JP2010004968A - Image processing method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate an actual focal distance of a subject's eye, accurately measure the three-dimensional shape of the subject's eye based thereon and appropriately perform an ophthalmic diagnosis based on the measured three-dimensional shape. <P>SOLUTION: The image processing apparatus stereoscopically captures the fundus oculi of the subject's eye at a predetermined parallax via a fundus photography optical system, when performing a three-dimensional shape measuring process of the fundus oculi of the subject'eye, traces a ray in the optical model of the subject's eye consisting of the cornea (sf1), the lens (sf2 and sf3) and a retina (sf4) using a diopter, an axial distance (D12+D23+D34) and a corneal curvature (R1) measured from the subject's eye, estimates the curvature (R2) of the lens, estimates the focal distance f of the subject's eye by a paraxial calculation, obtains a parallax angle (Sa) formed by two light paths of stereoscopic imaging based on the focal distance f and the parallax of the imaging optical system, and measures the depth amount (ed) of a specific portion using the parallax angle (Sa) and the parallax amount (Sd) of the specific portion captured during the parallax image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing method and an image processing apparatus, in particular, stereo imaging of a subject's fundus with a predetermined parallax via a fundus imaging optical system, and measurement of the three-dimensional shape of the fundus of the subject's eye using the obtained parallax images. The present invention relates to an image processing method and an image processing apparatus for performing processing.

  2. Description of the Related Art Conventionally, for the purpose of diagnosing glaucoma, an image processing apparatus such as a fundus camera that captures a three-dimensional image of the fundus of the eye to be examined is known in order to grasp the shape of the fundus of the eye to be examined. For example, there is a device that stereo-photographs the fundus of the eye to be examined by moving the diaphragm in a single optical system of the fundus camera to different positions that are decentered from the optical axis to the left and right (or up and down). Known (Patent Document 1 below).

  Image processing for three-dimensional measurement of the fundus can be performed as follows. For example, pattern matching is performed on left and right (or upper and lower) images taken in stereo to search for corresponding image points, that is, corresponding points. If the corresponding points can be searched, each of the object points conjugated with the corresponding points using the principle of triangulation along the xy axes (two orthogonal axes parallel to the image plane) and the z axis (one axis parallel to the optical axis). Coordinates can be calculated. If a three-dimensional coordinate value of a sufficient number of object points is obtained, a three-dimensional model of the fundus of the eye to be examined can be created.

Further, the captured left and right parallax images are three-dimensionally displayed (3D display) using a 3D monitor or the like using various methods, that is, the captured left and right parallax images are independently displayed on both the left and right sides of the observer (examiner). By observing each of the eyes, the state of the photographed eye fundus can be observed stereoscopically.
JP-A-10-75932

  In order to construct three-dimensional information of a subject's eye from a stereo image, information on the focal length of the subject's eye is necessary. Conventionally, the focal length of the subject's eye with individual differences is simply and accurately determined. A method for measuring is not known, and in the calculation of three-dimensional information, a generally known average focal length of the human eye (for example, 16.8 mm) is adopted for all eyes to be examined. Many. For this reason, the three-dimensional shape of the eye to be inspected constructed as a numerical model may not be accurate and may not always match the actual patient's retinal shape.

  For example, when the axial length is long for a myopic eye, the focal length is considered to be longer than the above-mentioned average value of 16.8 mm. On the other hand, when the axial length is short for a hyperopic eye, the average value is 16.8 mm. The focal length is considered short. If there is such an error, there will be a problem in calculating the depth of the depression of the optic nerve head, which is very important for glaucoma, for example.

  That is, if the parallax angle taken in stereo is constant, the focal distance is assumed to be shorter than the actual distance in the case of the above-mentioned myopic eye, so the concavity is shallower than the actual distance. There was a possibility. When it is assumed that a deep recess is an index for diagnosing glaucoma, there is a problem that calculating an incorrect numerical value as the shape data of the recess may lead to misdiagnosis.

