Abstrict An ocular blood-flow meter includes an optical system for applying
measuring light to a blood vessel of a subject eye, and for receiving
light scattered by the blood vessel of the subject eye. A mechanism
is provided for changing a direction in which the measuring light
is applied and a direction in which the scattered light is received
so as to enable a plurality of measurements in different directions.
A controller performs the plurality of measurements in the different
directions by using the optical system and the mechanism so as to
obtain information concerning a blood flow. An output device provides
a received-light signal obtained by the optical system or the information
concerning the blood flow. An input device enables an operator to
select a re-measurement operation in a desired direction from the
different directions and to instruct the selected re-measurement
operation.
Claims What is claimed is:
1. An ocular blood-flow meter comprising: an optical system configured
and positioned to apply measuring light to a blood vessel of a subject
eye, and to receive light scattered by the blood vessel of the subject
eye; a mechanism configured and positioned to change the direction
in which the measuring light is applied to the blood vessel or the
direction in which the scattered light is received by at least a
portion of said optical system so as to enable a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received by at least a portion of said optical system in different
directions; a device configured and positioned to receive the scattered
light from said optical system, wherein said device outputs a received-light
signal containing information on blood flow in the blood vessel
in response to receiving the scattered light from said optical system;
a controller connected to said device to receive the received-light
signal and configured to perform the plurality of measurements of
the blood flow in the blood vessel using the received-light signal
generated from measuring light being applied to the blood vessel
in different directions and scattered by the blood vessel or generated
from the scattered light received by at least a portion of said
optical system in different directions, wherein said controller
is also configured to perform a re-measurement operation to re-measure
the blood flow in the blood vessel using a received-light signal
generated from measuring light being applied to the blood vessel
in a desired direction and then scattered by the blood vessel or
generated from the scattered light received by at least a portion
of said optical system in a desired direction in response to an
instruction by an operator to perform a re-measurement operation
in the desired direction; and an input device, wherein said input
device is electrically coupled to said controller, wherein said
input device is configured to enable an operator to select a re-measurement
operation to re-measure the blood flow in the blood vessel using
a received-light signal generated from measuring light being applied
to the blood vessel in a desired direction and then scattered by
the blood vessel or generated from the scattered light received
by at least a portion of said optical system in a desired direction,
wherein said input device also is configured to instruct said controller
to perform the selected re-measurement operation selected by the
operator.
2. An ocular blood-flow meter according to claim 1 wherein said
input device comprises a selector, wherein said selector is configured
to enable the operator to select a desired measurement result from
a plurality of measurement results obtained in the desired direction
in which the re-measurement operation is performed.
3. An ocular blood-flow meter according to claim 1 further comprising:
a tracking system configured to track movement of the subject eye;
and a display device connected to said tracking system and configured
to display tracking information obtained by said tracking system.
4. An ocular blood-flow meter according to claim 1 further comprising:
a measurement system configured to measure blood vessel size; and
a display device connected to said measurement system and configured
to display the measurement result obtained by said measurement system,
wherein said measurement system is connected to said device.
5. An ocular blood-flow meter according to claim 1 further comprising
a display device connected to said controller, said display device
presenting to the operator a plurality of measurement results using
the received light signal output from said device so as to provide
information to the operator to enable the operator to determine
whether the re-measurement operation is required.
6. The ocular blood-flow meter according to claim 1 wherein said
optical system comprises: a measuring light source; and a lens,
wherein said mechanism is positioned between said measuring light
source and said lens and comprises: a retractable optical path switching
mirror; and a stationary mirror, and wherein said optical path switching
mirror is retractable out of and insertable into the path of measuring
light from said measuring light source and said lens, wherein when
said optical path switching mirror is in the optical path from said
measuring light source to said lens, said optical path switching
mirror reflects measuring light from said measuring light source
to said stationary mirror, which reflects the measuring light to
a first portion of said lens, and wherein when said optical path
switching mirror is out of the optical path from said measuring
light source to said lens, measuring light from said measuring light
source is projected directly to a second portion of said lens, whereby
said mechanism changes the direction in which the measuring light
is applied to the blood vessel.
7. The ocular blood-flow meter according to claim 1 wherein said
mechanism changes the position of said device so as to change the
direction in which the scattered light is received by at least a
portion of said optical system.
8. The ocular blood-flow meter according to claim 1 wherein said
input device comprises a selection switch panel on which first,
second, and third switches are disposed to select only a first direction,
only a second direction, and both said first and second directions,
respectively, in which the operator desires the measuring light
to be applied to the blood vessel and then scattered by the blood
vessel or to select only a first direction, only a second direction,
and both said first and second directions, respectively, in which
the operator desires that the scattered light be received by at
least a portion of said optical system.
9. The ocular blood-flow meter according to claim 1 further comprising:
a tracking system configured to track movement of the subject eye,
wherein said tracking system is configured to produce a blood-vessel
image of the blood vessel and a signal representing the blood-vessel
image, wherein said tracking system is connected to said controller,
wherein said controller determines the position and amount of movement
of the blood-vessel image from the signal produced by said tracking
system, wherein the amount of movement of the blood-vessel image
that is determined by said controller is indicative of the quality
of the tracking performed by said tracking system; and a display
device connected to said tracking system and said controller; wherein
said controller processes the received-light signal over time and
determines an evaluation value over time that represents the quality
of the received-light signal, wherein said controller calculates
the variation in the frequency of over time of the processed received-light
signal, wherein said display device displays a first graph of the
processed received-light signal over time processed by said controller,
wherein said display device displays a second graph of the evaluation
value determined by said controller before and during measurement
of the blood flow in the blood vessel, wherein said display device
displays a third graph representing the variation over time in the
amount of movement of the blood-vessel image during measurement
of the blood flow in the blood vessel, and wherein said display
device displays a fourth graph representing the variation in the
frequency of over time of the processed received-light signal after
measurement of the blood flow in the blood vessel.
10. The ocular blood-flow meter according to claim 9 wherein said
controller processes the received-light signal over time by performing
a fast Fourier Transform operation on the received-light signal
to produce a fast Fourier Transform waveform over time, wherein
said display device displays the fast Fourier Transform waveform
over time as the first graph, wherein said controller determines
the maximum frequency when the power spectrum of the fast Fourier
Transform waveform exceeds a predetermined threshold, and wherein
said display device displays the variation in the frequency over
time of the power spectrum of the fast Fourier Transform waveform
as the fourth graph.
11. The ocular blood-flow meter according to claim 1 further comprising:
an image forming system forming a blood-vessel image, wherein said
controller is configured to determine variations in the amount of
movement over time of the blood-vessel image, wherein said controller
is also configured to process the received-light signal to produce
a processed received-light signal and determine the frequency over
time of the processed received-light signal, and wherein said meter
further comprises a display device connected to said controller,
wherein said display device displays the variations in the amount
of movement over time of the blood-vessel image, and where in said
display device displays the frequency over time of the processed
received-light signal.
12. The ocular blood-flow meter according to claim 1 wherein said
controller determines an evaluation value over time that represents
the quality of the received-light signal generated from measuring
light being applied to the blood vessel in a first direction and
scattered by the blood vessel or generated from the scattered light
received by at least a portion of said optical system in a first
direction, wherein said controller determines an evaluation value
over time that represents the quality of the received-light signal
generated from measuring light being applied to the blood vessel
in a second direction and scattered by the blood vessel or generated
from the scattered light received by at least a portion of said
optical system in a second direction, wherein said meter further
comprises a display device, connected to said controller, wherein
said display device displays the evaluation values over time associated
with the first and second directions, simultaneously.
13. The ocular blood-flow meter according to claim 12 further
comprising an image forming system forming a blood vessel image,
wherein said meter captures the blood vessel image at different
times during the plurality of measurements of the blood flow to
produce a plurality of blood-vessel images of the same blood vessel
over time, wherein said meter further comprises a tracking system
comprising at least one optical element tracking the blood vessel
during movement of the blood vessel so that the blood vessel image
of the blood vessel formed by said image forming system is positioned
at substantially the same position over time during the plurality
of measurements and during a re-measurement operation when tracking
is properly performed, wherein when tracking by said tracking system
is not properly performed, the position of the blood-vessel image
changes over time, wherein said display device displays in an overlapping
manner the plurality of captured blood-vessel images while receiving
the light generated from measuring light being applied to the blood
vessel in the first direction and scattered by the blood vessel
or generated from the scattered light received by at least a portion
of said optical system in the first direction, wherein the thickness
of the displayed, overlapped blood-vessel images associated with
the first direction is greater when said tracking system performs
tracking improperly than when said tracking system performs tracking
properly, wherein said display device displays in an overlapping
manner the plurality of captured blood-vessel images while receiving
the light generated from measuring light being applied to the blood
vessel in the second direction and scattered by the blood vessel
or generated from the scattered light received by at least a portion
of said optical system in the second direction, and wherein the
thickness of the displayed, overlapped blood-vessel images associated
with the second direction is greater when said tracking system performs
tracking improperly than when said tracking system performs tracking
properly.
