JP3702981B2 - Fundus camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a fundus camera capable of photographing the fundus by automatic focusing.
[0002]
[Prior art]
Conventionally, an imaging optical system for imaging the fundus of the eye to be inspected and an alignment index projection means for projecting a pair of alignment indices onto the eye to be examined are provided, and the fundus is adjusted by adjusting the alignment between the eye to be examined and the optical axis of the imaging optical system. Is known (for example, see Japanese Examined Patent Publication No. 60-52820). Also, an imaging optical system for photographing the fundus of the eye to be examined, focus index projection means for projecting a pair of focus indices on the fundus through the pupil of the eye to be examined, and fundus reflected light of the focus index disposed at a position substantially conjugate with the fundus There is also known a fundus camera that includes a light receiving unit that receives light, detects a focus based on a match between a pair of focus indexes projected onto the fundus by the light receiving unit, and thereby automatically photographs the fundus ( For example, see Japanese Patent Publication No. 62-51618). A fundus camera having a combination of both is also known.
[0003]
[Problems to be solved by the invention]
However, some fundus cameras that perform automatic focusing while aligning the eye to be examined with the optical axis of the imaging optical system using the alignment index include a variable magnification optical system. If the alignment is not appropriate when shooting is performed by automatic focusing immediately after switching from high-magnification observation to high-magnification imaging, automatic focusing is hindered.
[0004]
In addition, when the optical axis of the eye to be examined and the imaging optical system are shifted during the automatic focusing operation and the alignment is in an inappropriate state, a part of the pair of focus indexes projected on the fundus of the eye to be examined is lost. The balance of the amount of reflected light of the pair of focus indicators reflected from the fundus may be lost, which may hinder automatic focusing. Furthermore, when the subject blinks during the automatic focusing operation, the blinking causes an alignment error that the alignment between the eye to be examined and the optical axis of the imaging optical system cannot be detected, and the pair of focus indicators is not projected onto the fundus of the eye to be examined. In addition, since the amount of reflected light of the focus index from the fundus is completely lost, there is a problem that the automatic focusing is similarly hindered.
[0005]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a fundus camera capable of determining whether or not alignment is appropriate without depending on an alignment index.
[0006]
[Means for Solving the Problems]
The fundus camera according to claim 1 includes a photographing optical system that has a zooming unit and photographs the fundus of the eye to be examined, a focus index projection unit that projects a focus index on the fundus, and a position substantially conjugate with the fundus. A light receiving means for receiving the fundus reflected light of the focus indicator, a focus control means for performing focus control based on the light receiving output of the light receiving means, and an alignment in the vertical and horizontal directions is appropriate based on the light receiving output of the light receiving means. An alignment determining means for determining whether or not there is, storing a light receiving output based on a reflected light amount of the focus index of the light receiving means at the time of low magnification photographing, and storing the received light receiving output at the time of high magnification photographing. When the amount of reflected light decreases more than a predetermined amount compared to the light receiving output based on the amount of reflected light of the focus indicator of the light receiving means, the vertical / horizontal alignment is inappropriate. Characterized by determining that that.
The fundus camera according to claim 2, further comprising display means for displaying that the alignment is inappropriate based on an output of the alignment determination means when the alignment is inappropriate. .
According to a third aspect of the present invention, the fundus camera includes a photographing prohibiting unit that prohibits photographing based on an output of the alignment determining unit when the alignment is inappropriate.
According to a fourth aspect of the present invention, the fundus camera includes a display unit that displays a direction in which the alignment is appropriate based on an output of the determination unit when the alignment is inappropriate.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[0012]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1
In the following, the present invention will be described in detail based on the embodiment of the illustrated fundus camera.