  An object of the present invention is to estimate an actual focal length of an eye to be examined, and to accurately measure the three-dimensional shape of the eye to be examined based on the estimated focal length so that an accurate ophthalmologic diagnosis can be performed from the measured three-dimensional shape. is there.

  In order to solve the above problems, in the present invention, the fundus oculi fundus is stereo-photographed with a predetermined parallax via a fundus imaging optical system, and the three-dimensional shape measurement processing of the fundus oculi fundus to be examined using the obtained parallax images. In the image processing method and the image processing apparatus for performing in the eye to be examined at the time of the stereo photographing from the step of estimating the focal length of the eye to be examined, the estimated focal length of the eye to be examined, and the parallax condition of the photographing optical system A step of obtaining a parallax angle formed by two stereo imaging optical paths, a step of obtaining a parallax amount in a fundus of a subject's eye taken in a stereo parallax left and right parallax images, and the parallax angle and the specific part And a step of measuring a depth amount of the specific part using a parallax amount.

  Alternatively, in the step of estimating the focal length of the eye to be inspected, the light beam in the optical model of the eye to be inspected comprising the cornea, the lens, and the retina is used by using the diopter, the axial length, and the corneal curvature measured from the eye to be examined. A configuration was adopted in which tracking was performed, the curvature of the lens was estimated, and the focal length of the eye to be examined was estimated by paraxial calculation using the estimated curvature of the lens.

  According to the above configuration, the focal length of the subject eye is estimated from conditions such as diopter, eye geometry, and corneal curvature measured from the subject eye, and the estimated focal length of the subject eye and the imaging optical system From the parallax conditions, the parallax angle formed by the two optical paths of stereo shooting within the eye to be examined at the time of stereo shooting is obtained, and the amount of parallax at the fundus of the eye to be examined at a specific part taken in the left and right parallax images taken in stereo is obtained. Thus, the depth amount of the specific part can be measured using the parallax angle and the parallax amount of the specific part. For this reason, the focal length f of the actual eye to be examined can be accurately estimated, and based on this, a predetermined part of the eye to be examined, in particular, the three-dimensional shape of the fundus of the eye to be examined can be accurately measured. Excellent ophthalmologic diagnosis is possible.

  In addition, using the diopter, axial length, and corneal curvature measured from the eye to be examined, ray tracing is performed in an optical model of the eye to be examined consisting of the cornea, lens, and retina, and the curvature of the lens is estimated and further estimated. By estimating the focal length of the eye to be examined by paraxial calculation using the curvature of the crystalline lens, it is possible to accurately measure a three-dimensional shape of a predetermined portion of the eye to be examined, particularly the fundus of the eye to be examined. There is an excellent effect that an ophthalmologic diagnosis can be performed.

  Hereinafter, as an example of the best mode for carrying out the present invention, the fundus of the eye to be examined is photographed in stereo via a stereo photographing optical system, and three-dimensional measurement processing and three-dimensional display are performed on the obtained photographed image data. An embodiment relating to the ophthalmic measuring apparatus to be performed will be described.

<Configuration of ophthalmic measurement device>
In the fundus camera 10 illustrated in FIG. 1 surrounded by an alternate long and short dash line, an observation lamp 11 that emits infrared illumination light is disposed at the center of curvature of the spherical mirror 12. Is incident on the total reflection mirror 17 through the condenser lens 14, the visible light strobe 15 which is a photographing light source, and the condenser lens 16.

  The illumination light reflected by the total reflection mirror 17 passes through the relay lens 22 through the illumination diaphragm 19, is reflected by the perforated total reflection mirror 23, and passes through the objective lens 24 to the anterior eye part (pupil) Ep of the eye E to be examined. Incident. The illumination stop 19 is disposed in a position substantially conjugate with the anterior segment Ep (pupil) of the eye to be examined in the illumination optical system.

