HK1203043B - Examination instrument - Google Patents

Description

Inspection instrument

Technical Field

Exemplary, non-limiting embodiments of the present invention relate generally to eye examination instruments.

Background

The optical design of a fundus camera includes several challenging requirements: the image needs to be sharp and uniformly illuminated with a high brightness sufficient to overcome the noise in the detection. The field of view should be wide enough to capture a large portion of the retina. The image needs to be free of glare (glare). In particular, reflection from the lens of the fundus camera, reflection from the cornea and lens of the eye tend to impair the quality of the image. It is also desirable that: imaging may be performed with a non-dilated pupil, i.e. in a way that avoids mydriasis. Preferably, the device should allow for handheld operation. Finally, the device should be compact and easily aligned with the eye during imaging, and the working distance needs to be sufficiently long.

Attempts have been made to create a good ophthalmoscope. In the prior art, problems associated with reflections have typically been solved by using a black-dot conjugate (black-dot conjugate) method in combination with a suitably shaped lens common to illumination and imaging. However, they reduce the quality of the image or limit the available field of view due to the increased aberrations. Thus, there is clearly a need for a suitable ophthalmoscope.

Disclosure of Invention

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention.

One aspect of the invention relates to an apparatus for imaging an eye, comprising: an illumination unit, a beam splitter, an objective lens, a relay lens system, and a camera unit; the illumination unit comprises an optical radiation source and is configured to direct optical radiation of the source from an exit pupil of the illumination unit to the beam splitter; a beam splitter configured to direct the optical radiation to the objective lens; the illumination unit is configured to illuminate a retina of the eye with optical radiation, and the objective lens is configured to form an intermediate real image (real image) of the retina between the objective lens and the camera unit with the optical radiation reflected from the retina, wherein a real image of an exit pupil of the illumination unit and a real image of an entrance pupil of the camera unit can be formed in a position ranging from a cornea of the eye to a rear side of a crystalline lens; the beam splitter configured to direct optical radiation from the retina to the camera unit, the beam splitter configured to deviate the path of the illuminating radiation from the path of the imaging radiation in a predetermined manner to at least prevent the image of the exit pupil from overlapping with the image of the entrance pupil in the lens; and the camera unit comprises a detection component, the relay lens system being configured to form a real image of the intermediate image on the detection component using the light radiation reflected from the retina for showing the optical image.

One aspect of the invention relates to a method for imaging an eye, comprising: directing optical radiation of the source from an exit pupil of the illumination unit to a beam splitter; a beam splitter directing the optical radiation to an objective lens along a path of the illuminating radiation; illuminating the retina of the eye through the objective lens with the optical radiation such that a real image of the exit pupil of the illumination unit and a real image of the entrance pupil of the camera unit can be formed in a position ranging from the cornea of the eye to the rear side of the crystalline lens; forming an intermediate real image of the retina between the objective lens and the camera unit in the path of the imaging radiation by means of the objective lens using the optical radiation reflected from the retina; a beam splitter directing optical radiation from the retina to the camera unit; a beam splitter deviating the path of the illuminating radiation and the path of the imaging radiation in a predetermined manner to prevent at least the image of the exit pupil and the image of the entrance pupil from overlapping on the surface of the lens; and a relay lens system forms a real image of the intermediate image on the detection member using the optical radiation reflected from the retina for showing the optical image.

Further embodiments of the invention are disclosed in the dependent claims.

The present solution enables a non-mydriatic imaging of the eye, which produces a non-glare image with a suitable field of view.

While various aspects, embodiments and features of the invention are set forth separately, it should be understood that: all combinations of aspects, embodiments and features of the invention are also possible and fall within the claimed scope of the invention.

Drawings

The invention will be described in more detail below by means of exemplary embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows the architecture of an eye examination apparatus;

FIG. 2 shows an alternative configuration of an eye's inspection apparatus;

FIG. 3 illustrates a deviation of an axis of illuminating radiation from an axis of imaging radiation;

fig. 4 shows the optical radiation path in the eye according to the gulsterland principle;

fig. 5 shows an optical radiation path which is easier than the requirements of the gulst land principle;

figure 6 shows the pupil of the eye, where the path of the illuminating radiation and the path of the imaging radiation are separated only in the crystalline lens;

figures 7 to 10 show some variants of the path;

FIG. 11 shows a projection of a path of illumination radiation and a path of imaging radiation larger than the pupil of the eye;

FIG. 12 shows an example in which the pupil of the eye is small;

figures 13 to 14 show the projection of the path of the illuminating radiation and the path of the imaging radiation on the pupil of the eye;

fig. 15 shows a camera unit having an optical function part;

FIG. 16 shows a fixation target and its projection on the retina;

FIG. 17 shows the structure of a fixation target;

FIG. 18 shows an inspection instrument with a fixed target;

FIG. 19 shows an image of a fixation target on the retina;

FIG. 20 shows a structure for providing fixation targets; and

fig. 21 shows a flow chart of a method.

Detailed Description

Exemplary embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Although the specification may refer to "an", "one", or "some" embodiment(s) in several places, this does not necessarily mean that each such reference refers to the same embodiment(s), or that the feature only applies to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments.

An example of the architecture of a device, for example an eye examination apparatus, is shown in fig. 1, which is a simplified structure showing only some elements and functional entities, the implementation of which may vary. An examination instrument for imaging an eye may include an illumination unit 100, a beam splitter 102, an objective lens 104, and a camera unit 106. The irradiation unit 100 comprises one or more lenses 108 and an optical radiation source 110, which optical radiation source 110 in turn comprises one or more source elements. The illumination unit may emit at least one of: ultraviolet light (about 250nm to 400 nm), visible light (about 400nm to 700 nm), infrared light (about 700nm to 1400 nm).

The illumination unit 100 may direct optical radiation of the source 110 from an exit pupil 112 of the illumination unit 100 to the beam splitter 102. The exit pupil 112 is an image of a physical stop in the illumination unit 100 formed by optical elements behind the stop. The beam splitter 102 directs the optical radiation to the objective 104 in the path 134 of the illuminating radiation. The path of the optical radiation may be defined as the volume occupied by the optical radiation. The size and shape of the path depends on the characteristics of the lens and other optical elements. The eye may also have some effect on the path. In fig. 1, a beam splitter 102 reflects a portion of the optical radiation towards an objective lens 104.

Typically, the beam splitter will reflect a part of the optical radiation directed towards it and allow the remaining part of the optical radiation to pass through it. Typically, a beam splitter splits an optical radiation beam into two beams such that both beams have about the same intensity, which may range from a few percent or less of the intensity of the original, undivided beam to nearly 50%.

In one embodiment, beam splitter 102 may include a polarizer. The beam splitter 102 with the polarizer may be, for example, a polarizing beam splitter. Alternatively or additionally, there may be one or more polarizers for polarizing both the illuminating radiation and the imaging radiation. A polarizer associated with the beam splitter 102 may cause the optical radiation to be linearly polarized.

