JP2016140388A - Ocular fundus imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a good ocular fundus image suitable for analysis on cells of ocular fundus.SOLUTION: An ocular fundus imaging apparatus 1 includes an imaging optical system 100 equipped with a light receiving element 56 for receiving light reflected from an eye to be examined in a state that the wavefront aberration is compensated for by a wavefront compensation device 72, a signal amplification part 57 for outputting an amplified light receiving signal which is a signal amplifying the amplitude of a light receiving signal output from the light receiving element 56, and an A/D converter 58 and a control part 800 for quantizing the amplified light receiving signal in a predetermined gradation range, and importing it as a cell image. The control part 800 analyzes the imported cell image, acquires the gradation distribution in a part or all of the region in the cell image as a histogram, and controls the signal amplification part on the basis of the histogram so that at least one of offset and gain for amplifying the light receiving signal is adjusted. The ocular fundus imaging apparatus 1 further imports a new cell image after the signal amplification part 57 is adjusted.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a fundus imaging apparatus that captures a fundus image of a subject's eye while correcting wavefront aberration of the subject's eye.

  2. Description of the Related Art There is known an apparatus that detects wavefront aberration of an eye using a wavefront sensor such as a Shack-Hartmann sensor, controls a wavefront compensation device based on the detection result, and photographs a fundus image after wavefront compensation at a cellular level. The fundus image obtained by such an apparatus can be used, for example, for analysis processing relating to cells of the fundus such as cell density analysis (see Patent Document 1).

JP 2014-110825 A

  Here, in the fundus image, when the so-called overexposure occurs due to too bright, or the so-called blackout occurs due to insufficient brightness, each cell becomes difficult to be detected properly. As a result, for example, an appropriate processing result may not be obtained by the analysis processing related to the cells. In order to obtain a good processing result in the analysis processing, it is necessary to consider the contrast of the image.

  An object of the present disclosure is to provide a fundus imaging apparatus capable of obtaining a good fundus image suitable for analysis related to cells of the fundus in view of the problems of the conventional technology.

  A fundus imaging apparatus according to a first aspect of the present disclosure is an ophthalmologic imaging apparatus that acquires a cell image that forms a predetermined part of an eye to be examined, and is obtained from a subject eye in a state where wavefront aberration is compensated for by a wavefront compensation device. An imaging optical system including a light receiving element that receives reflected light, a signal amplification unit that outputs an amplified light reception signal that is an amplified signal of the light reception signal output from the light reception element, and amplified light reception from the signal amplification unit An image forming unit for quantizing a signal in a predetermined gradation range and taking it in as a cell image, and analyzing a cell image acquired by the image forming unit to generate a gradation distribution in a part or all of the cell image Is acquired as a histogram relating to the number of pixels for each gradation value in the cell image, and the light amplification signal is amplified by controlling the signal amplification unit based on the histogram. And an amplification control unit that adjusts at least one of offset and gain, and the image forming unit newly captures the cell image after the signal amplification unit is adjusted by the amplification control unit .

  According to the fundus imaging apparatus of the present disclosure, there is an effect that a good fundus image suitable for analysis related to cells of the fundus can be obtained.

It is the schematic diagram which showed the optical system of the fundus imaging apparatus in this embodiment. It is the figure which showed an example of the 1st fundus image. It is the block diagram which showed the control system of the fundus imaging apparatus. In particular, FIG. 3 is a diagram showing in more detail the configuration of the circuit used for forming the first fundus image (AO-SLO image). It is the flowchart which showed an example of the main process performed by the control part. It is the flowchart which showed an example of the amplification control process. It is an example of the histogram in the gradation distribution of the 1st fundus image, and shows an example of the histogram when the amplification control in the signal amplification unit is appropriate. It is an example of the histogram in the gradation distribution of the 1st fundus image, and shows an example of the histogram in the 1st fundus image in which both overexposure and blackout occur. It is an example of the histogram in the gradation distribution of the 1st fundus image, and shows an example of the histogram in the 1st fundus image in which overexposure occurs. It is an example of the histogram in the gradation distribution of the 1st fundus image, and shows an example of the histogram in the 1st fundus image in which blackout has occurred. It is an example of the histogram in the gradation distribution of the 1st fundus image, and shows an example of the histogram in the 1st fundus image in a state where the gain is too high. It is the figure which showed an example of the 1st fundus image when ROI is set.

  In the following, exemplary embodiments will be described with reference to the drawings. The fundus imaging apparatus 1 is a fundus imaging apparatus with wavefront aberration compensation (AO-SLO) that captures a fundus image of the eye to be examined while correcting the wavefront aberration of the eye to be examined.

  First, the optical system of the fundus imaging apparatus 1 will be described with reference to FIG. The imaging apparatus 1 of the present embodiment includes a fundus imaging optical system 100, a wavefront aberration detection optical system (hereinafter referred to as an aberration detection optical system) 110, aberration compensation units 20, 72, and a second imaging unit 200. An anterior ocular segment observation unit 700.

  The fundus imaging optical system 100 projects laser light (illumination light) on the eye E and receives reflected light from the fundus of the laser light to capture a fundus image of the eye E. The fundus of the eye E is photographed by the fundus imaging optical system 100 with high resolution (high resolution) and high magnification. As described below, the fundus imaging optical system 100 may have a configuration of a scanning laser ophthalmoscope using a confocal optical system, for example. The fundus imaging optical system 100 includes a first illumination optical system 100a and a first imaging optical system 100b. In the present embodiment, the aberration compensation units 20 and 72 are arranged in the fundus imaging optical system 100 in order to correct the aberration of the eye to be examined. The aberration compensation unit includes a diopter correction unit 20 for correcting low-order aberrations (diopter: for example, spherical power) of the eye to be examined and high-order aberration compensation for correcting high-order aberrations of the eye to be examined. Part (wavefront compensation device) 72.

