A multi-mode dual off-axis retinal imaging device and method

Abstract

The present invention relates to a multi-mode dual off-axis retinal imaging device, characterized in that it includes an imaging optical path, an illumination optical path, a focusing optical path and a fixation optical path; the imaging optical path is used to form a retinal image, the illumination optical path is used to form uniform illumination on the fundus; the focusing optical path is used to perform refractive compensation when forming a retinal image to ensure the clarity of the captured photo; the fixation optical path is used to stabilize the human eye. This device can eliminate the beam splitter element between the imaging optical path and the illumination optical path. By means of the off-axis method, the two optical paths are separated in space, and both optical paths form converging circular light spots on the human cornea, without the need for annular illumination, greatly simplifying the processing and alignment difficulty of the illumination optical path.

Description

Technical Field

[0001] The present invention belongs to the technical field of ophthalmic imaging, and relates to a fundus retina imaging device and method that uses white light and near-infrared LEDs as illumination light sources and forms images through an optical lens and a digital camera. Specifically, it relates to a multi-mode dual off-axis retina imaging device and method. Background Art

[0002] Retina imaging technology has been widely applied in the field of fundus disease detection. Medical research shows that both ophthalmic diseases and systemic diseases of the body will cause lesions in the fundus retina at the early stage of onset. Accurate and timely detection of retinal lesions can play a significant role in the early diagnosis of diseases and provide a good platform for the pathological research of major diseases.

[0003] The most common fundus disease diagnostic device is a fundus camera. Its optical system consists of at least two modules: an imaging optical path and an illumination optical path. Some also include modules such as an alignment optical path and a focusing optical path. After years of research and development, two optical structures have gradually emerged: an external illumination structure and an internal illumination structure. The main difference between the two structures is that the beam splitter in the external illumination structure serves as the beam splitting element for the illumination optical path and the imaging optical path, and there is no shared lens group for the two optical paths. While the internal illumination method uses a hollow mirror as the beam splitting element for the two optical paths, and the two optical paths share the eyepiece objective lens. Generally speaking, for the internal illumination structure, the fundus illumination energy is uniform and the energy utilization rate is high, so it has a broader scientific research value and market space. The external illumination structure is more suitable for portable fundus cameras and contact fundus cameras. However, whether it is the external illumination structure or the internal illumination structure, they both have a beam splitting element and are coaxial optical systems, that is, the human eye visual axis, the illumination optical path optical axis, and the imaging optical path optical axis coincide.

[0004] The light emitted by the illumination optical path will be reflected in the central area of the human eye cornea, forming stray light, which seriously affects the imaging quality of the fundus retina. For the stray light formed by human eye reflection, the method of annular illumination is usually adopted to avoid it. That is, the illumination optical path forms an illumination ring at the human eye cornea. There is no illumination light in the area within the ring, and the fundus reflected light exits from the center of this area and enters the imaging optical path. In this design, the illumination optical path and the imaging optical path are separated in space and do not interfere with each other. However, in actual situations, to form a high-quality ring, a high-quality illumination optical path is often required. Such an optical path has many lenses, a precise structure, great assembly and adjustment difficulty, a large volume, and a high cost. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and propose a retinal imaging device with a double off-axis structure. This device can eliminate the beam splitter element between the imaging optical path and the illumination optical path. By using the off-axis method, the two optical paths are separated in space, and both optical paths form converging circular light spots on the human cornea, eliminating the need for annular illumination and greatly simplifying the processing and alignment difficulties of the illumination optical path. This device can capture large-field color and near-infrared images of the fundus retina under the condition of non-mydriasis, and can also achieve fluorescence angiography imaging and autofluorescence imaging through the combination of different filter plates, forming multiple examination modes.

[0006] The present invention solves its technical problems by adopting the following technical solutions:

[0007] A multi-mode double off-axis retinal imaging device, characterized in that it includes an imaging optical path, an illumination optical path, a focusing optical path, and a fixation optical path; the imaging optical path is used to form a retinal image, the illumination optical path is used to form uniform illumination on the fundus, the focusing optical path is used to perform refractive compensation when forming a retinal image to ensure the clarity of the captured photo, and the fixation optical path is used to stabilize the human eye. During operation, after the fixation optical path stabilizes the human eye, the infrared LEDs in the illumination optical path and the focusing optical path light up simultaneously, and the imaging optical path forms an infrared fundus image. The alignment in the X and Y directions is completed according to the infrared fundus image. At the same time, the focusing in the Z direction is completed according to the slit pattern formed by the focusing optical path. Finally, the white light LED in the illumination optical path flashes, and the imaging optical path forms a color fundus image.