14. The ocular blood-flow meter according to claim 13 wherein
a measurement operation performed using a received-light signal
generated from measuring light being applied to the blood vessel
in the first direction and scattered by the blood vessel or generated
from the scattered light received by at least a portion of said
optical system in the first direction is denoted as the first path
1 measurement, wherein a re-measurement operation performed using
a received-light signal generated from measuring light being applied
to the blood vessel in the first direction and scattered by the
blood vessel or generated from the scattered light received by at
least a portion of said optical system in the first direction is
denoted as the second path 1 measurement, wherein a measurement
operation performed using a received-light signal generated from
measuring light being applied to the blood vessel in the second
direction and scattered by the blood vessel or generated from the
scattered light received by at least a portion of said optical system
in the second direction is denoted as the first path 2 measurement,
wherein a re-measurement operation performed using a received-light
signal generated from measuring light being applied to the blood
vessel in the second direction and scattered by the blood vessel
or generated from the scattered light received by at least a portion
of said optical system in the second direction is denoted as the
second path 2 measurement, wherein said input device comprises:
a first selector switch permitting the operator to instruct said
meter to perform a second path 1 measurement; a second selector
switch permitting the operator to instruct said meter to perform
a second path 2 measurement; a third selector switch permitting
the operator to instruct said meter to perform a re-measurement
operation using a received-light signal generated from measuring
light being applied to the blood vessel in the first and second
directions and scattered by the blood vessel or generated from the
scattered light received by at least a portion of said optical system
in the first and second directions; a fourth selector switch permitting
the operator to instruct said controller to determine the blood
flow in the blood vessel using: the second path 1 measurement and
the second path 2 measurement when the operator selects the third
selector switch; the second path 1 measurement and the first path
2 measurement when the operator selects the first selector switch;
and the second path 2 measurement and the first path 1 measurement
when the operator selects the second selector switch; a fifth selector
switch permitting the operator to instruct said controller to determine
the blood flow using the first path 1 measurement and the first
path 2 measurement after the operator has used said first selector
switch to instruct said meter to perform a second path 1 measurement;
a sixth selector switch permitting the operator to instruct said
controller to determine the blood flow using the second path 1 measurement
and the first path 2 measurement after the operator has used said
first selector switch to instruct said meter to perform a second
path 1 measurement; a seventh selector switch permitting the operator
to instruct said controller to determine the blood flow using the
first path 2 measurement and the first path 1 measurement after
the operator has used said second selector switch to instruct said
meter to perform a second path 2 measurement; and an eighth selector
switch permitting the operator to instruct said controller to determine
the blood flow using the second path 2 measurement and the first
path 1 measurement after the operator has used said second selector
switch to instruct said meter to perform a second path 2 measurement.
15. An ocular blood-flow meter comprising: an optical system configured
and positioned to apply measuring light to a blood vessel of a subject
eye, and to receive light scattered by the blood vessel of the subject
eye; a mechanism configured and positioned to change the direction
in which the measuring light is applied to the blood vessel or the
direction in which the scattered light is received by at least a
portion of said optical system so as to enable a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received by at least a portion of said optical system in different
directions; a controller configured to perform the plurality of
measurements of the blood flow in the blood vessel using the measuring
light being applied to the blood vessel in different directions
and scattered by the blood vessel or using the scattered light received
by at least a portion of said optical system in different directions,
wherein said controller is also configured to perform a re-measurement
operation to re-measure the blood flow in the blood vessel using
the measuring light being applied to the blood vessel in a desired
direction and then scattered by the blood vessel or using scattered
light received by at least a portion of said optical system in a
desired direction, wherein said controller is also configured to
determine whether a re-measurement operation is required; and an
output device connected to said controller, wherein said output
device is configured to present information to an operator indicating
whether re-measurement is required in response to said controller
determining that a re-measurement operation is required.
16. An ocular blood-flow meter according to claim 15 further comprising
a device configured and positioned to receive the scattered light
from said optical system, wherein said device outputs received-light
signals containing information on blood flow in the blood vessel
in response to receiving measuring light being applied to the blood
vessel in different directions and scattered by the blood vessel
or in response to receiving scattered light that has been received
by at least a portion of said optical system in different directions,
wherein said controller is connected to said device and receives
the received-light signals and performs the plurality of measurements
and the re-measurement operation using the received-light signals,
wherein said output device comprises a display device configured
to display a representation of the received-light signals or information
concerning the blood flow in the blood vessel, wherein said controller
is configured to determine the quality of the received-light signals
obtained by performing each of the plurality of measurements, and
to compare the quality of the received-light signals so as to determine
whether the re-measurement operation is required; and wherein said
display device displays information that a re-measurement operation
is required in response to said controller determining that the
re-measurement operation is required.
17. An ocular blood-flow meter according to claim 16 wherein said
controller determines the quality of the received-light signal obtained
by performing a re-measurement operation, and compares the quality
of the received-light signal before the re-measurement operation
with the quality of the received-light signal after the re-measurement
operation, so as to calculate the blood flow based on the received-light
signal having the better quality.
18. An ocular blood-flow meter according to claim 15 wherein said
optical system comprises: a measuring light source; and a lens,
wherein said mechanism is positioned between said measuring light
source and said lens and comprises: a retractable optical path switching
mirror; and a stationary mirror, and wherein said optical path switching
mirror is retractable out of and insertable into the path of measuring
light from said measuring light source and said lens, wherein when
said optical path switching mirror is in the optical path from said
measuring light source to said lens, said optical path switching
mirror reflects measuring light from said measuring light source
to said stationary mirror, which reflects the measuring light to
a first portion of said lens, and wherein when said optical path
switching mirror is out of the optical path from said measuring
light source to said lens, measuring light from said measuring light
source is projected directly to a second portion of said lens, whereby
said mechanism changes the direction in which the measuring light
is applied to the blood vessel.
19. The ocular blood-flow meter according to claim 16 wherein
said mechanism changes the position of said device so as to change
the direction in which the scattered light is received by at least
a portion of said optical system.
20. The ocular blood-flow meter according to claim 15 further
comprising an input device connected to said controller, wherein
said input device comprises a selection switch panel on which first,
second, and third switches are disposed to select only a first direction,
only a second direction, and both said first and second directions,
respectively, in which the operator desires the measuring light
to be applied to the blood vessel and then scattered by the blood
vessel or to select only a first direction, only a second direction,
and both said first and second directions, respectively, in which
the operator desires that the scattered light be received by at
least a portion of said optical system.
21. The ocular blood-flow meter according to claim 15 wherein
said controller processes the received-light signals over time,
wherein said controller determines an evaluation value over time
that represents the quality of each received-light signal, by comparing
the evaluation value for each received-light signal with a reference
value, wherein said controller determines that a re-measurement
operation is required when the evaluation value for a received-light
signal is below the reference value.
22. The ocular blood-flow meter according to claim 21 wherein
said controller processes each received-light signal over time by
performing a fast Fourier Transform operation on each received-light
signal to produce a fast Fourier Transform waveform over time for
each received-light signal, from which said controller determines
an evaluation value for each received-light signal.
23. An ocular blood-flow meter comprising: optical means for applying
measuring light to a blood vessel of a subject eye, and for receiving
light scattered by the blood vessel of the subject eye; direction-changing
means for changing the direction in which the measuring light is
applied to the blood vessel or the direction in which the scattered
light is received by at least a portion of said optical means so
as to enable a plurality of measurements of the blood flow in the
blood vessel using measuring light applied to the blood vessel in
different directions or using scattered light received by at least
a portion of said optical means in different directions; signal-outputting
means for outputting a received-light signal containing information
on blood flow in the blood vessel in response to receiving the scattered
light from said optical means; control means for performing the
plurality of measurements of the blood flow in the blood vessel
using the received-light signal generated from measuring light being
applied to the blood vessel in different directions and scattered
by the blood vessel or generated from the scattered light received
by at least a portion of said optical means in different directions,
wherein said control means comprises means for performing a re-measurement
operation to re-measure the blood flow in the blood vessel using
a received-light signal generated from measuring light being applied
to the blood vessel in a desired direction and then scattered by
the blood vessel or generated from the scattered light received
by at least a portion of said optical means in a desired direction
in response to an instruction by an operator to perform a re-measurement
operation in the desired direction; and input means for enabling
an operator to select a re-measurement operation to re-measure the
blood flow in the blood vessel using a received-light signal generated
from measuring light being applied to the blood vessel in a desired
direction and then scattered by the blood vessel or generated from
the scattered light received by at least a portion of said optical
means in a desired direction, wherein said input means comprises
means for instructing said control means to perform the selected
re-measurement operation selected by the operator.
24. An ocular blood-flow meter according to claim 23 wherein said
input means comprises selector means for enabling the operator to
select a desired measurement result from a plurality of measurement
results obtained in the desired direction in which the re-measurement
operation is performed.
25. An ocular blood-flow meter according to claim 23 further comprising:
tracking means for tracking movement of the subject eye; and display
means for displaying tracking information obtained by said tracking
means.
26. An ocular blood-flow meter according to claim 23 further comprising:
measurement means configured to measure blood vessel size; and display
means for displaying the measurement results obtained by said measurement
means.
27. An ocular blood-flow meter according to claim 23 further comprising
display means for presenting to the operator a plurality of measurement
results using the received light signal output from said signal-outputting
device so as to provide information to the operator to enable the
operator to determine whether the re-measurement operation is required.