  The first illumination optical system 100a illuminates the fundus two-dimensionally by irradiating the eye E with laser light and scanning the laser light on the fundus. The first illumination optical system 100a includes a light source 11, a lens 12, a polarization beam splitter (PBS) 14, a beam splitter (BS) 71, a concave mirror 16, in an optical path from the light source 11 (first light source) to the fundus. Concave mirror 17, flat mirror 18, aberration compensation unit 72 (wavefront compensation device 72), beam splitter (BS) 75, concave mirror 21, concave mirror 22, scanning unit 25, concave mirror 26, concave mirror 27, flat mirror 31, Lens 32, plane mirror 33, aberration compensation unit 20 (diopter correction unit 20), plane mirror 35, concave mirror 36, deflection unit 400, dichroic mirror 90, concave mirror 41, plane mirror 42, plane mirror 43, and concave surface A mirror 45.

  The light source 11 emits laser light. The laser light emitted from the light source 11 is converted into parallel light by the lens 12 and then enters the wavefront compensation device 72 via the PBS 14, BS 71, concave mirrors 16 and 17, and the flat mirror 18. In the present embodiment, the laser light passes through the PBS 14 and becomes a light beam having only an S-polarized component. The wavefront compensation device 72 corrects higher-order aberrations of the eye to be examined by controlling the wavefront of the incident light. The detailed configuration of the wavefront compensation device 72 will be described later. In the present embodiment, the laser light is guided from the wavefront compensation device 72 to the BS 75, reflected by the concave mirror 21 and the concave mirror 22, and travels toward the scanning unit 25.

  In the present embodiment, the scanning unit 25 is used together with the deflecting unit 400 in order to scan laser light two-dimensionally on the fundus. The scanning unit 25 is a resonant mirror used for main scanning of laser light. The laser light is scanned in the X direction on the fundus by the scanning unit 25.

  The light that has passed through the scanning unit 25 enters the diopter correction unit 20 via the concave mirrors 26 and 27, the plane mirror 31, the lens 32, and the plane mirror 33.

  The diopter correction unit 20 is a unit for performing diopter correction. The diopter correction unit 20 includes a pair of lenses and plane mirrors in addition to the drive unit 20a. The optical path length is adjusted by moving the plane mirror and lens of the diopter correction unit 20 in a predetermined direction by the drive unit 20a. As a result, the diopter error of the eye E is corrected.

  The illumination light guided from the diopter correction unit 20 to the plane mirror 35 is reflected by the concave mirror 36 and travels toward the deflection unit 400.

  The deflection unit 400 scans the laser light emitted from the light source 11 in the vertical direction (Y direction) on the fundus. Furthermore, the deflecting unit 400 is also used to move the scanning range of the laser light on the fundus. For example, in the present embodiment, the deflecting unit 400 may include two optical scanners (specifically, an X galvanometer mirror and a Y galvanometer mirror) having different directions of deflecting laser light.

  The light that has passed through the deflecting unit 400 is guided into the pupil of the eye E through the dichroic mirror 90, the concave mirror 41, the plane mirrors 42 and 43, and the concave mirror 45. The laser light is collected on the fundus of the eye E. As described above, the laser beam is two-dimensionally scanned on the fundus by the operations of the scanning unit 25 and the deflecting unit 400.

  Further, the dichroic mirror 90 has a characteristic of transmitting a light beam from the second photographing unit 200 described later and reflecting a light beam from the light source 11 and a light source 76 described later. Note that the emission ends of the light sources 11 and 76 and the fundus of the eye E are conjugate. In this way, the first illumination optical system 100a is formed.

  Next, the first photographing optical system 100b will be described. The first imaging optical system 100 b receives the reflected light of the laser light irradiated on the fundus by the light receiving element 56. The fundus imaging apparatus 1 acquires a first fundus image (in this embodiment, an AO-SLO image, see FIG. 2) based on a signal from the light receiving element 56. The first imaging optical system 100b shares the optical path from the eye E to the BS 71 with the first illumination optical system 100a. The first imaging optical system 100 includes elements arranged in the reflection side optical path of the BS 71, that is, a plane mirror 51, a PBS 52, a lens 53, a pinhole plate 54, a lens 55, and a light receiving element 56. . In this embodiment, the light receiving element 56 is an APD (avalanche photodiode). Further, the pinhole plate 54 is placed at a position conjugate with the fundus.

  The fundus reflection light of the laser light from the light source 11 traces the first illumination optical system 100 a in the reverse direction, is reflected by the BS 71 and the flat mirror 51, and only the S-polarized light is transmitted by the PBS 52. This transmitted light is focused on the pinhole of the pinhole plate 54 via the lens 53. The reflected light focused by the pinhole is received by the light receiving element 56 through the lens 55. A part of the illumination light is reflected on the cornea, but most of the illumination light is removed by the pinhole plate 54. Therefore, the light receiving element 56 can receive the reflected light from the fundus while suppressing the influence of corneal reflection.

  As will be described in detail later, the first fundus image is formed by processing the light reception signal from the light receiving element 56 by an image processing unit (for example, the control unit 800). In this embodiment, a fundus image of one frame is formed by main scanning of the scanning unit 25 and sub-scanning of a Y-scan galvanometer mirror provided in the deflection unit 400. Note that the deflection angle (swing angle) of the mirror in the scanning unit 25 and the deflection unit 400 is determined so that the angle of view of the fundus image (fundus image) acquired by the first imaging unit 100 becomes a predetermined angle. Here, in order to observe and photograph a predetermined range of the fundus at a high magnification (here, observation at a cell level or the like), the angle of view is set to about 1 to 5 degrees. In this embodiment, the angle is 1.5 degrees. Although depending on the diopter of the eye to be examined, the imaging range of the first fundus image is about 500 μm square.

  Further, when the reflection angle of the X-scanning galvanometer mirror and the Y-scanning galvanometer mirror provided in the deflection unit 400 is moved larger than the imaging field angle of the first fundus image, the first fundus image is captured on the fundus. The position (that is, the scanning range of the laser beam) is changed.

  The second photographing unit 200 is a unit for obtaining a fundus image (second fundus image) having a wider angle of view than the angle of view of the first photographing unit 100. The second fundus image is used, for example, as an image for position designation and position confirmation for obtaining the first fundus image. The second imaging unit 200 of the present embodiment preferably has a configuration capable of acquiring and observing a fundus image of the eye E to be examined in real time with a wide angle of view (for example, about 20 to 60 degrees). For example, as the second imaging unit 200, an observation / imaging optical system of an existing fundus camera and an optical system and a control system of a scanning laser ophthalmoscope (SLO) may be used.

