JP2001112717A - Eye fundus blood flow meter and method for processing its signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine the SN ratio of the measurement signal of an eye fundus blood flow meter in a short time so that, when the SN ratio is poor, a process is performed for precluding measurement or for regarding the poor SN ratio as resulting from a measurement error. SOLUTION: A blood vessel on the fundus oculi of an eye E to be examined is irradiated with coherent measurement light, and signal light derived from scattering of the measurement light by particles within the blood vessel and reference light scattered from peripheral tissue are received; a spectrum distribution resulting from the frequency analysis of those reflected light signals is divided into at least two regions, that is, a noise region approximated to a white noise existing in a high frequency range, and a signal region existing at a lower frequency than the noise region. For this division, an integrated curve accumulated from high frequencies is originated, after which the integrated curve and its approximate straight line are obtained in two signal regions; an SN ratio is calculated from the two Y-axis sections thereof. Thus, by dividing the spectrum distribution into the signal region and the noise region, it can be effectively used, not only in the calculation of the SN ratio but also in subsequent velocity analysis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser Doppler-type fundus blood flow meter for measuring a blood flow velocity in a blood vessel on the fundus and a signal processing method.

[0002]

2. Description of the Related Art Conventionally, a laser Doppler fundus blood flow meter irradiates a measured blood vessel in the fundus of an eye to be examined with a laser beam having a wavelength of λ, and receives a scattered reflected light thereof with a photodetector.
This is an apparatus that detects an interference signal between a Doppler-shifted component that is scattered reflected light from a blood flow and a scattered reflected light from a stationary blood vessel wall, and analyzes the frequency to obtain a blood flow velocity.

Assuming that the blood flow in a target blood vessel is a Poiseuille flow having a uniform blood cell distribution and that the scattering intensity is proportional to the number of blood cells, the spectral density of the Doppler shift obtained is the maximum flow velocity at the center of the blood vessel. It is derived that the spectrum distribution has a substantially flat shape up to the corresponding cutoff frequency Δfmax, and the laser Doppler fundus blood flow meter detects Δfmax as a physical quantity proportional to the maximum flow velocity.

In the two-directional observation method, the cutoff frequency Δfmax is determined for signals received from two different directions, and the relationship between Δfmax and Vmax is determined by the configuration of the apparatus and the axial length as shown in the following equation. And the magnitude of the wave number vector k, that is, 2π / λ. Vmax = {λ / (n · α)} · | Δfmax1−Δfmax2 | / cosβ (1)

Here, the maximum shift of the frequency calculated from the light receiving signals received by the two light receivers is represented by Δfmax1 and Δfmax2.
, The wavelength of the laser beam is λ, the refractive index of the measurement site is n, the angle between the two light receiving optical axes in the eye is α, and the plane formed by the two light receiving optical axes in the eye and the blood flow velocity vector are formed. The angle is β.

As described above, by performing measurement from two directions, the contribution of the incident direction of the measurement light is cancelled, and the blood flow at an arbitrary site on the fundus can be measured. Also, by making the intersection line between the plane formed by the two light receiving optical axes and the fundus and the angle β formed between the blood flow velocity vector and β = 0 °, the true maximum blood flow velocity is measured. Can be.

Conventionally, each cutoff frequency Δfmax is determined visually by an operator, but as a paper automatically determined, APPLIED OPTICS, Vol. 27, No. 6,
pp. 1126-1134 (1988) "Retinal laser Doppl
er velocimetry: towardits computer-assisted cl
inical use "(B.L. Petrig, CERiva) is known. Although there is no specific description in this paper, FFT
It is presumed that the cutoff frequency Δfmax is determined in consideration of an ideal model in which the power spectrum of the waveform is discontinuous, that is, drops vertically at the cutoff frequency Δfmax.

