Abstrict This specification discloses an eye fundus blood flow meter having
a blood flow measuring system for measuring the blood flow of the
fundus of an eye to be examined, and a malfunction detecting unit
for detecting measurement malfunction occurring during the measurement
by the blood flow measuring system. The specification also discloses
an eye fundus tracking apparatus for tracking a predetermined position
on the fundus of an eye to be examined having a tracking mechanism
for tracking a predetermined position on the eye to be examined,
an abnormality detecting system for detecting the operational abnormality
of the tracking mechanism, and a control unit for executing predetermined
control on the tracking mechanism when the operational abnormality
occurs.
Claims What is claimed is:
1. An apparatus for observing a fundus of an eye to be examined
comprising:
a tracking mechanism for tracking a portion of the fundus of the
eye to be examined;
detecting means, disposed independently from said tracking mechanism,
for detecting a blink of the eye to be examined; and
controlling means for controlling said tracking mechanism according
to an output of said detecting means.
2. An apparatus according to claim 1 wherein said controlling
means controls said tracking mechanism to stop tracking a portion
of the eye fundus when a blink is detected by said detecting means.
3. An apparatus according to claim 2 wherein said controlling
means controls said tracking mechanism to restart tracking from
the state where tracking is stopped, when the blink is detected
to be completed by said detecting means.
4. An apparatus according to claim 3 wherein said controlling
means stores a plurality of tracking states of said tracking mechanism
before the blink is generated and controls said tracking mechanism
to restart tracking at the time of completion of the blink, based
on the stored tracking states.
5. An apparatus according to claim 1 wherein the portion to be
tracked is a blood vessel of a fundus of the eye to be examined.
6. An apparatus according to claim 5 further comprising a blood
flow state detecting system for detecting a state of blood flow
flowing through the blood vessel,
said blood flow state detecting system comprising:
a beam illuminating unit for illuminating the portion of the fundus
of eye to be examined with a measuring beam; and
a light receiving unit for receiving reflected light of the measuring
beam reflected by the portion to measure the state of the blood
flow.
7. An apparatus according to claim 6 wherein said tracking mechanism
comprises:
a tracking beam illuminating unit for illuminating a portion of
the fundus of the eye to be examined with a tracking beam for tracking;
a tracking beam receiving unit for receiving a tracking beam reflected
by the portion, and
a controlling unit for controlling a position to be illuminated
by the measuring beam according to the receiving state of said tracking
beam receiving unit.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an eye fundus blood flow meter for measuring
the condition of a blood flow in a blood vessel of the fundus of
an eye and an eye fundus tracking apparatus.
2. Related Background Art
FIG. 1A of the accompanying drawings shows an example of an eye
fundus blood flow meter according to the conventional art, in which
a slit lamp usually used for ophthalmologic diagnosis has been adapted
for blood flow measurement. An illuminating optical system is disposed
on an optical path K1 and a white light beam from a light source
1 for observation is reflected by an apertured mirror 2 and illuminates
a blood vessel Ev on the fundus Ea of an eye E to be examined through
a slit 3 a lens 4 and a contact lens 5 for offsetting the refractive
power of the cornea of the eye E to be examined and making the fundus
Ea of the eye observable. Also, a light source 6 for measurement,
emitting an He-Ne laser beam for measurement, is disposed on an
optical path behind the apertured mirror 2 and the measurement
light from the light source 6 for measurement passes through the
central opening portion of the apertured mirror 2 and is made coaxial
with the light beam from the light source 1 for observation and
irradiates the fundus Ea of the eye in a spot-like form.
Light scattered and reflected by blood corpuscles flowing through
the blood vessel Ev and the blood vessel wall passes through the
objective lenses 7a and 7b of light receiving optical systems for
stereoscopic observation, disposed on optical paths K2 and K3 forming
an angle .alpha.' therebetween, is reflected by mirrors 8a, 8b and
mirrors 9a, 9b and is observed as the image of the fundus of the
eye by an examiner through eyepieces 10a and 10b, and the examiner
looks into the eyepieces 10a and 10b and selects a region to be
measured while observing the fundus Ea of the eye.