  The reflected light from the fundus Er illuminated with the illumination light is transmitted through the objective lens 24, the aperture 23a of the perforated total reflection mirror 23, the aperture of the 2 aperture aperture stop (2 aperture aperture) 28, the focusing lens 35, and the imaging lens 36. Then, the light passes through the zoom lens 38a and enters the return mirror 39. When the return mirror 39 is in the position shown in the figure, the reflected light from the fundus is incident on a CCD (imaging means) 40 that is substantially conjugate with the fundus and is sensitive to infrared light, and the fundus is imaged by the CCD 40, and the return mirror. When 39 leaves the optical path, the reflected light from the fundus is incident on a CCD (imaging means) 41 that is at a position almost conjugate with the fundus and is sensitive to visible light, and the fundus is photographed by the CCD 41.

  As shown in FIGS. 2A and 2B, the photographing aperture 28 is provided with two rectangular openings 28a and 28b. The photographing aperture 28 is disposed such that the openings 28a and 28b are decentered with respect to the optical axis 26 and are symmetric with respect to the optical axis 26, and are substantially conjugate with the anterior eye portion (pupil) of the eye to be examined. .

  The positions and sizes of the openings 28a and 28b are set so that the opening 23a of the perforated total reflection mirror 23 includes the entire openings 28a and 28b.

  The apertures 28a and 28b of the photographing aperture 28 are opened or closed by shutter plates 29 and 30 moved along guides 28c and 28d, respectively.

  For this opening and closing, switching means comprising rotary solenoids 31 and 32 is provided. When the rotary solenoids 31 and 32 are not energized, the shutter plates 29 and 30 are at the position of FIG. , 28b are opened.

  On the other hand, when the rotary solenoids 31 and 32 are energized, the rods 31a and 32a of the rotary solenoids 31 and 32 rotate, and the other ends of the rods 31a and 32a are connected to pins 29a and 30a provided on the shutter plates 29 and 30, respectively. Engagement causes the shutter plates 29 and 30 to move inward to close the openings 28a and 28b.

  Note that reference numeral 33 in FIGS. 2A and 2B denotes an optical fiber for forming a working distance index (WD index).

  In the above configuration, the fundus image captured by the CCD 40 is input to the control calculation unit 60 configured by a CPU or the like, and the image is displayed on the monitor 62 as a moving image. The examiner (operator) can see the image displayed on the monitor 62 and perform operations such as alignment and focus adjustment as will be described later. Further, a stereo monitor 63 is provided as a stereoscopic display, and the examiner can stereoscopically view the fundus image by observing the left and right images through the stereo monitor 63.

  The display method of the stereo monitor 63 includes various methods such that the polarization direction and display color are different between the left and right stereo images, and the left and right stereo images are independently observed through an observation scope that separates the left and right visual fields. However, the display method of the stereo monitor 63 according to the present embodiment is arbitrary, and any display device can be used as long as the left and right parallax images can be observed independently by the left and right eyes of the examiner. A stereo display system can be used.

  Further, the fundus illuminated by the strobe 15 when the shutter switch 66 is operated can be photographed as a still image by the CCD 41. This fundus image is temporarily stored in the high-speed memory 61 and recorded on a recording means realized by a low-speed hard disk (HDD) 64 as an external recording device via the control calculation unit 60, or a monitor 62 and a stereo monitor 63. Is displayed.

  Also, input means such as a keyboard 67 and a mouse 68 are provided, and various data can be input via these input means.

  Further, the fundus camera is provided with a control unit 65 composed of a CPU or the like. The control unit 65 is connected to the control calculation unit 60 and exchanges signals with each other. When the shutter switch 66 is operated, the control unit 65 returns. The mirror 39 is removed from the optical path, and the strobe 15 is caused to emit light with an appropriate amount of light. The control unit 65 controls insertion / removal of the variable magnification lens 38a and the like into the optical path, and controls driving of the rotary solenoids 31 and 32 described above.

  Further, the fundus camera is provided with an operation unit (operation panel) 69, and a shooting mode can be selected by the operation unit 69. Further, a left / right eye detection unit 70 for detecting whether the subject eye to be photographed is the left eye or the right eye is provided, and information on whether the left eye or the right eye is detected by the left / right eye detection unit 70 is input to the control unit 65. The

  Here, an outline of stereo imaging of the fundus of the eye to be examined in the above configuration will be described.