[0008] Moreover, the imaging optical path includes an eyepiece group, an imaging filter plate, an imaging lens group, and an imaging camera. An imaging lens group is arranged at the upper front of the eyepiece group, and an imaging filter plate and an imaging camera are arranged in sequence from near to far in front of the imaging lens group.

[0009] Moreover, the eyepiece group includes a retinal objective lens, a relay lens, and an aperture diaphragm plate arranged in sequence from the back to the front. The retinal objective lens is used to collect the return light from the fundus of the human eye and form a clear intermediate image plane; the relay lens and the retinal objective lens together make the human eye pupil and the aperture diaphragm plate form a conjugate object-image relationship, and make the light rays emerging from the aperture diaphragm plate approximate parallel light;

[0010] The retinal objective lens is an optical lens group, with the number of lenses being 1 to 3. When there is a single lens, it is an aspherical lens, and when there are multiple lenses, they are all spherical lenses, and at least one of them is a cemented lens;

[0011] The relay lens is an optical lens group, with the number of lenses being 1 to 2, and at least one of them is a cemented lens;

[0012] The aperture diaphragm is a black thin sheet, on which circular holes with different diameters are arranged at intervals. The circular holes arranged on the left and right respectively form the illumination optical path aperture and the imaging optical path aperture. A fixation optical path aperture is arranged between the illumination optical path aperture and the imaging optical path aperture, and focusing optical path apertures are arranged at both the upper and lower ends of the fixation optical path aperture;

[0013] The imaging filter is a band-pass optical coating filter with a working angle of 0° and a cut-off depth of not less than OD4. Its function is to transmit the fluorescence excited by the illumination light while blocking the light of other wavelength bands to form a high-contrast fluorescence image.

[0014] Moreover, the imaging lens group is an optical lens group with 1 to 5 lenses, at least including 2 cemented lenses. Its function is to re-image the intermediate image plane formed by the retinal objective lens, correct the remaining aberrations, and form a clear retinal image on the digital camera.

[0015] Moreover, the imaging camera is a CCD or CMOS camera with a photosensitive area of not less than 1 / 3 inch and a resolution of not less than 3 million pixels.

[0016] Moreover, the illumination optical path includes a white light LED, an infrared LED, an illumination filter, a first condenser lens, a second condenser lens, an illumination beam splitter, an illumination lens group, and an eyepiece group. An illumination lens group is arranged at the lower front of the eyepiece group. An illumination beam splitter, a first condenser lens, an illumination filter, and a white light LED are arranged in sequence from back to front in front of the illumination lens group. A second condenser lens and an infrared LED are arranged in sequence from top to bottom directly below the illumination beam splitter.

[0017] Moreover, the white light LED is a surface-mounted LED with a color temperature range of 4000K - 5500K and a color rendering index of not less than 80%;

[0018] The infrared LED is a surface-mounted LED in the near-infrared band with a central wavelength range of 830nm - 980nm. It is an infrared monitoring light source used for infrared imaging of the fundus before taking pictures;

[0019] The illumination filter is a band-pass optical coating filter with a working angle of 0° and a cut-off depth of not less than OD4. Its function is to separate the light wavelength band required for fluorescence imaging from the white light LED and project it onto the condenser lens;

[0020] The first condenser lens and the second condenser lens are optical lens groups, each with 1 to 2 lenses. Their function is to collect the light emitted by the white light LED light source and the infrared LED light source and project it onto the illumination lens group through the illumination beam splitter.

[0021] The illumination beam splitter is a dichroic optical transmissive-reflective mirror with a working angle of 45°. Its function is to reflect visible light while transmitting near-infrared light, enabling visible light and near-infrared light incident from mutually perpendicular directions to propagate in the same direction after passing through the lens, achieving the purpose of beam combination.

