Abstrict An eye fundus blood flow meter has probing beam applying device
for applying probing beam to a blood vessel on the fundus of an
eye to be examined, a light receptor for receiving the scattered
light of the probing beam from the vicinity of the blood vessel
from two different directions of light reception, a signal processor
for obtaining the information of the blood flow speed in the blood
vessel on the basis of Doppler shift information in the output from
the light receptor, and changing device for changing the angle of
incidence of the probing beam onto the fundus of the eye or the
two directions of light reception of the light receptor.
Claims What is claimed is:
1. A fundus blood flow meter comprising:
probing beam applying means for applying a probing beam to a blood
vessel on a fundus of an eye to be examined;
light detecting means for detecting a scattered light of the probing
beam from a vicinity of the blood vessel from two different directions
of light detection;
signal processing means for obtaining information about blood flow
speed in the blood vessel based on a Doppler shift signal being
output from said light detecting means;
changing means for changing at least one of a direction of incidence
of the probing beam onto the fundus of the eye and the two directions
of light detection of said light detecting means, along a direction
parallel to a direction of arrangement of the two directions of
light detection; and
control means for controlling the changing by said changing means,
and obtaining the information about the blood flow speed by said
signal processing means in each stage before and after said changing,
wherein true blood flow speed is obtained based on information
each obtained before and after said changing.
2. A fundus blood flow meter comprising:
probing beam applying means for applying a probing beam to a blood
vessel on a fundus of an eye to be examined;
light detecting means for detecting a scattered light of the probing
beam from a vicinity of the blood vessel from two different directions
of light detection;
signal processing means for obtaining information about blood flow
speed in the blood vessel based on a Doppler shift signal being
output from said light detecting means;
changing means for changing at least one of a direction of incidence
of the probing beam onto the fundus of the eye and the two directions
of light detection of said light detecting means, along a direction
parallel to a direction of arrangement of the two directions of
light detection; and
comparing means for comparing the blood flow speed information
obtained by said signal processing means before and after the direction
of incidence after at least one of the direction of incidence and
the two directions of light detection are changed by said changing
means.
3. The apparatus according to claim 2 further comprising control
means for controlling said apparatus based the comparison by said
comparing means.
4. The apparatus according to claim 3 wherein said control means
determines at least one of the direction of incidence and the two
directions of light detection based on the comparison by said comparing
means and controls said apparatus to conduct a subsequent measurement
of the blood flow speed.
5. The apparatus according to claim 3 wherein said probing beam
applying means comprises incidence direction switching means for
switching the direction of incidence of the probing beam onto the
fundus of the eye.
6. The apparatus according to claim 5 wherein said control means
controls said incidence direction switching means based on the comparison
by said comparing means.
7. The apparatus according to claim 3 wherein said light detecting
means receives the scattered light from at least two of a plurality
of different locations arranged in a straight line and selects two
light detecting positions from the plurality of positions.
8. The apparatus according to claim 7 wherein said control means
selects two light detecting positions from the plurality of positions
based on the comparison by said comparing means.
9. The apparatus according to claim 7 wherein said control control
said signal processing means to selectively process the light detecting
signals from two of said plurality of positions based on the comparison
by said comparing means.
10. The apparatus according to claim 3 wherein said control means
controls said signal processing means to perform a calculation based
on the comparison by said comparing means.
11. A fundus blood flow meter comprising:
a light source which generates a probing beam;
a beam incident optical system for directing the probing beam from
said light source to a blood vessel on a fundus of an eye to be
examined;
light detecting elements;
a light detecting optical system for directing scattered light
of the probing beam from blood cells in the blood vessel and a wall
of the blood vessel from two different directions of light detecting
to said light detecting elements;
a circuit unit for obtaining information about blood flow speed
in the blood vessel based on a Doppler shift signal output from
said light detecting elements in the two directions;
a changing mechanism for changing at least one of a direction of
incidence of the probing beam onto the fundus of the eye and the
two directions of light detection of said light detecting optical
system, along a direction parallel to a direction of arrangement
of the two directions of light detection; and
a controller for controlling the changing by said changing mechanism,
and obtaining the information of the blood flow speed by said circuit
unit in each stage before and after said changing,
wherein true blood flow speed is obtained based on the information
each obtained before and after said changing.
12. The apparatus according to claim 11 wherein said changing
mechanism comprises, in said light detecting optical system, a switching
mirror for switching an optical path of incidence onto the fundus
of the eye to be examined.
13. The apparatus according to claim 11 wherein said changing
mechanism operates to switch a calculation expression used in said
circuit unit.
14. A fundus blood flow meter comprising:
a light source which generates a probing beam;
a beam incident optical system for directing the probing beam from
said light source to a blood vessel on a fundus of an eye to be
examined;
light detecting elements;
a light detecting optical system for directing scattered light
from said probing means from blood cells in the blood vessel and
a wall of the blood vessel from two different directions of light
detecting to said light detecting elements;
a circuit unit for obtaining information about blood flow speed
in the blood vessel based on a Doppler shift signal in outputs from
said light detecting elements in the two directions;
a changing mechanism for changing at least one of a direction of
incidence of the probing beam onto the fundus of the eye and the
two directions of light detection of said light detecting optical
system, along a direction parallel to a direction of arrangement
of the two directions of light detection; and
wherein said changing mechanism comprises a plurality of optical
fibers disposed in said light detecting optical system, and a driving
mechanism for switching a disposition of said light detecting elements
relative to said plurality of optical fibers.
15. A fundus blood flow meter comprising:
a light source which generates a probing beam;
a beam incident optical system for directing the probing beam from
said light source to a blood vessel on a fundus of an eye to be
examined;
light detecting elements;
a light detecting optical system for directing scattered light
from said probing means from blood cells in the blood vessel and
a wall of the blood vessel from two different directions of light
detecting to said light detecting elements;
a circuit unit for obtaining information about blood flow speed
in the blood vessel based on a Doppler shift signal in outputs from
said light detecting elements in the two directions;
a changing mechanism for changing at least one of a direction of
incidence of the probing beam onto the fundus of the eye and the
two directions of light detection of said light detecting optical
system, along a direction parallel to a direction of arrangement
of the two directions of light detection; and
a control unit for comparing the blood flow speed information obtained
in said circuit unit before and after the angle of incidence of
the probing beam onto the fundus of said light detecting optical
system are changed by said changing mechanism.
