JPH039723A - Ophthalmic measurement method and apparatus - Google Patents

Abstract

PURPOSE:To enable the following of a blood vessel portion automatically with accurate identification of a blood vessel part at the eyeground by a method wherein a speckle signal is converted to a digital signal, compared with a specified value to identify a blood vessel part or a part other than the blood vessel and blood vessel edges are discriminated to identify a noise or not to clarify the position of a blood vessel edge. CONSTITUTION:Laser light from a laser light source 1 reaches the eyeground 16a via an objective lens 15 to irradiate a blood vessel to be measured or followed. Speckle light is received with a CCD 43 with the start of a measurement and an output signal from the CCD 43 is sent to a signal processing section 44 and the signal processing section 44 obtains a blood vessel discrimination signal to be outputted as digital signal with an analog/digital conversion. An arithmetic section 45 detects a position of the blood vessel by the blood vessel discrimination signal digitized. Thus, the speckle signal is converted to a digital signal to be compared with a specified value, thereby identifying a blood vessel portion or a part other then the blood vessel. When the blood vessel portion is identified, a blood vessel edges are discriminated by identifying a noise or not and a speckle signal for identifying the position of the blood vessel is turned to a digital signal to identify the position of the blood vessel, thereby enabling the identifying of the blood vessel portion at the eyeground accurately.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an ophthalmological measurement method and apparatus, and more specifically, to irradiating the fundus of the eye with a laser beam of a predetermined diameter and measuring the amount of light formed by scattered reflected light from the fundus of the eye. The present invention relates to an ophthalmological measurement method and apparatus that performs ophthalmological measurements by detecting the movement of a laser speckle pattern as a change in light intensity at an observation point and analyzing the resulting speckle signal.

[Prior Art] Various methods are known for performing ophthalmological measurements by irradiating the fundus with a laser beam, detecting scattered reflected light from the fundus, and analyzing or evaluating it. rInvestigat is a method to measure blood flow.
ive Ophthalmology”, Vol. 11
．． N.

, 11. P936. November 1972, rscie
nceJ Vol, 186, Nov, 29.1
974: P830 and other Japanese patent publications 1986-75668
゜75669, 75670, or JP-A-52-14
2885 (UK 13132/76, USP 4,1
66.6951. JP-A-56-125033 + UK [
GB] 79/377991. Japanese Patent Publication No. 58-11873
0 (USP4,402,601) or USP4.1
The laser Doppler method shown in No. 42.796 is known. However, the Doppler method is currently difficult to put into practical use due to the complexity and precision of the optical system, the complexity of handling, and the instability and uncertainty of the measurement results.

On the other hand, it is known that when a scattering object is irradiated with laser light, the scattered light forms a random speckle pattern due to the interference phenomenon of coherent light. A laser speckle method is known that utilizes this method to evaluate the blood flow state of the fundus tissue. This method, for example,
Japanese Patent Publication No. 62-275431 (USP 4,473.107
．． EPC234869), Japanese Patent Publication No. 63-238843
(EPC2842481, JP-A-63-242220
fEPc 285314), and when measuring the fundus, time-varying specs are formed on an optical Fourier transform surface for the fundus, a Fraunhofer diffraction surface, or an imaging plane (or magnified imaging plane) conjugate with the fundus. By extracting the intensity change of the speckle pattern using a detection aperture and evaluating the resulting speckle signal, blood flow conditions are measured and ophthalmological measurements are performed.

[Problems to be solved by the invention] However, due to eye movement, movement of the subject, vibration, etc., the speckle pattern on the detection surface may move unnecessarily, the laser spot may shift, or the detection aperture position may shift. There are many cases in which the measurement point easily shifts during measurement and results in failure, which is a major clinical problem. On the other hand, in the Doppler method, as shown in JP-A-56-125033, the fundus image is mechanically scanned on a detection surface, and blood vessels are recognized from the difference in light reflectance between the vessel wall and other parts. The positional deviation is corrected. However, this method requires a mechanism for mechanically scanning the fundus image, making the device complex and large-scale, making it impractical.

