JP2009178174A - Ophthalmologic measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ophthalmologic measuring apparatus capable of measuring the accurate severity of dry eyes even with flicks. <P>SOLUTION: Illumination light is projected to a lacrimal fluid layer on a cornea of an eye to be examined. The lacrimal fluid layer is imaged by a CCD camera 14, and the image is processed to compute the vertical moving amount of the lacrimal fluid layer. A fixation bright point projected on the cornea by a fixation light source 12 is imaged by the CCD camera 10 to obtain the fixation moving amount of the eye to be examined. The moving amount of the lacrimal fluid layer is corrected based on the fixation moving amount, and a value indicating the amount of lacrimal fluid stored in the eye to be examined is determined from the rate of temporal change of the corrected moving amount of the lacrimal fluid layer. With this constitution, a symptom of the dry eye even in a moderate dry eye state can be quantified with high reliability even with flicks during measurement. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ophthalmic measurement apparatus, and more particularly to an ophthalmic measurement apparatus that quantitatively measures the severity of dry eye.

  In recent years, the number of dry eye patients has increased due to an increase in the number of VDT (visual display terminal) workers and the drying of rooms by air conditioning. Dry eye may cause corneal epithelial disorder, conjunctival disorder, and various other eye disorders. Dry eye diagnosis is an important theme in ophthalmologic diagnosis.

  Conventionally, dry eye was diagnosed by a vital staining test, a tear secretion test using a Schirmer test, etc., but suffering from the subject was unavoidable due to drug instillation and foreign object contact. Therefore, in order to detect dry eye in a non-contact manner, a method of observing color interference fringes (interference patterns) in the tear film by irradiating the eye to be examined with coherent light has been attempted. With these devices, the interference pattern formed by the tear fluid layer of the eye to be examined is imaged, displayed on a monitor and observed to know the state of the tear fluid layer, and a simple diagnosis of dry eye is performed. Yes.

  Further, in order to quantitatively evaluate the severity of dry eye, the strength of the interference pattern of the tear fluid layer is measured, and a value indicating the severity of dry eye is calculated from the measured value (Patent Document 1). Alternatively, by setting a plurality of areas in the image of the interference pattern and evaluating the tear surface layer based on the hue of each area (Patent Document 2), or analyzing the temporal change of the hue of the interference fringe, Diagnosis is performed (Patent Document 3). As another example of identifying dry eye from such interference patterns, color images of interference patterns formed by the tear film of the eye to be examined are taken, the color image is decomposed into color components, and each color component is determined. The progress of dry eye is determined based on the number of interference fringes or the change in signal level thereof (Patent Document 4).

  Also, instead of judging the dry eye from the interference pattern, the change over time in the dry spot area that occurs when the tear film is crushed after the eye is opened is grasped as the change over time in the area ratio data of the dry spot area. In addition, a change in the dry spot area over time is displayed on a monitor to examine abnormal stability of dry eye tears (Patent Document 5). Furthermore, quantification of dry eye is performed by applying a tracer to the eye to be examined and measuring the movement of the instilled tracer (Patent Document 6).

  Further, it has been described that the stretch state of the tear fluid layer after blinking in a dry eye patient can be well approximated by the Voit model and is related to the tear fluid accumulation amount (Non-patent Document 1). Furthermore, a rectangular observation region is set in the captured oil layer image, and a rectangular region that most closely matches the oil layer image of the observation region is recognized from the oil layer image after a certain time by using the correlation method, and the vertical direction of the region is recognized. The initial velocity of oil layer extension in the vertical direction is obtained from the amount of displacement using a Voit model, and the relationship between this initial velocity and the lacrimal meniscus radius of curvature has been studied (Non-Patent Document 2).