  First, at the time of observation, the observation lamp 11 is turned on, and the illumination diaphragm 19 is inserted into the optical path. The rotary solenoids 31 and 32 are driven to the positions shown in FIG. 2A, whereby the two openings 28a and 28b of the photographing aperture 28 are in the open positions. Reflected light from the fundus of the subject's eye irradiated with infrared light through the illumination diaphragm 19 is received by the observation CCD 40 through the openings 28a and 28b of the imaging diaphragm 28, and the fundus image is displayed on the monitor 62. .

  In this state, alignment and focusing with the eye to be examined are performed. At this time, alignment and focusing operations of the examiner are supported by a target projection system (not shown).

  When the alignment and focusing are completed, the examiner presses the shutter switch 66. In response to this operation, the control unit 65 drives the rotary solenoid 31 to move the shutter plate 29 to the right, and closes the opening 28a on the left side of the photographing aperture 28. The strobe 15 emits light in synchronization with the operation of the shutter switch 66, and the return mirror 39 leaves the optical path, so that the light flux from the fundus illuminated by the strobe passes through the opening 28b of the photographing aperture 28 that is open. The light enters the image receiving surface of the CCD 41, and the first fundus image for stereoscopic viewing is captured as a still image by the CCD 41 and stored in the memory 61.

  Subsequently, the rotary solenoids 31 and 32 are controlled to move the shutter plates 29 and 30 to the left, and when the opening 28a is opened and the opening 28b is closed, the strobe 15 is caused to emit light again. At this time, the second fundus image for stereoscopic viewing that has passed through the opening 28 a is captured as a still image by the CCD 41 and stored in the memory 61.

  In this way, two parallax images photographed from two left and right viewpoints in succession by one shutter operation, that is, stereo photography, are the positions of the aperture of the photographing aperture that is open, the left position, and the right position. (Information indicating at least one of the left and right parallax images) is stored in the HDD 64 from the memory 61.

<3D image processing>
An example of three-dimensional image processing that can be performed in the above configuration will be described with reference to FIGS. 3, 4, and 5.

  FIG. 5 shows the overall flow of image processing executed by the control unit 65 including the CPU of this embodiment. The control procedure of FIG. 5 can be stored in the ROM unit of the control calculation unit 60 or the HDD 64 as a program executed by the control calculation unit 60, for example.

  In this embodiment, these parallax images 121 and 122 are read from the HDD 64 (step S101 in FIG. 5).

  In steps S106 to S108 and S109, a parallax amount calculation and a depth amount (Z coordinate) calculation process between the left and right parallax images of the stereo imaged fundus blood vessel are performed. This parallax amount calculation processing is as follows.

  First, for example, a region of interest of 15 × 15 pixels centered on a point of interest for obtaining the amount of parallax in the L image is set (FIGS. 3A and 3B). Then, a region having the highest correlation with the region of interest (15 × 15 pixels: FIG. 3C) of the L image is searched from the R image (FIG. 3D).

  At this time, since it takes a calculation time to search from the entire image, the search area is limited to 20 × 20 pixels. That is, the search is performed in the range of 20 × 20 pixels in the R image with the point for obtaining the parallax amount of the L image as the center.

  The attention points for obtaining the amount of parallax are all points in the L image, and the region having the highest correlation in the R image is searched for each point. However, instead of searching for each pixel, for example, about 4 pixels Searches may be performed at intervals.

  Then, the center point of the region in the R image having the highest correlation with the region of interest in the L image is extracted as a corresponding point in the R image corresponding to the point of interest in the L image.

  Such detection of corresponding points in the R image is executed for all pixels in the L image, and the obtained pairs of attention points and corresponding points are stored in a memory as matrix data. In this case, two matrix data are prepared: a table for reading the corresponding point of the R image from the pixel address of the target point of the L image, and a table for reading the corresponding point of the L image from the pixel address of the target point of the R image. You may make it keep.