In addition, the magazine rApplied Optics J Vol.
27. No, 6. March 15.1988
P 1113 or JP-A-63-288133 (U
SP-014994) similarly scans images and performs blood vessel recognition, demonstrating the possibility of automatic tracking, but sequentially illuminates and detects light with multiple different wavelengths and utilizes the wavelength dependence of reflected light. Therefore, the device becomes extremely complicated, which has the drawbacks of lacking practicality and making the device expensive. Another problem is that it is difficult to detect eye movements with sufficient accuracy to correct blood vessel movement based on eye movement detection using corneal reflexes.

Conventional methods for detecting eyeball movements include shining illumination light onto the corneal surface and detecting and following the eyeball movement based on the movement of the corneal reflected light. On the other hand, a method is known in which movement is detected and tracked by taking the difference between two images.

However, since such a method detects the movement of the surface of the eye, only low accuracy can be obtained when attempting to follow the movement of the fundus of the eye. In addition, the fundus image carried by the TV left camera lacks light intensity and cannot obtain a sufficient signal-to-noise ratio, so the equipment that detects movement by taking the difference between the two images is extremely large and complicated. The disadvantage is that it becomes

Therefore, the present invention has been made to solve the drawbacks of such traffic, and uses the laser speckle phenomenon to accurately identify the canal part of the fundus surface with a simple configuration, and enables automatic tracking of the blood vessel part. An object of the present invention is to provide an ophthalmological measurement method and device that can

[Means for Solving the Problems] In order to solve such problems, the present invention irradiates the fundus of the eye with a laser beam of a predetermined diameter, and uses a laser beam formed by diffusely reflected light from blood cells in living tissues. The movement of the speckle pattern is detected as a change in speckle light intensity at an observation point, and the speckle signal is converted into a digital signal and compared with a predetermined value to distinguish whether it is a vascular area or an extravascular area. If it is determined, we adopted a configuration that discriminates whether it is noise or not, determines the blood vessel edge, and identifies the position of the blood vessel.

[Function 1] In such a configuration, the projection optical system irradiates the fundus of the eye with a laser beam of a predetermined diameter, and the reception optical system detects the movement of the laser speckle pattern formed by the diffusely reflected light from the blood cells of the living tissue. A photoelectric conversion element is used to detect changes in the light intensity of speckles. The speckle signal reflects the blood cell migration speed in living tissue. By optimally setting the speckle diameter on the photoelectric conversion element and the scanning speed of the photoelectric conversion element, when the blood cell movement speed in biological tissue is fast, the speckle light intensity changes rapidly, so it is possible to Averaging reduces the output. Conversely, if it is slow, the output decreases less.

The strength and weakness of these differences are determined and the blood vessels are recognized.

[Example] In particular, the present invention irradiates the fundus with a laser beam of a predetermined diameter, detects the movement of a laser speckle pattern formed on the observation surface by scattered reflected light from the fundus tissue as a change in speckle intensity, and obtains a result. The present invention is applied to an ophthalmological measuring device that measures the blood flow state of the fundus tissue based on the analysis result of the speckle signal obtained.

Therefore, in the embodiments shown below, a case will be described using as an example a case of a type attached to an ophthalmological measuring device that measures the blood flow state of the fundus tissue based on the optical system of a fundus camera.
The present invention is not limited to such an ophthalmological apparatus, but can also be applied to other ophthalmological apparatuses.

In FIG. 1, for example, the laser beam from a red Ice-Ne (wavelength 632.8 nm) laser light source 1 is as follows.

The light passes through a light amount adjustment filter 3 via a condenser lens 2. Further, the collimating lens 4 converts the beam into a parallel beam, and an aperture 5.6 is installed in the parallel beam, thereby making it possible to select the size and shape of the irradiation area of the laser beam on the fundus 16a of the eye 16 to be examined. There is.

Furthermore, the laser beam passes through a relay lens 7, a movable mirror 8, and a condensing lens 9, and then passes through a mirror installed in a part of the transparent annular aperture 11a of the ring slit 11 in the fundus camera illumination optical system, as shown in FIG. 10, the light beam for fundus observation and photography is guided to the same optical path that enters the fundus (in Fig. 2, the shaded area is an opaque area). The light reaches the fundus 16a through the lens 15, and is irradiated onto the blood vessels to be measured and tracked.