The objective lens 104 may include one or more lenses. The objective lens 104 may have the following design characteristics: when the examination instrument is moved to a working distance from the eye, a real image of the exit pupil 112 of the illumination unit 100 is formed in a position ranging from the cornea 120 of the eye 122 to the back side 126 of the crystalline lens 124 to illuminate the retina 128 of the eye 122 with optical radiation. Similarly, objective 104 may have the following design characteristics: when the examination instrument is moved to a working distance from the eye, a real image of the entrance pupil 114 of the camera unit 106 is formed in a position ranging from the cornea 120 of the eye 122 to the back side 126 of the crystalline lens 124. The illuminating optical radiation may pass through the pupil 127 of the eye as it propagates to the retina 128. Similarly, imaging optical radiation traveling toward the detection may pass through the pupil 127 of the eye.

The objective 104 may also have the following design characteristics: an intermediate real image 130 of the retina 128 is formed between the objective lens 104 and the camera unit 106 in the path 132 of the imaging radiation, which is optical radiation reflected from the retina 128. In one embodiment, the intermediate real image 130 may be located between the objective 104 and the beam splitter 102.

The beam splitter 102 may direct optical radiation from the retina 128 to the camera unit 106. In fig. 1, a beam splitter 102 passes a portion of the optical radiation towards the detection component. Beam splitter 102 may be designed and/or positioned such that beam splitter 102 causes path 134 of illumination radiation and path 132 of imaging radiation to deviate from each other in a predetermined manner. The offset may at least prevent the image and/or beam of radiation of exit pupil 112 from overlapping with the image and/or beam of radiation of entrance pupil 114 in lens 124.

The beam splitter 102 may be located between the objective lens 104 and the aperture 116 of the relay lens system 138. The beam splitter 102 may be located between the entrance pupil 114 of the relay lens system 138 and the objective lens 104. The entrance pupil is an image (projected to the object space) of the aperture 116 of the relay lens system 138 formed by optical elements preceding the aperture 116. The beam splitter 102 may be located between the intermediate image 130 and the relay lens system 138. The beam splitter 102 may form a deviation between the illuminating optical radiation and the imaging radiation. For example, beam splitter 102 may be located at an optical halfway position between exit pupil 114 of relay lens system 138 and intermediate image 130. A certain distance between intermediate image 130 and beam splitter 102 is beneficial to avoid dust on the beam splitter, for example, which may become visible in the image.

If the beam splitter 102 comprises a polarizer, the optical radiation reflected from the beam splitter 102 towards the objective 104 is polarized. The polarized optical radiation then propagates to the retina 128 of the eye 122 and is reflected by the retina 128. Since the surface of the retina 128 is optically rough, the polarized optical radiation becomes at least partially depolarized. When the reflected optical radiation impinges on the polarizing beam splitter 102, the polarized part of the optical radiation is reflected from the beam splitter 102 towards the illumination unit 100 without being detected. However, a portion of the depolarized portion of the reflected optical radiation passes through the beam splitter 102 and propagates towards the detection component.

In addition to or instead of a polarizing beam splitter, a beam splitter with a front polarizer 140 for the illuminating radiation and a rear polarizer 142 for the imaging radiation may be used. The front polarizer 140 may perform linear polarization on the illuminating optical radiation 134 before the beam splitter 102. The rear polarizer 142 may also be a linear polarizer and may be located at an crossed position with respect to the front polarizer 140, i.e., the polarization axis of the rear polarizer 142 is rotated by 90 ° with respect to the polarization axis of the front polarizer 140. In this configuration, any optical radiation having a linear polarization that passes through the front polarizer 140 does not necessarily pass through the rear polarizer 142. Therefore, for example, the reflection from the objective lens 104 does not necessarily pass through the rear polarizer 142 and thus does not necessarily propagate to the detection part 106. However, a portion of the depolarized optical radiation reflected from the retina 128 can pass through the rear polarizer 142 to the detection component 106.

The camera unit 106 includes a detection component 136 and may include a relay lens system 138. The relay lens system 138 may also be a separate component from the camera unit 106. The camera unit 106 may be an integrated combination of the detection component 136 and the relay lens system 138 such that the camera unit 106 is the commercial product in question. The camera unit 106 may also include an image processing unit 148 and a screen 150 in a common architecture. Alternatively, the camera unit 106 may be designed to be constituted by separate optical components specific to the examination instrument.

The relay lens system 138 may include at least one lens. The relay lens system 138 may use the reflected optical radiation to form a real image of the intermediate image 130 on the detection component 136. The detection component 136 may include a plurality of pixels that may be in a matrix form. The purpose of the detection component 136 may be to convert the optical image into electrical form. However, the detecting member 136 may also be a photographic film instead of a photodetector. The detection part 136 may be a CCD (charge coupled device) unit or a CMOS (complementary metal oxide semiconductor) unit. The camera unit 106 may have a function such as a digital camera. The image, one or more still images or video in electrical form may be processed in an image processing unit 148 and then presented to the user on a screen 150 of the examination apparatus. The image processing unit 148 may include a processor and memory.

Fig. 2 shows an alternative configuration of the eye examination apparatus. This configuration is otherwise similar to that of fig. 1, except that the camera unit 106 and the illumination unit 100 have changed positions. If the beam splitter 102 comprises a polarizer, the optical radiation passing through the beam splitter 102 and towards the objective 104 is polarized. The polarized optical radiation then propagates to the retina 128 of the eye 122 and is reflected by the retina 128. When the reflected optical radiation hits the polarizing beam splitter 102, the polarized part of said optical radiation passes the beam splitter 102 towards the illumination unit 100. However, the depolarized part of the reflected optical radiation is reflected from the beam splitter 102 towards the detection member.

In the embodiment shown in fig. 2, the polarizing beam splitter may be replaced by a non-polarizing beam splitter, a polarizer 144, and a quarter wave plate 146. Polarizer 144 may polarize illumination radiation 134 after reflection from the beam splitter. The quarter wave plate 146 may convert the linearly polarized illumination radiation 134 into circularly polarized radiation. Optical radiation strikes the objective lens 104 and the cornea 120 before entering the eye 122. The polarization of the optical radiation propagating toward the detection component 106 may be passed a second time from circularly polarized radiation back to linearly polarized radiation in the quarter wave plate 146. However, the linear polarization is then rotated by 90 ° with respect to the illuminating radiation. Imaging radiation 132 may then strike polarizer 144 again. Since the polarization of the optical radiation is rotated by a total of 90 deg. after the second pass through the quarter-wave plate, the portion of the optical radiation that has maintained polarization (particularly reflection) does not necessarily pass through the polarizer 144. However, at least a portion of the polarized optical radiation reflected from the retina 128 may pass through the polarizer 144.