The accuracy of determining the cutoff frequency increases as the result of the frequency analysis approaches the ideal model. That is, by evaluating the difference from the ideal model, the reliability of the measured value can be expressed. In the above-mentioned paper, the difference from the ideal model is determined after the cutoff frequency is determined, and evaluated using the cutoff frequency Δfmax to obtain the measurement reliability.

[0009]

However, in the above-mentioned conventional evaluation method, it takes a long time to determine the final cutoff frequency, and it is difficult to obtain the result instantaneously. Therefore, for example, in the case where the confirmation of the set measurement conditions, such as the position of the measurement light with respect to the blood vessel, is previously determined based on the quality of the acquired measurement signal, calculation time is required. Difficult to do. Furthermore, when an evaluation method for judging the quality of a signal from the shape of a spectrum is used, the signal component of the Doppler signal does not have sufficient strength, and in the case of a signal for which a correct measurement value cannot be obtained, the shape comparison is not correctly performed. There is a problem that the signal is judged to be extremely good.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a fundus blood flow meter capable of determining an SN ratio of a measurement signal in a short time and accurately determining whether the signal is good or not and a signal processing method thereof.

[0011]

A fundus blood flow meter according to the present invention for achieving the above object has a measuring light irradiating means for irradiating a blood vessel on a fundus of an eye to be examined with coherent measuring light; Light receiving means for receiving signal light in which light is scattered by intravascular particles and reference light scattered from surrounding tissue; frequency analyzing means for frequency analyzing a light receiving signal of the light receiving means; A first step of calculating an integral curve obtained by accumulating a spectrum distribution based on the frequency analysis result from a high frequency side, in a laser Doppler-type fundus blood flow meter having calculation means for calculating a blood flow velocity; At least two regions, a noise region existing in a high frequency region and approximated to white noise using the integration curve and a signal region existing on a lower frequency side than the noise region Characterized in that it has a signal processing unit of the light receiving signal and a second step of dividing.

Further, in the signal processing method of the fundus blood flow meter according to the present invention, the blood vessel on the fundus of the eye to be inspected is irradiated with coherent measurement light by the measurement light irradiation means, and the measurement light is scattered by intravascular particles. A laser for receiving, by a light receiving means, a signal light to be emitted and a reference light scattered from a surrounding tissue, frequency-analyzing a light receiving signal from the light receiving means by a frequency analyzing means, and calculating a blood flow velocity based on the frequency analysis result A signal processing method for a received light signal of a Doppler fundus blood flow meter, comprising: a first step of calculating an integral curve obtained by accumulating a spectrum distribution of the frequency analysis result from a high frequency side; and a high frequency region using the integral curve. And the second step of dividing the received light signal into at least two regions, a noise region approximated to white noise and a signal region existing on a lower frequency side than the noise region. And performing a physical.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 shows a configuration diagram of a fundus blood flow meter according to an embodiment. A condenser lens 3 is provided on an illumination optical path from an observation light source 1 composed of a tungsten lamp or the like that emits white light to an objective lens 2 facing the eye E. For example, the band-pass filter 4 that transmits only light in the yellow range, the eye E
A ring slit 5 provided at a position substantially conjugate with the pupil of the eye, a transmissive liquid crystal plate 6, which is a fixation target display element movable along the optical path, a relay lens 7, a perforated mirror 8, wavelength light in the yellow range The band-pass mirrors 9 that pass through the mirror and almost reflect other light beams are sequentially arranged to form fundus illumination optics.

A fundus observation optical system is provided behind the perforated mirror 8, and a focus lens 10, a relay lens 11, a scale plate 12, and an eyepiece 13 which are movable along an optical path are sequentially arranged. The person has reached the point e.

An image rotator 14 and a double-side polished galvanometric mirror 15 having a rotation axis perpendicular to the paper are arranged on the optical path in the reflection direction of the bandpass mirror 9.
A second focus lens 16 that is movable along the optical path is disposed in the reflection direction of 5a, a lens 17 is disposed in the reflection direction of the upper reflection surface 15b, and a focus unit 18 that is movable along the optical path is disposed. I have. The lens 17
Has a conjugate relationship with the pupil of the eye E to be examined, and a galvanometric mirror 15 is disposed on the focal plane.

