JPWO2014084139A1 - Optical image measuring device - Google Patents

Abstract

The signal light is scanned by the signal light scanning means 40, and an optical path length adjusting means 66 for adjusting the optical path length of the reference light in synchronization with the signal light scanning is provided. The optical path length adjusting unit adjusts the optical path length of the reference light so that there is no difference between the optical path lengths of the signal light and the reference light generated by the bending of the target object in synchronization with the signal light scanning. In such a configuration, even when the target object is curved, a tomographic image like a flat target can be acquired, and a clear tomographic image can be obtained over the entire region.

Description

  The present invention relates to an optical image measurement device for observing the form of a target object such as an eye to be examined.

  An optical image measuring device applying a so-called OCT (Optical Coherence Tomography) technique for photographing a fundus observation device for photographing the fundus of the eye to be examined and a tomographic image of the fundus is disclosed (Patent Document 1). ). This memorizes the position of the reference mirror at the time of the previous measurement so that the same setting state can be reproduced at the next time. The appropriate reference mirror position can be predicted from the axial length data, and the measurement can be performed efficiently. It is what you want to do. Since the position of the reference mirror differs depending on the scanning location, it is possible to perform the reproduction measurement by scanning the same position as the previous time and recording the reference mirror position at that time.

  The optical image measuring device disclosed in Patent Document 1 is intended to correct the difference in the person to be measured and the position of the appropriate reference mirror when the same person is measured at different locations. Yes, it is not a processing within one slice screen. Once the position of the reference mirror is determined, the reference mirror is not moved until one tomographic image is taken.

Japanese Patent No. 4823669

  Consider fundus photography of a patient with high myopia. Intense myopia is a condition in which the length of the front and back of the eyeball (axis length) is significantly longer than a certain standard, which means that the fundus is very curved, and the center of the fundus during scanning There is a significant difference in optical path length between the peripheral portion and the periphery thereof. When the reference mirror is positioned and scanned as described above, a difference in the optical path length between the center and the periphery that does not fit within the tomographic range of one tomographic image occurs (exceeds the range that can be photographed). For this reason, there is a problem that a partial defect of the tomographic image and the quality of the obtained tomographic image are deteriorated.

  Therefore, an object of the present invention is to provide an optical image measurement device that can obtain a clear tomographic image over the entire region even when the target object is curved.

The present invention for solving the above problems
Interference light generated by splitting the light output from the light source into signal light traveling toward the target object and reference light traveling toward the reference object, and superimposing the signal light traveling through the target object and the reference light traveling through the reference object An optical image measurement device for forming a tomographic image of a target object based on
A signal light scanning means for scanning the signal light toward the target object;
Optical path length adjusting means for adjusting the optical path length of the reference light in synchronization with the signal light scanning by the signal light scanning means,
The optical path length adjusting unit adjusts the optical path length of the reference light so that there is no difference between the optical path lengths of the signal light and the reference light generated by the bending of the target object in synchronization with the signal light scanning.

  In the present invention, the optical path length of the reference light is adjusted so as to eliminate the difference in optical path length between the signal light and the reference light generated by the bending of the target object in synchronization with the scanning by the signal light scanning unit. Even in this case, a tomographic image like a flat target object can be acquired, and a clear tomographic image can be obtained over the entire region.

It is a block diagram which shows the whole optical image measuring device. It is an optical diagram which shows the optical system of a scanning unit. It is an optical diagram which shows the optical system of an OCT unit. It is a functional block diagram of an optical image measuring device. It is a figure which shows an example of the mechanism which adjusts the optical path length of reference light. It is a figure explaining the scanning area | region of a fundus. It is a flowchart which shows operation | movement of an optical image measuring device. It is a figure which shows the example of a tomographic image. It is a figure which shows the example of a tomographic image. It is a figure which shows the positional relationship of a tomographic image. It is a figure which shows the positional relationship of a tomographic image. It is a figure explaining the example of the adjustment signal which adjusts the optical path length of reference light, and the control signal of a galvanometer mirror drive mechanism. It is a figure which shows the example of the tomographic image formed with the conventional optical image measuring device. It is a figure which shows the example of the tomographic image formed with the optical image measuring device of this invention.

