JP2020174852A - Objective lens and fundus imaging apparatus including objective lens - Google Patents

Abstract

To acquire a wide-angle fundus image using a low-cost, compact optical system.SOLUTION: The objective lens provided in the fundus imaging apparatus with an imaging angle of θ is formed of a single convex lens or a two-piece cemented convex lens, in which, when the ratio of a curvature radius r1 of a first surface to a subject eye and a curvature radius r2 of a final surface is Rr, a refractive index when the convex lens is a single convex lens or an equivalent refractive index when the convex lens is a two-piece cemented lens is n, and an imaging magnification of the pupil of the subject eye when the objective lens is placed at a predetermined differential distance is Pm, relations θ>80°, Pm<4.5, 3.0<Rr and [(Pm+1)×Rr/{Pm×(Rr+1)}]×tan(θ/2)+1<n<2.0 hold.SELECTED DRAWING: Figure 1

Description

The present invention relates to an objective lens provided in a fundus photography device used for acquiring an image of the fundus of an eye to be inspected, and a fundus photography device provided with the objective lens.

Currently, an imaging device (hereinafter referred to as an OCT device) using an optical coherence tomography (OCT) utilizing interference by low coherent light has been put into practical use. The OCT device can take a tomographic image of the object to be inspected with high resolution.

In the OCT apparatus, the light from the light source is divided into measurement light and reference light by a beam splitter or the like. The measurement light is applied to an object to be inspected such as an eye through the measurement optical path. Then, the return light from the object to be inspected is combined with the reference light and guided to the detector as interference light through the detection optical path. The return light described here is reflected light or scattered light that includes information about the interface of the light to be inspected in the irradiation direction. A tomographic image of the inspected object can be obtained by detecting and analyzing the interference light between the return light and the reference light with a detector. Therefore, the OCT device is used in the field of ophthalmology as a fundus photography device capable of taking a tomographic image of the eye to be inspected, for example, the retina.

Further, in the field of ophthalmology, a scanning laser ophthalmoscope (SLO: Scanning Laser Opthermoscope, hereinafter referred to as an SLO device) for photographing an eye to be inspected by laser scanning has been put into practical use. According to the SLO apparatus, it is possible to take a surface image of, for example, the fundus of the eye to be inspected with high resolution.

In the SLO device, the light from the light source is irradiated by scanning on the eye to be inspected by a galvanometer mirror or the like. The reflected light from the eye to be inspected is separated from the illumination optical path by a perforated mirror or the like and guided to the detector. By detecting the intensity of the reflected light with a detector, a two-dimensional surface image of the eye to be inspected can be obtained.

Here, in recent fundus examinations using an OCT device, an SLO device, or the like, it is required to take a wide range of images including the peripheral portion of the fundus due to a disease. As a fundus photography device for a wide angle of view capable of photographing a wide range, for example, one disclosed in Patent Document 1 is known. The configuration disclosed in Patent Document 1 includes a device main body and a wide-angle lens attachment, and by attaching the wide-angle lens attachment to the device main body, the angle of view of the obtained fundus image is widened.

JP-A-2016-123467

In order to widen the angle of view of the optical system, it is conceivable to shorten the focal length of the objective optical system of the main body of the apparatus or the lens of the objective optical system such as the lens attachment. A simple method of shortening the focal length is to reduce the radius of curvature of the lens, but this method makes the thickness of the end face of the lens very thin. When the thickness of the end face of the lens becomes thin, it becomes difficult to handle the lens without touching the optically effective surface used as the optical system, and the difficulty of the process of processing and assembling the lens increases. As a result, for example, the man-hours for processing and assembling the lens are increased, and the use of a special jig is required, which increases the cost for processing and assembling the lens.

On the other hand, in order to secure the thickness of the end face of the lens, a design in which the optical system is enlarged as a whole can be considered. For example, in the case of a lens having a lens end face having a thickness of 1 mm, when the entire lens is magnified twice, the thickness of the lens end face becomes 2 mm, and when the entire lens is magnified three times, the thickness of the lens end face becomes 3 mm. However, as the optical system becomes larger, the entire device also becomes larger, which makes it difficult to make a compact device configuration. It is also conceivable to design the lens to be thicker without enlarging the optical system as a whole. However, if the lens is made thicker, it becomes difficult to secure the distance (working distance) between the pupil of the eye to be inspected and the objective lens. In this case, the objective lens and the eye to be inspected tend to physically interfere with each other, which makes it difficult to align the device with respect to the eye to be inspected and to take an image.

The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to enable the acquisition of a wide-angle fundus image with an optical system having a low cost and a compact configuration.

In order to solve the above problems, the objective lens according to one aspect of the present invention is
An objective lens provided in a fundus photography device with a shooting angle of view θ.
Consists of a monoconvex lens or a two-element convex lens
The ratio of the radius of curvature r1 of the first surface to the eye to be inspected and the radius of curvature r2 of the final surface is Rr.
The refractive index when the convex lens is a monoconvex lens or the equivalent refractive index when the convex lens is a two-element junction lens is n.
When the imaging magnification of the pupil of the eye to be inspected when the objective lens is placed at a predetermined differential distance is Pm,
θ> 80 °, Pm <4.5, 3.0 <Rr and [(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ / 2) + 1 <n <2.0
It is characterized by satisfying.

According to one of the objects of the present invention, it is possible to acquire a fundus image having a wide angle of view with an optical system having a low cost and a compact configuration.

It is a schematic diagram which shows the outline of an example of the fundus photography apparatus provided with the objective lens which concerns on this invention. It is a flowchart explaining the process leading to the acquisition of the tomographic image using the fundus photography apparatus shown in FIG. It is a figure which shows the shape of the signal obtained at the time of acquisition of a tomographic image. It is a figure which shows an example of the intensity image generated from the signal shown in FIG. It is a figure which shows an example of the obtained tomographic image. It is a figure which shows an example of the structure of the optical system in embodiment of this invention. It is a figure which shows the objective lens of Example 1 in Embodiment of this invention. It is a figure which shows the objective lens of Example 2 in Embodiment of this invention. It is a figure which shows the objective lens of Example 3 in Embodiment of this invention. It is a figure which shows the objective lens of Example 4 in Embodiment of this invention.

