Patent Publication Number: US-9888846-B2

Title: Ophthalmological apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an ophthalmological apparatus that optically inspects a subject&#39;s eye. 
     Description of the Related Art 
     The ophthalmological apparatus includes an ophthalmological imaging device for acquiring an image of a subject&#39;s eye, and an ophthalmological measuring device for measuring characteristics of the subject&#39;s eye. 
     Examples of the ophthalmological imaging device are as follows: an optical coherence tomograph that acquires a tomographic image by using optical coherence tomography (OCT); a fundus camera for photographing a fundus; a scanning laser ophthalmoscope (SLO) that acquires an image of a fundus by using laser scanning with a confocal optical system; a slit lamp that acquires an image by using slit light to cut off an optical section of a cornea; and the like. 
     In addition, examples of the ophthalmological measuring device are as follows: an inspection device for refraction of eye (a refraction meter, or a keratometer) that measures refraction characteristics of a subject&#39;s eye; a tonometer; a specular microscope that acquires characteristics of a cornea (such as cornea thickness, and cell distribution); a wavefront analyzer that acquires aberration information on a subject&#39;s eye by using a Hartmann-Shack sensor; and the like. 
     In an ophthalmological inspection using these devices above, from a viewpoint of accuracy and correctness of an inspection, positioning of an optical system for inspection (device optical system) and a subject&#39;s eye is very important. This positioning is called alignment. The alignment includes operation of aligning an optical axis of the optical system for inspection with an axis of the subject&#39;s eye (xy-alignment), and operation of adjusting a distance between the subject&#39;s eye and the optical system for inspection (z-alignment). 
     There is known a conventional ophthalmological apparatus including an alignment optical system that projects an alignment index (such as luminous point alignment) for positioning of an optical system for inspection with respect to a subject&#39;s eye on the subject&#39;s eye (refer to Japanese Patent Laid-Open No. 2010-181172, for example). In this ophthalmological apparatus, while an observation image of a subject&#39;s eye, displayed in a monitor, is observed, positioning of optical system for inspection with respect to a subject&#39;s eye is performed by operating a control lever to three-dimensionally move the optical system for inspection so that two alignment index images enter within an alignment reference position mark (an alignment scale). 
     SUMMARY OF THE INVENTION 
     In the conventional ophthalmological apparatus, when a central portion of a fundus is photographed, a vision fixation target is projected toward a subject&#39;s eye from a direction along an optical axis of the optical system for inspection in advance so that a line of sight of the subject&#39;s eye is aligned with the optical axis of the optical system for inspection before photograph. On the other hand, when a peripheral portion of the fundus is photographed, the vision fixation target is projected from a direction different from the optical axis of the optical system for inspection so that the line of sight of the subject&#39;s eye is pointed to the direction different from the optical axis of the optical system for inspection, and then photographing is performed. At this time, while a tip of a cornea and a center of a pupil agree with each other at the time when the central portion of the fundus is photographed, the tip of the cornea and the center of the pupil are displaced from each other in a case where the peripheral portion of the fundus is photographed. In this case, if the optical system for inspection is aligned with the tip of the cornea, there is a possibility that illumination light for the fundus may be blocked by an iris. Thus, when the peripheral portion of the fundus is photographed, an alignment reference position is changed so that the optical system for inspection is aligned with a portion abound the center of the pupil. 
     Unfortunately, in this kind of conventional ophthalmological apparatus, if positional displacement of an optical system for inspection with respect to a subject&#39;s eye is large, one or two alignment index images may be eliminated from a screen of a monitor. In particular, when a peripheral portion of a fundus is photographed, photographing is performed in a state where a line of sight of a subject&#39;s eye is pointed to a direction different from an optical axis of an optical system for inspection as described above. As a result, as an alignment reference position changes, an alignment index image projected in a peripheral portion of a cornea tends to be easily eliminated from a screen of the monitor. Since this kind of case is difficult to understand for a person unskilled in operation, there is a possibility that even if alignment of the optical system for inspection with respect to the subject&#39;s eye is improper, it may be identified as proper by mistake. In addition, it is necessary that an operator moves the optical system for inspection until two alignment index images appear in a screen of the monitor while repeating trial and error on the basis of experience and intuition of the operator, whereby it takes time to adjust alignment. 
     Meanwhile, there are conventional ophthalmological apparatuses each of which has a different type of method of displaying an alignment index image. For example, in the conventional ophthalmological apparatus described above, a distance between two alignment index images changes in accordance with a position of the optical system for inspection in a direction of an optical axis with respect to a subject&#39;s eye. Specifically, if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is improper, the two alignment index images are displayed while being away from each other, and if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is proper, the two alignment index images are displayed while agreeing with each other. In another conventional ophthalmological apparatus, if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is proper, the two alignment index images are displayed while being away from each other, and then a size of each of the alignment index images changes in accordance with the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye. 
     Since there are the conventional ophthalmological apparatuses, each of which has a different type of method of displaying an alignment index image, an operator, who is familiar with alignment operation of any one of the methods of display, may feel that it is hard to perform the alignment operation by the other of the methods of display. Thus, it is required to efficiently perform the alignment operation with a familiar operational feeling. 
     Unfortunately, in order to allow the conventional ophthalmological apparatus to prepare a plurality of methods of displaying an alignment index image to allow a user to arbitrarily select a method, an alignment optical system corresponding to each of the methods of display is required. As a result, there is a problem in which an increase in the number of components, or the like, causes costs to increase as well as the apparatus to increase in size. 
     The present invention is made in light of the above-mentioned circumstances, and it is an object to provide an ophthalmological apparatus capable of smoothly and easily performing alignment of an optical system for inspection with respect to a subject&#39;s eye by hand with an operational feeling similar to that of conventional apparatuses without causing costs to increase as well as the apparatus to increase in size. 
     In order to achieve the object described above, an ophthalmological apparatus in accordance with a first aspect of the present invention includes: an optical system for inspection including a photographic optical system for photographing a fundus of a subject&#39;s eye; a display device that displays a fundus image of the subject&#39;s eye acquired by the photographic optical system; a subject&#39;s eye position acquisition processor that acquires a three-dimensional position of the subject&#39;s eye; and a control processor that acquires information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye on the basis of the three-dimensional position to allow an alignment index image for performing alignment of the optical system for inspection with respect to the subject&#39;s eye in accordance with the information on positional displacement to be displayed in a screen of the display device in a pseudo manner, and in the ophthalmological apparatus, the control processor has a plurality of display modes, in each of which the alignment index image is displayed in a different display form to allow the alignment index image to be displayed in a display mode selected from the plurality of display modes. 
     In the first aspect, an ophthalmological apparatus in accordance with a second aspect of the present invention includes a display mode selection processor that selects one display mode from among the plurality of display modes in response to user operation, and in the ophthalmological apparatus, the control processor allows the alignment index image to be displayed in the display mode selected by the display mode selection processor. 
     In the first or second aspect, an ophthalmological apparatus in accordance with a third aspect of the present invention allows the control processor to change a distance between a pair of alignment index images in accordance with a position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye if a first display mode is selected from the plurality of display modes. 
     In the third aspect, an ophthalmological apparatus in accordance with a fourth aspect of the present invention allows the control processor to allow the pair of alignment index images to be displayed while the pair of alignment index images are away from each other if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is improper, as well as allows the control processor to allow the pair of alignment index images to be displayed while the pair of alignment index images agree with each other if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is proper. 
     In any one of the first to fourth aspects, an ophthalmological apparatus in accordance with a fifth aspect of the present invention allows the control processor to change a size of the alignment index images in accordance with the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye if a second display mode is selected from the plurality of display modes. 
     In the fifth aspect, an ophthalmological apparatus in accordance with a sixth aspect of the present invention allows the control processor to allow the alignment index image to be displayed at a first size if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is improper, as well as allows the control processor to allow the alignment index image to be displayed at a second size smaller than the first size if the position of the optical system for inspection in the direction of the optical axis with respect to the subject&#39;s eye is proper. 
     In any one of the first to sixth aspects, an ophthalmological apparatus in accordance with a seventh aspect of the present invention allows the subject&#39;s eye position acquisition processor to include two or more photographing devices each of which substantially simultaneously photographs an anterior eye of the subject&#39;s eye from a different direction, and an analysis processor that analyzes photographed images acquired by the two or more photographing devices to acquire a three-dimensional position of the subject&#39;s eye. 
     According to the present invention, it is possible to smoothly and easily perform alignment of an optical system for inspection with respect to a subject&#39;s eye by hand with a familiar operational feeling without causing costs to increase as well as the apparatus to increase in size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing an example of an entire configuration of an embodiment of an ophthalmological apparatus in accordance with the present invention; 
         FIG. 2  is a schematic view showing an example of a configuration of an OCT unit in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 3  is a schematic block diagram view showing an example of a configuration of a control system of the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 4A  is a schematic view showing an example of an appearance configuration of the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 4B  is a schematic view showing an example of an appearance configuration of the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 5A  is a schematic view to describe processing performed in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 5B  is a schematic view to describe processing performed in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 6A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 6B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 7A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 7B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 8A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 8B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 9  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 10  is a flow chart showing an example of operation of the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 11  is a schematic view showing an example of a display mode selection screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 12A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 12B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 13  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 14  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 15  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 16A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 16B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; 
         FIG. 17A  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention; and 
         FIG. 17B  is a schematic view showing an example of a display screen in the embodiment of the ophthalmological apparatus in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An example of an ophthalmological apparatus in accordance with an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The ophthalmological apparatus in accordance with the present invention is used for an optical inspection of a subject&#39;s eye. This kind of ophthalmological apparatus includes an ophthalmological imaging device, and an ophthalmological measuring device, as described before. The ophthalmological imaging device includes such as an optical coherence tomograph, a fundus camera, a scanning laser ophthalmoscope, and a slit lamp. The ophthalmological measuring device includes such as an inspection device for refraction of eye, a tonometer, a specular microscope, and a wavefront analyzer. Although the embodiments below describe in detail in a case where the present invention is applied to an optical coherence tomograph, the present invention is applicable to any another ophthalmological apparatus. 