In the above laser irradiation optical system, the movable mirror 8 is used to move the beam or robot position on the fundus 16a, and before starting measurement, for example, the track pole 17
The control is performed via the output section 46 by operating the .

The measurement and tracking area of the fundus is illuminated by an illumination optical system used as a fundus camera to facilitate observation. This illumination optical system includes an observation light source 18 arranged on the same optical axis as the machine shadow light source 20, a condenser lens 19, 21, a filter 22. It is composed of a mirror 23.

In the illumination optical system described above, the filter 22 disposed between the condenser lens 2I and the mirror 23 is configured as a wavelength separation filter having spectral characteristics as shown in FIG. The red component is cut.

Appropriate spectral characteristics are used depending on the wavelength of the laser light source used.

Both the speckle light generated when the laser light is scattered on the fundus and the reflected light for other observation machine images are received by the objective lens 15 again and pass through the hole of the perforated mirror 14 to the focusing lens 24 and the focusing lens 24. Once imaged in space via the image lens 25 or 26, it is reflected again by the movable mirror 30 via two relay lenses, and then imaged near the perforated mirror 32 via the relay lens 31. The light reflected by the perforated mirror 32 is separated by a wavelength separation mirror 34 via a relay lens 33. Speckle light is transmitted through wavelength separation mirror 3
4 and is reflected by the cylindrical imaging lenses 42a, 42.
b, an image is formed on the CCD 43, which is a scanning sensor. Note that the wavelength separation mirror 34 is approximately 45 mm away from the optical axis.
°, and like the wavelength separation filter 22,
It has the spectral characteristics shown in Figure 3, and has red IT e -
Reflects most of the speckle light from the Ne laser light.

The light that has passed through the wavelength separation mirror 34 is imaged on the surface of the reticle 36 via the imaging lens 35, and is then focused on the eyepiece lens 37.
observed by the examiner via Here, the eyepiece lens 37 is configured so that the examiner can correct the diopter using the reticle 36 as a reference.

Further, as shown in FIG. 4, the reticle 36 has a pattern in which one of the reticles is marked at right angles so that one can be distinguished, and the part that intersects at right angles is the hole 3 of the perforated mirror 32.
It coincides with the center of 2a. It is also possible to rotate around the parts that intersect at right angles. Furthermore, by rotating the reticle 36 to match the inclination of the image of the blood vessel 16b as shown in FIG. 4, the cylindrical lenses 42a, 42b, and the CCD 43 are rotated in synchronization in that direction, and the CCD 43 and the blood vessel image are automatically aligned perpendicularly. become the direction.

The fundus image formed on the surface of the CCD 43 at this time is
As shown in the figure. 1a indicates a spot of a laser beam to be irradiated.

Note that the fundus image formed on the CCD 43 is based on the speckle diameter, the boiling movement of the speckle pattern, and the CCD 43.
Due to the sensitivity relationship, as shown in FIG. 5, the cylindrical imaging lenses 42a and 42b are set so that the magnification in the same direction as the blood vessel L6b is smaller than the magnification in the direction perpendicular to the blood vessel direction. Further, as shown in FIG. 5, a CCD 43 is installed on the surface of the CCD 43 at a position that does not intersect with the image of the hole 32a of the perforated mirror 32, and the CCD 43 is installed in a direction perpendicular to the direction of the blood vessel 16b. .

During photographic manipulation, the flip-up mirror 27 is flipped up to 27 degrees in the direction of the arrow with 27a as a fulcrum, and the shadow light beam from the observation device, including the laser speckle light from the fundus, reflected by the flip-up mirror 27 is transferred to the photographic film 28. An image is formed above and photographed.

