JP5063985B2 - Obtaining the actual fundus distance - Google Patents

Description

  The present invention relates to a fundus actual distance acquisition method for obtaining an actual distance on the fundus based on a fundus image photographed by a fundus photographing apparatus.

In recent years, photodynamic therapy (hereinafter referred to as PDT therapy) is known in which a lesion is irradiated with a laser beam in a spot shape to treat age-related macular degeneration or the like in which a new blood vessel is formed on the fundus (Patent Document 1). reference). In this PDT therapy, it is required to form an appropriate spot size of the irradiation laser beam. Therefore, the fundus image captured by the fundus imaging apparatus such as a fundus camera is displayed on the display unit, the lesion is designated on the image displayed on the display unit, the diopter of the patient's eye, the axial length, the imaging condition, etc. A technique for obtaining the actual distance of the lesion on the fundus based on the size variation factor of the fundus image is known from Patent Document 2. The technique described in Patent Document 2 is substantially the same as that of Patent Document 3 that has been known since then.
JP 2000-60893 A JP 2006-122160 A Japanese Patent Laid-Open No. 10-179517

  When calculating the actual distance of the measurement location (lesioned part, etc.) on the fundus based on the fundus image taken by the fundus camera, the patient's eye is part of the optical system. Information relating to the photographing magnification of the photographing optical system itself of the camera is required. Usually, if it is a retinal camera manufacturer, the information related to the photographing magnification of the photographing optical system itself is known from the optical design value. If information on the photographing optical system is obtained from the manufacturer, the actual distance in the fundus image can be obtained using this information.

  However, there are many types of fundus cameras, and the lens arrangement and configuration of the photographing optical system are different for each model, and furthermore, the optical system is greatly different for each manufacturer. For this reason, when there is no photographing optical system information from the manufacturer, it is necessary to disassemble the fundus camera and check the characteristics and arrangement relationship of each lens, but this is not easy.

  Even in the same type of fundus camera, the camera unit having a CCD camera (imaging device) and a relay lens attached to the fundus camera may be replaced depending on the purpose of photographing. In this case, since the information related to the photographing magnification of the photographing optical system itself also changes, it is necessary to know according to the camera unit attached to the fundus camera, but it is not easy to obtain the information.

  In view of the problems of the above-described conventional apparatus, the present invention is photographed with a photographing optical system by obtaining information regarding the photographing magnification of the photographing optical system even if the fundus photographing apparatus has an unknown design value of the photographing optical system. Another object of the present invention is to provide a fundus actual distance acquisition method capable of obtaining the actual distance on the fundus based on the fundus image.

In order to solve the above problems, the present invention is characterized by having the following configuration.
(1) In a fundus actual distance acquisition method for obtaining an actual distance on the fundus based on a fundus image captured by a fundus photographing apparatus including a photographing optical system in which an image sensor is arranged, and optical characteristic information of a patient's eye A model eye having a lens and an index having a predetermined dimension arranged at a fundus position whose distance from the principal point of the lens is known by design, and prepared with a different diopter A step of photographing each model eye with a fundus photographing apparatus to obtain an image of the index, and a step of obtaining a photographing magnification of the index on the image sensor for each model eye based on the obtained index image. Determining the scale variable of the imaging optical system for different diopters for each model eye based on the obtained imaging magnification and the distance from the principal point of the lens of the model eye to the index, and the obtained result From the photographic optical system And setting a function of the scale variable for each diopter with respect to the diopter range that can be photographed with, based on the function of the scale variable and the optical characteristic information of the patient's eye. It is characterized in that the actual distance of the measurement location set in the fundus image is obtained.
(2) In the fundus actual distance acquisition method of (1), the photographing optical system of the fundus photographing apparatus has a second image sensor different from the image sensor (referred to as the first image sensor). When the unit is replaceable and the scale variable of the photographing optical system including the replaced camera unit is set, the model eye created with at least one predetermined diopter is used to A scale variable of the photographing optical system with respect to the diopter is obtained, and each view of the diopter range that can be photographed by the photographing optical system based on a change between the scale variable and the scale variable set by the first image sensor. Setting a function of a scale variable with respect to degrees.
(3) In the fundus actual distance acquisition method according to any one of (1) and (2), the fundus imaging apparatus includes an outer cylinder that holds the objective lens of the imaging optical system, and the model eye is fitted to the outer cylinder. A housing having a fitting portion to be mounted, wherein the lens and the index are arranged, and the lens adjusts the alignment of the imaging optical system when the fitting portion is fitted to the outer cylinder. It is characterized in that it is arranged at a position where the is unnecessary.