     In the present specification, an image acquired by the OCT may be collectively called an OCT image. In addition, measurement operation to form an OCT image may be called OCT measurement. Contents of a description of a document described in the present specification may be appropriately applied as contents of the embodiment below. 
     Although the embodiment below describes an optical coherence tomograph that is provided with a low coherence light source and a spectroscope, and that uses an OCT of so-called a spectral domain type, the present invention is applicable to an optical coherence tomograph using an OCT method of a type other than the spectral domain type, such as a swept source type, and an en-face type. The swept source OCT is a method of sweeping wavelengths of light emitted to an object to be measured (wavelength sweep) to detect an interfering light acquired by superimposing a reflected light each of lights with the respective wavelengths and a reference light to acquire spectra intensity distribution, and then in the method, Fourier transform is applied to the spectra intensity distribution to image a form of the object to be measured. The en-face OCT is a method of emitting light with a predetermined beam diameter to an object to be measured to analyze components of an interfering light acquired by superimposing a reflected light of the emitted light and a reference light to form an image of the object to be measured in a cross section orthogonal to a direction of travel of the light, and the method is also called a full-field type. 
     Although the embodiment below describes an apparatus that is a combination of an OCT device and a fundus camera, an application item of the present invention is not limited to this kind of complex machine, the present invention is also applicable to an ophthalmological apparatus as a single machine (such as a fundus camera alone). 
     (Configuration) 
     As shown in  FIG. 1 , an ophthalmological apparatus  1  includes a fundus camera unit  2 , an OCT unit  100 , and a calculation control unit  200 . The fundus camera unit  2  has an optical system that is almost the same as that of a conventional fundus camera. The OCT unit  100  is provided with an optical system for acquiring an OCT image of a fundus. The calculation control unit  200  includes a computer that performs various calculation processes, control processes, and the like. 
     (Fundus Camera Unit) 
     The fundus camera unit  2  shown in  FIG. 1  is provided with an optical system for acquiring a two-dimensional image (fundus image) showing a surface form of a fundus Ef of a subject&#39;s eye E. The fundus image includes images such as an observation image and a photographed image. The observation image is a monochrome dynamic image formed by using near infrared light at a predetermined frame rate, for example. If the optical system is focused on an anterior eye Ea of the subject&#39;s eye E, the fundus camera unit  2  is able to acquire an observation image of the anterior eye Ea. The photographed image, for example, may be a color image acquired by flashing visible light, or a monochrome still image acquired by using near infrared light or visible light as illumination light. The fundus camera unit  2  may be configured to be able to acquire images other than the above, such as a fluorescein fluorescent image, an indocyanine green fluorescent image, and a spontaneous emission fluorescent image. 
     The fundus camera unit  2  is provided with a chin mount and a forehead pad to support a face of a subject. The chin mount and the forehead pad correspond to a support part  440  shown in  FIGS. 4A and 4B . In  FIGS. 4A and 4B , reference numerals  410 ,  420 , and  430 , designate: a base that stores a driving system, such as an optical system driving unit  2 A and a calculation control circuit; a body provided on the base  410  to store an optical system; and a lens accommodation unit that is provided so as to project from a front face of the body  420  to store an objective lens  22 , respectively. 
     The fundus camera unit  2  is provided with an illumination optical system  10  and a photographic optical system  30 . The illumination optical system  10  emits illumination light to the fundus Ef. The photographic optical system  30  guides light reflected by the fundus in the illumination light to imaging devices (CCD image sensors  35  and  38 , or may be simply called CCDs). The photographic optical system  30  guides signal light from the OCT unit  100  to the fundus Ef as well as the signal light passing through the fundus Ef to the OCT unit  100 . 
     An observation light source  11  of the illumination optical system  10  is composed of a halogen lamp, for example. Light outputted from the observation light source  11  (observation illumination light) is reflected by a reflection mirror  12  with a curved reflection surface to pass through a visible light cut filter  14  via a condenser lens  13  to become near infrared light. In addition, the observation illumination light temporarily converges at a portion near a photographing light source  15  to be reflected by a mirror  16  to pass through relay lenses  17  and  18 , a diaphragm  19 , and a relay lens  20 . Then the observation illumination light is reflected by a peripheral portion in a mirror with an aperture  21  (an area of a periphery of the aperture) to pass through a dichroic mirror  46  to be refracted by the objective lens  22  to illuminate the fundus Ef. For the observation light source, a light emitting diode (LED) is also available. 
     Light reflected by the fundus in the observation illumination light is refracted by the objective lens  22  to pass through the dichroic mirror  46  to pass through an aperture formed in a center area of the mirror with an aperture  21 , and then passes through a dichroic mirror  55  to be reflected by a mirror  32  via a focal lens  31 . In addition, the light reflected by the fundus passes through a half mirror  39 A to be reflected by a dichroic mirror  33 , and then is imaged in a receiving surface of a CCD image sensor  35  through a condenser lens  34 . The CCD image sensor  35  detects the light reflected by the fundus at a predetermined frame rate, for example. A display device  3  displays an image (observation image) based on the light reflected by the fundus detected by the CCD image sensor  35 . If the photographic optical system is focused on the anterior eye, an observation image of the anterior eye of the subject&#39;s eye E is displayed. 
     The photographing light source  15  is composed of a xenon lamp, for example. Light outputted from the photographing light source  15  (photographing illumination light) passes through a path, as with observation illumination light, to be emitted to the fundus Ef. The light reflected by the fundus in the photographing illumination light passes through a path, as with the observation illumination light, to be guided to the dichroic mirror  33  to pass through the dichroic mirror  33 , and then is reflected by a mirror  36  to be imaged in a receiving surface of a CCD image sensor  38  through a condenser lens  37 . The display device  3  displays an image (photographed image) based on the light reflected by the fundus detected by the CCD image sensor  38 . The display devices  3  for displaying the observation image and the photographed image may be the same or different. In a case where the subject&#39;s eye E is illuminated with infrared light to perform similar photographing, an infrared photographed image is displayed. An LED is also available for the photographing light source. 
     A liquid crystal display (LCD)  39  displays a vision fixation target and an index of eyesight measurement. The vision fixation target is an index for vision fixation of the subject&#39;s eye E to be used at the time of fundus photographing, OCT measurement, or the like. 
     A part of light outputted from the LCD  39  is reflected by the half mirror  39 A to be reflected by the mirror  32 , and then passes through the aperture of the mirror with an aperture  21  via the focal lens  31  and the dichroic mirror  55  to pass through the dichroic mirror  46 , and subsequently is refracted by the objective lens  22  to be projected on the fundus Ef. 
     Changing a display position of the vision fixation target in a screen of the LCD  39  enables a projection direction of the vision fixation target with respect to the subject&#39;s eye E, or a vision fixation position of the subject&#39;s eye E, to be changed. For example, as with a conventional fundus camera, the vision fixation position of the subject&#39;s eye E includes positions, such as: a position for acquiring an image in which a macula lutea of the fundus Ef is centered; a position for acquiring an image in which an optic disk is centered; and a position for acquiring an image in which the center of the fundus, positioned between the macula lutea and the optic disk, is centered. In addition, it is also possible to arbitrarily change the display position of the vision fixation target. A configuration for vision fixation of the subject&#39;s eye E corresponds to an example of “Vision Fixation Optical System”. 
     Means for projecting a vision fixation target on the subject&#39;s eye E is not limited to the above. For example, providing a LED group composed of an array of a plurality of LEDs to allow the LEDs to selectively light enables a vision fixation position to be changed. In addition, providing one or more movable LEDs also enables a vision fixation position to be changed. 
     The fundus camera unit  2  includes a focus optical system  60 . The focus optical system  60  creates an index (split index) for focusing on the fundus Ef. 
     When focus adjustment is performed, a reflection surface of a reflection bar  67  is provided at an angle in an optical path of the illumination optical system  10 . Light (focus light) outputted from a LED  61  of the focus optical system  60  passes through a relay lens  62  to be split into two pencils of light by a split index plate  63  to pass through a two-aperture diaphragm  64 , and then is reflected by a mirror  65  to be temporarily imaged on the reflection surface of the reflection bar  67  through a condenser lens  66  to be reflected. Then, the focus light is reflected by the mirror with an aperture  21  via the relay lens  20  to pass through the dichroic mirror  46 , and then is refracted by the objective lens  22  to be projected on the fundus Ef. 
     Light reflected by the fundus in the focus light passes through a path, as with light reflected a cornea in alignment light, to be detected by the CCD image sensor  35 . A light-receiving image (split index) created by the CCD image sensor  35  is displayed in the display device  3  together with the observation image. The calculation control unit  200 , as before, analyzes a position of the split index to allow the focal lens  31  and the focus optical system  60  to move for focusing (autofocus function). The focusing may be manually performed while the split index is visually identified. 
     The dichroic mirror  46  allows an optical path for OCT measurement to branch from an optical path for fundus photographing. The dichroic mirror  46  reflects light within a wavelength range to be used for the OCT measurement, and allows light for fundus photographing to pass therethrough. The optical path for OCT measurement includes a collimator lens unit  40 , an optical path length change unit  41 , a galvanoscanner  42 , a focal lens  43 , a mirror  44 , and a relay lens  45 , in order from an OCT unit  100  side. 