[0022] The illumination lens group is an optical lens group with 1 to 2 lenses. Its function is to project the light collected by the condenser lens into the human eye through the eyepiece group, forming uniform illumination on the fundus.

[0023] Moreover, the focusing optical path includes a focusing light source, a collimating mirror, a slit diaphragm, and an eyepiece group. The slit diaphragm, the collimating mirror, and the focusing light source are sequentially arranged from near to far in front of the eyepiece group.

[0024] The focusing light source is a direct-insert type near-infrared point light source LED with a central wavelength range of 830nm to 980nm. Its function is to illuminate the slit through the collimating mirror.

[0025] The collimating mirror is an optical lens with a focal length range of 5mm to 25mm and a numerical aperture not greater than 0.5. Its function is to collect the light emitted by the focusing light source and project it through the slit onto the eyepiece group.

[0026] The width of the slit diaphragm is not greater than 0.2mm, and the aspect ratio is not less than 3:1. Its function is to form an image of the slit on the fundus through the eyepiece objective. According to the relative position of the two slit images, the refractive state of the human eye is judged, and refractive compensation is performed by changing the distance between the retinal objective lens and the relay lens to ensure the clarity of the captured photo.

[0027] Moreover, the fixation optical path includes a fixation light source, a collimating mirror, and an eyepiece group. The collimating mirror is arranged in front of the eyepiece group, and the fixation light source is arranged in front of the collimating mirror.

[0028] The fixation light source is a direct-insert type visible light LED with a central wavelength range of 500nm to 650nm. Its function is to provide a fixed target for the human eye and stabilize the human eye.

[0029] The collimating mirror is an optical lens with a focal length range of 5mm to 25mm and a numerical aperture not greater than 0.5. Its function is to collect the light emitted by the fixation light source and project it onto the fundus through the eyepiece group.

[0030] A multi-mode dual off-axis retinal imaging method, characterized by comprising the following steps:

[0031] Step 1, the fixation light source emits light and projects it onto the fundus through the fixation optical path. After the human eye observes the fixation light source, it remains stable.

[0032] Step 2: The infrared LED emits near-infrared light at 850 nm. After passing through the second condenser lens, the illumination beam splitter, and the illumination lens group, it enters the eyepiece group through the illumination optical path aperture in the aperture stop sheet, and forms a converging light spot on the human cornea after being refracted by the relay lens and the retinal objective lens. The near-infrared light continues to propagate forward and diverges simultaneously to form uniform illumination on the fundus.

[0033] Step 3: The fundus retina reflects the above illumination light. After exiting from the pupil, it will pass through from the other side of the cornea and enter the imaging optical path.

[0034] The channels of the illumination optical path and the imaging optical path on the cornea are separated from each other and do not interfere with each other.

[0035] Step 4: After the light reflected from the fundus enters the imaging optical path, it passes through the imaging aperture stop sheet and is converged on the imaging camera by the imaging lens group to form an image.

[0036] At the same time, the focusing light source also emits light, projecting an image of two slits on the fundus. The slit image is captured by the imaging camera and superimposed on the fundus image. According to the relative position of the slits, refractive compensation is performed on the human eye, and after completion, the slits are aligned.

[0037] Step 5: Turn off the focusing light source and the infrared LED, and turn on the white light LED for flashing. The light emitted by the white light LED will again follow the path of the light emitted by the infrared LED, and finally form a clear color fundus image on the imaging CCD.

[0038] The advantages and positive effects of the present invention are as follows:

[0039] This multi-mode dual off-axis retinal imaging device eliminates the beam splitter element shared by the illumination optical path and the imaging optical path. The imaging optical path and the illumination optical path are symmetrically distributed on both sides centered on the visual axis of the human eye on the cornea, without interfering with each other, ensuring the imaging quality of the fundus retina. The present invention adopts a new optical design and does not need to use traditional "polarization imaging" and "black dot plate" schemes to eliminate stray light. The system structure is compact and simple, facilitating production, debugging, and cost control.