  According to the present invention, it is possible to easily obtain information relating to the photographing magnification of the photographing optical system provided in the fundus photographing apparatus, and to obtain the actual distance on the fundus based on the photographed fundus image.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a fundus image processing apparatus according to an embodiment of the present invention.

  Reference numeral 200 denotes a fundus image processing apparatus, and reference numeral 100 denotes a fundus camera including an imaging optical system that captures the fundus of a patient's eye connected to the fundus image processing apparatus 200. The fundus camera 100 obtains a fluorescence-contrast patient fundus image as an electronic image by photographing a color fundus image or photographing a patient eye administered with a fluorescent agent by fundus illumination using a visible light flash lamp. . Reference numeral 101 denotes an jaw holder attached to the main body of the fundus camera 100, and serves as a support for fixing the patient's eyes (patient's face). Reference numeral 102 denotes an outer cylinder that houses an objective lens 20 (described later), and has a cylindrical shape (circular shape) so as to surround the objective lens 20.

  The fundus image processing apparatus 200 is constituted by a personal computer (hereinafter abbreviated as PC), and the PC main body 210 which is the main body of the PC is storage means for storing a patient identification code (information), a patient's fundus image, and the like. A memory 211 (hard disk) and a CPU (Central Processing Unit) 212 which is a calculation means for processing a fundus image of a patient and the like are incorporated. Connected to the PC main body 210 are a color monitor 215 as display means and a mouse 216 and keyboard 217 as input means.

  The fundus image processing apparatus 200 (PC 210) and the fundus camera 100 are connected by a cable 201. As described above, the fundus image obtained by the fundus camera 100 is taken into the memory 211 when the CPU 212 receives a fundus image input instruction. Next, the fundus image captured from the fundus camera 100 will be described.

  FIG. 2 is a schematic diagram of an optical system as an example of a fundus camera. The optical system includes an illumination optical system 1, a photographing optical system 2, and an observation optical system 3.

  The illumination optical system 1 has an infrared LED 10 as an observation light source, a condenser lens 12, a dichroic mirror 15, a ring slit 16, a flash lamp 13 as a photographing light source, a relay lens 17a, a mirror 18, and a small black dot at the center. A black spot plate 19, a beam splitter 48, a relay lens 17b, a perforated mirror 21, an objective lens 20, and a focus index projection optical system 45 are provided.

  The photographing optical system 2 includes an objective lens 20, an aperture of a perforated mirror 21, a photographing aperture 22, a focus lens 23 movable in the optical axis direction, an imaging lens 24, a half mirror (or return mirror) 25, and a relay lens 26. A color CCD camera 27 is provided as an image sensor having sensitivity in the visible range. The fundus image captured by the CCD camera 27 is stored as a still image in an image memory (not shown) in the fundus camera 100. The observation optical system 3 shares the objective lens 20 to the half mirror 25 of the photographing optical system 2 and includes a relay lens 30 in the reflection direction of the half mirror 25 and an observation CCD camera 32 having sensitivity in the infrared region.

  Depending on fundus imaging conditions, the relay lens 26 and the CCD camera 27 are replaced with a camera unit 37 having a CCD camera 37 and a relay lens 36 which are different imaging elements (second imaging elements). For example, in fluorescence imaging of the fundus, when the fluorescent agent (vascular contrast agent) emits infrared light, the CCD camera 37 has sensitivity in the infrared region. In this case, an excitation filter is disposed in the illumination optical system 1, and a filtration filter is disposed in the photographing optical system.

  Further, when the diopter of the patient's eye is out of a predetermined focus range due to the movement of the focus lens 23, a correction lens 28 for enabling the focus is disposed in the photographing optical system 2. It is assumed that the photographing optical system 2 can photograph a range of −10D to 6D when the correction lens 28 is not provided. As the correction lens 28, for example, a first correction lens that can shoot a range of −9D to −23D, a second correction lens that can shoot a range of + 5D to + 23D, and a range of + 22D to + 41D can be shot. Three types of third correction lenses are prepared.