  Note that the L image (pixels) and the R image (pixels) are interchangeable in the corresponding point extraction process and the parallax amount measurement process described below.

  Further, the shift in the position of the region in the R image that has the highest correlation with the region of interest in the L image can be obtained as parallax (the number of parallax pixels). In this way, one amount of parallax is calculated for each point of interest, and the depth (Z coordinate) of a specific part of the fundus can be obtained based on the amount of parallax.

  From the actual amount of parallax on the retina (fundus) of a specific pixel or specific part, the depth of the specific pixel or specific part (or the coordinate value in the z-axis direction parallel to the optical axis) is Can be obtained in this way.

That is, in specific imaging, the depth amount (depth or coordinates in the z-axis direction) Zc of a specific part is the focal length of the eye to be examined, the imaging distance, the positions of the stops 28a and 28b (right and left optical path difference: parallax), etc. From the parallax angle inside the eye to be examined determined by the above condition and the parallax amount on the fundus of the specific part, using the principle of triangulation as shown in FIG. 4, Zc = (parallax amount / 2) / tan (parallax angle / 2) (1)
It can be asked.

  For example, if the parallax angle in specific imaging is assumed to be 8 degrees, when the parallax amount on the fundus of the specific part is calculated to be, for example, 0.1 mm by the above calculation, the depth amount (depth, Or, the coordinate in the z-axis direction) Zc is calculated as 0.715 mm (relative amount from the part where the parallax amount is 0) by the equation (1).

  As described above, a set of three-dimensional coordinate values (x, y, z) constituting the fundus can be obtained, and based on this, a three-dimensional model of the fundus can be created (step S111). Here, for example, a CG image that can be stereoscopically viewed on the stereo monitor 63 can be generated from the three-dimensional coordinate values, and the depth of the depression of the optic disc that is important in the diagnosis of a specific part of the fundus, particularly glaucoma. Can be output by display or printing.

  Note that the parallax angle used for the calculation of the depth amount largely depends on the focal length of the eye to be examined. Conventionally, the focal length of the eye to be examined is calculated by using the parallax angle of Expression (1) using other conditions such as optical path differences as a fixed value (for example, 16.8 mm). In this way, the focal length of the eye to be examined is estimated from the actual values of the eye to be examined, such as the corneal curvature of the eye to be examined, the geometry of the eye to be examined, and the diopter of the eye to be examined. Can be done. Hereinafter, a method for estimating the focal length of the eye to be examined will be described.

<Estimation of focal length of eye to be examined>
The three-dimensional coordinate measurement method described above is one of the basic measurement methods known so far. However, as described above, conventionally, the three-dimensional coordinate measurement method does not consider individual differences of the eye to be examined. In the calculation of dimensional information, the generally known average focal length of the human eye is often adopted for all eyes to be examined.

  Conventionally, in the case of a fundus camera, the shooting distance is adjusted to a specific working distance by alignment before shooting, and the parallax angle (8 degrees in the above example) determined by the positions of the stops 28a and 28b is assumed to be constant. A dimension measurement process is performed. In this respect, the conventional three-dimensional measurement processing described above has a problem that individual differences of the eye to be examined are not taken into consideration.

  That is, in the example of FIG. 4, the parallax angle at the part where the parallax amount is 0 (usually the part of the fundus of the eye to be inspected through the imaging optical axis) is described as 8 degrees for convenience, but this angle is determined by the left and right stops 28a. , 28b, the distance between the left optical path and the right optical path, and the focal length of the eye to be examined.

  For example, FIG. 10 shows a case where the distance between the left optical path and the right optical path, which are two optical paths for stereo imaging, is 2.0 mm, and the focal length of the eye to be examined is a fixed value f = 16.8 mm as in the past. In this case, the angle of the light beam that passes through the left optical path and the right optical path and passes through the center of the optical axis, ie, the parallax angle Sa, is 6.81 degrees from the tan calculation.

