Patent Publication Number: US-2022233068-A1

Title: Ophthalmologic apparatus and cover

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims a priority benefit of Japanese patent application No. 2021-008402, filed on Jan. 22, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     FILED OF THE INVENTION 
     The present invention relates to an ophthalmologic apparatus and a cover. 
     BACKGROUND 
     A known ophthalmologic apparatus provided with an optical system including an objective lens is configured to acquire information of a subject&#39;s eye with an eye information acquisition unit that acquires information of the subject&#39;s eye by moving the eye information acquisition unit up and down, from side to side, and back and forth to align the eye information acquisition unit relative to the subject&#39;s eye (see, for example, JP 2010-17279 A). In an ophthalmologic apparatus disclosed in JP 2010-17279 A, a device body including an eye information acquisition unit (optical system unit) is covered with a cover. Inside this cover, the eye information acquisition unit moves up and down, from side to side, and back and forth, and the eye information acquisition unit acquires information of a subject&#39;s eye through an opening (imaging window) disposed in the cover. 
     SUMMARY 
     However, when acquiring information of a subject&#39;s eye by the technique in the related art, a subject visually recognizes through the opening that the eye information acquisition unit is moving, particularly, that the eye information acquisition unit is moving forward and approaching the subject&#39; eye. Therefore, the subject may feel a sense of fear that an “object” is closing in on the subject&#39; eye and the subject may not be able to concentrate on the examination. Furthermore, for example, the subject may put a finger from the imaging window by mistake, or dirt, dust, and foreign matters may enter the imaging window. 
     The present invention has been made in light of the above problems, and an object of the present invention is to hide the movement of an eye information acquisition unit appropriately and to acquire information of a subject&#39;s eye appropriately. 
     In order to achieve the object, an ophthalmologic apparatus according to an embodiment of this disclosure includes: a device body; and a casing covering the device body, in which the device body includes: an eye information acquisition unit including an objective optical system that opposes a subject&#39;s eye of a subject, being configured to acquire information of the subject&#39;s eye; a drive unit configured to move the eye information acquisition unit relative to the subject&#39;s eye in upward-downward direction, rightward-leftward direction, and forward-rearward direction perpendicular to each other; and a control unit configured to control the eye information acquisition unit and the drive unit, and the casing includes an opening on one surface opposing the subject&#39;s eye, the opening being provided with a cover configured to cover the opening, and the cover including: a first cover portion movable relative to the casing in the upward-downward direction and the rightward-leftward direction, being disposed in the opening not to move in the forward-rearward direction; and a second cover portion attached to an outer periphery of the objective optical system and inserted into the first cover portion, being movable relative to the first cover portion in the forward-rearward direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view illustrating an external appearance of an ophthalmologic apparatus according to a first embodiment of this disclosure. 
         FIGS. 2A to 2C  are views for describing configurations of a cover and a casing. 
         FIG. 3  is a view for describing a process for assembling the cover and the casing. 
         FIGS. 4A and 4B  are views for describing configurations of a cover and a casing according to a first modification. 
         FIGS. 5A and 5B  are views for describing configurations of a cover and a casing according to a second modification. 
         FIGS. 6A and 6B  are views for describing configurations of a cover and a casing according to a third modification. 
     
    
    
     DETAILED DESCRIPTION 
     With respect to the use of plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     First Embodiment 
     Hereinafter, an ophthalmologic apparatus  10  as an embodiment of this disclosure will be described with reference to the drawings.  FIG. 1  is a side view illustrating an external appearance of the ophthalmologic apparatus  10  according to this embodiment. Herein, X-axis, Y-axis, and Z-axis are set as illustrated in  FIG. 1 . As viewed from a subject P&#39;s perspective, a direction from side to side is defined as “X direction” (positive direction of X-axis is rightward direction, negative direction of X-axis is leftward direction), a direction from the upper side to the lower side (vertical direction) is defined as “Y direction” (positive direction of Y-axis is upward direction, negative direction of Y-axis is downward direction), and a direction from the front to the back (depth direction of the device body  20 , where the side closer to the subject P is the front and the opposite side is the back (rear)) is defined as “Z direction” (positive direction of Z-axis is frontward direction, negative direction of Z-axis is rearward direction). In addition, the front side of the ophthalmologic apparatus  10  (the side closer to the subject P) is defined as the front, and the back side (the side closer to an examiner) is defined as the rear. 