FIG. 1B of the accompanying drawings shows the image of the fundus
of the eye observed by the examiner, and when the blood vessel Ev
to be measured in an area being illuminated by the illuminating
light is made coaxial with a scale Sc prepared in advance on the
focal planes of the eyepieces 10a and 10b, the laser beam from the
light source 6 for measurement and the blood vessel Ev are made
coaxial with each other, and the region to be measured is determined
by the spot light beam Ps from the light source 6 for measurement.
At this time, the reflected light beam on the fundus Ea of the eye
by the measurement light is received by photomultipliers 12a and
12b through optical fibers 11a and 11b.
This light reception signal includes a predetermined beat signal
component created by a component Doppler-shifted by blood flowing
through the blood vessel Ev and a component reflected by the blood
vessel wall, which is stationary, interfering with each other, and
this beat signal can be frequency-analyzed to thereby find the velocity
of the blood flow in the blood vessel Ev.
FIG. 1C of the accompanying drawings shows an example of the result
of frequency analysis of the light reception signal measured by
the photomultipliers 12a and 12b, and axis of the abscissas represents
the frequency .DELTA.f and the axis of the ordinates represents
the output .DELTA.S thereof. The relation among the maximum value
.DELTA.fmax of the frequency, the wave number vector .kappa.i of
the incident light beam, the wave number vector .kappa.s of the
received light beam and the velocity vector .nu. of the blood flow
can be expressed as
Accordingly, when expression (1) is modified by the use of the
maximum values .DELTA.fmax1 and .DELTA.fmax2 of the frequency calculated
from the respective light reception signals of the photomultipliers
12a and 12b, the wavelength .lambda. of the laser beam, the refractive
index n of the region to be measured, the angle .alpha. formed between
light receiving optical axes K2 and K3 in the eye, and the angle
.beta. formed between the plane made by the light receiving optical
axes K2 and K3 in the eye and the velocity vector v of the blood
flow, the maximum blood flow velocity Vmax can be expressed as
By measurement being thus effected from two directions, the contribution
of the measurement light in the direction of incidence thereof is
offset, and the blood flow in any region on the fundus Ea of the
eye can be measured.
Further, assuming that the blood vessel Ev is cylindrical, the
blood flow quantity Q is expressed as
where .alpha. is the diameter of the blood vessel Ev.
Also, to measure the true velocity of the blood flow from the line
of intersection A between the plane formed by the two light receiving
optical paths K2 K3 shown in FIG. 1A and the fundus Ea of the eye,
and the angle .beta. formed between the velocity vector v of the
blood flow and the line of intersection A, it is necessary to make
the line of intersection A coincident with the velocity vector v,
with .beta.=0.degree. being assumed in expression (2). Therefore,
in the example of the prior art, the entire light receiving optical
system is rotated or an image rotator is disposed in the light receiving
optical system so that the line of intersection A may be made optically
coincident with the velocity vector.
In this apparatus, however, the slit lamp is the base and therefore,
the eye E to be examined must wear a contact lens when the observation
of the fundus of the eye is effected. Thus, the contact lens affects
the state of the blood flow on the fundus of the eye.
In order to eliminate such an ill effect of the contact lens, an
apparatus using a unique optical system is disclosed in Japanese
Laid-Open Patent Application No. 1-28133. In this apparatus, however,
the fact that the eye E to be examined can move freely makes it
difficult to project a measurement beam always onto a blood vessel
which is the object of measurement. Accordingly, two galvanometric
mirrors, of which the axes of rotation are orthogonal to each other,
are disposed at a position conjugate with the center of turning
of the eye E to be examined, and an eye fundus tracking apparatus
for controlling these galvanometric mirrors by the output from photographing
means is added to thereby project a tracking beam onto the blood
vessel in the fundus of the eye so that the blood vessel image by
the beam may be picked up and the optical system may be controlled
by the use of a signal indicative of the position of the image to
thereby always hold a measurement beam on the blood vessel to be
measured.
However, when use is made of the eye fundus tracking apparatus
and the eye fundus blood flow meter as described above, there arises
the necessity of considering also the situation when an abnormal
state such as an examinee's blink has occurred.
SUMMARY OF THE INVENTION
In view of the above-described example of the conventional art,
the present invention has as an object thereof to provide an eye
fundus tracking apparatus which, even when an abnormal state such
as a blink occurs, can resume tracking after the termination of
the abnormal state and/or an eye fundus blood flow meter which avoids
becoming incapable of measuring the blood flow after the occurrence
of the abnormal state and can resume measurement after the termination
of the abnormal state.