[Embodiment]
Embodiments of the present invention will be described in detail below with reference to the drawings. What can be photographed by the apparatus of this embodiment is, for example, a tomographic image of a human retina or the like. However, the dimensions, materials, shapes, relative positions of the components, etc. described in the following examples are arbitrary and can be changed according to the configuration of the device to which the present invention is applied or various conditions. Also, in the drawings, the same reference numerals are used between the drawings to indicate elements that are the same or functionally similar.

(Device configuration)
First, a fundus image acquisition system (fundus imaging device) including an objective lens according to an embodiment of the present invention will be described with reference to FIG. The fundus image acquisition system includes a tomographic image capturing unit, a fundus image capturing unit, an anterior ocular segment imaging unit, a control unit, and a display unit. The objective lens according to the embodiment of the present invention is on the optical path common to each photographing unit and is arranged so as to face the eye to be inspected. Hereinafter, the details of each of the above-described parts will be described in sequence.

The layer imaging unit includes a light source 1, a light dividing unit 3, a sample arm 1001, a reference arm 1002, and a spectroscope 1003. The light source 1 is a light source for generating light (low coherence light). As the light source 1, an SLD (Super Luminescent Diode) light source having a center wavelength of 850 nm and a band of 50 nm is used. An ASE (Amplified Spontaneous Emission) light source can also be applied to the light source 1. Further, an ultrashort pulse laser light source such as a titanium sapphire laser can also be applied to the light source 1. As described above, the light source 1 may be any light source that can generate low coherence light. Further, the wavelength of the light generated from the light source 1 is not particularly limited, but is selected in the range of 400 nm to 2 μm depending on the object to be inspected. The wider the wavelength band, the better the vertical resolution. Generally, when the center wavelength is 850 nm, a vertical resolution of 6 μm can be obtained in the band of 50 nm, and a vertical resolution of 3 μm can be obtained in the band of 100 nm.

The light source 1 is connected to the light dividing unit 3 by a light guide unit 2 composed of an optical fiber or the like. The optical dividing unit 3 is further connected to the sample arm 1001, the reference arm 1002, and the spectroscope 1003 by the light guide units 4, 10 and 14 composed of an optical fire or the like. The light emitted from the light source 1 is guided to the light dividing unit 3 by the light guide unit 2. A fiber coupler or the like can be applied to the optical dividing portion 3 that acts as the optical dividing means. The light emitted from the light source 1 is divided into a measurement light guided to the sample arm 1001 via the light guide unit 4 and a reference light guided to the reference arm 1002 via the light guide unit 10 by the light dividing unit 3. Will be done. The ratio of division can be selected appropriately according to the object to be inspected.

The sample arm 1001 includes a collimator lens 5, a focus lens 6, an optical scanning unit 7, a relay lens 26, a wavelength branch mirror 35, a wavelength branch mirror 8, and an objective lens 9 arranged on the optical path in order from the light guide unit 4. Including. The measurement light obtained by being divided by the light dividing unit 3 is guided to the sample arm 1001 by the light guide unit 4 and emitted from the fiber end 4a toward the collimator lens 5. A galvano mirror or a resonance mirror that scans light in the X and Y directions orthogonal to each other, which are arranged adjacent to each other in the optical axis direction (tandem arrangement), are applied to the optical scanning unit 7.

The wavelength branching mirror 8 transmits the light emitted from the light source 1 (wavelength: λ = 825-875 nm) and reflects the light (λ = 940 nm) of the anterior segment illumination described later. The wavelength branching mirror 35 transmits the light emitted from the light source 1 (wavelength: λ = 825 to 875 nm), and is the illumination light for fundus photography (λ = 780 nm) and the light of the internal fixation lamp (λ = 590 nm), which will be described later. To reflect. The measurement light guided to the light guide unit 4 passes through the sample arm 1001 and reaches the fundus Ef of the eye E to be inspected, and scans on the fundus Ef by the operation of the optical scanning unit 7.

The reference arm 1002 includes a collimator lens 11 and a reference mirror 12 which are arranged on the optical path in order from the light guide unit 10. The reference light obtained by being divided by the light dividing unit 3 is guided to the reference arm 1002 by the light guide unit 10 and emitted from the fiber end 10a toward the collimator lens 11. The reference mirror 12 is arranged on the linear motion stage 13, and the optical path length of the reference light in the reference arm 1002 can be adjusted by moving the linear motion stage 13 in the direction of the optical axis indicated by the arrow in the drawing.

The measurement light that has passed through the fundus Ef of the eye E to be inspected and the reference light that has passed through the reference mirror 12 are combined by the light dividing unit 3 via the light guide units 4 and 10 to generate interference light. The interference light is guided to the spectroscope 1003 by the light guide unit 14. The spectroscope 1003 includes a collimator lens 15, a spectroscope 16, a lens 17, and an imaging unit 18 which are arranged on the optical path in order from the light guide unit 14. The spectroscopic unit 16 is composed of a diffraction grating, a prism, or the like. The imaging unit 18 has a photoelectric conversion element such as CMOS or CCD as a detection means.

Next, the fundus imaging unit will be described. The fundus imaging unit includes a light source 28, a collimator lens 29, a wavelength branch mirror 30, a perforated mirror 31, a focus lens 32, an optical scanning unit 33, a lens 34, a wavelength branch mirror 35, a wavelength branch mirror 8, and an objective lens 9. .. The light source 28 is a light source for generating light having a wavelength different from that of the light source 1. As the light source 28, an LED (Light-emitting Diode) light source having a center wavelength of 780 nm is used. An LD (Laser Diode) light source can also be applied to the light source 28. As described above, as the light source 28, various light sources that generate light having a wavelength different from that of the light source 1 can be used. On the optical path of the illumination light emitted from the light source 28, the above-mentioned collimator lens 29, wavelength branch mirror 30, perforated mirror 31, focus lens 32, optical scanning unit 33, lens 34, wavelength branch mirror 35, and wavelength branch mirror 8 , And the objective lens 9 are arranged in this order.

The illumination light emitted from the light source 28 is reflected by the wavelength branch mirror 30 and passes through a hole formed on the optical axis of the perforated mirror 31. A pair of galvanometer mirrors or resonance mirrors, which are arranged adjacent to each other in the optical axis direction (tandem arrangement) and scan illumination light in the X and Y directions orthogonal to each other, are applied to the optical scanning unit 33. The illumination light reflected by the wavelength branch mirror 35 passes through the wavelength branch mirror 8 and the objective lens 9 and reaches the fundus Ef of the eye E to be inspected.

