Fundus camera

A fundus camera being capable of moving a fixation target surely and precisely to a position intended for photographing with an adequate degree of freedom for moving the fixation target. The fundus camera is provided with an observation optical system having an objective lens and a photographing element for photographing a fundus illuminated with illumination light, a monitor on which an image of the photographed fundus is displayed, a fixation-target presenting optical system for presenting a fixation target via the objective lens, a fixation-target moving unit by which a position to present the fixation target is shifted to a desired position, a first display-control unit by which the position of the fixation target is superposed on the fundus image to be displayed on the monitor, and a second display-control unit by which a guide target for moving the fixation target is displayed in a predetermined position on the monitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fundus camera for photographing a fundus of an eye to be examined.

2. Description of Related Art

Fundus cameras for photographing a periphery of a fundus are known constructed such that an internal fixation target (fixation light) may be moved to guide a line of sight of an examinee. For moving a fixation target, several methods have been suggested, for example, a method by which a point light source as a fixation target is moved with a lever and the like, and a method by which one of a plurality of point light sources provided in predetermined positions is selectively lit. For recognizing a travel position of the fixation target, a method has been suggested by which an image of the fixation target is optically synthesized and displayed together with an image of the fundus on a monitor for observation.

According to the method by which the point light source is moved with the lever and the like, the position of the fixation target maybe recognized through observation on the monitor. However, if a periphery of the fundus is divided every 60° degrees into six sections for photographing to obtain six images, for instance, it is difficult to place the fixation target in each position intended for photographing. On the other hand, according to the method by which one of the plurality of point light sources is selectively lit, the fixation target may be placed in the position intended for photographing provided that coordinates of lighting positions are predetermined. This method, however, ensures only a low degree of freedom for photographing outside the predetermined positions.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a fundus camera capable of moving a fixation target surely and precisely to a position intended for photographing with an adequate degree of freedom for moving the fixation target.

To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, a fundus camera for photographing a fundus of an eye to be examined is provided with: an observation optical system; a monitor; a fixation-target presenting optical system; a fixation-target moving unit; a first display-control unit; and a second display-control unit. The observation optical system has an objective lens and a photographing element for photographing the fundus of the eye to be examined via the objective lens while illuminating the fundus with illumination light for observation. An image of the photographed fundus is displayed on the monitor. In the fixation-target presenting optical system, a fixation target is presented via the objective lens to be visually identified by the eye. The fixation-target moving unit shifts a position to present the fixation target to a desired position. The position of the fixation target to be shifted is superposed on the fundus image to be displayed on the monitor by the first display-control unit. A guide target for moving the fixation target is displayed in a predetermined position on the monitor by the second display-control unit.

In another aspect of the invention, the fundus camera is provided with: an observation optical system; a monitor (a display); a fixation-target presenting optical system; a fixation-target moving unit; a first display-control unit; a second display-control unit; and a specifying unit. The observation optical system has an objective lens and a photographing element for photographing the fundus of the eye to be examined via the objective lens while illuminating the fundus with illumination light for observation. An image of the photographed fundus is displayed on the monitor. In the fixation-target presenting optical system, a fixation target is presented via the objective lens to be visually identified by the eye. The fixation-target moving unit shifts a position to present the fixation target to an intended position. The position of the fixation target to be shifted is superposed on the fundus image to be displayed on the monitor by the first display-control unit. The second display unit has a program by which at least one of plural patterns of guide targets for moving the fixation target is displayed in a predetermined position on the monitor. The specifying unit specifies at least one of the plural patterns of the guide targets.

Additional objects and advantages of the invention are set forth in the following description, are obvious from the description, or may be learned by practicing the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations particularly pointed out in the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of preferred embodiments of a fundus camera consistent with the present invention will now be given referring to the accompanying drawings.FIG. 1is a view showing a schematic configuration of an optical system in a fundus camera of a non-midriasis type as a first preferred embodiment. The optical system is provided with an illumination optical system1, a photographing optical system2, an observation optical system3and a fixation-target presenting optical system35.

Illumination light emitted from a halogen lamp10being a light source for observation passes through a condenser lens11to be converted into infrared illumination light by an infrared filter12having a wavelength-selecting property of transmitting infrared light. Thereafter, the light is reflected by a half mirror15and illuminates a ring slit16having a ring-shaped aperture. Alternatively, instead of the halogen lamp10, it may be possible to use such an infrared light source as an infrared LED, which would eliminate the need for the filter12. Besides, instead of the half mirror15, it may also be possible to use a dichroic mirror having a wavelength-selecting property of reflecting infrared light and transmitting visible light.