  For example, as shown in FIG. 11, if there is a depression with a depth ed in the fundus, the left optical path and the right optical path do not intersect with each other, and a parallax amount corresponding to the depression depth ed is generated. As a result, the specific part in the recess is photographed with a specific amount of parallax on the right parallax image 121 and the left parallax image 122 respectively captured by the CCD 41.

  Here, from the corresponding point search shown in FIG. 3, the same point (121a, 122a) on the fundus is photographed as shown in FIG. 12 on the right parallax image 121 and the left parallax image 122 photographed by the CCD 41, respectively. Suppose that it was done. In FIG. 12, the left optical path and the right optical path indicated by broken lines correspond to the left optical path and the right optical path inside the eye to be examined in FIG. 10, and the right parallax image 121 and the left parallax image 122 are shown at conjugate positions on the object point side for convenience. It is. If the right and left parallax amounts Sd on the screens of the right parallax image 121 and the left parallax image 122 correspond to the parallax amount Sd in FIG. 11 and the value is 0.02 mm, the calculation of the equation (1) causes The depth ed of the recess is calculated as ed = 0.336 mm.

  However, as shown in FIG. 10, the parallax angle of 6.81 degrees is merely obtained by calculation with the focal length of the eye to be inspected as a fixed value f = 16.8 mm. However, the depth ed of the recess (and therefore the Z coordinate among the three-dimensional coordinates, in particular) is not necessarily obtained correctly.

  Therefore, in the present embodiment, a technique for accurately estimating the focal length of the eye to be examined and accurately obtaining a three-dimensional coordinate of a predetermined portion of the eye to be examined, particularly the fundus is presented.

  Here, a calculation example for estimating the focal length of the eye to be inspected using the optical structure model of the human eye in FIG. 6 will be described.

  In FIG. 6, the first surface sf1 is the cornea, the second surface sf2 is the front surface of the crystalline lens, the third surface sf3 is the rear surface of the crystalline lens, and the fourth surface sf4 is the retinal surface, and each surface is R1, R2, R3, respectively. Assume that the radius of curvature is R4. The distances between the first surface sf1 to the fourth surface sf4 are D12, D23, and D34, respectively, and the refractive indexes between these surfaces are N12, N23, and N34.

  Among the above, the first surface sf1 is a convex surface when viewed from the left, and the curvature R1 is equal to the corneal curvature. Since the curvature R1 depends on the individual difference of the eye to be examined, it is measured in advance with a keratometer (corneal curvature meter) or the like.

  The second surface sf2 is a convex surface as viewed from the left, and the curvature R2 is determined by the refractive power as a variable depending on the individual difference of the eye to be examined. The curvature R2 of the second surface sf2 (front surface of the crystalline lens) is difficult to actually measure, and is an important factor for determining the focal length f of the eye to be examined. The curvature R2 is first estimated from the diopter, and then the focal length is estimated by paraxial calculation.

  The third surface sf3 is a concave surface as viewed from the left, and the curvature R3 is R3 = −R2 / 1.65. The fourth surface sf4 is concave when viewed from the left, the curvature R4 is R4 = -12.0 mm, the surface distance D12 between the first surface sf1 and the second surface sf2 is a fixed value of about 3.6 mm, and the refractive index N12 is about 1. 337, the surface distance D23 between the second surface sf2 and the third surface sf3 is a fixed value of about 4.2 mm, the refractive index N23 is about 1.42, and the surface distance D34 between the third surface and the fourth surface is D34 = [eye Axial length] -D12-D23 and the refractive index N34 is about 1.336.

  Here, [Axial length] corresponds to D12 + D23 + D34 in FIG. 6 and also depends on the individual difference of the eye to be examined, and uses a value measured in advance by ultrasonic echo (or CT scan or MRI). Here, for ease of explanation, D12 and D23 are fixed values, but of course, values measured by ultrasonic echo (or CT scan or MRI) may be used. With respect to other eye geometry (for example, the curvature (R4) of the retina (sf4)), an actual measurement value directly measured by an ultrasonic echo (or CT scan or MRI) may be used.