The illumination light reflected by the fundus Ef returns to the same optical path as when it was incident on the fundus, and is reflected by the peripheral portion of the perforated mirror 31. A lens 36 and a detection unit 37 having a photoelectric conversion element such as an APD are arranged on the optical path of the illumination light reflected by the perforated mirror 31.

A light source 38 of an internal fixation lamp is arranged after the wavelength branch mirror 30. The light source 38 is a light source for generating light having a visible wavelength (fixed light) different from that of the light source 1 and the light source 28. Here, an LED light source having a center wavelength of 590 nm is used as the light source 38. An LD light source can also be applied to the light source 38. As described above, as the light source 38, various light sources capable of generating light having a visible wavelength different from that of the light source 1 and the light source 28 are used.

On the optical path of the fixation light emitted from the light source 38, a collimator lens 39, a wavelength branch mirror 30, a perforated mirror 31, a focus lens 32, an optical scanning unit 33, a lens 34, a wavelength branch mirror 35, a wavelength branch mirror 8, The objective lens 9 is arranged. The fixed-view light from the light source 38 passes through the wavelength branching mirror 30 and passes through a hole formed on the optical axis of the perforated mirror 31. Then, it reaches the fundus Ef of the eye E to be inspected through the optical scanning unit 33, the lens 34, the wavelength branch mirror 35, the wavelength branch mirror 8, and the objective lens 9 in the same optical path as the illumination light from the light source 28.

The anterior segment illumination light sources 21a and 21b are arranged around the objective lens 9. The image of the anterior segment of the eye to be inspected E illuminated by the light from these light sources passes through the objective lens 9 and is reflected by the wavelength branch mirror 8. A lens 22 and an imaging unit 23 are arranged in the reflection direction of the wavelength branch mirror 8 as an image capturing unit for the anterior segment. The image of the anterior segment reflected by the wavelength branch mirror 8 is two-dimensional by the lens 22. An image is formed on the imaging surface of the imaging unit 23.

The fundus image acquisition system including each of the above-described units is controlled by the control unit 19. More specifically, the control unit 19 controls the above-mentioned optical scanning unit 7, the linear motion stage 13, the imaging unit 18, the imaging unit 23, the optical scanning unit 33, the detection unit 37, the light source 38, and the like. Further, a pointing device 25 such as a display unit 20, a memory 24, and a mouse is connected to the control unit 19. The control unit 19 generates a tomographic image, a fundus image, and an anterior eye portion image based on the output signals from the imaging unit 18, the imaging unit 23, and the detection unit 37, and displays these on the display unit 20. In addition, the operator can input various instructions to the fundus image acquisition system using the pointing device 25.

The display unit 20 illustrated here is provided with an image display area of an anterior segment image display area 20a, a tomographic image display area 20b, and a fundus image display area 20e. The display unit 20 is also provided with a focus adjustment display area 20c, a coherence gate adjustment display area 20d, a working distance adjustment display area 20g, and a shooting button 20h. These are used when an instruction is input to the control unit 19 by using the pointing device 25. Further, a mark 20f indicating the lighting position of the fixation lamp (corresponding to the fixation position of the eye E to be inspected) is superimposed and displayed on the fundus image displayed in the fundus image display area 20e.

(Measuring method)
Next, a method of capturing a tomographic image of the retina of the fundus Ef of the eye fundus E to be examined by using the fundus image acquisition system described above will be described with reference to the flowchart of FIG. 2 showing the process.

When the subject is seated in a predetermined position and the eye E is placed in front of the fundus image acquisition system, the anterior segment of the eye E is illuminated by the light emitted by the anterior eye illumination light sources 21a and 21b. To. The illuminated image of the anterior segment passes through the objective lens 9, is reflected by the wavelength branch mirror 8, and is imaged on the imaging surface of the imaging unit 23 by the lens 22. The video signal from the imaging unit 23 is input to the control unit 19 and converted into digital data in real time to generate an anterior segment image (step S1). The control unit 19 determines the eccentricity of the eye E to be inspected and the focus state of the fundus image acquisition system from the pattern of the iris in the anterior eye portion image of the eye E to be inspected. In this fundus image acquisition system, the center of the imaging surface is adjusted so that the optical axis of the optical system of the sample arm 1001 coincides with each other. Therefore, the amount of eccentricity between the pupil center and the imaging center of the anterior segment image captured by the imaging unit 23 corresponds to the eccentricity of the optical system of the eye E to be inspected and the sample arm 1001.

The optical system of the sample arm 1001 is arranged on a stage (not shown) so that the position of the sample arm 1001 can be adjusted vertically and horizontally and further in the optical axis direction with respect to the eye E to be inspected. Therefore, the control unit 19 adjusts the vertical and horizontal positions of the sample arm 1001 so that the center of the pupil of the eye E to be inspected and the optical axis of the optical system of the sample arm 1001 coincide with each other. Further, the control unit 19 adjusts the position of the sample arm 1001 in the optical axis direction so that the contrast of the iris pattern is the highest (step S2). As a result, the distance (working distance) between the pupil of the eye E to be inspected, which is flush with the iris, and the objective lens 9 of the optical system of the sample arm 1001 is kept constant. The anterior segment image is displayed in the anterior segment image display area 20a of the display unit 20. The operator can confirm the optical axis eccentricity from this image, and can also perform the above-mentioned position adjustment using the pointing device 25. It is also possible to adjust the reference working distance by instructing the working distance adjustment display area 20g with the cursor by operating the pointing device 25.

When the amount of eccentricity between the center of the pupil and the center of imaging becomes equal to or less than a predetermined value due to the position adjustment, the light source 28 is turned on by the control unit 19, and imaging of the fundus image for alignment is started (step S3). The illumination light emitted from the light source 28 is converted into parallel light by the collimator lens 29 and reflected by the wavelength branch mirror 30. The illumination light after the wavelength branch mirror 30 is reflected passes through the hole of the perforated mirror 31, passes through the focus lens 32, and passes through the lens 34 via the optical scanning unit 33. Further, the illumination light transmitted through the lens 34 is reflected by the wavelength branch mirror 35, passes through the wavelength branch mirror 8, passes through the objective lens 9, and reaches the fundus Ef from the pupil of the eye E to be inspected. At that time, the illumination light is two-dimensionally scanned on the fundus Ef by the operation of the X scan mirror and the Y scan mirror of the optical scanning unit 33.

