Abstract:
An ophthalmic photography apparatus is provided in which focus and alignment can be adjusted over the whole period of infrared light-excited fluorescence photography. During alignment and focus adjustments, the brightness of index light sources used for such adjustments is increased. When the shutter is operated, the brightness of the index light sources is decreased, dimming the indexes. When the automatic gain control of the imaging device functions in the later phase of the photography, the brightness of the indexes is gradually increased. In the first part of the photography period, the indexes are dimmed to prevent the images thereof from showing up on the recording images, and are brightened in the later stages to make the indexes easier to see.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an ophthalmic photography apparatus, and more particularly to an ophthalmic photography apparatus that can be used for non-mydriatic and mydriatic eye fundus color photography, visible light-excited fluorescence image photography, and infrared light-excited fluorescence image photography.  
         [0003]     2. Description of the Prior Art  
         [0004]     There are ophthalmic photography apparatuses such as fundus cameras and the like that, in addition to being capable of non-mydriatic and mydriatic color photography of the eye fundus, are also capable of photography by visible light-excited fluorescence (also designated as fluorescein angiography; FAG) and photography by infrared light-excited fluorescence (also designated as indocyanine green angiography; ICG). In each of these photographic modes, the apparatus is aligned and focused while observing the eye fundus, and the eye fundus is then photographed by operating a shutter switch.  
         [0005]     The alignment and focusing prior to photography are done by projecting an alignment index and a focus index onto the eye to be examined and controlling the index light quantities according to the state of a photoelectric transducer receiving the image from the eye fundus (Japanese Laid Open Patent Publication No. 1987-41637), controlling the index brightness in accordance with the gain of an electronic camera (Japanese Laid Open Patent Publication No. 1997-66032), shielding the indexes during the fluorescence photography (Japanese Laid Open Patent Publication No. 1999-197113), shielding the indexes during photography (Japanese Laid Open Utility Model Publication No. 1993-102), or changing the wavelength of the observation light with the passing of the time during infrared light-excited fluorescence photography (Japanese Laid Open Patent Publication No. 2004-81255).  
         [0006]     However, in the case of fundus cameras used to carry out infrared light-excited fluorescence photography in which a CCD is used for both observation and dynamic image photography, the focus index and alignment index that are not required for diagnosis are also recorded because the images that are observed are the same images that are recorded.  
         [0007]     If, in order to avoid this problem, the indexes are not used during the infrared light-excited fluorescence photography, focusing and alignment have to be adjusted visually. Such visual adjustments may be possible during the initial phase when there is a sufficient level of infrared light-excited fluorescence, but become difficult in the later phase in which there is insufficient infrared light-excited fluorescence. Thus, during the transition from the initial to the later phase, the examiner has to switch the indexes on and off, using his or her own judgment, which increases the burden on the examiner when making a dynamic image recording.  
         [0008]     It is therefore an object of the present invention to provide an ophthalmic photography apparatus that is able to carry out infrared light-excited fluorescence photography and recordings by securely enabling focusing and alignment adjustments to be made over the entire period of the infrared light-excited fluorescence photography.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an ophthalmic photography apparatus that has at least an infrared light-excited fluorescence photography.mode and is capable of infrared light-excited fluorescence photography of an eye fundus. The ophthalmic photography apparatus comprises an index light source for forming a focus or alignment index projected onto the eye during infrared light-excited fluorescence photography; an imaging device for capturing an infrared light-excited fluorescence image of the eye fundus; a recorder for recording the captured infrared light-excited fluorescence images of the eye fundus as dynamic images; and a control means for controlling the index light source during infrared light-excited fluorescence photography to provide different quantities of light for when infrared light-excited fluorescence images are being recorded and not recorded.  
         [0010]     When infrared light-excited fluorescence images are being recorded as moving images, it is possible to darken the focus and alignment indexes, which are not necessary for diagnosis, thereby substantially eliminating the index images from the recording images.  
         [0011]     During the later phase of the infrared light-excited fluorescence photography wherein there is insufficient infrared light-excited fluorescence, an automatic gain control function on the imaging device comes into effect, or the quantity of light of the index light source is increased during recording. This increases the index brightness, making the alignment or focusing easy, thereby enabling stable infrared light-excited fluorescence photography and recording of dynamic images.  
         [0012]     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic view showing an ophthalmic photography apparatus according to the present invention.  
         [0014]      FIG. 2  is a timing chart showing sequences of capturing still and dynamic images of an eye fundus.  