A concave mirror 19 is arranged behind the galvanometric mirror 15, and a relay optical system through which a laser beam reflected by the upper reflecting surface 15 b of the galvanometric mirror 15 passes through a notch of the galvanometric mirror 15 is provided. It is configured.

In the focus unit 18, a dichroic mirror 20, a condenser lens 21, and a measurement light source 22 composed of a laser diode are arranged on the same optical path as the lens 17.
Are sequentially arranged, and a mask 23 and a mirror 24 are arranged on an optical path in a reflection direction of the dichroic mirror 20, and the focus unit 18 can be integrally moved in an arrow direction. Further, on the optical path in the incident direction of the mirror 24, a tracking light source 25 that emits, for example, green light different from other light sources of high luminance is arranged.

On the optical path in the direction of reflection of the lower reflecting surface 15a of the galvanometric mirror 15, behind the second focus lens 16, a dichroic mirror 26, a magnifying lens 27, and a one-dimensional image sensor 28 with an image intensifier. Are sequentially arranged to form a blood vessel detection system. Further, photomultipliers 29a and 29b are arranged on the optical path in the reflection direction of the dichroic mirror 26 to constitute a light receiving optical system for measurement. Although all the optical paths are shown on the same plane for convenience of illustration, the photomultipliers 29a and 29b are respectively arranged in a direction perpendicular to the paper surface.

The output of the one-dimensional image pickup device 28 is connected to a tracking control circuit 30, and the output of the tracking control circuit 30 is connected to the galvanometric mirror 15 and a system control unit 31 for controlling the entire apparatus. The system control unit 31 includes a signal processing unit 31a and a storage unit 3
1b, the output of the system control unit 31 is connected to the transmission type liquid crystal panel 6, the display monitor 32, and the operation unit 3
3 is connected to the system controller 31.

The white light emitted from the observation light source 1 passes through the condenser lens 3, and only the yellow wavelength light is transmitted by the band pass filter 4, and the light flux passing through the ring slit 5 illuminates the transmission type liquid crystal plate 6 from behind. Then, the light is reflected by the perforated mirror 8 through the relay lens 7. After that, only the light in the yellow range passes through the band-pass mirror 9 and the objective lens 2
, And once formed as a ring slit image on the pupil of the eye E to be examined, the fundus oculi Ea is almost uniformly illuminated. At this time, a fixation target is displayed on the transmissive liquid crystal plate 6, and the fixation target is projected on the fundus oculi Ea of the eye E by illumination light and presented to the subject as a target image. The ring slit 5 is for separating the fundus illumination light and the fundus observation light in the anterior segment of the subject's eye E, and its shape and number do not matter as long as it forms a necessary light shielding area. .

The reflected light from the fundus Ea returns along the same optical path,
It is extracted as a fundus observation light beam from the pupil, passes through the center opening of the perforated mirror 8, the focus lens 10, the relay lens 11, forms an image as a fundus image Ea 'on the scale plate 12, and then passes through the eyepiece 13. To the examiner's eye e. The examiner performs alignment of the apparatus while observing the fundus image Ea ′.

The measuring light emitted from the measuring light source 22 passes eccentrically above the condenser lens 21 and passes through the dichroic mirror 20. On the other hand, the tracking light emitted from the tracking light source 25 is reflected by the mirror 24, is shaped into a desired shape by the mask 23, is reflected by the dichroic mirror 20, and is reflected by the condensing lens 21.
3 is superimposed on the measurement light which is formed in a spot shape at a position conjugate with the center of the opening.