  Hereinafter, an optical image measurement device (tomographic image acquisition device) of the present invention will be described in detail based on examples with reference to the drawings. Here, an example will be described in which a tomographic image of the fundus (an example of a target object) of the eye to be examined is acquired by an optical image measurement device for ophthalmologic examination, but the target object in the present invention is not limited to the fundus.

  FIG. 1 is a block diagram showing the entire optical image measurement device. The optical image measuring device 1 controls the fundus camera unit 2 that observes and images the fundus oculi Ef of the eye E, the OCT unit 50 that captures a tomographic image of the fundus oculi Ef using light interference, and controls these two units. And a tomographic image of the fundus oculi is acquired. The fundus camera unit 2 and the OCT unit 50 are optically connected by a connection line 56 and a connector 58.

  The fundus camera unit 2 includes an illumination optical system 10, a photographing optical system 20, and a scanning unit 30. The illumination optical system 10 includes an observation light source such as a halogen lamp and a photographing light source such as a xenon lamp, and guides light emitted from these light sources to the fundus oculi Ef along an illumination optical path composed of optical elements such as lenses and mirrors. Illuminate the fundus.

  The photographing optical system 20 includes an optical system such as an objective lens and a photographing lens, and an imaging device such as a CCD (Charge Coupled Device). The photographing optical system 20 guides the photographing light reflected by the fundus oculi Ef to the imaging device along the photographing optical path, and the fundus oculi Ef. Take a picture of. Further, the signal light LS reflected by the fundus oculi Ef described later is guided to the OCT unit 50. Although not shown, a display for displaying the fundus imaged by the imaging device is also provided.

  The scanning unit 30 is a mechanism for scanning the signal light LS in the X direction and the Y direction in FIG. 1 and constitutes a signal light scanning means, and its optical diagram is shown in FIG.

  The scanning unit 30 includes galvanometer mirrors 33 and 34. The signal light LS generated by the OCT unit 50 and guided by the optical fiber 54 inserted through the connection line 56 is emitted from the end of the connector 58, converted into a parallel light beam by the lens 32, and then guided to the galvano mirror 33. . The signal light LS reflected by the galvanometer mirror 33 enters the photographing optical system 20 via the galvanometer mirror 34. The galvanometer mirror 33 is configured to be rotatable around a rotation shaft 37 parallel to the paper surface in FIG. The galvanometer mirror 34 is configured to be rotatable about a rotation axis 38 perpendicular to the paper surface and the rotation axis 37. Therefore, the signal light LS can be scanned in the X direction in FIG. 1 by rotating the galvanometer mirror 33 and the signal light LS can be scanned in the Y direction by rotating the galvanometer mirror 34.

  FIG. 3 is an optical diagram of the OCT unit 50. The OCT unit 50 includes a low-coherence light source 51 (an example of a light source), an optical coupler 59 (an example of an interference light generation unit), a reference mirror 63 (an example of a reference object), and an OCT signal detection device 70 (an example of a detection unit). Configured as a spectrometer). The low coherence light source 51 is composed of, for example, a broadband light source such as a light emitting diode, a broadband mode-locked laser, or the like, and generates low coherence light L0 having a temporal coherence length of about several μm to several tens of μm. The wavelength of the low coherence light L0 is 700 nm to 1100 nm, which is slightly longer than visible light, for example, for ophthalmic use. The optical coupler 59 is an optical element that splits and superimposes light rays. The reference mirror 63 is movable in the arrow direction in FIG. 3 (Z direction in FIG. 1). The OCT signal detection device 70 is a device that detects interference light and forms an image on an imaging device such as a CCD.