28. The ocular blood-flow meter according to claim 23 wherein
said optical means comprises: measuring light source means for emitting
measuring light; and means for refracting said measuring light,
wherein said direction-changing means comprises: movable reflecting
means for reflecting the measuring light incident thereon; and stationary
reflecting means for reflecting the measuring light received from
said movable reflecting means to said means for refracting when
said movable reflecting means is in the optical path from said measuring
light source means to said means for refracting, wherein said movable
reflecting means comprises means for changing the direction in which
the measuring light is applied to the blood vessel by moving out
of or into the path of measuring light from said measuring light
source means and said refracting means.
29. The ocular blood-flow meter according to claim 23 wherein
said direction-changing means comprises means for changing the position
of said signal outputting means so as to change the direction in
which the scattered light is received by at least a portion of said
optical means.
30. The ocular blood-flow meter according to claim 23 wherein
said input means comprises first, second, and third selection means
for selecting only a first direction, only a second direction, and
both said first and second directions, respectively, in which the
operator desires the measuring light to be applied to the blood
vessel and then scattered by the blood vessel or to select only
a first direction, only a second direction, and both said first
and second directions, respectively, in which the operator desires
that the scattered light be received by at least a portion of said
optical means.
31. The ocular blood-flow meter according to claim 23 further
comprising: tracking means for tracking movement of the subject
eye, wherein said tracking means comprises: blood-vessel image forming
means for producing a blood-vessel image of the blood vessel; and
blood-vessel-image-signal producing means for producing a signal
representing the blood-vessel image, wherein said control means
comprises means for determining the position and amount of movement
of the blood-vessel image from the signal produced by said tracking
means, wherein the amount of movement of the blood-vessel image
that is determined by said control means is indicative of the quality
of the tracking performed by said tracking means; and display means
for displaying data, wherein said control means comprises means
for processing the received-light signal over time and determining
an evaluation value over time that represents the quality of the
received-light signal, wherein said control means comprises means
for calculating the variation in the frequency of over time of the
processed received-light signal, wherein said display means comprises
means for displaying a first graph of the processed received-light
signal over time processed by said control means, wherein said display
means comprises means for displaying a second graph of the evaluation
value determined by said control means before and during measurement
of the blood flow in the blood vessel, wherein said display means
comprises means for displaying a third graph representing the variation
over time in the amount of movement of the blood-vessel image during
measurement of the blood flow in the blood vessel, and wherein said
display means comprises means for displaying a fourth graph representing
the variation in the frequency of over time of the processed received-light
signal after measurement of the blood flow in the blood vessel.
32. The ocular blood-flow meter according to claim 31 wherein
said control means comprises means for processing the received-light
signal over time by performing a fast Fourier Transform operation
on the received-light signal to produce a fast Fourier Transform
waveform over time, wherein said display means comprises means for
displaying the fast Fourier Transform waveform over time as the
first graph, wherein said control means also comprises means for
determining the maximum frequency when the power spectrum of the
fast Fourier Transform waveform exceeds a predetermined threshold,
and wherein said display means also comprises means for displaying
the variation in the frequency over time of the power spectrum of
the fast Fourier Transform waveform as the fourth graph.
33. The ocular blood-flow meter according to claim 23 further
comprising: image forming means forming a blood-vessel image, wherein
said control means comprises: means for determining variations in
the amount of movement over time of the blood-vessel image, and
means for processing the received-light signal to produce a processed
received-light signal for determining the frequency over time of
the processed received-light signal, and wherein said meter further
comprises display means for displaying the variations in the amount
of movement over time of the blood-vessel image, and wherein said
display means comprises means for displaying the frequency over
time of the processed received-light signal.
34. The ocular blood-flow meter according to claim 23 wherein
said control means comprises: means for processing the received-light
signal over time, means for determining an evaluation value over
time that represents the quality of the received-light signal generated
from measuring light being applied to the blood vessel in a first
direction and scattered by the blood vessel or generated from the
scattered light received by at least a portion of said optical means
in the first direction, and means for determining an evaluation
value over time that represents the quality of the received-light
signal generated from measuring light being applied to the blood
vessel in a second direction and scattered by the blood vessel or
generated from the scattered light received by at least a portion
of said optical means in the second direction, wherein said meter
further comprises display means for displaying the evaluation values
over time associated with the first and second directions, simultaneously.
35. The ocular blood-flow meter according to claim 34 further
comprising: image forming means forming a blood-vessel image, wherein
said meter further comprises: means for capturing the blood-vessel
image at different times during the plurality of measurements of
the blood flow to produce a plurality of blood-vessel images of
the same blood vessel over time, tracking means for optically tracking
the blood vessel during movement of the blood vessel so that the
blood-vessel image of the blood vessel formed by said image forming
means is positioned at substantially the same position over time
during the plurality of measurements and during a re-measurement
operation when tracking is properly performed, wherein when tracking
by said tracking means is not properly performed, the position of
the blood-vessel image changes over time, wherein said display means
comprises means for displaying in an overlapping manner the plurality
of captured blood-vessel images while receiving the light generated
from measuring light being applied to the blood vessel in the first
direction and scattered by the blood vessel or generated from the
scattered light received by at least a portion of said optical means
in the first direction, wherein the thickness of the displayed,
overlapped blood vessel images associated with the first direction
is greater when said tracking means performs tracking improperly
than when said tracking means performs tracking properly, wherein
said display means comprises means for displaying in an overlapping
manner the plurality of captured blood-vessel images while receiving
the light generated from measuring light being applied to the blood
vessel in the second direction and scattered by blood vessel or
generated from the scattered light received by at least a portion
of said optical means in the second direction, and wherein the thickness
of the displayed, overlapped blood-vessel images associated with
the second direction is greater when said tracking means performs
tracking improperly than when said tracking means performs tracking
properly.
36. The ocular blood-flow meter according to claim 23 or 35 wherein
a measurement operation performed using a received-light signal
generated from measuring light being applied to the blood vessel
in the first direction and scattered by the blood vessel or generated
from the scattered light received by at least a portion of said
optical means in the first direction is denoted as the first path
1 measurement, wherein a re-measurement operation performed using
a received-light signal generated from measuring light being applied
to the blood vessel in the first direction and scattered by the
blood vessel or generated from the scattered light received by at
least a portion of said optical means in the first direction is
denoted as the second path 1 measurement, wherein a measurement
operation performed using a received-light signal generated from
measuring light being applied to the blood vessel in the second
direction and scattered by the blood vessel or generated from the
scattered light received by at least a portion of said optical means
in the second direction is denoted as the first path 2 measurement,
wherein a re-measurement operation performed using a received-light
signal generated from measuring light being applied to the blood
vessel in the second direction and scattered by the blood vessel
or generated from the scattered light received by at least a portion
of said optical means in the second direction is denoted as the
second path 2 measurement, wherein said input means comprises: first
selector means for permitting the operator to instruct said meter
to perform a second path 1 measurement; second selector means for
permitting the operator to instruct said meter to perform a second
path 2 measurement; third selector means for permitting the operator
to instruct said meter to perform a re-measurement operation using
a received-light signal generated from measuring light being applied
to the blood vessel in the first and second directions and scattered
by the blood vessel or generated from the scattered light received
by at least a portion of said optical means in the first and second
directions; fourth selector means for permitting the operator to
instruct said control means to determine the blood flow in the blood
vessel using: the second path 1 measurement and the second path
2 measurement when the operator selects the third selector means;
the second path 1 measurement and the first path 2 measurement when
the operator selects the first selector means; the second path 2
measurement and the first path 1 measurement when the operator selects
the second selector means; fifth selector means for permitting the
operator to instruct said control means to determine the blood flow
using the first path 1 measurement and the first path 2 measurement
after the operator has used said first selector means to instruct
said meter to perform a second path 1 measurement; sixth selector
means for permitting the operator to instruct said control means
to determine the blood flow using the second path 1 measurement
and the first path 2 measurement after the operator has used said
first selector means to instruct said meter to perform a second
path 1 measurement; seventh selector means for permitting the operator
to instruct said control means to determine the blood flow using
the first path 2 measurement and the first path 1 measurement after
the operator has used said second selector means to instruct said
meter to perform a second path 2 measurement; and eighth selector
means for permitting the operator to instruct said control means
to determine the blood flow using the second path 2 measurement
and the first path 1 measurement after the operator has used said
second selector means to instruct said meter to perform a second
path 2 measurement.
37. An ocular blood-flow meter comprising: optical means for applying
measuring light to a blood vessel of a subject eye, and for receiving
light scattered by the blood vessel of the subject eye; direction-changing
means for changing the direction in which the measuring light is
applied to the blood vessel or the direction in which the scattered
light is received by at least a portion of said optical means so
as to enable a plurality of measurements of the blood flow in the
blood vessel using measuring light applied to the blood vessel in
different directions or using scattered light received by at least
a portion of said optical means in different directions; control
means for performing the plurality of measurements of the blood
flow in the blood vessel using the measuring light being applied
to the blood vessel in different directions and scattered by the
blood vessel or using the scattered light received by at least a
portion of said optical means in different directions, wherein said
control means comprises means for performing a re-measurement operation
to re-measure the blood flow in the blood vessel using measuring
light being applied to the blood vessel in a desired direction and
then scattered by the blood vessel or using scattered light received
by at least a portion of said optical means in a desired direction,
wherein said control means also comprises means for determining
whether a re-measurement operation is required; and output means
for presenting information to an operator indicating whether re-measurement
is required in response to said control means determining that a
re-measurement operation is required.