Visible illumination light emitted from a flash lamp13being a light source for photographing passes through a condenser lens14, and is transmitted by the half mirror15to be made coaxial with the infrared illumination light, so that the visible illumination light illuminates the ring slit16.

The illumination light having passed through the slit16(ring-slit light) forms an intermediate image in the vicinity of an aperture of an apertured mirror21via a relay lens17a, a mirror18, a black-dot plate19with a small black dot on its center, and a relay lens17b. The light is then reflected to be coaxial with an optical axis of the photographing optical system2. Once the illumination light (the ring-slit light) reflected by the mirror21forms an image via an objective lens20in the vicinity of the pupil of an eye E to be examined, the light is diffused to illuminate a fundus Ef of the eye E uniformly. When entering the lens20, the illumination light (the ring-slit light) may generate some amount of reflected light which would be detrimental at the time of observing and photographing an image of the fundus Ef. Therefore, it is arranged that the detrimental light should be absorbed by a small black dot provided in the center of the black-dot plate19.

Once the light reflected from the fundus Ef forms an intermediate image of the fundus Ef via the lens20, the reflected light enters a return mirror25through the aperture of the mirror21, a photographic diaphragm22, a focusing lens23movable in the direction of the optical axis, and an image forming lens24. The return mirror25is placed in a position indicated by solid lines at the time of observation while it is placed in a position indicated by broken lines at the time of photographing. The visible light reflected from the fundus Ef, which is not reflected by the return mirror25if the mirror25is placed in the position of the broken lines, enters a color CCD camera26having a sensitivity to the visible region, and then forms an image of the fundus Ef on a photographing surface of the camera26.

The return mirror25is placed in the position of the solid lines except when photographing is performed.) A half mirror30has a reflectance larger than its transmittance. On an optical path in the direction of reflection from the half mirror30are disposed a relay lens31and a CCD camera32for observation having a sensitivity to the visible region through the infrared region. The infrared light reflected from the fundus Ef, which is reflected by the return mirror25if the mirror25is placed in the position of the solid lines, is further reflected by the half mirror30, and then enters the camera32through the lens31to form an image of the fundus Ef on a photographing surface of the camera23. Output from the camera32is inputted to a color monitor50which doubles as a monochrome monitor, so that an image ER of the fundus Ef is displayed on the monitor50.

A fixation-target presenting optical system35comprises a point light source36as a fixation target and a relay lens37, and shares the optical path from the return mirror25to the lens20with the observation optical system3via the half mirror30. It is arranged that the point light source36should be moved within a plane approximately conjugate with the fundus Ef and the photographing surface of the camera32by operating a lever40. The point light source36is mounted on the lever40. The lever40, in which an oblong hole40ais formed, is retained on an enclosure part45of the fundus camera by a screw43and the like so as to slide smoothly. Part of the lever40extends off the enclosure45, enabling an examiner to operate the lever40to move the point light source36, so that the fundus Ef (a line of sight) may be guided to a desired part for photographing.

A reflecting mirror39is provided in the opposite side of the lens31beyond the half mirror30. The mirror39is disposed at a position approximately conjugate with the photographing surface of the camera32via the lens31and also approximately conjugate with the point light source36via the lens37. When the point light source36is lit, part of its light is reflected by the half mirror30to head for the mirror39, by which the light is reflected again to return to the mirror30. Part of the light transmitted by the half mirror30forms an image on the photographing surface of the camera32via the lens31. Thus, an image36′ of the fixation target is superposed on the fundus image ER to be displayed on the monitor50. (The position of the fixation target on the fundus image ER is indicated.)

FIG. 2is a block diagram illustrating a primary part of a control system in the fundus camera consistent with the present invention. Outputs from the cameras32and26are inputted to an image-processing part51, which receives control signals from a control part55so as to graphically generate guide targets100for guiding the travel position of the fixation target. The image-processing part51then superposes the guide targets100on the fundus image (an image observed) through the camera32and displays the resultant on the monitor50. The fundus image (an image photographed) with the camera26is stored in an image memory52contained in the image-processing part51. Thereafter, outputs from the image-processing part51are switched in response to control signals from the control part55, so that the fundus image ER from the camera26is displayed in color on the monitor50.

Connected to the control part55are a switch part56including a photographing-mode selection switch56a, an image-storage part57, a photographing switch58, and the like. Also, connected to the control part55may be an external computer60. Image data stored in the image-storage part57may be transferred to and outputted on the computer60.

