JP5209377B2 - Fundus photographing device - Google Patents

Description

  The present invention relates to a fundus imaging apparatus that captures a tomographic image of an eye to be examined.

  An optical tomography interferometer (Optical Coherence Tomography: OCT) using low-coherent light is known as an ophthalmologic imaging apparatus that can obtain a tomographic image of an eye to be examined non-invasively. Then, an OCT optical system as described above is combined with an observation optical system capable of acquiring a frontal image of the fundus, such as a scanning laser ophthalmoscope (SLO) optical system or a fundus camera optical system. An apparatus capable of acquiring a front image has also been proposed (see Patent Document 1).

In such an apparatus, the examiner can check the focus state of the fundus front image acquired by the SLO optical system or the fundus camera optical system or the positional relationship of the focus index projected on the fundus on the display monitor. The focus adjustment knob provided is operated to focus the fundus front image and fundus tomographic image. That is, for the focus adjustment of the fundus tomographic image, the focus adjustment of the fundus front image is applied to the OCT optical system.
JP 2006-212153 A

  However, since the focus position in the fundus front image acquired by the observation optical system and the focus position in the fundus tomographic image acquired by the OCT optical system do not necessarily match, the focus accuracy for the tomographic image is not always sufficient. There wasn't.

  In view of the above problems, an object of the present invention is to provide a fundus imaging apparatus capable of appropriately performing focus adjustment on a tomographic image.

  In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) An illumination optical system that irradiates illumination light to the fundus of the eye to be examined, and a light receiving optical system that has a first focusing optical member that is movable in the optical axis direction and that receives fundus reflected light by the first light receiving element. A fundus oculi observation means that includes a fundus oculi observation optical system and obtains a front fundus image of the subject's eye based on a light reception signal output from the first light receiving element;
A second focus optical member movable in the optical axis direction and an optical path length variable optical member, splitting the light emitted from the light source into measurement light and reference light, and guiding the measurement light to the fundus of the eye to be examined; After the reference light is guided to the reference optical system, the second light receiving element has an interference optical system that detects the combined light of the measurement light reflected from the fundus and the reference light, and is output from the second light receiving element. Optical coherence tomography for obtaining a fundus tomographic image of the subject's eye based on the received light signal;
First autofocus means for acquiring in-focus position information with respect to the fundus of the fundus oculi observation optical system based on a light reception result output from the first light-receiving element, and moving the first focus optical member to the in-focus position; ,
After the second focus optical member is moved to the vicinity of the focus position based on the focus position information, the second focus optical member is further moved at a plurality of positions near the focus position. A second autofocus unit that acquires in-focus position information for the fundus of the interference optical system based on the acquired tomographic image, and moves the second focus optical member to the in-focus position. To do.
(2) In the fundus imaging apparatus according to (1), the second autofocus unit moves the second focusing optical member to the vicinity of the in-focus position, and then moves the optical path length varying optical member to each position. The optical path length is automatically adjusted based on the tomographic image acquired at, and further, the second focusing optical member is moved, and based on the tomographic images acquired at a plurality of positions near the in-focus position. Focus position information on the fundus of the interference optical system is acquired, and the second focus optical member is moved to the focus position.
(3) In the fundus imaging apparatus according to (2), the second autofocus unit uses the luminance level of the entire tomographic image acquired at a plurality of positions to focus position information on the fundus of the interference optical system. It is characterized by acquiring.
(4) an illumination optical system that irradiates the fundus of the subject's eye with illumination light, and a light receiving optical system that has a first focusing optical member that is movable in the optical axis direction and that receives the fundus reflected light by the first light receiving element. A fundus oculi observation means that includes a fundus oculi observation optical system and obtains a front fundus image of the subject's eye based on a light reception signal output from the first light receiving element;
A second focus optical member movable in the optical axis direction and an optical path length variable optical member, splitting the light emitted from the light source into measurement light and reference light, and guiding the measurement light to the fundus of the eye to be examined; After the reference light is guided to the reference optical system, the second light receiving element has an interference optical system that detects the combined light of the measurement light reflected from the fundus and the reference light, and is output from the second light receiving element. Optical coherence tomography for obtaining a fundus tomographic image of the subject's eye based on the received light signal;
First autofocus means for acquiring in-focus position information with respect to the fundus of the fundus oculi observation optical system based on a light reception result output from the first light-receiving element, and moving the first focus optical member to the in-focus position; ,
A focus position information for the fundus of the interference optical system is acquired by correcting the focus position information by a preset offset amount, and the second focus optical member is moved to the focus position. And an autofocus means.
(5) Having a focusing optical member movable in the optical axis direction, dividing the light emitted from the light source into measurement light and reference light, guiding the measurement light to the fundus of the eye to be examined, and guiding the reference light to the reference optical system And an interference optical system that detects, by a light receiving element, a spectrum of light that is a combination of the measurement light reflected from the fundus and the reference light, and Fourier-transforms the light reception signal output from the light receiving element, Optical coherence tomography to obtain fundus tomographic images of
Moving the optical member for the focus, the evaluation value for evaluating the luminance level of the entire tomographic image acquired by the moving position of the interference optical system based on the obtained evaluation value at each moved position Auto focus means for acquiring in-focus position information with respect to the fundus and moving the focusing optical member to the in-focus position.