38. An ocular blood-flow meter according to claim 37 further comprising
signal-outputting means for outputting received-light signals containing
information on blood flow in the blood vessel in response to receiving
measuring light being applied to the blood vessel in different directions
and scattered by the blood vessel or in response to receiving scattered
light that has been received by at least a portion of said optical
means in different directions, wherein said control means comprises
means for receiving the received-light signals and performing the
plurality of measurements and the re-measurement operation using
the received-light signals, wherein said signal-outputting means
comprises display means for displaying a representation of the received-light
signals or information concerning the blood flow in the blood vessel,
wherein said control means also comprises means for determining
the quality of the received-light signals obtained by performing
each of the plurality of measurements, and for comparing the quality
of the received-light signals so as to determine whether the re-measurement
operation is required; and wherein said display means comprises
means for displaying information that a re-measurement operation
is required in response to said control means determining that the
re-measurement operation is required.
39. An ocular blood-flow meter according to claim 38 wherein said
control means comprises means for determining the quality of the
received-light signal obtained by performing a re-measurement operation,
and for comparing the quality of the received-light signal before
the re-measurement operation with the quality of the received-light
signal after the re-measurement operation, so as to calculate the
blood flow based on the received-light signal having the better
quality.
40. An ocular blood-flow meter according to claim 37 wherein said
optical means comprises: measuring light source means for emitting
the measuring light; and refracting means for refracting the measuring
light from said measuring light source means, wherein said direction-changing
means comprises: movable reflecting means for reflecting the measuring
light from said measuring light source means; and stationary reflecting
means for reflecting measuring light reflected by said movable reflecting
means to said refracting means when said movable reflecting means
is positioned in the optical path from said measuring light source
to said refracting means, and wherein said movable reflecting means
is retractable out of and insertable into the path of measuring
light from said measuring light source means and said refracting
means so as to change the direction in which the measuring light
is applied to the blood vessel.
41. The ocular blood-flow meter according to claim 37 wherein
said direction-changing means comprises means for changing the position
of said signal-outputting means so as to change the direction in
which the scattered light is received by at least a portion of said
optical means.
42. The ocular blood-flow meter according to claim 37 further
comprising input means for permitting an operator to input selections
into said meter, wherein said input means comprises first, second,
and third selector means for selecting only a first direction, only
a second direction, and both said first and second directions, respectively,
in which the operator desires the measuring light to be applied
to the blood vessel and then scattered by the blood vessel or to
select only a first direction, only a second direction, and both
said first and second directions, respectively, in which the operator
desires that the scattered light be received by at least a portion
of said optical means.
43. The ocular blood-flow meter according to claim 37 wherein
said control means comprises: means for processing the received-light
signals over time; means for determining an evaluation value over
time that represents the quality of each received-light signal,
by comparing the evaluation value for each received-light signal
with a reference value; and means for determining that a re-measurement
operation is required when the evaluation value for a received-light
signal is below the reference value.
44. The ocular blood-flow meter according to claim 43 wherein
said control means further comprises means for processing each received-light
signal over time by performing a fast Fourier Transform operation
on each received-light signal to produce a fast Fourier Transform
waveform over time for each received-light signal, from which said
control means determines an evaluation value for each received-light
signal.
45. A method of measuring ocular blood flow in an ocular blood
vessel comprising the steps of: applying measuring light to a blood
vessel of a subject eye; receiving light scattered by the blood
vessel of the subject eye; changing the direction in which the measuring
light is applied to the blood vessel in said applying step or the
direction in which the scattered light is received in said receiving
step so as to enable the performing of a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received in different directions; outputting a received-light signal
containing information on blood flow in the blood vessel generated
from the scattered light received in said receiving step; performing
the plurality of measurements of the blood flow in the blood vessel
using the received-light signal generated from measuring light being
applied to the blood vessel in different directions and scattered
by the blood vessel or generated from the scattered light received
in different directions; and performing a re-measurement operation
to re-measure the blood flow in the blood vessel using a received-light
signal generated from measuring light being applied to the blood
vessel in a desired direction and then scattered by the blood vessel
or generated from the scattered light received in a desired direction
in response to an instruction by an operator to perform a re-measurement
operation in the desired direction.
46. A method according to claim 45 further comprising the steps
of: tracking movement of the subject eye; and displaying tracking
information obtained by said tracking step.
47. A method according to claim 45 further comprising the steps
of: measuring blood vessel size; and displaying the measurement
result obtained by said measuring step.
48. A method according to claim 45 further comprising the step
of presenting to the operator a plurality of measurement results
using the received light signal output in said signal-outputting
step so as to provide information to the operator to enable the
operator to determine whether the re-measurement operation is required.
49. A method according to claim 45 wherein said applying step
comprises the steps of: emitting measuring light; and refracting
the measuring light with refracting means, wherein said direction-changing
step comprises the step of: changing the position at which the measuring
light emitted in said emitting step is incident upon said refracting
means.
50. A method according to claim 45 wherein said signal-outputting
step is performed by signal-outputting means, wherein said direction-changing
step comprises the step of changing the position of said signal-outputting
means.
51. A method according to claim 45 further comprising the steps
of: performing a re-measurement operation in only a first direction
in response to the operator actuating first selection means; performing
a re-measurement operation in only a second direction in response
to the operator actuating second selection means; and performing
a re-measurement operation in both the first and second directions
in response to the operator actuating third selection means.
52. A method according to claim 45 further comprising the steps
of: tracking movement of the subject eye comprising the steps of:
forming a blood-vessel image of the blood vessel; and producing
a signal representing the blood-vessel image; and determining the
position and amount of movement of the blood-vessel image from the
signal produced by said tracking producing step, wherein the amount
of movement of the blood-vessel image that is determined by said
determining step is indicative of the quality of the tracking performed
by said tracking step; processing the received-light signal over
time and determining an evaluation value over time that represents
the quality of the received-light signal; calculating the variation
in the frequency of over time of the processed received-light signal;
displaying a first graph of the processed receivedlight signal over
time; displaying a second graph of the evaluation value determined
before and during measurement of the blood flow in the blood vessel;
displaying a third graph representing the variation over time in
the amount of movement of the blood-vessel image during measurement
of the blood flow in the blood vessel; and displaying a fourth graph
representing the variation in the frequency of over time of the
processed received-light signal after measurement of the blood flow
in the blood vessel.
53. A method according to claim 52 further comprising the steps
of: processing the received-light signal over time by performing
a fast Fourier Transform operation on the received-light signal
to produce a fast Fourier Transform waveform over time; displaying
the fast Fourier Transform waveform over time as the first graph;
determining the maximum frequency when the power spectrum of the
fast Fourier Transform waveform exceeds a predetermined threshold;
and displaying the variation in the frequency over time of the power
spectrum of the fast Fourier Transform waveform as the fourth graph.
54. A method according to claim 45 further comprising the steps
of: forming a blood-vessel image; determining variations in the
amount of movement over time of the blood-vessel image; processing
the received-light signal to produce a processed received-light
signal for determining the frequency over time of the processed
received-light signal; displaying the variations in the amount of
movement over time of the blood-vessel image; and displaying the
frequency over time of the processed received-light signal.
55. A method according to claim 45 further comprising the steps
of: processing the received-light signal over time; determining
an evaluation value over time that represents the quality of the
received-light signal generated from measuring light being applied
to the blood vessel in a first direction and scattered by the blood
vessel or generated from the scattered light received in the first
direction; determining an evaluation value over time that represents
the quality of the received-light signal generated from measuring
light being applied to the blood vessel in a second direction and
scattered by the blood vessel or generated from the scattered light
received in the second direction; and displaying the evaluation
values over time associated with the first and second directions,
simultaneously.
56. A method according to claim 55 further comprising the steps
of: forming a blood-vessel image; capturing the blood vessel image
at different times during the plurality of measurements of the blood
flow to produce a plurality of blood-vessel images of the same blood
vessel over time; optically tracking the blood vessel during movement
of the blood vessel so that the blood-vessel image of the blood
vessel is positioned at substantially the same position over time
during the plurality of measurements and during a re-measurement
operation when tracking is properly performed, wherein when tracking
is not properly performed, the position of the blood-vessel image
changes over time, displaying in an overlapping manner the plurality
of captured blood vessel images while receiving the light generated
from measuring light being applied to the blood vessel in the first
direction and scattered by the blood vessel or generated from the
scattered light received in the first direction; displaying a greater
thickness for the displayed, overlapped blood-vessel images associated
with the first direction when tracking is performed improperly than
when tracking is performed properly; displaying in an overlapping
manner the plurality of captured blood-vessel images while receiving
the light generated from measuring light being applied to the blood
vessel in the second direction and scattered by the blood vessel
or generated from the scattered light received in the second direction;
and displaying a greater thickness for the displayed, overlapped
blood-vessel images associated with the second direction when tracking
is performed improperly than tracking is performed properly.