     The ophthalmologic apparatus  10  of this embodiment is a fundus imaging device for observing the fundus of a subject&#39;s eye E and capturing images of the fundus. Note that the ophthalmologic apparatus of this disclosure is not limited to a fundus imaging device and may be, for example, an ophthalmologic apparatus that enables one or both of subjective examination and objective examination (to be described), an optical coherence tomography (OCT) device, an axis length measuring device, or a tonometer. 
     As illustrated in  FIG. 1 , the ophthalmologic apparatus  10  of this embodiment includes a device body  20  and a casing (body cover)  30  that covers the device body  20 . The device body  20  includes a base  11 , a drive unit  12 , a mount  13 , a measurement head  14  as an eye information acquisition unit, a chin rest  15 , a head rest  16 , an operation unit  17 , a monitor  18 , and a control unit (control device)  19 . The base  11 , the drive unit  12 , the mount  13 , the measurement head  14 , and the control unit  19  of the device body  20  are covered by the casing  30 . The chin rest  15 , the head rest  16 , and the operation unit  17  project outward from the casing  30 . 
     In the ophthalmologic apparatus  10  of this embodiment, the mount  13  is disposed in the base  11  with the drive unit  12  involved, and the drive unit  12  enables the mount  13  to move back and forth and from side to side (in Z direction and X direction) relative to the base  11 . The mount  13  is provided with the control unit  19  and the measurement head  14 . The measurement head  14  is moved up and down (in Y direction) relative to the mount  13  by the drive unit  12 . 
     In this embodiment, the base  11  is also covered by the casing  30 , but the present invention is not limited to the configuration. The casing  30  may be fixed to the base  11  to cover the mount  13 , the measurement head  14 , the drive unit  12 , the control unit  19 , and the like on the base  11 . 
     The base  11  is provided with the chin rest  15  and the head rest  16  used for fixing the position of the subject P&#39;s face, or the subject&#39;s eye E, relative to the measurement head  14  when acquiring eye information. The chin rest  15  and the head rest  16  are moved up and down relative to the base  11  by a known drive unit (or manually). The ophthalmologic apparatus  10  acquires information associated with, for example, observation, imaging, and examination of the subject&#39;s eye E while the subject P opposes the measurement head  14 , resting his/her head on the head rest  16  and his/her chin on the chin rest  15 . 
     The operation unit  17  is operated when an examiner or the subject P gives the ophthalmologic apparatus  10  instructions such as actions and settings of the chin rest  15 , the measurement head  14 , and the drive unit  12 . The operation unit  17  of this embodiment includes a tiltable control lever  17   a  disposed on the mount  13 . The examiner operates the control lever  17   a  to move the measurement head  14  three-dimensionally relative to the base  11 . Furthermore, the control lever  17   a  is provided with a button switch  17   b  at the top. The examiner presses the button switch  17   b  to start optometry by the measurement head  14 . 
     The operation unit  17  also includes software keys such as control buttons shown on the screen  18   a  of the monitor  18 . Operating the control buttons enables various actions such as alignment relative to the subject&#39;s eye E, setting of various examination conditions, and adjustment of the screen  18   a . Note that the operation unit  17  may include input devices such as various buttons, a keyboard, and a mouse disposed around the control lever  17   a  and around the monitor  18 . 
     The monitor  18  is attached to the top of the casing  30 . The monitor  18  is, for example, a liquid crystal display (LCD monitor) and includes the screen  18   a  of touch panel type. Under control of the control unit  19 , the monitor  18  appropriately shows, for example, images of the subject&#39;s eye E (such as anterior segment images, fundus images, and OCT images) based on image data from the measurement head  14 , various kinds of examination information (such as examiner information, examination conditions, examination results, and measurement images) from the measurement head  14 , and an image of the control buttons functioning as the operation unit  17 . The monitor  18  of this embodiment is rotatably supported by the casing  30  via a rotary support mechanism  18   b , and the orientation of the screen  18   a  can be changed appropriately. For example, the screen  18   a  can be oriented to the subject, or the screen  18   a  can be turned sideways (in X direction). 