  According to the present invention, it is possible to appropriately perform focus adjustment on a tomographic image.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an optical system and a control system of the fundus imaging apparatus of the present embodiment. In the present embodiment, the depth direction of the eye to be examined is described as the Z direction (the optical axis L1 direction), the horizontal direction is the X direction, and the vertical direction is the Y direction.

  In FIG. 1, the optical system uses an interference optical system (hereinafter referred to as an OCT optical system) 200 for non-invasively obtaining a tomographic image of the fundus of the eye to be examined using an optical interference technique, and infrared light. A scanning laser ophthalmoscope (SLO) optical system 300 that acquires an SLO fundus image for illuminating and observing the fundus of the eye to be examined is roughly classified.

  Reference numeral 40 denotes a dichroic mirror as a light splitting member, which reflects measurement light (for example, near λ = 840 nm) emitted from the measurement light source 27 used in the OCT optical system 200 and is used in the SLO optical system 300. 61 has a characteristic of transmitting laser light emitted from 61 (light having a wavelength different from that of the light source 27, for example, near λ = 780 nm). In this case, the dichroic mirror 40 makes the measurement optical axis L2 of the OCT optical system 200 and the measurement optical axis L1 of the SLO optical system 300 coaxial.

  First, the configuration of the OCT optical system 200 provided on the reflection side of the dichroic mirror 40 will be described. Reference numeral 27 denotes an OCT light source that emits low-coherent light used as measurement light and reference light of the OCT optical system 200. For example, an SLD light source is used. For the OCT light source 27, for example, a light source having a center wavelength of 840 nm and a bandwidth of 50 nm is used. Reference numeral 26 denotes a fiber coupler that doubles as a light splitting member and a light coupling member. The light emitted from the OCT light source 27 is split into reference light and measurement light by the fiber coupler 26 via an optical fiber 38a as a light guide. The measurement light goes to the eye E through the optical fiber 38b, and the reference light goes to the reference mirror 31 through the optical fiber 38c.

  In the optical path for emitting the measurement light toward the eye E, the end 39b of the optical fiber 38b for emitting the measurement light, the focusing lens 24 movable in the optical axis direction according to the refractive error of the eye to be examined, and the scanning drive mechanism A scanning unit 23 composed of a combination of two galvanometer mirrors capable of scanning measurement light in the XY directions on the fundus by driving 51 and a relay lens 22 are arranged. The dichroic mirror 40 and the objective lens 10 serve as a light guide optical system that guides OCT measurement light from the OCT optical system 200 to the fundus of the eye to be examined. Note that the scanning unit 23 of the present embodiment has a configuration in which the scanning direction of the measurement light to be scanned on the fundus can be arbitrarily set by arbitrarily adjusting the reflection angle of the measurement light by the two galvanometer mirrors. Yes. Therefore, it is possible to obtain a tomographic image of an arbitrary region of the fundus of the eye to be examined. Note that the end 39b of the optical fiber 38b is disposed so as to be conjugate with the fundus of the eye to be examined. Further, the two galvanometer mirrors of the scanning unit 23 are arranged at a position substantially conjugate with the eye pupil to be examined.

  The measurement light emitted from the end 39b of the optical fiber 38b reaches the scanning unit 23 via the focusing lens 24, and the reflection direction is changed by driving the two galvanometer mirrors. Then, the measurement light reflected by the scanning unit 23 is reflected by the dichroic mirror 40 via the relay lens 22 and then condensed on the fundus of the eye to be examined via the objective lens 10.

  Then, the measurement light reflected from the fundus is reflected by the dichroic mirror 40 via the objective lens 10, travels to the OCT optical system 200, passes through the relay lens 22, the two galvanometer mirrors of the scanning unit 23, and the focusing lens 24. The light enters the end 39b of the optical fiber 38b. The measurement light incident on the end 39b reaches the end 84a of the optical fiber 38d through the optical fiber 38b, the fiber coupler 26, and the optical fiber 38d.

  On the other hand, an end portion 39c of an optical fiber 38c that emits the reference light, a collimator lens 29, and the reference mirror 31 are arranged in the optical path that emits the reference light toward the reference mirror 31. The reference mirror 31 is configured to be movable in the optical axis direction by the reference mirror drive mechanism 50 in order to change the optical path length of the reference light.

  The reference light emitted from the end 39c of the optical fiber 38c is converted into a parallel light beam by the collimator lens 29, reflected by the reference mirror 31, collected by the collimator lens 29, and incident on the end 39c of the optical fiber 38c. The reference light incident on the end 39c reaches the fiber coupler 26 through the optical fiber 38c.

  Then, the reference light generated as described above by the light emitted from the light source 27 and the fundus reflection light by the measurement light irradiated on the eye fundus to be examined are combined by the fiber coupler 26 to be interference light, The light is emitted from the end portion 84b through the fiber 38d. A spectroscopic optical system 800 (spectrometer unit) 800 separates interference light into frequency components in order to obtain an interference signal for each frequency, and includes a collimator lens 80, a grating mirror (diffraction grating) 81, a condensing lens 82, and a light receiving element. 83. The light receiving element 83 is a one-dimensional element (line sensor) having sensitivity in the infrared region.