         [0015]      FIG. 3  is another timing chart showing sequences of capturing still and dynamic images of an eye fundus.  
         [0016]      FIG. 4  is a table showing operations performed in each photographic mode. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     An ophthalmic photography apparatus is realized in the form of a fundus camera that is able to carry out infrared light-excited fluorescence photography and captures the infrared light-excited fluorescence images of an eye fundus as moving images.  
         [0018]      FIG. 1  shows such a fundus camera. A light beam from an observation light source  1  such as a halogen lamp or the like is concentrated by a concave mirror  2 , passes through a strobe  3  serving as a photographing light source, and a condenser lens  4 . The light beam is then reflected by a mirror  5 , passes through relay lenses  20  and  21 , and is reflected by an apertured total-reflection mirror  22 . An objective lens  23  concentrates the beam thus reflected by the total-reflection mirror  22  to form an image at the pupil Ep of an eye E to be examined for illumination of the eye fundus Er.  
         [0019]     During non-mydriatic examination, a filter  6  that transmits infrared light is inserted into the optical path of the fundus illumination system on the downstream side of the observation light source  1 . A ring slit switcher  10  is provided that enables switching among a standard ring slit  11 , a small-pupil ring slit  12  and a fluorescence ring slit  13 . The standard ring slit  11  is the ring slit that is normally used; the small-pupil ring slit  12  is used when the patient&#39;s eye is not sufficiently dilated or when the patient is someone with a small pupil, such as a child; and the ring slit  13  is used during infrared light-excited fluorescence photography. These slits are imaged substantially at the location of the pupil Ep of the eye E, and the illuminating light falling incident on the ring-shaped aperture provides uniform illumination of the eye fundus.  
         [0020]     Behind the ring slit switcher  10 , there is located an illumination filter switcher  15  that can switch between a through-filter  16 , a visible light-excited fluorescence exciter filter  17  that transmits blue light having a wavelength of 450 nm to 520 nm, and an infrared light-excited fluorescence exciter filter  18  that transmits infrared light having a wavelength of 700 nm to 800 nm. When the through-filter  16  is inserted into the optical path, all light is transmitted. The visible light-excited fluorescence exciter filter  17  is inserted into the optical path during visible light-excited fluorescence photography, and the infrared light-excited fluorescence exciter filter  18  is inserted during infrared light-excited fluorescence photography so that only infrared light is transmitted.  
         [0021]     Light reflected from the eye fundus Er passes back through the pupil Ep, the objective lens  23 , the aperture of the total-reflection mirror  22 , a photography stop  24  on the optical path of the photographic optical system, focus lenses  25  and  26  and image-formation lens  27 , and falls incident on return mirror  30 . The image-formation lens  27  can be replaced by an image-formation lens  28  having a different magnifying power, thereby constituting a variable-power mechanism. Also on this photographic optical path, there is a barrier filter  42  that transmits visible light-excited fluorescence from the eye fundus and that can be inserted between a half-mirror  74  and the focus lens  25  during visible light-excited fluorescence photography.  
         [0022]     Light from the fundus that is reflected by the return mirror  30  is reflected by a return mirror  31  onto an ocular lens  32  via which the examiner can observe the eye fundus image. When the filter  6  is inserted into the optical path and the return mirror  31  is retracted from the optical path, light from the eye fundus is reflected by a return mirror  33  onto an infrared observation optical system having an infrared CCD  35  serving as an imaging device that is sensitive to infrared light. Infrared images of the eye fundus captured by the infrared CCD  35  are displayed, via a switching circuit  39 , on a monitor  40 . The infrared CCD  35  has an automatic gain control (AGC) that is used to boost sensitivity when the image of the object being photographed darkens.  
         [0023]     The infrared CCD  35  is used to capture images of the eye fundus during observation. The images captured are displayed on the monitor  40  as infrared dynamic images. This makes it possible for the examiner to carry out alignment and focusing adjustments while viewing the eye fundus image on the monitor  40 . As described later, during infrared light-excited fluorescence photography, the infrared CCD  35  can also be used to capture dynamic (moving) infrared light-excited fluorescence images of the eye fundus.  