Embodiments are now more closely dissected in which the path of the illuminating radiation is separated from the path of the imaging radiation by using a polarizing beam splitter instead of a mirror or a non-polarizing beam splitter. A polarizing beam splitter may be used to separate the path of the illumination radiation and the path of the imaging radiation away from the entrance pupil 114 of the relay lens system 138. A beam splitter with (or without) a polarizer may be included inside the inspection instrument. The camera unit 106 may be a stand-alone unit and include one or more common lenses that may be used for other purposes.

As shown in fig. 1, the illumination radiation and the imaging radiation share at least the objective lens 104 and potentially also other lenses located between the objective lens 104 and the beam splitter 102, which beam splitter 102 may or may not include a polarizer. The advantage of sharing the objective 104 is that the working distance between the examination instrument and the eye 122 can be made comfortably long, which is also beneficial for the operation of a handheld examination instrument.

The use of a polarizing beam splitter enables free design of the shared lens without disturbing the reflection. When the linearly polarized illumination radiation reflected from the polarizing beam splitter is reflected from a shared surface (e.g., the front and back surfaces of the objective lens 104), the illumination radiation retains its polarization state and is reflected by the polarizing beam splitter towards the illumination unit 100. However, when the illuminating radiation is scattered from the retina 128, the illuminating radiation is substantially depolarized, and thus the image of the retina 128 is transmitted to the detection component 136 by the polarizing beam splitter. Naturally, the shared lenses should be substantially free of birefringence, or their birefringence should be compensated by using a suitable compensator, such as a retardation plate.

In one embodiment, hybrid glare elimination may be used such that glare from the first shared surface may be eliminated based on polarization, and glare from the posterior (i.e., closer to the eye) surface may be eliminated based on polarization using at least one compensator or by using prior art methods, for example, by appropriately designing the shape and/or using a black-dot conjugation method.

Fig. 3 shows a deviation of the optical axis 300 of the path of the illumination radiation from the optical axis 302 of the path of the imaging radiation fig. 3 refers to the configuration in fig. 1, however, a corresponding deviation in direction may also be present in a configuration similar to fig. 2 the angle α between the direction of the optical axis 300 of the path of the illumination radiation and the direction of the optical axis 302 of the path of the imaging radiation may be several degrees angle α may be, for example, 3 ° to 12 ° this deviation is used to at least prevent overlap of the image of the exit pupil 112 with the image of the entrance pupil 114 in the lens 124 (see fig. 4 to 6).

The possibility of eliminating the reflections caused by the eye is now analyzed. Fig. 4 shows the light path in the eye in an embodiment according to the gulst-land principle. A common problem associated with fundus cameras is glare from the front of the eye. The sources of the reflections are the two surfaces of the crystalline lens 124 and the cornea 120. These reflections can be avoided by separating the path 400 of the illuminating radiation and the path 402 of the imaging radiation from each other on these surfaces, according to the Golsland principle. As shown in fig. 4, the path 400 of the illuminating radiation and the path 402 of the imaging radiation are non-overlapping on the surface of the cornea 120 and the anterior and posterior surfaces 125, 126 of the crystalline lens 124. Before the narrow waist, the path is convergent, and then the path diverges. The narrow waist between the cornea 120 and the posterior surface 126 of the crystalline lens 124 refers to the focal point of the exit pupil 112 of the illumination unit 100. Similarly, the image of the entrance pupil 114 of the camera unit 106 is focused at the waist of the path 402 of the imaging radiation.

Fig. 5 and 6 show an embodiment whose requirements are easier than those of the gulsterland principle. Fig. 5 shows the fields of view in the following configuration: wherein the path of the illuminating radiation is separated from the path of the imaging radiation in a range from the anterior surface 125 to the posterior surface 126 of the lens 124. In embodiments where at least one polarizer, such as a polarizing beam splitter, is used, the reflection from cornea 120 may be eliminated or attenuated so much that it does not interfere with the inspection or measurement of the retina. Since there is no need to be concerned with reflections from the cornea 120, the path 400 of the illuminating radiation and the path 402 of the imaging radiation may be separated only on the surface of the crystalline lens 124, which enables the field of view of the inspection instrument to be substantially larger. The real image of the exit pupil 112 of the illumination unit 100 and the real image of the entrance pupil 114 of the camera unit 106 may be designed to be located at the same position or at different positions on a straight line parallel to the optical axis of the path 134 of the illumination radiation or the optical axis of the path 132 of the imaging radiation.

Fig. 6 shows the pupil of the eye, wherein the path 400 of the illuminating radiation and the path 402 of the imaging radiation are separated only inside the crystalline lens 124. In general, more than one illumination radiation path may be directed to the eye. Similarly, more than one imaging radiation path may be directed from the eye to the detection component 136. The great circle 600 represents the projection of the pupil of the eye to the focal plane (which is actually inside the eye). The upper circle 602 represents the projection of the path 402 of the imaging radiation onto the focal plane. The lower circle 604 represents the projection of the path 400 of the illuminating radiation onto the focal plane. Both projections of the waist of the path may be circular discs with a diameter of about 1mm (which means efficient use of illumination and imaging optics), and there is a distance of about 1mm between the paths of the radiation. The upper dashed circle 606 shows the projection of the imaging radiation at the eye pupil. The lower dashed circle 608 shows the projection of the illumination radiation at the eye pupil 600. Both paths of the optical radiation are fitted inside the pupil 600 of the eye having a diameter of about 4 mm.

For the path of optical radiation using NIR (near infrared) wavelengths and visible light, a size of several millimeters or less is suitable. The inspection instrument may be aligned with the correct position for capturing the image, after which a still image or short video may be captured in flash mode using visible light. The NIR wavelength does not cause light reflection from the pupil, so the inspection instrument can be designed to operate with larger pupil sizes.

The projections of the path 400 of the illuminating radiation and the path 402 of the imaging radiation may have various sizes and shapes. The projection may be a complete circle or a truncated circle (ellipse) or an ellipse, a rectangle, or have any shape that provides separation of the paths 400, 402 and a non-vignetting (non-vignetting) representation. The distance between the paths is substantially free of optical radiation, but small amounts of optical radiation may be tolerated as long as its power is below an acceptable level, the size of the distance between the paths depending on the desired field of view and the desired minimum pupil size of the eye. The minimum distance between the radiation paths may be, for example, 0.3mm to 1.5mm or a maximum of 3 mm. In fig. 4 to 6, the projections of the path of the illuminating radiation and the path of the imaging radiation have about the same size, but naturally their size may vary depending on, for example, the brightness and the light transmission loss of the light radiation source. However, when the goal is to achieve a smaller path projection area on or in the eye, the required image brightness may be a limiting factor.

Fig. 7-10 illustrate some variations in the shape and size of the path. In fig. 7, the projection has, for example, a rectangular shape.

In fig. 8, for example, the projection of the illuminating radiation is a small circle and the projection of the imaging radiation is a large circle.

In fig. 9, the projection of the illuminating radiation is a small circle and the projection of the imaging radiation is a truncated circle, which may be approximately rectangular, for example.