  Furthermore, in order to estimate the focal length via the curvature R2 of the lens front surface (sf2), it is necessary to perform ray tracing by a computer. In this case, diopter conditions are necessary, but the diopter of this eye to be examined is required. For, a value measured in advance with a refractometer (ophthalmoscope) or the like is used.

  In summary, the following conditions are used for measuring the focal length of the eye to be inspected (values obtained by actual measurement of the eye to be inspected are indicated with []).

R1 = [corneal curvature]
R2 = variable R3 = −R2 / 1.65
R4 = -12.0 mm (fixed value but may be measured)
D12 = 3.6 mm (fixed value but may be measured)
D23 = 4.2 mm (fixed value but may be measured)
D34 = [Axial length] -D12-D23
N12 = 1.337
N23 = 1.42
N34 = 1.336
Object distance = -1000mm / [Diopter]
With such an optical model, ray tracing is performed using a computer or the like, and the fourth surface is used as an image surface to search for an optimum value of the curvature R2 that is most focused on this image surface. When the curvature R2 is determined, all numerical values are determined and the optical model is determined by the above calculation, and the focal length f of the eye to be examined can be calculated by paraxial calculation.

  In the above example, the corneal curvature R1 of the eye to be measured measured with a keratometer, the geometry of the eye to be measured (such as the axial length, or D34, D12, D23, etc. determined by it), a refractometer, etc. The focal length f of the eye to be examined is obtained from the measured diopter of the eye to be examined. Conditions such as the corneal curvature R1, the diopter of the eye measured by a geometric refractometer of the eye measured by ultrasonic echo, etc. are not actually measured every time stereo imaging and three-dimensional coordinate measurement are performed. A value measured in advance may be recorded in a database or the like and introduced into the measuring apparatus of FIG. 1 via a network or the like.

  Needless to say, if the curvature R2 of the front surface of the lens can be measured by MRI or the like, the focal length f of the eye to be examined can be calculated by paraxial calculation without the need for ray tracing.

<Parallax calculation using the focal length of the eye to be examined>
Here, the parallax calculation using the focal length of the eye to be examined obtained as described above will be described with reference to FIGS.

  Based on the above calculation method, first, the focal length is estimated (calculated) from the diopter, corneal curvature, and axial length of the eye to be examined, and the parallax angle (Sa: FIG. 8) is obtained. This calculation may be performed at any timing in the flowchart of FIG. 5 as long as it is before step S109 in which the value of the parallax angle is required.

  Here, it is assumed that these pieces of eye information measured in advance (or recorded in a database or the like) have a diopter = −4.0 diopter, an axial length L2 = 25.0 mm, and a corneal curvature 7.9 mm.

And said R1 = 7.9, R2 = variable, R3 = -R2 / 1.65, R4 = -12.0, D12 = 3.6, D23 = 4.2, D34 = 25.0-3. In the calculation model of 6-4.2 = 17.2, N12 = 1.337, N23 = 1.42, N34 = 1.336 object point = −1000 / (− 4.0) = 250,
This condition is input to the model eye, the luminous flux emitted from the object point is put into the model eye, and the radius of curvature of R2 that gives the best focus on the fundus is calculated. As a result, R2 = 9.265 is calculated, and R3 = −9 .265 / 1.65 = −5.615. The shape of the model eye in this state is as shown in FIG. In FIG. 7, the eye to be examined is schematically shown by the first surface sf1 to the fourth surface sf4, and the paraxial focal distance of this model eye is calculated to be 16.01 mm.

  In FIG. 8, as in FIGS. 10 and 11, the left-right distance of the entrance pupil of the stereo fundus camera is set to 2.0 mm, and as a result of photographing the eye to be examined here, the parallax amount at the same point of the stereo image Is 0.02 mm on the retinal surface.

  In FIG. 8, assuming that the focal length of the eye to be examined is f = 16.01 mm calculated as described above, in this case, the fundus passes through the left optical path and the right optical path, which are two optical paths for stereo imaging, and passes through the center of the optical axis. The angle of the light beam focused at the center of Exr, that is, the parallax angle Sa is 7.15 degrees from the tan calculation.