  Here, the interference light emitted from the end portion 84 a is collimated by the collimator lens 80, and then is split into frequency components by the grating mirror 81. Then, the interference light split into frequency components is condensed on the light receiving surface of the light receiving element 83 via the condenser lens 82. Thereby, spectrum information of interference fringes is recorded on the light receiving element 83. Then, the spectrum information is input to the control unit 70 and analyzed using Fourier transform, whereby information in the depth direction of the subject's eye can be measured. Here, the control unit 70 can acquire a tomographic image by causing the scanning unit 23 to scan the measurement light on the fundus in a predetermined transverse direction. For example, a tomographic image on the XZ plane or YZ plane of the fundus of the eye to be examined can be acquired by scanning in the X direction or the Y direction. And a method for obtaining a tomographic image is referred to as a B-scan). The acquired tomographic image is stored in a memory 72 connected to the control unit 70. Furthermore, it is also possible to acquire a three-dimensional image of the fundus of the eye to be examined by two-dimensionally scanning the measurement light in the XY direction. The acquisition of the OCT image in the present embodiment is performed by two galvanometer mirrors provided in the scanning unit 23.

  Next, the SLO optical system (confocal optical system) 300 disposed in the transmission direction of the dichroic mirror 40 will be described. The SLO optical system 300 is broadly divided into an illumination optical system that illuminates the fundus of the eye to be examined and a light receiving optical system that receives the reflected light of the eye to be examined illuminated by the illumination optical system by the light receiving element, and is output from the light receiving element. A front image of the fundus of the eye to be examined is obtained based on the received light signal.

  Reference numeral 61 denotes an SLO light source that emits highly coherent light. For example, a laser diode light source of λ = 780 nm is used. In the optical path for emitting the laser light emitted from the SLO light source 61 toward the eye E to be examined, the focusing lens 63 that can move in the optical axis direction according to the refractive error of the eye to be examined, and the scanning drive mechanism 52 drive the fundus. A scanning unit 64, a relay lens 65, and an objective lens 10, which are a combination of a galvanometer mirror and a polygon mirror capable of scanning measurement light at high speed in the XY directions, are arranged. Further, the reflection surfaces of the galvanometer mirror and the polygon mirror of the scanning unit 23 are arranged at a position substantially conjugate with the eye pupil to be examined.

  A beam splitter 62 is disposed between the SLO light source 61 and the focusing lens 63. In the reflection direction of the beam splitter 62, a condensing lens 66 for constituting a confocal optical system, a confocal aperture 67 placed at a conjugate position to the fundus, and an SLO light receiving element 68 are provided. Yes.

  Here, the laser light (measurement light) emitted from the SLO light source 61 passes through the beam splitter 62, then reaches the scanning unit 64 via the focusing lens 63, and the reflection direction is driven by driving the galvanometer mirror and polygon mirror. be changed. The laser light reflected by the scanning unit 64 is transmitted through the dichroic mirror 40 via the relay lens 65 and then condensed on the fundus of the eye to be examined via the objective lens 10.

  Then, the laser light reflected from the fundus is reflected by the beam splitter 62 through the objective lens 10, the relay lens 65, the galvano mirror and polygon mirror of the scanning unit 64, and the focusing lens 63. Thereafter, the light is condensed by the condenser lens 66 and then detected by the light receiving element 68 through the confocal aperture 67. Then, the light reception signal detected by the light receiving element 68 is input to the control unit 70. The control unit 70 acquires a front image of the fundus of the eye to be examined based on the light reception signal obtained by the light receiving element 68. The acquired front image is stored in the memory 72. The acquisition of the SLO image is performed by vertical scanning (sub-scanning) of laser light by a galvanometer mirror provided in the scanning unit 64 and horizontal scanning (main scanning) of laser light by a polygon mirror.

  The control unit 70 is connected to the display monitor 75 and controls the display image. Further, the control unit 70 includes a memory 72, a measurement start switch 74a, a measurement position setting switch 74b, an imaging start switch 74c, an autocoherence switch 74d, an autofocus start switch 74f, a reference mirror driving mechanism 50, and a focusing lens 63. A first drive mechanism 63a for moving in the direction, a second drive mechanism 24a for moving the focusing lens 24 in the optical axis direction, and the like are connected.

  Next, a method of acquiring a tomographic image (B scan image) on the XZ plane by B scan will be described. FIG. 2 is a diagram illustrating an operation when sequentially acquiring an OCT image and an SLO image (left side). Here, the control unit 70 alternately turns on the OCT light source 27 and the SLO light source 61 to emit irradiation light applied to the fundus of the subject's eye via the OCT optical system 200 in order to obtain the fundus image of the subject's eye. Switching between the measurement light irradiated and the laser light irradiated via the SLO optical system. Therefore, an interference signal detected by the light receiving element 83 disposed in the OCT optical system 200 and a light reception signal detected by the light receiving element 68 disposed in the SLO optical system 300 are sequentially input to the control unit 70.

  Here, the control unit 70 divides the upper and lower end areas (hatched portions in FIG. 2) of the scanning area for one frame of the SLO image that hardly affect the image acquisition for the time required for the OCT image acquisition. The SLO light source 61 is turned OFF while it is located in that area. Then, while the SLO light source 61 is OFF, the OCT light source 27 is turned ON and an OCT image is acquired by B scan. On the other hand, in the scanning area (non-hatched portion in FIG. 2) set to obtain the SLO image, the control unit 70 turns on the SLO light source 61 and turns off the OCT light source 27 to acquire the SLO image. The control unit 70 continuously performs such control, and displays the alternately obtained SLO images and OCT images as moving images on the display monitor 75 at the same time.