In fig. 10, the projections of both the illumination radiation and the imaging radiation are truncated circles, which may be approximated by rectangles, for example.

Notably, alignment of the inspection instrument with the eye becomes easier as it is more tolerant of variations in working distance and lateral displacement. The minimum diameter of the eye pupil required also becomes smaller, which helps in non-mydriatic imaging.

Fig. 11 shows projections 604, 602 of paths 400, 402 larger than the pupil of the eye 600. When the focal planes for both the illuminating and imaging radiation are located in the middle of the crystalline lens 124, the projections of the paths 400, 402 may be small enough to pass through the eye pupil, avoiding vignetting (although some vignetting may be tolerated, in practice since the vignetting of the path of the imaging radiation is opposite to the vignetting of the path of the illuminating radiation, they may compensate each other in whole or in part to achieve an image with uniform illumination). Therefore, the image of the exit pupil 112 of the illumination unit 100 and the image of the entrance pupil 114 of the camera unit 106 are not necessarily larger than necessary. However, when the examination apparatus is optimized for the highest brightness mode (even for use in case of a dilated pupil), the focal planes for both illumination radiation and imaging radiation can be located substantially in the position of the eye pupil (as is the case in fig. 11), by which vignetting is avoided, the size of the image of the exit pupil 112 of the illumination unit 100 and the size of the image of the entrance pupil 114 of the camera unit 106 can be larger than the eye pupil. Then, an unsharp (unsharp) beam of radiation may be provided regardless of the size of the pupil of the eye. Of course, the distance between the paths 400, 402 may need to be longer to achieve the same full field of view as a configuration (set-up) with projections of illumination radiation and imaging radiation smaller than the eye pupil.

Fig. 12 shows an example where the eye pupil is small. To achieve a wider full field of view (e.g., wider than 20 ° or 30 °) with a smaller eye pupil, the focal plane (i.e., the waist of the radiation path) may be close to the eye pupil, which may be as small as about 2mm in diameter. This minimizes vignetting. The image of the exit pupil 112 of the illumination unit 100 and the image of the entrance pupil 114 of the camera unit 106 may be so small that they both fit inside the pupil of the eye, or they may be larger. In one embodiment, the focal plane may be 0.1mm to 0.5mm inside the lens 124 from the eye pupil and the vignetting may be compensated by opposing vignetting in the illuminating radiation path and the imaging radiation path. The configuration enables imaging of the fundus using continuous visible light (e.g., white light) without the need to dilate the pupil. The imaging may be performed in the form of still images or video.

Fig. 13 and 14 show the projection of the path of the illuminating radiation and the path of the imaging radiation on the pupil of the eye. In fig. 13, for example, the projection has a rectangular shape larger than the pupil of the eye. In fig. 14, for example, the projection of the illuminating radiation is a small circle and the projection of the imaging radiation is a smaller rectangle.

The eye has substantial birefringence between the cornea 120 and the crystalline lens 124. Thus, if the path 400 of the illuminating radiation is not separated from the path 402 of the imaging radiation in the lens 124, the reflections from the lens 124 will become visible. However, in some embodiments, these reflections can be avoided by using a polarization compensator (e.g., at least one retardation plate) that is also adjustable. The compensator may compensate for the birefringence of the cornea, so the paths 400, 402 need not be separated at the cornea 120. As a result, the etendue of the optical instrument is maximized. The maximized etendue means that the optical power directed into the eye can be optimized to be high enough so that the acquisition power of the examination apparatus can be increased. The maximized etendue provides the following advantages: such as increased brightness and a larger field of view.

In one embodiment, the polarization state of the light may be mixed or modulated in a desired manner and/or degree by using a polarization scrambler or a suitable (possibly adjustable) compensator before the light enters the eye 122. The path of the illuminating radiation and the path of the imaging radiation may be separated in a range from the cornea 120 to the posterior surface 126 of the crystalline lens 124. This enables polarization-dependent properties of the retina 128 to be imaged, measured or eliminated.

We can now look closer to the camera unit 100. The exit pupil 112 of the illumination unit 100 may be defined as an illumination pupil, i.e. a real or virtual pupil from which the illumination radiation appears to originate when viewed from outside the illumination unit 100 (e.g. from the beam splitter 102). The exit pupil 112 of the illumination unit 100 may have different forms and sizes. In one embodiment, the illumination pupil may be circular, but it may also be elliptical, rectangular, truncated circular, or truncated elliptical. When the device is optimized for a small eye pupil (particularly a diagonal of less than 3 mm), the illumination pupil may be non-vignetting, although the brightness may vary from point to point in the image of the retina.

The path of the illumination radiation from the exit pupil 112 of the illumination unit 100 may have a divergent shape and the illumination radiation substantially uniformly illuminates the required portion of the intermediate image plane. The required portion is the same as the conjugate image of the full field of view region of the retina 128. Light outside the desired area may be blocked to avoid stray light. The blocking may be performed as early as possible, for example by adding a vignetting baffle inside the illumination unit 100 or after the illumination unit 100, or by designing and using a field stop (which may also be referred to as illumination field stop) inside the illumination module. In addition to stray light blocking, an illumination field stop may be used to shape the illumination onto the retina 128. The illumination may be shaped, for example, as a circle, an ellipse, or a straight line. Other shapes are also possible. The ellipses, straight lines, etc. may have different orientations. The illumination field stop may include an iris diaphragm so that the user can change the size and shape of the illumination on the retina. Another possibility is to use a spatial light modulator, such as an LCD (liquid crystal display), LcoS (liquid crystal on silicon) or DMD (digital micro-mirror device) micro-display, which electrically adjusts the size and shape, or even the wavelength, of the illumination of the retina 128.

The irradiation unit 100 is now examined. In embodiments in which more than one element is used, each element may emit optical radiation in a predetermined wavelength band. The optical band may vary from a single wavelength to hundreds or even thousands of nanometers. In one embodiment, the optical radiation source 110 may be a single element whose optical wavelength band may be controlled. The bandwidth and average wavelength may be varied in a predetermined manner. The control of the wavelength band may be performed electrically. For example, the average wavelength may be varied by electrically varying the generation of optical radiation in the element.

In one embodiment, the optical radiation source may comprise a broadband source element and a tunable filter. The output band of the optical radiation source may be selected on the basis of a filter. The filter may have multiple filter elements, each passing a different band or different set of wavelengths. Each filter element may be used individually or several filter elements may be used together to select the output wavelength of the illumination unit 100. The tunable filter may also be tuned by electrically changing the optical characteristics of the tunable filter to pass one or more desired optical bands.

The illumination unit 100 may include lenses, light pipes, dichroic mirrors, apertures, etc. required to form the exit pupil 112 of the illumination unit 100 and appropriate illumination to the plane of the intermediate image 130. The source element may for example be an LED (light emitting diode), an organic LED, a light emitting plasma, a laser, an incandescent lamp, a halogen lamp, an arc lamp (e.g. a xenon arc lamp), a fluorescent lamp or any lamp emitting a suitable wavelength and having other suitable properties for the device.