Further, the measuring light and the tracking light are transmitted through the lens 1
7, the light is once reflected by the upper reflection surface 15b of the galvanometric mirror 15, further reflected by the concave mirror 19, and returned to the galvanometric mirror 15 again.
Here, the galvanometric mirror 15 is arranged at a conjugate position with respect to the pupil of the eye E, and has a shape that is asymmetric on the pupil of the eye E. The concave mirror 19 is arranged concentrically on the optical axis, and has a function of a relay optical system for forming an image of the upper and lower reflecting surfaces of the galvanometric mirror 15 by -1 times.

For this purpose, the galvanometric mirror 1
The two luminous fluxes reflected by 5b are returned to the positions of the cutout portions of the galvanometric mirror 15 and proceed to the image rotator 14 without being reflected by the galvanometric mirror 15 again. Then, both light beams deflected to the objective lens 2 by the bandpass mirror 9 via the image rotator 14 are transmitted to the fundus Ea of the eye E through the objective lens 2.
Is irradiated.

At this time, the tracking light is shaped so as to illuminate a rectangular area covering the blood vessel, including the measurement point by the mask 23, and has a size of about 300 to 500 μm in the blood vessel running direction and a right angle to the blood vessel. 50 in direction
It is preferable that the thickness be about 0 to 1200 μm. Also,
The measurement light is a circular spot having a thickness of about 50 to 120 μm of the blood vessel to be measured, or an elliptical shape in which the running direction of the blood vessel is the longitudinal direction.

The scattered and reflected light from the fundus oculi Ea is collected again by the objective lens 2, reflected by the band-pass mirror 9, passed through the image rotator 14, and reflected by the lower reflecting surface 15a of the galvanometric mirror 15. The measurement light and the tracking light pass through the focus lens 16 and are separated by the dichroic mirror 26.

The tracking light is a dichroic mirror 2
6 is formed on the one-dimensional image pickup device 28 as a blood vessel image Ev ′ enlarged by the magnifying lens 27 from the fundus oculi image Ea ′ by the fundus oculi observation optical system. It is almost the same size as the range. This blood vessel image signal is input to the tracking control circuit 30 and is converted into a position signal of the blood vessel Ev. The tracking control circuit 30 controls the rotation angle of the galvanometric mirror 15 using this signal, and performs tracking of the blood vessel Ev.

A part of the scattered reflected light on the fundus oculi Ea due to the measurement light and the tracking light passes through the band-pass mirror 9 and is guided to the fundus observation optical system behind the perforated mirror 8.
The tracking light forms an image on the scale plate 12 as a bar-like indicator, and the measurement light forms an image as a spot image at the center of the indicator. These images are the eyepiece 1
3 and is observed by the examiner together with the fundus image Ea ′ and the optotype image. At this time, the spot image of the measurement beam is superimposed on the center of the indicator, and the indicator is
By rotating the galvanometric mirror 15 by 3, it is possible to move one-dimensionally on the fundus oculi Ea.

At the time of measurement, the examiner first focuses the fundus image Ea '. When the focus knob of the operation means 33 is adjusted, the transmission type liquid crystal plate 6, the focus lenses 10, 16 and the focus unit 18 are moved along the optical path in conjunction with the drive means (not shown). When the fundus image Ea 'is in focus, the transmissive liquid crystal plate 6, the scale plate 12, and the one-dimensional imaging device 28 are simultaneously conjugated to the fundus Ea.

In an actual examination, the examiner obtains a fundus image E
After focusing on a ', the line of sight of the eye E is guided to change the observation area, and the operation means 33 is operated to move the blood vessel Ev to be measured to an appropriate position. Then, the system control unit 31 controls the transmissive liquid crystal plate 6 to move the optotype image, rotate the image rotator 14, and move the photomultipliers 29 a and 29 b in the traveling direction of the blood vessel Ev to be measured. Operate so that the lines connecting the centers are parallel. At this time, by rotating the galvanometric mirror 15, the direction of the pixel array of the one-dimensional image sensor 28 and the direction of the moving measurement light are adjusted in a direction perpendicular to the blood vessel Ev at right angles thereto.