     The optical path length change unit  41  is movable in a direction of an arrow shown in  FIG. 1  to change length of the optical path for OCT measurement. This change in length of the optical path is used for correction of length of the optical path in accordance with eye axial length of the subject&#39;s eye E, adjustment of conditions of interference, and the like. The optical path length change unit  41  includes, for example, a corner cube, and a mechanism for moving the corner cube. 
     The galvanoscanner  42  changes a direction of travel of light (signal light LS) passing through the optical path for OCT measurement. Accordingly, it is possible to scan the fundus Ef with the signal light LS. The galvanoscanner  42  includes, for example, a galvanomirror that allows the signal light LS to sweep in an x-direction, a galvanomirror that allows the signal light LS to sweep in a y-direction, and a mechanism for independently driving the galvanomirrors. Accordingly, it is possible to allow the signal light LS to sweep in any direction in an xy-plane. 
     The fundus camera unit  2  includes an anterior eye camera  300 . The anterior eye camera  300  substantially simultaneously photographs the anterior eye Ea from different directions. In this embodiment, the fundus camera unit  2  is provided in its face on a subject side with two cameras (refer to anterior eye cameras  300 A and  300 B shown in  FIG. 4A ). Each of the anterior eye cameras  300 A and  300 B, as shown in  FIGS. 1 and 4A , is provided at a position away from the optical path of the illumination optical system  10  and an optical path of the photographic optical system  30 . Hereinafter, the two anterior eye cameras  300 A and  300 B may be collectively designated by a reference numeral  300 . 
     Although the two anterior eye cameras  300 A and  300 B are provided in this embodiment, the number of anterior eye cameras in the present invention is an arbitrary number of two or more. However, in consideration of calculation processing described later, even configuration capable of substantially simultaneously photographing an anterior eye from two different directions is available. In addition, in this embodiment, although the illumination optical system  10  and the photographic optical system  30  are individually provided with the anterior eye camera  300 , at least the photographic optical system  30  enables similar anterior eye photographing to be performed. Thus, a configuration in which one of two or more anterior eye cameras is provided in the photographic optical system  30  may be available. That is, this embodiment allows any configuration capable of substantially simultaneously photographing an anterior eye from two (or more) different directions. 
     The term, “substantially simultaneously”, shows that a deviation of photographing timing that is negligible compared with eye movement is allowed in photographing with two or more anterior eye cameras. Accordingly, it is possible to acquire images at the time when the subject&#39;s eye E is at substantially the same position (direction) with two or more anterior eye cameras. 
     Although the photographing with two or more anterior eye cameras is available for taking a moving image and a still image, this embodiment will particularly describe a case of taking a moving image in detail. In a case of taking a moving image, control of matching timing of starting taking the image, and of a frame rate and timing of taking an image at each frame, enables photographing of an anterior eye of the “substantially simultaneously” described above to be achieved. Meanwhile, in a case of taking a still image, control of matching timing of starting taking the image enables the photographing of an anterior eye described above. 
     This embodiment, as described in detail later, enables positioning (alignment) of an optical system for inspection with respect to the subject&#39;s eye E to be performed by using two anterior eye cameras  300 A and  300 B. 
     (OCT Unit) 
     With reference to  FIG. 2 , an example of a configuration of the OCT unit  100  will be described. The OCT unit  100  is provided with an optical system for acquiring an OCT image of the fundus Ef. The optical system has a similar configuration to that of an OCT device of a conventional spectral domain type. That is, the optical system is configured to split low coherence light into reference light and signal light, and allows the signal light via the fundus Ef and the reference light via a reference optical path to interfere with each other to create interfering light so as to detect spectra components of the interfering light. This detection result (detection signal) is transmitted to the calculation control unit  200 . 
     An OCT device of a swept source type includes a wavelength swept light source instead of a light source for outputting low coherence light, but does not include an optical member for applying spectral resolution to interfering light. Generally, a well-known of the OCT unit  100 . 
     The light source unit  101  outputs wide-band low coherence light L 0 . The low coherence light L 0  has, for example, a wavelength range in a near infrared region (of the order of 800 nm to 900 nm), and temporal coherence length of the order of a few tens micro meters. A wavelength range invisible to a human eye, such as near infrared light having a central wavelength of the order of 1040 nm to 1060 nm, may be available for the low coherence light L 0 . 
     The light source unit  101  includes an optical output device, such as a super luminescent diode (SLD), an LED, and a semiconductor optical amplifier (SOA). 
     The low coherence light L 0  outputted from the light source unit  101  is guided to a fiber coupler  103  through an optical fiber  102  to be split into the signal light LS and reference light LR. 
     The reference light LR is guided through the optical fiber  104  to reach an optical attenuator  105 . The optical attenuator  105  automatically adjusts an amount of reference light LR to be guided into the optical fiber  104  by using a well-known art under control of the calculation control unit  200 . The reference light LR, whose amount is adjusted by the optical attenuator  105 , is guided through the optical fiber  104  to reach a polarization regulator (polarization controller)  106 . The polarization regulator  106  applies stress to the optical fiber  104  formed into the shape of a loop from the outside, for example, to adjust a polarization state of the reference light LR guided through the optical fiber  104 . The polarization regulator  106  is not limited to this configuration, and thus any well-known art is available. The reference light LR, whose polarization state is adjusted by the polarization regulator  106 , reaches a fiber coupler  109 . 
     The signal light LS created by the fiber coupler  103  is guided through the optical fiber  107  to be formed into a parallel pencil by the collimator lens unit  40 . In addition, the signal light LS reaches the dichroic mirror  46  via the optical path length change unit  41 , the galvanoscanner  42 , the focal lens  43 , the mirror  44 , and the relay lens  45 . Then the signal light LS is reflected by the dichroic mirror  46  to be refracted by the objective lens  22  to illuminate the fundus Ef. The signal light LS is scattered (including reflection) in various depth positions of the fundus Ef. Backscattered light of the signal light LS scattered by the fundus Ef inversely travels through the same path as that of incidence to be guided through the fiber coupler  103  to reach the fiber coupler  109  via the optical fiber  108 . 
     The fiber coupler  109  allows the backscattered light of the signal light LS and the reference light LR via the optical fiber  104  to interfere with each other. The interfering light LC created in this way is guided through the optical fiber  110  to be emitted from an emission end  111 . In addition, the interfering light LC is formed into a parallel pencil through a collimator lens  112  to be dispersed (spectral resolution) through a diffraction grating  113 , and then is concentrated through a condenser lens  114  to be projected on a receiving surface of a CCD image sensor  115 . Although the diffraction grating  113  shown in  FIG. 2  is a transmission type, a spectroscopic element of another type, such as a diffraction grating of a reflection type, is also available. 
     The CCD image sensor  115  is, for example, a line sensor that detects each spectra component of the interfering light LC dispersed, and converts it into electric charge. The CCD image sensor  115  accumulates the electric charge to create a detection signal, and then transmits the signal to the calculation control unit  200 . 
     Although this embodiment uses a Michelson type interferometer, any type of interferometer, such as a Mach-Zehnder type, may be appropriately used. Instead of the CCD image sensor, an image sensor of another type, such as a complementary metal oxide semiconductor (CMOS) image sensor, is available. 
     (Calculation Control Unit) 
     A configuration of the calculation control unit  200  will be described. The calculation control unit  200  analyzes a detection signal received from the CCD image sensor  115  to create an OCT image of the fundus Ef. Calculation processing for that is the same as that of an OCT device of a conventional spectral domain type. 
     The calculation control unit  200  controls each of the fundus camera unit  2 , the display device  3 , and the OCT unit  100 . For example, the calculation control unit  200  allows the display device  3  to display an OCT image of the fundus Ef. 
     In addition, the calculation control unit  200  performs control of the fundus camera unit  2 , such as: control of operation of the observation light source  11 , the photographing light source  15 , and the LED  61 ; control of operation of the LCD  39 ; 
     control of movement of the focal lenses  31  and  43 ; control of movement of the reflection bar  67 ; control of movement of the focus optical system  60 ; control of movement of the optical path length change unit  41 ; control of operation of the galvanoscanner  42 ; and control of operation of the anterior eye camera  300 . 
     Further, the calculation control unit  200  performs control of the OCT unit  100 , such as: control of operation of the light source unit  101 ; control of operation of the optical attenuator  105 ; control of operation of the polarization regulator  106 ; and control of operation of the CCD image sensor  115 . 
     The calculation control unit  200 , for example, as with a conventional computer, includes a microprocessor, a RAM, a ROM, a hard drive, a communication interface, and the like. A storage device, such as the hard drive, stores a computer program for controlling the ophthalmological apparatus  1 . The calculation control unit  200  may include various circuit boards, such as that for forming an OCT image. In addition, the calculation control unit  200  may include an operation device (input device), such as a keyboard and a mouse, and a display device, such as a LCD. 
     The fundus camera unit  2 , the display device  3 , the OCT unit  100 , and the calculation control unit  200 , may be integrally formed (or formed in a single body), or may be separately formed in two or more bodies. 
     (Control System) 
     A configuration of a control system of the ophthalmological apparatus  1  will be described with reference to  FIG. 3 . 
     (Control Unit) 
     The control system of the ophthalmological apparatus  1  is mainly composed of a control unit  210 . The control unit  210 , for example, includes the microprocessor, the RAM, the ROM, the hard drive, the communication interface, and the like, described before. The control unit  210  is provided with a main control unit  211 , a storage unit  212 , and an optical system position acquisition unit  213 . 