[0040] The present invention has multiple working modes. In addition to being able to capture color fundus images, it can also capture infrared images, fluorescence angiography images, and autofluorescence images through different combinations of filter plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic diagram of the structure of the imaging optical path and the illumination optical path of the present invention (top view);

[0042] Figure 2 is a schematic diagram of the aperture distribution of each optical path in the aperture stop sheet of the present invention;

[0043] Figure 3 is a schematic diagram (front view) of the focusing optical path and the fixation optical path structure of the present invention;

[0044] Figure 4 is a schematic diagram of the double-slit positions of the focusing optical path of the present invention under different diopters (Figure a is for hyperopia, Figure b is for myopia, and Figure c is for emmetropia);

[0045] Figure 5 is a schematic diagram comparing the imaging channels and illumination channels of the human eye on the cornea between the traditional annular illumination method and the illumination method of the present invention (Figure d is for the traditional annular illumination method, and Figure e is for the illumination method of the present invention).

[0046] Explanation of reference numerals

[0047] 1 - Human eye, 2 - Retinal objective lens, 3 - Relay lens, 4 - Aperture stop sheet, 5 - Triplet lens, 6 - Imaging filter, 7 - Imaging camera, 8 - Illumination beam splitter, 9 - First condenser lens, 10 - Illumination filter, 11 - White light LED, 12 - Second condenser lens, 13 - Infrared LED, 14 - Focusing optical path aperture, 15 - Fixation optical path aperture, 16 - Imaging optical path aperture, 17 - Illumination optical path aperture, 18 - Slit diaphragm, 19 - Collimating lens, 20 - Focusing light source, 21 - Fixation light source. Detailed implementation manners

[0048] The following further details the embodiments of the present invention with reference to the accompanying drawings:

[0049] The optical system of this implementation scheme is composed of an imaging optical path, an illumination optical path, a focusing optical path, and a fixation optical path. The imaging optical path includes an eyepiece group, an imaging filter 6, an imaging lens group, and an imaging camera 7, as Figure 1 shown.

[0050] The eyepiece group includes a retinal objective lens 2, a relay lens 3, and an aperture stop sheet 4, which is a common component of all optical paths.

[0051] Among them, the retinal objective lens is a double-sided aspherical mirror, with a double-convex lens surface type and a focal length of about 25 mm. It can collect the return light from the fundus of the human eye 1 and form a relatively good intermediate image plane. Considering cost control, the material of the retinal objective lens is selected as low-melting-point glass, which can be processed by molding.

[0052] Among them, the relay lens contains 2 optical lenses, one of which is a doublet lens, and the combined focal length is about 150 mm. Its function is to form a conjugate relationship between the human eye pupil and the aperture stop together with the retinal objective lens, and make the light rays emerging from the aperture stop approximately parallel.

[0053] Among them, the aperture stop sheet is a black thin sheet, which contains 5 round holes with different diameters, respectively serving as the aperture stops of different optical paths. AsFigure 2 As shown, the diaphragm diameter of the illumination optical path aperture 17 is 10 mm, the diaphragm diameter of the imaging optical path aperture 16 is 8 mm, the two apertures are horizontally distributed left and right, and the distance between them is 16 mm. There are 2 focusing optical path apertures 14 with a diaphragm diameter of 4 mm, which are vertically distributed up and down, with a distance of 16 mm between them. The fixation optical path aperture 15 has a diaphragm of 2 mm and is located at the center of the aperture diaphragm, that is, on the optical axis of the system.

[0054] Among them, the imaging filter is a band-pass optical coating filter with a working angle of 0° and a cut-off depth of OD6. Its function is to transmit the fluorescence excited by the illumination light while blocking the light of other wavelength bands, forming a fluorescence image with high contrast. The imaging filter used for fluorescence angiography can transmit green light with a wavelength of 510 nm to 550 nm, and the imaging filter used for autofluorescence can transmit red light with a wavelength of 620 nm to 670 nm.

[0055] Among them, the imaging lens group is an optical lens group composed of 2 triplet lenses 5 with a combined focal length of 45 mm. Its function is to re-image the intermediate image plane formed by the retinal objective lens, correct the remaining aberrations, and form a clear retinal image on the digital camera. The purpose of using the triplet lens is to better correct the secondary chromatic aberration.

[0056] Among them, the imaging camera is a CMOS camera with a photosensitive area of 2 / 3 inch and a resolution of 5 million pixels.