FIG. 2 shows a flow chart of the measurement operation. The examiner first starts the provisional measurement by depressing the measurement switch of the operation means 33 by one step. At this time, after confirming the tracking state and the quality of the obtained signal, the second measurement switch is pressed to start the main measurement. During this time, the measurement light is retained on the blood vessel Ev by the function of the blood vessel tracking system, but the scattered and reflected light is reflected by the dichroic mirror 26 and received by the photomultipliers 29a and 29b. The outputs of the photomultipliers 29a and 29b are output to the system control unit 31, respectively, stored in the storage unit 31b, and then converted into blood flow velocities by the signal processing unit 31a through processing such as frequency analysis.

FIG. 3 shows the state of the fundus oculi Ea at that time.
The measurement light M and the tracking light T are applied to the blood vessel Ev to be measured on the fundus oculi Ea. The signals received by the two photomultipliers 29a and 29b are intermittently output for 10 ms, for example, as shown in the timing chart of FIG.
/ D conversion, fetched into the storage unit 31b of the system control unit 31, and the signal processing unit 31a first performs frequency analysis (FFT processing) on each output signal.
The difference from the theoretically obtained FFT signal is quantified. The degree of pass / fail of the digitized signal is converted into a visually recognizable shape such as a bar graph, and displayed on the display monitor 32 together with the FFT result waveform. As a result, even an inexperienced examiner can instantaneously grasp the difference from the theoretical FFT signal, which is difficult without sufficient experience, by looking at the shape of the FFT.

The analysis method shown here is usually actually incorporated into the apparatus as software. This software is supplied on an external medium such as a floppy disk or CDROM, and is installed in the main body before use. However, for example, when performing only analysis with another device such as a general personal computer, it is also possible to install this software on another device, in which case it is necessary to have an optical system for measurement and the like. There is no.

In the provisional measurement, the above operation is repeatedly performed, and the examiner can display the FF displayed on the display monitor 32 in real time.
By looking at the T-waveform and the bar graph, the conditions and parts where correct measurement can be performed in this measurement are set. For example, when there is a deviation of the measurement light caused by astigmatism of the eye E, the examiner looks at the display on the display monitor 32 and the operation means 33 provided on the operation means 33 so that the measurement light M irradiates the blood vessel. When the dial is turned, the system control unit 31 gives a shift amount to the galvanomirror 11 via the tracking control circuit 30 and moves the irradiation position of the measurement light M relatively to the blood vessel that is tracking.

As the irradiation position of the measuring light M moves, the FFT waveform / bar display displayed on the display monitor 32 changes to include the center of the blood vessel at the maximum blood flow velocity and to include as little as possible outside the blood vessel. The best state is displayed when the measuring light M comes to the position. Here, the examiner presses the measurement switch again to start the main measurement. When the main measurement is started, the system control unit 31 stores the photomultipliers 29a and 29 for a predetermined time such as 2 seconds in the storage unit 31b.
Store the continuous output signal from b. The stored output signal is FFT-transformed by the signal processing means 31a after the measurement, and the maximum Doppler shift amounts Δfmax1 and Δfmax2 are obtained to calculate the maximum blood flow velocity.

FIG. 5 is a flow chart for quantifying the difference between the shape of the FFT in the above operation and the theoretically obtained FFT signal. When the size of the light receiving pupil is ignored, the shape of the theoretically obtained FFT diagram becomes a step shape as shown in FIG. 6, and the signal portion S indicating the Doppler shift and the white noise portion N on the high frequency side Can be divided. When this waveform is integrated from the high frequency side, a broken line indicated by L1 is obtained, and a straight line L2 connecting the start point and the end point thereof is obtained.
The value obtained by subtracting L1 from the result is a triangle indicated by ope.