     The control unit  19  collectively controls each unit in the ophthalmologic apparatus  10 . The control unit  19  includes a CPU and a storage unit such as RAM, ROM, EEPROM, and hard disk drive. To the control unit  19 , for example, the drive unit  12 , the chin rest  15 , the operation unit  17 , the monitor  18 , the measurement head  14 , and the storage unit are connected. The control unit  19  unfolds a computer program stored in the storage unit in advance on, for example, RAM, thereby collectively controlling actions of the ophthalmologic apparatus  10  (drive unit  12 , chin rest  15 , monitor  18 , measurement head  14 ) according to the operation of the operation unit  17 . 
     The measurement head (eye information acquisition unit)  14  acquires eye information of the subject&#39;s eye E. Examples of the eye information include not only anterior segment images of the subject&#39;s eye E, fundus images of the subject&#39;s eye E, and tomographic images of the retina of the subject&#39;s eye E but also corneal endothelial images of the subject&#39;s eye E and characteristics of the subject&#39;s eye E such as refractive power, corneal shape, and intraocular pressure. 
     The measurement head  14  includes an objective optical system unit  21  that opposes the subject&#39;s eye E and a measurement optical system  22  that includes optical elements such as relay lens, imaging element, eyepiece, and light source. The objective optical system unit  21  includes an objective optical system  21   a  including at least one objective lens and a lens barrel  21   b  housing the objective optical system  21   a . As illustrated in  FIG. 1 , the objective optical system unit  21  projects outward from an opening  31  disposed in the front of the casing  30  (the side closer to the subject&#39;s eye E), which enables the objective optical system  21   a  to oppose the subject&#39;s eye E. 
     At least one of subjective examination and objective measurement is performed with the measurement head  14 . The subjective examination is an approach to acquiring information of the subject&#39;s eye E using a response from the subject P. Examples of the subjective examination include perimetry and subjective refractometry such as distance vision test, near vision test, contrast sensitivity test, and glare test. The objective measurement is an approach to acquiring information of the subject&#39;s eye E mainly using a physical method without referring to a response from the subject P. The objective measurement includes acquiring characteristics of the subject&#39;s eye E and capturing images of the subject&#39;s eye E. Examples of the objective measurement include objective refractometry, corneal topography, tonometry, fundus imaging, and optical interferometry. Since the ophthalmologic apparatus  10  of this embodiment is an ophthalmic imaging device, the measurement head  14  mainly captures fundus images. 
     The objective optical system unit  21  is disposed in the opening  31  of the casing  30 , being capable of moving up and down, from side to side, and back and forth. For this reason, the opening  31  has a size that does not prevent the objective optical system unit  21  from moving up and down and from side to side. In other words, a dimension of the opening  31  in the upward-downward direction corresponds to a length obtained by adding outside diameters of the objective optical system unit  21  and a second cover portion  42  (to be described later) that houses the objective optical system unit  21  and a moving distance in the upward-downward direction, and a dimension of the opening  31  in the rightward-leftward direction corresponds to a length obtained by adding the above outside diameters and a moving distance in the rightward-leftward direction. 
     In the related art, the subject P visually recognizes the measurement head  14  inside the casing  30  through the opening  31  with no cover  40  and sees how the measurement head  14  moves up and down, from side to side, and back and forth. Particularly, the forward movement of the measurement head  14  possibly gives the subject P a sense of fear that the measurement head  14  is approaching. For this reason, the subject P may not be able to concentrate on the examination and may glance away from a target or separate his/her face from the chin rest  15  or the head rest  16 , which affects the acquisition of the eye information. In addition, someone may put a finger in the opening  31  by mistake, or dirt, dust, and foreign matters may enter the opening  31 . The opening  31  may be covered with a curtain or the like. However, the curtain may be opened along with the movement of the objective optical system unit  21 , and it is difficult to appropriately hide the inside of the casing  30 . 
     In order to solve these problems, in the ophthalmologic apparatus  10  of this embodiment, the cover  40  is attached to the opening  31  to close the opening  31  as illustrated in  FIGS. 1 and 2A to 2C  so that the subject P does not visually recognize the inside of the casing  30 . 