  The operation of the apparatus having the above configuration will be described. Here, the control unit 70 drives and controls the OCT optical system 200 and the SLO optical system 300 to acquire each image of the OCT image and the SLO image for each frame, and controls the display of the monitor 75 to the monitor 75. The displayed OCT image and SLO image are updated as needed. Note that a scanning position (for example, the X direction) with the center position of the SLO image as a reference is set as the first OCT image acquisition position that is not set by the examiner.

  First, the examiner instructs the subject to look at a fixation lamp (not shown), and then observes the anterior ocular segment observation image captured by the anterior ocular segment observation camera (not shown) on the monitor 75. An alignment operation is performed using a joystick (not shown) so that the measurement optical axis L1 is placed at the center of the pupil. When the alignment with respect to the eye to be examined is completed in this way, a front image (SLO fundus image) of the eye fundus to be examined by the SLO optical system 300 is acquired, and the SLO fundus image appears on the monitor 75.

  Next, the examiner presses an autofocus start switch 74 f arranged in the control unit 74. When an operation signal is issued from the autofocus start switch 74f, the control unit 70 issues a trigger signal for starting autofocus control, and starts autofocus on the SLO fundus image.

  Here, the control unit 70 acquires in-focus position information of the SLO optical system 300 based on the SLO fundus image acquired by the light reception signal output from the light receiving element 68, and a focusing lens disposed in the SLO optical system 300. 63 is moved to the in-focus position (first autofocus).

  More specifically, first, the control unit 70 differentiates the image data of the SLO fundus image acquired based on the light reception signal output from the light receiving element 68, and obtains differential histogram information based on the result of the differentiation process. get. In other words, the control unit 70 converts the image data of the SLO fundus image acquired by the SLO optical system 300 into a contour image by applying a filter for edge extraction (for example, Laplacian conversion, SOBEL, etc.), and then the histogram of the contour image. Create

  FIG. 3 is a diagram illustrating an example of a differential histogram after differential processing is performed on the image signal of the SLO fundus image acquired by the SLO optical system 300. In FIG. 3, the horizontal axis represents the absolute value of differentiation (hereinafter abbreviated as differential value) d (d = 1, 2,... 254), and the vertical axis represents the number of pixels H (d) corresponding to each differential value. The normalized value ((H (d) / H (dp)) of the number of pixels H (dp) in the differential value at which the number of pixels showed a peak is expressed in percentage (%). The histogram excludes two data points (d = 0, d = 255), where the differential value d represents the luminance value in the contour image in 255 gradations.

  In the differential histogram H (d), when the focus is appropriate, the edge in the blood vessel region of the fundus is sharpened, so the number of pixels having a larger differential value increases, and the edge becomes dull as the focus shifts. As a result, the number of pixels having a larger differential value decreases.

  Here, the control unit 70 uses the maximum value of the luminance value (differential value) having the number of pixels equal to or higher than a predetermined ratio in the entire image in the histogram information acquired as described above (SLO fundus image formation state ( Focus state) Evaluation value is calculated. For example, as the imaging state evaluation value C1 for evaluating the imaging state of the SLO fundus image, a difference between the maximum value Dmax and the minimum value Dmin of the differential value at a threshold S1 (for example, 20%) or more is obtained (C1 = Dmax-Dmin). The threshold value S1 is set to a value such that the evaluation value C1 changes sensitively to changes in the imaging state of the SLO fundus image while avoiding the influence of noise. In the present embodiment, the threshold S1 is set to about 20% in order to accurately detect a change in edge sharpness in a fundus blood vessel region having a small range in the entire SLO image. In the above description, only the maximum differential value Dmax above the threshold S1 may be set as the imaging state evaluation value C1.

  The imaging state evaluation value C1 shows a high value when the focusing lens 63 is at the in-focus position (when the SLO fundus image is in focus), and decreases as the focusing lens 63 deviates from the in-focus position. Therefore, it can be used to determine the focus state (image formation state) of the SLO fundus image.

  Here, the control unit 70 samples the imaging state evaluation value C1 while moving the position of the focusing lens 63 arranged in the light receiving optical system of the SLO optical system 300, determines the in-focus state based on the sampling result, and performs focusing. The lens 63 is driven to the in-focus position.

  For example, the control unit 70 drives and controls the drive mechanism 63a to search for an appropriate focus position, and moves the focusing lens 63 to a plurality of discretely set movement positions within the movable range of the focusing lens 63. The SLO fundus image at each moving position is acquired. Then, the control unit 70 creates a differential histogram of each SLO fundus image acquired for each movement position, and calculates an imaging state evaluation value C1. In this case, the control unit 70 may continuously move the focusing lens 63 and continuously calculate the imaging state evaluation value C1.

  FIG. 4 is a diagram showing an example of a graph showing the relationship between the imaging state evaluation value C1 and the moving position Z1 of the focusing lens 63. As shown in FIG. In FIG. 4, when the focusing lens 63 is moved in the positive direction by 2D sequentially from the position corresponding to −12D, the evaluation value C1 is calculated sequentially, and the focusing lens 63 is moved to the position corresponding to + 12D. belongs to.