The actually obtained signal does not become a flat spectrum due to the variation in blood cell density, but becomes a sum of spike-like spectra generated according to existing blood cells, contains various electric noises, and has a light receiving pupil shape. Due to the influence of the scattered light, the influence of multi-scattering, the misalignment of the measurement light and the bleeding of the beam due to tears of the eye E, the shape becomes considerably different from the theoretical shape. Therefore, even if the same processing is performed, a clear triangle is not obtained as described above.
This makes it difficult to determine the cutoff frequency fc.

However, since the noise portion corresponds to white noise, pe is almost a straight line, and if the signal is almost good, the maximum value p is almost in the vicinity of the cutoff frequency fc. Further, when the obtained spectrum is close to the theoretical one, op is also close to a straight line.

FIG. 7 shows the result of applying the actual FFT processing, and is a substantially triangular waveform obtained by connecting epo.
n is a straight line obtained by linearly approximating the high frequency portion, and Ls is a straight line obtained by linearly approximating the low frequency portion. When the respective approximate ranges are separated at, for example, a point p which is the maximum peak frequency of the obtained curve, a straight line Ln extends from the maximum frequency to the point p, and a straight line Ls extends from the point o to the point p. At this time, since the approximation range of the straight line Ls is greatly affected by the tracking state, eyelashes, and the like, the lowest frequency portion is, for example, from p × 0.1 to p. Also, regarding the approximate range of the straight line Ln, considering that the noise is white noise, it is possible to correctly evaluate the multi-scattering noise portion by setting the maximum frequency to about p × 0.8, for example.

Here, an index for judging the quality of the signal is calculated based on the residual between the approximate straight line Ls and the actual curve, so that F is theoretically calculated in the signal level region.
The difference between the rectangular portion of the FT waveform and the FFT waveform calculated from the output signal can be calculated and digitized. If the calculated value is displayed on the screen of the display monitor 32, the examiner can more objectively judge the quality of the measurement.

On the other hand, if the alignment is bad, or if the eye E has a large corneal astigmatism, the tracking center of the tracking light T and the measuring light M are displaced. As shown in FIG. 8A, when the measurement light M is irradiated onto the blood vessel Ev with a shift, the measurement light M is positioned at the center of the blood vessel Ev even if tracking is accurately performed on the blood vessel Ev. Since the light is not irradiated, the signal light from the maximum blood flow velocity disappears, and the reflected light irregularly scattered by the retina other than the blood vessel mixes with the signal light from the blood vessel Ev.

For this purpose, the photomultiplier 29
The FFT waveform calculated by the signal processing unit 31a in response to the output signals from the signals a and 29b is shown in FIG. 9 (a) when the measurement light M is applied to the center of the blood vessel Ev as shown in FIG. 9 (a). b)
8 has a sharply falling waveform as shown in FIG.
As shown in (b), the waveform from the Doppler shifted region to the noise level is smoothly connected. Accordingly, since the calculated low-frequency portion of the substantially triangular curve has a large residual with respect to the approximate straight line, it is quantified that the quality of the signal is poor. The examiner sees the visualized bar graph and FFT waveform of this numerical value, and can judge that a correct result cannot be obtained even if the main measurement is performed and the blood flow velocity is obtained.

In the actual measurement, for example, when the measurement is performed on a part where the blood flow is very slow or does not flow at all, the obtained signal cannot be correctly evaluated.
For example, when measuring a bloodless region, the spectrum obtained theoretically should be only white noise. However, there are cases where a signal having a slight level difference is obtained due to the frequency characteristics of the circuit or fluctuations in tracking. The above-mentioned index is used to determine the quality of the signal from the shape of the spectrum. In this case, the signal may show a very good signal even though the signal portion S does not have sufficient strength. In order to avoid this, S
The N ratio is calculated and used as one index for evaluating the reliability of the blood flow velocity information.

FIG. 10 is a flowchart for calculating the SN ratio. Theoretically, the white noise portion N which is the high frequency portion of the integral straight line L1 of the spectrum shown in FIG. 6 becomes a straight line L1n, and the straight line L1n is extended. Y-axis intercept Yn
Indicates the sum of the noise portions of the obtained spectrum. Further, since the Y-axis intercept Yt of the straight line L1 is the sum of the spectra, S = Yt−Yn may be taken as the sum of the signal components. Therefore, the signal is: SN ratio = S / Yt = (Yt−
Yn) / Yt.