Other objects of the present invention will become apparent from
the following description of some embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows the construction of an example of the conventional
art.
FIG. 1B is an illustration of an observation image.
FIG. 1C is a graph of a frequency analysis of a light reception
signal.
FIG. 2A shows the construction of a first embodiment of the present
invention.
FIG. 2B is a block circuit diagram of tracking control means.
FIG. 3 is a block circuit diagram of a blood flow velocity calculating
unit.
FIG. 4 is a block circuit diagram of a blood vessel diameter calculating
unit.
FIG. 5 is a block circuit diagram showing the operation of a control
device when automatic tracking is resumed.
FIG. 6 is an illustration of an observed eye fundus image.
FIG. 7 is a timing chart of a blood vessel position calculation.
FIG. 8 is an illustration of an irradiating light beam and an observation
light beam.
FIG. 9 is a timing chart of the blood vessel diameter calculating
unit.
FIG. 10 is a flow chart of the operation of the control device
when automatic tracking is resumed.
FIG. 11 shows the construction of a second embodiment of the present
invention.
FIG. 12 is an illustration of the image picked-up area of an eye
fundus image.
FIG. 13 is a graph of the output of a CCD.
FIG. 14 is a flow chart of the operation of resuming automatic
tracking by the detection of a blink.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will hereinafter be described in detail with respect
to some embodiments thereof shown in FIGS. 2A and 2B to 14.
Referring to FIG. 2A, which shows the construction of an eye fundus
camera according to a first embodiment, on an optical path leading
from an illuminating light source 21 such as a tungsten lamp emitting
visible light, to an objective lens 22 there are disposed in succession
a band-pass filter 23 transmitting yellow-green light therethrough,
a condenser lens 24 a mirror 25 a field lens 26 for making an
eye E to be examined efficiently receive a light beam, a ring slit
27 having a ring-shaped opening portion, relay lenses 28 29 an
apertured mirror 30 and an image rotator 31. A blink detecting unit
32 is provided near the objective lens 22.
On an optical path behind the apertured mirror 30 there are disposed
in succession a pair of small mirrors 33a and 33b, an aperture 34
an image stabilizer 35 an observation optical system 36 a lens
37 an aperture 38 a lens 34 an ND filter changeover portion 40
and a light source 41 for measurement emitting an He-Ne laser beam.
On the optical paths in the directions of reflection of the pair
of small mirrors 33a and 33b, there are disposed lenses 42a, 42b
and photomultipliers 43a, 43b. In FIG. 2A, only the member on the
optical axis of the small mirror 33a is shown to avoid overlapping.
In the image stabilizer 35 there are arranged in succession lenses
44 45 a galvanometric mirror 46 lenses 47 48 and a galvanometric
mirror 49 and the galvanometric mirrors 46 and 49 are adapted to
be rotated by the operation of an operating rod 50 attached to the
outside. In this image stabilizer 35 the fundus Ea of the eye is
made conjugate with the galvanometric mirror 46 by the lenses 44
45 and conjugate with the galvanometric mirror 49 by the lenses
47 48.
In the observation optical system 36 there are provided a focusing
lens 51 movable on the optical path and a dichroic mirror 52 and
in the direction of reflection of the dichroic mirror 52 there
are arranged a half mirror 53 a lens 54 and a television camera
55 the output of which is connected to a monochromatic television
monitor 56. Also, in the direction of reflection of the half mirror
53 there is provided a blood vessel detecting system 57 and there
are arranged a mirror 58 a lens 59 a filter 60 and a one-dimensional
CCD sensor 61 with an image intensifier.
The outputs of the photomultipliers 43a and 43b are connected to
the input side of a blood flow velocity calculating unit 62 the
output of which is connected to a blood flow quantity calculating
unit 63 and a display unit 64 and the output of the blood flow
quantity calculating unit 63 is connected to the display unit 64.
