JPH0224531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a fundus camera in which the field of view for fundus imaging is asymmetric with respect to the optical axis, which effectively provides fundus illumination even to a subject's eye with a small pupil diameter and removes harmful light to perform fundus imaging. Regarding.

In order to obtain high-quality photographs with a fundus camera, it has been a challenge to prevent part of the illumination light from being reflected on the cornea. However, as is well known, this problem involves installing a ring slit in the illumination system that combines a circular light shielding part and an aperture diaphragm, forming an image of the ring slit on the cornea of the eye being examined, and capturing the photographic light flux emitted from the fundus. The problem was solved by passing the image of the circular light-shielding part of the ring slit so that the illuminating light and photographing light do not overlap on the cornea.

However, since fundus cameras at the time had a small angle of view of about 30°, the harmful light generated by the crystalline lens was not a problem. As the shadow formed by the ring slit image increased, the shadow formed by the ring slit image became shorter, and the crystalline lens was exposed to the illumination light flux, resulting in the generation of harmful light. Harmful light from the crystalline lens was first noticed as reflection from its surface, but it was later discovered that scattering on the surface and within the lens was also a cause.

In order to separate the two beams, a ring slit is placed in the optical path of the illumination system at a position conjugate to the vicinity of the cornea, and a circular light-shielding plate is placed at a position conjugate to the posterior surface of the crystalline lens (surface on the fundus side) or the center of the crystalline lens. Alternatively, a ring slit is placed at a position conjugate to the pupil, a circular light shielding plate is placed at a position conjugate to the posterior surface of the crystalline lens, and a ring slit is placed at a position conjugate to the cornea or pupil, and a ring slit is placed at a position conjugate to the cornea or a tiny anterior surface of the lens. A method of arranging a circular aperture stop is known.

At that time, if you try to achieve sufficient luminous flux separation, you will have to increase the diameter of the light-shielding plate and the diameter of the circular light-shielding part of the ring slit. An increase in diameter is required. However, for ordinary people, a pupil diameter of 6 to 7 mm is normal even when using mydriatic drugs, and there is no reason to require a particularly large pupil diameter.
Furthermore, since a non-mydriatic fundus camera photographs with a pupil diameter of approximately 4 to 5 mm, simply increasing the inner light-shielding portion of the ring slit will not provide sufficient illumination to the fundus of the subject's eye.

The purpose of the present invention is to utilize the fact that the size of the inner light-shielding part of the ring slit is smaller when the field of view for fundus imaging is narrower than when it is wide. The object of the present invention is to achieve sufficient separation of the fundus illumination light flux and the light flux for photographing or observation even with a relatively small pupil diameter, as well as improving illumination efficiency.

FIG. 1 depicts a fundus camera with what is known as a ring slit. In the figure, E is the eye to be examined, Ef is the fundus, 1 is the objective lens, 2 is the perforated mirror,
3 is an imaging lens, and 4 is a photographic film.

Further, a photographing aperture is arranged near the perforated mirror 2.
Reference numeral 5 denotes a photographing field diaphragm, and as a result of being placed near the photographic film 4, the photographing field has a centrally asymmetrical shape in which the size in the first radial direction and the size in the second radial direction are different, for example, as shown in FIG. As shown in the figure, it has a circular shape with the top and bottom missing. As mentioned above, the members 1 to 5 constitute the photographing system, and the objective lens 1 forms an intermediate image Ef' of the fundus, and the imaging lens 3 has the function of re-forming the intermediate image on the film 4. . In addition,
The shutter is omitted.

Furthermore, 6 is a quick return mirror, 7 is a reflector, and 8 is an eyepiece for observing aerial images.
Members 1 to 3 and members 6 to 8 constitute an observation system. Also, 10 and 11 are relay lenses, and 12 is a reflector. 13 is a well-known ring slit as shown in FIG.
b, and the gap between them forms an annular slit. 14 is a condenser lens, 15 is a photographing light source such as a xenon discharge tube, 16 is another condenser lens, and 17 is an observation light source such as a halogen bulb. Above, 10 to 17 members and 1 and 2
The members constitute the fundus illumination system, and the light sources 15 and 17 are conjugate with the ring slit 13 with respect to the condenser lenses 14 and 15, and the ring slit 13 and the pupil of the eye to be examined are connected to the reflector 12, the relay lenses 10 and 1
1. As a result of the conjugate arrangement with respect to the aperture mirror 2 and the objective lens 1, an annular secondary light source is formed above the pupil, uniformly illuminating the fundus of the eye.