16. A fundus blood flow meter comprising:
probing beam applying means for applying a probing beam to a blood
vessel on a fundus of an eye to be examined;
light detecting means for detecting a scattered light of the probing
beam from a vicinity of a blood vessel from two different directions
of light detection;
signal processing means for obtaining information about blood flow
speed in the blood vessel based on a Doppler shift signal being
output from said light detecting means; and
changing means for changing at least one of a direction of incidence
of the probing beam onto the fundus of the eye and the two directions
of light detection of said light detecting means;
said signal processing means measuring the blood flow speed based
on outputs from said light detecting means obtained before and after
said changing means performs the changing.
17. A fundus blood flow measuring method, comprising the steps
of:
applying a probing beam to a blood vessel on a fundus of an eye
to be examined;
detecting a scattered light of the probing beam from a vicinity
of the blood vessel from two different directions of light detection;
obtaining information about blood flow velocity in the blood vessel
based on a Doppler shift signal obtained in said detecting step;
changing at least one of a direction of incidence of the probing
beam onto the fundus of the eye and the two different directions
of light detection, along a direction parallel to a direction of
arrangement of the two directions of light detection; and
executing automatically said changing step, and obtaining the information
about the blood flow speed in each stage before and after said changing,
wherein true blood flow speed is obtained based on the information
each obtained before and after said changing.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an eye fundus blood flow meter for measuring
a blood flow in a blood vessel on the fundus of an eye to be examined.
2. Related Background Art
FIG. 1A of the accompanying drawings shows an example of an eye
fundus blood flow meter according to the prior art which is an improvement
over a slit lamp generally used for ophthalmic diagnosis and treatment.
An illuminating optical system is disposed on an optical path K1
and a white beam of light from an illuminating light source 1 is
reflected by an apertured mirror 2 and illuminates a blood vessel
Ev on the fundus Ea of an eye E to be examined through a slit 3
a lens 4 and a contact lens 5 which offsets the refractive power
of the cornea of the eye E to be examined to thereby enable the
fundus Ea of the eye to be observed. A laser light source 6 for
measurement emitting He-Ne laser light is disposed on an optical
path behind the apertured mirror 2 and the probing beam from the
laser light source 6 for measurement passes through the central
opening portion of the apertured mirror 2 is made coaxial with
the beam of light from the illuminating light source 1 and irradiates
the fundus Ea of the eye in the form of a point.
A beam of light scattered and reflected by Red blood cells flowing
through the blood vessel Ev and the wall of the blood vessel passes
through the objective lenses 7a, 7b of a light detecting optical
system for stereoscopic observation disposed on optical paths K2
and K3 forming an angle .alpha.'therebetween, is reflected by mirrors
8a, 8b and mirrors 9a, 9b and is observed as the image of the fundus
of the eye by an examiner through eyepieces 10a, 10b, and the examiner
selects a measured region while looking into the eyepieces 10a,
10b and observing the fundus Ea of the eye.
FIG. 1B of the accompanying drawings shows the image of the fundus
of the eye observed by the examiner. When in an area I being illuminated
by the illuminating light, the blood vessel Ev which is the object
of measurement is aligned with a scale SC prepared in advance on
the focal plane of the eyepieces 10a, 10b, the probing beam from
the laser light source 6 for measurement and the blood vessel Ev
are aligned with each other, and the measured region is indicated
by a spot beam of light PS formed by the laser light source 6 for
measurement. At this time, the reflected beam of light of the probing
beam by the fundus Ea of the eye is detected by photomultipliers
12a, 12b through optical fibers 11a, 11b.
This detection signal by photomultipliers includes a beat signal
component created by a component Doppler-shifted by a blood flow
flowing through the blood vessel Ev and a component reflected by
the stationary blood vessel wall interfering with each other, and
this beat signal is frequency-analyzed to thereby find the speed
of the blood flow in the blood vessel Ev.
FIG. 1C of the accompanying drawings shows an example of the result
of the frequency analysis of the detection signal by the photomultipliers
12a, 12b, and in this figure, the axis of abscissas represents a
frequency .DELTA.f and the axis of ordinates represents the power
.DELTA.S thereof. The relation among the maximum shift .DELTA.fmax
of the frequency, the wave number vector .kappa.i of the incident
beam of light, the wave number vector .kappa.s of the received beam
of light and the speed vector .nu. of the blood flow can be expressed
as
Accordingly, modifying expression (1) by the use of the shifts
.DELTA.fmax1 and .DELTA.fmax2 of the frequency calculated from the
respective light detection signals by the photomultipliers 12a and
12b, the wavelength .lambda. of the laser light, the refractive
index n of the measured region, the angle .alpha. formed between
light detecting optical axes K2 and K3 in the eye and the angle
.beta. formed between a plane made by the light detecting optical
axes K2 and K3 in the eye and the speed vector .nu. of the blood
flow, the maximum speed Vmax of the blood flow can be expressed
as
Thus, by effecting measurement from two directions, the contribution
in the direction of incidence of the probing beam is offset, whereby
a blood flow in any region on the fundus Ea of the eye can be measured.
Also, to measure the true speed of the blood flow from the relation
between the line of intersection A of the plane made by the two
light detecting optical paths K2 K3 with the fundus Ea of the eye
and the angle .beta. formed between this line of intersection A
and the speed vector .nu. of the blood flow, it is necessary to
make the line of intersection A coincident with the speed vector
.nu. with .beta.=0.degree. in expression (2). Therefore, in the
example of the prior art, the entire light detecting optical system
is rotated or an image rotator is disposed in the light receiving
optical system, thereby making the line of intersection A optically
coincident with the speed vector .nu..
In the above-described example of the prior art, however, the maximum
value .DELTA.fmax of the Doppler shift is detected as the interference
signal between the component shifted by the blood flow and the stationary
blood vessel wall and thus, the maximum shift .DELTA.fmax obtained
by frequency analysis becomes .vertline..DELTA.fmax.vertline. which
lacks sign information.