In practice, an integral curve is calculated as shown in FIG. 11, and an approximate straight line L1s obtained from, for example, p × 0.1 to p is approximated to an approximate straight line L1s, for example, from the maximum frequency to about p × 0.8. A straight line L1n is obtained, an approximate range is obtained by setting the Y-axis intercept of the straight line L1s to Yt and the Y-axis intercept of L1n to Yn, and the SN ratio is calculated based on the approximate ranges.

The analysis method shown here is usually actually incorporated into the apparatus as software. This software is supplied by an external medium such as a floppy disk or CDROM, and is installed in the main body before use. However, for example, if it is desired to perform analysis only on another device such as a general personal computer, it is possible to install this software on another device.
In this case, it is not necessary to have an optical system or the like for measurement.

In the tentative measurement according to the flowchart of FIG. 2, the S / N ratio is calculated after quantifying the quality of the signal, and the S / N ratio is calculated.
When the ratio is out of the range of the allowable value, the numerical value is replaced with the optimum value. By performing the above operation, it is possible to avoid erroneous recognition as a good signal when the S / N ratio is bad, that is, when the measurement is bad. In the main measurement shown in FIG. 2, if the SN ratio is poor at the start of the measurement, the main measurement is disabled, and useless measurement such as displaying an error is canceled. Further, the average of the SN ratio in the measurement time is taken, and when the value is out of the allowable range, the measurement is regarded as an error, or the error is determined that the correct measurement was not performed for a specific time having a bad numerical value. May be used.

The system control unit 31 compares a previously set permissible value with the calculated value, and outputs a measurement start input signal for shifting to the main measurement when the calculated value is less than the permissible value. By performing such control, the labor of the examiner can be saved. Further, the output signals from the two photomultipliers 29a and 29b are processed at the time of provisional measurement, but the two photomultipliers 29a and 29b are processed.
Since only the light receiving direction differs with respect to the measurement site, if the light receiving state of one photomultiplier 29a is known, the light receiving state of the other photomultiplier 29b can be almost predicted. Therefore, in order to reduce the load on the signal processing unit 31 and the processing time, one photomultiplier 29 is used.
A configuration may be adopted in which signal processing is performed only from a and displayed.

In the above embodiment, the method of using the SN ratio separately from the numerical value for judging the quality of the previous signal has been described. However, the SN ratio is added to this numerical value to determine the new signal. May be created, and the average value of the numerical values in the measurement time may be used as the reliability of the measurement.

[0050]

As described above, the fundus blood flow meter and the signal processing method according to the present invention reduce the influence of spectrum omission by performing integration once when calculating the S / N ratio of the Doppler signal. By calculating the peak frequency, the noise region and the signal region can be roughly relatively stably separated from each other, and the S / N ratio can be calculated and the signal quality can be determined by a simple operation before the cutoff frequency is determined. You can create an index to do. In addition, if the processing is performed by provisional measurement, the examiner can correctly judge whether the measurement in the main measurement is good or not by looking at the FFT waveform and the bar graph displayed in real time on the display monitor. Therefore, the burden on the subject can be reduced and the measurement time can be shortened.

Further, by separating a certain frequency region and a white noise region of a signal, there are various uses not only for calculating the SN ratio of the signal but also for speed analysis.
When the difference from the theoretically obtained FFT signal is used in the actual speed calculation, the level of the white noise obtained by the present method can be used for determining the theoretical shape of the FFT signal. As a result, it is possible to improve the consistency between the theoretical shape and the actually obtained signal, and it is possible to calculate the speed in accordance with the actual.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a fundus blood flow meter according to an embodiment.

FIG. 2 is a flowchart of an operation and signal processing.