         [0024]     For alignment purposes, the system of  FIG. 1  is provided with an alignment index light source  60 , a projection lens  61  and an optical fiber  62  that guides the index to the total-reflection mirror  22 . The alignment index light source  60  comprises a two-color LED constituted by a visible-red-light LED and an infrared LED, located at the same position. The infrared LED is used during infrared light-excited fluorescence photography; in other photographic modes, the red-light LED is used. During observation using the infrared CCD  35 , the infrared-light source can be used preferably as the alignment light source because it will not contract the eye, but since the wavelength will cause a change in the point at which the image is formed, the red-light LED is used for all photographic modes other than infrared light-excited fluorescence photography. There is a slight demerit of the pupil contracting as compared with infrared light. To prevent the pupil contracting, the red-light LED is preferably dimmed when in use.  
         [0025]     The infrared or visible red light index thus formed by the alignment index light source  60  is projected onto the anterior part of the eye via the projection lens  61  and the optical fiber  62 .  
         [0026]     For focusing adjustment, a focus index light source  70  is provided that makes individual use of an infrared LED and a visible-red-light LED. The focus index used to adjust the focus is projected from the focus index light source  70  onto the eye fundus via lens  71 , mirror  72 , lens  73  and half-mirror  74 . The focus index light source  70  makes individual use of two LEDs and a different optical system is used for each LED. The infrared LED is used in the infrared light-excited fluorescence photography mode, and the red-light LED is used in other photography modes. In  FIG. 1 , the focus index projection system is shown as using a red-light LED as the focus index light source  70 ; the apparatus also has a different optical system in which the infrared LED is used as the focus index light source  70 , although it is not shown in  FIG. 1 .  
         [0027]     During infrared light-excited fluorescence photography, a barrier filter  43  that transmits infrared light having a wavelength of 820 nm to 900 nm can be inserted into the optical path between return mirrors  31  and  33 .  
         [0028]     When the return mirror  33  is retracted from the optical path, the light from the eye fundus impinges on a dichroic mirror  34 , which splits the beam into visible light and infrared light components. The visible light is reflected by the dichroic mirror  34  onto a color CCD  36  that is sensitive to visible light, while the infrared light is transmitted by the dichroic mirror  34  onto a CCD  37  that is sensitive to infrared light. The eye fundus image captured by the color CCD  36  is the image reflected by the dichroic mirror  34 , so the image captured by the infrared CCD  37  is an inverse image of the eye fundus. Therefore, an image inversion circuit  38  is provided to carry out inversion processing of images from the color CCD  36  or infrared CCD  37  to vertically match the observed and captured images.  
         [0029]     Using light emitted by the strobe  3  during photography, still images of the eye fundus can be obtained by the color CCD  36  and infrared CCD  37  and displayed on the monitor  40 , via the switching circuit  39 , and recorded and stored on a recorder  50 . The recorder  50  can also record dynamic images from the infrared CCD  35 .  
         [0030]     When the return mirror  30  is retracted from the optical path, fundus images can be captured on photographic film  44  such as 35 mm film. Instead of the photographic film, an imaging device equivalent to the color CCD  36  can be used to capture the fundus images.  
         [0031]     A timer  51  is provided to measure the time elapsed from intravenous injection of a fluorescent agent during infrared and visible light-excited fluorescence photography. The time signal from the timer  51  is input to a control circuit  52  comprised by a microcomputer or the like. A signal from a mode setting means  53  indicating the photographic mode, and a signal from a photographing switch (shutter)  54 , are also input to the control circuit  52 . Based on these signals, in accordance with each mode, the control circuit  52  controls the ring slit switcher  10  and the illumination filter switcher  15  to retract or insert the filter  6 , barrier filters  42  and  43  and mirrors  30 ,  31  and  33 , drives the CCDs  35 ,  36  and  37 , controls the brightness of the alignment and focus index light sources  60  and  70 , controls the operation of the strobe  3 , and controls the magnification by selecting lens  27  or  28 .  
         [0032]     The operation of the ophthalmic photography apparatus thus configured will now be explained with reference to  FIG. 2 . The ophthalmic photography apparatus of this invention is capable of carrying out mydriatic and non-mydriatic photography, visible light-excited fluorescence photography and infrared light-excited fluorescence photography. Normal color photography is carried out in mydriatic or non-mydriatic mode.  
         [0033]     In  FIG. 2 , still image photography of the eye fundus was carried out from time t 1  to time t 9  in mydriatic, non-mydriatic, visible light and infrared light modes. Dynamic fundus image photography by infrared light-excited fluorescence was carried out from time t 11  to time t 17 . When the main switch (not shown) is closed at time t 1 , the observation light source  1  comes on and, as indicated in  FIG. 2 , the alignment index light source  60  and focus index light source  70  come on and the infrared CCD  35  is driven with a prescribed gain.  