Thus, when measuring the blood flows in blood vessels in different
regions of the fundus Ea of the eye, there are cases where the signs
of the maximum frequency shifts .DELTA.fmax1 and .DELTA.fmax2 both
have the positive sign, both have the negative sign, and have the
positive and the negative sign, respectively. Accordingly, this
gives a rise to a problem that depending on the area to be measured,
it becomes impossible to determine the maximum blood flow speed
Vmax by expression (2).
This problem will now be described by the use of FIG. 1D of the
accompanying drawings. When in FIG. 1D, signal light enters from
the center hi=0 of the pupil Ep and scattered light is received
from the predetermined regions hs1 and hs2 of the pupil Ep, the
angle at which the predetermined regions hs1 and hs2 are subtended
from the fundus Ea of the eye is the angle .alpha. formed between
the light detecting optical axes in the example of the prior art
shown in FIG. 1A.
Considering now a case where a blood vessel Ev1 at the center of
the fundus Ea of the eye and a blood vessel Ev2 in the marginal
region of the fundus Ea of the eye are to be measured, when the
measurement of the blood vessel Ev1 is effected, the maximum frequency
shift .DELTA.fmax1 obtained by the light reception signal from the
direction of the region hs1 and the maximum frequency shift .DELTA.fmax2
obtained by the light detection signal from the direction of the
region hs2 assume different signs. In this case, the signal light
is incident on the blood vessel Ev1 perpendicularly thereto and
thus, the frequency shift caused by the direction of the signal
light is null and the frequency shift obtained is only caused by
the direction of observation. Considering here the speed vector
.upsilon. of the blood flow in the blood vessel Ev1 the wave number
vector .kappa.s1 in the direction of hs1 and the wave number vector
.kappa.s2 in the direction of hs2 these exist in different directions
relative to the perpendicular to the speed vector .upsilon. and
therefore, the inner product thereof assumes a different sign and
frequency shifts of different signs occur.
On the other hand, when the measurement of the blood vessel Ev2
in the marginal region is effected, the direction of hsl and the
direction of hs2 exist in the same direction relative to positive
reflected light .kappa.' whose frequency shift is 0 and thus, frequency
shifts of the same sign occur. Here, the angle formed between a
straight line linking the center Eo of the fundus Ea of the eye
and the blood vessel Ev2 i.e., the perpendicular at the blood vessel
Ev2 of the fundus Ea of the eye, and the direction of the wave number
vector .kappa.i of the signal light is .phi.i, and a wave number
vector indicative of the positive reflected light of the vector
.kappa.i being at an angle .phi.c with respect to the perpendicular
and facing in opposite direction to the vector .kappa.i is .kappa.i'.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-noted
problems and to provide an eye fundus blood flow meter which can
effect the detection of the above-described sign determining area
and can always effect correct measurement irrespective of the region
and direction of the blood vessel on the fundus of an eye.
Other objects of the present invention will become apparent from
the following detailed description of some embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows the construction of an example of the prior art.
FIG. 1B is an illustration of the image of the fundus of an eye
observed.
FIG. 1C is a graph of the frequency distribution of a light reception
signal.
FIG. 1D is an illustration of the arrangement of beams of light
in the eye.
FIG. 2 shows the construction of an embodiment of the present invention.
FIG. 3 is an illustration of the arrangement of beams of light
on the pupil.
FIG. 4 is an illustration of the image of the fundus of an eye
observed.
FIG. 5 shows the construction of another embodiment of the present
invention.
FIG. 6 is an illustration of the arrangement of optical fibers
and photomultipliers.
FIG. 7 is an illustration of the arrangement of beams of light
in the pupil.
FIG. 8 is an illustration of the image of the fundus of an eye
observed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will hereinafter be
described in detail with reference to FIGS. 2 to 4.
Referring to FIG. 2 which shows the construction of an eye fundus
blood flow meter according to the present embodiment, a band-pass
filter 23 transmitting only yellow and green beams of light therethrough,
a condenser lens 24 a mirror 25 a field lens 26 a ring slit 27
relay lenses 28 29 an apertured mirror 30 and an image rotator
31 are disposed on an optical path leading from an illuminating
light source 21 comprising a tungsten lamp or the like emitting
white light to an objective lens 22. Light detecting optical system
35 in which a pair of small mirrors 32a, 32b, a pair of lenses 33a,
33b and a pair of photomultipliers 34a, 34b are disposed on optical
paths extending upwardly in two directions from the opening portion
of the apertured mirror 30. In FIG. 2 in order to avoid duplication,
only the members on the optical axis of the small mirror 32a of
the pair of small mirrors 32a, 32b are shown.
An image stabilizer 36 is disposed on an optical path behind the
apertured mirror 30 and lenses 37 38 a galvanometric mirror 39
lenses 40 41 and a galvanometric mirror 42 are disposed in succession
in the image stabilizer 36. The galvanometric mirrors 39 and 42
are rotatable by means of an operating rod 43 the galvanometric
mirror 39 is rotated about a rotational axis perpendicular to the
plane of the drawing sheet of FIG. 2 and the galvanometric mirror
42 is rotated about a rotational axis parallel to the plane of the
drawing sheet orthogonal to the first-mentioned rotational axis.
A focusing lens 45 a lens 46 and a dichroic mirror 47 which are
movable along the optical axis are disposed on an optical path behind
the galvanometric mirror 42 and a half mirror 48 a lens 49 and
a television camera 50 are disposed on an optical path in the direction
of reflection of the dichroic mirror 47 whereby an observation
optical system 52 is constituted, and the output of the television
camera 50 is connected to a television monitor 51. Also, a mirror
53 a lens 54 a filter 55 and a one-dimensional CCD array sensor
56 with an image intensifier are disposed on an optical path in
the direction of reflection of the half mirror 48 whereby a blood
vessel detecting system 57 is constituted. The dichroic mirror 47
is made conjugate with the galvanometric mirrors 39 and 42.
At the passage side of the dichroic mirror 47 there are disposed
a lens 59 an aperture 60 lying at a location conjugate with the
fundus Ea of an eye E to be examined, an imaging lens 61 and a laser
optical system for measurement emitting laser light which is signal
light. The laser optical system for measurement is constituted by
an aperture 62 with two holes, a fixed mirror 63 disposed rearwardly
of one of the holes in the aperture 62 an optical path switching
mirror 64 disposed rearwardly of the other hole in the aperture
62 and a laser light source 65 for measurement disposed rearwardly
of the switching mirror 64 and the aperture 62 with two holes is
at a location substantially conjugate with the dichroic mirror 47
the pupil of the eye E to be examined and the two galvanometric
mirrors 39 42.
