state of a
NTSC/HDTV switch 31. That is, when the NTSC/HDTV switch 31 is at the NTSC
position, the polygonal scanner 9 is scan driven at 15.75 KHz and the
galvano scanner 12 is driven at 30 Hz, and the number of the scanning
lines becomes 525 for one frame portion. On the other hand, when the
NTSC/HDTV switch 31 is at the HDTV side, the polygonal scanner 9 is driven
at 15.75 KHz and the galvano scanner 12 is scan driven at 15 Hz, and the
number of the scanning lines become 1050 for one frame portion. As the
HDTV monitor has scanning lines of 1125 in the number, the speed is
changed slightly when reading and displayed. Owing to the foregoing
construction, a high resolution image can be photographed by scan driving
at a comparatively low speed according to necessity.
On the other hand, the vertical switch signal and one frame scanning end
signal are input into a memory synchronous control portion 32 and the
synchronous signal generating portion 28 from the scanning signal counter
26, and the vertical synchronous signal is input into the memory
synchronous control portion 32 from the vertical synchronous control
portion 29. Synchronous signals are input into first and second memories
33 and 34 and a reading control portion 35 from this memory synchronous
control portion 32. Similarly, control signals are input into the memories
33 and 34 from the reading control portion 35.
Also, output signals are input into the memories 33 and 34 from the light
receiving devices 19 and 20 through an A/D converter 36. This A/D
converter 36 is controlled by the sampling control portion 29 and output
signals are input into the memories 33 and 34 from the light receiving
devices 19 and 20. This input timing is performed every time a laser beam
spot to be scanned to the retina Ef is moved for one portion.
Such spot quantity (i.e. an image information signal) for each spot is
stored in sequence at predetermined addresses of the memory 33 by the
memory synchronous control portion 32 every time one horizontal scanning
is effected. That is, when the mirror 8a is removed out of the optical
path, a blue reflected laser beam from the retina Ef is stored in sequence
in a predetermined address of a memory portion B of the memory 33 by the
memory synchronous control portion 32 every time one horizontal scanning
is effected. When a memory construction of image information signals for
one frame portion has been built up in the memory portion B and the mirror
8a has been inserted into the optical path, a green reflected laser beam
from the retina Ef is stored in sequence in a predetermined address of a
memory portion G of the memory 33 by the memory synchronous control
portion 32 every time one horizontal scanning is effected and a red
reflected laser beam from the retina Ef is stored in sequence in a
predetermined address of a memory portion R of the memory 33 by the memory
synchronous control portion 32 every time one horizontal scanning is
effected. As a result, a memory construction for one frame portion is
built up in the memory portions G and R. The memory storage for the memory
portions G and R is completed in one frame scanning time period.
When a memory action to this frame memory 33 has been finished, a memory
storage for the frame memory 34 is performed in the same manner. Such
memory storage for the memories 33 and 34 is repeated.
When a storage operation to the memory 33 has been finished and a storage
operation to the memory 34 is started, image information of the various
memory portions B, G and R of the memory 33 is output by a read control
portion. Similarly, when a storage operation to the memory 34 has been
finished and a storage operation to the memory 33 is started, image
information of the various memory portions B, G and R of the memory 34 is
output by the read control portion. The image information of B, G and R
output from the memories 33 or 34 is input into a display circuit 38
through a D/A converter 37. This display circuit 38 composes one color
retina image from the image information of B, G and R. The A/D, D/A and
memory circuit A of FIG. 3 include the memories 33 and 34, A/D converter,
D/A converted, and other corresponding elements shown in FIG. 4.
The image signal is then input into an NTSC monitor 40 or an HDTV monitor
41 through a switch circuit 31. A synchronous signal is input into the
display circuit 38 from the synchronous signal generating portion 28, and
a signal is input into the switch circuit from the NTSC/HDTV switch 31.
Also, when laser beams emitted from the lasers 1, 2, and 3 are made
incident to the scanning optical system 4, the laser beams are detected by
the light receiving device 21. An output from the light receiving device
21 is input into a light quantity control portion to control the lasers 1,
2, and 3 to make the laser light quantity constant. The respective outputs
of the lasers 1, 2, and 3 are set such that when an image of the various
wavelengths is composed, it becomes white in color of course, the
sensitivity of the light receiving element must be taken into
consideration.
In the above-mentioned embodiment, retina photographing for one frame is
performed with a laser beam of one wavelength within B, G and R and retina
photographing for the next one frame portion is performed with laser beams
of the other two wavelengths to obtain a retina image of wavelengths of B,
G and R. By composing the various images obtained, one color retina image
is obtained. However, the present invention is not necessarily so limited.
For example, as shown in FIG. 6, it can be designed such that retina
photographing for one frame is performed with two wavelengths of R and G
and retina photographing for one frame is performed with laser beams of
two wavelengths of R and B to obtain a retina image of B, G and R. By
composing the various images, one color retina image may be obtained. In
this case, since retina reflectance is high in R, the overlapping accuracy
becomes good when images for two frames are composed and therefore, a
clear image can be obtained.
Accordingly, the retina photographing and the monitor reproduction by the
memories 33 and 34 are alternatively performed as shown by the timing
diagram in FIG. 5.
Also, as shown in FIG. 7, an embodiment may be designed such that a half
mirror 42 is disposed between the lens 5 and the first laser 1, and two
reflecting mirrors 43 and 44 are disposed between the dichroic mirror 7
and the half mirror 42, an optical path O1 between the reflecting mirrors
43 and 44 being parallel with an optical path O2 between the half mirror
42 and the first laser 1, a rotating plate 45, a half portion of which
forms a light transmitting portion 45a, being disposed over the two
optical paths O1 and O2, the rotating plate 45 being able to be rotated by
180.degree.. In this case, the optical paths O1 and O2 can be switched by
rotating the rotating plate 45 by 180.degree..
FIG. 8 may be designed as such that the rotating plate 45 and the two
reflecting mirrors 43 and 44 of FIG. 7 are omitted, and high speed
shutters 46 and 47 formed of a liquid crystal, or the like, are disposed
between the half mirror 42 and the first laser 1, and between the dichroic
mirror 7 and the half mirror 42 respectively.
As the present invention has been constructed as described above, there can
be provided a laser scanning type eye fundus camera in which a retina
color photographing can be performed in a shorter period of time than the
conventional laser scanning type eye fundus camera and a clear color
retina image can be obtained.
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