  When the evaluation value C1 at each focus position is obtained as described above, interpolation processing is performed on the characteristics of the moving position Z1 of the focusing lens 63 and the evaluation value C1 obtained discretely, and the result of the integration of the SLO optical system 200 is obtained. The focal position is detected. For example, the curve is approximated by a function having a maximum value in the moving range of the focusing lens 63, and the moving position Z1p at which the evaluation value C1 is maximum in this curve is acquired as the focusing position information of the SLO optical system 300. As a method for detecting the in-focus position of the SLO optical system 300 by the interpolation process as described above, a method using function approximation, center of gravity, calculation of an average value, or the like can be considered.

  Next, the control unit 70 controls the drive mechanism 63a to move the focusing lens 63 to the movement position corresponding to the focus position information acquired as described above, thereby completing the focus adjustment for the SLO fundus image. To do.

  Note that, when the imaging state evaluation value C1 is sampled as described above, the movement of the focusing lens 63 may be stopped when the acquired imaging state evaluation value C1 starts to decrease after the increase.

  In the above description, the in-focus state is detected based on the contour image obtained when the SLO fundus image is differentiated. However, the confocal aperture included in the SLO optical system 300 is narrow and the in-focus state is detected. In the case of a configuration in which the change in the brightness of the entire image due to the change in is sensitive, the in-focus state may be detected based on the SLO fundus image before the differentiation process. For example, a cumulative value of luminance values of the entire SLO fundus image may be used as an imaging state evaluation value, and a position where the cumulative value of luminance values exhibits a peak may be detected as a focus position.

  Next, the control unit 70 moves the focusing lens 24 of the OCT optical system 200 based on the in-focus position information of the SLO optical system 300 by the first autofocus control, and then is acquired by the OCT optical system 200. The focus position information of the OCT optical system 200 is acquired based on the tomographic image, and the focusing lens 24 is moved to the focus position (second auto focus).

  First, the control unit 70 acquires the focus position information of the OCT optical system 200 based on the focus position information of the SLO optical system 300 by the first autofocus control, and moves the focusing lens 24 to the vicinity of the focus position ( Coarse autofocus for OCT images). Here, the control unit 70 acquires the moving position of the focusing lens 63 by the first autofocus control as the focus position information of the OCT optical system 200, and controls the drive mechanism 24a based on the focus position information to perform the focusing. The lens 24 is moved to the vicinity of the in-focus position.

  For example, if the focus position of the SLO optical system 300 is a position corresponding to −3D, the focus position of the OCT optical system 200 is similarly controlled to be a position corresponding to −3D. In this case, the diopter conversion is performed between the moving position of the focusing lens 63 and the moving position of the focusing lens 24 so that the focus position of the OCT optical system 200 can be set to a focus position corresponding to the in-focus position of the SLO optical system 200. Correspondence is made.

  Thus, when the focusing lens 24 of the OCT optical system 200 is moved to the movement position corresponding to the in-focus position of the SLO optical system 300, the focusing lens 24 is moved to the vicinity of the in-focus position. The fundus reflection light incident on the end 39b increases.

  Here, after the focusing lens 24 is moved to the vicinity of the in-focus position, the control unit 70 acquires the reference mirror 51 as an optical path length variable optical member disposed in the OCT optical system 200 by the OCT optical system 200. The optical path length is automatically adjusted by moving based on the tomographic image. In this case, when the optical path length of the reference light and the optical path length of the measurement light substantially coincide with each other, the interference signal output from the light receiving element 83 can be acquired as a tomographic image of the fundus (hereinafter referred to as an OCT fundus image). .

  After the rough autofocus control is completed, the controller 70 controls the drive mechanism 50 to move the reference mirror 51 in the optical axis direction and change the optical path length of the reference light until an OCT fundus image is acquired. . FIG. 5 is a diagram showing a luminance distribution in the depth direction of the OCT image.

  Here, the control unit 70 detects the peak P1 of the luminance value in the depth direction of the OCT image acquired based on the interference signal from the light receiving element 83 while moving the reference mirror 51 in the optical axis direction. Whether or not an OCT fundus image is acquired is determined based on whether or not the value peak P1 exceeds a predetermined threshold value SP.

  Then, the control unit 70 determines that the OCT fundus image is acquired when the luminance value peak P1 exceeds the predetermined threshold value SP, and determines whether the OCT fundus image is a real image or a virtual image. judge. In this case, when the half width W with respect to the peak P1 is smaller than the predetermined allowable width, the OCT fundus image is determined as a real image. In the above description, the real image / virtual image is determined based on the half-value width W. However, the real image / virtual image is acquired based on the acquisition order of the real image / virtual image of the OCT fundus image sequentially acquired when the optical path length is changed. A virtual image may be determined.

  When it is determined that the real image has been acquired as described above, the control unit 70 regards the position where the luminance distribution peak P1 in the depth direction is detected as the image position as shown in FIG. A displacement amount between the set optical path length adjustment position (see dotted line K in FIG. 6) and the image position is calculated, and the reference mirror 31 is moved so that the displacement amount disappears.