Hole 32a of perforated mirror 32 in the light receiving optical system that receives speckle light from the fundus of the eye and reflected light for observation and photographing.
The light passing through forms an image of the fundus 16a on the pinhole 38. The light that passed through the pinhole 38 is
After passing through the interference filter 39, the speckle signal is received by a photomultiplier (photomultiplier tube) 40 at the start of measurement, and the speckle signal detected by the photomultiplier 40 is sent to an analysis section 41, where the state of blood flow is analyzed. Note that the interference filter 39 has a spectral characteristic that allows only the light with a wavelength of 632.8 nm of the red + (e - Ne laser) to pass through.

In addition, in the light-receiving optical system that receives reflected light from the fundus for speckle light observation and projection, a movable mirror 30 images the blood vessels on the fundus 16a of the subject 16 onto a pinhole 38 via a perforated mirror 32. This is for correcting the position so as to make the measurement, and the control is performed via the output section 46 by operating the trackball 17, for example, before the start of measurement.

Here, the trackball 17 is attached to the movable mirror 8 before the start of measurement.
However, the movable mirror 8 and the movable mirror 30 can each be operated at an operating rate of 4 independently using, for example, a changeover switch or the like.

In the light-receiving optical system, the imaging lens 25 is a wide-angle imaging lens, while the imaging lens 26 is a narrow-angle imaging lens. By observing at high magnification using this high magnification lens, it becomes possible to align the blood vessel layer within the laser spot 16b on the fundus 16a onto the pinhole 38 via the perforated mirror 32.

In addition, in the light receiving optical system, the hole diameter of the perforated mirror 32 is the same as that of the test object III! The blade is small enough to allow the light flux from above the blood vessel to be measured on the fundus 16a of the eye 16 to pass through, and the perforated mirror 32 is installed at a position substantially co-located with the fundus 16a of the eye 16 to be examined. The observer can reliably align the image of the blood vessel to be measured by overlapping the hole of the perforated mirror 32. FIG. 4 shows the image observed at that time. Since the speckle light slightly passes through the wavelength separation mirror 34, the observer can confirm the position of the laser spot la.

When the measurement starts, the speckle light is received by CCD43 and C
The output signal from the CD 43 is sent to the signal processing section 44 (
(See FIG. 6) The signal processing unit 44 obtains the blood vessel discrimination signal, A/D converts it, and outputs it as a digital signal. Arithmetic unit 4
In step 5, the position of the blood vessel is detected from the digitized blood vessel discrimination signal, and if the blood vessel moves due to eye movement or the like, the amount of movement is detected and a correction amount is calculated to return it to the initial position.

The calculation result is outputted to the output section 46, and the output section controls the movable mirror 30 and the movable mirror 8 based on the calculation result so that the fundus image is always at the same position on the pinhole 38, and the fundus 16a is Perform feedback correction so that the laser spot is at the same position.

Note that during the measurement, the observation/photographing light beam other than the red component that has passed through the wavelength separation mirror 34 and the speckle light beam that has passed through the wavelength separation mirror 34 form a fundus image on the reticle 36 in the same way as the measurement section, and can be observed by the observer. It is possible to monitor whether the target position has shifted, and an extremely favorable effect can be obtained.

Next, the electrical system after the signal processing section 44 will be explained in detail.

FIG. 6 is a block diagram of the signal processing section. Signal processing section 44
are a drive circuit 56, a bypass filter 51, and an amplifier 52.
, an absolute value circuit 53, an amplifier with limiter 54, and an A/D converter 55. A drive pulse generated by a drive circuit 56 is supplied to a linear CCD 43 having 1024 pixels. C.C.
In D43, the light intensity of the speckle light is converted to obtain a speckle signal. The speckle signal obtained by CCD43 is
It passes through a bypass filter 51 and only high frequency components are extracted. The speckle signal containing only high frequency components is amplified by an amplifier 52 and passed through an absolute value circuit 53 to obtain the absolute value of the signal.

The output signal of the absolute value circuit 53 is as shown in FIG. Note that in the figure, the signal waveform is not a waveform from the entire CCD, but only a waveform near the center. This is shown in Figure 14.
The same applies to FIG. The absolute value of the signal is inputted to the amplifier with limiter 54, and the necessary portion is selectively processed.
For example, a blood vessel discrimination signal is extracted by amplifying a portion of the signal in the dotted line range A shown in FIG. 7, and limiting the portion that is always necessary with a limiter. The signal from the limiter amplifier 54 has a waveform as shown in FIG. The obtained blood vessel discrimination signal is A/D converted by an A/D conversion circuit 55 and outputted to the calculation section 45 as digital signal data.