[0013]
In FIG. 1, reference numeral 1 denotes an observation light source that constitutes a part of the illumination means. Illumination light emitted from the light source 1 passes through a condenser lens 2 and a relay lens 3 and is directed to the eye E by a perforated mirror 4. The light is reflected and illuminates the fundus of the eye E through the objective lens 5. Then, the reflected light from the fundus passes again through the objective lens 5 and straightly through the perforated mirror 4, and further, a focusing lens 6, an imaging lens 7 and a flip-up mirror 8 constituting a part of the photographing optical system Q1. The image is formed on the film 9 via.
[0014]
The flip-up mirror 8 is retracted from the photographing optical path at the moment of photographing, but is lowered to the state shown in FIG. 1 when observing the fundus, and is relayed via the field lens 10 of the light receiving optical system arranged in the reflection direction. 11, a fundus image is formed on the surface of the imaging tube 12 serving as a light receiving means disposed at a conjugate position on the fundus and is observed on the monitor 13.
[0015]
A mirror 14 is disposed between the relay lenses 2 and 3, and light from distance measuring light sources 15 and 15 ′ (see FIG. 2) as focus index projection means Q 2 for projecting a focus index is disposed on the mirror 14. Is incident through the transmission windows 16 'and 16' of the first aperture 16 shown in FIG. 3, the slit 17 'of the second aperture 17 shown in FIG. The slit image as a focus index is projected onto the fundus of the eye E through the apertured mirror 4 and the objective lens 5 and through the slit 17 ′ of the aperture 17. Here, the first aperture 16 is in a position conjugate with the pupil of the eye E to be examined. The distance measuring light sources 15 and 15 'are repeatedly turned on and off at predetermined time intervals by a control circuit (not shown).
[0016]
FIG. 5 shows the slit images S1 and S2 on the cathode ray tube 13a of the monitor 13, and the slit images S1 and S2 match in a focused state, and the relative positions of the slit images S1 and S2 according to the focused state. Are different. FIG. 6A shows a video signal of the scanning line L1 on the slit images S1 and S2, and the optical signal S0 from the observation light source 1 is biased to the slit images S1 and S2. FIG. 6B shows the optical signal S0 from the scanning line L1 when the distance measuring light sources 15 and 15 ′ are turned off, and FIG. 6C is obtained by subtracting the signal of FIG. 6B from the signal of FIG. ) Becomes the signals of the slit images S1 and S2 excluding the influence of the background light, whereby the positions of the slit images S1 and S2 can be accurately determined. That is, the distance measuring light sources 15 and 15 'are blinked in synchronization with the electronic scanning, and the signals shown in FIGS. 6A and 6B are input to a differential signal generating circuit (not shown), and the signals shown in FIG. Generate a signal. The relative distance between the slit images S1 and S2 can be compared by the focus control means Q3 to determine whether or not it is in focus.
[0017]
That is, FIG. 7A shows a case where the in-focus state is deviated, and as is clear from the figure, the interval between the slit images S1 and S2 is considerably deviated. FIG. 7B shows a case where the focus is very close, and the slit images S1 and S2 are mostly overlapped. FIG. 7C shows an in-focus state, in which the slit images S1 and S2 are completely overlapped. FIGS. 8A to 8C show a difference signal S4 between the slit image S1 and the slit image S3. When the difference signal S4 is within the threshold value Δ, it means in-focus, and the focus control means outputs the difference signal. Focus control is performed by determining whether or not S4 is within the threshold value Δ.
[0018]
These structures are known from Japanese Examined Patent Publication No. 62-51618.
[0019]
The fundus camera of the present invention includes an alignment determination unit that determines whether or not the alignment is appropriate based on the light reception output of the light reception unit. This alignment determination means is provided in the focus control means Q3, and the optical axis of the imaging optical system is based on the light level of the slit image signals S1 and S2 shown in FIGS. 7 (a) to 7 (c). Judge whether it is aligned with the optical axis.