A description will now be given to operations performed in the above-described configuration. First, how to move the fixation target to a desired position will be explained.

An image of an eye E illuminated with infrared light from the lamp10and through the filter12is formed on the photographing surface of the camera32, and the formed image is displayed on the monitor50. An examiner performs alignment (position adjustments) of a main body of the fundus camera with respect to the eye E. Also, he moves the lens23to achieve proper focus. When he lights the point light source36, the light is collected into the fundus Ef through the lens37, the half mirror30, the return mirror25, the lens24, the lens23, the diaphragm22, the aperture of the mirror21, and the lens20. Thus, an examinee (the eye E) visually identifies the point light source36as a fixation target, and a line of sight of the examinee (the eye E) is guided accordingly.

Part of the light emitted from the point light source36, which has been reflected by the mirror30, is further reflected by the mirror39, and the reflected light forms an image on the photographing surface of the camera32via the half mirror30and the lens31. As a result, the fixation-target image36′ is displayed on the monitor50as well as the fundus image ER.

While observing the fundus image ER and the fixation-target image36′ on the monitor50, the examiner operates the lever40to move the point light source36to a desired position so that he may observe a desired part of the fundus Ef. When he determines a position to be photographed, he depresses the switch58to perform photographing.

Next, an explanation will now be given to a fundus image111obtained by photographing a posterior pole of the fundus Ef such that it appears in the center and six fundus images112–117obtained by splitting a periphery of the posterior pole every 60° degrees and by photographing each section as shown inFIG. 3. These kinds of fundus images are needed for examining such a disease as diabetic retinopathy.FIG. 4shows a sequence of photographing while moving the fixation-target image36′ to seven spots in total from the center to the periphery (of which circumference is split every 60° degrees) on the monitor50in order to obtain the images shown inFIG. 3.

Prior to photographing, a guide-target displaying mode is selected with the switch56a. When this mode is selected, a cross mark101indicating the center and six peripheral line marks102–107splitting the circumference every 60° degrees are graphically synthesized to be displayed as the guide targets100on the monitor50where the fundus image ER and the fixation-target image36′ are displayed (seeFIG. 2.)

The examiner moves the point light source36according to the guide targets100displayed on the monitor50. First, in order to photograph a first image, namely, the fundus image111in which the posterior pole appears in the center, he moves the point light source36by operating the lever40so as to place the fixation-target image36′ in the center of the position where the cross mark101is displayed. After having guided the line of sight of the examinee (the eye E) successfully by moving the point light source36, he depresses the switch58to obtain a fundus image. When trigger signals from the switch58are consequently inputted to the control part55, the control part55lays the return mirror25in the position of the broken lines and lights the lamp13to illuminate the fundus Ef with visible light. The light reflected from the fundus Ef travels along the optical path of the photographing optical system2to enter the photographing surface of the camera26, so that the fundus image is obtained.

When the image photographed with the camera26is stored in the image memory52, the image thus stored is displayed as a still-frame image on the monitor50by the image-processing part51. The examiner checks the image, and if it is sharp enough, he depresses an image-storage switch56band proceeds to photograph the next part. When the switch56bis depressed, the image stored in the image memory52is transferred to and stored in the image-storage part57. If the photographed image is not sharp enough, the examiner depresses a cancellation switch56cto redo the photographing.

The depression of the switch56bor56cchanges the display on the monitor50to the image observed from the camera32, and the guide targets100are then displayed, superposed on the fundus image ER (the observed image.)

In order to photograph a second image, namely, the image112of the periphery of the fundus Ef, the examiner moves the point light source36by operating the lever40so as to place the fixation-target image36′ in a position where the line mark102is displayed, and then performs photographing. Subsequently, in a like manner, the fundus images113,114,115,116and117may be obtained by photographing while moving the point light source36so as to place the fixation-target image36′ sequentially in the positions where the line marks103,104,105,106and107are each displayed. Thus, the present preferred embodiment adopts a method by which the fixation target may be moved arbitrarily while it is presented. The method therefore enables the line of sight of the examinee to follow a movement of the fixation target more easily than a method by which a position for the fixation target to be displayed is changed over selectively.