The illumination light applied to the fundus Ef is reflected and scattered by the layers constituting the retina of the fundus Ef, and returns to the same optical path as the incident light as return light. The return light is reflected at the peripheral portion of the perforated mirror 31, passes through the lens 36, and is guided to the detection unit 37. The detection unit 37 obtains a light intensity signal from the return light, and after the light intensity signal is converted into a digital signal by an A / D converter (not shown), it is input to the control unit 19 to generate a fundus image. The operator observes the fundus image and adjusts the focus by operating the button in the focus adjustment display area 20c with the cursor using the pointing device 25 so that the fundus image becomes the brightest. The obtained fundus image is displayed in the fundus image display area 20e of the display unit 20. Note that this focus adjustment may be performed by the control unit 19 according to the evaluation result of evaluating the image of the fundus image using a known image evaluation technique.

When the fundus image is displayed, the light source 38 is turned on by the control unit 19, and the display of the internal fixation lamp is started (step S4). The light from the light source 38 is converted into parallel light by the collimator lens 39 and passes through the wavelength branch mirror 30. The light transmitted through the wavelength branch mirror 30 reaches the fundus Ef of the eye E to be inspected through the same optical path as the observation light described above. The display position of the internal fixation lamp on the fundus Ef is superimposed and displayed as a mark 20f marked with a cross on the fundus image display area 20e. The operator specifies that the display position of the fixation lamp is a desired position by manipulating the position of the mark 20f on the display screen. The control unit 19 controls the lighting timing of the light source 38 according to the position designated by the operator, thereby displaying the internal fixation lamp at the position designated by the operator.

When the operator completes the position designation of the internal fixation lamp, the light source 1 is turned on by the control unit 19, and the imaging of the tomographic image for alignment is started (step S5). The light from the light source 1 is guided to the light dividing unit 3 by the light guide unit 2, and is divided so that the ratio of the amount of light guided to the light guide unit 4 and the light guide unit 10 is, for example, 1: 9. The light guided to the light guide portion 4 side reaches the fiber end 4a. The light emitted from the fiber end 4a as a point light source is converted into parallel light by the collimator lens 5 as measurement light and transmitted through the focus lens 6. The measurement light transmitted through the focus lens 6 reaches the fundus Ef from the pupil of the eye E to be inspected by the objective lens 9 via the optical scanning unit 7, the relay lens 26, the wavelength branch mirror 35, and the wavelength branch mirror 8. At that time, the measurement light is scanned on the fundus Ef by the operation of the optical scanning unit 7, for example, the X scan mirror.

The measurement light is reflected and scattered by a plurality of layers constituting the retina of the fundus Ef, and returns to the same optical path as the incident light as return light. That is, the return light enters the light guide section 4 from the fiber end 4a via the collimator lens 5 and is guided to the light dividing section 3 again.

The light guided from the light dividing unit 3 to the light guide unit 10 side reaches the reference arm 1002 and reaches the fiber end 10a. The light emitted from the fiber end 10a as a point light source is converted into parallel light by the collimator lens 11 as reference light and directed to the reference mirror 12. The reference mirror 12 is arranged on the linear motion stage 13 so as to be movable perpendicular to the parallel light and in the direction of the optical axis indicated by the arrow in the drawing. By moving the reference mirror 12 in the optical axis direction by the linear motion stage 13, the optical path length of the measurement light and the optical path length of the reference optical path can be matched even for the eye E to be inspected having a different optical axis length. The operator can adjust the position of the reference mirror 12 by instructing the coherence gate adjustment display area 20d on the display unit 20 with the cursor by operating the pointing device 25.

The reference light reflected by the reference mirror 12 is collected by the collimator lens 11 at the fiber end 10a of the light guide unit 10 and guided to the light dividing unit 3 by the light guide unit 10. In the light dividing unit 3, the measurement light (return light) returned from the eye E to be inspected and the reference light passing through the reference arm 1002 are combined to generate interference light. The generated interference light is divided by the light dividing unit 3 into the light directed to the light guide unit 2 and the light directed to the light guide unit 14 so that the ratio of the amount of light is 9: 1. That is, the division ratio at which the interference light directed to the spectroscope 1003 is divided is opposite to the division ratio at the time of generation of the return light from the fundus Ef of the eye E to be inspected.

As described above, the return light and the reference light are combined by the optical dividing unit 3 to generate combined light or interference light. The interference light that has reached the spectroscope 1003 via the light guide unit 14 is emitted from the fiber end 14a. The interference light is further converted into parallel light by the collimator lens 15 and incident on the spectroscopic unit 16. A large number of diffraction gratings having dimensions close to the wavelength of light are formed at equal intervals in the spectroscopic unit 16, and the incident light is separated by diffraction.

At that time, since the diffraction angle of the dispersed light differs depending on the wavelength, the diffracted light is imaged in the line-shaped imaging region of the imaging unit 18 as a line image by the lens 17. That is, the light emitted from the fiber end 14a is imaged as a dispersed slit image. Therefore, the imaging unit 18 outputs a signal corresponding to the intensity of each wavelength. The signal from the imaging unit 18 is input to the control unit 19 which is the image forming means in the present embodiment. The control unit 19 performs various processes on this signal to generate a tomographic image. The generated tomographic image is displayed in the tomographic image display area 20b of the display unit 20 (step S6).

The operator observes the tomographic image and operates the button in the focus adjustment display area 20c with the cursor using the pointing device 25 to adjust the focus so that the tomographic image becomes the brightest. Similarly, the position of the reference mirror 12 (coherence gate adjustment) is adjusted by operating the button of the coherence gate adjustment display area 20d so that all the tomographic images of the site of interest are included in the desired area of the tomographic image display area 20b. Do. When the coherence gate adjustment display area 20d is instructed, the control unit 19 moves the position of the linear motion stage 13 in the instructed direction. At the same time, the control position information of the linear motion stage 13 stored in the memory 24 is changed according to the amount of movement.

The linear motion stage 13 is driven and controlled by a stepping motor (not shown), and the position of the linear motion stage 13 corresponds to the number of steps instructed by the stepping motor. For example, when a stroke of 60 mm is driven in 60,000 steps, the amount of movement per step is 1 μm. The number of steps from 0 to 60,000 corresponds to the position of the linear motion stage from 0 to 60 mm. Further, the distance from the reference position of the linear motion stage 13 to the collimator lens 11 is arranged with high accuracy in design, and the relationship between the reference position and the stage position is also clear in design, so from this number of steps. The reference optical path length can be calculated.