The output of the CCD sensor 61 is connected to tracking control
means 65 and a blood vessel diameter calculating unit 66 the output
of the tracking control means 65 is connected to a drive circuit
68 for driving the galvanometric mirrors 46 and 49 through a control
device 67 and the output of the blood vessel diameter calculating
unit 66 is connected to the blood flow quantity calculating unit
63 and the display unit 64. Also, the outputs of the blink detecting
portion 32 and the operating rod 50 are connected to the control
device 67 and the output signal SS of a synchronizing signal generating
circuit 69 is connected to the CCD sensor 61 the blood flow velocity
calculating unit 62 and the blood vessel diameter calculating unit
66.
FIG. 2B shows a block circuit diagram of the tracking control means
65 and the output of the CCD sensor 61 is connected to a differentiator
72 via an amplifier 70 and a low-pass filter 71. The output of the
differentiator 72 is connected to a counter 74 through a zero-cross
comparator 73 and the output of the counter 74 is connected from
an output portion 76 to the control device 67 through a D/A converter
75. Also, the design of the device is such that the synchronizing
signal SS of the synchronizing signal generating circuit 69 is inputted
to the CCD sensor 61 the counter 74 and the D/A converter 75.
Referring to FIG. 3 which shows a block circuit diagram of the
blood flow velocity calculating unit 62 the blood flow velocity
calculating unit 62 is comprised of two spectrum analyzers 77a,
77b and signal processing means 78 for receiving the signals thereof.
The outputs of the photomultipliers 43a and 43b, receiving the reflected
lights from the pair of small mirrors 33a and 33b, are connected
to the spectrum analyzers 77a and 77b, and the output of the signal
processing means 78 is connected to the blood flow quantity calculating
unit 63 and the display unit 64.
Referring to FIG. 4 which shows a block circuit diagram of the
blood vessel diameter calculating unit 66 the output SG of the
CCD sensor 61 and the reference voltage output Ve of a reference
voltage generating circuit 80 are connected to the comparator 79
of the blood vessel diameter calculating unit 66 and the output
Wa of the comparator 79 is connected to an integrator 81 so that
a blood vessel diameter signal may be outputted to the integrator
81. Also, the output IS of an initializing signal circuit 82 is
connected to the integrator 81 and the synchronizing signal SS
of the synchronizing signal generating circuit 69 is connected to
the CCD sensor 61 and the initializing signal circuit 82.
FIG. 5 shows a block diagram of the control device 67 and also
shows a mechanism for automatically resuming blood flow measurement
when tracking operation is poor. The control device 67 is adapted
to judge the tracking state and send out a drive signal to the galvanometric
mirrors 46 and 49 suitable for that state through the drive circuit
68.
The output of a counter 83 in the tracking control means 65 is
connected to a tracking error detecting portion 84 for detecting
the tracking impossible state and a blood vessel position memorizing
portion 85 the output of which is connected to a blood vessel position
calculating portion 86. The output of the tracking error detecting
portion 84 the changeover state signal of the ND filter changeover
portion 40 and the output of the blink detecting unit 32 are connected
to the discriminating portion 87 of the control device 67 and the
output of the start-stop switch 88 of the operating rod 50 is also
connected thereto. Also, the output of the discriminating portion
87 is connected to a signal changeover portion 89 and the blood
vessel position calculating portion 86. Three kinds of signals,
i.e., the output of the blood vessel position calculating portion
86 the output of the operating rod 50 and the output of the tracking
control means 65 having a tracking mechanism, are connected to the
signal changeover portion 89 the output of which is connected to
the drive circuit 68.
In the eye fundus blood flow meter having the above-described construction,
the illuminating light emitted from the illuminating light source
21 is imaged on the ring slip 27 through the band-pass filter 23
the condenser lens 24 the mirror 25 and the field lens 26. The
illuminating light having emerged from the ring slit 27 is once
imaged on the apertured mirror 30 by the relay lenses 28 and 29
whereafter it passes through the image rotator 31 and is imaged
on the pupil of the eye E to be examined by the objective lens 22
and substantially uniformly illuminates the fundus Ea of the eye
E to be examined.
The reflected light from the fundus Ea of the eye again passes
through the objective lens 22 and the image rotator 31 and enters
the image stabilizer 35 via the central aperture of the apertured
mirror 30 and the aperture 34. At this time, the operating rod 50
is operated to thereby rotatively move the galvanometric mirrors
46 and 49 and designate a region to be measured on the fundus Ea
of the eye.