     Details of the cover  40  will be described with reference to  FIGS. 2A to 2C .  FIG. 2A  is a front view of the cover  40  and the vicinity of an engagement holder  32  of the casing  30 , and  FIG. 2B  is a side view (cross-sectional view) thereof.  FIG. 2C  is a side view (cross-sectional view) of the cover  40  moved to a position different from that in  FIG. 2B . 
     As illustrated in  FIGS. 2A and 2B , the cover  40  includes a first cover portion  41  disposed in the opening  31  and the second cover portion  42  attached to an outer periphery of the objective optical system unit  21 . The first cover portion  41  disposed in the opening  31  is capable of moving up and down and from side to side but not back and forth relative to the casing  30 . The second cover portion  42  is inserted into the first cover portion  41 , being capable of moving back and forth relative to the first cover portion  41 . In other words, the first cover portion  41  and the second cover portion  42  have a nested structure (telescopic structure). 
     The first cover portion  41  has a protruding shape in side view, including a disk-shaped base plate  43  disposed in the opening  31  and a cylindrical guide  44  projecting from the base plate  43  toward the subject&#39;s eye E (the front). 
     The base plate  43  functions as a cover of the opening  31  and as an engagement portion with respect to the opening  31 . In other words, the base plate  43  engages with the engagement holder  32  disposed along the opening  31  in an inner surface of the casing  30 . The engagement holder  32  has a ring shape in plan view and has a U-shape in cross-sectional view, including a pair of holding walls  33  for holding the base plate  43  and a housing space  34  partitioned by the pair of holding walls  33  to house the base plate  43 . A distance between inner surfaces of the pair of holding walls  33  (width of the housing space  34 ) is substantially equal to a thickness of the base plate  43  (length in the forward-rearward direction). 
     Accordingly, the base plate  43  can freely move up and down and from side to side (that is, in X-Y plane) within the housing space  34  while touching the inner surfaces of the pair of holding walls  33  and closing the opening  31 . Simultaneously, the movement of the base plate  43  in the forward-rearward direction is suppressed (blocked). Furthermore, when the first cover portion  41  moves in X-Y plane, an outer peripheral edge of the base plate  43  abuts a bottom face  35  of the housing space  34  or an outer periphery of the guide  44  abuts a peripheral edge of the opening  31 , thereby suppressing further movement. Therefore, the engagement holder  32  functions as a movement controller that allows the first cover portion  41  to move up and down and from side to side by a predetermined distance but suppresses the movement of the first cover portion  41  in the forward-rearward direction and functions as a retainer that prevents the cover  40  from coming off the opening  31 . In addition, closing the opening  31  by the base plate  43  appropriately prevents penetration of dirt and the like into the casing  30  from the opening  31  and prevents insertion of a finger. 
     The guide  44  of the first cover portion  41  has a cylindrical shape with both ends opened, including an inward flange  44   a  projecting toward the center from a peripheral edge of one (front) end opposing the subject&#39;s eye E. An inner peripheral edge of the inward flange  44   a  is an insertion hole  44   b  through which the second cover portion  42  is inserted. 
     In this embodiment, the engagement holder  32 , a separate member from the casing  30 , is fixed to the inner surface of the casing  30 , but the present invention is not limited to this configuration. For example, an L-shaped member in cross-sectional view may be fixed to the inner surface of the casing  30 , and a wall of this member and a wall of the casing  30  may form an engagement holder. Alternatively, the casing  30  may have a thick wall, and the wall may be hollowed out along an inner periphery of the opening  31  to form a housing space, thereby forming an engagement holder. 
     The second cover portion  42  is a tubular member with both ends opened (cylindrical member in this embodiment), including a housing space  45  for housing the objective optical system unit  21 . In other words, the second cover portion  42  is attached to the outer periphery of the objective optical system unit  21 , being capable of moving up and down, from side to side, and back and forth together with the measurement head  14  including the objective optical system unit  21 . The second cover portion  42  is inserted into the insertion hole  44   b  of the guide  44  of the first cover portion  41 , being capable of moving back and forth. An inside diameter of the insertion hole  44   b  and an outside diameter of the second cover portion  42  are substantially equal. While the second cover portion  42  closes the insertion hole  44   b , the second cover portion  42  touches an inner surface of the insertion hole  44   b  and moves back and forth. However, the movement of the second cover portion  42  relative to the first cover portion  41  is suppressed in the upward-downward direction and the rightward-leftward direction. 