The output of the CCD array sensor 56 is connected to a control
circuit 66 which has a blood vessel image analyzing circuit constituted
by a tuning memory circuit, a memory processing circuit, a control
unit, etc. and whose output is connected to the galvanometric mirror
39. The output of a system control unit 67 is connected to the control
circuit 66 and the output of the system control unit 67 is also
connected to mirror driving means 68 for driving the optical path
switching mirror 64. The outputs of the photomultipliers 34a and
34b are connected to the system control unit 67.
FIG. 3 shows the arrangement of beams of light relative to the
pupil of the eye E to be examined. The image 27' of the ring slit
27 indicates the position of the illuminating beam of light for
the whole of the fundus Ea of the eye, the images 32a' and 32b'
of the pair of small mirrors 32a and 32b indicate the positions
of the received beams of light of a Doppler signal, and the images
62a' and 62b' of the two hole portions 62a and 62b of the aperture
62 with two holes in the laser optical system for measurement indicate
the positions of the incident beams of light of laser light which
is signal light. Also, the image 30' of the opening portion of the
apertured mirror 30 and the image 47' of the dichroic mirror 47
indicate the positions of beams of light for observation.
The illuminating beam of light from the illuminating light source
21 is imaged on the opening portion of the ring slit 27 via the
band-pass filter 23 the condenser lens 24 the mirror 25 and the
field lens 26 and is again imaged on the apertured mirror 30 by
the relay lenses 28 29 whereafter it passes through the image
rotator 31 and the objective lens 22 is imaged as the slit ring
image 27' on the pupil of the eye E to be examined, and substantially
uniformly illuminates the fundus Ea of the eye.
The reflected light by the fundus Ea of the eye is taken out from
the image 30' of the opening portion of the apertured mirror 30
returns along the same optical path, passes from the opening portion
of the apertured mirror 30 and through the lenses 37 38 galvanometric
mirror 39 lenses 40 41 and the galvanometric mirror 42 of the
image stabilizer 36 is reflected by the dichroic mirror 47 via
the focusing lens 45 and the lens 46 passes through the half mirror
48 and the lens 49 is imaged as an eye fundus image Ea' on the
television camera 50 and is displayed on the television monitor
51. An examiner effects the alignment of the apparatus and the selection
of a measured region while observing the television monitor 51.
Also, the beam of light reflected by the half mirror 48 passes
through the mirror 53 lens 54 and filter 55 of the blood vessel
detecting system 57 and is received by the CCD array sensor 56 as
a blood vessel image Ev' more enlarged than the eye fundus image
Ea' picked up by the television camera 50. The output signal from
the CCD array sensor 56 is processed into data indicative of the
amount of movement of the blood vessel Ev, in the blood vessel image
analyzing circuit in the control circuit 66 whereafter the galvanometric
mirror 39 is driven and controlled so that said amount of movement
may be compensated for by the control circuit 66.
On the other hand, the signal light from the laser light source
65 for measurement passes through one hole 62a in the aperture 62
with two holes because the optical path switching mirror 64 deviates
from the optical path, whereafter it passes through the aperture
60 for specifying the measured region by the image lens 61 and
thereafter reversely returns along the above-mentioned optical path
and is projected onto the blood vessel Ev on the fundus Ea of the
eye E to be examined with the position of the beam of light specified
by the image 62a' of the opening portion of the aperture 62 with
two holes on the pupil through the objective lens 22.
The hole portions 62a and 62b of the aperture 62 with two holes
are imaged outside the image 47' of the dichroic mirror 47 lying
at the conjugate location and therefore, the signal light is not
eclipsed by the dichroic mirror 47 and the reflected beam of light
from the blood vessel Ev returns along the same optical path and
a part thereof is reflected in two directions by the pair of small
mirrors 32a and 32b. The beams of light reflected by the pair of
small mirrors 32a and 32b, respectively, are beams of light taken
out from mirror images 32a' and 32b' on the pupil, and are imaged
on the photomultipliers 34a and 34b, respectively, via the lenses
33a and 33b. These light reception signals are sent to the system
control unit 67 for the measurement of flow speed, and frequency
analysis is effected therein as in the example of the prior art.
On the other hand, the beam of light which is not reflected by
the pair of small mirrors 32a and 32b is a beam of light taken out
from the opening image 30' on the pupil, and passes through the
opening portion of the apertured mirror 30 the image stabilizer
36 the focusing lens 45 and the lens 46 and a part of it is reflected
by the dichroic mirror 47 and is formed as a spot image on the television
camera 50 via the half mirror 48 and the lens 49 and is displayed
on the television monitor 51 with the eye fundus image Ea' by the
illuminating light source 21 and acts on the index mark of the measured
region.
The reflected beam of light on the fundus Ea of the eye by the
laser light source 65 for measurement enters the blood vessel detecting
system 57 via the half mirror 48 but since the filter 55 intercepts
the wavelength of the laser light source 65 for measurement, the
CCD array sensor 56 picks up only the blood vessel image Ev' by
the illuminating light source 21.
The probing beam from the laser light source 65 for measurement
is imaged on the focal plane of the aperture 60 in which the imaging
lens 61 is conjugate with the fundus Ea of the eye E to be examined,
and that conjugate relation is adjusted by the focusing lens 45.
Accordingly, when the examiner operates a focusing knob, not shown,
to thereby effect focusing, the focusing lens 45 is moved along
the optical axis and the image pickup surface of the television
camera 50 the image pickup surface of the CCD array sensor 56 and
the focal plane of the aperture 60 of the lens 61 become conjugate
with the fundus Ea of the eye at a time, and a spot image PS is
also focused with the eye fundus image Ea'.
At this time, the eye fundus image Ea' is displayed on the television
monitor 51 as shown in FIG. 4. The above-mentioned spot image PS
is fixed at the center of the field of view and therefore, the selection
of the measured region is effected by bringing the spot image PS
into coincidence with a predetermined measured region by means of
the operating rod 43 rotating the image rotator 31 and aligning
the blood vessel image Ev' which is the object of measurement with
an axis A. The direction of the coordinates axis A indicates the
direction of the line of intersection of a plane linking the centers
of the pair of small mirrors 32a and 32b with the fundus Ea of the
eye, and is displayed on the television monitor 51 as an index mark
for adjusting the image rotator 31. When the examiner rotates the
image rotator 31 the image Ea' of the fundus of the eye E to be
examined rotates as indicated by arrow C.