In one embodiment, the illumination unit 100 comprises one white LED chip and one LED chip emitting Near Infrared (NIR) wavelengths, the radiation of which may be combined together, for example, by using dichroic mirrors. The white LED chip may emit visible light in a wavelength band of 400nm to 700nm, while the NIR LED chip may emit light in a wavelength band of 700nm to 1200nm or a narrower wavelength band of, for example, 800nm to 900 nm. By using NIR wavelengths, the inspection instrument can be aligned with the correct position for image capture, after which white light can be used in flash mode to capture still images or (short) video. NIR wavelengths do not cause pupillary light reflections, so the inspection instrument can be designed to operate with larger pupil sizes, which in turn helps balance the trade-offs in optical design.

In one embodiment, the eye is illuminated using only near infrared radiation, and the optical inspection device is held out of focus of the near infrared radiation so that the visible light will be in focus. Such a setting (i.e. focusing) of the optical components is possible since the refraction of the lens for near infrared radiation differs slightly from the refraction for visible light and the difference in refractive index and thus the difference in focus is known in advance. When the visible light flashes, no action needs to be taken to focus, since the imaging optics are already in focus.

For many diagnostic purposes, such as in fluorescein angiography, it is beneficial to irradiate and/or image at a predetermined optical band. In these and other spectral analysis purposes, the illumination unit 100 may include one or more sources that emit broad-band optical radiation, which may then be filtered by using a band-pass filter to provide at least one desired wavelength band. In fluorescein angiography, suitable illumination may be between 465nm and 490nm, for example. When using one or more source elements that can emit light in one or more suitable wavelength ranges, the use of filters can be avoided. An example of such an unfiltered implementation is a blue LED emitting a central wavelength of 470nm for angiography. In one embodiment, a wavelength tunable filter may be used.

It may also be useful to filter the imaging optical radiation before it reaches the detection component 136. The filtering may limit the imaging optical radiation to at least one desired wavelength band. The bandwidth of the at least one band may vary from a single wavelength (a very narrow notch filter) to, for example, a few hundred nanometers. However, the bandwidth of the optical band is not limited to the example.

Filters may also be required to block one or more optical bands in the IR or UV domain. For example, UV radiation can cause damage to the eye. Different filters may be used in the path of the imaging radiation and the path of the illuminating radiation to obtain at least one image having a wavelength band that is partially or completely different from the wavelength band of the illumination.

In one embodiment, the illumination unit 100 may be based on the teachings of kohler illumination, although critical illumination or some other illumination scheme may also be used. The emission area of the LED chip may be imaged onto the exit pupil 112 (i.e., illumination pupil) of the illumination unit 100. The angled output of the chip imaged at the illumination field stop 160 may then be imaged onto the plane of the intermediate image 130, which may be imaged by the objective 104 onto the retina 128. In addition to this advantage of having an illumination field stop for blocking annoying stray light, this may provide the retina 128 with a well-defined illumination pupil and a uniform and vignetting-free illumination.

In one embodiment, simple illumination may be based on an aspheric condenser lens that collects light from the LEDs and images the emission area into the exit pupil 112 of the illumination unit 100, and at the same time images the illumination field stop 160 onto the plane of the intermediate image 130.

In one embodiment, the illumination unit 100 may comprise an LED with collection optics or a LED chip alone.

The objective lens 104 is now more closely profiled. The inspection instrument may include an objective lens 104 and a relay lens system 138. The objective lens 104 may form an intermediate real image 130 of the retina 128 between the objective lens 104 and the detection component 136. The relay lens system 138 may form an image of the intermediate image 130 on the detection component 136. Such imaging that occurs twice or secondary imaging (double imaging) in which the intermediate image 130 is imaged may bring about the following advantages: for example, there is room for beam splitter 102. Otherwise, the beam splitter 102 should be inserted outside the objective 104, i.e. between the objective 104 and the eye 122. This leads to several disadvantages: such as a short working distance to the eye, a narrow field of view, and problems associated with image brightness.

Alternatively, the beam splitter 102 may be inserted into the objective 104, which may significantly limit the objective design and may lead to other disadvantages: such as for the required larger size of the detection member 136. Another advantage of the secondary imaging structure is: the magnification from the retina 128 to the detection component 136 is easily adjusted and set to an appropriate value for the desired size of the detection component 136. The magnification is also adjustable, i.e. the system may comprise an optical zoom function, for example by adjusting the optical elements or possibly by adjusting the distance between the intermediate image 130 and the detection means. Yet another advantage of the secondary imaging structure may be: the intermediate image 130 may or may not be sharp, which means that aberrations caused by the eye 122 and the objective 104 do not need to be corrected by the objective 104 alone. Since the possibility of correcting aberrations using the objective lens 104 is limited, some aberrations may instead be corrected in the relay lens system 138. Therefore, it is possible to obtain a clear image with a wide field of view.

Yet another advantage of the secondary imaging structure is: the camera unit 106 with the relay lens system 138 and the detection component 136 may be part of a kit that additionally includes optical functional components 1500-1504 that can be repeatedly mounted and dismounted on the camera unit 106. Such an inspection apparatus is shown in fig. 15. The camera unit 106 itself may be used in a wide range of applications, for example in the examination of external parts of the body, such as the skin. An optical function 1500 may then include, for example, beam splitter 102 and objective 104. At least one other optical function 1502 (or 1504) in the kit can capture an image of at least one organ that is different from both the eye 122 and the at least one organ on the exterior surface of the body.

The objective lens 104 may be in its simplest form a single lens (singlet), which may have one or two aspheric surfaces. The angle between the optical axis of the objective 104 and the optical axis of the imaging radiation may be, for example, but not limited to, between 0 and 9 degrees.

The objective lens 104 may be made of glass or optical plastic. Birefringence can be minimized by grinding the glass of objective lens 104 followed by annealing. In one embodiment, objective 104 includes a doublet, which may be used to minimize chromatic aberration. Naturally, the number of elements is not limited to one or two, and there may be many variations of the design. If some lenses introduce birefringence, appropriate compensators can be used to compensate for the birefringence. Another possibility is to use an objective lens with a suitable surface shape. Another possibility is to apply a black dot conjugation method.

The focal length of the objective lens 104 may vary from 10mm to 50mm, for example. The full field of view may be, for example, from 20 ° to 60 °. The working distance to the eye may be, for example, from 8mm to 40 mm. The magnification from the retina 128 to the intermediate image 130 may be, for example, from 1.2 to 2.0.

The relay lens system 138 may form the intermediate image 130 onto the detection component 136. The beam splitter 102, with or without polarization effects, may be located between the intermediate image 130 and the relay lens system 138, but it may also be located inside the relay lens system 138. However, the beam splitter 102 is not necessarily arranged between an aperture stop of the relay lens system 138, which serves as the entrance pupil 114 of the camera unit 106, and the detection section 136. It may be considered an advantage that the relay lens system 138 and the objective 104 may be different lens systems, i.e. the multi-purpose camera unit 106, where the detection component 136 may form itself together with the relay lens system 138.