The optical system of the fundus camera 100 described above is an example, and the configuration of the photographing optical system 2 differs depending on the manufacturer (manufacturing company). The structure of the fundus camera may be different even within the manufacturer. In addition, since the patient's eye is part of the optical system when calculating the actual distance of the measurement site (lesioned part, etc.) on the fundus based on the fundus image taken by the fundus camera, Information relating to the optical characteristics of the eye and the photographing magnification of the photographing optical system itself of the fundus camera is required. If it is a manufacturer of a fundus camera, information related to the photographing magnification of the photographing optical system itself is known from the optical design value, but if the optical design value is unknown, it is necessary to obtain this beforehand. . Therefore, a plurality of model eyes with known optical characteristics and different diopters are prepared, and the photographing magnification of the subject of the photographed model eye is calculated, and the photographing magnification of the photographing optical system itself of the fundus camera 100 is calculated from each photographing magnification. For each diopter. The scale variable referred to in this specification refers to the main object side of the lens with respect to the imaging magnification for each diopter determined by the optical characteristics of the imaging optical system of the fundus camera 100 and the model eye 300 (or the patient's eye) that is the subject. By dividing by the distance from the point to the index, the information about the imaging magnification of the imaging optical system itself does not depend on the distance from the object-side principal point of the lens of the eyeball to the index. That is, the scale variable is information that defines the imaging magnification of the imaging optical system that does not depend on optical characteristics other than the diopter of the model eye 300 or the patient's eye. In the following description, the scale variable is a function of diopter, but since the diopter is closely related to the position of the focus lens 23 and the correction lens 28 , the scale variable is determined by the focal lens 23 and the correction lens 28. It can be said that it is a function related to presence or absence.

  Hereinafter, a method for measuring information (scale variable) relating to the photographing magnification of the photographing optical system itself will be described (see the flowchart of FIG. 9). First, a plurality of model eyes having different diopters are prepared. FIG. 3 shows a model eye 300 for measuring the optical magnification of the fundus camera. 3A is an external perspective view of the model eye 300, FIG. 3B is a cross-sectional view of the model eye head 301, and FIG. 3C shows a reticle of the model eye 300. The model eye 300 is provided on a cylindrical member 310 having a plano-convex lens 320 that is an optical element, a plate 330 having a reticle that serves as an index during photographing, and the like, and a lower part of the head 301 to support the head 301. The shaft 302 extends in the vertical direction, and the base 302 is attached to the shaft 302 and supports the shafts 302 and 301. The base 303 is attached to the jaw receiver (details are omitted). As shown in FIG. 3C, the reticle 330a drawn on the plate 330 has a scale of a predetermined dimension with respect to a line segment extending in the xy direction. The plate 330 is formed of a transparent body such as glass, and the reticle 330a can be observed from the plano-convex lens 310 by light from the outside.

  The tubular member 310 is hollow, and a hollow spacer 340 disposed between the plano-convex lens 320 and the plate 330 is disposed at the center of the tubular member 310. N indicates the length of the spacer 340 in the optical axis direction, and the distance between the lens 310 and the plate 330 can be changed by replacing the space 340 having a different length N. The model eye 300 is designed in consideration of the size close to the human eye. For example, the length N is the average length of the axial axis, about 24 mm, the curvature of the plano-convex lens 320 is about 8 mm which is an average corneal curvature, and the refractive power of the plano-convex lens 320 is 60D which is the average refractive power of the eyeball. (Tiopta) grade. The diopter is defined as a refraction error with respect to a 0D normal eye. However, this value may be greatly changed depending on the shooting conditions. By simulating the characteristics of the model eye with the human eye, the reticle 330a can be easily photographed.

  In the model eye 300, the diopter of the model eye on which light that enters parallel to the cornea forms an image on the fundus is set to 0D (diopter) as in the human eye. By changing the length of the spacer 340, the distance S from the principal point Ls of the plano-convex lens 320 to the plate 330 as the object point is changed, and the axial length of the eyeball is virtually changed to change axial myopia. Simulate hyperopia. In addition, refractive myopia and hyperopia are simulated by changing the curvature and refractive power of the plano-convex lens 320. For example, 11 types of such model eyes 300 are prepared in 5D increments from -25D to + 25D. At this time, the diopter of the model eye 300 does not necessarily have to be increased or decreased in 5D increments, and the distance S from the principal point Ls of the planoconvex lens 320 to the plate 330 with respect to the diopter may be known. The diopter of the prepared model eye 300 is at least two different diopters when the correction lens 28 is not used. For example, when there is no correction lens, one combination of one near 0D and a diopter far away from 0D such as + 6D or −10D, or two far away from 0D such as + 6D or −10D It is a combination. Preferably, it is only necessary to prepare three points of diopter in the vicinity of 0D and two diopters far apart from 0D such as + 6D and -10D. When a different correction lens 28 is used, a model eye 300 is prepared according to the diopter correction range of the correction lens 28.