     (Main Control Unit) 
     The main control unit  211  performs various control processes of operation described before. Control of movement of the focal lens  31  is performed by controlling a focal driving unit (not shown) to move the focal lens  31  in the direction of the optical axis. Accordingly, an in-focus position of the photographic optical system  30  is changed. In addition, the main control unit  211  is capable of controlling the optical system driving unit  2 A to move an optical system provided in the fundus camera unit  2  in a three-dimensional manner. 
     Although the optical system driving unit  2 A of this embodiment moves the optical system provided in the fundus camera unit  2 , the optical system driving unit  2 A may be configured so as to move the optical system provided in the fundus camera unit  2  as well as an optical system provided in the OCT unit  100 . 
     Since the anterior eye camera  300  of this embodiment is provided in a body of the fundus camera unit  2 , controlling the optical system driving unit  2 A enables the anterior eye camera  300  to be moved. It is also possible to provide a photographing moving unit capable of independently moving each of two or more anterior eye cameras  300 . Specifically, the photographing moving unit may include a drive mechanism (such as an actuator, and a power transmission mechanism) provided in each of the anterior eye cameras  300 . In addition, the photographing moving unit may be configured so as to transmit power generated by a single actuator to a power transmission mechanism provided for each of the anterior eye cameras  300  to move the two or more anterior eye cameras  300 . 
     The main control unit  211  performs processing of writing data into the storage unit  212 , and processing of reading out data from the storage unit  212 . 
     (Storage Unit) 
     The storage unit  212  stores various data items. The data stored in the storage unit  212  includes, for example, image data on an OCT image, image data on a fundus image, information on a subject&#39;s eye, and the like. The information on a subject&#39;s eye includes information on a subject, such as a patient ID and a name, and information on a subject&#39;s eye, such as information on identification of left eye/right eye. In addition, the storage unit  212  stores various programs and data items for operating the ophthalmological apparatus  1 . 
     The storage unit  212  previously stores information on aberration (not shown). The information on aberration includes information on distortion aberration that occurs in a photographed image due to influence of an optical system provided in each of the anterior eye cameras  300 . The optical system provided in the anterior eye camera  300  includes, for example, optical elements, such as a lens that causes distortion aberration to occur. It can be said that the information on aberration is a parameter in which distortion given to a photographed image by these optical elements is quantified. A specific example of a method of creating the information on aberration is, for example, described in Japanese Patent Laid-Open No. 2013-248376 filed by the present applicant. 
     (Optical System Position Acquisition Unit) 
     The optical system position acquisition unit  213  acquires a current position of the optical system for inspection provided in the ophthalmological apparatus  1 . The optical system for inspection is used to optically inspect the subject&#39;s eye E. The optical system for inspection in the ophthalmological apparatus  1  (a complex machine of a fundus camera and an OCT device) of this embodiment is used to acquire an image of a subject&#39;s eye, and thus includes the photographic optical system  30 . 
     The optical system position acquisition unit  213 , for example, receives information showing contents of control of movement of the optical system driving unit  2 A by the main control unit  211  to acquire a current position of the optical system for inspection moved by the optical system driving unit  2 A. A specific example of this processing will be described. The main control unit  211  controls the optical system driving unit  2 A at predetermined timing (such as at the time of starting a device, and of inputting information on a patient) to move the optical system for inspection to a predetermined initial position. After then, the main control unit  211  records contents of control every time when the optical system driving unit  2 A is controlled. Accordingly, it is possible to acquire history of contents of the control. The optical system position acquisition unit  213  acquires contents of the control up to the present with reference to the history to acquire a current position of the optical system for inspection on the basis of the contents of the control. 
     In addition, every time when the main control unit  211  controls the optical system driving unit  2 A, contents of the control may be transmitted to the optical system position acquisition unit  213  so that the optical system position acquisition unit  213  sequentially acquires a current position of the optical system for inspection every time when receiving the contents of the control. 
     As another example of a configuration, a position sensor for detecting a position of the optical system for inspection may be provided in the optical system position acquisition unit  213 . 
     In a case where the optical system position acquisition unit  213  acquires a current position of the optical system for inspection as above, the main control unit  211  is able to acquire information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye E on the basis of the current position acquired and a three-dimensional position of the subject&#39;s eye E acquired by an analysis unit  231  described later. Specifically, the main control unit  211  identifies the current position of the optical system for inspection by using a result acquired by the optical system position acquisition unit  213 , as well as the three-dimensional position of the subject&#39;s eye E by using a result analyzed by the analysis unit  231 . Next, the main control unit  211  acquires an amount and direction of the positional displacement from a proper position of the optical system for inspection with respect to the subject&#39;s eye E in each of the x-direction (side-to-side direction), the y-direction (vertical direction), and the z-direction (direction of working distance), on the basis of the current position of the optical system for inspection, and the three-dimensional position identified by the analysis unit  231 . Then, the main control unit  211  allows a pseudo alignment index image to be displayed at a predetermined position in a screen of a display  240 A by superimposing it on an observation image to form a composite display in accordance with the amount of positional displacement in each of the directions and the direction of positional displacement acquired. The pseudo alignment index image changes in display position, size, and the like, in accordance with the amount of positional displacement in each of the directions and the direction of positional displacement of the optical system for inspection with respect to the subject&#39;s eye E. A user (examiner) operates an operation unit  240 B to move the optical system for inspection in a three-dimensional manner while checking the pseudo alignment index image displayed in a screen of the display  240 A to perform alignment of the optical system for inspection with respect to the subject&#39;s eye E. 
     In this embodiment, the control unit  210  (the main control unit  211 ) has first and second display modes as a plurality of display modes, in each of which the pseudo alignment index image is displayed in a different form, to allow the pseudo alignment index image to be displayed in the screen of the display  240 A in a pseudo manner in a display mode selected from the display modes. Selection of the display mode is performed through a user interface  240  described later. The user interface  240  is an example of a display mode selection unit. Details of each of the display modes, and a method of selecting a display mode, will be described later. 
     (Image Formation Unit) 
     An image formation unit  220  forms image data on a tomographic image of the fundus Ef on the basis of a detection signal from the CCD image sensor  115 . This processing includes noise elimination (noise reduction), filter processing, fast fourier transform (FFT), and the like, as with the optical coherence tomography of a conventional spectral domain type. In a case of an OCT device of another type, the image formation unit  220  performs well-known processing corresponding to the type. 
     The image formation unit  220 , for example, includes the circuit board described before. In the present specification, the “image data” and the “image” based on it may be identified. 
     (Image Processing Unit) 
     An image processing unit  230  applies various image processing items and analysis processing to an image formed by the image formation unit  220 . For example, the image processing unit  230  performs various correction processing items, such as luminance correction of an image, and dispersion correction. In addition, the image processing unit  230  applies the various image processing items and the analysis processing to an image acquired by the fundus camera unit  2  (such as a fundus image, and an anterior eye image). 
     The image processing unit  230  performs well-known image processing, such as interpolation processing of interpolating pixels between tomographic images, to form image data on a three-dimensional image of the fundus Ef. The image data on a three-dimensional image means that a position of a pixel is defined by a three-dimensional coordinate system. The image data of a three-dimensional image includes image data composed of voxels arranged in a three-dimensional manner arrangement. The image data is called volume data, voxel data, or the like. In a case where an image based on volume data is displayed, the image processing unit  230  applies rendering processing (such as, volume rendering, and maximum intensity projection (MIP) or maximum value projection) to the volume data to form pseudo image data of a three-dimensional image as viewed from a specific line of sight direction. The display  240 A displays the pseudo three-dimensional image. 
     It is also possible to form stack data on a plurality of tomographic images as image data of a three-dimensional image. The stack data is acquired by arranging a plurality of tomographic images acquired along a plurality of scanning lines in a three-dimensional manner on the basis of a positional relationship of the scanning lines. That is, the stack data is acquired by allowing a plurality of tomographic images defined by an originally individual two-dimensional coordinate system to be expressed by one three-dimensional coordinate system (or to be embedded in one three-dimensional space). 
     (Analysis Unit) 
     The image processing unit  230  is provided with the analysis unit  231 . The analysis unit  231  analyzes two photographed images that are substantially simultaneously acquired by the anterior eye cameras  300 A and  300 B to acquire a three-dimensional position of the subject&#39;s eye E. As an example of a configuration to perform this processing, the analysis unit  231  includes an image correction unit  2311 , a feature point identification unit  2312 , and a three-dimensional position calculation unit  2313 . 
     (Image Correction Unit) 
     The image correction unit  2311  corrects distortion of each of photographed images acquired by the anterior eye camera  300  on the basis of the aberration information stored in the storage unit  212 . This processing, for example, is performed by using a well-known image processing art based on a correction coefficient for correcting distortion aberration. If distortion aberration of an optical system of the anterior eye camera  300  to be applied to a photographed image is sufficiently small, it is unnecessary to provide the aberration information and the image correction unit  2311 , described above. 
     (Feature Point Identification Unit) 
     The feature point identification unit  2312  analyzes each of the photographed images, whose distortion aberration is corrected by the image correction unit  2311 , to identify a position (referred to as a feature point position) in the photographed image corresponding to a predetermined feature point of the anterior eye Ea. For example, the center of a pupil or the tip of the cornea of the subject&#39;s eye E is applied to the predetermined feature point. Hereinafter, a specific example of processing of identifying the center of a pupil will be described. 
     First, the feature point identification unit  2312  identifies an image area (pupil area) corresponding to a pupil of the subject&#39;s eye E on the basis of distribution of pixel values (such as luminance values) of a photographed image. In general, since a pupil is imaged at brightness lower than other portions, searching for an image area with low brightness enables the pupil area to be identified. At this time, the pupil area may be identified in consideration of the shape of the pupil. That is, searching for an image area in a substantially circular shape as well as with low brightness enables the pupil area to be identified. 