  The anterior segment observation unit 700 is a unit that illuminates the anterior segment of the eye E with visible light and captures a front image of the anterior segment. An image captured by the anterior segment observation unit 700 is output to the monitor 850. The anterior ocular segment image acquired by the anterior ocular segment observation unit 700 is used for alignment between the imaging unit 500 and the eye E to be examined. The dichroic mirror 95 has a characteristic of transmitting the light beam from the second photographing unit 200 and reflecting the light beam from the anterior ocular segment observation unit 700.

  Next, the aberration detection optical system 110 will be described. The aberration detection optical system 110 includes a wavefront sensor 73. The aberration detection optical system 110 projects measurement light onto the fundus of the eye E, and receives (detects) the fundus reflection light of the measurement light as an index pattern image with the wavefront sensor 73. The aberration detection optical system 110 has a part of optical elements on the optical path of the first illumination optical system 100a and the first photographing optical system 100b (in the present embodiment, on the common optical path), and the optical paths of the optical systems 100a and 100b. Some are shared. That is, the aberration detection optical system 110 of the present embodiment shares the BS 71 to the concave mirror 45 arranged on the optical path of the optical systems 100a and 100b with the optical systems 100a and 100b. Further, the aberration detection optical system 110 includes a light source 76, a lens 77, PBS 78, BS 75, BS 71, a dichroic mirror 86, a PBS 85, a lens 84, a plane mirror 83, and a lens 82.

  The light source 76 is used for detecting the aberration of the eye E. In the present embodiment, the light source 76 emits light having a wavelength different from that of the light source 11. The measurement light emitted from the light source 76 is converted into a parallel light beam by the lens 77 and then incident on the PBS 78.

  The PBS 78 is an example of first polarization means provided in the wavefront compensation unit. The PBS 78 polarizes the light emitted from the light source 76 in a predetermined direction. More specifically, the PBS 78 is polarized in a direction (ie, P-polarized light) orthogonal to the polarization direction (ie, S-polarized light) of the PBS 14. The light that has passed through the PBS 78 is reflected by the BS 75 and guided to the optical path of the first illumination optical system 100a. As a result, the measurement light is condensed on the fundus of the eye E through the optical path of the first illumination optical system 100a.

  The measurement light is reflected at the condensing position of the fundus (for example, the retina surface). The fundus reflection light of the measurement light follows the optical path of the first illumination optical system 100a (that is, the optical path of the first photographing optical system 100b) in the opposite direction to that during projection. On the way, the measurement light is reflected by the wavefront compensation device 72. Thereafter, the measurement light is reflected by the BS 71, thereby deviating from the optical path of the first illumination optical system 100a. Thereafter, the measurement light is reflected by the dichroic mirror 86 and guided to the wavefront sensor 73 through the PBS 85, the lens 84, the plane mirror 83, and the lens 82.

  The PBS 85 is a second polarization unit provided in the wavefront compensation unit. The PBS 85 is used to guide light to the wavefront sensor 73 by transmitting light polarized in one direction (here, S-polarized light) out of the light irradiated to the eye E from the light source 76. The The PBS 85 blocks a component polarized in a direction orthogonal to the transmitted component (P-polarized light). The dichroic mirror 86 has a characteristic of transmitting light (840 nm) having the wavelength of the light source 11 and reflecting light (780 nm) having the wavelength of the light source 76 for detecting aberration. Therefore, the wavefront sensor 73 detects light having an S-polarized component from the fundus reflection light of the measurement light. In this way, light reflected by the cornea and the optical element is suppressed from being detected by the wavefront sensor 73.

  The wavefront sensor 73 receives fundus reflection light of measurement light for aberration measurement in order to detect wavefront aberration of the eye E. As the wavefront sensor 73, an element that can detect wavefront aberration including low-order aberration and high-order aberration (more specifically, a Hartmann Shack detector, a wavefront curvature sensor that detects a change in light intensity, and the like) is used. May be. In the present embodiment, the wavefront sensor 73 includes, for example, a microlens array composed of a number of microlenses, a two-dimensional imaging element 73a (or a two-dimensional light receiving element) for receiving a light beam that has passed through the microlens array, Have The microlens array of the wavefront sensor 73 is disposed at a position substantially conjugate with the pupil of the eye E to be examined. Further, the imaging surface (light receiving surface) of the two-dimensional imaging element 73a is disposed at a position substantially conjugate with the fundus of the eye E to be examined.

  An index pattern image 61 (Hartmann image in this embodiment) is formed on the imaging surface of the two-dimensional imaging element 73a by the light beam that has passed through the microlens array (not shown). Therefore, the fundus reflection light passes through the microlens array and is received by the two-dimensional imaging element 73a, thereby being imaged as a Hartmann image (dot pattern image). In the present embodiment, the aberration information of the eye to be examined is acquired from the Hartmann image, and the wavefront compensation device 72 is controlled based on the aberration information. Details of the Hartmann image will be described later.

  The wavefront compensation device 72 is disposed in the optical path of the fundus imaging optical system 100, and compensates the wavefront aberration of the eye E by controlling the wavefront of the incident light. In the present embodiment, a liquid crystal spatial light modulator may be used for the wavefront compensation device 72. As an example, a description will be given below assuming that a reflective LCOS (Liquid Crystal On Silicon) or the like is used. In this case, the wavefront compensation device 72 has predetermined laser light (S-polarized light) from the light source 11, fundus reflected light (S-polarized light) of the laser light, reflected light (S-polarized component) of wavefront aberration detection light, and the like. Are arranged in a direction capable of correcting the aberration with respect to the linearly polarized light (S-polarized light). As a result, the wavefront compensation device 72 can modulate the S-polarized component of the incident light. In the present embodiment, the reflection surface of the wavefront compensation device 72 is arranged at a position that is substantially conjugate with the pupil of the eye to be examined.

  In the wavefront compensation device 72 of the present embodiment, the alignment direction of the liquid crystal molecules in the liquid crystal layer is substantially parallel to the polarization plane of incident reflected light. The predetermined plane on which the liquid crystal molecules rotate according to the change in the voltage applied to the liquid crystal layer includes the incident optical axis and the reflected optical axis of the fundus reflection light with respect to the wavefront compensation device 72, and the mirror layer of the wavefront compensation device 72. And a plane that includes the normal line.