The arithmetic unit 45 temporarily stores the digital signal data from the signal processing unit 44 in a memory.

If the COD has n pixels and n pieces of data are stored in the memory, then if each address is given to the data read from the memory, the address of the first read data is O, and the address of the nth data is n. -1. The read data has large values for blood vessel portions and small values for non-blood vessel portions.

Here, for ease of explanation, a large value of data indicating a blood vessel portion is assumed to be 1, and a small value of data indicating a non-blood vessel portion is assumed to be O. The data read from the memory is 1 for the blood vessel portion, but the data for non-blood vessel portions may also be 1 or 0 due to the influence of speckles.

A method for reducing the influence of speckles will be explained according to the blood vessel discrimination flowchart in FIG. 9. Block Bl is
This is the part that searches for edges that become blood vessels from parts that are not blood vessels. That is, the data is read in step Sl, and the data is read in step S1.
Step 2 determines whether it is extravascular or vascular, ie, 0 or l. If it is 0, it is extravascular, and if it is l, it is blood vessel. If it is 0, that is, outside the blood vessel, the address to be checked is counted up in step S3. It is determined in step S4 whether all pixel data has been read out by counting up. If all pixel data have been read out, blood vessel discrimination is ended, and if all pixel data have not been read out, the process returns to Sl.

If 1 is read in step S2, there is a possibility that it is a blood vessel edge, so in step S5 the memory address l is read.
The pixel number is stored in , and the address is counted up in step S6. In step S7, it is determined whether reading has been completed for all pixels. If reading has been completed, the process ends; if reading has not been completed, the process proceeds to block B2.

Block B2 is a part for searching for an edge from the blood vessel to outside the blood vessel. In step S5 of block B1 described above, the pixel signal is 1, and after storing the pixel number at address l in the memory, the data of the next pixel is read in step S8, and in step S9 it is determined whether the pixel is a blood vessel or an extravascular one. Determine. If 1. That is, if it is a blood vessel, the address is counted up in step S10 in order to search for an edge outside the blood vessel. At this time, in step Sll, if the data has been read for all addresses, the process goes to step S12; if the data has not been read, the process returns to step S8.

Step S12 is a process when the end of the CCD is a blood vessel. In this case, the edge of the blood vessel that is halfway is set as the final address of the CCD, and its pixel number is stored in address 2. After that, the process advances to step S16.

On the other hand, if it is determined in step S9 that it is O1, that is, outside the blood vessel, it is necessary to determine whether it is really outside the blood vessel or not, and whether it is affected by blood column reflection or the like.

In step S13, it is determined whether the pixel has just become 0 or if several pixels have already become 0 in a row. If it has just become 0, there is a possibility that it is an edge, so in step S14 it is set to address 2. The pixel number is stored and the process advances to step S15.

In step SL5, the influence of blood column reflection etc. is set to a maximum of m-1 pixels, and when m pixels become 0 consecutively, it is determined that the area is outside the blood vessel, and the process proceeds to step S16. If there is no pixel data, it is not determined that the pixel is outside the blood vessel, and the process moves to step S10 to read the next pixel data.

In step S16, it is determined whether the parts corresponding to the pixel numbers stored in address l and address 2 are both edges of the blood vessel, that is, whether they have sufficient width as a blood vessel. If so, it is determined that it is a blood vessel in step S17.

The pixel numbers are stored in edges 1 and 2 of the memory as blood vessel edges, and if there is no P pixel, it is determined that it is not a blood vessel, and addresses 1 and 2 are cleared, and the process returns to step S3 to search for the next blood vessel edge. , loop.