57. A method according to claim 45 or 56 wherein a measurement
operation performed using a received-light signal generated from
measuring light being applied to the blood vessel in the first direction
and scattered by the blood vessel or generated from the scattered
light received in the first direction is denoted as the first path
1 measurement, wherein a re-measurement operation performed using
a received-light signal generated from measuring light being applied
to the blood vessel in the first direction and scattered by the
blood vessel or generated from the scattered light received in the
first direction is denoted as the second path 1 measurement, wherein
a measurement operation performed using a received-light signal
generated from measuring light being applied to the blood vessel
in the second direction and scattered by the blood vessel or generated
from the scattered light received in the second direction is denoted
as the first path 2 measurement, wherein a re-measurement operation
performed using a received-light signal generated from measuring
light being applied to the blood vessel in the second direction
and scattered by the blood vessel or generated from the scattered
light received in the second direction is denoted as the second
path 2 measurement, wherein said method further comprises the steps
of: performing a second path 1 measurement in response to the operator
actuating first selector means; performing a second path 2 measurement
in response to the operator actuating second selector means; performing
a re-measurement operation using a received-light signal generated
from measuring light being applied to the blood vessel in the first
and second directions and scattered by the blood vessel or generated
form the scattered light received in the first and second directions
in response to the operator actuating third selector means; determining
the blood flow in the blood vessel in response to the operator actuating
fourth selector means using: the second path 1 measurement and the
second path 2 measurement when the operator selects the third selector
means; the second path 1 measurement and the first path 2 measurement
when the operator selects the first selector means; and the second
path 2 measurement and the first path 1 measurement when the operator
selects the second selector means; determining the blood flow using
the first path 1 measurement and the first path 2 measurement after
the operator has used said first selector means to instruct said
meter to perform a second path 1 measurement in response to the
operator actuating fifth selector means; determining the blood flow
using the second path 1 measurement and the first path 2 measurement
after the operator has used said first selector means to instruct
said meter to perform a second path 1 measurement in response to
the operator actuating sixth selector means; determining the blood
flow using the first path 2 measurement and the first path 1 measurement
after the operator has used said second selector means to instruct
said meter to perform a second path 2 measurement in response to
the operator actuating seventh selector means; and determining the
blood flow using the second path 2 measurement and the first path
1 measurement after the operator has used said second selector means
to instruct said meter to perform a second path 2 measurement in
response to the operator actuating eighth selector means.
58. A method of determining the ocular blood flow in an ocular
blood vessel comprising the steps of: applying measuring light to
a blood vessel of a subject eye; receiving light scattered by the
blood vessel of the subject eye; changing the direction in which
the measuring light is applied to the blood vessel in said applying
step or the direction in which the scattered light is received in
said receiving step so as to enable a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received in different directions; performing the plurality of measurements
of the blood flow in the blood vessel using the measuring light
being applied to the blood vessel in different directions and scattered
by the blood vessel or using the scattered light received in different
directions; performing a re-measurement operation to re-measure
the blood flow in the blood vessel using measuring light being applied
to the blood vessel in a desired direction and then scattered by
the blood vessel or using scattered light received in a desired
direction; determining whether a re-measurement operation is required;
and presenting information to an operator indicating whether re-measurement
is required in response to said determining step determining that
a re-measurement operation is required.
59. A method according to claim 58 further comprising the steps
of: outputting received-light signals containing information on
blood flow in the blood vessel in response to receiving measuring
light being applied to the blood vessel in different directions
and scattered by the blood vessel or in response to receiving scattered
light that has been received in different directions; performing
the plurality of measurements and the re-measurement operation using
the received-light signals; displaying a representation of the received-light
signals or information concerning the blood flow in the blood vessel;
determining the quality of the received-light signals obtained by
performing each of the plurality of measurements, and comparing
the quality of the received-light signals so as to determine whether
the re-measurement operation is required; and displaying information
that a re-measurement operation is required in response to determining
that the re-measurement operation is required.
60. A method according to claim 59 further comprising the steps
of: determining the quality of the received-light signal obtained
by performing a re-measurement operation, and comparing the quality
of the received-light signal before the re-measurement operation
with the quality of the received-light signal after the re-measurement
operation, so as to calculate the blood flow based on the received-light
signal having the better quality.
61. A method according to claim 58 wherein said applying step
comprises the steps of: emitting measuring light; and refracting
the measuring light with refracting means, wherein said direction-changing
step comprises the step of: changing the position at which the measuring
light emitted in said emitting step is incident upon said refracting
means.
62. A method according to claim 58 wherein said signal-outputting
step is performed by signal-outputting means, wherein said direction-changing
step comprises the step of changing the position of the signal-outputting
means so as to change the direction in which the scattered light
is received in said receiving step.
63. A method according to claim 58 further comprising the steps
of: performing a re-measurement operation in only a first direction
in response to the operator actuating first selection means; performing
a re-measurement operation in only a second direction in response
to the operator actuating second selection means; and performing
a re-measurement operation in both the first and second directions
in response to the operator actuating third selection means.
64. A method according to claim 58 further comprising the steps
of: processing the received-light signals over time; determining
an evaluation value over time that represents the quality of each
received-light signal, by comparing the evaluation value for each
received-light signal with a reference value; and determining that
a re-measurement operation is required when the evaluation value
for a received-light signal is below the reference value.
65. A method according to claim 64 further comprising the steps
of: processing each received-light signal over time by performing
a fast Fourier Transform operation on each received-light signal
to produce a fast Fourier Transform waveform over time for each
received-light signal, from which said evaluation value determining
step determines an evaluation value for each received-light signal.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to an ocular blood-flow
meter for measuring the flow rate of blood in a blood vessel of
a patient's eye.
[0003] 2. Description of the Related Art
[0004] An ocular blood-flow meter utilizing the Doppler effect
determines the flow rate of blood in the following manner. A laser
beam is applied to a blood vessel of a subject eye, and the light
scattered and reflected by the blood vessel is received by a photodetector.
Then, an interference signal of a Doppler shift component, i.e.,
the light scattered and reflected by the blood flow, and the light
scattered and reflected by a stationary blood-vessel wall is detected.
Upon analyzing the frequency of the interference signal, the blood-flow
rate is determined. That is, the blood-flow rate (maximum rate V.sub.max)
is determined according to the following equation:
V.sub.max={.lambda./(n.multidot..alpha.)}.multidot..vertline..vertline..DE-
LTA.f.sub.max1.vertline.-.vertline..DELTA.f.sub.max2.vertline..vertline./c-
os.beta. (1)
[0005] wherein .DELTA.f.sub.max1 and .DELTA.f.sub.max2 indicate
the maximum frequency shifts calculated from the received-light
signals received by two photodetectors; .lambda. represents the
wavelength of the laser light; n designates the index of refraction
of a portion to be examined; a indicates the angle between the two
light-detecting optical axes within the eye; and .beta. represents
the angle between the plane formed by the two light-detecting optical
axes and the velocity vector of the blood flow. By measuring the
flow rates from the two directions as discussed above, contributions
due to the directions of incidence of the measuring beams are canceled,
thereby making it possible to measure the flow rate of blood at
a certain portion on the eye fundus. By matching the line of intersection
between the plane formed by the two light-detecting optical axes
and the eye fundus to the angle .beta., .beta. becomes 0 degrees,
thereby measuring the true maximum flow rate.
[0006] In measuring the flow rate with an ocular blood-flow meter,
if the relative position of an optical system of the ocular blood-flow
meter with respect to a portion of the eye to be examined is changed
due to involuntary eye movement, it becomes difficult to perform
precise measurements. In order to solve this problem, U.S. Pat.
No. 4856891 discloses a tracking device. As described in this
patent, a beam of light is applied from a tracking light source
to a subject vessel, and the resulting blood-vessel image is captured
by a charge-coupled device (CCD) camera. Then, the tracking device
performs tracking by scanning the beam of light from the tracking
light source so that the blood vessel image can be stabilized at
a fixed position of the CCD camera in accordance with the eye movement.
[0007] However, the maximum value .DELTA.f.sub.max1 of the Doppler
shift in equation (1) is detected as an interference signal between
the Doppler component shifted by the flow of blood and the stationary
vessel wall. Thus, the maximum frequency shift .DELTA.f.sub.max
obtained by analyzing the frequencies lacks sign information since
what is measured is .vertline..DELTA.f.sub.max.vertline.. In measuring
the flow rates in different portions of the eye fundus, the signs
of the maximum frequency shifts .DELTA.f.sub.max1 and .DELTA.f.sub.max2
may both be positive, or they may both be negative, or one value
may be positive and the other value may be negative. Accordingly,
the maximum flow rate V.sub.max cannot be determined for some portions
according to equation (1).