The size and shape of the aperture stop (i.e., entrance pupil 114) is determined such that a desired image of the aperture stop can be provided to the front of the eye 122. In one embodiment, the relay lens system 138 is a conventional camera lens system with a circular aperture. In one embodiment, the focal length of relay lens system 138 may be between 8mm and 100 mm. Focal lengths of 12mm to 35mm have generally been found to be satisfactory.

In the embodiment shown in fig. 1, the examination apparatus may have, for example, a field lens 160 for field flattening or for pupil matching purposes. The field lens 160 may be near the plane of the intermediate image 130. The field lens 160 may be part of the objective lens 104 or the relay lens system 138, or it may also be partially common to the objective lens 104 and the relay lens system 138.

As schematically illustrated in fig. 16, in one embodiment, the inspection instrument may include a beam splitter 1702 located between the objective 104 and the intermediate image 130 and one or more fixed targets 1704 positioned substantially at a virtual mirror 1706 of the intermediate image 130 via the beam splitter 1702. Beam splitter 1702 may correspond to beam splitter 102. The fixation target 1704 may be used to guide the viewing direction and focal length of the patient's eye 122 to facilitate capturing one or more images of the retina 128 concentrated in different parts of the retina and to facilitate focusing the device on the retina.

As shown in fig. 17, the one or more fixed targets 1704 may include an aperture plate 1802 having an aperture 1804 illuminated by one or more source units 1806, such as LEDs emitting visible radiation 1808 via an aperture 1804. One or more source units without aperture plates may also be used as fixed targets. The beam splitter 1702 may be a glass baffle, for example, that reflects a portion of the emitted radiation 1808 into the eye. There may be a suitable coating on the beam splitter 1702.

Another embodiment including a fixation target is shown in fig. 18, which is similar in part to the system described in fig. 1 except that it has an additional second illumination unit that can create one or more fixation targets visible to the eye 122, and is referred to as a fixation target unit 1902. Similar to the first irradiation unit 100, the fixation target unit 1902 may comprise optical components, such as a lens or lenses, and an optical radiation source 1904, which may comprise one or more source elements. The optical radiation source of the fixation target unit may operate in the visible region such that one or more images of the fixation target are visible through the patient. The optical radiation can be generated, for example, by LED chips emitting red, green, blue or white radiation.

The fixed target unit 1902 may direct optical radiation of a source 1904 from an exit pupil 1906 of the fixed target unit 1902 to the beam splitter 102. The exit pupil 1906 may be an image of the physical aperture of the fixed target unit 1902 formed by the optical element after the aperture. The beam splitter 102 may direct the optical radiation to the objective 104 in a path 1908 of the fixed target radiation. The beam splitter 102 may reflect a desired portion of the optical radiation via the objective lens 104 into the eye 122.

The same principle of constructing a fixation target shown in fig. 18 can be applied to the embodiment described in fig. 2 or other described embodiments.

The fixed target unit 1902 may include a field stop 1910, which may include a fixed target whose image may be seen by the patient's eye 122 and which may be used to direct the patient's eye in a desired direction. When the objective is to obtain an image covering a 180 ° range of the inner horizontal surface (inner horizontal surface) of the eye, three images each covering a 60 ° range may be captured, if necessary. The first image may be captured when the person is directed to look to the left, the second image may be captured when the person is directed to look straight ahead, and the third image may be captured when the person is directed to look to the right. A panoramic image may be formed from the three images. The image of the fixation target may also be used to guide the eye to adjust the desired distance. Typically, the field stop 1910 may be conjugated with the intermediate image 130 and the retina 128 so that the patient can see the target image in focus. Because the eye is generally accustomed to focusing on a visible image, a fixed target at the field stop 1910 guides the eye 122 to focus to a predetermined distance.

Fig. 19 shows an example of a real image of a fixation image formed on the retina 128 by the fixation target unit 1902. The image may include five circular spots 2002 in predetermined positions: one spot 2002A may be located on the axis of the device and the other spot 2002B may be spaced from the axis of the device by a distance determined by the angle of the field of view. The angular interval field of view may be set to, for example, 8 ° to 25 °. The angle of the field of view may depend on the field of view used by the inspection device. Each spot 2002 may be formed by a separate light source unit. One or more light sources may output one spot 2002 at the same time, such that eye 122 sees only one spot 2002 at each instant and focuses to that spot. More than one spot 2002 may also be output by the light source at the same time. Thus, the eye 122 can see and focus on several spots 2002 at each moment.

The fixed target unit 1902 does not need to radiate light during image capture. Therefore, reflections from the cornea and lens of the eye do not necessarily disturb the image quality, and therefore the size and position of the exit pupil 1906 of the fixation target unit 1902 does not need to be carefully arranged with respect to the entrance pupil 114 of the camera unit 106 as the size and position of the exit pupil 112 of the illumination unit. Inside the eye, the exit pupil 1906 of the fixed target unit 1902 may be imaged, for example, approximately between the image of the exit pupil 112 and the image of the entrance pupil 114, or approximately above the image of the entrance pupil 114.

In one embodiment, the fixation target unit 1902 and the illumination unit 100 may use separate beam splitters 102 to direct the illumination beam 134 and the fixation target beam 1908 into the eye. In fig. 18, a fixed target unit 1902 may use the same optional front polarizer 140 as the illumination unit 100. However, they may also use different front polarizers. The fixation target unit 1902 and the irradiation target unit 100 may also share other common components, such as a fold mirror, a lens, or a heat sink for a printed circuit board or LED, for example.

The embodiment of the fixation target unit 1902 shown in fig. 20 is now observed more closely. The fixed target unit 1902 may include one or more LED sources 2102, an aperture plate 2104, one or more relay lenses 2106, and an aperture pupil stop 2108. The LEDs' 2102 may illuminate the holes 2110 in the aperture plate 2104 such that the holes 2110 are imaged by the relay lens 2106 onto the retina 128 via the intermediate image 130. The aperture plate 2104 may be located at a field stop 1910 of the fixed target unit 1902. The path of the stationary target radiation in this configuration is shown by line 1908.

In the exemplary case, the physical aperture pupil stop 2108 coincides with the exit pupil 1906 of the fixed target unit 1902, but they may also be different. If the aperture pupil stop 2108 is located between the aperture plate 2104 and the at least one relay lens 2106, the aperture pupil stop 2018 need not coincide with the exit pupil 1906 of the stationary target unit 1902. The aperture pupil stop 2108 may also be formed by the clear aperture of the relay lens, so that a separate physical aperture is not required.