By bringing the blood vessel Ev into coincidence with the axis
A to thereby provide .beta.=0.degree. in FIG. 1B, there are obtained
the following advantages (a), (b) and (c):
(a) When from expression (2), .beta.=90.degree., that is, cos .beta.=0
it becomes impossible to obtain the absolute value of the maximum
blood flow speed Vmax from the maximum frequency shifts .DELTA.fmax1
and .DELTA.fmax2 but if the eye fundus image Ea' is rotated so
that .beta.=0.degree., the unmeasurable position can be avoided.
(b) Since it becomes unnecessary to measure the angle .beta., error
factors decrease and the work is simplified.
(c) As described with respect to the example of the prior art,
the blood flow speed is found from the interference signal between
the scattered reflected light from the blood vessel wall and the
scattered reflected light in the blood and therefore, even when
during measurement, the fundus Ea of the eye moves in the direction
of the axis A, the result of measurement will not be affected if
the blood vessel Ev is made substantially parallel to the direction
of the axis A.
On the other hand, when the fundus Ea of the eye moves in the axial
direction orthogonal to the axis A, the signal light from the laser
light source 65 for measurement deviates from the blood vessel Ev
in the measured region and the measured value becomes unstable,
but in such case, the amount of movement of the blood vessel Ev
can be detected only with respect to that direction and therefore,
in the present embodiment, tracking only in that one direction is
effected by the blood vessel detecting system 57 and the image stabilizer
36.
In this tracking, to measure the blood flow speed accurately and
quickly with respect to any blood vessel Ev to be detected, the
CCD array sensor 56 for detecting the amount of movement of the
blood vessel image Ev' can be disposed perpendicularly to the blood
vessel image Ev' which is the object of measurement, and further
by providing .beta.=0.degree., it becomes unnecessary to use any
two-dimensional sensor.
In the present embodiment, the elements of the CCD array sensor
56 are arranged in a direction orthogonal to the axis A, and when
the selection of the measured region has been completed as shown
in FIG. 3 the CCD array sensor 56 of the blood vessel detecting
system 57 enlarges the eye fundus image Ea' indicated by a bar-like
area I in the direction orthogonal to the axis A and picks it up
as the blood vessel image Ev'.
When the examiner depresses a measuring switch, not shown, to start
measurement after the alignment has been thus completed, the system
control unit 67 receives this signal and imparts a tracking start
command to the control circuit 66. At the same time, the signals
of the photomultipliers 34a and 34b are introduced into the system
control unit 67 and the maximum frequency shifts .vertline..DELTA.fmax1.vertline.
and .vertline..DELTA.fmax2.vertline. by the signal light entering
from the location of the hole portion image 62a' of the aperture
62 on the pupil of the eye E to be examined are first found. The
maximum frequency shift .vertline.fmax1.vertline. is the result
of the processing of the output signal from the photomultiplier
34a, and the maximum frequency shift .vertline..DELTA.fmax2.vertline.
is the result of the processing of the output signal from the photomultiplier
34b.
Here, the incident signal light is located on the hole portion
image 62a' and is provided at a location in the same direction relative
to the positions 32a' and 32b' of the received beams of light and
therefore, if usual, the maximum speed Vmax will be found by providing
cos .beta.=1 in expression (2) and by Vmax={.lambda./(n.alpha.)}.multidot..parallel..DELTA.fmax1.vertline.-.vert
line..DELTA.fmax2.parallel., but depending on the location of the
blood vessel Ev on the fundus of the eye, there is also a case where
the true flow speed must be Vmax={.lambda./(n/.alpha.)}.multidot..parallel..DELTA.fmax1.vertline.+.ver
tline..DELTA.fmax2.parallel.. In the present embodiment, at first,
as pre-measurement, the maximum speed Vmax by expression (2) is
calculated in this state, whereafter the optical path switching
mirror 64 is inserted into the optical path by the output of the
system control unit 67 and the signal light is caused to enter from
the other hole portion 62b of the aperture 62 with two holes to
thereby effect measurement.
The hole portion image 62b' which this hole portion 62b makes on
the pupil of the eye E to be examined is disposed so as to have
its center on a straight line passing through the center of the
other hole portion image 62a' and parallel to a straight line linking
the centers of the images 32a' and 32b' of the pair of small mirrors
32a and 32b, as shown in FIG. 3 and particularly in the present
embodiment, the spacing thereof is selected so as to be greater
than the distance between the centers of the images 32a' and 32b'
and so that a straight line linking the midpoints of two straight
lines (a straight line linking the centers of the images 32a' and
32b' and a straight line parallel thereto and passing through the
center of the hole portion image 62a') is orthogonal to the straight
line linking the respective centers.
After the position of the incident beam of light has been switched
from the hole portion image 62a' of the aperture 62 to the thus
selected hole portion image 62b', the system control unit 67 again
introduces signals from the two photomultipliers 34a and 34b, calculates
respective maximum frequency shifts .vertline..DELTA.fmax1'.vertline.
and .vertline..DELTA.fmax2'.vertline. and calculates the maximum
speed Vmax in accordance with expression (2), and when the maximum
speed Vmax at this time is placed as Vmax', it becomes possible
to select the incident beam of light as described above to thereby
separate the area of the angle .phi.i in FIG. 1D in which the signs
of the maximum frequency shifts .vertline..DELTA.fmax1.vertline.
and .vertline..DELTA.fmax2.vertline. are switched and an area in
which the signs of the maximum frequency shifts .vertline..DELTA.fmax1'.vertline.
and .vertline..DELTA.fmax2'.vertline. are switched. In an area wherein
the signs are not switched, Vmax.congruent.Vmax'. Also, in an area
wherein the sign of one of the maximum speeds Vmax and Vmax' is
switched, it becomes possible to create the relation that (the side
on which the switching of the sign does not take place)>(the
side on which the switching of the sign takes place).