Next, reference numeral 20 denotes an illumination field diaphragm, which has an aperture similar in shape to the photographic screen as shown in FIG. Since the image of this field diaphragm is formed on the fundus Ef, the parts that are not visible on the photographic screen are not illuminated by the illumination light, and as a result,
Since the light that is diffusely reflected in that area is removed, it is possible to prevent the generation of harmful light. Note that if the eye to be examined has an abnormal refractive power, the apparent optical path from the cornea to the fundus will change, so it goes without saying that the diaphragm should be moved in the direction of the optical axis in conjunction with a focusing device, etc., and always kept conjugate. It is. Also, when changing the range to be photographed by inserting a variable magnification lens into the photographing optical path, the aperture is replaced with a diaphragm of the same shape but a different size aperture. On the other hand, 21 is a light shielding plate, which has an outer edge similar to the photographing screen as shown in Fig. 5, and is arranged conjugately with the rear surface of the crystalline lens in relation to the relay optical system, and has the function of removing reflected light and scattered light by the crystalline lens. have Note that this light shielding plate has an effect equivalent to blocking an unnecessary portion of the illumination light that has entered the subject's eye, but the aperture diaphragm 22 has the effect of blocking an unnecessary portion of the illumination light that has entered the subject's eye. In that case, the light shielding plate 21 shall be removed.

The function of the light shielding plate 21 will be explained in detail below, in which the long radial direction of the photographing screen size is called the wide-angle direction, and the short radial direction is called the narrow-angle direction.

FIG. 6 depicts a wide-angle direction (horizontal direction) cross section of the eye to be examined, and the illumination light flux and photographing light flux. In the figure, the shaded light flux indicates the fundus illumination flux, and the dotted light flux indicates the imaging light flux. 18 is the cornea, 19 is the crystalline lens, 13' is the image of the ring slit, and 21' is the image of the ring slit. , is an image of a light shielding plate formed on the posterior surface of the crystalline lens. Further, FIG. 7 shows a cross section of the light beam illuminating the center of the fundus at the ring slit image plane, and FIG. 8 shows a cross section of the light beam illuminating the periphery at the ring slit image plane. Further, the diameter of the photographing light beam is set by the photographing aperture.

In these figures, especially in FIG. 6, the illumination light flux directed towards the center is blocked by the image 21', and is therefore shown here as a virtual light flux 22; however, if this light flux 22
If there had been, harmful light would have overlapped with the photographing light beam 25 emitted from the periphery at the rear surface of the crystalline lens, and harmful light would have mixed into the photographing light beam. Furthermore, among the illumination light beams 23 and 24 directed toward the periphery, the light beam 24 is blocked by the image 21', so that harmful light is prevented from entering the photographing light beam 26 emitted from the center.

The optical effect described above is the same as when the shape of the light shielding plate 21 is circular, but since a part of the light shielding plate 21 is cut out, the light beam 27 shown in FIG. 7 illuminates the center.

FIG. 9 depicts a cross section of the eye to be examined in a narrow angle direction, and the illumination light flux and photographing light flux. FIG. 10 shows a cross section of the light beam illuminating the center of the fundus at the ring slit image plane, and FIG. 11 shows a cross section of the ring slit image plane of the light beam illuminating the periphery. Since this figure is in the narrow-angle direction, the height at which the photographing light beam 34 intersects with the rear surface of the crystalline lens is lower than that in the wide-angle direction, and the image 21' of the light-shielding plate is narrower in width than in the wide-angle direction. Become. Of the luminous fluxes 32 and 33 directed toward the periphery, the luminous flux 33 is blocked by the image 21' of the light shielding plate, so that this luminous flux does not overlap with the imaging luminous flux 26 emitted from the center of the fundus at the position of the posterior surface of the crystalline lens.