  In this embodiment, the wavefront compensation device 72 is a liquid crystal modulation element, and in particular, a reflective LCOS or the like is used, but the present invention is not limited to this. Other reflective wavefront compensation devices may be used. For example, a deformable mirror that is a form of MEMS (Micro Electro Mechanical Systems) may be used. Further, a transmissive wavefront compensation device may be used instead of the reflective wavefront compensation device. In the transmission type device, the wavefront aberration is compensated by transmitting the reflected light from the fundus.

  In the above description, a light source that emits illumination light having a wavelength different from that of the first light source is used as the aberration detection light source. However, the first light source may also serve as the aberration detection light source.

  In the present embodiment described above, the wavefront sensor and the wavefront compensation device are the pupil conjugate of the eye to be examined. However, the position may be a position that is substantially conjugate with a predetermined part of the anterior eye portion of the eye to be examined. There may be.

  Next, with reference to the block diagram of FIG. 3, the electrical configuration of the fundus imaging apparatus 1 of the present embodiment will be described. The fundus imaging apparatus 1 includes a control unit 800 (calculation control unit). The control unit 800 is a processor that performs overall control and arithmetic processing in the fundus imaging apparatus 1. The control unit 800 is composed of, for example, a combination of a CPU and a memory. In the present embodiment, the control unit 800 also serves as an image processing unit that performs image processing such as formation of various first fundus images. However, the present invention is not necessarily limited to this, and an image processing circuit that performs various types of image processing may be provided separately from the control unit 800.

  In the present embodiment, a storage unit 801, an operation input unit 802, and a monitor 850 are electrically connected to the control unit 800. In addition, the light source 1, the drive unit 10 a, the scanning unit 15, the wavefront compensation device 72, the wavefront sensor 73, the light source 76, the second imaging unit 200, and the deflection unit 400 are electrically connected to the control unit 800. In addition, the light receiving element 56, the signal amplifying unit 57, and an analog / digital converter 58 (hereinafter abbreviated as “A / D converter”) are connected in series to the control unit 800. In the present embodiment, the image forming unit for quantizing the amplified light reception signal from the signal amplifying unit 57 and capturing it as an image (specifically, a cell image) expressed with a predetermined gradation is A / D for convenience. It is assumed that the converter 58 and the control unit 800 are combined.

  The storage unit 801 stores various control programs and fixed data. Further, the storage unit 801 may store an image photographed by the fundus photographing apparatus 1, temporary data, and the like.

  The control unit 800 controls each member described above such as the first imaging unit 100 based on the operation signal output from the operation input unit 802. The operation input unit 802 includes an operation member such as a mouse (not shown) as an operation member operated by the examiner.

  The monitor 850 may be a display monitor mounted on the fundus photographing apparatus 1 or may be a general-purpose display monitor that is separate from the fundus photographing apparatus 1. Moreover, the structure in which these were used together may be sufficient. The monitor 850 can display fundus images (first fundus image and second fundus image) captured by the fundus imaging apparatus 1 as moving images and still images.

  The control of the wavefront compensation device 72 by the controller 800 is executed based on the wavefront aberration detected by the wavefront sensor 73. In the present embodiment, feedback control of the wavefront compensation device 72 based on the detection signal from the wavefront sensor 73 is performed. By controlling the wavefront compensation device 72, the high-order aberrations of the laser light emitted from the light source 1 and the fundus reflection light of the laser light are removed together with the S-polarized component of the reflected light of the light source 76. In this way, the aberrations of the laser light emitted from the light source 1 and the fundus reflection light of the laser light are removed. As a result, a high-resolution first fundus image (that is, a wavefront compensated image) from which high-order aberrations of the eye E are removed (wavefront compensated) is acquired by the fundus imaging apparatus 1. At this time, the low-order aberration is corrected by the diopter correction unit 10.

  The signal amplification unit 57 outputs an amplified light reception signal that is a signal obtained by amplifying the amplitude of the light reception signal output from the light receiving element 56. The amplified received light signal is quantized (analog / digital converted) at a predetermined gradation (that is, a range of gradation values) by the A / D converter 58 and then acquired by the control unit 800. As a result, the control unit 800 forms a pixel having a gradation value corresponding to the amplitude of the amplified light reception signal. In the first embodiment, the gradation is determined based on the signal input range and signal resolution in the A / D converter 57 (for example, 256 gradations). Then, the control unit 800 forms a first fundus image of one frame based on pixels generated from the amplified light reception signal for one frame. In this manner, the amplified light reception signal is captured as a cell image represented by a predetermined gradation by the A / D converter 58 and the control unit 800 (that is, the image forming unit in the present embodiment).

  As shown in FIG. 4, the signal amplification unit 57 receives a control signal from the control unit 800. Thereby, the signal amplifying unit 57 can adjust the offset and gain with respect to the input (that is, the light reception signal) based on the control signal from the control unit 800. An example of a specific configuration of such a signal amplifying unit 57 is shown in FIG. For example, the signal amplifier 57 may be formed by a combination of a multiplier 57a and an adder 57b inserted in series between the light receiving element 56 and the A / D converter 58. For example, in the signal amplifying unit 57 of FIG. 4, the signal from the light receiving element 56 is input to the multiplier 57a. Further, the signal amplified by the multiplier 57a is input to the adder 57b. As a result, the signal amplitude multiplication by the multiplier 57a and the offset by the adder 57b are performed independently. In the example of FIG. 4, the control unit 800 individually adjusts the offset and the gain by individually outputting control signals to the adder 57b and the multiplier 57a.

  The operation of the present apparatus having the above configuration will be described with reference to the flowchart shown in FIG. The fundus imaging apparatus 1 operates according to a control program stored in the storage unit 801 after the power is turned on.

  First, the imaging unit 500 is aligned with the eye E (S1). For example, the control unit 800 acquires a real-time anterior segment image using the anterior segment observation unit 700 and causes the monitor 850 to display the anterior segment image. The examiner performs alignment by manually or automatically adjusting the position of the chin rest 610 while observing the anterior segment image on the monitor 850. In this case, the examiner instructs the subject to fixate a fixation target (not shown).

  In the present embodiment, after the alignment is completed, when the start switch provided in the operation input unit 802 is operated by the examiner, acquisition of the first fundus image using the first imaging unit 100 is started.