The aperture pupil stop 2108 may comprise an adjustable iris diaphragm that may be used to adjust the brightness of a fixed target image without affecting the shape of the feature. The brightness may also be adjusted by adjusting the output brightness of the radiation source. Brightness adjustment of the target image may be used to open and close the iris 127 of the eye 122. When the pupil is larger, it is easier to inspect the eye. Also, more optical radiation can be fed to the eye with a larger pupil. In addition, when the pupil of the eye is large, mechanical adjustment and optical adjustment of the examination instrument are easier to perform.

One or more homogenizing elements or light dispersing elements 2112 may be present between the LED2102 and the aperture plate 2104 or within the aperture 2110 to homogenize the light distribution in the viewing area within the aperture 2110. In this way, the structure of the LED cannot be seen by the person being inspected. Another possibility is to use an aperture long enough to act as a small light guide to provide a uniform spatial output. Yet another possibility is to feed the light from the LED2102 to an optical fiber that mixes the light distribution. The filter may then output the light toward the beam splitter 104.

In addition to a circular spot, a stationary target may provide any image onto the retina. The images may include lines, crosses, rings, characters, numbers, symbols, and the like. The image of the fixation target may be a single color or have different colors. In one embodiment, the field stop 1910 of the fixed target unit may be fully illuminated and the aperture 2104 may be changed so that the operator may select the desired fixed target features for each task. Additionally or alternatively, an image of a fixed target may be formed by operating an LED matrix or OLED matrix (organic LEDs) in a similar manner to the aperture plate 2104. In one embodiment, the target image may be formed by an illuminated micro-display such as an LCD or LcoS (liquid crystal on silicon) or a micro-mirror array such as a DMD (digital micromirror device) that provides simple adjustment of the target image. In one embodiment, the target image may form various models or arrays on the retina, such as line arrays, spot arrays, and circular arrays. Any of the models or arrays, alone or in combination, may be used to aid in the focus of the examination apparatus, or for measuring the size or shape of the eye or for analyzing the eye.

One or more fixation targets imaged on the retina may be adjusted in various ways. The one or more fixation targets may be continuously imaged on the retina. In one embodiment, the fixation target may be turned off during image capture, while in other cases it may be continuously imaged on the retina. On the retina, the one or more fixed targets may be repeatedly flashed at a desired frequency, and the flashing frequency is synchronized, for example, with the image capture frequency. During video capture, the one or more fixation targets may be imaged on the retina and between each frame capture so that the patient can see the fixation target but the fixation target cannot be recorded in the video. In one embodiment, the one or more fixed targets may be displayed in a shorter time interval and the captured frames comprising images of the one or more fixed targets may be removed from the final video sequence.

In one embodiment, the position of the field stop 1910 of the fixed target unit 1902 may be adjusted in the axial direction such that the eye 122 may be directed to focus to different distances based on the position of the fixed unit 1902. The field stop position adjustment may also be matched to the focus of the camera unit. In one embodiment of the invention, the movable field stop 1910 of the fixed target unit 1902 may be used to test or measure the accommodation of the eye 122 and/or the range of accommodation of the eye. The fixation target image can be adjusted in a direction perpendicular to the optical axis, for example, so that the operator can freely guide the observation direction of the patient's eye without being restricted to a predetermined position.

In addition, in one embodiment, the fixed target may include a source unit operating in the IR region. Thus, target images can be formed by IR light and they can be used for refractive measurements of the eye.

Typically, the focal length of the objective lens 104 may be between 23mm and 27mm, for example. The working distance of the examination instrument, i.e. the distance from the cornea to the closest surface of the objective lens, may be between 18mm and 26mm, for example. The optical distance from the illumination pupil to the intermediate image 130 may be, for example, between 90mm and 130 mm. The optical distance from the entrance pupil of the relay lens to the intermediate image is equal to the optical distance from the illumination pupil to the intermediate image within 10 mm. The focal length of the relay lens system 138 may be, for example, between 15mm and 25 mm. The entrance pupil 114 may be between 3mm and 6mm in diameter. The intermediate image 130 may be about 18mm to 30mm from the objective lens 104. A full field of view of 45 deg. may correspond to an intermediate image diameter of about 12mm to 22 mm.

FIG. 21 is a flow chart of an apparatus according to an embodiment of the present invention. In step 2200, optical radiation of the source 110 is directed from the exit pupil 112 of the illumination unit 100 to the beam splitter 102. In step 2202, the beam splitter 102 directs optical radiation to the objective lens 104 along a path 134 of the illuminating radiation. In step 2204, the retina 128 of the eye 122 is illuminated such that a real image of the exit pupil 112 of the illumination unit 100 and a real image of the entrance pupil 114 of the camera unit 106 can be formed in a position ranging from the cornea 120 of the eye 122 to the rear side 126 of the crystalline lens 124 by means of the objective 104 with optical radiation. In step 2206, an intermediate real image 130 of the retina 128 is formed between the objective lens 104 and the camera unit 106 in the path 132 of the imaging radiation by the objective lens 104 using the optical radiation reflected from the retina 128. In step 2206, the beam splitter 102 directs optical radiation from the retina 128 to the camera unit 106. In step 2208, beam splitter 102 deviates path 134 of the illumination radiation from path 132 of the imaging radiation in a predetermined manner to prevent at least the image of exit pupil 112 and the image of entrance pupil 114 from overlapping on surfaces 125, 126 of lens 124. In step 2210, the relay lens system 138 forms a real image of the intermediate image 130 on the detection component 136 using the optical radiation reflected from the retina 128 to convert the optical image into an electrical form to be displayed on the screen 150.

The image processing unit 148 may include a processor, controller, etc. connected to the memory and various interfaces of the examination instrument. In general, the image processing unit 148 may be a central processing unit or an additional operational processor. The processor may include an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), and/or other hardware components programmed to perform one or more functions of at least one embodiment. The processor may be implemented as the electrical circuitry of a digital state machine executing logic operations based on the instructions of a computer program. In one exemplary embodiment, the at least one processor may be implemented as a microprocessor that performs the functions of a Central Processing Unit (CPU) on an integrated circuit. The CPU is a logic state machine that executes a computer program comprising program instructions. The instructions are encoded as a computer program using a programming language, which may be a high-level programming language. The CPU may include a set of registers, an Arithmetic Logic Unit (ALU), and a Control Unit (CU). The control unit is controlled by a sequence of instructions transferred from the working memory to the CPU. The control unit may include a number of microinstructions of basic operations. The implementation of the microinstructions may vary depending on the CPU design. The microprocessor may also have an operating system (a dedicated operating system for embedded systems, or a real-time operating system) that may provide computer programs for system services. In one embodiment, the one or more memories further store instructions that, when executed by the one or more processors, cause the inspection instrument to perform its operations.

The memory may include volatile and/or non-volatile memory and typically stores content, data or the like. For example, the memory may store computer program code, such as software applications or operating systems, information, data, content, etc., for the processor to perform steps associated with operation of the device according to embodiments. The memory may be, for example, Random Access Memory (RAM), a hard drive, or other fixed data storage or storage. In addition, the memory or a portion of the memory may be a removable memory that is removably connectable to the device.