As shown in Figures 6 and 9, the photographing light flux and the illumination light flux are completely separated on the surface and inside of the cornea or crystalline lens, so even if the illumination light flux generates harmful light on the cornea or crystalline lens. , it does not mix into the photographing light beam. By the way, in the above explanation, the light flux that illuminates the center of the fundus is much smaller than the light flux that illuminates the periphery, and therefore the two light fluxes are unbalanced. This was done to clarify the effect caused by The luminous flux can be balanced. The increase in the illumination light flux can be understood from a comparison between FIG. 12 and FIG. 10, and since this increased illumination light flux is located outside the light flux 22 in FIG. 6, it does not generate harmful light.

FIG. 13 shows the cross-sectional shape of the illumination light flux toward the periphery in the wide-angle direction, and FIG. 14 shows the cross-sectional shape of the illumination light flux toward the periphery in the narrow-angle direction.

Here, the shape of the inner light-shielding plate 13b of the well-known ring slit 13 shown in FIGS. 1 and 3 is made similar to the shape of the imaging screen, that is,
The sizes of the inner light-shielding portions of the ring slit are set to a first size (narrow-angle direction) and a second size (wide-angle direction) corresponding to the imaging field size (narrow-angle direction) and the second imaging field size (wide-angle direction), respectively. This is useful for increasing the central illumination luminous flux, and as a result of cutting out the upper and lower parts of the light shielding part 13b' as shown in FIG. The diameter can be reduced compared to the illumination light beam 40, and therefore it is possible to obtain bright photographs even in elderly people whose pupil diameter is difficult to increase or with a non-mydriatic fundus camera. 1st
FIG. 6 shows the cross-sectional shape of the illumination light flux toward the periphery in the wide-angle direction.

On the other hand, an aperture stop 2 is used instead of the light shielding plate 21 in FIG.
2 is provided to remove harmful light from the crystalline lens, but even if the edge of the aperture of this diaphragm 22 is formed to resemble the shape of the photographing screen as shown in FIG. It is possible to increase the central illumination flux without generating harmful flux. As described above, according to the present invention, it is possible to obtain a bright and clear fundus photograph by reducing the inner light-shielding portion of the ring slit even in the eyes of an elderly person whose pupil diameter is difficult to increase.

[Brief explanation of drawings]

Fig. 1 is an optical cross-sectional view of a fundus camera using what is known as a ring slit, Fig. 2 is a view showing the photographing screen, and Figs. 3, 4, and 5 are plan views showing the constituent members. , Fig. 6 is a wide-angle cross-sectional view showing the optical effect of the eye to be examined, Figs. 7 and 8 are cross-sectional views of the illumination beam seen at the pupil plane, and Fig. 9 is a narrow-angle view showing the optical effect of the eye to be examined. Directional cross-sectional view, from Figure 10 to Figure 1
Figures up to Figure 6 are cross-sectional views of the illumination light flux viewed from the pupil plane, and Figure 17 is a plan view showing the constituent members. In the figures, 1 is an objective lens, 2 is an aperture mirror, 3 is an imaging lens, and 4 is a Photographic film, 5 is photographic field aperture,
15 and 17 are light sources, 13 is a ring slit, 18
is the cornea, 19 is the crystalline lens, 20 is the illumination field diaphragm, 2
1 is a light shielding plate, and 22 is an aperture stop.

Claims (1)

[Scope of Claims] 1. In addition to a ring slit provided at a position optically conjugate with the anterior segment of the subject's eye, harmful light from the anterior segment of the subject's eye is removed at a position optically conjugate with the anterior segment of the subject's eye. a fundus illumination system equipped with a light-shielding member for the imaging screen; and a center-asymmetric imaging screen having different dimensions in a first radial direction in the wide-angle direction and in a second radial direction in the narrow-angle direction. In a fundus camera having a fundus imaging system, the shape of the inner light shielding part of the ring slit is approximately similar to the centrally asymmetrical shape of the imaging screen so that the light shielding area is smaller in the narrow angle direction than in the wide angle direction. A fundus camera that is characterized by: 2. The fundus camera according to claim 1, wherein the light shielding member is a light shielding plate provided conjugately with the crystalline lens. 3. The fundus camera according to claim 1, wherein the light shielding member is an aperture diaphragm provided conjugately with the vicinity of the cornea. 4. The fundus camera according to claim 1, wherein the shape of the light shielding member is asymmetrical to the center so that the light shielding area is smaller in the narrow angle direction than in the wide angle direction.