Figure 10 shows how blood vessels are identified using the above method. Figure 10(a) shows the waveform written in the memory.
The horizontal axis indicates the address number, and the vertical axis indicates whether the signal of the pixel corresponding to the address number is 1 (vascular area) or 0 (extravascular area). The parts K1 and K2 are not determined to be blood vessel parts in step 516 because the number of pixels is not more than P pixels, and the part 2 is not determined to be a blood vessel part even if the partially stored signal is O, but m pixels are continuous. Since this is not the case, it is determined to be noise, and since the total number of pixels that are 1 is greater than or equal to P, it is determined to be a blood vessel portion. This state is illustrated in FIG. 10(b), which is the waveform of a blood image recognized by blood vessel discrimination.

Note that the parameters m and P in FIG. 9 are determined by the optical system magnification up to the CCD, etc.

Also, during ophthalmological measurements, the blood vessels may shift from the CCD due to movement of the examinee or vibration of the equipment.
The blood vessel part must be automatically tracked. Blood vessel tracking uses the initial waveform just before tracking starts as a reference, performs cross-correlation with the newly captured waveform, and corrects the amount of deviation to the position with the highest correlation value. However, calculating the correlation each time requires a long calculation time. Therefore, a method for shortening the calculation time is shown in FIG.

Let n be the amount of shift required to match the blood vessel waveform newly read in step T1 and the initial waveform for a certain edge, and in step T2 shift the newly read waveform by n pixels overall for a certain edge. For the matched waveforms, the area of the shared portion is determined in step T3, and in step T4, it is checked whether the shared area has been determined for all combinations of edges, and if the shared area has not been determined for all combinations, the process loops to step T2.
Step T5 when all combinations are completed
Proceed to.

In step T5, since the waveform when giving the maximum area among the shared areas calculated up to that point matches the initial waveform well, the shift amount n at that time is set as the amount of movement of the blood vessel image, and the amount of shift is Output and follow the correction. In step T6, it is determined whether further tracking is necessary,
If necessary, the process loops to step Tl; if not, the process ends.

The operations performed in step T2 and step T3 are illustrated in FIGS. 12(a)-(f).

Assuming that the initial waveform is shown in Fig. 12(a) and the newly captured waveform is shown in Fig. 12(b), the edges are respectively (A
, B), (C, D), and (a, b), (c, d). In step T2, edges A and a, c, edges C and a, c, edges B and d, and edges D and d are made to match, respectively. Waveforms when A and a match are shown in FIGS. 12(c) and (d), and waveforms when C and a match are shown in FIGS. 12(e) and (f). 12th
In the case of FIGS. (c) and (d), the waveform almost matches the initial waveform, and the area of the shared portion is the shaded area.

In the cases of FIGS. 12(e) and 12(f), the waveform deviates from the initial waveform, and the area of the shared portion is the shaded area, which is smaller than that in FIG. 12(d). In this example, other combinations will also be shown in Figure 12(d) or 12(f), so
The amount of shift for making a in FIG. 12(b) match A is determined as the amount of movement in step T5, and a correction amount is output.

Since the amount of correction is obtained in this way, the output section 46 drives the pulse motor based on the amount of correction from the calculation section 45 to control the movable mirror 8 and the movable mirror 30 connected to the pulse motor. . By driving the movable mirror 8, the irradiation position of the laser beam is adjusted, and the irradiation position of the laser beam is moved to the center of the blood vessel to be tracked in the fundus of the eye, thereby performing automatic tracking. Further, the observation point of the speckle pattern is adjusted by driving the movable mirror 30, and the observation point of the speckle pattern is moved to the center of the blood vessel to be followed by the fundus, and automatic tracking is performed.

When trying to obtain information from blood vessels on the fundus of the eye, there may be a difference in measurement results depending on whether the measurement point is at the center or at the edge of the blood vessel. In order to eliminate variations caused by this, center position correction is performed.

A center position correction flowchart is shown in FIG. Step R1 is a detection part that detects the blood vessel position near the center of the CCD, and the blood vessel position is constantly detected until the examination is started in step R2. In step R3, immediately after the start of the examination, the blood vessel center position of the blood vessel closest to the COD is determined from the latest blood vessel position information, the amount of deviation from the center position of the CCD 43 is calculated, and correction is made to eliminate the deviation between the blood vessel center and the CCD center.