[0057] The illumination optical path is Kohler illumination, including white light LED 11, infrared LED 13, illumination filter 10, first condenser lens 9, second condenser lens 12, illumination beam splitter 8, illumination lens group and eyepiece group, as Figure 1 shown.

[0058] Among them, the white light LED is a surface-mounted LED. The color temperature is 4200K and the color rendering index is 92%. It is a color imaging light source and also the imaging light source for fluorescence angiography and autofluorescence functions.

[0059] Among them, the infrared LED is a surface-mounted LED in the near-infrared band. The central wavelength is 850 nm. It is an infrared monitoring light source used for infrared imaging of the fundus before taking pictures to facilitate alignment and focusing.

[0060] Among them, the illumination filter is a band-pass optical coating filter with a working angle of 0° and a cut-off depth of OD4. Its function is to separate the light wavelength band required for fluorescence imaging from the white light LED and project it onto the condenser lens. Different illumination filters are used for fluorescence angiography and autofluorescence respectively. The illumination filter used for the fluorescence angiography function can transmit blue light with a wavelength of 460 - 490 nm. The illumination filter used for the autofluorescence function can transmit green light with a wavelength of 530 - 580 nm.

[0061] Among them, the condenser is an optical lens group composed of two plano-convex lenses with a combined focal length of 25 mm. Its function is to collect the light emitted by the LED light source and project it onto the illumination lens group through the illumination beam splitter.

[0062] Among them, the illumination beam splitter is a dichroic optical transmissive and reflective mirror with a working angle of 45°. Its function is to reflect the visible light emitted by the white LED while transmitting the 850 nm near-infrared light emitted by the near-infrared LED. This enables the visible light and near-infrared light incident from mutually perpendicular directions to propagate in the same direction after passing through this lens, achieving the purpose of beam combination.

[0063] Among them, the illumination lens group is an optical lens group composed of one plano-convex lens and one meniscus lens with a combined focal length of 50 mm. Its function is to project the light collected by the condenser onto the human eye through the eyepiece group, forming uniform illumination on the fundus.

[0064] The focusing optical path includes a focusing light source 20, a collimating lens 19, a slit diaphragm 18, and an eyepiece group, as Figure 3 shown.

[0065] Among them, the focusing light source is a plug-in near-infrared point light source LED with a central wavelength range of 850 nm. Its function is to illuminate the slit through the collimating lens.

[0066] Among them, the collimating lens is an optical lens with a focal length of 15 mm and a numerical aperture of 0.2. Its function is to collect the light emitted by the focusing light source and project it through the slit onto the eyepiece group.

[0067] Among them, the width of the slit is 0.1 mm, and the aspect ratio is 5:1. Its function is to form an image of the slit on the fundus through the eyepiece objective lens. According to the relative positions of the two slit images, the refractive state of the human eye can be judged. As Figure 4 shown, the white rectangular block is the slit. When the left slit is higher than the right slit in Figure a, it is a case of hyperopia. When the left slit is lower than the right slit in Figure b, it is a case of myopia. Refractive compensation is performed by changing the distance between the retinal objective lens and the relay lens. When the compensation is completed, as shown in Figure c, the left and right slits are just aligned, and this is a case of emmetropia. In addition, since the reflectivity of the optic disc is very high, when the optic disc is located in the central area of the fundus, it may affect the recognition of the double slit. Therefore, to avoid the possible interference caused by the optic disc, the design position of the double slit is not at the center of the fundus, but at a position slightly below the center.

[0068] The fixation optical path includes a fixation light source 21, a collimating lens, and an eyepiece group, as Figure 3 shown.

[0069] Among them, the fixation light source is a plug-in visible light LED with a central wavelength of 590 nm. Its function is to provide a fixed target for the human eye and stabilize the human eye.

[0070] Among them, the collimating mirror is an optical lens with a focal length of 15 mm and a numerical aperture of 0.2. Its function is to collect the light emitted by the fixation light source and project it onto the fundus through the eyepiece group.

[0071] When this implementation scheme works, the fixation light source emits light and projects it onto the fundus through the fixation optical path. After the human eye observes the fixation light source, it remains stable. The infrared LED emits near-infrared light of 850 nm, which enters the eyepiece group from the illumination optical path aperture in the aperture stop after passing through the condenser lens, the illumination beam splitter, and the illumination lens group. After being refracted by the relay lens and the retinal objective lens, a converging light spot is formed on the human cornea. The light continues to propagate forward and diverges at the same time, and uniform illumination can be formed on the fundus.