     Therefore, when the measurement head  14  moves back and forth, the second cover portion  42  moves back and forth within the guide  44  of the first cover portion  41  independently from the first cover portion  41 . When the measurement head  14  moves up and down and from side to side, the second cover portion  42  moves up and down and from side to side together with the first cover portion  41 . In addition, dirt and the like are prevented from penetrating into the casing  30  from the insertion hole  44   b.    
     Furthermore, the second cover portion  42  is provided with an outward flange  46  projecting radially outward from a peripheral edge of the rear end. The outward flange  46  has a dimension large enough to touch a guide surface  44   c  of the guide  44  of the first cover portion  41 . When the second cover portion  42  moves back and forth, the outward flange  46  moves along the guide surface  44   c  while touching the guide surface  44   c . The guide  44  appropriately guides the movement of the second cover portion  42  in the forward-rearward direction, suppresses rattles, vibrations, and the like during the movement, and supports smooth movement of the second cover portion  42 . 
     When the second cover portion  42  moves forward, the outward flange  46  abuts the inward flange  44   a  of the guide  44  to suppress further movement. Therefore, the outward flange  46  and the inward flange  44   a  double as a movement controller and as a retainer of the second cover portion  42 . 
     A moving distance of the second cover portion  42  in the forward-rearward direction substantially accords with a moving distance of the measurement head  14  in the forward-rearward direction (operating distance for alignment). When the measurement head  14  moves forward to the maximum together with the second cover portion  42 , it is desirable that the outward flange  46  abuts the inward flange  44   a  or is arranged at a position leaving a predetermined margin without abutting the inward flange  44   a . On the other hand, when the measurement head  14  moves backward to the maximum together with the second cover portion  42  as illustrated in  FIG. 2C , it is preferable that one (front) end surface of the first cover portion  41  (more specifically, the guide  44 ) and one (front) end surface of the second cover portion  42  are flush with each other. In this manner, adjusting the dimension of each member prevents the second cover portion  42  from coming off the first cover portion  41  or coming off the objective optical system unit  21  and prevents influences on the movement of the measurement head  14 . 
     The first cover portion  41  and the second cover portion  42  are not particularly limited in material and may employ a metallic material, a resin material, or the like. However, a resin material is desirable from viewpoints of, for example, cost reduction, enhancement of adhesion between the members, and reduction of noise and abrasion caused by a rub between the members. Examples of the resin material include, but are not limited to, polycarbonate resin, ABS resin, polyacetal resin, and nylon resin. 
     The first cover portion  41 , the second cover portion  42 , and even the engagement holder  32  preferably employ, for example, an elastic resin material such as polyurethane resin or polyester resin. Such a resin material enhances the adhesion of a sliding portion, or a contacting portion, between the engagement holder  32  and the first cover portion  41  and a sliding portion between the first cover portion  41  and the second cover portion  42 , which further prevents formation of a gap that allows penetration of dust and the like. Even when one of two contacting parts includes an elastic resin material and the other includes a relatively hard resin material, the contacting parts can move smoothly while adhering to each other not to form a gap. 
     It is also preferable to provide a friction reducer that reduces frictional resistance on the sliding portion (contacting surface) between the engagement holder  32  and the first cover portion  41  and the sliding portion (contacting surface) between the first cover portion  41  and the second cover portion  42 . Examples of the friction reducer include fluororesin applied to the surface of each sliding portion (contacting surface) and a fluororesin-processed sheet spread on the surface of each sliding portion. It is also preferable to dispose a slide bearing on each sliding portion (contacting surface). Accordingly, it is possible to reduce friction of the sliding portions, which appropriately prevents noise and abrasion, and what is more, it is possible to move the first cover portion  41  and the second cover portion  42  more smoothly without causing rattles and vibrations. 
     Moving distances of the first cover portion  41  in the upward-downward direction and the rightward-leftward direction substantially accords with moving distances of the measurement head  14  in the upward-downward direction and the rightward-leftward direction. The measurement head  14  moves up and down depending on a distance between the base  11  and the chin rest  15  in the upward-downward direction and a distance between the chin rest  15  and the subject&#39;s eye E in the upward-downward direction. In the ophthalmologic apparatus  10  that acquires eye information of one subject&#39;s eye E on the right or left and then acquires eye information of the other, the measurement head  14  moves from the position of one subject&#39;s eye E to the position of the other in the rightward-leftward direction. In other words, since the measurement head  14  moves within at least an interpupillary distance PD between right and left subject&#39;s eyes E, the first cover portion  41  also moves together with the second cover portion  42  within a moving distance corresponding to the interpupillary distance PD. 