  First, the control unit 800 starts wavefront compensation control (S2). Thus, the wavefront aberration of the eye to be examined is sequentially detected by the wavefront sensor 73, and the wavefront compensation device 72 is sequentially driven based on the detection result. As a result, the reflected light from the eye to be examined in a state where the wavefront aberration is compensated is received by the light receiving element 56. Therefore, the influence of wavefront aberration is suppressed in the first fundus image formed by the image forming unit. In addition, the control unit 800 may automatically perform diopter correction by controlling the diopter correction unit 10 based on the result of wavefront detection of the eye E. In addition, after the process of S2 is performed, wavefront compensation control shall be performed sequentially in parallel with each process mentioned later.

  Next, the control unit 800 repeatedly executes the processing from S3 to S5 until an imaging instruction is input (that is, until S5: Yes), and sequentially performs amplification control of the light reception signal from the light receiving element 56. The first fundus image is sequentially generated.

  In the loop processing from S3 to S5, the control unit 800 first forms a first fundus image. More specifically, the control unit 800 performs a quantized light reception signal (more specifically, output from the A / D converter 58) for each scan of one frame using the scanning unit 25 and the deflection unit 400. One first fundus image is formed based on the amplified light reception signal. In the present embodiment, the gradation value of each pixel in the first fundus image is represented by a value in the range of 0 to 255. In this embodiment, it is assumed that the brighter pixel has a higher gradation value and the darker pixel has a lower gradation value. In addition, the control unit 800 causes the monitor 850 to display the formed first fundus image. Note that the range of gradation values representing the first fundus image is not limited to the above-described 0 to 255 (that is, 256 gradations), and other ranges such as 0 to 511 (that is, 512 gradations) are possible. A range of gradation values may be employed. Moreover, the structure which selects the range of the gradation value showing a 1st fundus image from several candidates according to the operation input from an examiner may be sufficient.

  Next, the control unit 800 performs an amplification control process (S4). Thereby, the amplification degree of the light reception signal output from the light receiving element 56 is adjusted in the signal amplification unit 57. In the amplification control process (S4) in the present embodiment, at least one of the offset and the gain is adjusted based on the gradation distribution of the first fundus image. As described above, in the present embodiment, the capture of the first fundus image and the amplification control of the received light signal based on the captured first fundus image are repeatedly performed until the photographing instruction is input. . As a result, a good first fundus image suitable for cell-related analysis can be obtained (details will be described later).

  Here, an example of processing included in the amplification control processing (S4) will be described with reference to FIG.

  In the example of FIG. 6, first, the control unit 800 analyzes the first fundus image captured in advance by the process of S3, and acquires the gradation distribution in the first fundus image (S21). In this case, in this embodiment, the control unit 800 acquires a histogram (for example, see FIGS. 7A to 7E) indicating the number of pixels of the first fundus image for each gradation value. However, the bins constituting the histogram need not be set for each gradation value, and may be set for every certain width (for example, every five gradations).

  Next, the control unit 800 analyzes the histogram and acquires boundary values (Lpv, Hpv) that define a range of gradation values in which pixels are distributed in the histogram (that is, a pixel distribution range) (S22). As shown in FIGS. 7A to 7E, Lpv and Hpv are the gradation value at the low luminance side end and the gradation value at the high luminance side end in the pixel distribution range in the histogram, respectively.

  More specific definition of the boundary values (Lpv, Hpv) can be appropriately set by a so-called person skilled in the art. At this time, the calculation may be performed in consideration of noise, device characteristics, and the like. For example, the maximum value and minimum value of the distribution may be simply set as the boundary values (Lpv, Hpv) of the distribution range. Each boundary value (Lpv, Hpv) is the median (or average value, mode value, etc.) side from the maximum and minimum values of the distribution by the number of bins (for example, only three). May be determined as the value of. The boundary values (Lpv, Hpv) may be determined in consideration of the cumulative frequency (number of pixels) for each gradation value. For example, about 99.98% of the number of pixels in the first cell image is included between Lpv and Hpv, and the number of pixels outside Lpv and Hpv is, for example, about 0.01% each. Boundary values (Lpv, Hpv) may be determined. Furthermore, a boundary value (Lpv, Hpv) may be obtained by obtaining a histogram from the binned first fundus image.

  In the amplification control process (S4), one of the offset and the gain is adjusted by the processes after S23. Although details will be described later, in the present embodiment, the control unit 800 has the high luminance side boundary Hpv lower than the maximum gradation value (255) that can be taken in the first fundus image, and the low luminance side boundary Lpv in the first fundus image. It is set higher than the minimum gradation value (0) that can be taken.

  In the present embodiment, the control unit 800 adjusts at least one of the offset and the gain so that the difference between Hpv and Lpv is larger than the threshold value Wth. The threshold value Wth may be a threshold value for identifying each cell included in the cell image in the cell analysis. For example, in the analysis process, when the photoreceptor cell is identified by detecting the cell apex (cell center), the gray level of the apex portion of the cell and the peripheral portion surrounding the apex portion are different in the detection range. The value that can be displayed with is preferably set as Wth.

  Here, the threshold value Wth is closer to a value indicating the difference between the maximum gradation value and the minimum gradation value in the gradation range representing the first cell image (for example, the first fundus image is represented by 256 gradations). In this case, the closer to 256), the first fundus image can be expressed with many gradations. Therefore, the cell can be analyzed better. However, in this case, it is difficult for the histogram to converge to a constant state. That is, the image quality of the first fundus image acquired sequentially is likely to be unstable. In addition, it takes a long time to stabilize. That is, there is a trade-off relationship between the stability of the image quality and the range of gradation values that are substantially used for cell rendering in the first fundus image. In order to obtain the first fundus image in which the image quality is quickly stabilized and the cells are expressed in many gradations, for example, the maximum gradation value and the minimum gradation value in the gradation range representing the first cell image are obtained. It is preferable to set Wth to a value of 70% or more and 90% or less of the difference (more preferably, 75% or more and 85% or less). In the present embodiment, a value of about 80 percent (for example, about 200) is set as the threshold value Wth. However, the above preferable range is an example, and the preferable range of the threshold value Wth may vary depending on the characteristics of the signal amplification unit 57, the processing speed of the control unit 80, and the like.