In the embodiment described above, the spacer 340 is replaced and the distance from the plano-convex lens 310 to the plate 330 is changed. However, the present invention is not limited to this. Instead of the spacer 340, an expansion / contraction member is arranged so that the hollow cylindrical member expands / contracts by the rotation of a screw, and a lens or a plate is joined to the end face, and there is an axial length (distance from the lens principal point to the plate). It is good also as a structure which can be changed arbitrarily in the range. In this way, the diopter can be set arbitrarily . The shaft length can be measured with an external measuring device, or a scale or the like can be attached to the telescopic member so that the operator can know the shaft length at present.

  The fundus camera 100 photographs the reticle 330a of the model eye 300 prepared in this way. In order to photograph the reticle 330a, first, the model eye 300 prepared with the parameters of the optical characteristics as described above is set on the jaw receiver 101, respectively. Next, the optical system of the fundus camera 100 is moved to align the model eye 300 in the same manner as the fundus imaging of the patient's eye. At this time, since the diopter varies depending on the pattern of the model eye 300, focusing is performed by moving the focus lens 23, the center of the reticle 330a on the plate 330 is focused, and the reticle 330a is photographed. At this time, the plate 330 is photographed with external light without using a flash.

  A method for calculating and measuring the scale of the reticle 330a photographed by the fundus camera 100 will be described. In order to obtain the scale of the captured image, the size per pixel (one pixel) of the CCD camera 27 is obtained. For example, if the light receiving size of the CCD is 1900 × 1472 pixels, and the actual size of the CCD (the size of the CCD itself) is 11.88 × 9.2 mm, the size per pixel is CCD actual size / CCD light receiving. The size is 9.2 mm / 1472 pixels = 6.25 μm. The captured image acquired by the CCD camera 27 may be changed in size when displayed on the monitor 215 or the like. The size per pixel at this time is, for example, 9.2 mm / 635 pixels≈14.488 μm when the display size on the monitor 215 is 820 × 635 pixels.

As described above, the size per pixel is obtained, and how many pixels (how many pixels) are included in the 1 mm scale of the reticle 330a in the captured image of the reticle 330a is calculated, and the length is calculated. Thus, the photographing magnification (optical magnification) of the entire optical system including the model eye 300 and the photographing optical system 2 can be obtained. In this way, the photographing magnification of the photographed reticle 330a is obtained for each model eye. The model eye is then divided by the distance S of each model eye 330 (the distance from the principal point Ls of the lens 320 having the total refractive power of the model eye 300 to the reticle 330a). Optical characteristics other than the diopter of 300 are canceled, and the scale variable C (α) of the photographing optical system 2 accompanying the movement of the focus lens 23 is obtained. The unit of the scale variable is the reciprocal of the length (mm). Since the movement of the focus lens 23 corresponds to the diopter of the model eye 300 (that is, the diopter of the patient's eye), the scale variable obtained here corresponds to each diopter.

  FIG. 4 is a graph in which the scale variables of the fundus camera 100 having the respective diopters are plotted. In FIG. 4, for each correction lens, the scale variables at the diopter of 4 points are calculated by the above-mentioned method and plotted as a group. Each of the four points in each group is fitted with a linear function (or a quadratic expression or the like) of a linear expression.

  In the actual scale calculation of the actual fundus image, a scale variable for any patient eye diopter is required. Therefore, the relationship of the scale variable with the diopter as a variable is set for the diopter range that can be photographed by the photographing optical system from the measured data points. For example, as shown in FIG. 5, a function expression of a scale variable for diopter is set. The diopter is expressed as α, and the scale variable is expressed as C (α). The line in FIG. 4 is the result of linear fitting of data points. The fitting function was defined as linear function: C (α) = A + B × α with the patient's eye diopter α on the horizontal axis and the scale variable C (α) on the vertical axis. The fitting by function is not limited to a linear function, and may be a quadratic function or a cubic function. If the prepared model eye has three or more diopters, it is possible to fit a scale variable by a quadratic function or a cubic function.