  The low coherence light L0 generated by the low coherence light source 51 is guided to the optical coupler 59 by the optical fiber 52, and is divided into the reference light LR and the signal light LS. The reference light LR reaches the reference mirror 63 through the optical fiber 53, the collimator lens 60, the glass block 61, and the density filter 62. The glass block 61 and the density filter 62 act as delay means for matching the optical path lengths (optical distances) of the reference light LR and the signal light LS, and as means for matching the dispersion characteristics of the reference light LR and the signal light LS. ing. The reference light LR is reflected by the reference mirror 63 and returns to the optical coupler 59 following the above path in the reverse direction.

  The signal light LS is guided to the fundus camera unit 2 through the optical fiber 54 inserted through the connection line 56, reaches the fundus oculi Ef via the scanning unit 30 and the imaging optical system 20 in FIG. Scan in the direction. The signal light LS that has reached the fundus oculi Ef is reflected by the fundus oculi Ef and returns to the optical coupler 59 following the above path in the reverse direction.

  The reference light LR reflected by the reference mirror 63 and the signal light LS reflected by the fundus oculi Ef are superimposed by the optical coupler 59 to become interference light LC. The interference light LC is guided to the OCT signal detection device 70 by the optical fiber 55. The interference light LC is converted into a parallel light beam by the collimator lens 71 in the OCT signal detection device 70, and then enters the diffraction grating 72 and is split. The split interference light LC is imaged on the CCD 74 by the imaging lens 73.

  FIG. 4 is a functional block diagram of the optical image measurement device 1. The galvanometer mirror driving means 40 is constituted by, for example, a motor or a solenoid, and rotates the galvanometer mirror 33 around the rotation axis 37 and the galvanometer mirror 34 around the rotation axis 38. The scanning unit 30 and the galvanometer mirror driving means 40 are an example of signal light scanning means.

  The reference mirror driving means 65 is conventionally used, and is a mechanism for positioning the reference mirror 63 in the Z direction so that the optical path lengths of the reference light LR and the signal light LS are equal before the start of imaging. For example, a motor or a solenoid can be used. After being positioned, the reference mirror driving unit 65 does not operate while the signal light LS is being scanned by the scanning unit 30 and the galvanometer mirror driving unit 40.

  The optical path length adjusting unit 66 operates in synchronization with the galvanometer mirror driving unit 40, and adjusts the optical path length of the reference light so that there is no difference between the optical path lengths of the signal light and the reference light caused by the curvature of the object. Generate an adjustment signal. The optical path length adjustment signal can be generated by obtaining a tomographic image by matching the reference light and the signal light by the reference mirror driving means 65 and obtaining the curvature of the fundus from the analysis of the acquired tomographic image. Alternatively, the optical path length adjustment signal can be generated by obtaining the curvature of the fundus from the shape parameters of the target object such as the diopter parameters (diopter correction amount, axial length) of the eye to be examined. As will be described later, the optical path length adjustment signal generated in this way adjusts the optical path length of the reference light in synchronization with the signal light scanning, and calculates the difference between the optical path length of the signal light and the reference light caused by the curvature of the object. Let go.

  FIG. 5 shows a configuration example of the optical path length adjusting means 66. An optical fiber 53 that guides the reference light LR to the collimator lens 60 is wound around the piezo element 67. When the optical path length adjustment signal is input to the piezo element 67, the piezo element 67 expands and contracts in the direction of the arrow in FIG. 5, and the optical fiber 53 expands and contracts accordingly, resulting in the optical path length of the reference light LR. Changes. In addition, the optical path length adjusting unit 66 can be realized by a configuration in which the position of the reference mirror 63 in the Z direction is changed according to the optical path length adjustment signal using a rotary motor, a solenoid, or the like.

  The arithmetic and control unit 100 is constituted by, for example, a microcomputer built in the fundus camera unit 2, a personal computer connected to the fundus camera unit 2, etc., and controls the fundus camera unit 2 and the OCT unit 50, and also the OCT unit 50. Analysis of data obtained by the above, generation of a tomographic image, generation of an optical path length adjustment signal for adjusting the optical path length of the reference light, and the like.