The optical path length of the reference light changes as the position of the reference mirror 12 in the optical axis direction changes. As a result, the display position of the tomographic image in the tomographic image display area 20b changes. The position of the reference mirror 12 is always stored in the memory 24. After the above preparation for shooting, when the shooting button 20h is pressed, a still image of the tomographic image is shot (step S7). The details of the operation of acquiring the tomographic image (step S8) will be described later. The tomographic image taken by this is stored in the memory 24.

(Tomographic image generation)
Next, the tomographic image generation process will be described. At the time of capturing the tomographic image, the light guide unit 14 guides the combined light of the return light from the fundus Ef of the eye E to be inspected and the reference light reflected from the reference mirror 12. Due to the difference between the optical path length from the optical dividing unit 3 to the fundus Ef and the optical path length from the optical dividing unit 3 to the reference mirror 12, when the light is combined in the optical dividing unit 3, the return light and the reference light have a phase difference. Have. The tomographic image detects the intensity of the interference signal based on this phase difference and is formed based on this detection result.

More specifically, since this phase difference differs depending on the wavelength, interference fringes occur in the spectral intensity distribution appearing on the light receiving region of the imaging unit 18. Further, since the retina has a plurality of layers and the return light from each layer boundary has a different optical path length, the interference fringes include interference fringes having different frequencies. From the frequency of the interference fringes included in this intensity distribution and its intensity, the position of the reflecting object and the brightness corresponding to the reflection / scattering from that position can be obtained.

In the B scan mode for scanning one line on the fundus, the control unit 19 drives only one of the X and Y scan mirrors of the optical scanning unit 7, for example, the X scan mirror, from the imaging unit 18. Read the output. Data indicating the angle of the scan mirror is output from the optical scanning unit 7. This data is converted into an incident angle θi at which light is incident on the eye to be inspected, further converted into digital data, and then stored in the memory 24. The angle of the scan mirror and the incident angle θi of the light beam correspond to each other and can be obtained from the design value of the optical system.

Next, an example of a signal processing procedure for generating a tomographic image from a spectral intensity distribution will be described. FIG. 3 shows the intensity distribution of the light on the imaging unit 18 at each angle when the incident angle θi of the measured light with respect to the fundus is taken as the angle of the scan mirror. The horizontal axis is the sensor position on the imaging unit 18, which corresponds to the wavelength. The vertical axis is the signal strength. Here, the waveform due to the interference fringes overlaps with the intensity distribution of the center wavelength λ0 and the half width δλ.

The intensity information of this waveform is read out, converted into digital data by an A / D converter, and stored in the memory 24. When this data is wavenumber-converted and frequency-converted, an intensity distribution as shown in FIG. 4 can be obtained. This indicates that the interference intensities at the distances h1, h2, and h3 (distance from the coherence gate corresponding to the upper side of the tomographic image in FIG. 5) are I2, I1, and I3. Therefore, the interference intensity is measured while changing θi, which is the angle of the scan mirror, from θs to θe. By displaying the interference intensity I (θi, hj) acquired in this way with θ on the horizontal axis and h on the vertical axis, a B-scan image of the fundus (an image based on an optical distance) as shown in FIG. Can be obtained.

(Objective optical system)
Next, an objective optical system according to an embodiment of the present invention corresponding to a wide angle of view will be described. FIG. 6 shows a schematic configuration of the optical system of the sample arm 1001 in the present embodiment. In FIG. 6, the optical path from the fiber end 4a to the light source 1 side, the wavelength branch mirror 8 and the wavelength branch mirror 35 are omitted.

FIG. 6 schematically shows the on-axis and off-axis luminous fluxes. In FIG. 6, the light emitted from the fiber end 4a passes through the collimator lens 5 and the focus lens 6 and is scanned by the optical scanning unit 7. The luminous flux (measurement light) deflected by the optical scanning unit 7 passes through the relay lens 26 and the objective lens 9 and is focused on the fundus Ef of the eye E to be inspected. Further, the position on the optical axis of the focus lens 6 maximizes the amount of return light reflected by the fundus Ef and incident on the fiber end 4a through the backlight path, and the brightness of the tomographic image displayed on the display unit 20. Is set to the maximum.

At this time, the optimum position of the focus lens 6 on the optical axis differs depending on the diopter of the eye to be inspected. However, in the present embodiment, unlike the configuration in which the optical path length is changed to focus, the optical path length of the sample arm 1001 does not change even if the position of the focus lens 6 on the optical axis is changed. Therefore, it is not necessary to change the optical path length of the reference arm 1002 according to the diopter of the eye to be inspected, and it is not necessary to move the reference mirror 12 according to the diopter of the eye to be inspected. Therefore, the operation at the time of alignment becomes easy. Further, since it is not necessary to secure a wide moving range of the reference mirror 12 so as to cope with individual differences in diopter, it is advantageous for miniaturization of the device.

Next, the relationship between the focal length of the objective lens and the angle of view will be described. In the optical system shown in FIG. 6, the optical scanning unit 7 and the pupil of the eye E to be inspected are configured to have an optically conjugate relationship (pupil conjugate relationship). Here, the magnification of pupil imaging is determined by the ratio of the focal lengths of the objective lens 9 and the relay lens 26. As shown in FIG. 6, when the focal length of the objective lens 9 is short with respect to the relay lens 26, the distance between the objective lens 9 and the eye E to be inspected becomes short. Therefore, the light is incident on the eye E to be examined at a larger angle, and the imaging range on the fundus Ef is widened. By shortening the focal length of the objective lens with respect to the relay lens in this way, the angle of incidence on the eye to be examined can be made larger than the swing angle of the scanning portion, so that the fundus is scanned with a small swing angle and a wide angle of view. It will be advantageous to.

Here, in order to widen the angle of view of the fundus photography range, it is preferable to shorten the focal length of the objective lens. However, as described above, if the radius of curvature of the objective lens is shortened accordingly, it becomes difficult to secure the thickness of the end face portion of the lens. As a countermeasure, it is effective to use a glass material having a high refractive index for the objective lens in order to make the radius of curvature relatively long while shortening the focal length of the objective lens. It is preferable to use a glass material having a refractive index as low as possible in order to reduce the chromatic aberration caused by the objective lens, but it is desirable to use a glass material having a high refractive index in order to reduce other aberrations. Therefore, it is effective to use a glass material having a high refractive index from the viewpoint of ensuring a degree of freedom in designing the lens shape.