The light beam having emerged from the image stabilizer 35 enters
the observation optical system 36 and is distributed to two optical
paths by the half mirror 53 via the focusing lens 51 and the dichroic
mirror 52 and one of the two light beams is imaged on the television
camera 55 via the lens 54 and an eye fundus image Ea' is displayed
on the monochromatic television monitor 56 and an examiner effects
the alignment of the apparatus and the selection of the region to
be measured while observing the eye fundus image Ea'.
Referring to FIG. 6 which shows the eye fundus image Ea' observed
on the television monitor 56 the direction of the coordinate axis
A represents the direction of the line of intersection between a
plane passing through the centers of the pair of small mirrors 33a
and 33b and fundus Ea of the eye, and the image PS of the laser
beam for measurement is a spot image representing the region to
be measured. The examiner first operates the operating rod 50 and
makes the spot image PS coincident with the blood vessel Ev to be
measured. At this time, the spot image PS is fixed while remaining
positioned at the center relative to the examiner's field of view,
and the eye fundus image Ea' moves and is observed.
When the image rotator 31 is rotated thereafter, the eye fundus
image Ea' rotates about the center of the field of view in the direction
of arrow, and the examiner makes the direction of the blood flow
in the blood vessel Ev to be measured coincident with the direction
of the axis A. This means that .beta.=0.degree. is brought about
in FIG. 1B. When the region to be measured is selected in this manner,
a one-dimensional image in the direction of an axis D, orthogonal
to the axis A, is picked up by the CCD sensor 61 of the blood vessel
detecting system 57 and the galvanometric mirror 46 of the image
stabilizer 35 is driven so that the position of the blood vessel
Ev in the direction of the axis D, may become constant during measurement.
Also, the other light beam distributed by the half mirror 53 enters
the blood vessel detecting system 57 and is imaged on the one-dimensional
CCD sensor 61 via the mirror 58 the lens 59 and the filter 60.
At this time, the filter 60 intercepts the wavelength of the laser
beam of the light source 41 for measurement and therefore, this
laser beam does not arrive at the CCD sensor 61 which thus picks
up a blood vessel image by only the illuminating light from the
illuminating light source 21. The CCD sensor 61 of the blood vessel
detecting system 57 forms an image enlarged more than the image
on the television camera 55 and a detailed blood vessel image is
displayed on the display unit 63 via the blood vessel diameter calculating
unit 66. The output of the CCD sensor 61 is also sent to the tracking
control means 65 which thus produces a tracking signal for the
drive circuit 68.
Referring to FIG. 7 which shows a timing chart of the operation
of producing a tracking signal for the drive circuit 68 by the tracking
control means 65 the image output W1 of the one-dimensional CCD
61 comprising 256 pixels is amplified by the amplifier 70 of the
tracking control means 65 shown in FIGS. 2A and 2B, whereafter it
is shaped into a waveform W2 by the suitable low-pass filter 71
which does not deform the waveform of the actual eye fundus image
Ea' and is differentiated by the differentiator 72 and becomes a
differentiated waveform W3. Thereafter, it passes through the zero-cross
comparator 73 and is binarized and becomes a waveform W4. The count
value the waveform W4 counts between low levels is cleared during
each measurement in synchronism with the signal SS from the synchronizing
signal generating circuit 69 and the count value at the end of
one scan corresponds to the blood vessel position as indicated by
a waveform W5. A position signal for driving the galvanometric mirrors
46 and 49 is outputted to the drive circuit 68 so that this count
value may become a predetermined value. In the present embodiment,
this operation is performed at a rate of 1 kHz, whereby control
is automatically effected so as to keep the relation among the position
of the blood vessel, which is the object to be measured moved by
the movement of the eyeball, the applied position of the laser beam,
and the position of the detecting portion constant.
That is, the galvanometric mirror 46 makes a movement which automatically
compensates for the fine fixation movement of the eye E to be examined
by the operation of the drive circuit 68 and once the examiner
designates the blood vessel position to be measured, the blood vessel
at this position is image-picked up on the CCD sensor 61 and at
this time, the laser beam for measurement is made coaxial with the
observation optical system 36 by the half mirror 53 and thereafter
returns reversely along the optical path and is directed onto the
fundus Ea of the eye, and is projected always onto the designated
blood vessel to be measured.