     Next, the feature point identification unit  2312  identifies a center position of the pupil area identified. Since the pupil is in a substantially circular shape as described above, a contour of the pupil area is identified to allow a center position of an approximate ellipse of the contour to be identified to enable the center position to be set as the center of the pupil. In addition, the center of gravity of the pupil area may be acquired to be set as the center of a pupil. 
     Even if another feature point is applied, it is possible to identify a position of the feature point on the basis of distribution of pixel values of a photographed image, as described above. 
     (Three-dimensional Position Calculation Unit) 
     The three-dimensional position calculation unit  2313  calculates a three-dimensional position of a feature point of the subject&#39;s eye Eon the basis of a position of each of the two or more anterior eye cameras  300 , and a position of the feature point in each of two or more photographed images identified by the feature point identification unit  2312 . This processing will be described with reference to  FIGS. 5A and 5B . 
       FIG. 5A  is a top view showing a positional relationship between the subject&#39;s eye E and the anterior eye cameras  300 A and  300 B.  FIG. 5B  is a side view showing a positional relationship between the subject&#39;s eye E and the anterior eye cameras  300 A and  300 B. A distance (baseline length) between the two anterior eye cameras  300 A and  300 B, a distance (photographing distance) between a baseline of the two anterior eye cameras  300 A and  300 B, and a feature point P of the subject&#39;s eye E, and a distance (screen distance) between each of the anterior eye cameras  300 A and  300 B, and its screen plane, are designated by “B”, “H”, and “f”, respectively. 
     In this kind of arrangement, resolution of a photographed image acquired by the anterior eye cameras  300 A and  300 B is expressed by the following expressions.
 
Resolution in a  xy -directions (plane resolution): Δ xy=H×Δp/f  
 
Resolution in the  z -direction (depth resolution): Δ z=H×H×Δp /( B×f )
 
where Δp is pixel resolution.
 
     The three-dimensional position calculation unit  2313  applies well-known trigonometry in consideration of the arrangement relationship shown in  FIGS. 5A and 5B  to a position of each of the anterior eye cameras  300 A and  300 B, which is known, and a position in each of two photographed images, corresponding to the feature point P, to calculate a three-dimensional position of the feature point P, or a three-dimensional position of the subject&#39;s eye E. 
     The three-dimensional position of the subject&#39;s eye E calculated by the three-dimensional position calculation unit  2313  is transmitted to the control unit  210 . 
     In this embodiment, the anterior eye cameras  300 A and  300 B, and the analysis unit  231  are an example of the “subject&#39;s eye position acquisition unit”. That is, in this embodiment, although the analysis unit  231  analyzes two photographed images that are substantially simultaneously acquired by the anterior eye cameras  300 A and  300 B to acquire a three-dimensional position of the subject&#39;s eye E, an aspect of acquiring the three-dimensional position of the subject&#39;s eye E is not limited to this embodiment. For example, the three-dimensional position of the subject&#39;s eye E may be acquired from a front face image of the subject&#39;s eye E (an observation image of the anterior eye Ea) by using an optical lever method, or may be acquired from an external device. 
     The image processing unit  230  serving as above includes, for example, the microprocessor, the RAM, the ROM, the hard drive, the circuit board, and the like, described before. A storage device, such as the hard drive, previously stores a computer program for allowing the microprocessor to perform the function described above. 
     (User Interface) 
     The user interface  240  includes the display  240 A, and the operation unit  240 B. The display  240 A includes a display device of the calculation control unit  200  described before, and the display device  3 . The operation unit  240 B includes an operation device of the calculation control unit  200  described before. The operation unit  240 B may include various buttons and keys, provided in a body of the ophthalmological apparatus  1  or in the outside. For example, if the fundus camera unit  2  has a body similar to that of a conventional fundus camera, the operation unit  240 B may include a joystick, an operation panel, and the like, provided in the body. In addition, the display  240 A may include various display devices, such as a touch panel provided in the body of the fundus camera unit  2 . 
     It is unnecessary that each of the display  240 A and the operation unit  240 B is configured as an individual device. For example, a device having a display function and an operation function, which are integrated, such as a touch panel, is also available. In that case, the operation unit  240 B includes the touch panel, and a computer program. Operation contents with respect to the operation unit  240 B are inputted into the control unit  210  as an electric signal. In addition, a graphical user interface (GUI) displayed in the display  240 A and the operation unit  240 B may be used for operation and information input. 
     (Display Mode) 
     In this embodiment, as described above, the control unit  210  (main control unit  211 ) has first and second display modes as a plurality of display modes, in each of which a pseudo alignment index image is displayed in a different display form. Hereinafter, the first and second display modes will be described. 
     (First Display Mode) 
     With reference to  FIGS. 6A and 6B , the first display mode will be described.  FIGS. 6A and 6B  show an example of a display screen to be used for alignment adjustment in a case where the first display mode is selected. This display screen corresponds to a display screen displayed in the display  240 A. While not shown, an observation image (a fundus image of the subject&#39;s eye E) acquired by the fundus camera unit  2  is displayed in the display screen shown in  FIGS. 6A and 6B . 
     In  FIGS. 6A and 6B , an alignment reference position mark (parentheses mark)  309  is displayed at a reference position in a display screen  308 . The reference position means a central position of the observation image. The alignment reference position mark  309  is an image showing a position of a moving target of pseudo alignment index images  310 . The display screen  308  displays the two pseudo alignment index images  310  and  310 . A display position of each of the two pseudo alignment index images  310  and  310  changes in accordance with information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye E. That is, the control unit  210  controls the display position of each of the two pseudo alignment index images  310  and  310  in accordance with displacement (an amount and direction of positional displacement) of the optical system for inspection with respect to the subject&#39;s eye E in each of the x-direction (side-to-side direction), the y-direction (vertical direction), and the z-direction (direction of working distance). 
     For example, if positions of the optical system for inspection with respect to the subject&#39;s eye E in the xy-directions (vertical and side-to-side directions) as well as in the z-direction (direction of working distance) are proper, that is, if alignment of the optical system for inspection with respect to the subject&#39;s eye E in all the xyz-directions is proper, as shown in  FIG. 6A , the two pseudo alignment index images  310  and  310  are displayed inside the alignment reference position mark  309  while superimposed with each other (while agreeing with each other). Meanwhile, if the optical system for inspection is displaced in the xy-directions with respect to the subject&#39;s eye E, as shown in  FIG. 6B , each of the two pseudo alignment index images  310  and  310  is displayed at a position away from the alignment reference position mark  309 . In addition, if the optical system for inspection is displaced in the z-direction with respect to the subject&#39;s eye E, as shown in  FIG. 6B , each of the two pseudo alignment index images  310  and  310  is displayed away from each other (in a separated state) at a predetermined interval. 
     That is, a display position of each of the pseudo alignment index images  310  and  310  with respect to the alignment reference position mark  309  is controlled so as to change in accordance with displacement of the optical system for inspection in the xy-directions with respect to the subject&#39;s eye E (an amount and direction of positional displacement in the xy-directions from a proper position). In addition, an interval (distance) between the pseudo alignment index images  310  and  310  displayed is controlled so as to change in accordance with displacement of the optical system for inspection in the z-direction with respect to the subject&#39;s eye E (an amount of positional displacement in the z-direction from the proper position). 
     According to the first display mode described above, it is possible to manually perform alignment adjustment while an observation image (a fundus image of the subject&#39;s eye E) displayed in a screen of the display  240 A is observed with a familiar operational feeling. 
     In this embodiment, since the pseudo alignment index image  310  is displayed in a pseudo manner, it is possible to always display the alignment reference position mark  309  at a predetermined reference position regardless of change of an inspection portion (or a projection position of a vision fixation target). Accordingly, for example, even if a fundus peripheral portion is selected as an inspection portion, there is less possibility that the pseudo alignment index image  310  is eliminated in the screen of the display  240 A, as compared with a conventional ophthalmological apparatus. As a result, it is possible to smoothly perform alignment adjustment on the basis of quantitative information without depending on experience and proficiency of a user. 
     In addition, in this embodiment, since the pseudo alignment index image  310  is displayed in the screen of the display  240 A in a pseudo manner, it is possible to change the reference position, at which the alignment reference position mark  309  is to be displayed, in accordance with an inspection portion (or a projection position of a vision fixation target). Thus, it is possible to displace a reference position, at which the alignment reference position mark  309  is to be displayed, toward a peripheral portion from a central position of an observation image, as shown in  FIGS. 7A and 7B . Accordingly, even if a high brightness portion, such as an optic disk, is selected as an inspection portion, the alignment reference position mark  309  and the alignment index image  310  are prevented from being difficult to be viewed by being superimposed with the high brightness portion. As a result, it is possible to manually perform alignment adjustment accurately while an observation image (fundus image of the subject&#39;s eye E) is observed. 
     (Second Display Mode) 
     With reference to  FIGS. 8A and 8B , the second display mode will be described.  FIGS. 8A and 8B  show an example of a display screen to be used for alignment adjustment in a case where the second display mode is selected. This display screen corresponds to a display screen of the display  240 A. While not shown, an observation image (a fundus image of the subject&#39;s eye E) acquired by the fundus camera unit  2  is displayed in the display screen shown in  FIGS. 8A and 8B . 