  When the optical path length is adjusted as described above, the OCT fundus image is displayed on the monitor 75 together with the SLO fundus image. Here, the control unit 70 acquires focus position information of the OCT optical system 200 based on the tomographic image acquired after the automatic adjustment of the optical path length, and moves the focusing lens 24 to the focus position (OCT fundus image). Precise autofocus control).

  More specifically, the control unit 70 acquires histogram information of the OCT fundus image acquired by the OCT optical system 200. FIG. 7 is a diagram illustrating an example of a histogram of an image signal of an OCT fundus image acquired by the OCT optical system 200. In FIG. 7, the horizontal axis represents the luminance value k (k = 1, 2,... 254), the vertical axis represents the number of pixels H (k) at each luminance value, and the luminance value at which the number of pixels showed a peak. What is normalized by the number of pixels H (kp) (H (k) / H (kp)) is expressed in percentage (%). In addition, in the histogram of FIG. 7, the data of two points of the end points (k = 0, k = 255) are excluded.

  In the histogram H (k), when the focus is appropriate, the luminance level of the entire image increases, so the number of pixels having a larger luminance value increases, and the luminance of the entire image decreases as the focus shifts. The number of pixels with the larger luminance value decreases.

  Here, the control unit 70 evaluates the imaging state (focus state) of the OCT fundus image using the maximum value of the luminance value having the number of pixels equal to or higher than a predetermined ratio in the entire image in the histogram information acquired as described above. Calculate the value. For example, as the imaging state evaluation value C2 for evaluating the imaging state of the OCT fundus image, a difference between the maximum value Lmax and the minimum value Lmin of the luminance value at a threshold value S2 (for example, 5%) or more in the histogram is obtained ( C2 = Lmax−Lmin). The threshold value S2 is preferably set to a value such that the evaluation value C2 changes sensitively to changes in the imaging state of the OCT fundus image while avoiding the influence of noise. In the present embodiment, the threshold value S2 is set to about 5% because it corresponds to a portion of the entire OCT fundus image that has a large change in luminance value with respect to a change in focus position (particularly, the photoreceptor cell layer in the OCT fundus image) This is because the change of the luminance value in the region to be detected is detected with high accuracy. In the above description, the maximum value Lmax of the luminance values at or above the threshold value S2 (for example, 5%) may be set as the imaging state evaluation value C2.

  The imaging state evaluation value C2 shows a high value when the focusing lens 24 is in the in-focus position (when the OCT fundus image is in focus) and decreases as the focusing lens 24 deviates from the in-focus position. Therefore, it can be used to determine the focus state (image formation state) of the OCT fundus image.

  Here, the control unit 70 samples the imaging state evaluation value C2 while moving the position of the focusing lens 24 arranged in the light receiving optical system of the OCT optical system 200, determines the in-focus state based on the sampling result, and performs focusing. The lens 24 is driven to the in-focus position.

  For example, the control unit 70 drives and controls the drive mechanism 24 to search for an appropriate focus position of the OCT fundus image, and performs focusing corresponding to the in-focus position of the SLO optical system 300 by the first autofocus control described above. The focusing lens 24 is moved before and after the movement position of the lens 24, and an OCT fundus image is acquired for each movement position. Then, the control unit 70 creates a histogram of each acquired OCT fundus image and calculates an imaging state evaluation value C2.

  FIG. 8 is a graph showing the relationship between the imaging state evaluation value C2 and the movement position Z2. In FIG. 8, a 0.25D step within a predetermined range (for example, within a range of ± 2.0D) with respect to a position (−0.5D in FIG. 8) corresponding to the in-focus position of the SLO optical system 300. Then, the focusing lens 24 is moved to sequentially calculate the evaluation value C2.

  When the evaluation value C2 at each focus position is obtained as described above, an interpolation process is performed on the characteristics of the moving position Z2 of the focusing lens 24 and the evaluation value C2 obtained discretely, and the result of the OCT optical system 200 is obtained. Get focal position information. For example, the curve is approximated by a function having a maximum value in the moving range of the focusing lens 24, and the moving position Z2 at which the evaluation value C2 is maximum in this curve is detected as the in-focus position. As a method for detecting the in-focus position of the OCT optical system 200 by interpolation as described above, interpolation using function approximation, calculation of the center of gravity, average value, or the like can be considered.

  Next, the control unit 70 drives and controls the drive mechanism 24a, and moves the focusing lens 24 to a movement position corresponding to the in-focus position of the OCT optical system 200 acquired as described above, so that the OCT fundus image is obtained. The focus adjustment ends.

  Here, as shown in FIG. 9, when the focus of the OCT fundus image and the SLO fundus image displayed on the same screen is in an appropriate state, the examiner can view the SLO fundus image on the display monitor 75 observed in real time. The position of the tomographic image that the examiner wants to take is set. The examiner operates the measurement position setting switch 74b to move the line LS representing the measurement position (acquisition position) electrically displayed on the SLO fundus image on the screen with respect to the SLO fundus image, Set the measurement position. Then, the control unit 70 performs an XZ plane tomographic image capturing operation by B-scan based on the set measurement position.

  Here, when the line LS is moved with respect to the SLO fundus image by the examiner, the control unit 70 sets the measurement position at any time, and acquires the tomographic image at the corresponding measurement position. Then, the acquired tomographic image is displayed on the display screen of the monitor 75 as needed. Thus, the tomographic image desired by the examiner is displayed on the monitor 75, and when the imaging start switch 74 c is pressed by the examiner, the desired tomographic image and the front image are stored in the memory 72.