[0072] The fundus retina reflects the above light, and after exiting from the pupil, it will pass through the other side of the cornea and enter the imaging optical path. The channels of the illumination optical path and the imaging optical path on the cornea are separated from each other and do not interfere with each other, as shown in Figure 5 Figure e of the figure. Figure d is the existing annular illumination method. After the light enters the imaging optical path, it passes through the imaging aperture stop and is converged on the imaging camera by the imaging lens group to form an image.

[0073] At the same time, the focusing light source also emits light, and projects the image of 2 slits on the fundus. The slit image will also be captured by the imaging camera and superimposed on the fundus image. According to the relative position of the slits, refractive compensation is performed on the human eye. After completion, the slits are aligned.

[0074] Finally, turn off the focusing light source and the infrared LED, and turn on the white light LED for flashing. The light emitted by the white light LED will again follow the path of the light emitted by the infrared LED, and finally a clear color fundus image is formed on the imaging CCD.

[0075] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that: without departing from the spirit and scope of the present invention and the appended claims, various substitutions, changes, and modifications are possible. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. A multi-mode dual off-axis retinal imaging device, characterized in that: It includes an imaging optical path, an illumination optical path, a focusing optical path, and a fixation optical path; the imaging optical path is used to form a retinal image, the illumination optical path is used to form uniform illumination on the fundus of the eye; the focusing optical path is used to perform refractive compensation when forming a retinal image to ensure the clarity of the captured photo; the fixation optical path is used to stabilize the human eye, and the imaging optical path and the illumination optical path are off-axis arranged to form a converging circular light spot on the human cornea; The imaging optical path includes an eyepiece group, an imaging filter, an imaging lens group, and an imaging camera. An imaging lens group is arranged at the upper front of the eyepiece group, and an imaging filter and an imaging camera are sequentially arranged from near to far in front of the imaging lens group; The eyepiece group includes a retinal objective lens, a relay lens, and an aperture diaphragm arranged in sequence from back to front. The retinal objective lens is used to collect the return light from the fundus of the human eye and form a clear intermediate image plane; the relay lens and the retinal objective lens together make the human eye pupil and the aperture diaphragm form an object-image conjugate relationship, and make the light rays emerging from the aperture diaphragm approximate parallel light.

2. The multi-mode double off-axis retinal imaging device according to claim 1, wherein: The aperture diaphragm is a black thin sheet, and round holes with different diameters are respectively arranged at intervals on the black thin sheet. The round holes arranged on the left and right respectively form the illumination optical path aperture and the imaging optical path hole. A fixation optical path hole is arranged between the illumination optical path aperture and the imaging optical path hole, and focusing optical path holes are arranged at both the upper and lower ends of the fixation optical path hole.

3. The multi-mode dual off-axis retinal imaging device according to claim 1, characterized in that: The imaging lens group is an optical lens group with 1 - 5 lenses, and at least 2 cemented lenses are included. Its function is to re-image the intermediate image plane formed by the retinal objective lens, correct the remaining aberrations, and form a clear retinal image on the digital camera.

4. A multi-mode double off-axis retinal imaging device according to claim 1, characterized in that: The illumination optical path includes a white light LED, an infrared LED, an illumination filter, a first condenser lens, a second condenser lens, an illumination beam splitter, an illumination lens group, and an eyepiece group. An illumination lens group is arranged at the lower front of the eyepiece group, and an illumination beam splitter, a first condenser lens, an illumination filter, and a white light LED are sequentially arranged from back to front in front of the illumination lens group. A second condenser lens and an infrared LED are sequentially arranged from top to bottom directly below the illumination beam splitter.