The laser beam for measurement forms a spot on the aperture 38
at a position conjugate with the fundus Ea of the eye by the lens
37 before it is coupled to the observation optical system 36 by
the dichroic mirror 52 and the conjugate relation thereof is adjusted
via the lens 37. Accordingly, when the examiner moves the focusing
lens 51 on the optical axis to thereby effect the focusing of the
fundus Ea of the eye, the image pickup surface of the television
camera 55 and the image pickup surface of the one-dimensional CCD
sensor 61 become conjugate with the fundus Ea of the eye at the
same time. Of the measurement laser beam reflected from the blood
vessel Ev on the fundus Ea of the eye, the light beam rectilinearly
travelling through the apertured mirror 30 is intactly directed
to the observation optical system 36 and acts as an index indicative
of the region to be measured on the television camera 55.
On the other hand, a part of the measurement laser beam is reflected
by the pair of small mirrors 33a and 33b provided rearwardly of
the apertured mirror 30. FIG. 8 represents the disposition of each
light beam on the pupil, the images Ma and Mb by the pair of small
mirrors 33a and 33b represent the position of the light beam to
be received, the image PA of the aperture 34 represents the position
of the light beam for observation and the laser beam for measurement,
and the image PR of the light projecting portion of the ring slit
27 represents the position of the illuminating light beam. The angle
facing the region to be measured from the images Ma and Mb corresponds
to the measurement angle .alpha. in FIG. 1A.
According to the principle of the velocity detection described
with respect to the example of the conventional art, the blood flow
velocity is obtained from the interference signal between the scattered
reflected light from the blood vessel wall and the scattered reflected
light in the blood flow and therefore, even if the fundus Ea of
the eye moves in the direction of the axis A during measurement,
the result of measurement will not be affected if the blood vessel
Ev is made parallel to the axis A. On the other hand, when the fundus
Ea of the eye has moved in the direction of the axis D orthogonal
to the axis A, the laser beam for measurement deviates from the
blood vessel Ev and measurement becomes impossible. Accordingly,
the blood vessel detecting system 57 and the image stabilizer 35
cooperate with each other to effect one-dimensional tracking in
the direction of this axis D.
The light beams reflected by the pair of small mirrors 33a and
33b are condensed by the lenses 42a and 42b, are received by the
photomultipliers 43a and 43b and are photoelectrically converted
and become electrical signals, which are sent to the spectrum analyzers
77a and 77b of FIG. 3 in synchronism with the synchronizing signal
SS from the synchronizing signal generating circuit 69. These signals
are Fourier-transformed and are inputted to the signal processing
means 78 in which two maximum blood flow quantities fmax1 and fmax2
are calculated and the blood flow velocity is found. This blood
flow velocity data is sent to the blood flow quantity calculating
unit 63 and the display unit 64.
FIG. 9 shows a timing chart of the blood vessel diameter calculation,
and in the blood vessel diameter calculating unit 66 a signal SG
from the CCD sensor 61 is inputted to the comparator 79 in synchronism
with the synchronizing signal SS from the synchronizing signal generating
circuit 69. The comparator 79 compares a predetermined reference
voltage Ve from the reference voltage generating circuit 80 and
the signal SG with each other, and finds an output Wa exceeding
the reference voltage Ve, and integrates the output and obtains
potential V. This potential V is cleared by a signal IS from the
initializing signal circuit 82 during each measurement, and the
output potential V of the integrator 81 immediately before the potential
V is cleared corresponds to the blood vessel diameter d.
The thus found blood vessel diameter d, like the blood flow velocity,
is sent to the blood flow quantity calculating unit 63 and the display
unit 64 and in the blood flow quantity calculating unit 63 the
blood flow quantity is calculated from the blood flow velocity and
the blood vessel diameter supplied from the blood flow velocity
calculating unit 62 and the blood vessel diameter calculating unit
66 respectively. The blood flow velocity, the blood vessel diameter
and the blood flow quantity can be used, for example, for the diagnosis
of arteriosclerosis, diabetes, etc.
In the present embodiment, the synchronizing signal SS from the
synchronizing signal generating circuit 69 is used to progress the
operation of the circuit, but the synchronizing signal generating
circuit 69 may be replaced by a clock circuit to progress the operation
by a clock signal. That is, the clock signal from the clock circuit
can be supplied to the blood vessel diameter calculating unit 66
and the blood flow velocity calculating unit 62 and the clock signal
can be counted by a unique internal counter, and the internal counter
can be set so as to determine the calculation timing.