  With the above configuration, since the OCT fundus image can be focused smoothly, it is possible to easily capture an OCT tomographic image at a desired fundus site.

  Further, in the above description, the focus position information of the SLO optical system 300 is acquired based on the front fundus image acquired by the SLO optical system 300, and the focus position of the OCT optical system 100 is roughly set based on this information. Although it was supposed to be adjusted, it is not limited to this.

  More specifically, the front of the eye is illuminated by illuminating the entire fundus of the subject's eye with infrared light emitted from an infrared light source (for example, a halogen lamp, LED, etc.), and the fundus reflection light is imaged by a two-dimensional image sensor. The present invention can also be applied to a fundus imaging apparatus including an imaging optical system (so-called fundus camera optical system) that acquires a fundus image and an OCT optical system 200 that acquires an OCT fundus image using a low-coherent light source. . In this case, focus position information of the fundus camera optical system is acquired based on an infrared fundus image captured by a two-dimensional imaging device for capturing a front fundus image (for example, focusing based on the aforementioned SLO fundus image). Application of position detection method is conceivable). In this case, the method is not limited to the above method, and any method may be used as long as the focus position information of the fundus camera optical system is acquired based on the light reception result output from the light receiving element that receives the fundus reflection light. For example, a projection optical system that projects a focus index (for example, split index) on the fundus of the eye to be examined is provided, and an index image (fundus reflection image) of the fundus reflected light is received by the two-dimensional image sensor, and the two-dimensional image sensor The focus position information may be acquired based on the light reception result output from.

  In the above description, the focus is adjusted by moving the focusing lens 63 and the focusing lens 24 in the optical axis direction. However, if the focusing optical member can adjust the imaging state of the optical system, This is not a limitation. For example, it is conceivable to use a configuration in which a mirror unit that folds a received light beam by two mirrors is moved in the optical axis direction (see, for example, JP-A-2005-279121).

  In the above description, the focusing optical member is separately disposed in the OCT optical system 200 and the SLO optical system 300. However, the light source, the optical scanning system, etc. of the OCT optical system and the SLO optical system, etc. The present invention can be applied even when the focusing lens is arranged in the common optical path of the OCT optical system and the SLO optical system. In this case, when the shared focusing lens is moved in the optical axis direction, the focus states of the OCT optical system and the SLO optical system are changed. In such a configuration, when the OCT fundus image is acquired, the focusing lens is moved to the in-focus position of the OCT optical system, and when the SLO fundus image is acquired, the focusing lens is moved to the in-focus position of the SLO optical system. Control can be considered.

  In the above configuration, the focusing lens 63 may be moved based on the in-focus position specified using the OCT fundus image in order to perform the focus adjustment on the SLO fundus image with higher accuracy. More specifically, the focusing lens 63 may be moved to a movement position obtained by multiplying the movement position of the focusing lens 63 corresponding to the in-focus position specified using the OCT fundus image by a predetermined offset amount. Good. Note that the predetermined offset amount refers to the position of the moving position of the focusing lens 63 in consideration of focusing on the retina surface in the SLO optical system 300 while focusing on the inside of the retina in the OCT optical system 100. With respect to the adjustment, the focus position deviation amount is corrected with respect to the in-focus position specified based on the OCT fundus image.

  In the above description, when performing autofocus control on the OCT fundus image, precise autofocus control is performed based on the OCT fundus image acquired by the OCT optical system 300. However, autofocus on the SLO fundus image is performed. The focus position information of the interference optical system 300 is acquired by correcting the focus position information of the interference optical system 300 acquired based on the focus position information of the SLO optical system 200 by the control by a preset offset amount. Then, the focusing lens 24 arranged in the interference optical system 200 may be moved to the in-focus position.

  In addition, when performing autofocus with respect to an OCT image using the focus position information of the SLO optical system 300, it is not restricted to the said method, The focus position information of the SLO optical system 300 by the above-mentioned 1st autofocus control is used. The focus position information of the OCT optical system 200 is acquired by correcting the focus position information of the OCT optical system 200 acquired based on the offset amount set in advance, and the focusing lens 24 is moved to the focus position. You may do it.

  More specifically, an average value of the deviation amounts between the in-focus position of the SLO optical system 300 and the in-focus position of the OCT optical system 200 is obtained in advance by experiments and stored in the memory 72 in advance as an offset amount. The control unit 70 calculates the focus position of the OCT optical system 200 corresponding to the in-focus position of the SLO optical system 300 when the first autofocus control is performed, and then offsets the calculated focus position. The corrected focus position with the amount added is set as the focus position of the OCT optical system 200, and the focusing lens 24 is moved to the focus position. In this case, for example, when the offset amount obtained by experiment is +0 or 5D, when the focus position of the SLO optical system 300 is −2.5D, the focus position of the OCT optical system 200 is set as −2.0D. Is done.

  Note that, according to the present method, the focus accuracy may be inferior to the focus adjustment based on the OCT fundus image acquired by the OCT optical system 200 as described above, but the in-focus position of the SLO optical system 300 Since the focusing position subjected to the above correction is set as the focusing position of the OCT optical system 200, the focusing lens 24 is arranged at the focus position corresponding to the focusing position of the SLO optical system 300. Better focus accuracy can be obtained.