[0008] U.S. Pat. No. 5640963 discloses an eye-fundus-blood-flow
meter provided with a mechanism for switching the directions of
incidence of the light beams in order to precisely measure the flow
rate of blood regardless of the eye-fundus-vessel portion measured
or the direction of the eye fundus vessel. However, there is still
room for improvement in this flow meter. That is, when measurements
are performed in a single direction of incidence, the patient's
eyelashes may eclipse the beam of light, or a displacement in the
alignment or blinking, or a poor fixation point may be selected,
thereby causing a failure to perform correct measurement in this
direction of incidence. Due to the incorrect measurement in this
direction, even if a correct measurement is performed in the other
direction, it is determined that measurements are incorrectly performed
in both directions, thereby wasting the measurement of correctly
measured paths. Additionally, after performing re-alignment, measurements
must be performed once again in both directions of incidence, thereby
subjecting a patient to a long measurement time.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
improve a conventional eye-fundus-blood-flow meter, and more specifically,
to provide a highly precise and easy-to-use ocular blood-flow meter
in which it can be easily determine whether measurements should
be repeated.
[0010] In order to achieve the above objects, according to one
aspect of the present invention, there is provided an ocular blood-flow
meter comprising an optical system configured and positioned to
apply measuring light to a blood vessel of a subject eye, and to
receive light scattered by the blood vessel of the subject eye.
The meter also comprises a mechanism configured and positioned to
change the direction in which the measuring light is applied to
the blood vessel or the direction in which the scattered light is
received by at least a portion of the optical system so as to enable
a plurality of measurements of the blood flow in the blood vessel
using measuring light applied to the blood vessel in different directions
or using scattered light received by at least a portion of the optical
system in different directions. The meter further comprises a device
configured and positioned to receive the scattered light from the
optical system. The device outputs a received-light signal containing
information on blood flow in the blood vessel in response to receiving
the scattered light from the optical system. In addition, the meter
comprises a controller connected to the device to receive the received-light
signal and configured to perform the plurality of measurements of
the blood flow in the blood vessel using the received-light signal
generated from measuring light being applied to the blood vessel
in different directions and scattered by the blood vessel or generated
from the scattered light received by at least a portion of the optical
system in different directions. The controller is also configured
to perform a re-measurement operation to re-measure the blood flow
in the blood vessel using a received-light signal generated from
measuring light being applied to the blood vessel in a desired direction
and then scattered by the blood vessel or generated from the scattered
light received by at least a portion of the optical system in a
desired direction in response to an instruction by an operator to
perform a re-measurement operation in the desired direction. In
addition, the meter comprises an input device. The input device
is electrically coupled to the controller. The input device is configured
to enable an operator to select a re-measurement operation to re-measure
the blood flow in the blood vessel using a received-light signal
generated from measuring light being applied to the blood vessel
in a desired direction and then scattered by the blood vessel or
generated from the scattered light received by at least a portion
of the optical system in a desired direction. The input device also
is configured to instruct the controller to perform the selected
re-measurement operation selected by the operator.
[0011] According to another aspect, the present invention that
achieves at least one of these objectives relates to an ocular blood-flow
meter comprising an optical system configured and positioned to
apply measuring light to a blood vessel of a subject eye, and to
receive light scattered by the blood vessel of the subject eye.
The meter also comprises a mechanism configured and positioned to
change the direction in which the measuring light is applied to
the blood vessel or the direction in which the scattered light is
received by at least a portion of the optical system so as to enable
a plurality of measurements of the blood flow in the blood vessel
using measuring light applied to the blood vessel in different directions
or using scattered light received by at least a portion of the optical
system in different directions. In addition, the meter comprises
a controller configured to perform the plurality of measurements
of the blood flow in the blood vessel using the measuring light
being applied to the blood vessel in different directions and scattered
by the blood vessel or using the scattered light received by at
least a portion of the optical system in different directions. The
controller is also configured to perform a re-measurement operation
to re-measure the blood flow in the blood vessel using measuring
light being applied to the blood vessel in a desired direction and
then scattered by the blood vessel or using scattered light received
by at least a portion of the optical system in a desired direction.
The controller is also configured to determine whether a re-measurement
operation is required. The meter further includes an output device
connected to the controller. The output device is configured to
present information to an operator indicating whether re-measurement
is required in response to the controller determining that a re-measurement
operation is required.
[0012] According to still another aspect, the present invention
that achieves at least one of these objectives relates to an ocular
blood-flow meter comprising optical means for applying measuring
light to a blood vessel of a subject eye, and for receiving light
scattered by the blood vessel of the subject eye. The meter also
includes direction-changing means for changing the direction in
which the measuring light is applied to the blood vessel or the
direction in which the scattered light is received by at least a
portion of the optical means so as to enable a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received by at least a portion of the optical means in different
directions. In addition, the meter includes signal-outputting means
for outputting a received-light signal containing information on
blood flow in the blood vessel in response to receiving the scattered
light from the optical means. Also, the meter includes control means
for performing the plurality of measurements of the blood flow in
the blood vessel using the received-light signal generated from
measuring light being applied to the blood vessel in different directions
and scattered by the blood vessel or generated from the scattered
light received by at least a portion of the optical means in different
directions. The control means comprises means for performing a re-measurement
operation to re-measure the blood flow in the blood vessel using
a received-light signal generated from measuring light being applied
to the blood vessel in a desired direction and then scattered by
the blood vessel or generated from the scattered light received
by at least a portion of the optical means in a desired direction
in response to an instruction by an operator to perform a re-measurement
operation in the desired direction. The meter also includes input
means for enabling an operator to select a re-measurement operation
to re-measure the blood flow in the blood vessel using a received-light
signal generated from measuring light being applied to the blood
vessel in a desired direction and then scattered by the blood vessel
or generated from the scattered light received by at least a portion
of the optical means in a desired direction. The input means comprises
means for instructing the control means to perform the selected
re-measurement operation selected by the operator.
[0013] According to still another aspect, the present invention
that achieves at least one of these objectives relates to an ocular
blood-flow meter comprising optical means for applying measuring
light to a blood vessel of a subject eye, and for receiving light
scattered by the blood vessel of the subject eye. The meter also
comprises direction-changing means for changing the direction in
which the measuring light is applied to the blood vessel or the
direction in which the scattered light is received by at least a
portion of the optical means so as to enable a plurality of measurements
of the blood flow in the blood vessel using measuring light applied
to the blood vessel in different directions or using scattered light
received by at least a portion of the optical means in different
directions. The meter further includes control means for performing
the plurality of measurements of the blood flow in the blood vessel
using the measuring light being applied to the blood vessel in different
directions and scattered by the blood vessel or using the scattered
light received by at least a portion of the optical means in different
directions. The control means comprises means for performing a re-measurement
operation to re-measure the blood flow in the blood vessel using
measuring light being applied to the blood vessel in a desired direction
and then scattered by the blood vessel or using scattered light
received by at least a portion of the optical means in a desired
direction. The control means also comprises means for determining
whether a re-measurement operation is required. The meter further
comprises output means for presenting information to an operator
indicating whether re-measurement is required in response to the
control means determining that a re-measurement operation is required.
[0014] According to still another aspect, the present invention
that achieves at least one of these objectives relates to a method
of measuring ocular blood flow in an ocular blood vessel comprising
the steps of applying measuring light to a blood vessel of a subject
eye, receiving light scattered by the blood vessel of the subject
eye, changing the direction in which the measuring light is applied
to the blood vessel in the applying step or the direction in which
the scattered light is received in the receiving step so as to enable
the performing of a plurality of measurements of the blood flow
in the blood vessel using measuring light applied to the blood vessel
in different directions or using scattered light received in different
directions, outputting a received-light signal containing information
on blood flow in the blood vessel generated from the scattered light
received in the receiving step, performing the plurality of measurements
of the blood flow in the blood vessel using the received-light signal
generated from measuring light being applied to the blood vessel
in different directions and scattered by the blood vessel or generated
from the scattered light received in different directions, and performing
a re-measurement operation to re-measure the blood flow in the blood
vessel using a received-light signal generated from measuring light
being applied to the blood vessel in a desired direction and then
scattered by the blood vessel or generated from the scattered light
received in a desired direction in response to an instruction by
an operator to perform a re-measurement operation in the desired
direction.
[0015] According to still another aspect, the present invention
that achieves at least one of these objectives relates to a method
of determining the ocular blood flow in an ocular blood vessel comprising
the steps of applying measuring light to a blood vessel of a subject
eye, receiving light scattered by the blood vessel of the subject
eye, changing the direction in which the measuring light is applied
to the blood vessel in the applying step or the direction in which
the scattered light is received in the receiving step so as to enable
a plurality of measurements of the blood flow in the blood vessel
using measuring light applied to the blood vessel in different directions
or using scattered light received in different directions, performing
the plurality of measurements of the blood flow in the blood vessel
using the measuring light being applied to the blood vessel in different
directions and scattered by the blood vessel or using the scattered
light received in different directions, performing a re-measurement
operation to re-measure the blood flow in the blood vessel using
measuring light being applied to the blood vessel in a desired direction
and then scattered by the blood vessel or using scattered light
received in a desired direction, determining whether a re-measurement
operation is required, and presenting information to an operator
indicating whether re-measurement is required in response to the
determining step determining that a re-measurement operation is
required.