In the mechanism for automatically resuming the blood flow measurement
when the tracking operation is bad which is shown in FIG. 5 the
tracking error detecting portion 84 manages the count value outputted
from the tracking control means 65 and when a numerical value outside
the range of management is detected, it outputs an error signal.
Also, the ND filter changeover portion 40 outputs data indicating
the occurrence of a tracking impossible state occurring due to the
interception of the laser beam when it changes over the ND filter
for adjusting the quantity of light of the laser, and the blink
detecting portion 32 outputs data indicating the occurrence of a
tracking impossible state in which the optical path is intercepted
by the eyelid. Besides these, a decrease in the quantity of scattered
light from the fundus of the eye, the impossibility of the calculation
of the blood flow velocity, etc., may be inputted to the discriminating
portion 87 to thereby effect the control of tracking. The discriminating
portion 87 judges the states of these signals and send instructions,
and the signal changeover portion 89 changes over the output on
the basis of the instructions.
Referring to FIG. 10 which shows a flow chart of the operation
of automatically resuming blood flow measurement, the control device
67 effects initialization so that the measurement beam spot may
be applied to the center of the observation field of view at the
start of the application of the measurement beam before tracking
is entered, and outputs an operation signal to the drive circuit
68 in accordance with the instructions of the operating rod 50 to
thereby move the measurement beam to a position indicated by the
examiner.
Next, when a measurement starting signal is outputted from the
start-stop switch 88 of the operating rod 50 the discriminating
portion 87 confirms an error signal from the tracking error detecting
portion 84 the ND filter changeover portion 40 and the blink detecting
portion 32. When it confirms that the error signal is not being
outputted from these, the discriminating portion 87 outputs to the
signal changeover means 89 a signal which makes the input from the
tracking control means 65 effective, and the signal changeover means
89 outputs a signal from the tracking control means 65 to the drive
circuit 68 to thereby effect eye fundus tracking.
When a tracking error arises during the tracking operation, the
error signal from the tracking error detecting portion 84 is inputted
to the discriminating portion 87 and therefore, the discriminating
portion 87 outputs a calculation starting signal for the restart
position to the blood vessel position calculating portion 86 and
at the same time, outputs to the signal changeover portion 89 a
signal which makes the input from the blood vessel position calculating
portion 86 effective. When the calculation starting signal for the
restart position is inputted, the blood vessel position calculating
portion 86 calculates the restart position to the drive circuit
68. The signal changeover portion 89 outputs the signal from the
blood vessel position calculating portion 86 to the drive circuit
68 and therefore, the drive circuit 68 sets the galvanometric mirror
46 at the restart position, and tracking is interrupted. When the
tracking error becomes null again, the input of the error signal
to the discriminating portion 87 becomes null and therefore, the
discriminating portion 87 outputs a calculation terminating signal
for the restart position to the blood vessel position calculating
portion 86 and at the same time, outputs a signal which makes the
input from the tracking control means 65 effective.
When by the above-described operation, a tracking error is caused
during eye fundus tracking, the tracking is temporarily interrupted
and the apparatus waits at the restart position, and when the tracking
error becomes null, the tracking can be resumed from the restart
position. Also, when it is desired to discontinue measurement, the
start-stop switch 88 of the operating rod 50 is operated, whereby
a stop signal is detected and tracking can be discontinued. Further,
eye fundus tracking can be resumed by a similar operation in a tracking
impossible state occurring due to the laser beam being intercepted
when the ND filter is changed over, or in a tracking impossible
state in which the optical path is intercepted by the eyelid.
Next, the measurement beam application position at the restart
is calculated in the blood vessel position calculating portion 86.
50 numbers of blood vessel position data relative to the present
measuring apparatus converted from the counter 83 of the tracking
control means 65 are stored at an interval of 10 msec. in the blood
vessel position memorizing portion 85 and the eye fundus blood
vessel position at the restart of tracking is foreseen on the basis
of these stored positions.