[In the case of an objective lens consisting of a group]
In fundus photography, an angle of view of 80 ° or more can be considered as a wide angle of view. The conditions for obtaining this shooting angle of view will be described below. Here, an objective lens consisting of a group, a single lens having convex on both sides, or a convex lens with two elements joined is targeted. Here, the ratio of the radius of curvature r1 of the first surface of the objective lens on the side to be inspected to the radius of curvature r2 of the final surface of the objective lens (the surface farthest from the eye to be inspected) is Rr, and the objective lens is a single lens. Let n be the refractive index of the case or the equivalent refractive index when the objective lens is a junction lens. In this case, if the focal length of the objective lens is f,
1 / f = (n-1) x [(1 / r1)-{1 / (-r2)}]
= (N-1) × {(1 / r1) + (1 / r2)}
= (N-1) x (1 + Rr) / (Rr x r2) ... (Equation 1)
Is established.

Further, a predetermined differential distance from the cornea (pupil) to the objective lens is defined as WD, and the imaging magnification of the pupil of the eye to be inspected when the objective lens is placed at a distance WD from the pupil is defined as Pm. The distance from the objective lens to the pupil conjugate point is Pm × WD. In this case, the focal length f of the objective lens is
f = 1 / {(1 / WD) + (1 / Pm x WD)}
= WD x Pm / (1 + Pm) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 2)
Can also be expressed as.
In this case, the radius of curvature r2 is determined by Equation 1 and Equation 2.
r2 = (n-1) x {(1 + Rr) / Rr} x {Pm / (1 + Pm)} x WD
・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 3)
It is expressed as.

Here, assuming that the lens diameter of the objective lens is φ and the shooting angle of view is θ, φ / 2 = tan (θ / 2) × WD ... (Equation 4)
Since this φ / 2 cannot be larger than r2, which is the radius of curvature of the lens, the equation (4) shows.
Tan (θ / 2) × WD <r2, and from Equation 3 described above,
(N-1) / tan (θ / 2)> {(1 + Pm) / Pm} × {Rr / (1 + Rr)}
・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 5)
Is obtained.

Considering the spherical aberration of the pupil, Rr needs to be a value larger than 3 in order to reduce it to an appropriate level. Actually, in order to provide an image suitable for diagnosis, it is preferable that the value is larger than 5.0. Further, when Rr is larger than 22, it becomes necessary to increase the refractive index, which makes it impractical in selecting a glass material. Considering the refractive index of the glass material actually used, Rr is preferably smaller than 11.0. That is, Rr is appropriately selected in the range of 3 <Rr <22, and more preferably determined in the range of 5.0 <Rr <11.0.

Further, when the WD becomes smaller, there is a risk of contact with the subject or the eye to be inspected, and further, there is a possibility that the lens may be soiled by tears or the like. Therefore, it is necessary to make it larger than 20 mm. In addition, if the size becomes too large, the size of the device becomes large, which goes against the recent demand for miniaturization. From the above, it is preferable that WD is determined in the range of 20 mm <WD <45 mm.

Further, as for Pm, the amount of movement of the focus lens increases as the size increases, resulting in an overall increase in size of the device. Therefore, there is an upper limit allowed as the amount of movement of the focus lens. Further, when it becomes smaller, a small scanner is required, and it becomes necessary to further improve the accuracy of the configuration and arrangement of each component such as a diaphragm, and there is a lower limit value in the achievable value. Further, when it becomes smaller, the aberration generated in the objective lens becomes larger, and it is necessary to design so as not to fall below the lower limit in this respect as well. Therefore, it is preferable to set a large value if possible. From the above, it is preferable that Pm is determined in the range of 2.0 <Pm <4.5.

here,
g (Pm, Rr) = (Pm + 1) × Rr / {Pm × (Rr + 1)}
・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 6)
Consider the function. In this case, Rr / (Rr + 1) is a monotonically increasing function and (Pm + 1) / Pm is a monotonically decreasing function in the above-mentioned preferable range of Rr, WD and Pm described above. Therefore,
g (Pm _max , Rr _min ) <g (Pm, Rr) <g (Pm _min , Rr _max )
・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 7)
From each of the above critical values,
0.917 <g (Pm, Rr) <1.435 ..... (Equation 8)
Will be.

Here, glass materials having a high refractive index are limited, and from the viewpoint of freedom of selection, cost, and the like, glass materials having a refractive index of 2.0 or more at present are not suitable for use in objective lenses. Therefore, it is preferable that n <2.0. From the above-mentioned equations (5) and (8) and the condition of n,
[(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ / 2) +1
<N <2.0 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 9)
Then, from the condition of g (Pm _max , Rr _min ), Pm <4.5 and 3.0 <Rr.
From the above, by using a glass material satisfying the condition of the formula (9) and further satisfying the conditions of Pm <4.5 and 3.0 <Rr, for example, for use in an ophthalmic apparatus without enlarging the optical system. An objective lens that is easy to process can be obtained.

The higher the refractive index, the larger the color dispersion by the objective lens. In the above-mentioned conditions, the refractive index n <2.0 is set by paying attention to the aberration. However, when the image is obtained by visible light or when the influence of color dispersion is reduced to obtain the image, the refractive index Is preferably smaller than 1.85.

The objective lens described above is preferably a single lens made of one type of glass material. It is conceivable to use an objective lens bonded lens for chromatic aberration correction or the like, but if a bonded lens is used, the center thickness of the lens becomes thick, which is disadvantageous for securing WD. By using a single lens made of one type of glass material, WD can be secured for a relatively long time with a simple configuration.

[In the case of an objective lens consisting of two groups]
As described above, in order to obtain an objective lens that is easy to process and suitable for miniaturization of the apparatus, it is preferable to use a glass material having a refractive index of less than 2.0 or a bonded lens having an equivalent refractive index of less than 2.0. However, when the refractive index is 1.85 or more, the influence of color dispersion by the objective lens becomes large. On the other hand, the objective lens has a two-group configuration, and the focal position on the opposite side of the first lens group to the eye subject side and the focal position on the first lens group side of the second lens group match. It is possible to reduce the refractive index of the first lens group by making the light rays parallel. In the following, the conditions of the refractive index of the glass material used for the first lens group when the objective lens has a two-group configuration will be described.