Accordingly, in the apparatus of the present embodiment, the system
control unit 67 can determine the direction of incidence of appropriate
signal light for finding a true maximum flow speed, by comparing
the two maximum speeds Vmax and Vmax' with each other. By this information,
the system control unit 67 brings the optical path switching mirror
64 into an appropriate state (for example, when Vmax.noteq.Vmax',
it brings the optical path switching mirror 64 into a state in which
the greater speed has been detected) and controls it so as to effect
main measurement, and in the main measurement, it repeats the measurement
and calculation of the maximum speed Vmax or Vmax' at suitable time
intervals, whereby continuous measurement is effected.
In the present embodiment, there has been shown a method of judging
the maximum speeds Vmax and Vmax' before the main measurement, but
instead of this, it is also possible to cope with the situation
using software for measuring and calculating the maximum speeds
Vmax and Vmax' before the main measurement, and then checking the
presence or absence of the reversal of the sign and for example,
reversing the sign of the calculation of expression (2) by the presence
or absence of the reversal of the sign.
As described above, according to the eye fundus blood flow meter
of the above-described embodiment, when detecting the Doppler shifts
created from two directions by the blood flow on the fundus of the
eye, it becomes possible to switch the direction of incidence of
the probing beam therefor and effect the measurement of the blood
flow speeds, and compare the results of the measurement with each
other to thereby avoid the problem of the reversal of the sign of
the measurement signal. Thus, it is possible to measure always a
correct blood flow speed for any blood vessel existing at any location
and in any direction in the eyeball.
A second embodiment of the present invention will now be described
in detail with reference to FIGS. 5 to 8 although the description
may include some duplication with the description of the first embodiment.
Referring to FIG. 5 which shows the construction of a second embodiment
of the eye fundus blood flow meter of the present invention, a band-pass
filter 123 transmitting only yellow and green beams of light therethrough,
a condenser lens 124 a mirror 125 a field lens 126 a ring slit
127 relay lenses 128 129 an apertured mirror 130 and an image
rotator 131 are disposed in succession on an optical path leading
from an illuminating light source 121 such as a tungsten lamp emitting
white light to an objective lens 122.
In the opening portion of the apertured mirror 130 there are provided
optical fibers 132a, 132b and 132c for directing scattered light
from the fundus Ea of the eye as shown in FIG. 6 and photomultipliers
133a and 133b selectively connected to the optical fibers 132a,
132b and 132c are further disposed, whereby a light receiving optical
system 134 is constituted. In FIG. 5 only the optical fiber 121a
and photomultiplier 133a are shown to avoid duplication.
An image stabilizer 135 is disposed on an optical path behind the
apertured mirror 130 lenses 136 137 a galvanometric mirror 138
lenses 139 140 and a galvanometric mirror 141 are provided in succession
in the image stabilizer 135 the galvanometric mirrors 138 and 141
are rotatable by means of an operating rod 142 the galvanometric
mirror 138 has a rotational axis in a direction orthogonal to the
plane of the drawing sheet of FIG. 5 and the galvanometric mirror
141 has a rotational axis in a direction parallel to the plane of
the drawing sheet of FIG. 5. Further, the output of control means
143 is connected to the galvanometric mirror 138.
A focusing lens 144 a lens 145 and a dichroic mirror 146 which
are movable along the optical axis are disposed on an optical path
behind the galvanometric mirror 141 a half mirror 147 a lens 148
and a television camera 149 are disposed on an optical path in the
direction of reflection of the dichroic mirror 146 and the output
of the television camera 149 is connected to a television monitor
150 whereby an observation optical system 151 is constituted. The
dichroic mirror 146 is made conjugate with the galvanometric mirrors
138 and 141.
At the passage side of the dichroic mirror 146 there are disposed
a lens 152 an imaging lens 153 whose focal plane is at a location
conjugate with the fundus Ea of the eye, and a probing beam source
154 emitting laser light which is signal light. Also, a mirror 155
a lens 156 a filter 157 and a CCD array sensor 158 with an image
intensifier are disposed on an optical path in the direction of
reflection of the half mirror 147 whereby a blood vessel detecting
system 159 is constituted. The output of the CCD array sensor 158
is connected to the control means 143 in which is contained a blood
vessel image analyzing circuit constituted by a tuning memory circuit,
a memory processing circuit, a control unit, etc. Further, the photomultipliers
133a, 133b and the control means 143 are connected to a system control
unit 160.
The entrance ends of the three optical fibers 132a, 132b and 132c
are arranged on a straight line in the opening portion of the apertured
mirror 130 as shown in FIG. 6 and the exit ends thereof are fixed
likewise on a straight line with the gaps therebetween widened.
Rearwardly of the exit ends, the photomultipliers 133a and 133b
are individually supported by a support member 161 for movement
in the direction of arrow C. There is shown a state in which the
emergent light from the optical fiber 132a is received by the photomultiplier
133a and the emergent light from the optical fiber 132b is received
by the photomultiplier 133b, but when the support member 161 is
moved by an actuator, not shown, with the aid of the system control
unit 160 the state changes over to a state in which the emergent
light from the optical fiber 132b is received by the photomultiplier
133a and the emergent light from the optical fiber 132c is received
by the photomultiplier 133b.
The illuminating beam of light from the illuminating light source
121 is imaged on the opening portion of the ring slit 127 via the
band-pass filter 123 the condenser lens 124 the mirror 125 and
the field lens 126 and is once imaged on the apertured mirror 130
by the relay lenses 128 and 129 whereafter it passes through the
image rotator 131 and the objective lens 122 is imaged on the pupil
of the eye E to be examined and illuminates the fundus Ea of the
eye substantially uniformly.
FIG. 7 shows the positions of the beams of light relative to the
pupil of the eye E to be examined, the image 127' of the ring slit
indicates the position of the illuminating beam of light on the
entire fundus Ea of the eye, the images 132a', 132b' and 132c' of
the end surfaces of the light receiving optical fibers indicate
the positions of the received beams of light, the image F of the
focal plane of the imaging lens 153 of the measuring laser optical
system indicates the position of the incident beam of light of the
laser light, and the image 130' of the apertured mirror 130 and
the image 146' of the dichroic mirror 146 indicate the position
of the beam of light for observation.