The impossibility of tracking when the count value outputted from
the tracking control portion 84 is a value outside the range or
when the ND filter for adjusting the quantity of light of the laser
is changed over is not a tracking error occurring due to the movement
of the eyeball and therefore, the position immediately before the
tracking error occurs is designed to be outputted. In the case of
a tracking impossible state in which the optical path is intercepted
by the eyelid during blinking, the blink results in the movement
of the eyeball and therefore, if the position immediately before
the tracking error has occurred is outputted, the blood vessel cannot
be detected at the restart of tracking and therefore, in such case,
the restart position is calculated on the basis of the stored blood
vessel position data.
Since a blink usually ends in 100 msec., the position before 100
msec. is defined as the restart position, but depending on an examinee's
will, there is conceivable a case where the examinee closes his
eyes for 100 msec. or longer and therefore, in such case, the probability
with which tracking can be resumed with the center position of the
amplitude of the relative position data resulting from the movement
of the eyeball as the restart position is highest, and the average
value of 50 numbers of data is defined as the restart position.
Besides this, there are also conceivable a system for carrying
out a weighted mean process, a system in which those of blood vessel
position data which are low in frequency are thinned to reduce the
influences of the abnormality of the output of the counter 83 the
abnormality of the fixating state, the malfunction due to the deficiency
of the quantity of light from the fundus Ea of the eye caused at
the early stage of the examinee's blink, etc., and a system in which
in order to attach importance to new data, the new data is multiplied
by such a coefficient that the weight becomes greater in proportion
to time to thereby find the mean.
To detect a blink by the blink detecting portion 32 for example,
a light beam may be projected onto the eye E to be examined, and
the reflected light from the eyelid, iris and pupil of the eye E
to be examined may be continuously detected, and the eyelid covers
may be detected from the received shape of this reflected light.
Also, there may be provided a form in which a portion which becomes
a dark portion on the fundus Ea of the eye is intentionally provided
in the measurement beam application optical path to thereby pick
up the eye fundus image including the dark portion, and a blink
can be detected by detecting the contrast thereof. Such an example
will be shown below.
FIG. 11 shows the construction of a second embodiment of the present
invention, and in FIG. 11 the same reference numerals as those
in FIGS. 1A, 1B and 1C designate the same members. A blink detecting
portion 32 is not provided in front of the eye E to be examined,
and the output of a one-dimensional CCD 61 is connected to a blink
detecting portion 32' comprised of a circuit, and as shown in FIG.
12 an image pickup area S in a range wider than the application
area P of a measurement beam is image-picked up by the CCD 61. Here,
the application optical path of the measurement beam and a photographing
optical path are the same optical path and therefore, even if tracking
is effected, the relation between the measurement beam and the image
pickup device always becomes constant, and the output signal of
the CCD 61 becomes such as shown in FIG. 13.
Accordingly, by comparing the contrast of the measurement beam
application area P and the area to which the measurement beam is
not applied, it becomes possible to detect a blink. When the contrast
is great, it means that the eye is a state in which the eye fundus
image Ea' is caught, and when the contrast becomes small, it indicates
the occurrence of a state in which a measurement beam spot P is
not applied to the fundus Ea of the eye, such as a state in which
a blink is being performed, and when the contrast assumes a predetermined
value or greater thereafter, the blink is regarded as having ended
and a tracking possible signal is generated, and on the basis of
this signal, the control device 67 restarts tracking.
Referring to FIG. 14 which shows a flow chart of the automatic
tracking resuming operation by blink detection, the blink detecting
portion 32' detects a blink during eye fundus tracking, and the
blood vessel position calculating portion 86 foresees and calculates
the examinee's eye fundus blood vessel position at the restart of
tracking on the basis of the stored blood vessel position. On the
basis of this calculated value, the position of the measurement
beam is determined and the angles of the galvanometric mirrors 46
and 49 are controlled, whereafter when the completion of the blink
is detected, eye fundus tracking is automatically resumed.
While the above embodiments have been described with respect to
an eye fundus blood flow meter, the tracking apparatus of the present
invention may be provided even in the case of another ophthalmologic
photographing apparatus or measuring apparatus having a tracking
mechanism for eyeball movement other than this meter, whereby when
a tracking impossible state occurs due to a malfunction such as
a blink state, tracking can be discontinued, and after the malfunction
has been eliminated, tracking can be automatically resumed to thereby
continue photographing and measurement. |