The data storage medium or memory unit may be implemented within the processor/computer or external to the processor/computer, in which case it can be communicatively coupled to the processor/computer via various means as is known in the art.

The image data formed by the image processing unit 148 may be stored in a memory 152 of the optical system. Additionally or alternatively, the image data may be stored in a database 154 of a patient data system of the hospital. Images stored in memory 152 or database 154 may be retrieved for viewing in an optical system or in a computer.

The examination apparatus may be used as a portable ophthalmoscope and/or a portable fundus camera. The reason for this is that the examination apparatus can be made compact enough and light enough to be hand-held while examining the eye.

It is obvious to a person skilled in the art that as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims (20)

1. An apparatus for imaging an eye, comprising: an illumination unit, a beam splitter, an objective lens, a relay lens system, a fixation target unit, and a camera unit;

the illumination unit comprises an optical radiation source and is configured to direct optical radiation of the optical radiation source from an exit pupil of the illumination unit to the beam splitter;

the beam splitter is configured to direct the optical radiation to the objective lens to illuminate a retina of an eye;

the fixation target unit is configured to illuminate the retina of the eye with visible radiation by means of at least one fixation target image such that the fixation target unit is configured to direct optical radiation to the beam splitter, wherein the beam splitter is configured to direct optical radiation from the fixation target unit to the objective lens to form at least one image associated with the fixation target unit on the retina;

the objective lens is configured to form an intermediate image of the retina between the objective lens and the camera unit using optical radiation reflected from the retina, wherein a real image of an exit pupil of the illumination unit and a real image of an entrance pupil of the camera unit can be formed in a position ranging from a cornea of an eye to a rear side of a crystalline lens;

the beam splitter is located between an aperture of the relay lens system and the objective lens and is configured to direct optical radiation from the retina to the camera unit, the beam splitter being configured to deviate the path of the illuminating radiation from the path of the imaging radiation in a predetermined manner to prevent overlapping of the image of the exit pupil with the image of the entrance pupil at least in the lens; and

the camera unit comprises a detection component on which the relay lens system is configured to form a real image of the intermediate image using optical radiation reflected from the retina for showing an optical image;

wherein the fixed target unit comprises a field stop and the field stop is conjugate to the intermediate image and the retina such that the at least one fixed target image is visible in focus.

2. The apparatus of claim 1, wherein the objective lens is configured to form a real image of the exit pupil of the fixation target unit at least approximately in a position ranging from a cornea of the eye to a posterior side of a crystalline lens.

3. The apparatus of claim 1, wherein the detection component is configured to convert the optical image to an electrical form.

4. The apparatus of claim 1, wherein the beam splitter comprises at least one polarizer.

5. The apparatus according to claim 1, wherein the objective lens is configured to form a real image of the exit pupil of the illumination unit substantially inside the lens.

6. The apparatus of claim 1, wherein the objective lens is configured to form a real image of the entrance pupil of the camera unit substantially inside the lens.

7. The apparatus of claim 1, wherein a real image of the exit pupil of the illumination unit and a real image of the entrance pupil of the camera unit are located at different positions on a straight line parallel to an optical axis of the path of the imaging radiation or the path of the illumination radiation.

8. The apparatus of claim 1, wherein the illumination unit is configured to continuously illuminate the retina with infrared radiation, and the illumination unit is configured to flash visible light to capture at least one still image of the retina.

9. The apparatus of claim 1, wherein the beam splitter is located between an aperture of the relay lens system and the objective lens.

10. The device of claim 1, wherein a kit comprises the camera unit and a plurality of optical functions;

the optical functional component is repeatedly attachable to and detachable from the camera unit;

the camera units individually configured to capture images of at least one organ on an outer surface of a body;

one of the optical functions includes the beam splitter and the objective lens for imaging the eye; and

the camera unit with at least one further optical function in the kit is configured to capture an image of at least one organ different from the eye and the at least one organ on the outer surface of the body.

11. A method for imaging an eye, comprising: directing optical radiation of the source from an exit pupil of the illumination unit to a beam splitter;

the beam splitter directing the optical radiation to an objective lens along a path of the illumination radiation;

a fixation target unit illuminating the retina of the eye with visible radiation by means of at least one fixation target image;

directing optical radiation through the fixation target unit to the beam splitter and directing optical radiation from the fixation target unit through the beam splitter to the objective lens to form at least one image associated with the fixation target unit on the retina;

illuminating the retina of the eye through the objective lens with the optical radiation such that a real image of an exit pupil of the illumination unit and a real image of an entrance pupil of a camera unit can be formed in a position ranging from the cornea to the rear side of the crystalline lens of the eye;

forming an intermediate image of the retina between the objective lens and the camera unit in the path of imaging radiation through the objective lens using optical radiation reflected from the retina;

directing optical radiation from the retina to the camera unit through the beam splitter;

deviating the path of the illuminating radiation from the path of the imaging radiation in a predetermined manner between an aperture of a relay lens system and the objective lens by means of the beam splitter to prevent an image of the exit pupil from overlapping with an image of the entrance pupil at least on the surface of the lens; and

forming a real image of the intermediate image on a detection component using optical radiation reflected from the retina for showing an optical image by a relay lens system;

wherein the fixed target unit comprises a field stop and the field stop is conjugate to the intermediate image and the retina such that the at least one fixed target image is visible in focus.

12. The method of claim 11, further comprising: a real image of the exit pupil of the fixation target unit is formed by the objective lens at least approximately in a position ranging from the cornea of the eye to the posterior side of the crystalline lens.

13. The method of claim 11, further comprising: converting the optical image into electrical form by the detection component.

14. The method of claim 11, further comprising: the optical radiation is directed by a polarizing beam splitter.

15. The method of claim 11, further comprising: forming a real image of the exit pupil of the illumination unit inside the lens by the objective lens.

16. The method of claim 11, further comprising: a real image of the entrance pupil of the camera unit is formed substantially inside the lens by the objective lens.

17. The method of claim 11, further comprising: forming a real image of the exit pupil of the illumination unit and a real image of the entrance pupil of the camera unit at different positions on a straight line parallel to an optical axis of the path of the imaging radiation or the path of the illumination radiation.

18. The method of claim 11, further comprising: continuously illuminating the retina with infrared radiation; and flashing visible light to capture at least one still image of the retina.

19. The method of claim 11, wherein the beam splitter located between the aperture of the relay lens system and the objective lens forms a deviation between the illuminating optical radiation and the imaging radiation at a location different from the relay lens system.

20. The method of claim 11, wherein a kit comprises the camera unit and a plurality of optical functional components that are repeatedly attachable to and detachable from the camera unit;

the camera units individually configured to capture images of at least one organ on an outer surface of a body;

one of the optical functions includes the beam splitter and the objective lens for imaging the eye; and

the camera unit with at least one further optical function in the kit is capable of capturing an image of at least one organ different from both the eye and the at least one organ on the outer surface of the body.