  When the scale variable of the photographing optical system 2 for each arbitrary diopter can be obtained as described above, this is stored in the memory 211 of the fundus image processing apparatus 200. As described above, in addition to being stored as a function expression, it may be stored in the form of a scale variable table for each diopter. In order to obtain the optical magnification (imaging magnification), the scale variable may be multiplied by the distance S from the principal point Ls of the plano-convex lens 320 of the model eye 300 to the plate 330.

  Next, an operation for obtaining an actual distance on the fundus from the fundus image obtained by the fundus camera 100 will be described. Here, a procedure for calculating the spot diameter of the laser irradiated by PDT (Photodynamic Therapy) will be described.

  By pressing a transfer button (not shown) of the fundus camera 100, the fundus image of the patient's eye photographed by the fundus camera 100 is transferred to the fundus image processing apparatus 200 side. The fundus image is stored in the memory 211, and the fundus image is displayed on the monitor 215.

  FIG. 6 is a diagram showing a fundus image 530 displayed on the monitor 215. When the operator clicks a plurality of points in a circle along the periphery of the lesioned part 540 with the mouse cursor 560 to specify the lesioned part 540, the lesioned part region 581 is set by connecting the designated points. Then, a circle 583 circumscribing this region 581 is drawn. The diameter of the circumscribed circle 583 is the maximum lesion diameter (GLD). Further, after calculating the actual distance on the fundus, a spot circle 584 is drawn by adding a diameter of 1000 μm (radius of 500 μm) to the circumscribed circle 583. This spot circle 584 becomes the spot diameter of the irradiation laser. These series of drawing and calculation are performed by the mouse cursor 560 and the CPU 212. The designation of the region (region 581) of the lesioned part 540 may be automatically performed by the CPU 12 by image processing based on the luminance distribution of the fundus image.

  The spot diameter (the diameter of the spot circle 584) obtained as described above indicates the distance on the fundus image 530, and does not represent the actual distance on the fundus of the patient. The procedure for converting the obtained spot diameter distance to the actual distance will be briefly described below. The operator inputs patient eye information such as diopter (refractive error), axial length, and corneal curvature of the patient eye measured in advance on the data input screen shown in FIG. Further, the presence / absence of a correction lens when the patient's eye is photographed by the fundus camera 100 is input. Based on the input patient eye information, the measurement area set on the fundus image, and the imaging optical system scale variable stored in the memory 211, the CPU 12 sets the measurement location area 581 (the circumscribed circle 583). Calculate the actual distance. Thereafter, a spot circle 584 where the actual distance is obtained is drawn.

In the calculation of the actual distance, first, the distance d from the object side principal point of the patient's eye to the fundus is obtained from the axial length data of the patient's eye and the corneal curvature. This distance d is determined from the data of the axial length data and the corneal curvature based on a general eyeball model. An example of an eyeball model is Gullstrand's model eye. Further, the scale variable C (α) of the photographing optical system is determined based on the diopter data of the patient's eyes. The optical magnification β of the entire optical system from the fundus of the patient's eye to the imaging device (CCD camera 27) of the imaging optical system is
β = C (α) / d
Is calculated as Then, the actual distance of the diameter of the circumscribed circle 583 is obtained by dividing the set diameter of the circumscribed circle 583 by the optical magnification β. If the actual distance of the diameter of the circumscribed circle 583 is known, the size of the spot circle 584 which is the spot diameter of the irradiation laser can be obtained.

  In calculating the actual distance, as disclosed in Japanese Patent Laid-Open No. 2006-122160, from the relationship between diopter and axial length, the relationship between diopter and corneal curvature, and the relationship of scale variable C (α). A table in which the optical magnification β is determined may be created in advance and stored in the memory 211. In the present embodiment, the measurement value of the diopter of the patient's eye is input on the data input screen. However, the present invention is not limited to this. For example, the position (movement) information of the focus lens 23 and the information of the correction lens 23 are stored in a memory (not shown) or the like of the fundus camera 100, and the information is transferred to the memory 212 or the like. The diopter required for calculating the actual distance may be calculated based on information such as the focus lens 23.