     In  FIGS. 8A and 8B , the display screen  308  displays the two pseudo alignment index images  310  and  310 . A display position and size of each of the two pseudo alignment index images  310  and  310  change in accordance with information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye E. Specifically, the control unit  210  controls the display position of each of the pseudo alignment index images  310  and  310  in accordance with displacement (an amount and direction of positional displacement) of the optical system for inspection with respect to the subject&#39;s eye E in each of the x-direction (side-to-side direction), and the y-direction (vertical direction). In addition, the control unit  210  controls the size of each of the two pseudo alignment index images  310  and  310  in accordance with displacement (an amount and direction of positional displacement) of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction (direction of working distance). 
     For example, if positions of the optical system for inspection with respect to the subject&#39;s eye E in the xy-directions (vertical and side-to-side directions) as well as in the z-direction (direction of working distance) are proper, that is, if alignment of the optical system for inspection with respect to the subject&#39;s eye E in all the xyz-directions is proper, as shown in  FIG. 8A , the two pseudo alignment index images  310  and  310  are displayed at respective reference positions preset in the display screen  308  (positions away from each other in the side-to-side direction by centering a central position of the display screen  308 ) in a separated state. At the time, the pseudo alignment index images  310  and  310  are displayed at the size (second size) of a minimum diameter. 
     Meanwhile, if positions of the optical system for inspection with respect to the subject&#39;s eye E in the xy-directions (vertical and side-to-side directions) are proper but a position of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction (direction of working distance) is improper, as shown in  FIG. 8A  by broken lines, the two pseudo alignment index images  310  and  310  are displayed at the size (first size) more than the size (second size) of the two pseudo alignment index images  310  and  310  in a case where the position of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction (direction of working distance) is proper. In addition, if alignment of the optical system for inspection with respect to the subject&#39;s eye E in all the xyz-directions is improper, as shown in  FIG. 8B , the two pseudo alignment index images  310  and  310  are displayed at respective reference positions away from each other in the vertical or side-to-side direction, as well as displayed at the size (first size) more than the size (second size) of the two pseudo alignment index images  310  and  310  in a case where the position of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction (direction of working distance) is proper. 
     That is, a display position of each of the pseudo alignment index images  310  and  310  is controlled so as to change in accordance with displacement of the optical system for inspection in the xy-directions with respect to the subject&#39;s eye E (an amount and direction of positional displacement in the xy-directions from a proper position). In addition, the size of the pseudo alignment index images  310  and  310  displayed is controlled so as to change in accordance with displacement of the optical system for inspection in the z-direction with respect to the subject&#39;s eye E (an amount of positional displacement in the z-direction from the proper position). 
     According to the second display mode described above, it is possible to manually perform alignment adjustment while an observation image (a fundus image of the subject&#39;s eye E) displayed in a screen of the display  240 A is observed with a familiar operational feeling. 
     In this embodiment, since the pseudo alignment index image  310  is displayed in a pseudo manner, it is possible to acquire the same effect as that of the first display mode. 
     That is, it is possible to always fix a reference position of the pseudo alignment index image  310  regardless of change of an inspection portion (or a projection position of a vision fixation target). Accordingly, for example, even if a fundus peripheral portion is selected as an inspection portion, there is less possibility that the pseudo alignment index image  310  is eliminated in the screen of the display  240 A, as compared with a conventional ophthalmological apparatus. As a result, it is possible to smoothly perform alignment adjustment on the basis of quantitative information without depending on experience and proficiency of a user. 
     In addition, it is possible to change the reference position of the pseudo alignment index image in accordance with an inspection portion (or a projection position of a vision fixation target). Accordingly, such as shown in  FIG. 9 , displacing a reference position of the alignment index image  310  to a central position side of an observation image, in a case where alignment of the optical system for inspection with respect to the subject&#39;s eye E in all the xyz-directions is proper, enables the alignment index image  310  are prevented from being difficult to be viewed by being superimposed with a high brightness portion, such as an optic disk. As a result, it is possible to manually perform alignment adjustment accurately while an observation image (fundus image of the subject&#39;s eye E) is observed. 
     (Operation) 
     Operation of the ophthalmological apparatus  1  will be described. A flow chart shown in  FIG. 10  shows an example of the operation of the ophthalmological apparatus  1 . 
     (S 1 : Selection of Display Mode) 
     First, when a power source of the ophthalmological apparatus  1  is turned on, a display mode is selected. Specifically, the display mode is selected as follows. 
     The display  240 A displays a display mode selection screen  242  shown in  FIG. 11 . Next, a user selects one display mode from the first and second display modes displayed in the display mode selection screen  242  by using the user interface  240 . The display mode selected by the user is transmitted to the control unit  210 . 
     It is unnecessary to select a display mode every time when the power source of the ophthalmological apparatus  1  is turned on, and thus it may be configured to allow a user to select a display mode if necessary. In this case, the control unit  210  may automatically select the display mode selected at the time of previous startup. If a user wants to change a selected display mode, the user may call the display mode selection screen  242  by using the user interface  240  to select a display mode as described above. 
     (S 2 : Patient Registration) 
     Next, the user inputs patient information on a subject by using the user interface  240 . The patient information includes a patient ID, a patient name, and the like. 
     (S 3 : Selection of Inspection Types) 
     Subsequently, the user selects and inputs inspection types to be applied to the subject by using the user interface  240 . Items of the inspection types include: an inspection portion (such as a fundus central portion, a fundus peripheral portion, an optic disk, and a macula lutea); a subject&#39;s eye (such as a left eye, a right eye, both eyes); an image photographing pattern (such as only a fundus image, only an OCT image, and both the images); an OCT scan pattern (such as a line scan, a cross scan, a radial scan, a circular scan, and a three-dimensional scan); and the like. In this example of the operation, a peripheral portion in the fundus Ef is selected as an inspection portion. 
     (S 4 : Start of Manual Alignment) 
     When the selection of inspection types is completed, a start of manual alignment is instructed. The control unit  210  may automatically instruct the start after receiving the selection of inspection types shown in step S 3 , or the user may manually instruct the start by using the operation unit  240 B. 
     (S 5 : Start of Photographing of Anterior Eye) 
     When the start of manual alignment is instructed, the control unit  210  allows each of the anterior eye cameras  300 A and  300 B to start photographing the anterior eye Ea. This photographing is of a moving image for the anterior eye Ea. Each of the anterior eye cameras  300 A and  300 B performs photographing of a moving image at a predetermined frame rate. Photographing timing of each of the anterior eye cameras  300 A and  300 B may be synchronized by the control unit  210 . Each of the anterior eye cameras  300 A and  300 B sequentially transmits an acquired frame to the control unit  210  in real time. The control unit  210  allows frames acquired by both the anterior eye cameras  300 A and  300 B to be associated with each other in accordance with the photographing timing. That is, the control unit  210  allows frames that are substantially simultaneously acquired by both the anterior eye cameras  300 A and  300 B to be associated with each other. This association, for example, is made up on the basis of synchronization control as described above, or input timing of the frames from the anterior eye cameras  300 A and  300 B. The control unit  210  transmits a pair of frames associated with each other to the analysis unit  231 . 
     (S 6 : Identification of Feature Point) 
     The image correction unit  2311  corrects distortion of each of the frames transmitted from the control unit  210  on the basis of aberration information stored in the storage unit  212 . This correction processing is performed according to the manner described before. The pair of frames, in which distortion is corrected, is transmitted to the feature point identification unit  2312 . 
     The feature point identification unit  2312  performs processing of analyzing each of the frames transmitted from the image correction unit  2311  to identify a position in each of the frames corresponding to a feature point (center of a pupil) of the anterior eye Ea. 
     If identification of the feature point fails, it is possible to control processing of identifying the feature point so as to be performed again after the anterior eye cameras  300 A and  300 B are moved in a direction away from the support part  440  and/or an outward direction from the support part  440 . Moving the anterior eye cameras  300 A and  300 B in the direction away from the support part  440  increases a distance between the anterior eye cameras  300 A and  300 B, and the subject (subject&#39;s eye E) to enable a range wider than the subject&#39;s face to be photographed. Accordingly, a possibility that the subject&#39;s eye E may be arranged within a favorably photographable range by the anterior eye cameras  300 A and  300 B increases. In addition, moving the anterior eye cameras  300 A and  300 B in the outward direction from the support part  440  moves the anterior eye cameras  300 A and  300 B toward the subject&#39;s ear side to increase a possibility that the subject&#39;s eye E may be arranged within a favorably photographable range. Combination of movements in these two directions further increases a possibility that the subject&#39;s eye E may be arranged within a favorably photographable range. 
     It is also possible to determine whether an image corresponding to the anterior eye Ea is positioned within a prescribed area in a frame. If it is determined that the image of the anterior eye Ea is not positioned within the prescribed area, it is possible to perform control of movement of the anterior eye cameras  300 A and  300 B as with the description above. 
     (S 7 : Calculation of Three-dimensional Position of Subject&#39;s eye) 
     The three-dimensional position calculation unit  2313  calculates a three-dimensional position of a feature point (center of a pupil) of the subject&#39;s eye E on the basis of a position of each of the anterior eye cameras  300 A and  300 B, and a position of a feature point of each of the pair of frames identified by the feature point identification unit  2312 . This processing is performed according to the manner described before. 
     (S 8 : Acquisition of Information on Positional Displacement) 
     The control unit  210  acquires information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye E on the basis of the three-dimensional position of the feature point (center of a pupil) calculated in step S 7 . This processing, for example, is performed as follows. First, the control unit  210  acquires a current position of the optical system for inspection. The current position, for example, is acquired from control history with respect to the optical system driving unit  2 A that moves the fundus camera unit  2 . It is also possible to provide a position sensor that detects a position of the fundus camera unit  2  to acquire the current position from a detection result acquired by the position sensor. A coordinate system defining the three-dimensional position (coordinate) of the subject&#39;s eye E acquired in step S 7  and a coordinate system defining current position (coordinate) of the optical system for inspection are to be common. Alternatively, coordinate transformation between both the coordinate systems is to be known. 