FIG. 3 is an explanatory diagram of an observation fundus image.

FIG. 4 is a timing chart of a processing signal;

FIG. 5 is a flowchart of digitizing the quality of a signal.

FIG. 6 is a graph showing a theoretical shape of a received light signal.

FIG. 7 is a graph showing the actual shape of a received light signal.

FIG. 8 is a graph showing a signal change when the measurement light is displaced from the blood vessel.

FIG. 9 is a graph showing a signal change when the measurement light is irradiated on a blood vessel.

FIG. 10 is a flowchart of an SN ratio calculation.

FIG. 11 is a graph showing an actual shape of a light receiving signal.

[Decoding of sign]

 DESCRIPTION OF SYMBOLS 1 Observation light source 2 Objective lens 6 Imaging light source 8 Perforated mirror 9 Bandpass mirror 14 Image rotator 15 Galvanometric mirror 22 Measurement light source 25 Tracking light source 28 One-dimensional image sensor 29a, 29b Photomultiplier 30 Tracking control circuit 31 System control unit 31a Signal processing unit 31b Storage unit 32 Display monitor 33 Operation unit

Claims (7)

[Claims] 1. A measuring light irradiating means for irradiating a coherent measuring light to a blood vessel on a fundus of an eye to be inspected, and a signal light in which the measuring light is scattered by intravascular particles and a reference light scattered from a surrounding tissue. In a laser Doppler-type fundus blood flow meter having a light receiving means for receiving light, a frequency analyzing means for frequency-analyzing a light receiving signal of the light receiving means, and a calculating means for calculating a blood flow velocity based on an output of the frequency analyzing means. A first step of calculating an integral curve obtained by accumulating a spectrum distribution based on the frequency analysis result from a high frequency side, and using the integral curve to obtain a result of the frequency analysis in a high frequency region and approximating white noise. Signal processing means for receiving light signals having a second step of dividing into at least two regions of a noise region and a signal region present on a lower frequency side than the noise region. And a fundus blood flow meter. 2. The signal processing means includes: a third step of linearly approximating an integral curve in each of the two frequency regions; and a signal processing unit for generating the light-receiving signal based on the two approximate lines obtained in the third step. The fundus blood flow meter according to claim 1, further comprising: a SN ratio calculation unit for the light reception signal to which a fourth step of calculating the SN ratio is added. 3. The fundus blood according to claim 1, wherein the second step divides the region based on a frequency at which a distance between the integration curve and a straight line connecting a start point and an end point of the integration curve becomes maximum. Flow meter. 4. The fundus blood flow meter according to claim 1, further comprising control means for performing operation control using a result of said SN ratio calculation means. 5. The control device according to claim 2, wherein the control unit temporarily receives the light receiving signal prior to the measurement, and performs an operation of disabling the measurement when the output result of the SN ratio calculating unit with respect to the light receiving signal is out of an allowable range. 2. A fundus blood flow meter according to item 1. 6. A blood vessel on the fundus of an eye to be inspected is irradiated with coherent measurement light by a measurement light irradiation unit, and the measurement light is converted into signal light scattered by intravascular particles and reference light scattered from surrounding tissue. A signal is received by a light receiving means, and a light receiving signal from the light receiving means is frequency-analyzed by a frequency analyzing means, and a signal processing method of a light receiving signal of a laser Doppler type fundus blood flow meter for calculating a blood flow velocity based on the frequency analysis result. A first step of calculating an integral curve obtained by accumulating the spectrum distribution of the frequency analysis result from a high frequency side; and a noise area existing in a high frequency area and approximated to white noise using the integral curve. Signal processing by a second step of dividing the received light signal into at least two regions including a signal region existing on a lower frequency side than a noise region. Method. 7. A third step of linearly approximating each of said integral curves in said two frequency domains to obtain an approximate straight line, and said light receiving signal based on said two approximate straight lines obtained in said third step. And a fourth step of calculating the S / N ratio of the fundus blood flow meter.