  In the example of FIG. 6, the control unit 800 performs the processing of S23 so that the gradation value Hpv of the high luminance side boundary in the histogram distribution range is the maximum gradation value 255 and the low luminance side boundary in the histogram distribution range. It is determined whether or not the tone value Lpv is the minimum tone value 0 (S23). The histogram when Hpv is the maximum gradation value 255 and Lpv is the minimum gradation value 0 (S23: Yes) is, for example, as shown in FIG. 7B. That is, in this case, the gain is high, and it is considered that both blackout and whiteout occur in the first fundus image. Therefore, in this case (S23: Yes), the control unit 800 decreases the gain (S28). As a result, in the first fundus image acquired thereafter, blackout and overexposure are reduced. Then, the amplification control process (S4) is terminated, and the process proceeds to S5 (see FIG. 5).

  If Hpv is not the maximum gradation value 255 and / or Lpv is not the minimum gradation value 0 (S23: No), the determination process of S24 is executed. That is, it is determined whether or not Hpv is the maximum gradation value 255 (S24). In the present embodiment, since S23: No is determined before S24 is determined, when Hpv is determined to be the maximum gradation value 255 (S24: Yes), Lpv is the minimum gradation value. It is a value other than 0. In this case, the histogram is as shown in FIG. 7C, for example. That is, in this case, the offset is high, and it is considered that overexposure occurs in the first fundus image. Therefore, in this case (S24: Yes), the control unit 800 decreases the offset (S29). Thereby, overexposure is suppressed. Then, the amplification control process (S4) is terminated, and the process proceeds to S5 (see FIG. 5).

  On the other hand, when it is determined that Hpv is not the maximum gradation value 255 (S24: No), the determination process of S25 is executed. That is, it is determined whether Lpv is the minimum gradation value 0 (S25). In this embodiment, since S23: No is determined before S24 is determined, when it is determined that Lpv is the minimum gradation value 0 (S25: Yes), Hpv is the maximum floor. It is a value other than the adjustment value 255. In this case, the histogram is as shown in FIG. 7D, for example. That is, in this case, the offset is low, and it is considered that blackout occurs in the first fundus image. Therefore, in this case (S25: Yes), the control unit 800 increases the offset (S30). This suppresses black crushing. Then, the amplification control process (S4) is terminated, and the process proceeds to S5 (see FIG. 5).

  Further, when it is determined in S25 that Lpv is different from the minimum gradation value 0 (S25: No), the control unit 800 further sets Lpv to the lowest reduction brightness in the cells of the first fundus image. It is determined whether or not it is larger than a threshold value Lth (third threshold value) (S26). The threshold value Lth is set to stabilize the gradation value (so-called black level) of the low luminance part of the first fundus image. For example, the difference between the maximum gradation value and the minimum gradation value in the gradation value range representing the first fundus image may be set to a value of about 3%, for example. In the case of S23: No and S24: No, the determination of S25 is performed. In this case, it is considered that neither overexposure nor underexposure occurs in the first fundus image. However, if it is determined in the process of S25 that Lpv> Lth (that is, S26: Yes), it is considered that the overall brightness (brightness) of the image is high and the contrast is low. Therefore, in this embodiment, in this case (S26: Yes), the offset is lowered (S31). As a result, the black level of the first fundus image can be made constant for each image and the contrast can be improved. Thereafter, the amplification control process (S4) is terminated, and the process proceeds to S5 (see FIG. 5).

  In S26, when it is determined that Lpv is equal to or less than the threshold value Lth (S26: No), the process of S27 is performed. In S27, it is determined whether or not the difference between Hpv and Lpv is smaller than the threshold value Wth. If Hpv−Lpv <Wth (S27: Yes), the first fundus image has substantially fewer tones than Wth. In this case, for example, the histogram is as shown in FIG. 7E. Therefore, in this case (S27: Yes), the control unit 800 increases the gradation that is substantially used by increasing the gain (S32). Thereby, in the first fundus image, the cells are represented using abundant gradations. Thereafter, the amplification control process (S4) is terminated, and the process proceeds to S5 (see FIG. 5). Moreover, also in the process of S27, also when it determines with the difference of Hpv and Lpv being larger than the threshold value Wth, an amplification control process (S4) is complete | finished and it transfers to the process of S5.

  Of the above amplification control process (S4), the amount of change in offset, gain, or both adjusted in each process of S28 to S32 may be a constant value. Further, control for adjusting the amount of change according to the state of the histogram may be performed. More specific values can be appropriately set according to the processing speed of the controller 800, the characteristics of the adder 57b and the multiplier 57a, and the like. By appropriately setting the target change amount, the offset and gain adjustment can be completed in a short time (that is, the offset and gain values are converged). Further, the order and contents of the processing in S4 are not limited to the above. It can be changed as appropriate according to the characteristics of the apparatus and the target time until the adjustment is completed. For example, in the present embodiment, a case has been described in which adjustment of only one of the offset and gain is executed each time the amplification control process S4 is executed once. However, the present invention is not necessarily limited to this, and both the offset and gain may be adjusted.

  Returning to FIG. As described above, the control unit 800 alternately and repeatedly performs capture of the first fundus image (S3) and adjustment of the received light signal amplification amount by amplification control processing (S4). Therefore, a new first fundus image is captured in a state where the amplification amount of the received light signal is adjusted based on the first fundus image acquired previously. By repeating this, as a result, a good first fundus image suitable for cell analysis is obtained. More specifically, it is possible to obtain a first fundus image that has less overexposure and underexposure and is represented using at least more gradations than the threshold value Wth. In the present embodiment, since wavefront compensation control is performed, the state of the first fundus image sequentially changes according to the change in the driving state of the wavefront compensation device 72. However, even for such an image, the amplification control of the received light signal is effective in obtaining a good first fundus image.

  In the present embodiment, the acquisition of the first fundus image (S3) and the amplification control process (S4) are performed in parallel with the wavefront compensation control. That is, by correcting the wavefront, the first fundus image is captured in a state where the intensity of light received by the light receiving element 56 is appropriately increased. Therefore, the offset and gain can be adjusted based on a good first fundus image. As a result, the offset and gain tend to converge quickly.