  The control module 101 controls each part of the fundus camera unit 2, the OCT unit 50, and the arithmetic control device 100. The control module 101 is realized, for example, by executing a computer program stored in the storage unit 106 by a CPU (not shown, Central Processing Unit) included in the personal computer.

  The display unit 102 is configured by, for example, a display device such as an LCD or a CRT, and displays accompanying information such as a tomographic image of the fundus oculi Ef formed by the tomographic image forming unit 104 and information on the subject.

  The operation unit 103 is used by an operator to give an instruction to the optical image measurement device 1 with, for example, a mouse or keyboard connected to a personal computer or an operation panel provided in the fundus camera unit 2.

  The tomographic image forming unit 104 (an example of a tomographic image forming unit) generates a tomographic image of the fundus oculi Ef based on the OCT signal detected by the OCT signal detection device 70. The tomographic image forming unit 104 is realized by a dedicated electronic circuit that executes a known analysis method such as a Fourier domain method (spectral domain method) or an image forming program executed by the CPU.

  The image analysis unit 105 analyzes the image data formed by the tomographic image forming unit 104 to acquire the curvature of the fundus, and generates an optical path length adjustment signal for controlling the optical path length adjustment unit 66 based on the curvature.

  The storage unit 106 includes, for example, a semiconductor memory, a hard disk device, and the like, and stores a program executed by the control module 101, a created optical path length adjustment signal, and the like.

  Next, the operation of the optical image measurement apparatus 1 when creating a tomographic image by scanning the scanning region of FIG. 6 will be described with reference to the flowchart of FIG. FIG. 6 schematically shows a state in which the fundus oculi Ef of the eye E is viewed from the positive direction of the Z axis (the right side in FIG. 1). Here, two rectangular scanning areas R1 and R2 are set. The scanning region R1 is a region where the optic nerve head is present, and the scanning region R2 is a region where the macula is present. In the scanning region R1 and the scanning region R2, n scanning lines A1, A2,..., An and B1, B2,. , Bn are set.

  First, in accordance with an instruction from the operator, the control module 101 controls the reference mirror driving mechanism 65 to position the reference mirror 63 in the Z direction so that the optical path lengths of the reference light LR and the signal light LS are equal (S1).

  The control module 101 searches the information stored in the storage unit 106 and determines whether or not the optical path length adjustment signal is stored (S2). The optical path length adjustment signal can be stored, for example, as digital data obtained by sampling the waveform at a predetermined sampling rate and digitizing it.

  If it is stored, the control module 101 reads the optical path length adjustment signal from the storage unit 106 (determination of S2 is true, S11). The optical path length adjustment signal is created based on the average eyeball shape according to the race, age, etc. of the subject, or is created based on the past examination data of a specific subject, for example, the axial length Etc. can be used.

  If the optical path length adjustment signal is not stored, preliminary photographing is performed (determination of S2 is false, S21). Specifically, the control module 101 controls the fundus camera unit 2 and the OCT unit 50 by a conventional method to perform measurement, and the tomographic image forming unit 104 forms a tomographic image of the fundus oculi Ef. At this time, the optical path length adjusting means 66 is not operated. 8 and 9 schematically show examples of tomographic images of the fundus oculi Ef obtained by preliminary imaging. The tomographic images are obtained for each of the scanning regions R1 and R2 for each scanning line, for a total of n, and FIGS. 8 and 9 show the first three. 8, reference numeral 121 is a tomographic image at the position of the scanning line A1, reference numeral 122 is a tomographic image at the position of the scanning line A2, reference numeral 123 is a tomographic image at the position of the scanning line A3, and reference numeral 124 in FIG. 9 is the position of the scanning line B1. , The reference numeral 125 is a tomographic image at the position of the scanning line B2, and the reference numeral 126 is a tomographic image at the position of the scanning line B3. In this example, it can be seen that the fundus oculi Ef has a three-layer structure that is distinguished by oblique lines having different directions. Reference numerals 131 to 136 in FIGS. 8 and 9 are curvatures (irregularities) of the surface of the fundus extracted from the image, which are not included in the original image but are added for explanation. FIGS. 10 and 11 schematically show the three-dimensional positional relationship between the three images of FIGS. 8 and 9, respectively. These images show that the fundus oculi Ef was photographed on a plane parallel to the XZ plane with the position shifted in the Y direction.