Here, the focal length of the first lens group is f1, and the focal length of the second lens group is f2. Since the first lens group and the second lens group have the above-mentioned arrangement at the focal position, the same relational expression as in the case of the objective lens composed of the above-mentioned group lens can be used in the first lens group. Specifically, for Rr, Pm and WD, WD = f1 and Pm = f2 / f1 according to the above definitions. Further, as for the above-mentioned relational expression, equations 1 to 8 hold. Further, by adopting the two-group configuration of the objective lens described here, it is possible to establish the above-mentioned relational expression even if the refractive index is lowered. Therefore, the above-mentioned equation 9 is an objective lens having a two-group configuration. In
[(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ / 2) +1
<N <1.85 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 10)
Will be.

It is considered that the same conditions as those for WD described above are required for f1. However, in reality, f1 may be larger than 25 mm because the focus is located on the fundus. Further, f1 is preferably smaller than 50 mm from the viewpoint of avoiding an increase in the size of the optical system. Further, f2 / f1 is preferably larger than 2 and smaller than 4. By satisfying these conditions, it is possible to obtain, for example, an easily processed objective lens for use in an ophthalmic apparatus without increasing the size of the optical system. Since the refractive index can be made smaller than 1.85, the influence of color dispersion can be reduced during actual image observation, but this does not apply to spherical aberration due to the pupil. Therefore, it is preferable that the value of Rr is larger than 5.0 and smaller than 11.0, as in the case of the objective lens having a group configuration.

The objective lens may include an aspherical surface whose refractive power decreases toward the peripheral portion. In this case, the spherical aberration of the light converging on the pupil can be reduced. By reducing the spherical aberration, it is possible to suppress the eclipse of the luminous flux due to the pupil, and it is possible to obtain a good fundus image up to the peripheral portion even at a wide angle of view. Further, since the radius of curvature becomes large in the peripheral portion of the objective lens surface, it is also advantageous to secure the thickness of the lens end surface portion.

Further, it is preferable that the light from the light source telecentricly enters the objective lens 9. In the present embodiment, the optical scanning unit 7 is arranged at the focal position of the relay lens 26, and the pupil of the eye to be examined E is arranged at the focal position of the objective lens 9, so that the distance between the relay lens 26 and the objective lens 9 is provided. The light beam is configured to be telecentric. As a result, the range of the angle of light incident on the wavelength branch mirror 35 and the wavelength branch mirror 8 can be suppressed to a small size. The characteristics of the wavelength-branched mirror depend on the angle of incidence of the light beam. Therefore, by keeping the light incident angle range small as a telecentric optical configuration, it is possible to keep the design difficulty and the manufacturing difficulty of the wavelength branch mirror low.

As described above, the objective lens according to the present invention is an objective lens provided in a fundus imaging device having a photographing angle of view θ, and one aspect thereof is a monoconvex lens or a two-element convex lens. In the objective lens, the ratio of the radius of curvature r1 on the first surface to the eye to be inspected and the radius of curvature r2 on the final surface is Rr, the refractive index when the convex lens is a monoconvex lens, or the equivalent refractive index when the convex lens is a two-lens junction lens. Let n. Further, the imaging magnification of the pupil of the eye to be inspected when the objective lens is placed at a predetermined differential distance is defined as Pm. In this case, θ> 80 °, Pm <4.5, 3.0 <Rr, and [(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ / 2) + 1 <n <2.0
By satisfying the above conditions, a wide angle of view fundus image can be acquired with an optical system having a low cost and a compact configuration.

Further, in the objective lens, it is preferable to further satisfy 1.85> n in order to reduce the color dispersion of the objective lens. Further, in order to widen the selection range of the glass material and lower the refractive index in order to reduce the color dispersion, it is preferable that the objective lens is arranged so that the light from the light source in the fundus photography device telecentricly enters the objective lens. ..

Further, the objective lens according to the present invention is an objective lens provided in a fundus imaging device having a shooting angle of view θ, and the other aspect is a two-group configuration composed of a first lens group and a second lens group. It becomes an objective lens. In this case, the focal position on the side opposite to the side to be inspected in the first lens group is arranged so that the focal position on the first lens group side of the second lens group coincides with each other. In the objective lens, the ratio of the radius of curvature r1 of the first surface of the monoconvex or two-lens convex lens used for the first lens group on the side of the eye to be inspected to the radius of curvature r2 of the final surface is Rr. To do. Further, the focal length of the first lens group is f1 (mm), and the focal length of the second lens group is f2 (mm). In this case, θ> 80 °, 25 <f1 <50, 2 <f2 / f1 <4.5, 3.0 <Rr and [(Pm + 1) × Rr / {Pm × (Rr + 1)}] × It is preferable to satisfy tan (θ / 2) + 1 <n <1.85.

In the above-mentioned objective lens, it is preferable that the value of Rr is 5.0 <Rr <11.0 in order to reduce spherical aberration. Further, it is preferable that at least one of the first surface and the final surface of the objective lens is a rotationally symmetric aspherical surface in which the curvature becomes gentle from the optical axis toward the peripheral portion. By using such a rotationally symmetric aspherical surface, it is possible to reduce the spherical aberration of the light converging on the pupil, and it is possible to obtain a good fundus image up to the peripheral portion even at a wide angle of view. Further, since the radius of curvature becomes large in the peripheral portion of the objective lens surface, it is also advantageous to secure the thickness of the lens end surface portion. Further, the fundus imaging device may be SS-OCT.

Hereinafter, an embodiment of the objective lens 9 in this embodiment will be described.
[Example 1]
The objective lens of the first embodiment in this embodiment is shown in FIG. FIG. 7 schematically shows the on-axis and off-axis luminous fluxes. The first embodiment is an objective lens having a two-group configuration composed of a first lens 9a and a second lens 26a. The luminous flux from the second lens 26a is telecentricly incident on the first lens 9a. The r2 surface of the first lens 9a is an aspherical surface. In the first embodiment, the shooting angle of view θ = 80 °.
Focal length f1 = 28.3 mm of the first lens 9a, focal length f2 = 117.5 mm of the second lens 26a, pupil imaging magnification Pm = f2 / f1 = 4.2, ratio of radius of curvature of the first lens 9a Rr = R1 / r2 = 3.0. The refractive index n of the first lens 9a is 1.783.