     In view of the above configuration, the opening  31  is opened not to hinder the movement of the first cover portion  41  within the moving distances in the upward-downward direction and the rightward-leftward direction. The base plate  43  of the first cover portion  41  has a size (surface area) large enough to close the opening  31  constantly even when the base plate  43  moves up and down and from side to side within the moving distances. 
     The procedure for assembling the cover  40  and the casing  30  having the aforementioned configuration will be described with reference to  FIG. 3 .  FIG. 3  is a plan view of the cover  40  and the casing  30  as viewed from the upper side, describing the procedure for assembling the cover  40  and the casing  30 . As illustrated in  FIG. 3 , the casing  30  includes two right and left parts (casings  30   a  and  30   b ), and the engagement holder  32  is also divided into two right and left parts (engagement holders  32   a  and  32   b ) and fixed to inner surfaces of the casings  30   a  and  30   b . The two casings  30   a  and  30   b  are disposed around the device body  20  from both sides and are connected to each other by a fitting structure such as a recess and a protrusion or by a fixing member such as a screw, thereby covering the device body  20 . Note that the casing  30  is not limited to this configuration and may have any configuration as long as the casing  30  holds the first cover portion  41 . 
     First, as illustrated in  FIG. 3 , in the device body  20  having the drive unit  12 , the mount  13 , the measurement head  14 , the control unit  19 , and the like assembled on the base  11 , the second cover portion  42  is attached to the outer periphery of the objective optical system unit  21  of the measurement head  14 . Next, the first cover portion  41  is moved from the front to the rear of the second cover portion  42 , and the first cover portion  41  is disposed in the outer periphery of the second cover portion  42 . At this time, the second cover portion  42  is inserted into the guide  44  of the first cover portion  41 , and one end of the second cover portion  42  projects from the insertion hole  44   b.    
     Next, the two casings  30   a  and  30   b  are attached to the device body  20  from both sides, and the base plate  43  of the first cover portion  41  is engaged with the engagement holders  32   a  and  32   b . The two casings  30   a  and  30   b  are coupled to each other, thereby completing the attachment of the cover  40  to the casing  30 . Since the casing  30  and the cover  40  are assembled with such a structure, the first cover portion  41  is held by the casing  30  while being fixed to the casing  30 , which appropriately prevents the first cover portion  41  from moving back and forth and from falling off the casing  30 . In addition, the functions of the inward flange  44   a  and the outward flange  46  prevent the second cover portion  42  from falling off the first cover portion  41 . 
     The process for disassembling these components is opposite to the assembly. First, the casings  30   a  and  30   b  are uncoupled and detached from the device body  20 . Next, the first cover portion  41  is moved forward and detached from the second cover portion  42 , and then, the second cover portion  42  is moved forward and pulled out from the tip of the objective optical system unit  21 . In this manner, the cover  40  and the casing  30  are assembled and disassembled easily. 
     Hereinafter described are functions and effects of the cover  40  when acquiring eye information with the ophthalmologic apparatus  10  having the aforementioned configuration. First, a subject P puts his/her head on the head rest  16  and his/her chin on the chin rest  15  to oppose the ophthalmologic apparatus  10 . Next, an examiner operates the operation unit  17  to select a subject&#39;s eye E from which eye information is to be acquired and gives an alignment instruction. The control unit  19  receives instruction signals and drives the drive unit  12  to move the measurement head  14  up and down and from side to side, thereby aligning the measurement head  14  in the upward-downward direction and the rightward-leftward direction. At this time, following the movement of the measurement head  14 , the objective optical system unit  21  and the second cover portion  42  and the first cover portion  41  housing the objective optical system unit  21  move up and down and from side to side within the opening  31  of the casing  30 . Accordingly, the opening  31  is constantly covered with the first cover portion  41 , and the subject P does not visually recognize the movement of the measurement head  14  inside the casing  30 . 