[0020]
That is, as shown by the solid line in FIG. 9, when the optical axis of the imaging optical system is properly aligned with the optical axis of the eye to be inspected, the focus indexes S1 and S2 border the center O of the pupil 19 as shown by the solid line. The focus indices S1 and S2 are projected onto the fundus through the pupil 19, but when the optical axis of the imaging optical system and the optical axis of the eye to be inspected are not aligned properly, the focus is shown as indicated by a broken line. Since the indices S1 and S2 deviate from the symmetrical position with respect to the center O of the pupil 19 and vignetting at the iris 20, the peak light quantity levels L1 and L2 of either the focus indices S1 or S2 are lowered as shown in FIG. . If the ratio L2 / L1 between the peak light amount levels L1 and L2 is shifted by, for example, about 20%, it is determined that the alignment has shifted left and right. Further, as indicated by reference numerals S1 ″ and S ″, the alignment may be shifted in the vertical direction. In this case, the peak light quantity levels L1 and L2 of both the focus indicators S1 and S2 are lowered as shown in FIG. Therefore, the threshold value L3 is provided, and the vertical alignment can be determined depending on whether or not the peak light amount levels L1 and L2 are larger than the threshold value L3.
[0021]
The threshold L3 is determined by actual measurement of the amount of reflected light from the eye to be examined. This is because the absolute value of the amount of light reflected from the eye to be examined is the iris diameter (pupil diameter) of the subject eye, the transmittance of the intermediate translucent body (mainly the cornea, the lens, and the vitreous body) of the subject eye, and the reflectance of the subject eye. This threshold value L3 cannot be uniquely determined because it differs depending on the factors. Accordingly, when the amount of light is greater than a predetermined amount (required amount) for a certain period of time (or a certain period) and the fluctuation range is small, the threshold value L3 is used, and the light amount fluctuation from this threshold value L3 determined by actual measurement is If it is larger, it is judged as an alignment error. For example, similarly, when the light amount fluctuation is 20% or more, it is determined that the alignment is abnormal.
[0022]
As shown in FIG. 12, if the focus completion mark M1, the front pin mark M2, and the rear pin mark M3 are displayed at the same time while the fundus image G is displayed on the screen 13a, the focus can be adjusted when the image is out of focus. It is more desirable because it can indicate the focal direction. Similarly, when the alignment is inappropriate, the alignment operation direction arrow M4 is displayed on the screen 13a to indicate the operation direction, so that the alignment operation is easier.
[0023]
When the pair of focus indicators shown in FIG. 9 is projected onto the fundus, the left and right alignment operation directions can be determined by comparing the light amount levels L1 and L2 of the focus indicators, but the vertical alignment operation directions are determined. Can not. Therefore, as shown in FIG. 13, if two pairs of focus indexes S1 to S4 orthogonal to each other are projected, the vertical alignment operation direction can also be determined.
[0024]
Further, when the alignment is inappropriate, photographing may be prohibited.
[0025]
In the above embodiment, the imaging optical system can be aligned with the eye to be examined without providing a pair of alignment indexes.
[0026]
Second Embodiment of the Invention
In FIG. 14, the same components as those shown in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted, and only different portions will be described.
[0027]
In addition to the observation light source 1 and the condenser lens 2, the illumination means includes a photographing illumination light source 1 ′, a condenser lens 2 ′, a reflecting mirror 3 ′, a ring stop 4 ′, and a relay lens 5 ′. The light receiving optical system is provided with a half mirror 13 ′, and the half mirror 13 ′ plays a role of reflecting a part of the fundus image toward the eyepiece lens 14 ′. Reference numeral 15 'denotes an examiner's eye, and the examiner can observe a fundus image through the eyepiece 14'. Reference numeral 12 ′ denotes an imaging plane conjugate with the film 9.
[0028]
A focus index projection unit 30 is provided between the relay lens 3 and the relay lens 5 ′. The light sources 15 and 15 ′ are inclined at an angle α with respect to the optical axis L7, and are disposed so as to irradiate the pinholes of the pinhole plate 3a. The two-hole aperture 16, the projection lens 18, and the small mirror 32 are arranged on the optical axis L7, and the small mirror 32 is inclined with respect to each of the optical axes L9 orthogonal to the optical axis L7. The unit 30 is configured to be movable along the optical axis L9 in the direction of the arrow C. When the imaging lens 7 is moved along the optical axis L1 in the direction of the arrow B, the projection unit 30 interlocks with the arrow C. Moved in the direction.