  When the parallax angle Sa = 7.15 degrees and the parallax amount Sd on the left and right parallax images is 0.02 mm, the depth ed of the recess is calculated as ed = 0.320 mm by tan calculation. .

  According to the conventional calculation method shown in FIGS. 10 and 11, in the eye shown in FIG. 7, the depth ed of the recess is ed = 0.336 mm, and an error of 0.016 mm has occurred. I understand.

  In the actual calculation, prior to the processing of FIG. 5, the focal length of the eye to be examined is obtained as described above, and based on this, the parallax angle Sa used for the depth calculation is obtained, and this parallax angle Sa is obtained in the step of FIG. What is necessary is just to use by the depth calculation by Formula (1) in S109.

  As described above, according to the present embodiment, the corneal curvature R1 of the eye to be measured measured by a keratometer, the geometry of the eye to be measured by an ultrasonic echo or the like (the axial length, or D34, D12, D23 determined thereby). Etc.), the focal length f of the actual eye to be examined is obtained using conditions such as the diopter of the eye to be measured measured by a refractometer and the like, and based on this, a predetermined region of the eye to be examined, particularly the eye fundus of the eye to be examined is obtained. The three-dimensional shape can be accurately measured, and an accurate ophthalmologic diagnosis can be performed from the measured three-dimensional shape.

It is explanatory drawing which showed the structure of the retinal camera as an image processing apparatus which employ | adopted this invention. It is explanatory drawing which showed the structure around the imaging | photography diaphragm of FIG. It is explanatory drawing which showed the mode of the corresponding point extraction process in the apparatus of FIG. It is explanatory drawing which showed the parallax amount measurement process performed in the apparatus of FIG. It is the flowchart figure which showed the three-dimensional measurement process of the eye to be examined in the apparatus of FIG. It is explanatory drawing which showed the optical model of the eye to be used used in the apparatus of FIG. It is explanatory drawing which showed typically the measurement optical system containing the eye to be used used in the apparatus of FIG. It is explanatory drawing which showed the parallax amount measurement process of the eye to be examined performed in the apparatus of FIG. It is explanatory drawing which showed the depth amount measurement process of the to-be-examined eye performed in the apparatus of FIG. It is explanatory drawing which showed the parallax amount measurement process of the conventional eye to be examined. It is explanatory drawing which showed the depth amount measurement process of the conventional eye to be examined. It is explanatory drawing which showed the amount of parallax on the picked-up image by stereo imaging | photography.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fundus camera 24 Objective lens 28 Imaging stop 28a, 28b Aperture 35 Focusing lens 36 Imaging lens 62 Monitor 63 Stereo monitor

Claims (3)

In an image processing method for performing stereo imaging of a subject's eye fundus with a predetermined parallax via a fundus imaging optical system, and performing three-dimensional shape measurement processing of the subject's eye fundus using the obtained left and right parallax images,
Estimating the focal length of the eye to be examined;
Obtaining a parallax angle formed by two optical paths of stereo imaging in the eye to be examined at the time of stereo imaging from the estimated focal length of the eye to be examined and parallax conditions of the imaging optical system;
Obtaining the amount of parallax in the fundus of the eye to be examined taken in the left and right parallax images taken in stereo;
Measuring the depth of the specific part using the parallax angle and the parallax amount of the specific part;
An image processing method comprising:   2. The image processing method according to claim 1, wherein in the step of estimating the focal length of the eye to be inspected, the diopter, the axial length, and the corneal curvature measured from the eye to be inspected are used from the cornea, the lens, and the retina. An image processing method comprising: performing ray tracing in an optical model of the eye to be examined, estimating a curvature of the lens, and further estimating a focal length of the eye by paraxial calculation using the estimated curvature of the lens.   An image processing apparatus comprising: a fundus photographing optical system for performing the image processing method according to claim 1; and image processing means.

Images