  When the tomographic image is formed in this way, the image analysis unit 105 analyzes the tomographic image and extracts the curvature of the fundus for creating the optical path length adjustment signal (S22). This is performed, for example, by extracting the shape of the fundus oculi Ef surface or the like using a known contour extraction method or the like. 8 and 9 show examples of the curved shape of the fundus with thick solid lines 131 to 136. In this example, the shape of the surface of the fundus oculi Ef that appears relatively clearly (for example, the line indicated by reference numeral 141 in the image 121 in FIG. 8) is used as it is. It is preferable that the portion used as the curvature of the fundus is a plane that is substantially perpendicular to the optical axis of the signal light (Z axis in FIG. 1). In addition to the curvature of the surface of the fundus Ef, each layer (inner The curvature of the boundary surface of the boundary membrane, retinal pigment epithelium, etc.) can also be used.

  Next, the image analysis unit 105 generates an optical path length adjustment signal for controlling the optical path length adjustment unit 66 based on the curvature of the fundus (S23). The generated optical path length adjustment signal is stored in the storage unit 106.

  FIG. 12 shows an example of the optical path length adjustment signal generated from the image of FIG. The lower graph of FIG. 12 shows a control signal for controlling the galvanometer mirror 33 in order to scan the signal light LS in the X direction among the control signals of the galvanometer mirror driving means 40. The signal light LS is scanned from the left end to the right end of the scanning line A1 from time t1 to time t2, and returns to the left end from time t2 to time t3 (during this time, the galvano mirror 34 is controlled to change the position of the scanning line in the Y direction). Thereafter, the same control is performed for each scanning line.

  The upper graph in FIG. 12 shows the optical path length adjustment signal of the reference light. The waveform of the optical path length adjustment signal corresponds to the curved shape of the fundus in FIG. That is, when the scanning line A1 is scanned with the signal light LS, the fundus is in the shape of the curve 131 as shown in the upper part of FIG. 8, and when scanning with the scanning lines A2 and A3, the middle part of FIG. This corresponds to the shape of the fundus curvature 132, 133 as shown in the lower part. Similarly, the scanning with the scanning line An corresponds to the curved shape of the fundus obtained from the tomographic image with the scanning line at that time. In addition, when there is a portion with severe irregularities as in the image 123 of FIG. 8, the optical path length adjustment signal may be generated by interpolating the shape of the portion with another portion having a relatively flat shape.

  When the reading (S11) or generation (S23) of the optical path length adjustment signal is completed, the control module 101 controls the fundus examination unit 1 and the OCT unit 50 to perform main imaging (S3). At this time, the control module 101 scans the fundus in the X and Y directions with the signal light LS in accordance with the galvano mirror driving means control signal shown in FIG. 12, and refers to the optical path length adjustment signal in synchronization with the scanning of the signal light. The optical path length of the light is adjusted so that there is no difference between the optical path length of the signal light and the reference light caused by the curvature of the object. For example, as shown in the lower part of FIG. 8, when the fundus is remarkably curved in a concave shape, the difference in optical path length between the signal light and the reference light becomes large. Therefore, the optical path length adjusting means 66 outputs an optical path length adjusting signal having a small amplitude in synchronization with the signal light scanning at the time of scanning the concave portion, that is, the concave portion. Thereby, the optical path length of the reference light is shortened, and the difference between the optical path lengths of the signal light and the reference light is reduced to zero. Eliminating the difference between both optical path lengths corresponds to obtaining a tomographic image when there is no recess in the fundus, and a tomographic image with a flat surface is obtained.