  The examiner confirms the first fundus image displayed on the monitor 850, and inputs an imaging instruction to the operation input unit 802 when the amplification adjustment by the control unit 800 has settled. Thereby, the photographing process of the first fundus image is performed (S6). For example, the control unit 800 may obtain the plurality of images as the captured images of the first fundus image by capturing the first fundus image a plurality of times at the same position of the eye E. In addition, an averaged image obtained by performing an averaging process on a plurality of first fundus images may be generated as a captured image.

  Thereafter, the control unit 800 may perform image processing (for example, analysis processing) on cells (for example, photoreceptor cells and blood vessel cells) that form the fundus using the captured image of the first fundus image (S7). ). Here, as a specific example, a case where a photoreceptor cell image is obtained as a photographed image of the first fundus image and analysis on photoreceptor cells is performed will be described. In analysis relating to photoreceptor cells, for example, the number and density of photoreceptor cells may be analyzed. In such a case, it is important to accurately detect photoreceptor cells. In the first fundus image (see FIG. 2), the photoreceptor is indicated by reference numeral 901. The photoreceptor cell 901 is shown as an image in which the central portion (cell apex) of the cell is brighter than the outside. In the present embodiment, as a result of the above amplification control process, the brightness of the photoreceptor cell can be stabilized, and many gradations are used in the first fundus image. As a result, the difference in brightness between the central portion and the outer portion of the photoreceptor cell can be clarified, so that the photoreceptor cell can be easily detected. As a result, an accurate analysis result can be obtained.

  Although the description has been given based on the embodiment, the technique according to the embodiment may be modified as follows.

  For example, in the above-described embodiment, the case where the amplification amount of the received light signal is adjusted based on the gradation distribution in the entire range of the first fundus image has been described. However, the present invention is not necessarily limited to this, and the amplification amount of the received light signal may be adjusted based on the gradation distribution in a part of the first fundus image. In this case, in the first fundus image, the range in which the tone distribution is used to adjust the amplification amount (that is, the region of interest, hereinafter referred to as ROI) is a range specified by the examiner via a mouse or the like. There may be. Here, FIG. 10 shows an example of a fundus image in which the ROI is set. As shown in FIG. 10, the ROI may be set for a range desired by the examiner in the first fundus image. Further, the ROI range specification may be combined with the analysis range specification in S7. In this case, since the contrast and gradation are well set in the region that the examiner wants to analyze, the analysis result for the intended region can be obtained with high accuracy. For example, when such a ROI is set at a dense location of the photoreceptor cells 901, each photoreceptor cell at the dense location is clarified. Can be clarified.

  Further, in the first fundus image, an identification display for identifying the ROI in the first fundus image may be attached to a location designated as the ROI. As shown in FIG. 10, the identification display may be a line L surrounding the ROI setting range, or may be a display mode in which the ROI setting range is distinguished from the surroundings by different colors or the like.

  Further, the offset and gain set in the previous shooting are stored in the storage unit as shooting condition data, and the offset and gain of the previous shooting stored as shooting condition data can be used in the subsequent shooting. It may be a configuration. For example, when the adjustment of the offset and the gain is completed (for example, when the values of the offset and the gain are converged), the control unit 800 receives the imaging instruction or inputs the imaging condition storage instruction from the examiner. In this case, the offset and gain adjustment amounts at that time may be stored. In the case of performing at the same shooting position as this time, it is useful to reproduce the adjustment amount stored in advance. That is, the time required for adjusting the amplification amount of the received light signal can be shortened. Also, since images with the same shooting conditions are obtained, this is useful when comparing images shot at different times (for example, during follow-up shooting).

  Further, the first embodiment is a configuration capable of switching between a first shooting mode that is a shooting mode that performs offset and gain adjustment control and a second shooting mode that is a shooting mode in which the adjustment control is not performed. Also good. For example, as shown in the above embodiment, offset and gain adjustment control is useful when analyzing cells. However, the brightness of the image itself can be an important index for diagnosis of small mouth disease and the like. Therefore, in this case, it is preferable not to perform the above adjustment control. Therefore, in such a case, the control unit 800 may set the second mode based on an input instruction from the examiner so that imaging is performed with the offset and gain set to the specified values. Good.

  In the above embodiment, in the histogram of the first fundus image, the high luminance side boundary Hpv of the distribution range in which the pixels are distributed is lower than the maximum gradation value 255, and the low luminance side boundary Lpv of the distribution range is the minimum gradation value 0. Offset and gain so that the difference Hpv-Lpv between the gradation value of the high-luminance side boundary and the gradation value of the low-luminance side boundary is larger than the threshold value Wth for distinguishing cells. The case of adjusting at least one of the above has been described. However, the method for controlling the amplification amount of the received light signal is not necessarily limited to this. For example, the control unit 800 adjusts the gain so that the difference Hpv−Lpv between the gradation value of the high luminance side boundary and the gradation value of the low luminance side boundary is larger than the threshold value Wth, and the histogram or At least one of the offset and the gain is adjusted so that the number of pixels distributed in the maximum gradation region and the minimum gradation region in the pixel distribution range in the histogram is equal to or less than a predetermined threshold (second threshold). May be. Here, the maximum gradation area and the minimum gradation area may be areas extending over a plurality of gradation values (or bins). The maximum gradation area in the histogram may be an area corresponding to the gradation value 255 or a range of gradation values in the vicinity thereof as long as the gradation is 256 levels, and the minimum gradation area in the histogram is It may be a region corresponding to a gradation value range of 0 or a gradation value in the vicinity thereof. Further, the maximum gradation area in the distribution range may be an area corresponding to the range of gradation values in Hpv or the vicinity thereof, and the minimum gradation area in the distribution range is a range of gradation values in the vicinity of Lpv. It may be a region corresponding to. The second threshold value is, for example, a small value (for example, a value of 1/100 or less) with respect to the number of pixels obtained by dividing the total number of pixels constituting the histogram by the number of histogram bins. The value of the second threshold value may be appropriately determined in relation to the required accuracy, and may be, for example, about several percent (for example, 0.01 percent) of the pixels forming the histogram. Also by such processing, a good cell image suitable for cell-related analysis can be obtained as in the above embodiment.