     The information on positional displacement shows displacement (an amount and direction of positional displacement) from a proper position of the optical system for inspection with respect to the subject&#39;s eye E. The proper position is a target position of favorable alignment of the optical system for inspection to the subject&#39;s eye E inspect. At the proper position, an axis of the subject&#39;s eye E and an optical axis of the optical system for inspection agree with each other in the x-direction (side-to-side direction) and the y-direction (vertical direction). The proper position is away from the subject&#39;s eye E in the z-direction (fore-and-aft direction, or optical axis direction) by a predetermined operation distance. Since the operation distance is known and the three-dimensional position of the subject&#39;s eye E is acquired in step S 7 , it is easy to acquire a coordinate of the target position of alignment in the common coordinate system. 
     (S 9 : Display of Pseudo Alignment Index Image) 
     The control unit  210  allows a pseudo alignment index image to be displayed at a predetermined position in a screen of the display  240 A by superimposing it on an observation image to form a composite display. Then, the pseudo alignment index image is displayed in the display mode (first display mode or second display mode) selected in step S 1 . For example, if the first display mode is selected, the pseudo alignment index image is displayed as shown in  FIG. 6A or 6B . If the second display mode is selected, the pseudo alignment index image is displayed as shown in  FIG. 8A or 8B . 
     (S 10 : Implementation of Manual Alignment) 
     The user performs predetermined operation using the operation unit  240 B to move the optical system for inspection while observing the observation image displayed and checking the pseudo alignment index image. 
     At this time, the control unit  210  enables a display position of the pseudo alignment index image to be changed in accordance with contents of movement of the optical system for inspection. For example, the control unit  210  acquires information on positional displacement in real time again in accordance with the contents of movement of the optical system for inspection to update a display of the pseudo alignment index image in real time in accordance with the newly-acquired information on positional displacement. 
     Referring to information on the subject&#39;s eye enables correctness of manual alignment to be further improved. The information on the subject&#39;s eye, for example, is measurement information showing characteristics of the subject&#39;s eye acquired by an inspection previously performed with respect to the subject&#39;s eye E. The measurement information may be acquired by the ophthalmological apparatus or another ophthalmological apparatus. Then, the measurement information is previously stored in the storage unit  212  by being associated with a patient ID, and the like. 
     The control unit  210  selects the measurement information corresponding to the subject&#39;s eye E on the basis of the patient ID, and the like. In addition, the control unit  210  creates information on positional displacement on the basis of the measurement information selected and the three-dimensional position of the subject&#39;s eye E acquired by the analysis unit  231 . An example of this processing enables information on positional displacement (amount and direction of positional displacement) in the x-direction and the y-direction to be corrected on the basis of a deviation of a cornea shape. In addition, it is possible to correct information on positional displacement (amount and direction of positional displacement) in the z-direction on the basis of eye axial length. The latter is effective particularly in a case where a fundus is inspected. 
     In this way, creating information on positional displacement in consideration of the measurement information of the subject&#39;s eye E enables information on positional displacement with higher correctness in accordance with an individual difference of a subject&#39;s eye to be acquired and presented. 
     (S 11 : Start of Inspection) 
     When the processing of manual alignment in step S 10  is finished, the control unit  210  starts the inspection designated in step S 3 . 
     (S 12 : Finish of Inspection) 
     When the inspection of the subject&#39;s eye E is finished, this example of operation is finished. 
     (Function and Effect) 
     Function and effect of the ophthalmological apparatus  1  as described above will be described. 
     The ophthalmological apparatus  1  includes the optical system for inspection, the display  240 A, the two anterior eye cameras  300 A and  300 B (photographing unit), the analysis unit  231 , and the control unit  210 . The optical system for inspection inspects the subject&#39;s eye E, and includes the photographic optical system  30  for photographing a fundus of the subject&#39;s eye E. The two anterior eye cameras  300 A and  300 B substantially simultaneously photograph the anterior eye Ea of the subject&#39;s eye E from different directions. The analysis unit  231  analyzes a photographed image acquired by the anterior eye camera  300  to acquire a three-dimensional position of the subject&#39;s eye E. The control unit  210  acquires information on positional displacement of the optical system for inspection with respect to the subject&#39;s eye E on the basis of the three-dimensional position of the subject&#39;s eye E acquired by the analysis unit  231  to allow a pseudo alignment index image used for performing alignment of the optical system for inspection with respect to the subject&#39;s eye E to be displayed in a screen of the display  240 A in a pseudo manner in accordance with the information on positional displacement. In addition, the control unit  210  has first and second display modes as a plurality of display modes, in each of which the alignment index image is displayed in a different form, to allow the alignment index image to be displayed in a display mode selected from the display modes. 
     The ophthalmological apparatus  1  described above acquires information on positional displacement from a proper position of the optical system for inspection with respect to the subject&#39;s eye E on the basis of a three-dimensional position of the subject&#39;s eye E calculated from photographed images acquired by the anterior eye cameras  300 A and  300 B, and displays a pseudo alignment index image in a screen of a display in a pseudo manner in accordance with the information on positional displacement acquired. That is, the pseudo alignment index image created in a pseudo manner by the control unit  210  is displayed in the screen of the display  240 A instead of an alignment index image (optical alignment index image) projected on the subject&#39;s eye E by the alignment optical system. Thus, it is possible to always set a reference position of alignment preset in the screen of the display at a predetermined position regardless of an inspection portion (or a vision fixation position of the subject&#39;s eye E). In addition, it is also possible to change the reference position of alignment in accordance with the inspection portion. Accordingly, for example, even if a fundus peripheral portion is selected as an inspection portion, there is less possibility that an alignment index image is eliminated in a screen of a display, as compared with a conventional ophthalmological apparatus. As a result, it is possible to smoothly perform alignment adjustment on the basis of quantitative information without depending on experience and proficiency of a user. Thus, it is possible to smoothly and easily perform alignment adjustment of the optical system for inspection with respect to a subject&#39;s eye E by hand with a familiar operational feeling. 
     Since the ophthalmological apparatus  1  of this embodiment is capable of manually performing alignment adjustment without providing an alignment optical system that projects an alignment index on the subject&#39;s eye E, it is possible to reduce the apparatus in size as well as to reduce the number of components for cost reduction and improvement in maintenance as compared with an apparatus including the alignment optical system. 
     In addition, the ophthalmological apparatus  1  of this embodiment displays a pseudo alignment index image in a display mode selected from the plurality of display modes (first display mode and second display mode). These display modes allow an alignment index image (pseudo alignment index image) to be displayed in the same display form as that of a conventional ophthalmological apparatus. Accordingly, it is possible to efficiently perform alignment adjustment of the optical system for inspection with respect to the subject&#39;s eye E by allowing a user to select an arbitrarily display mode, while following familiar operability. 
     Although the ophthalmological apparatus  1  of this embodiment has the first and second display modes as a plurality of display modes, in each of which a pseudo alignment index image is displayed in a different form, another display mode may be included instead of the first or second display mode, or may be included along with any of the first and second display modes, or both of the display modes. 
     (Another Display Mode) 
     Examples of another display mode (first to third examples) will be described. Hereinafter, while variations of the first display mode will be described as the examples of another display mode, as a representative of the first and second display modes, the second display mode may be varied in like manner. 
     First Example 
     With reference to  FIGS. 12A and 12B , an example of another display mode (first example) will be described.  FIGS. 12A and 12B  show an example of display screens in cases of forward and backward positional displacement (alignment displacement) of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction, respectively, as the example of another display mode (first example). In the present specification, a direction toward a subject side is indicated as a forward direction, and an opposite direction is indicated as a backward direction. 
     In the first display mode in the embodiment described above (the same applies to the second display mode), if two alignment index images are displayed in the same display mode, it is difficult to grasp a direction of positional displacement in the z-direction from a positional relationship between the two pseudo alignment index images. 
     In contrast, the first example is configured to enable a direction of positional displacement in the z-direction to be intuitively grasped from a positional relationship between the two pseudo alignment index images. 
     That is, in the first example, as shown in  FIGS. 12A and 12B , the control unit  210  allows two pseudo alignment index images  310 A and  310 B to be displayed so that the first pseudo alignment index image  310 A is displayed in a first color (shown by a solid circle) and the second pseudo alignment index image  310 B is displayed in a second color different from the first color (shown by an open circle). 
     In addition, if positional displacement in the z-direction is the forward direction, as shown in  FIG. 12A , the control unit  210  allows the first pseudo alignment index image  310 A to be displayed on the left side, as well as the second pseudo alignment index image  310 B to be displayed on the right side. On the other hand, if the positional displacement in the z-direction is the backward direction, as shown in  FIG. 12B , the control unit  210  allows the first pseudo alignment index image  310 A to be displayed on the right side, as well as the second pseudo alignment index image  310 B to be displayed on the left side. As with the first display mode, an interval (distance) between the two pseudo alignment index images  310 A and  310 B changes in accordance with an amount of positional displacement of the z-direction (direction of working distance). 
     In this way, in the first example, the two alignment index images are displayed in display forms different from each other, and display positions of the two alignment index images change places depending on whether positional displacement in the z-direction of the optical system for inspection with respect to the subject&#39;s eye E is the forward direction or the backward direction. Accordingly, it is possible to intuitively grasp not only an amount of positional displacement in the z-direction, but also whether the positional displacement in the z-direction is the forward direction or the backward direction, from a positional relationship between the two pseudo alignment index images  310 A and  310 B. 