It should be noted that, in photographing with reference to the above-mentioned guide targets100, the examiner may distinguish easily which part is to be photographed if a display form of the respective marks of the guide targets100varies according to the sequence of photographing. In photographing with the fixation-target image36′ moved in the above-described sequence, for example, the image-processing part51blinks the cross mark101first. Upon input of photographing-completion signals with a depression of the switch56b, the image-processing part51blinks the line mark102for the next part to be photographed. Subsequently, upon every input of the photographing-completion signals, the image-processing part51blinks the line marks103–107in sequence so as to notify the examiner about the shift in the travel position of the fixation target. This process may prevent the examiner from skipping any intended part to be photographed. The respective marks of the guide targets100may be designed not to blink but to change their color instead, or it may be possible to display only one mark in the position to which the fixation target should be moved. In those cases, the sequence of photographing is preprogrammed and stored in a memory in the control part55, which instructs the image-processing part51to change the display form of the guide targets100.

Otherwise, the respective marks of the guide targets100may also be designed such that one of the marks disappears or changes its color when the fixation target is positioned at that particular mark or when the fixation target is positioned at the particular mark and the photographing is then completed (i.e. the trigger signals for photographing are inputted, or the photographing-completion signals are inputted, or the like.) That allows the examiner to be notified about the completion of the photographing, dispensing with any preprogrammed sequence of photographing. In this case, the control part55detects the travel position of the fixation target by detecting via the image-processing part51the position of the fixation-target image36′ which has entered the camera32. The position of the fixation-target image36′ is detected based on its size and quantity of light. (Since the quantity of light from the point light source36is larger than the fundus-reflected light which is rather feeble, a threshold level of the light quantity may be a basis of the detection.) Alternatively, the detection of the travel position of the point light source36may also be made possible by providing a light-beam separation mirror between the half mirror30and the reflecting mirror39and by disposing a two-dimensional position-detecting sensor such as PSD in the direction of light-beam separation. In addition, another alternative is to provide the vicinity of the point light source36with a sensor detecting the travel position of the point light source36so that the travel position of the fixation target is detected directly.

The travel position of the fixation target does not necessarily have to be detected precisely; it is sufficient to find a positional relationship of the fixation target with respect to the part to be photographed. Accordingly, the travel position of the fixation target is detected in each section of a seven-divided area as indicated by dotted lines inFIG. 5.

As described above, moving the point light source36according to the guide targets100may facilitate and ensure proper photographing of the periphery of a fundus in intended positions or at predetermined angles.

In addition, the images thus obtained mean that the line of sight has been guided based on proper positional relationships. A panoramic image of good quality may therefore be created when the images stored in the image-storage part57are transmitted to, and are linked together by the external computer60.

It should be noted that the guide targets are not limited to the above patterns; an optimum pattern of the guide targets may be selected from a plurality of patterns corresponding with various types of photographing. The plurality of patterns are preprogrammed and stored in the memory in the control part55, and the selected pattern is displayed by the image-processing part51under instructions from the control part55in correspondence with a selection made with a guide-target selection switch56d.

FIG. 6is a partial schematic view showing a second preferred embodiment, namely, a modification of the fixation-target presentation; an example in which, in contrast to the first preferred embodiment, a liquid crystal display (LCD)70is employed as a point light source for the fixation target to be moved to a desired position. The LCD70is disposed at a position approximately conjugate with the fundus Ef and the photographing surface of the camera32, and a light source71is disposed behind the LCD70. As shown inFIG. 7, the control part55controls placement of a light-transmitting portion (aperture)70aand a light-shielding portion70bboth included in the LCD70. The transmitting portion70ais illuminated by the light source71so as to function as a point light source. The lighting position (the position of the transmitting portion70a) may be shifted to a desired position by an examiner operating a fixation-target shift switch80such as a cross key.

According to the second preferred embodiment, the fixation target (the fixation-target image36′) to be displayed on the monitor50is electrically synthesized, while it is optically synthesized according to the first preferred embodiment. To be more specific, operating the switch80connected to the control part55shifts the position of the transmitting portion70aand its positional information is converted into electronic signals to be captured by the control part55. With reference to the positional information, a character70C, which has been generated by the image-processing part51, is superimposed on a fundus image ER to be displayed on the monitor50. (The position of the fixation target on the fundus image ER is indicated.) Since the guide targets100are also displayed on the monitor50in the second preferred embodiment, the fixation target is moved with the switch80such that the character70C is placed at one of the marks of the guide targets100as appropriate for photographing. As a matter of course, the display form of the guide targets100may be varied.

As described up to this point, according to the present invention, a fixation target may be moved surely and precisely to a position intended for photographing while an adequate degree of freedom is secured for moving the fixation target.