Further, in step R4, the center of the blood vessel closest to the CCD center at the initial position of the blood vessel is set to coincide with the CCD center. By setting the initial position as in step R4,
Also, the tracking in step R5 is always corrected so that the center of the blood vessel closest to the CCD coincides with the center position of C0D 43 until the examination is completed in step R6. With this method, even if the examiner's alignment deviates from the center of the blood vessel, the test can always be performed with the center of the blood vessel immediately after the start of the test.

C by rotating the reticle 36 about the optical axis.
As previously explained, the CD 43 also rotates about the optical axis and is structured so that the CCD can be set perpendicular to the blood vessel, but a potentiometer 47 is also attached to detect the rotation angle of the CCD. There is. Angle detection section 48
Then, the output of the potentiometer is A/D converted to 8 bits to obtain angle data. The obtained angle data is sent to the calculation section 45, and the rotation angle of the CCD is determined from the angle data. The calculation unit 45 calculates and outputs correction amounts in the X and Y directions for the movement of the blood vessel position.

Speckle size imaged on CCD43 and CCD43
If the relationship between the sizes of one pixel in the two pixels deviates greatly, it is not possible to obtain a good speckle signal. For example, Figure 14 (
If the size of the speckle 93゛ is larger than one pixel G of the CCD 43 as shown in a), the amount of light incident on one pixel of the CCD 43 decreases, making it impossible to obtain a speckle signal of sufficient intensity. A speckle signal 93a as shown in FIG. 14(b) is obtained. Conversely, if the size of the speckle 93° is smaller than one pixel G of the CCD 43 as shown in FIG. 14(e), the amount of light incident on each pixel of the CC043 is averaged, and As shown in FIG. 9(f), the result is a speckle signal 93a without contrast.

When the relationship between the speckle size and the size of one pixel of the CCD 43 is approximately equal as shown in FIG. 14(C), a good speckle signal 93a can be obtained as shown in FIG. 14(d).

Next, a method for determining objects having different moving speeds based on speckle signals will be explained.

The explanation of the boiling motion of speckles is complicated, so for simplicity, the explanation will be replaced with the translational motion of speckles. The left half of FIG. 15(a) shows a case where, for example, the moving speed of blood cells is slow in the surrounding tissue of a blood vessel, and therefore the moving speed of the speckle 93 is slow, and the right half shows a case where the moving speed of blood cells is slow in a blood vessel, etc. 15(b) is a diagram of the output signal of the sensor corresponding to each case. When the moving speed of the speckle pattern is faster than the scanning speed of the scanning sensor, the bright and dark parts of the speckle pass through the light receiving part of the CCD 43 in large numbers, so the output of the sensor is based on the bright part. ,
An averaged output of dark areas can be obtained, and there is little difference in signal output depending on the light receiving position.

On the other hand, if the moving speed of the speckle pattern is slower than the scanning speed of the scanning type sensor, the number of bright and dark parts of the speckles 93゛ passing through the light receiving part is not small, and the scanning type sensor Depending on the position of the light-receiving section of the CCD 43, which is a sensor, the output becomes stronger where many bright parts of speckles have passed, and the output becomes weaker where many dark parts of speckles have passed. Therefore, objects whose speckle patterns move at different speeds can be discriminated by optimally setting the scanning speed of the scanning sensor and determining the strength ratio of the output signal of the scanning sensor. I can do it.

As shown in FIG. 5, the blood vessel direction and blood vessel 16b in the blood vessel image of the fundus image formed by the laser speckle light formed on the surface of the CCD 43.
By changing the ratio in the direction perpendicular to the blood vessel and performing compression in the direction of the blood vessel, the amount of light incident on the CCD 43 can be increased without deteriorating the resolution in the direction perpendicular to the blood vessel. Also, the signal strength ratio between the bright and dark parts of the speckle will be slightly worse, but the extremely dark parts will be reduced.
Misjudgment is reduced during blood vessel discrimination.