5. A multi-mode double off-axis retinal imaging device according to claim 4, characterized in that: The white light LED is a surface-mounted LED, with a color temperature range of 4000K - 5500K and a color rendering index of not less than 80%; The infrared LED is a surface-mounted LED in the near-infrared band, with a central wavelength range of 830nm - 980nm. It is an infrared monitoring light source used to perform infrared imaging on the fundus before taking a photo; The illumination filter is a band-pass optical coating filter with a working angle of 0° and a cut-off depth of not less than OD4. Its function is to separate the light band required for fluorescence imaging from the white light LED and project it onto the condenser lens; The first condenser lens and the second condenser lens are optical lens groups, and the number of lenses in both is 1 - 2. Their function is to collect the light rays emitted by the white light LED light source and the infrared LED light source, and project them onto the illumination lens group through the illumination beam splitter; The illumination beam splitter is a dichroic optical transmissive-reflective mirror with a working angle of 45°. Its function is to reflect visible light while transmitting near-infrared light, enabling visible light and near-infrared light incident from mutually perpendicular directions to propagate in the same direction after passing through this lens, achieving the purpose of beam combination. The illumination lens group is an optical lens group with 1 to 2 lenses. Its function is to project the light collected by the condenser lens into the human eye through the eyepiece group to form uniform illumination on the fundus.

6. The multi-mode double off-axis retinal imaging device according to claim 1, characterized in that: The focusing optical path includes a focusing light source, a collimating lens, a slit diaphragm, and an eyepiece group. The slit diaphragm, collimating lens, and focusing light source are sequentially arranged from near to far in front of the eyepiece group. The focusing light source is a direct-insert type near-infrared point light source LED with a central wavelength range of 830 nm to 980 nm. Its function is to illuminate the slit through the collimating lens. The collimating lens is an optical lens with a focal length range of 5 mm to 25 mm and a numerical aperture not greater than 0.

5. Its function is to collect the light emitted by the focusing light source and project it through the slit onto the eyepiece group. The width of the slit diaphragm is not greater than 0.2 mm, and the aspect ratio of length to width is not less than 3:

1. Its function is to form an image of the slit on the fundus through the eyepiece objective. According to the relative position of the two slit images, the refractive state of the human eye is judged, and refractive compensation is performed by changing the distance between the retinal objective and the relay lens to ensure the clarity of the captured photo.

7. A multi-mode dual off-axis retinal imaging device according to claim 1, characterized in that: The fixation optical path includes a fixation light source, a collimating lens, and an eyepiece group. The collimating lens is arranged in front of the eyepiece group, and the fixation light source is arranged in front of the collimating lens. The fixation light source is a direct-insert type visible light LED with a central wavelength range of 500 nm to 650 nm. Its function is to provide a fixed target for the human eye to stabilize the human eye. The collimating lens is an optical lens with a focal length range of 5 mm to 25 mm and a numerical aperture not greater than 0.

5. Its function is to collect the light emitted by the fixation light source and project it onto the fundus through the eyepiece group.

8. A multi-mode dual off-axis retinal imaging method, characterized in that: This method is implemented based on the multi-mode dual off-axis retinal imaging device according to any one of claims 1-7. The method includes the following steps: Step 1, the fixation light source emits light and projects it onto the fundus through the fixation optical path. After the human eye observes the fixation light source, it remains stable. Step 2, the infrared LED emits near-infrared light with a wavelength of 850 nm. After passing through the second condenser lens, the illumination beam splitter, and the illumination lens group, it enters the eyepiece group from the illumination optical path aperture in the aperture diaphragm. After being refracted by the relay lens and the retinal objective, a converging light spot is formed on the human cornea. The near-infrared light continues to propagate forward and diverges simultaneously to form uniform illumination on the fundus. Step 3, the fundus retina reflects the illumination light. After exiting from the pupil, it will pass through from the other side of the cornea and enter the imaging optical path. The channels of the illumination optical path and the imaging optical path on the cornea are separated from each other and do not interfere with each other. Step 4, the light reflected from the fundus enters the imaging optical path, passes through the imaging aperture diaphragm, and is converged by the imaging lens group onto the imaging camera to form an image. Meanwhile, the focusing light source also emits light, projecting images of two slits on the fundus. The slit images are captured by the imaging camera and superimposed on the fundus image. According to the relative positions of the slits, refractive compensation for the human eye is performed, and after completion, the slits are aligned; Step 5: Turn off the focusing light source and the infrared LED, and turn on the white light LED for flashing. The light emitted by the white light LED will again follow the path of the light emitted by the infrared LED, and finally a clear color fundus image will be formed on the imaging CCD.

Images