  Next, a method for easily obtaining a fluctuating scale variable when the CCD camera 27 and the relay lens 26 are replaced with another camera unit 35 in the photographing optical system of the fundus camera 100 in which the scale variable is known will be described. . Even with the same kind of fundus camera, the CCD camera 27 and the relay lens 26 may be exchanged depending on the purpose of the user. This is because with the development of CCD integration technology, the pixels of the CCD camera will improve in a short period of time, and an appropriate CCD camera will be required depending on the shooting conditions (eg, visible color image, fluorescent image, etc.). It depends.

  FIG. 8 is a diagram illustrating an adjustment tool 400 that is a model eye for obtaining optical magnification information of the fundus camera 100. FIG. 8A is an external perspective view of the adjustment instrument 400 on the front side, and FIG. 8B is a cross-sectional view of the adjustment instrument 400 and a cross-sectional view of the outer cylinder 102 that holds the objective lens 20 of the fundus camera 100.

  The adjustment tool 400 has a structure similar to the model eye 300. The cylindrical member 410 as a housing is a cylindrical member having a hollow, and the inner diameter of the cylindrical fitting portion 411 is set to be a size that can be fitted into the outer cylinder 102 of the fundus camera 100. When the fitting part 411 is inserted into the outer cylinder 102, the restriction part 411 a is formed so that the front end 102 a of the outer cylinder 102 reaches the restriction part 411 a of the fitting part 411. A plano-convex lens 420 is disposed inside the cylindrical member 410, and a plate 430 (index) having a reticle serving as an index is disposed on the rear surface side. The reticle of the plate 430 is the same as the reticle 330a of the plate 330 described above. Here, the plate 430 is placed at the focal length position of the plano-convex lens 420. Therefore, the adjustment tool 400 has the same characteristics as a model eye of 0D (diopter). The distance S from the principal point of the plano-convex lens 420 to the plate 430 disposed at the fundus position is known by design.

  The plano-convex lens 420 is disposed so as to have a predetermined working distance with respect to the objective lens 20 when inserted into the outer cylinder 102 of the fundus camera 100. In addition, the plano-convex lens 420 is disposed so that the optical axis of the plano-convex lens 420 and the optical axis of the objective lens 20 coincide with each other. Thereby, when the fitting portion 411 is inserted into the outer cylinder 102, the alignment of the plano-convex lens 420 in the vertical and horizontal positions and the front and rear positions is completed, and the alignment for moving the imaging optical system 2 with respect to the model eye 300 as described above. Is unnecessary. It should be noted that if the above-described model eye 300 is also created in the same manner as the adjustment instrument 400 shown in FIG. 4, alignment adjustment is not necessary, which is convenient. At this time, for example, a slot in which the plano-convex lens 320 can be inserted into and removed from the cylindrical member of the model eye 300 may be provided so that the lens can be replaced with a different lens. In such a case, alignment is unnecessary, model eyes with different diopters can be prepared, and the reticle can be photographed efficiently.

A procedure for adjusting the optical magnification of the fundus camera 100 using an instrument having such a configuration will be described. The fitting portion 411 of the adjustment tool 400 is fitted into the outer cylinder 102 of the fundus camera 100. In this state, if the focus lens 23 is at the reference position (a position where the diopter is 0D), the reticle on the plate 430 is in focus. Note that the fundus camera 100 is configured such that the parallel light incident from the objective lens 20 forms an image on the CCD camera 27 when the focus lens 23 is at the reference position . In the same manner as described above, the reticle is photographed to obtain the photographing magnification ratio. The scale variable of the imaging optical system 1 including the exchanged camera unit is obtained from the scale of the reticle and the dimensions of the reticle in the imaging device (second CCD camera) of the exchanged camera unit. The scale variable is obtained by dividing the size of the reticle on the image sensor by the distance S from the principal point of the plano-convex lens 420 to the plate 430 disposed at the fundus position.

  If a scale variable (with K2) at a diopter 0D is obtained, a scale variable (at a diopter 0D) obtained at the time of the first CCD camera 27 (first image sensor) before replacement of the camera unit ( K2 / K1 is obtained from this rate of change. Then, by applying this rate of change K2 / K1 to all of the previously obtained scale variables for the diopter range that can be photographed, the scale variables of the photographing optical system 2 including the exchanged camera unit can be photographed. The diopter range is easily obtained. Since the optical magnification of the camera unit 35 (unit including the relay lens 36 and the CCD camera 37) may be considered to be fixed, if a scale variable for a certain diopter is calculated, this can be applied to all diopters. In the above description, the adjustment tool 400 that is a model eye with a diopter of 0D is used. However, the adjustment tool 400 that is a model eye with another known diopter may be used.