     Furthermore, the control unit  19  moves the measurement head  14  back and forth to align in the forward-rearward direction. The objective optical system unit  21  and the second cover portion  42  move back and forth inside the first cover portion  41 , following the movement of the measurement head  14 , but the first cover portion  41  engaged with the engagement holder  32  of the casing  30  does not move back and forth and keeps covering the opening  31 . Accordingly, the subject P does not visually recognize the movement of the measurement head  14  in the forward-rearward direction. This makes it possible for the subject P to concentrate on the acquisition of the eye information without feeling a sense of fear that the measurement head  14  is approaching the subject&#39;s eye E. 
     On completion of the alignment, the control unit  19  receives a measurement instruction from the examiner through the operation unit  17  or automatically controls the measurement head  14  so as to acquire the eye information of the subject&#39;s eye E. Since the subject P can concentrate on the acquisition of the eye information, it is possible to acquire the eye information appropriately and efficiently. In addition, the cover  40  attached to the opening  31  appropriately prevents dirt, dust, and foreign matters from penetrating into the opening  31  and prevents a finger or the like from entering the opening  31  by mistake. 
     Accordingly, it is possible to provide the ophthalmologic apparatus  10  and the cover  40  that appropriately hide the movement of the measurement head  14  as the eye information acquisition unit and appropriately acquire information of a subject&#39;s eye. Furthermore, the cover  40  having such excellent effects is formed by a simple configuration including the first cover portion  41  and the second cover portion  42 . Accordingly, it is possible to provide the cover  40  that is easy to assemble and disassemble. 
     Modification 
     Next, covers  40 A to  40 C of first to third modifications will be described with reference to  FIGS. 4A to 6B .  FIGS. 4A, 5A, and 6A  are front views of the vicinity of the covers  40 A to  40 C, and  FIGS. 4B, 5B, and 6B  are side views (cross-sectional views) thereof. The covers  40 A to  40 C of the first to third modifications are basically similar to the cover  40  of the first embodiment, each including a first cover portion  41  and a second cover portion  42 . Components similar to those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted. Hereinafter described are configurations different from the first embodiment. 
     First, the cover  40 A of the first modification illustrated in  FIGS. 4A and 4B  will be described. In the cover  40  of the first embodiment, the base plate  43  is used as an engagement portion, and the casing  30  includes the engagement holder  32  to be engaged with the base plate  43 . On the other hand, in the cover  40 A of the first modification, a wall around a peripheral edge of an opening  31  of a casing  30  functions as an engagement portion  36 , and an engagement holder  47  that engages with the engagement portion  36  is disposed on a base plate  43 . The base plate  43  of the first modification includes two disk-shaped holding walls  47   a  arranged at an interval substantially equal to a thickness of the wall of the casing  30  in the forward-rearward direction, and a space between the holding walls  47   a  is used as a housing space  47   b  that houses (engages with) the engagement portion  36 . 
     In the first modification, the second cover portion  42  and the first cover portion  41  housing the objective optical system unit  21  both move up and down and from side to side, following the movement of the measurement head  14  in the upward-downward direction and the rightward-leftward direction. At this time, the first cover portion  41  moves within the opening  31  along the engagement portion  36  while holding the engagement portion  36 . In addition, an outer periphery (a bottom face  47   c ) of a guide  44  abuts a peripheral edge of the engagement portion  36  inside the housing space  47   b  so as to suppress the movement of the first cover portion  41 . The movement of the first cover portion  41  in the forward-rearward direction is suppressed by the engagement between the engagement portion  36  and the holding walls  47   a  of the engagement holder  47 , and the second cover portion  42  housing the objective optical system unit  21  moves back and forth. Accordingly, the cover  40 A of the first modification can also exert effects similar to those of the first embodiment, and the structure around the opening  31  of the casing  30  can be made simpler. 
     In the cover  40 B of the second modification illustrated in  FIGS. 5A and 5B , the first cover portion  41  is composed of a disk-shaped base plate  43 . The base plate  43  is engaged with an engagement holder  32  of a casing  30 , being capable of moving up and down and from side to side. The second cover portion  42  is inserted into an insertion hole  43   a  disposed in the base plate  43 , being relatively movable in the forward-rearward direction. The second modification also offers functions and effects similar to those of the first embodiment and provides the cover  40 B having a simpler configuration. 