The reflected light on the fundus Ea of the eye is taken out from
the image 130' of the apertured portion of the apertured mirror
130 in the pupil and returns along the same optical path, passes
through the apertured portion of the apertured mirror 130 passes
through the lenses 136 137 galvanometric mirror 138 lenses 139
140 and galvanometric mirror 141 of the image stabilizer 135 is
further reflected by the dichroic mirror 146 via the focusing lens
144 and the lens 145 passes through the half mirror 147 and the
lens 148 is imaged as an eye fundus image Ea' on the television
camera 149 and is displayed on the television monitor 150. The examiner
effects the alignment of the apparatus and the selection of a measured
region while observing the television monitor 150.
The beam of light reflected by the half mirror 147 passes through
the mirror 155 lens 156 and filter 157 of the blood vessel detecting
system 159 and is received by the CCD array sensor 158 as a blood
vessel image more enlarged than the eye fundus image Ea' picked
up by the television camera 149. The output signal from the CCD
array sensor 158 is processed into data representative of the amount
of movement of the blood vessel Ev in the blood vessel image analyzing
circuit, whereafter the control means 143 drives and controls the
galvanometric mirror 138 so as to compensate for that amount of
movement.
On the other hand, the signal light from the measuring laser light
source 154 is condensed by the imaging lens 153 and returns along
the previously described optical path, and is projected from the
position F of the beam of light shown in FIG. 7 onto the blood vessel
on the fundus Ea of the eye E to be examined through the objective
lens 122. This position F of the beam of light is disposed outside
the dichroic mirror 146 lying at a conjugate location and therefore,
the signal light is never eclipsed by the dichroic mirror 146.
The reflected beam of light from the blood vessel returns along
the same optical path and a part of it is directed to the light
receiving optical system by the optical fibers 132a, 132b and 132c.
When the light receiving optical system is in the state shown in
FIG. 6 the beams of light received by the photomultipliers 133a
and 133b are beams of light located at 132a' and 132b' in FIG. 7
on the pupil, and as in the example of the prior art, frequency
analysis for the measurement of the blood flow speed is effected
by the use of this light reception signal.
On the other hand, the beam of light not received by the optical
fibers 132a, 132b and 132c is a beam of light taken out from the
opening image 130' on the pupil, and passes through the opening
portion of the apertured mirror 130 the image stabilizer 135 the
focusing lens 144 and the lens 145 and a part of it is reflected
by the dichroic mirror 146 is formed as a spot image by the television
camera 149 via the half mirror 147 and the lens 148 is displayed
on the television monitor 150 with the eye fundus image Ea' by the
illuminating light source 121 and acts as an index mark for the
measured region.
The reflected beam of light on the fundus Ea of the eye by the
measuring laser light source 154 enters the blood vessel detecting
system 159 via the half mirror 147 but since the filter 157 intercepts
the wavelength of the measuring laser light source 154 only the
blood vessel image by the illuminating light source 121 is picked
up by the CCD array sensor 158.
The measuring laser beam is condensed by the focal plane of the
imaging lens 153 and the conjugate relation thereof is adjusted
by the focusing lens 144. Accordingly, when the examiner operates
a focusing knob, not shown, to effect focusing, the focusing lens
144 is moved along the optical axis and the image pickup surface
of the television camera 149 the image pickup surface of the CCD
array sensor 158 and the focal plane of the imaging lens 153 become
conjugate with the fundus Ea of the eye at a time, and with the
focusing of the eye fundus image Ea', the focusing of the spot image
is done.
At this time, as shown in FIG. 8 the eye fundus image Ea' is displayed
on the television monitor 150. The spot image PS is fixed at the
center of the field of view, and for the selection of the measured
region, the spot image PS is brought into coincidence with a predetermined
measured region by the operating rod 142 the image rotator 131
is rotated and the blood vessel image Ev' which is the object of
measurement is aligned with the axis A. The direction of the coordinates
axis A indicates the direction of the line of intersection of a
plane linking the centers of the optical fibers 132a, 132b, 132c
in the direction of incidence with the fundus Ea of the eye, and
is displayed on the television monitor 150 as an index mark for
the adjustment of the image rotator 131. When the examiner rotates
the image rotator 131 the image Ea' of the fundus of the eye to
be examined rotates as indicated by arrow C.
Bringing the blood vessel Ev into coincidence with the axis A to
thereby provide .beta.=0.degree. leads to the obtainment of the
following advantages (d)-(f).
(d) When from expression (2), .beta.=90.degree., that is, cos .beta.=0
is provided, it becomes impossible to find the absolute value of
the maximum blood flow speed Vmax from only the maximum frequency
shifts .DELTA.fmax1 and .DELTA.fmax2 and therefore, if .beta.=0.degree.
is provided and the eye fundus image Ea' is rotated so as to provide
cos .beta.=1 an unmeasurable position can be avoided.
(e) It becomes unnecessary to measure the angle .beta. and thus,
error factors decrease and the work is simplified.
(f) As described with respect to the example of the prior art,
the principle of speed detection is obtained from the interference
signal between the scattered reflected light from the blood vessel
wall and the scattered reflected light in the blood and therefore,
even when during measurement, the fundus Ea of the eye moves in
the direction of the axis A, the result of measurement will not
be affected if the blood vessel Ev is made substantially parallel
to the direction of the axis A.
On the other hand, when the fundus Ea of the eye moves in the axial
direction orthogonal to the axis A, the signal light from the measuring
laser light source 154 deviates from the blood vessel Ev in the
measured region and the measured value becomes unstable, but in
that case, the amount of movement of the blood vessel Ev can be
detected with respect only to that direction, and in the present
embodiment, tracking is effected only in that one direction by the
blood vessel detecting system 159 and the image stabilizer 135.
In this case, to measure the blood flow speed accurately and quickly
with respect to any blood vessel EV to be examined, it will be good
if the CCD array sensor 158 for detecting the amount of movement
of the blood vessel image Ev' is disposed in a direction perpendicular
to the blood vessel image Ev' which is the object of measurement,
and this leads to an advantage that .beta.=0.degree. is provided,
whereby it becomes unnecessary to use any two-dimensional sensor.