[0016] Further objects, features and advantages of the present
invention will become apparent from the following description of
the preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic diagram illustrating an eye-fundus-blood-flow
meter according to a first embodiment of the present invention;
[0018] FIG. 2 illustrates the schematic arrangement of beams of
light on the pupil of an eye E;
[0019] FIG. 3 illustrates the screen of a display device while
a measurement operation is performed;
[0020] FIG. 4 illustrates a graph of a technique for obtaining
an evaluation value indicating the quality of a signal;
[0021] FIG. 5 is a schematic front view illustrating a selection
switch panel;
[0022] FIG. 6 illustrates the screen of the display device immediately
after a measurement operation;
[0023] FIG. 7 illustrates a graph of a technique for obtaining
a frequency fr;
[0024] FIG. 8 illustrates the screen of the display device immediately
after a measurement operation;
[0025] FIG. 9 is a schematic diagram illustrating an eye-fundus-blood-flow
meter according to a second embodiment of the present invention;
[0026] FIG. 10 illustrates a schematic arrangement of beams of
light on the pupil of the eye E;
[0027] FIG. 11 illustrates the screen of the display device immediately
after a measurement operation;
[0028] FIG. 12 is a schematic front view illustrating the selection
switch panel; and
[0029] FIG. 13 shows the relationship between FIG. 13A and 13B
and FIGS. 13A and 13B are a flow chart illustrating the operation
of a third embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] First Embodiment
[0031] The configuration of an eye-fundus-blood-flow meter according
to a first embodiment of the present invention is shown in FIG.
1. In the first embodiment, the present invention is discussed in
the context of an eye-fundus-blood-flow meter for measuring the
flow rate of blood in an eye-fundus blood vessel. However, the present
invention is applicable to a blood-flow meter for measuring the
flow rate of blood in a blood vessel in the sclera.
[0032] In FIG. 1 on an illumination optical path from an observation
light source 1 formed of a tungsten lamp, which emits white light,
to an objective lens 2 which faces an eye E, a condenser lens 3
a band-pass filter 4 which transmits, for example, only yellow-range
wavelength light, a ring slit 5 which is in a substantially conjugate
position with the pupil of the eye E, a transmitting-type liquid
crystal panel 6 for displaying a movable fixation point along the
optical path, a relay lens 7 an apertured mirror 8 and a band-pass
mirror 9 which transmits the yellow-range wavelength light and
reflects most of the other ranges of light, are sequentially disposed.
The ring slit 5 separates the eye-fundus illuminating light from
the eye-fundus observation light at the front portion of the eye.
Any configuration of the ring slit 5 and any number of slits can
be used as long as the ring slit 5 forms a required light-shielding
region.
[0033] Behind the apertured mirror 8 an observation optical system
for the eye fundus is formed, comprising a focusing lens 10 which
is movable along the optical path, a relay lens 11 a scale plate
12 and an eyepiece lens 13 which are sequentially disposed before
an operator's eye "e".
[0034] On the optical path in the reflecting direction of the band-pass
mirror 9 an image rotator 14 and a galvanometric mirror 15 having
both sides polished and having a rotational axis perpendicular to
the plane of the drawing, are disposed. A second focusing lens 16
movable along the optical axis, is provided in the reflecting direction
of a lower reflecting surface 15a of the galvanometric mirror 15.
A lens 17 and a focusing unit 18 which is movable along the optical
axis, are provided in the reflecting direction of an upper reflecting
surface 15b of the galvanometric mirror 15.
[0035] The front focal plane of the lens 17 is conjugate with the
pupil of the eye E, and the galvanometric mirror 15 which is asymmetrically
configured with respect to the pupil, is disposed at the focal plane.
A concave mirror 19 is concentrically located on the optical axis
behind the galvanometric mirror 15. With this arrangement, a relay
optical system, which forms an image on the upper reflecting surface
15b and the lower reflecting surface 15a with -1 times magnification,
is formed so that a laser beam reflected by the upper reflecting
surface 15b of the galvanometric mirror 15 passes through a slit
of the galvanometric mirror 15.
[0036] In the focusing unit 18 a dichroic mirror 20 and a condenser
lens 21 are sequentially disposed on the same optical path as the
lens 17 while a mask 22 and a mirror 23 are sequentially disposed
on the optical path of the reflecting direction of the dichroic
mirror 20. The focusing unit 18 is integrally movable in the directions
indicated by the double-sided arrow.
[0037] On the optical path in the direction of incidence of the
condenser lens 21 a stationary mirror 24 and an optical-path switching
mirror 25 which is retractable from the optical path, are located
in parallel to each other. A measurement light source 26 such as
a laser diode, is disposed on the optical path in the direction
of incidence of the optical-path switching mirror 25. A tracking
light source 27 for emitting high luminance light, for example,
green light, different from the other types of light sources used
in this blood-flow meter, is also disposed on the optical path of
the direction of incidence of the mirror 23.
[0038] A dichroic mirror 28 a magnifying lens 29 and a linear
CCD 30 provided with an image intensifier, are sequentially disposed
behind the second focusing lens 16 on the optical path in the reflecting
direction of the lower reflecting surface 15a of the galvanometric
mirror 15 thereby forming a blood-vessel-detection system. Mirrors
31a and 31b, which form a received-light pupil, and photomultipliers
32a and 32b are disposed on the optical path in the reflecting direction
of the dichroic mirror 28 thereby forming a measurement-light-receiving
system. For ease of representation, all the optical paths are shown
in the same plane. In actuality, however, the mirrors 31a and 31b
and the photomultipliers 32a and 32b are located perpendicularly
to the plane of the drawing.
[0039] The output of the linear CCD 30 is connected to a tracking
controller 33 and an output of the tracking controller 33 is connected
to the galvanometric mirror 15 and is also connected to a system
controller 34 which controls the overall operation of the flow
meter. The system controller 34 comprises a computer system for
executing a program with a processor. The system controller 34 is
connected to the liquid crystal panel 6 the optical-path switching
mirror 25 the photomultipliers 32a and 32b, an operation device
35 a selection switch panel 36 on which a plurality of switches
are disposed to select a certain direction from different directions
for performing re-measurements, and a memory 37. The output of the
system controller 34 is transmitted to a display device 38 for displaying
measurement results, which is connected to the system controller
34. A plurality of re-measurement selection buttons displayed on
the selection switch panel 36 form an input device for instructing
re-measurement.
[0040] FIG. 2 illustrates the arrangement of beams of light on
the pupil of the eye E. In FIG. 2 I denotes the image of the ring
slit 5 in a region to which yellow-range illuminating light is applied,
0 denotes the position of the beam of light for observing the eye
fundus and represents an image of the opening portion of the apertured
mirror 8 V denotes the positions of the measuring beam/light received
from the blood vessel, and represents an image of the effective
portions of the upper and lower reflecting surfaces 15b and 15a
of the galvanometric mirror 15 and Da and Db denote the two received
beams of light and represent images of the pair of mirrors 31a and
31b. P2 and P2' denote the positions of the measuring light selected
by switching the optical-path switching mirror 25 to the position
in the path from the light source 26 to the lens 21. A region M
surrounded by a one-dot chain line denotes the image of the lower
reflecting surface 15a of the galvanometric mirror 15. P1 and P1'
denote the position of spot images of the measurement light incident
on the eye fundus when the optical-path switching mirror retracts
from the optical path of light from light source 26 to lens 21.
[0041] A beam of white light emitted from the observation light
source 1 passes through the condenser lens 3 and the band-pass
filter 4 transmits only the yellow-range wavelength light. Then,
after passing through the ring slit 5 the beam of light illuminates
the liquid crystal panel 6 from behind, passes through the relay
lens 7 and is reflected by the apertured mirror 8. Thereafter,
the band-pass mirror 9 transmits only the yellow-range wavelength
light, which passes through the objective lens 2 and an image is
temporarily formed as a ring slit image on the pupil of the eye
E, which illuminates the eye fundus Ea almost uniformly. In this
case, a fixation target is displayed on the liquid crystal panel
6. The fixation target is projected on the eye fundus Ea of the
eye E by the illumination light, and is presented to the eye E as
a fixation point image.
[0042] The beam of light reflected by the eye fundus Ea returns
via the same optical path, and is extracted as a beam of light for
observing the eye fundus. The observation beam of light then passes
through the opening at the center of the apertured mirror 8 the
focusing lens 10 and the relay lens 11 and an image is formed
as an eye fundus image Ea' on the scale plate 12. Subsequently,
the eye fundus image Ea' is observed by the operator's eye "e"
via the eyepiece 13. While the eye fundus image Ea' is observed,
the alignment of the blood-flow meter is performed.
[0043] When the optical-path switching mirror 25 is placed in the
optical path of light from light source 26 to lens 21 the measuring
beam of light emitted from the measurement light source 26 is reflected
by the optical-path switching mirror 25 and the stationary mirror
24 and passes through the lower portion of the condenser lens 21
and the dichroic mirror 20 transmits the measuring beam of light.
In contrast, when the optical-path switching mirror 25 retracts
from the optical path, the measuring beam of light directly passes
through the upper portion of the condenser lens 21 and the dichroic
mirror 20 transmits the measuring beam of light.
[0044] The tracking beam of light emitted from the tracking light
source 27 is reflected by the mirror 23 and is then shaped into
a desired configuration by the mask 22. The tracking beam of light
is then reflected by the dichroic mirror 20 and is superimposed
on the measuring beam of light from the condenser lens 21 which
forms a spot-like image at a conjugate position with the center
of the opening of the mask 22. The superimposed measuring beam of
light and the tracking beam of light pass through the lens 17 and
are temporarily reflected by the upper reflecting surface 15b of
the galvanometric mirror 15. The superimposed measuring beam of
light and the tracking beam of light are then reflected by the upper
reflecting surface 15b to the concave mirror 19 are reflected by
the concave mirror 19 and return to the galvanometric mirror 15.