  When the corrected scale variable is obtained, the scale 211 is stored in the memory 211 in the form of a functional expression or a table of scale variables for each diopter as described above. In the fundus image processing apparatus 200, measurement points set on the fundus image photographed by the fundus photographing apparatus based on the scale variable of the photographing optical system for each diopter and the optical characteristic information of the patient's eye are measured on the fundus. Is required.

  In the above-described embodiment, the reticle is drawn on the flat plates 330 and 430. However, the present invention is not limited to this. The reticle may be drawn on a hemispherical member. Here, the hemisphere refers to a concave shape when viewed from the lens side. The hemispherical image plane is closer to the fundus shape, and the focus shift at the periphery of the reticle is reduced. The hemispherical member may be made of a material such as glass, and the reticle may be drawn by a laser processing technique. Moreover, although the model eye 300 and the lens of the adjustment tool 400 used in the present embodiment are plano-convex lenses, the present invention is not limited to this. A biconvex lens may be used. An aspheric lens may also be used. With an aspheric lens, aberrations and distortion on the imaging surface are reduced, and the reticle is observed over a wide range with little focus and distortion. In the present embodiment, a cylindrical member is used as an example of the casing. However, the casing is not limited to the cylindrical shape as long as the lens 420 and the plate 430 can be arranged in a predetermined positional relationship. The shape may be spherical or spherical.

1 is a diagram illustrating a configuration of a fundus image processing apparatus that is an embodiment of the present invention. FIG. It is an optical system schematic diagram of an example of a fundus camera. It is a figure which shows the model eye 300 for the optical magnification measurement of a fundus camera. 5 is a graph in which scale variables of the fundus camera 100 are plotted. It is a figure which shows the function type | formula of the scale variable with respect to a diopter. 6 is a diagram showing a fundus image 530 displayed on a monitor 215. FIG. It is a figure which shows a data input screen. It is a figure which shows the adjustment tool 400 which is a model eye for obtaining the optical magnification information of the fundus camera. It is a flowchart of the measuring method of a scale variable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Fundus camera 200 Fundus image processing apparatus 300 Model eye 211 Memory 212 CPU
320, 420 Plano-convex lens 330, 430 Plate 400 Adjusting instrument 540 Lesions

Claims (3)

In the fundus actual distance acquisition method for obtaining the actual distance on the fundus based on the fundus image captured by the fundus imaging apparatus including the imaging optical system in which the imaging element is disposed and the optical characteristic information of the patient's eye, A model eye having an index with a predetermined dimension arranged at a fundus position where the distance from the principal point of the lens is known by design, and preparing a model eye created with different diopters; Capturing each model eye with a fundus imaging device to obtain an image of the index, obtaining the imaging magnification of the index on the image sensor for each model eye based on the acquired index image, and obtaining Obtaining a scale variable of the photographing optical system for different diopters for each model eye based on the obtained photographing magnification and the distance from the principal point of the lens of the model eye to the index, and the photographing from the obtained result Taken with optical system A function of the scale variable for each diopter for a range of effective diopters, and a fundus image captured by a fundus imaging device based on the function of the scale variable and optical characteristic information of the patient's eye A method for obtaining an actual fundus distance, comprising: obtaining an actual distance of a measurement location set in step 1). 2. The fundus actual distance acquisition method according to claim 1, wherein a camera unit having a second image sensor different from the image sensor (referred to as a first image sensor) is replaced in the photographing optical system of the fundus photographing apparatus. When setting the scale variable of the photographing optical system including the exchanged camera unit, it is possible to use the model eye created with at least one predetermined diopter and to adjust the diopter of the model eye. A scale variable for each diopter with respect to a diopter range that can be photographed by the photographing optical system based on a change between the scale variable and the scale variable set by the first imaging element is obtained. A fundus actual distance acquisition method comprising a step of setting a function of a variable. 3. The fundus actual distance acquisition method according to claim 1, wherein the fundus imaging apparatus includes an outer cylinder that holds an objective lens of the imaging optical system, and the model eye includes a fitting portion that is fitted to the outer cylinder. A housing having the lens and the index disposed therein, wherein the lens does not require alignment adjustment of the imaging optical system when the fitting portion is fitted to the outer cylinder. The fundus oculi actual distance acquisition method, wherein