     In the first example, an aspect of changing a display form of each of the two pseudo alignment index images  310 A and  310 B is not limited to the example described above, and thus others except a color, such as a size, a shape, and a blinking pattern, may be changed, and a combination thereof may be available. In addition, any visually discriminable form, such as a pattern, brightness, density, and transparency, is available. 
     Variations of the first example (first to third variations) will be described with reference to  FIGS. 13 to 15 .  FIGS. 13 to 15  show a case where positional displacement in the z-direction is in the forward direction. If the positional displacement in the z-direction is in the backward direction, the two pseudo alignment index images  310 A and  310 B change display positions to be displayed. 
     The first variation shown in  FIG. 13  allows the two pseudo alignment index images  310 A and  310 B to be different from each other in shape. That is, in the present variation, as shown in  FIG. 13 , the two pseudo alignment index images  310 A and  310 B are displayed so that the first pseudo alignment index image  310 A is displayed by a quadrangular mark and the second pseudo alignment index image  310 B is displayed by a circular mark. 
     The second variation shown in  FIG. 14  allows the two pseudo alignment index images  310 A and  310 B to be different from each other in size. That is, in the present variation, as shown in  FIG. 14 , the two pseudo alignment index images  310 A and  310 B are displayed so that the first pseudo alignment index image  310 A is displayed large and the second pseudo alignment index image  310 B is displayed small. 
     The third variation shown in  FIG. 15  allows the two pseudo alignment index images  310 A and  310 B to be different from each other in a blinking pattern. For example, as shown in  FIG. 15 , the two pseudo alignment index images  310 A and  310 B are displayed so that the first alignment index image is always displayed (displayed by a solid line) and the second pseudo alignment index image  310 B is displayed in a blinking manner. 
     Second Example 
     With reference to  FIGS. 16A and 16B , an example of another display mode (second example) will be described.  FIGS. 16A and 16B  show an example of display screens in cases of frontward and rearward positional displacement of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction, respectively, as the example of another display mode (second example). 
     In the second example, as shown in  FIG. 16A , if the positional displacement in the z-direction is in the forward direction, the control unit  210  allows the two pseudo alignment index images  310 A and  310 B to be displayed in a first color (shown by a solid circle). On the other hand, as shown in  FIG. 16B , if the positional displacement in the z-direction is in the backward direction, the control unit  210  allows the two pseudo alignment index images  310 A and  310 B to be displayed in a second color (shown by an open circle) different from the first color. 
     In this way, in the second example, as with the first example, while the two pseudo alignment index images  310 A and  310 B are displayed in the same display form, a display form of each of the two pseudo alignment index images  310 A and  310 B is to be different from each other depending on whether positional displacement in the z-direction (direction of working distance) is in the forward direction or in the backward direction. Accordingly, it is possible to intuitively grasp whether the positional displacement in the z-direction is in the forward direction or the backward direction from the display form of each of the two pseudo alignment index images  310 A and  310 B, thereby enabling a user to smoothly perform alignment adjustment without doubt. 
     In the second example, an aspect of changing a display form of each of the two pseudo alignment index images  310 A and  310 B is not limited to the example described above, and thus, as with the second display mode, others except a color, such as a size, a shape, and a blinking pattern, may be changed, and a combination thereof may be available. In addition, any visually discriminable form, such as a pattern, brightness, density, and transparency, is available. 
     Third Example 
     With reference to  FIGS. 17A and 17B , an example of another display mode (third example) will be described.  FIGS. 17A and 17B  show an example of display screens in cases where positional displacement of the optical system for inspection with respect to the subject&#39;s eye E in the z-direction is in the forward direction, and where a position in the z-direction is proper, respectively, as the example of another display mode (third example). 
     In the third example, as shown in  FIGS. 17A and 17B , while the two alignment index images  310  and  310  are displayed in the same display form as that of the first display mode in the embodiment described above, an indicator  312  is displayed on the right side of the display screen  308 . The indicator  312  serves as an identification device that shows whether positional displacement in the z-direction of the optical system for inspection with respect to the subject&#39;s eye E is in the forward direction or the backward direction. Thus, it is possible to easily grasp whether the positional displacement in the z-direction of the optical system for inspection with respect to the subject&#39;s eye E is in the forward direction or the backward direction by checking a display state of the indicator  312 , thereby enabling a user to smoothly perform alignment adjustment without doubt. 
     The identification device that shows whether positional displacement in the z-direction of the optical system for inspection with respect to the subject&#39;s eye E is in the forward direction or the backward direction is not limited to the indicator  312  shown in  FIG. 17 , and thus, for example, a direction of positional displacement in the z-direction of the optical system for inspection with respect to the subject&#39;s eye E may be shown by a figure such as an arrow, or may be notified by voice or the like. 
     Fourth Example 
     In the fourth example, the control unit  210  determines whether positional displacement in all the xyz-directions of the optical system for inspection with respect to the subject&#39;s eye E is within a predetermined allowable range or not. If it is determined that the positional displacement is within the allowable range, a pseudo alignment index image is displayed in a display form different from that in a case where the positional displacement is out of the allowable range. For example, if the positional displacement is out of the allowable range, each of the two pseudo alignment index images is displayed in a first color. On the other hand, if the positional displacement is within the allowable range, each of the two pseudo alignment index image is displayed in a second color different from the first color. 
     In this way, the fourth example allows the two pseudo alignment index images to be changed in a display form if it is determined that positional displacement of the optical system for inspection with respect to the subject&#39;s eye E is within the allowable range, thereby enabling a user to easily perform alignment adjustment. 
     In a case where it is determined that the positional displacement is within the allowable range, an aspect of changing a display form of each of the two pseudo alignment index images is not limited to the example described above, and thus others except a color, such as a size, a shape, and a blinking pattern, may be changed, and a combination thereof may be available. In addition, any visually discriminable form, such as a pattern, brightness, density, and transparency, is available. 
     (Modification) 
     The configurations described above are only an example of suitably practicing the present invention. Thus, any modification (such as elimination, replacement, and addition) within the scope of the gist of the present invention is appropriately applicable. 
     The anterior eye camera  300  (photographing unit) may be arranged below a lens center of the objective lens  22  (−y-direction). Accordingly, it is possible to reduce a possibility that an eyelid or eyelashes of a subject may be displayed in a photographed image acquired by the anterior eye camera  300  (photographing unit). Thus, even if a subject has a deep hollow of the eye (orbit), it is possible to suitably perform anterior eye photographing. 
     The embodiment described above enables the image processing unit  230  to combine two photographed images that are substantially simultaneously acquired by the anterior eye cameras  300 A and  300 B to allow the composite image to be displayed. Accordingly, it is possible to observe a three-dimensional form of the anterior eye Ea. It is also possible to perform the analysis processing of the embodiment described above by using the composite image. 
     In the embodiment described above, the control unit  210  is capable of allowing at least one of two photographed images that are substantially simultaneously acquired by the anterior eye cameras  300 A and  300 B to be displayed. Accordingly, it is possible to observe a form of the anterior eye Ea from different visual points (photographing positions). 
     The anterior eye camera  300  may be attached to a front face of the body  420 , or stored in the body  420 . That is, the anterior eye camera  300  may be arranged so as to project from the front face of the body  420 , or arranged so as to be substantially in flush with the front face of the body  420 . The anterior eye camera  300  may be also provided so as to be arranged at a recessed position with respect to the front face of the body  420  from the front face. 
     In a case where the anterior eye camera  300 A is provided so as not to project from the front face of the body  420 , following advantages can be acquired: causing no obstruction to eyelid opening or external vision fixation operation, and avoiding failure of acquiring positional information due to vignetting of an image itself. 
     It is also possible to provide the anterior eye camera  300  at a position other than the front face of the body  420 . For example, the anterior eye camera  300  may be provided at a position in a side face of the body  420 , as well as an optical system (such as a mirror) that changes a direction of an optical axis of the anterior eye camera  300  to guide light into the subject&#39;s eye E may also be provided. In addition, the anterior eye camera  300  may be provided in the body  420 , as well as the same optical system may also be provided. If this kind of optical system is provided, it is perceived that providing the anterior eye camera  300  and the optical system in the body  420  is desirable in consideration of disturbance with respect to anterior eye photographing. In that case, it is perceived that applying a configuration in which the anterior eye camera  300  and an optical system are separated from another optical system to avoid influence on anterior eye photographing by another optical system (such as an optical system for inspection) is desirable. For separation of the optical system, an optical path separation member, such as a prism, and a dichroic mirror, is available. 
     In the embodiment described above, while a position of the optical path length change unit  41  is changed to change a difference in length between an optical path of the signal light LS and an optical path of the reference light LR, a method of changing the difference in the optical path length is not limited to this. For example, a reflection mirror (reference mirror) is arranged in an optical path of reference light, and then the reference mirror is moved in a direction of travel of the reference light to change optical path length of the reference light, thereby enabling a difference in the optical path length to be changed. In addition, the fundus camera unit  2  and the OCT unit  100  may be moved with respect to the subject&#39;s eye E to change optical path length of the signal light LS, thereby changing a difference in the optical path length. 
     It is possible to store a computer program for achieving the embodiment described above in any non-transitory computer-readable tangible medium readable by a computer. For this medium, for example, a semiconductor memory, an optical disk, a magneto-optical disk (such as a CD-ROM, a DVD-RAM, a DVD-ROM, and an MO), a magnetism recording medium (such as a hard disk, a floppy (registered trademark) disk, and ZIP), and the like, are available. 
     It is also possible to transmit and receive the program through a network, such as the Internet, and a LAN.