Because of the function of the relay optical system, both beams
of light reflected by the upper reflecting surface 15b of the galvanometric
mirror 15 return to the position of the slit of the galvanometric
mirror 15 and travel to the image rotator 14 without being reflected
by the galvanometric mirror 15.
[0045] After passing through the image rotator 14 the beams of
light are deflected to the objective lens 2 by the band-pass mirror
9 and irradiate the eye fundus Ea of the eye E via the objective
lens 2. In this case, the tracking beam of light has been shaped
by the mask 22 to a size of about 300 to 500 .mu.m in the blood-vessel
direction and about 500 to 1200 .mu.m in a direction perpendicular
to the blood vessel so that it illuminates a rectangular region
to cover the vessel including the measuring point. The measuring
beam of light is configured as a circular spot of about 50 to 120
.mu.m, which is roughly equivalent to the thickness of the blood
vessel to be examined, or in an elliptical shape, which is elongated
in the blood-vessel direction.
[0046] The two beams of light scattered and reflected by the eye
fundus Ea are again condensed by the objective lens 2 are reflected
by the band-pass mirror 9 and passes through the image rotator
14. The beams of light are then reflected by the lower reflecting
surface 15a of the galvanometric mirror 15 and pass through the
focusing lens 16. Then, the beams of light are separated into the
measuring beam of light and the tracking beam of light at the dichroic
mirror 28.
[0047] The tracking beam of light then passes through the dichroic
mirror 28 and forms a blood-vessel image, which is magnified at
a greater scale than the eye fundus image Ea' formed by the observation
optical system, on the linear CCD 30 by the magnifying lens 29.
The imaging region of the linear CCD 30 is substantially the same
as the illuminating range of the tracking light. The CCD 30 generates
a signal, which is input into the tracking controller 33 and is
converted into a blood-vessel-position signal. By using the blood-vessel-position
signal, the tracking controller 33 controls the rotational angle
of the galvanometric mirror 15 so as to track the blood vessel.
[0048] Part of the beams of light scattered and reflected by the
eye fundus Ea in response to irradiating the eye with the measuring
beam of light and the tracking beam of light passes through the
band-pass mirror 9 and is guided to the observation optical system
behind the apertured mirror 8. The tracking beam of light forms
an image as a bar-like indicator on the scale plate 12 while the
measuring beam of light forms an image as a spot image at the center
of this indicator. These images are observed together with the eye
fundus image and the fixation point image by the operator's eye
"e" via the eyepiece lens 13. In this case, the spot image
formed by the measuring beam of light is superimposed on the center
of the indicator. The indicator can be linearly moved on the eye
fundus Ea by rotating the galvanometric mirror 15 by using the operation
device 35.
[0049] In performing the measurements, the operator first focuses
the eye-fundus image. By adjusting the focus knob of the operation
device 35 the liquid crystal panel 6 the focus lenses 10 and 16
and the focusing unit 18 are moved along the optical path in association
with each other by a driving mechanism (not shown). When the eye
fundus image is focused, the liquid crystal panel 6 the scale plate
12 and the linear CCD 30 simultaneously become conjugate with the
eye fundus Ea.
[0050] After focusing the eye fundus image, the operator operates
the operation device 35 to change the observation region by guiding
the fixation of the eye E, and to move the subject blood vessel
V to a suitable position. The system controller 34 controls the
liquid crystal panel 6 to move the fixation point image. The operator
also rotates the image rotator 14 so that the line connecting the
centers of the photomultipliers 32a and 32b becomes parallel to
the direction of the subject blood vessel V. In this case, by rotating
the galvanometric mirror 15 the direction perpendicular to the
arrangement of the pixels of the linear CCD 30 and the moving direction
of the measuring beam are also adjusted to the direction perpendicular
to the blood vessel V. After completing the adjustment of the angle,
the operator actuates the operation device 35 to move the center
of the indicator to a portion to be examined. The operator then
actuates the operation device 35 to input a tracking start instruction.
[0051] Upon inputting the tracking start instruction into the tracking
controller 33 from the operation device 35 via the system controller
34 the tracking controller 33 calculates the amount of movement
of the blood vessel image from a linear reference position based
on the received light from the linear CCD 30. Based on this amount
of movement, the tracking controller 33 drives the galvanometric
mirror 15 so that the position of the blood vessel image on the
linear CCD 30 is fixed.
[0052] After checking the quality of the tracking position by starting
the tracking operation, the operator presses a measurement switch
of the operation device 35 to start the measurements. Then, the
optical-path switching mirror 25 is moved into the optical path
by the system controller 34. Then, the measuring beam of light incident
on the pupil of the eye E as spot images P1 and P2 i.e., the beam
of light from a path 1 defined as the path of measuring light from
measuring light source 26 to eye E when optical-path switching mirror
25 is placed in the optical path from measuring light source 26
to lens 21 and scattered and reflected by the eye fundus Ea is
received by the photomultipliers 32a and 32b. The photomultipliers
32a and 32b then generate a signal that is input into the system
controller 34 and is measured for, for example, two seconds. During
the measurements, the measuring beam is held on the blood vessel
by the function of the tracking controller 33.
[0053] The system controller 34 performs fast Fourier transform
(FFT) processing on the signal generated by the photomultiplier
32a at intervals of 20 ms, and the resulting FFT waveform is displayed
on the display device 38 simultaneously with receiving the signal.
The horizontal axis in this graph is time and the vertical axis
represents the values of the power spectrum. FIG. 3 illustrates
an example of what is displayed on the screen of the display device
38 i.e., an FFT waveform Ml is shown. As the FFT waveform M1 becomes
closer to the ideal rectangular waveform, a better measuring condition
is obtained. Under poor tracking conditions in which the measuring
beam is not applied to the center of the blood vessel, or under
poor measuring conditions, such as the patient blinking, or the
eclipse of the measuring beam of light by the patient's eyelashes,
the FFT waveform Ml becomes farther away from the ideal rectangular
waveform.
[0054] The system controller 34 also calculates an evaluation value
indicating the quality of the received-light signal generated by
photomultipliers 32a and 32b, i.e., the quality of the FFT waveform,
from the FFT waveform M1 and displays a bar M2 which becomes longer
or shorter according to the evaluation value, on the display device
38. In this embodiment, the bar M2 becomes longer as the quality
of the received-light signal improves, which enables the operator
to easily determine the quality of the signal generated by the photomultipliers
32a and 32b. In this embodiment, since the two photomultipliers
32a and 32b are different merely in the receiving directions with
respect to a portion of the eye to be examined, the received-light
signal only from the photomultiplier 32a is used to provide a simple
representation. However, both the photomultipliers 32a and 32b may
be used, in which case, the average of the evaluation values from
both the photomultipliers 32a and 32b may be calculated to determine
the quality of the received light signal with higher precision.
[0055] FIG. 4 illustrates a graph from which the evaluation value
can be obtained. S represents an example of the FFT waveform. From
the straight line connecting the start point and the end point of
the curve obtained by integrating the FFT waveform S from the higher
frequency range, the value of the curve at corresponding points
is subtracted to obtain the curve epo (not shown). Ls is a straight
line obtained by linearly approximating the curve epo at a frequency
lower than the frequency where the curve epo peaks. The level of
the power spectrum where the curve epo peaks is denoted by p. If
the size of the received-light pupil is not considered, the configuration
of the ideally obtained FFT waveform is a rectangle, and the portion
corresponding to the curve op becomes straight. Accordingly, the
difference between the approximated straight line Ls and the actual
curve epo is calculated in the frequency range from 0 to fp. This
difference is called the calculated residual. The difference between
the calculated residual and a sufficiently large reference value
is determined to be the evaluation value. When the evaluation value
is calculated in this way, the quality of the received-light signal
is higher with a larger evaluation value.
[0056] FIG. 5 illustrates details of the selection switch panel
36. Among four buttons, i.e., a "path 1 re-measurement"
button B1 a "path 2 re-measurement" button B2 a "both
paths re-measurement" button B3 and an "analyze"
button B4 one of the buttons B1 B2 and B3 which form an input
device, is selected to give a re-measurement instruction. When the
operator determines that the measurement condition of the path 1
is obviously unsatisfactory by checking the information of the measurement
condition on the display device 38 during the measurement operation,
he/she presses the "path 1 re-measurement" button B1 on
the selection switch panel 36 to re-adjust the alignment, and checks
the fixation state or the eyelid opening state of the patient. Then,
the operator performs the re-measurement of the path 1.
[0057] In this embodiment, the FFT waveform M1 obtained by processing
the received-light signal and the bar M2 indicating the evaluation
value are displayed on the display device 38. However, sound output
devices, such as a speaker, a headphone, and an earphone, may be
provided to convert the received-light signal into sound, and the
operator may determine the quality of the received-light signal
from the sound. In this case, it can be determined that the quality
of the received-light signal is higher with a clearer sound. This
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