[0029]
The light sources 15 and 15 ′ are flickering by a phase difference of 180 degrees below the critical flicker frequency (for example, 30 Hz) that is felt as flicker to the human eye, and the light flux passes through the pinhole 3 a and the two-hole aperture 16 to be a small mirror. 32, and converged by the relay lens 3, reflected by the perforated mirror 4, converged at the intersection F4 on the optical axis and turned in the direction of divergence. It converges near the fundus through the cornea.
[0030]
The light beam irradiating the fundus becomes a reflected light beam, passes through the objective lens 5 again, passes through the hole of the perforated mirror 4 and the imaging lens 7, is reflected by the flip-up mirror 8, and then reaches the imaging surface 12. This is magnified by an eyepiece lens 14 ′ through a half mirror 13 ′ and observed by an examiner eye 15.
[0031]
When focus adjustment by the imaging lens 7 is not performed correctly, the two upper and lower light beams are separated from each other at the fundus, and the two spots appear to be separated from each other. It will be visually recognized as two blinking spots where flicker is recognized.
[0032]
At the time of out-of-focus, the imaging lens 7 is moved back and forth along the optical axis in the direction of arrow B by the motor M, so that the two light fluxes match on the fundus, and each other due to a phase difference shifted by 180 degrees from each other. The light emitting part, that is, the lighting part overlaps with the light extinguishing part of the light beam on the other side, and only the continuous lighting part of about 60 Hz, which is twice about 30 Hz, is visually recognized, and flicker is not felt.
[0033]
Next, by operation of a photographing operation unit (not shown), the light sources 15 and 15 ′ are turned off, the flip-up mirror 8 is retracted from the photographing optical path, the illumination light source 2 ′ is emitted, and a fundus image is photographed on the film 9. Is done.
[0034]
Even with this optical system, alignment can be detected without providing an alignment index.
[0035]
Embodiment 3 of the Invention
In Embodiment 3 of the present invention, a plurality of variable magnification lenses 33, 34, and 35 are prepared as a variable magnification optical system, and the variable magnification lenses 33, 34, and 35 are formed by the focusing lens 6 and the imaging lens 16. It is provided in the optical path between them so that it can be inserted and removed. The zoom lens 33 is for, for example, an angle of view of 50 degrees, the zoom lens 34 is for an angle of view of 35 degrees, and the zoom lens 35 is for an angle of view of 20 degrees.
[0036]
In the photographing optical system 32, auxiliary lenses 38, 37, and 36 are provided on the optical path between the intermediate imaging point 19 and the imaging lens 16 corresponding to the variable power lenses 33, 34, and 35, respectively. . Since the roles of the auxiliary lenses 33, 34, and 35 are already known, the description thereof is omitted. A pair of alignment markers 50 are provided in the hole portion of the perforated mirror 4 and the alignment markers 50 are projected onto the fundus.
[0037]
FIG. 16 shows a pair of alignment indexes 50 ′ displayed on the television screen 13a, and the pair of alignment indexes is displayed on the screen 13a during low-magnification shooting at an angle of view of 50 degrees. However, at the time of high-magnification shooting with an angle of view of 20 degrees, as described in Japanese Patent Publication No. 3-60261, the alignment index 50 ′ cannot be confirmed. Therefore, it is necessary to determine whether or not the alignment is appropriate without depending on the alignment index.
[0038]
Normally, this type of fundus camera shoots at a low magnification (angle of view of 50 degrees) and then at a high magnification, so at the time of low magnification shooting, the alignment index 50 is used first. The amount of reflected light of the focus index is stored using the half mirror 39 and the light receiving element 40. Next, when shooting at high magnification (when shooting at an angle of view of 20 degrees), the amount of reflected light of the focus index is compared with the amount of reflected light at the time of low magnification shooting. Judge as abnormal.