         [0034]     In the case of mydriatic mode, drops of a mydriatic agent are put into the eye. When mydriatic mode is set using the mode setting means  53 , the control circuit  52  retracts the filter  6  from the optical path and drives the ring slit switcher  10  to insert the standard ring slit  11  or small-pupil ring slit  12  into the optical path. Also, the through-filter  16  is selected and inserted into the optical path, and since the barrier filters  42  and  43  are for fluorescence mode photography, they are retracted from the optical path and the return mirrors  30 ,  31  and  33  occupy the positions shown in  FIG. 1 .  
         [0035]     Light from the observation light source  1  that is reflected by the mirror  5  passes through the standard ring slit  11  (or the small-pupil ring slit  12 ), the through-filter  16 , the relay lenses  20  and  21 , and is reflected by the apertured total-reflection mirror  22  into the objective lens  23  to illuminate the eye fundus Er of the eye E. Reflected light from the eye fundus Er passes through the objective lens  23 , total-reflection mirror  22 , photographic stop  24 , half-mirror  74 , focus lenses  25  and  26  and the image-formation lens  27  and, via the return mirrors  30  and  31 , falls incident on the ocular lens  32 .  
         [0036]     During mydriatic photography, the alignment index light source  60  and focus index light source  70  are lit by a red-light LED. The examiner adjusts the alignment and focus while observing the alignment and focus indexes via the ocular lens  32 . When the alignment and focusing adjustments are completed, the shutter  54  is operated at time t 2 , at which the alignment index light source  60  and focus index light source  70  are switched off and the strobe  3  starts emitting light at time t 4 . The color CCD  36  is driven between times t 3  and t 5  before and after the strobe and the return mirror  33  is retracted from the optical path, whereby the color CCD  36  takes a still image of the eye fundus.  
         [0037]     When the shutter  54  continues to be pressed, image capture continues, the color CCD  36  being again driven at time t 6  and the strobe  3  emitting light at time t 7 , obtaining a second still image. When the shutter  54  is released at time t 8 , still image photography ends and the alignment index light source  60  and focus index light source  70  come on as the system goes into observation mode. The still images obtained are stored in the recorder  50 .  
         [0038]     Photography can be carried out using film  44 , in which case the mirror  30  is retracted from the optical path. Infrared observation can be carried out without using the ocular lens  32 , in which case the return mirror  31  is retracted from the optical path and fundus images are captured by the infrared CCD  35  as dynamic images which the examiner can view on the monitor  40  while adjusting the alignment and focus. When the infrared CCD  35  is used for observation, the infrared LED of the focus index light source  70  lights, projecting an infrared focus index.  
         [0039]     In the above mydriatic photography mode, as is also listed in  FIG. 4 , the standard ring slit  11  or small-pupil ring slit  12  is selected. The through-filter  16  is selected, so with respect to exciter filter, “None” is shown, and “None” is also shown with respect to barrier filter, since barrier filters  42  and  43  are withdrawn from the optical path. The quantity of light used for observation and photography is regulated by ring slit. In the case of a standard ring slit, the setting at which observation and photography takes place is “0”, which is the default value; in the case of a small-pupil ring slit, the setting used is “+1”. Since it is not fluorescence photography, “None” is also shown with respect to the timer used to measure the time that has elapsed from the intravenous injection of a fluorescence agent. The fundus is observed via the ocular lens  32  or via the images fed to the monitor  40  from the infrared CCD  35 , and 35 mm film  44  or the color CCD  36  is used as the photography means. During observation, the red-light LEDs of the alignment index light source  60  and the focus index light source  70  are on, and off during photography. When the infrared CCD  35  is used for observation, the red-light LED of the alignment index light source  60  is dimmed, which is denoted by “Red-”.  
         [0040]     For non-mydriatic photography, the filter  6  is inserted into the optical path and small-pupil ring slit  12  is selected. The return mirror  31  is retracted from the optical path, and observation is carried out via the images fed to the monitor  40  from the infrared CCD  35 . Continuous photography of still images is carried out by the same procedure shown in  FIG. 2 , and the still images thus obtained are recorded on film  44  or in the recorder  50 . As shown in  FIG. 4 , observation is carried out only via the infrared CCD  35 , and during observation, the red-light LED of the alignment index light source  60  is dimmed, so therefore emits visible red light at a muted level. On the other hand, the infrared LED of the focus index light source  70  lights, emitting infrared light for focus adjustment.  