  The tomographic image forming unit 104 forms a tomographic image of the fundus oculi Ef based on the signal acquired by the OCT signal detection device 70 (S4). The formed image is displayed on the display unit 102 and stored in the storage unit 106 as necessary. FIG. 13a schematically shows a tomographic image obtained by fixing the position of the reference mirror with a conventional optical image measuring device, and FIG. 13b schematically shows a tomographic image obtained by adjusting the optical path length of the reference light by the optical path length adjusting means 66. Shown in In FIG. 13a, the fundus is photographed in a curved shape as the original shape. However, the portion close to the reference position 142 for positioning the reference mirror (upper part in FIG. 13a) is photographed with high sensitivity, but the part far from the reference position 142 (lower part in FIG. 13a) is low-sensitivity, Become. On the other hand, in FIG. 13b, since the difference between the optical path length of the reference light and the optical path length of the signal light is reduced or becomes zero, the surface shape of the fundus oculi Ef becomes flat, so that the entire image is photographed with high sensitivity and clear. It becomes an image.

  FIG. 13b is a tomographic image obtained when the optical path length of the reference light is adjusted during scanning by the scanning line A3. Similar optical path length adjustment is performed for the other scanning lines An and Bn. In all tomographic images, a tomographic image having a flat surface shape of the fundus oculi Ef and a clear entire surface is obtained. Since the obtained flat and clear tomographic image is a controlled amount with a known optical path length adjustment amount, a curved tomographic image obtained by subtracting this adjustment amount from the obtained tomographic image and photographed by a normal photographing method. It can also be displayed as an image. (From the information on the adjustment amount of the optical path length, it is also possible to display a tomographic image of the fundus that is actually curved in an image view.)

DESCRIPTION OF SYMBOLS 1 Optical image measuring device 2 Fundus camera unit 10 Illumination optical system 20 Imaging optical system 30 Scanning unit 32 Lens 33, 34 Galvano mirror 40 Galvano mirror drive means 50 OCT unit 51 Low coherence light source 52, 53, 54, 55 Optical fiber 56 Connection Wire 58 Connector 59 Optical coupler 60 Collimator lens 61 Glass block 62 Density filter 63 Reference mirror 65 Reference mirror drive mechanism 66 Optical path length adjusting means 67 Piezo element 70 OCT signal detector 71 Collimator lens 72 Diffraction grating 73 Imaging lens 74 CCD
DESCRIPTION OF SYMBOLS 100 Arithmetic control apparatus 101 Control module 102 Display part 103 Operation part 104 Tomographic image formation part 105 Image analysis part 106 Memory | storage part E Eye to be examined Ef Fundus L0 Low coherence light LR Reference light LS Signal light LC Reference light

Claims (6)

Interference light generated by splitting the light output from the light source into signal light traveling toward the target object and reference light traveling toward the reference object, and superimposing the signal light traveling through the target object and the reference light traveling through the reference object An optical image measurement device for forming a tomographic image of a target object based on
A signal light scanning means for scanning the signal light toward the target object;
Optical path length adjusting means for adjusting the optical path length of the reference light in synchronization with the signal light scanning by the signal light scanning means,
The optical path length adjusting means adjusts the optical path length of the reference light so that there is no difference between the optical path lengths of the signal light and the reference light caused by the curvature of the target object in synchronization with the signal light scanning. Image measuring device.   The optical image measurement apparatus according to claim 1, wherein a tomographic image is acquired without performing optical path length adjustment by the optical path length adjusting unit, and the curvature of the target object is obtained from analysis of the acquired tomographic image.   The optical image measurement apparatus according to claim 1, wherein a curvature of the target object is obtained from a shape parameter of the target object.   4. The optical image measurement device according to claim 1, wherein the optical path lengths of the reference light and the signal light are made to coincide before obtaining the tomographic image.   The optical image measurement apparatus according to claim 1, wherein the target object is a fundus of the eye to be examined.   The optical image measurement apparatus according to claim 5, wherein the curvature of the fundus is obtained from a diopter parameter of the eye to be examined.

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