[0039]
In the case of the third embodiment, since it is obtained from the actual measurement of the eye to be examined at the time of low-magnification imaging (considering the pupil diameter, transmittance, and reflectance), only the difference in reflected light amount from the two light sources and the variation in light amount are obtained. In addition, the alignment abnormality can be determined by the absolute value.
[0040]
In these embodiments, the distance measuring light source is described as being configured to be alternately turned on. However, a split index of a general fundus camera (for example, Japanese Patent Publication No. 62-51618) The present invention can also be applied to the case of the configuration shown in FIGS.
[0041]
【The invention's effect】
Since the fundus camera according to the present invention is configured as described above, there is an effect that it is possible to determine whether or not the alignment is appropriate even when the alignment index cannot be observed during the high magnification observation photographing .
[Brief description of the drawings]
FIG. 1 is an optical diagram of Embodiment 1 of a fundus camera according to the present invention.
FIG. 2 is a partially enlarged view of the distance measuring light source shown in FIG. 1;
FIG. 3 is a plan view of a first aperture shown in FIG. 1;
4 is a plan view of a second aperture shown in FIG. 1. FIG.
FIG. 5 is a diagram showing a slit image displayed on a television screen.
FIG. 6 is a diagram illustrating a video signal of a slit image.
FIG. 7 is an explanatory diagram of focusing / non-focusing by a slit image signal.
FIG. 8 is an explanatory diagram of a differential signal.
FIG. 9 is a diagram showing a focus index projected on the anterior segment of the eye to be examined.
FIG. 10 is an explanatory diagram of a peak light amount level of a focus index.
FIG. 11 is an explanatory diagram showing a relationship between a peak light amount level of a focus index and a threshold value.
FIG. 12 is a diagram illustrating a fundus image and an alignment direction mark displayed on a television screen.
FIG. 13 is a diagram showing two pairs of focus indices projected on the anterior segment of the eye to be examined.
FIG. 14 is an optical diagram of a second embodiment of the invention of the fundus camera according to the present invention.
FIG. 15 is an optical diagram of Embodiment 3 of the invention for a fundus camera according to the present invention.
FIG. 16 is a diagram illustrating a pair of alignment indices and a fundus image displayed on a television screen during low-magnification shooting.
[Explanation of symbols]
12: photoelectric conversion element (light receiving means)
E ... Eye Q1 ... Imaging optical system Q2 ... Focus index projection means Q3 ... Focus control means (alignment judgment means)
S1, S2 ... Slit image (focus index)

Claims (4)

A photographing optical system for photographing the fundus of the eye to be examined with a zooming means ;
Focus index projection means for projecting a focus index on the fundus;
A light receiving means that is disposed substantially conjugate with the fundus and receives fundus reflected light of the focus index;
Focus control means for performing focus control based on the light reception output of the light receiving means;
Alignment determination means for determining whether the alignment in the vertical and horizontal directions is appropriate based on the light reception output of the light receiving means ,
The light reception output based on the reflected light amount of the focus index of the light receiving unit at the time of low magnification photographing is stored, and the stored light reception output is the light reception output based on the reflected light amount of the focus index of the light receiving unit at the time of high magnification photographing. A fundus camera characterized in that when the amount of reflected light is reduced by a predetermined amount or more, the vertical / horizontal alignment is determined to be inappropriate . Wherein when the alignment is improper, the alignment the alignment based on the output of the determination means is a fundus camera according to claim 1, further comprising display means for displaying that it is improper. Wherein when the alignment is improper, the fundus camera according to claim 1, further comprising a photographing prohibition means for prohibiting the shooting based on the output of the alignment determining means. Wherein when the alignment is incorrect, the fundus camera according to claim 1, wherein the alignment on the basis of an output of said determining means comprises display means for displaying the direction in which a proper.

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