         [0041]     For visible light-excited fluorescence photography, the standard ring slit  11 , small-pupil ring slit  12  or fluorescence ring slit  13  is selected and the observation light quantity is increased accordingly, to “+3”, “+4” or “+2”. Visible light-excited fluorescence exciter filter  17  is selected as the illumination filter, and barrier filter  42  as the photography filter.  
         [0042]     When observation is carried out by viewing images sent to the monitor  40  from the infrared CCD  35 , the filter  6  is inserted into, and the return mirror  31  is retracted from, the optical path. When observation is carried out via the ocular lens  32 , the filter  6  is retracted from, and the return mirror  31  is inserted into, the optical path. When observation is done via the ocular lens  32 , the visible light-excited fluorescence exciter filter  17  is inserted into the optical path.  
         [0043]     When observation is done via the ocular lens  32 , the red-light LEDs of the alignment index light source  60  and the focus index light source  70  are on, as shown in  FIG. 4 . When the infrared CCD  35  is used for observation, the red-light LED of the alignment index light source  60  is dimmed, and the infrared LED of the focus index light source  70  is on.  
         [0044]     Upon completion of the alignment and focusing adjustments, a fluorescence agent is intravenously injected, the exciter filter  17  and barrier filter  42  are inserted into the optical path, and the timer  51  starts measuring elapsed time. After a prescribed time T 1  has elapsed and the exciting light transmitted by the exciter filter  17  produces a visible light-excited fluorescence image in the fundus, the shutter  54  is pressed (at time t 2  in  FIG. 2 ), and the strobe  3  emits light. Depending on the position of the return mirror  30 , visible light-excited fluorescence images will be photographed using the 35 mm film  44  or the color CCD  36 . The same operation takes place each time the shutter  54  is operated, or the operation takes place continuously if the shutter is kept pressed. When the color CCD  36  is used to obtain still images, the return mirror  30  is inserted into the optical path and return mirrors  31  and  33  are retracted from the optical path. Still images photographed by the color CCD  36  are recorded and stored on the recorder  50 .  
         [0045]     During infrared light-excited fluorescence photography, observation cannot be done via the ocular lens  32 , but only via images from the infrared CCD  35  appearing on the monitor  40 . For observation via the monitor  40 , standard ring slit  11  or fluorescence ring slit  13  is selected and the observation light quantity is increased to “+6” or “+5”. The infrared LEDs of the alignment index light source  60  and the focus index light source  70  light, emitting infrared light. Infrared light-excited fluorescence exciter filter  18  is selected as the illumination filter, and barrier filter  43  as the photography filter. The infrared CCD  37  is used as the imaging device to take still images.  
         [0046]     Upon completion of the alignment and focus adjustments at time t 2 , the fluorescence agent is intravenously injected, the barrier filter  43  is inserted, and the timer  51  starts measuring elapsed time. After a prescribed time T 2  has elapsed and the exciting light transmitted by the exciter filter  18  produces an infrared light-excited fluorescence image in the fundus, the shutter  54  is pressed and the strobe  3  emits light (at times t 4  and t 7 ). At this time, the return mirror  30  is fixed in the position shown and return mirrors  31  and  33  are retracted, so infrared light-excited fluorescence images of the fundus are transmitted by the dichroic mirror  34  to fall incident on the infrared CCD  37  and be captured as still images. These images are vertically inverted by the image inversion circuit  38  and, via the switching circuit  39 , are displayed on the monitor  40  as still images and recorded and stored on the recorder  50  as still images.  
         [0047]     When infrared light-excited fluorescence photography is used to photograph and record dynamic images of the eye fundus, fluorescence ring slit  13  is selected and, as in the case of still image photography, infrared light-excited fluorescence exciter filter  18  is selected as the illumination filter and barrier filter  43  as the photography filter. The infrared LEDs of the alignment index light source  60  and the focus index light source  70  are on to each project an infrared index. Alignment and focus adjustments are carried out while using the monitor  40  to view the images of the alignment and focus indexes from the infrared CCD  35 . In  FIG. 2 , this state is the segment from time t 11  to time t 12 .  