In the present embodiment, the elements of the CCD array sensor
158 are arranged in a direction orthogonal to the axis A, and when
as shown in FIG. 8 the selection of a measured region has been
completed, the CCD array sensor 158 of the blood vessel detecting
system 159 enlarges the eye fundus image Ea' indicated by a bar-like
area I in the direction orthogonal to the axis A and picks it up
as the blood vessel image Ev'.
When the examiner depresses a measuring switch, not shown, to start
measurement after the alignment has thus been completed, the system
control unit 160 gives a tracking start command by the control means
143. At the same time, the signals of the photomultipliers 133a
and 133b are introduced into the system control unit 160 and the
maximum frequency shifts .vertline..DELTA.fmax1.vertline. and .vertline..DELTA.fmax2.vertline.
by signal lights received from the positions 132a' and 132b' of
the received beams of light on the pupil of the eye E to be examined
are first found. The maximum frequency shift .vertline..DELTA.fmax1.vertline.
is the result of the processing of the output from the photomultiplier
133a, and the maximum frequency shift .vertline..DELTA.fmax2.vertline.
is the result of the processing of the output signal from the photomultiplier
133b.
Here, the incident signal beam of light is located at F in FIG.
7 and is provided at a location in the same direction relative to
the positions of the received beams of light (the position 132b'
is at an angle 0) and therefore, if usual, cos .beta.=1 is provided
in expression (2) and the maximum blood flow speed Vmax is found
from Vmax={.lambda./(n.multidot..alpha.)}.multidot..parallel..DELTA.fmax1-.vert
line..DELTA.fmax2.parallel., but depending on the location of the
blood vessel Ev, there is also a case where the true blood flow
speed must be Vmax={.lambda./(n.multidot..alpha.)}.multidot..parallel..DELTA.fmax1.vertl
ine.+.vertline..DELTA.fmax2.parallel..
In the present embodiment, at first, as pre-measurement, the maximum
blood flow speed Vmax by expression (2) is calculated in this state,
whereafter the support member 161 is driven by an actuator, not
shown, to thereby move the locations of the photomultipliers 133a
and 133b and switch the positions of the received beams of light
from the set of 132a' and 132b' to the set of 132b' and 132c'.
In the present embodiment, the signals from two adjacent ones of
the three optical fibers 132a, 132b and 132c are selectively received
by switching the locations of the photomultipliers 133a and 133b,
and the three optical fibers 132a, 132b and 132c are disposed at
equal intervals and are made symmetrical with respect to the incidence
position of the probing beam. The switching method can be arbitrarily
set as by providing four optical fibers and selecting and receiving
the signals of two of the four optical fibers.
After the switching of the locations of the photomultipliers 133a
and 133b has been effected, the system control unit 160 again introduces
signals from the two photomultipliers 132a and 132b, calculates
respective maximum frequency shifts .vertline..DELTA.fmax1'.vertline.
and .vertline..DELTA.fmax2'.vertline. and calculates the maximum
blood flow speed Vmax in accordance with expression (2). Assuming
that the speed calculated at this time is Vmax', by selecting the
set of the positions of the received beams of light as described
above, it becomes possible to separate areas in which the signs
of the maximum frequency shifts .vertline..DELTA.fmax1.vertline.
and .vertline..DELTA.fmax2.vertline. switch, i.e., the area .phi.i
in FIG. 1D and the area in which the signs of .vertline..DELTA.fmax1'.vertline.
and .vertline..DELTA.fmax2'.vertline. switch, and Vmax.congruent.Vmax'
is provided in the area wherein the signs do not switch. Also, in
the area wherein the sign of one of the speeds Vmax and Vmax' switches,
it becomes possible to create the relation that (the side on which
the switching of the signs does not take place)>(the side on
which the switching of the signs takes place).
Thus, in the apparatus of the present embodiment, the system control
unit 160 can compare the two maximum blood flow speeds Vmax and
Vmax' with each other to thereby determine the appropriate set of
the directions of reception of the signal lights in order to find
the true maximum blood flow speed. By this information, the system
control unit 160 brings the locations of the photomultipliers 133a
and 133b into an appropriate state (for example, when Vmax.noteq.Vmax',
the photomultipliers 133a and 133b are disposed in a state in which
the greater one has been detected) and effects main measurement.
In the main measurement, the measurement and calculation of the
maximum blood flow speed Vmax or Vmax' are repeated at suitable
time intervals, whereby continuous measurement is effected.
In the present embodiment, there has been shown a method of judging
the maximum blood flow speeds Vmax and Vmax' before the main measurement,
and determining the direction of light reception in the main measurement,
but instead of the switching of the direction of light reception,
it is also possible to cope with the situation using software for
specifying the sign of expression (2), or using software for measuring
the blood flow speeds Vmax and Vmax' always or alternately during
the main measurement, checking the presence or absence of the reversal
of the sign after the measurement or at the interval of switching,
and selecting the sign of the calculation of expression (2). If
the situation is coped with by the software, it will be possible
to further simplify the construction of the apparatus.
Also, the present embodiment adopts an approach in which the locations
of the photomultipliers 133a and 133b are moved for the switching
of the direction of light reception, but alternatively, the photomultipliers
may be fixedly disposed at the exit ends of the respective optical
fibers and the output signals thereof may be electrically selected.
Further, the light directing system is not restricted to the optical
fibers, but for example, the use of a small mirror and a lens is
also possible if there is a space therefor.
Also, in the present embodiment, two adjacent directions of light
reception are selected from three directions of light reception,
but the selection thereof may also be effected from more directions
of light reception. The entrance ends of the light receiving optical
fibers may be made movable and the locations thereof may be changed
to thereby obtain a similar effect. Also, it is for simplifying
the subsequent calculating process that the selected directions
of light reception are made symmetrical with respect to the direction
of incidence of the probing beam, and this is not restrictive, but
any disposition is possible. However, it is necessary in avoiding
the duplication of the sign reversing area to design the directions
of light reception so as not to overlap each other.
As described above, in the eye fundus blood flow meter according
to the above-described embodiment, when detecting the Doppler shifts
created from two directions by the blood flow on the fundus of the
eye, the direction of reception of the probing beam thereof is switched
and the results of the measurement of the respective blood flow
speeds are compared with each other, whereby it becomes possible
to avoid the problem of the sign reversal of the measuring signal.
Accordingly, a correct blood flow speed can always be measured for
a blood vessel at any location and in any direction in the eyeball.
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