     The cover  40 C of the third modification illustrated in  FIGS. 6A and 6B  is used in an ophthalmologic apparatus including stereo cameras (imaging units)  23   a  and  23   b  that acquire images of a subject&#39;s eye E for alignment. In this ophthalmologic apparatus, a measurement optical system  22  housed in a measurement head  14  includes optical elements such as an objective optical system unit  21 , a lens, and an imaging element and also includes the stereo cameras  23   a  and  23   b  and light sources  24  for illumination. A total of four light sources  24  are disposed in pairs near the stereo cameras  23   a  and  23   b.    
     In the cover  40 C of the third modification, the second cover portion  42  is a rectangular tubular member having a rectangular shape elongated in the rightward-leftward direction in plan view as illustrated in  FIG. 6A  so as to house all of the objective optical system unit  21 , the stereo cameras  23   a  and  23   b , and the four light sources  24 . The second cover portion  42  is not limited to the rectangular tubular member and may be, for example, an elliptical cylindrical member having an elliptical or oval shape in plan view. The second cover portion  42  may have an appropriate shape according to, for example, design or angles of view and arrangements of the stereo cameras  23   a  and  23   b.    
     Furthermore, in the first cover portion  41  through which the second cover portion  42  is inserted, a guide  44  is a rectangular tubular member including a rectangular insertion hole  44   b , and a base plate  43  is formed into a rectangular shape. Still further, an engagement holder  32  with which the base plate  43  is engaged and an opening  31  are formed into a rectangular shape but are not limited thereto. According to moving distances of the measurement head  14  in the upward-downward direction and the rightward-leftward direction, these members may have a shape or size that appropriately covers the opening  31  without hindering the movement of the objective optical system unit  21  and the stereo cameras  23   a  and  23   b . The cover  40 C of the third modification may also include the engagement holder  47  as in the first modification or may include the first cover portion  41  composed of the base plate  43  as in the second modification. 
     The cover  40 C of the third modification houses the objective optical system unit  21 , the stereo cameras  23   a  and  23   b , and the four light sources  24  but is not limited thereto. For example, similarly to the second cover portion  42  of the first embodiment, the cover  40 C may be a cylindrical member and house the objective optical system unit  21 . In this case, an inward flange  44   a  or the base plate  43  of the first cover portion  41  is provided with openings on the right and left sides of an insertion hole  44   b  so that the stereo cameras  23   a  and  23   b  and the light sources  24  can be seen through the openings. A glass plate for preventing penetration of dust and the like is desirably disposed in the openings. Even with such a configuration, the first cover portion  41  and the second cover portion  42  move up and down and from side to side together with the objective optical system unit  21 , the stereo cameras  23   a  and  23   b , and the light sources  24 . In addition, even when the objective optical system unit  21 , the stereo cameras  23   a  and  23   b , and the light sources  24  move back and forth relative to the first cover portion  41 , the openings are located on optical paths (on optical axes) of the stereo cameras  23   a  and  23   b . Accordingly, it is possible to capture images of the subject&#39;s eye E by the stereo cameras  23   a  and  23   b  through the openings of the first cover portion  41 . 
     Although the ophthalmologic apparatus of this disclosure is described based on the embodiment and modifications, the specific configuration is not limited by these embodiment and modifications. Changes or additions of the design are allowed without departing from the gist of the disclosure according to the claims. 
     For example, in the above embodiment and modifications, the measurement head  14  moves up and down, from side to side, and back and forth, but the measurement head  14  may be configured to rotate about an axis parallel to Y-axis. Such a configuration makes it possible to acquire eye information of a subject&#39;s eye E not only from the front but also from a desired angle. In addition, the measurement head  14  may be configured to move in any one direction or two directions of the upward-downward direction, the rightward-leftward direction, and the forward-rearward direction. 
     In the embodiment, the monitor  18  is rotatable by the rotary support mechanism  18   b , but the present invention is not limited thereto. For example, the monitor  18  may be fixed to the casing  30  in a non-rotatable manner. Furthermore, the monitor  18  may be detachable from the casing  30  and may be connected to the control unit  19 , enabling transmission and reception of data by short-range wireless communication such as Wi-Fi (registered trademark) or Bluetooth (registered trademark).