         [0048]     Upon completion of the alignment and focus adjustments at time t 12 , the fluorescence agent is intravenously injected, the barrier filter  43  is inserted, and the timer  51  starts measuring elapsed time. After a prescribed time T 2  has elapsed and the exciting light transmitted by the exciter filter  18  produces an infrared light-excited fluorescence image in the fundus, the shutter  54  is pressed to start recording dynamic images, and infrared light-excited fluorescence images from the infrared CCD  35  are recorded and stored on the recorder  50  as dynamic images.  
         [0049]     When the recording of dynamic images commences at time t 12 , the control circuit  52  reduces the light quantity of the alignment index light source  60  and focus index light source  70 , reducing the index brightness. In  FIG. 2 , this state is shown as the index light sources  60  and  70  at point t 12  changing from “Bright” to “Dimmed”. In  FIG. 4 , this is shown as “Infrared-”.  
         [0050]     Thus, in the first phase in which there is a sufficient level of infrared light-excited fluorescence, the alignment and focus indexes are projected at a brightness that is not enough to show up on the observed images, thereby preventing the index images from becoming a hindrance to diagnosis without any real loss of image quality. When recording is not taking place, the brightness of the alignment and focus indexes can be increased to the same level used during normal observation (alignment), which is convenient for fundus camera operation during the recording of dynamic images.  
         [0051]     In the later stage there is a decrease in the brightness of infrared light-excited fluorescence, for example, when time t 13  is reached. At this time, the automatic gain control (AGC) of the infrared CCD  35  comes on and, as shown in  FIG. 2 , the gain increases with the passage of time to maintain the screen brightness at a constant level. As the sensitivity of the infrared CCD  35  is gradually amplified, the brightness of the alignment and focus indexes shown on the monitor  40  gradually rises. Since it is therefore possible to increase the screen brightness of the indexes in inverse proportion to the level of infrared light-excited fluorescence even if the infrared light-excited fluorescence images become darker, it does not hinder alignment and focus adjustments.  
         [0052]     At time t 14  in  FIG. 2 , the shutter  54  is operated, pausing the recording of dynamic images. At this time, the control circuit  52  again increases the light quantity of the alignment index light source  60  and focus index light source  70  to “Bright”, making it possible to carry out any alignment and focus adjustments required at the same index brightness levels used during observation.  
         [0053]     When the shutter  54  is again operated at time t 15 , the index light sources  60  and  70  are switched to “Dimmed”, decreasing the light quantities. The light quantities of the index light sources at this point are the same as those at time t 12 , so the projected indexes are dim. However, as shown in  FIG. 2 , the sensitivity of the infrared CCD  35  increases in inverse proportion to the brightness of infrared light-excited fluorescence, so on the monitor  40 , the indexes are clearly shown, enabling alignment and focus adjustments to be readily carried out even during the later stage of the infrared light-excited fluorescence photography.  
         [0054]     In the above embodiment, the AGC function of the infrared CCD  35  is utilized to increase the screen brightness of the alignment and focus indexes. The effect can be further increased by using the control circuit  52  to increase the light quantity of the index light sources. An example of this is shown in  FIG. 3 , in which, from time t 13  at which the AGC comes into effect, the brightness of the projected alignment and focus indexes gradually increases under the control of the control circuit  52  (from time t 13  to t 14 , and from time t 15  to t 16 ). This makes it possible to obtain indexes that become brighter in the later phase of the infrared light-excited fluorescence, ensuring that alignment and focus adjustments can be readily accomplished in the later stages.  
         [0055]     In the above embodiment, the increase in the light quantities of the index light sources during recording takes place from the point at which the AGC comes on. Instead, however, the brightness of the index light sources  60  and  70  can be increased during recording with the passage of time after the elapse of a prescribed time from the commencement of infrared light-excited fluorescence photography, as measured by the timer  51 .  
         [0056]     Thus, when there is enough infrared light-excited fluorescence to carry out focus and alignment adjustments, it is possible to prevent images of alignment and focus indexes showing up on recording images. On the other hand, when there is not enough infrared light-excited fluorescence for such adjustments, the alignment and focus indexes can be made to show up clearly on the images to enable the adjustments to be made.  
         [0057]     Dynamic images can be recorded during both phases of the infrared light-excited fluorescence photography process. However, for clinical diagnostic purposes, it is the dynamic images of the first phase that are important. In the invention, it is possible to prevent images of the indexes appearing on the recording images during the first phase. On the other hand, the indexes can be brightened in the later phase to facilitate the alignment and focus adjustments, thereby ensuring stable dynamic image capture and recording in infrared light-excited fluorescence photography.