It is a figure which shows the optical system and control system of the fundus imaging apparatus of this embodiment. It is a figure explaining the operation | movement at the time of acquiring OCT image and SLO image (left side) sequentially. It is a figure which shows an example of the differential histogram after differentiating the image signal of the SLO fundus image acquired by the SLO optical system. It is a figure which shows an example of the graph which shows the relationship between the image formation state evaluation value C1 and the movement position Z1 of a focusing lens. It is a figure which shows the luminance distribution in the depth direction of an OCT image. It is a figure when the image position of the OCT fundus image displayed on the monitor is adjusted. It is a figure which shows an example of the histogram of the image signal of the OCT fundus image acquired by the OCT optical system. It is a graph which shows the relationship between the image formation state evaluation value C2 and the movement position Z2. It is a figure when an OCT fundus image and an SLO fundus image are displayed in parallel on a monitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 23 Scan part 24 Focusing lens 24a 2nd drive mechanism 27 OCT light source 61 SLO light source 63 Focusing lens 63a 1st drive mechanism 63 Scan part 70 Control part 200 OCT optical system 300 SLO optical system

Claims (5)

Fundus observation optics having an illumination optical system for irradiating illumination light to the fundus of the eye to be examined and a light receiving optical system having a first focusing optical member movable in the optical axis direction and receiving fundus reflected light by the first light receiving element. A fundus oculi observation means for obtaining a front fundus image of the eye to be examined based on a light reception signal output from the first light receiving element,
A second focus optical member movable in the optical axis direction and an optical path length variable optical member, splitting the light emitted from the light source into measurement light and reference light, and guiding the measurement light to the fundus of the eye to be examined; After the reference light is guided to the reference optical system, the second light receiving element has an interference optical system that detects the combined light of the measurement light reflected from the fundus and the reference light, and is output from the second light receiving element. Optical coherence tomography for obtaining a fundus tomographic image of the subject's eye based on the received light signal;
First autofocus means for acquiring in-focus position information with respect to the fundus of the fundus oculi observation optical system based on a light reception result output from the first light-receiving element, and moving the first focus optical member to the in-focus position; ,
After the second focus optical member is moved to the vicinity of the focus position based on the focus position information, the second focus optical member is further moved at a plurality of positions near the focus position. A second autofocus unit that acquires in-focus position information for the fundus of the interference optical system based on the acquired tomographic image, and moves the second focus optical member to the in-focus position. Fundus photographing device. 2. The fundus imaging apparatus according to claim 1, wherein the second auto-focusing unit moves the second focusing optical member to the vicinity of the in-focus position, and then moves the optical path length variable optical member to obtain at each position. The optical path length is automatically adjusted based on the tomographic image, and the second focusing optical member is moved, and the interference optical is based on the tomographic images acquired at a plurality of positions near the in-focus position. A fundus photographing apparatus characterized by acquiring in-focus position information for the fundus of the system and moving the second focusing optical member to the in-focus position. 3. The fundus imaging apparatus according to claim 2, wherein the second autofocus unit acquires in-focus position information with respect to the fundus of the interference optical system using luminance levels of the entire tomographic image acquired at a plurality of positions. A fundus imaging apparatus characterized by the above. Fundus observation optics having an illumination optical system for irradiating illumination light to the fundus of the eye to be examined and a light receiving optical system having a first focusing optical member movable in the optical axis direction and receiving fundus reflected light by the first light receiving element. A fundus oculi observation means for obtaining a front fundus image of the eye to be examined based on a light reception signal output from the first light receiving element,
A second focus optical member movable in the optical axis direction and an optical path length variable optical member, splitting the light emitted from the light source into measurement light and reference light, and guiding the measurement light to the fundus of the eye to be examined; After the reference light is guided to the reference optical system, the second light receiving element has an interference optical system that detects the combined light of the measurement light reflected from the fundus and the reference light, and is output from the second light receiving element. Optical coherence tomography for obtaining a fundus tomographic image of the subject's eye based on the received light signal;
First autofocus means for acquiring in-focus position information with respect to the fundus of the fundus oculi observation optical system based on a light reception result output from the first light-receiving element, and moving the first focus optical member to the in-focus position; ,
A focus position information for the fundus of the interference optical system is acquired by correcting the focus position information by a preset offset amount, and the second focus optical member is moved to the focus position. And an autofocus means. Having a focusing optical member that can move in the direction of the optical axis, splits the light emitted from the light source into measurement light and reference light, guides the measurement light to the fundus of the eye to be examined, guides the reference light to the reference optical system, An interference optical system that detects, by a light receiving element, a spectrum of light obtained by combining the measurement light reflected from the fundus and the reference light, and performs a Fourier transform on the light receiving signal output from the light receiving element to obtain a fundus tomography of the eye to be examined Optical coherence tomography to obtain images,
Moving the optical member for the focus, the evaluation value for evaluating the luminance level of the entire tomographic image acquired by the moving position of the interference optical system based on the obtained evaluation value at each moved position A fundus photographing apparatus comprising: autofocus means for acquiring focus position information with respect to the fundus and moving the focusing optical member to the focus position.