[Example 2]
The objective lens of Example 2 in this embodiment is shown in FIG. FIG. 8 schematically shows the on-axis and off-axis luminous fluxes. The second embodiment is an objective lens having a two-group configuration composed of a first lens 9b and a second lens 26b. The luminous flux from the second lens 26b is telecentricly incident on the first lens 9b. The r2 surface of the first lens 9b is an aspherical surface. In the second embodiment, the shooting angle of view θ = 80 °.
Focal length f1 = 32.3 mm of the first lens 9b, focal length f2 = 142.3 mm of the second lens 26b, pupil imaging magnification Pm = f2 / f1 = 4.4, ratio of radius of curvature of the first lens 9b Rr = R1 / r2 = 3.8. The refractive index n of the first lens 9b is 1.828.

[Example 3]
The objective lens of Example 3 in this embodiment is shown in FIG. FIG. 9 schematically shows the on-axis and off-axis luminous fluxes. Example 3 is an objective lens having a two-group configuration composed of a first lens 9c and a second lens 26c. The luminous flux from the second lens 26c is telecentricly incident on the first lens 9c. The r2 surface of the first lens 9c is an aspherical surface. In the third embodiment, the shooting angle of view θ = 80 °.
Focal length f1 = 26.2 mm of the first lens 9c, focal length f2 = 111.2 mm of the second lens 26c, pupil imaging magnification Pm = f2 / f1 = 4.2, ratio of radius of curvature of the first lens 9c Rr = R1 / r2 = 10.4. The refractive index n of the first lens 9b is 1.965.

[Example 4]
The objective lens of Example 4 in this embodiment is shown in FIG. FIG. 10 schematically shows the on-axis and off-axis luminous fluxes. Example 4 is an objective lens having a two-group configuration composed of a first lens 9d and a second lens 26d. The luminous flux from the second lens 26d is telecentricly incident on the first lens 9d. The r2 surface of the first lens 9d is an aspherical surface. In the fourth embodiment, the shooting angle of view θ = 80 °.
Focal length f1 = 49.7 mm of the first lens 9d, focal length f2 = 139.5 mm of the second lens 26d, pupil imaging magnification Pm = f2 / f1 = 2.8, ratio of radius of curvature of the first lens 9d Rr = R1 / r2 = 3.3. The refractive index n of the first lens 9b is 1.885.

[Other Embodiments]
Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. The present invention also includes inventions modified within the scope not contrary to the gist of the present invention, and inventions equivalent to the present invention. Further, in the above-described embodiment, the SD-OCT (Spectral-domine OCT) system using a broadband light source and a spectroscope is applied as a system for acquiring tomographic images, but SS-OCT using a variable wavelength light source (SS-OCT) A Swept-Source OCT) system may be applied. Further, the fundus photography device described as an embodiment is an example, and the objective lens according to the present invention can be applied to an objective lens used in various fundus photography devices that require optical image angle. Further, the objective lens according to the present invention can be used as an objective lens provided in the fundus photography apparatus main body, but can also be in the form of a lens adapter attached to the fundus photography apparatus for optical angle photography.

1: Light source, 2: Light guide, 3: Light split, 4: Light guide, 5: Collimeter lens, 6: Focus lens, 7: Optical scanning unit, 8: Wavelength branch mirror, 9: Objective lens, 10 : Light guide unit, 11: Collimeter lens, 12: Reference mirror, 13: Stage, 14: Light guide unit, 15: Collimeter lens, 16: Spectro unit, 17: Lens, 18: Imaging unit, 19: Control unit, 20 : Display unit, 21: Anterior segment illumination light source, 22: Lens, 23: Imaging unit, 24: Memory, 25: Pointing device, 26: Relay lens, 28: Light source, 29: Collimeter lens, 30: Wavelength branch mirror, 31: Perforated mirror, 32: Focus lens, 33: Optical scanning unit, 34: Lens, 35: Wavelength branch mirror, 36: Lens, 37: Detection unit, 38: Light source, 39: Collimeter lens

Claims (8)

An objective lens provided in a fundus photography device with a shooting angle of view θ.
Consists of a monoconvex lens or a two-element convex lens
The ratio of the radius of curvature r1 of the first surface to the eye to be inspected and the radius of curvature r2 of the final surface is Rr.
The refractive index when the convex lens is a monoconvex lens or the equivalent refractive index when the convex lens is a two-element junction lens is n.
When the imaging magnification of the pupil of the eye to be inspected when the objective lens is placed at a predetermined differential distance is Pm,
θ> 80 °, Pm <4.5, 3.0 <Rr and [(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ / 2) + 1 <n <2.0
An objective lens characterized by satisfying. 1.85> n
The objective lens according to claim 1, wherein the objective lens satisfies. The objective lens according to claim 1 or 2, wherein the light from the light source in the fundus photography device telecentricly enters the objective lens. An objective lens provided in a fundus photography device with a shooting angle of view θ.
It consists of a first lens group and a second lens group.
It is arranged so that the focal position on the side opposite to the eye to be inspected side of the first lens group and the focal position on the first lens group side of the second lens group coincide with each other.
The ratio of the radius of curvature r1 of the first surface of the monoconvex lens or the two-lens convex lens used for the first lens group on the side of the eye to be inspected to the radius of curvature r2 of the final surface is Rr.
The focal length of the first lens group is f1 (mm), the focal length of the second lens group is f2 (mm),
When the imaging magnification of the pupil of the eye to be inspected when the objective lens is placed at a predetermined differential distance is Pm,
θ> 80 °, 25 <f1 <50, 2 <f2 / f1 <4.5, 3.0 <Rr and [(Pm + 1) × Rr / {Pm × (Rr + 1)}] × tan (θ) / 2) +1 <n <1.85
An objective lens characterized by satisfying. 5.0 <Rr <11.0
The objective lens according to any one of claims 1 to 4, wherein the objective lens satisfies. The objective lens is any one of claims 1 to 5, wherein at least one of the first surface and the final surface is a rotationally symmetric aspherical surface whose curvature becomes loose from the optical axis toward the peripheral portion. The objective lens described in the section. The objective lens according to any one of claims 1 to 6, wherein the fundus imaging device is SS-OCT. A fundus photography apparatus provided with the objective lens according to any one of claims 1 to 6.

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