[Effects of the Invention] As explained above, in the present invention, a speckle signal is converted into a digital signal and compared with a predetermined value to distinguish between a vascular portion and an extravascular portion, and when a vascular portion is determined, Converts the speckle signal into a digital signal by distinguishing whether it is noise or not, determining blood vessel edges, and identifying the position of the blood vessel.
Since the blood vessel position is identified, it becomes possible to reliably identify the blood vessel portion of the fundus. Furthermore, in the present invention, since the entire CCD field of view is viewed, the greater the number of blood vessels, the more stable tracking becomes possible. Therefore, even if the blood vessel moves, the amount of movement can be easily determined, and when the blood vessel moves, the laser beam irradiation position or observation point position can be controlled according to the amount of movement, and the blood vessel can be moved automatically. It becomes possible to follow.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of the device of the present invention, and FIG.
The figure is a block diagram showing the configuration of the ring slit, Figure 3 is an explanatory diagram showing the spectral characteristics of the filter, Figures 4 and 5 are
6 is a block diagram showing the configuration of the signal processing device; FIG. 7 is a waveform diagram showing the waveform of the output signal from the absolute value circuit; Fig. 8 is an output signal waveform diagram of the amplifier with limiter, Fig. 9 is a flowchart showing the flow of control when searching for blood vessels, and Figs. 10 (a) and (b) explain the determination of blood vessel parts. Figure 11 is a flowchart showing the flow of control during blood vessel tracking, Figures 12 (a) to (f') are signal waveform diagrams explaining the blood vessel tracking operation, and Figure 13 is a signal waveform diagram. , a flowchart showing the flow of control for center position correction, FIG. 14 (
a) to (f) are explanatory diagrams showing the relationship between speckle size and CCD pixel size and output signals; FIG. 15(a);
(b) is an explanatory diagram showing the moving speed of the speckle pattern and the waveform of the output signal of the CCD. 1... Laser light source 8... Movable mirror 16a--
Fundus 18-... Observation light source 20... Photography light source
30... Movable mirror 40... Photomaru 41-.
・Signal analysis section 44--Signal processing section 45--Calculation section Fig. 4 Explanatory diagram of fundus image Fig. 5 Output) Internal diagram Fig. Hook diagram of signal processing section Fig. 6 Fig. 10. Automatic direct flow chart. Fig. 12. Center position correction flowchart. Fig. 13. Fig. 1. Fig. 14 is an explanatory diagram showing the state of speckle detection.

Claims (1)

[Claims] 1) The fundus of the eye is irradiated with a laser beam of a predetermined diameter, and the movement of the laser speckle pattern formed by the scattered reflected light from the fundus is detected as a change in light intensity at an observation point. In an ophthalmological measurement method that performs ophthalmological measurements by analyzing the obtained speckle signal, the speckle signal is converted into a digital signal and compared with a predetermined value to distinguish whether it is a vascular portion or an extravascular portion. An ophthalmological measurement method characterized in that, when the detected value is determined, the blood vessel edge is determined by determining whether it is noise or not, and the position of the blood vessel is identified. 2) The blood vessel position data is shifted by a predetermined amount, the amount of shift that most closely matches the initial blood vessel position data is set as the amount of movement of the blood vessel image, and the measured blood vessel is automatically followed according to the amount of movement. Ophthalmological measurement method described in Section. 3) The fundus of the eye is irradiated with a laser beam of a predetermined diameter, the movement of the laser speckle pattern formed by the scattered reflected light from the fundus is detected as a change in light intensity at an observation point, and the resulting speckle signal is An ophthalmological measurement device that performs ophthalmological measurements through analysis includes an optical system that irradiates a laser beam to the fundus of the eye, including symmetric blood vessels, as a beam of a predetermined diameter, and a movement of a laser speckle pattern formed by scattered reflected light from the fundus of the eye. means for detecting the change in speckle light intensity at an observation point; means for converting the speckle signal obtained by the detection means into a digital signal; and means for comparing the digital signal with a predetermined value to discriminate a blood vessel portion. An ophthalmological measuring device comprising: means for discriminating the discriminated blood vessel portion and noise; and identifying a blood vessel position according to the blood vessel portion discriminated by the two discrimination means.