DESCRIPTION OF SYMBOLS 56 Light receiving element 57 Signal amplification part 58 A / D converter 72 Wavefront compensation device 73 Wavefront sensor 100 Fundus imaging optical system 110 Wavefront aberration detection optical system 800 Control part 801 Storage part 802 Operation input part

Claims (17)

An ophthalmologic imaging apparatus that acquires a cell image forming a predetermined part of an eye to be examined,
An imaging optical system including a light receiving element that receives reflected light from the eye to be examined in a state where wavefront aberration is compensated by the wavefront compensation device;
A signal amplification unit that outputs an amplified light reception signal that is a signal obtained by amplifying the amplitude of the light reception signal output from the light receiving element;
An image forming unit for quantizing the amplified received light signal from the signal amplification unit in a predetermined gradation range and capturing it as a cell image;
Analyzing the cell image acquired by the image forming unit, acquiring a gradation distribution in a part or all of the region of the cell image as a histogram relating to the number of pixels for each gradation value in the cell image, and the signal amplification An amplification control unit that adjusts at least one of an offset and a gain for amplifying the received light signal by controlling a unit based on the histogram,
The fundus imaging apparatus, wherein the image forming unit captures the cell image newly after the signal amplification unit is adjusted by the amplification control unit.   In the histogram, the amplification control unit calculates a difference between a gradation value of a high luminance side boundary of a distribution range in which pixels are distributed and a gradation value of a low luminance side boundary of the distribution range in the cell analysis. The fundus imaging apparatus according to claim 1, wherein at least one of the offset and the gain is adjusted so as to be larger than a first threshold value for identifying each cell included in.   The amplification controller adjusts at least one of the offset and the gain so that the number of pixels distributed in the maximum gradation region and the minimum gradation region in the distribution range or the minimum gradation region is equal to or less than a second threshold value. The fundus imaging apparatus according to claim 1, wherein:   In the histogram, the amplification control unit is configured such that a high luminance side boundary of a distribution range in which pixels are distributed is lower than a maximum gradation value in the predetermined gradation range, and a low luminance side boundary of the distribution range is the predetermined gradation. 4. The fundus imaging apparatus according to claim 1, wherein at least one of the offset and the gain is adjusted to be higher than a minimum gradation value in the range.   In the histogram, the amplification control unit is configured such that a high luminance side boundary of a distribution range in which pixels are distributed is lower than a maximum gradation value in the predetermined gradation range, and a low luminance side boundary of the distribution range is the predetermined gradation. The difference between the gradation value of the high luminance side boundary and the gradation value of the low luminance side boundary of the distribution range is set to be higher than the minimum gradation value in the range, and each cell included in the cell image in the cell analysis process The fundus imaging apparatus according to claim 1, wherein at least one of the offset and the gain is adjusted to be larger than a first threshold value for distinguishing cells.   In the histogram, the amplification control unit is configured such that a high luminance side boundary of a distribution range in which pixels are distributed is lower than a maximum gradation value in the predetermined gradation range, and a low luminance side boundary of the distribution range is the predetermined gradation. The offset and the number of pixels distributed in the maximum gradation region and the minimum gradation region in the distribution range or lower than the second threshold are set higher than the minimum gradation value in the range. The fundus imaging apparatus according to claim 1, wherein at least one of the gains is adjusted. The amplification controller is
The gradation value of the high luminance side boundary in the histogram distribution range is the maximum gradation value in the predetermined boundary range, and the gradation value of the low luminance side boundary in the histogram distribution range is the predetermined gradation. The fundus imaging apparatus according to any one of claims 4 to 6, wherein the gain is lowered when the gradation value is the minimum gradation value in the range. The amplification controller is
The gradation value of the high luminance side boundary in the histogram distribution range is the maximum gradation value in the predetermined gradation range, and the gradation value of the low luminance side boundary in the histogram distribution range is the predetermined level. If it is different from the minimum gradation value in the key range, lower the offset,
The gradation value of the low luminance side boundary in the histogram distribution range is the minimum gradation value in the predetermined gradation range, and the gradation value of the high luminance side boundary in the histogram distribution range is the predetermined level. The fundus imaging apparatus according to any one of claims 4 to 7, wherein the offset is increased when the gradation value is different from the maximum gradation value in the gradation range. The amplification control unit further includes:
If the gradation value at the low luminance side boundary in the distribution range of the histogram is larger than the third threshold value set on the high luminance side with respect to the minimum gradation value in the predetermined gradation range, the offset is decreased. The fundus imaging apparatus according to claim 8. The amplification controller is
The gain is increased when a difference between a gradation value at the high luminance side boundary and a gradation value at the low luminance side boundary is smaller than the first threshold value. Fundus photographing device.   The first threshold value is set to a value in a range of 70% or more and less than 90% with respect to a value indicating a difference between a maximum gradation value and a minimum gradation value in a predetermined gradation range. The fundus imaging apparatus according to any one of claims 2, 5, and 10. A wavefront detector for detecting wavefront aberration of the eye to be examined;
A wavefront compensation controller that sequentially drives the wavefront compensation device based on the wavefront aberration detected by the wavefront detector;
The image forming unit sequentially forms the cell image,
The amplification control unit sequentially controls the signal amplification unit in parallel with the drive control of the wavefront compensation device based on the sequentially formed cell images. Fundus photographing device. A region setting means for setting a region of interest for the cell image;
The fundus imaging according to any one of claims 1 to 11, wherein the amplification control unit adjusts an offset and a gain based on a gradation distribution in the attention area when the attention area is set. apparatus.   The fundus imaging according to claim 13, wherein the image forming unit sets an identification display for identifying the attention area in the cell image for the cell image when the attention area is set. apparatus. Imaging condition storage means for storing the offset and gain set in the imaging of the cell image in the storage unit as imaging condition data;
A first imaging mode that reproduces offset and gain based on the imaging condition data stored in advance in the storage unit when acquiring a new cell image; and a second imaging mode that does not reproduce offset and gain The fundus photographing apparatus according to claim 1, further comprising photographing mode switching means for switching between and. It has an operation input section for manually adjusting the offset and gain,
The fundus imaging apparatus according to claim 15, wherein the amplification control unit sets an offset and a gain according to a signal from the operation input unit when the second imaging mode is set.   The fundus imaging apparatus according to claim 1, further comprising an image analysis unit that performs the cell analysis using the cell image formed by the image forming unit.