Further, if the fixation state of the eye to be examined changes, reliable ophthalmic examination or measurement cannot be performed. Therefore, the captured image is corrected from the movement state of the fixation (Patent Document 7), or the pupil moves. However, stable wavefront correction is performed to measure the optical characteristics of the eye to be examined, or a fundus image is formed (Patent Document 8).
JP 2000-287930 A Japanese Patent No. 3556033 Japanese Patent No. 3718104 JP 2005-211173 A Japanese Patent No. 3699853 JP 2006-314651 A JP 2006-61328 A JP 2006-6362 A Frontiers in Dry Eye 2006.10 Vol.1 No.1 20,21 Medical Review The 31st Corneal Conference, The 23rd Annual Meeting of the Japan Corneal Transplant Society Program and Abstracts Collection, February 9, 2007, page 38 "1. Development of an automated analysis method for tear film fluid dynamics by correlation method and its clinical application"

  Conventionally, the method of measuring the severity of dry eye by examining the extension state of the tear fluid layer in the subject's eye has been known for severe dry eye (referred to as Grade 4) because the boundary of movement of the oil layer was clearly known. The area was automatically identified and the oil layer area could be calculated. However, with regard to moderate dry eyes (referred to as Grades 2 and 3), a clear boundary of the oil layer does not appear, so that conventional methods cannot cope with it. Incidentally, this method of measuring the area of the oil layer was impossible to manually draw a boundary surface from the image.

  Further, as can be seen in Patent Document 6 and Non-Patent Document 2, in the dry eye determination method that focuses on the amount of movement of the tear oil layer, when the subject's eye is fixed, the subject's eye is moved (fixed eye movement). Then, there is a problem that accurate measurement cannot be performed because the amount of fixation movement is reflected in the amount of movement of the oil layer.

  The present invention has been made to solve such problems, and it is possible to accurately measure the severity of dry eye even in a moderate dry eye state or in the presence of microscopic fixation. It is an object of the present invention to provide an ophthalmic measurement apparatus.

The present invention
An optical system that projects illumination light onto the tear fluid layer on the eye cornea;
An oil layer imaging means for receiving reflected light from the tear fluid layer and imaging the tear fluid layer;
An arithmetic processing means for processing the image of the taken tear film and calculating the amount of movement of the tear film on the cornea;
Detection means for detecting the amount of fixation movement of the eye to be examined,
Based on the detected amount of fixation movement, the amount of movement of the tear fluid layer is corrected, and the time change rate of the corrected amount of movement of the tear fluid layer is determined to indicate the amount of tear fluid stored in the eye to be examined. It is characterized by that.

  In the present invention, when performing measurement while fixing the eye to be examined, the amount of movement of the eye to be examined (the amount of fixation movement) is detected when the eye to be examined is moved, and tear fluid is detected based on the detected amount of fixation fixation. Since the amount of movement of the oil layer is corrected to determine the rate of change in the amount of movement of the tear oil layer over time, dry eye can be reliably measured even when there is slight eye movement during measurement or in moderate dry eye conditions. The symptoms of can be quantified.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows a schematic configuration of an ophthalmologic measuring apparatus according to the present invention. In the figure, what is indicated by reference numeral 1 is a white light source for illuminating the eye E, and is constituted by a halogen lamp or the like. The light emitted from the white light source 1 passes through the mask 2 that restricts the illumination visual field, and then passes through the lens 3, the half mirror 4, the lens 5, the variable power lens 6, the half mirror 7, and the objective lens 8 on the eye E. The predetermined point P is illuminated. The position of the point P is selected in the tear film on the cornea of the eye E to be examined. Note that the amount of light of the white light source 1 can be adjusted by a dimming circuit (not shown).

  The reflected light from the point P forms various interference patterns depending on the thickness and other states of the tear film oil layer (also referred to as a liquid film) as the uppermost layer of the tear film. The reflected light from the tear oil layer enters the objective lens 8 and is received by the color CCD camera (oil layer imaging means) 10 through the half mirror 7, the variable magnification lens 6, the lens 5, the half mirror 4, and the lens 9. The tear oil layer is imaged as a color image (RGB image) by the CCD camera 10.

  In FIG. 1, a portion surrounded by a one-dot chain line on the upper right side constitutes a dry eye optical system. In the present invention, in order to measure the fixation fine movement of the eye E, an optical system for observing and photographing the fixation is provided separately from the dry eye optical system. This fixation optical system has a fixation light source 12 composed of a visible light emitting diode (LED) or the like. A light beam from the fixation light source 12 is reflected by half mirrors 13 and 7, and the objective lens 8 is used for the eye E to be examined. Projected as bright spots in the form of dots on the cornea. The reflected image of the bright spot passes through the objective lens 8, is reflected by the half mirror 7, passes through the half mirror 13, and is picked up by a CCD camera (fixed image pickup means) 14 for fixation observation imaging.

  The images of the CCD cameras 10 and 14 are captured as still images by the video capture units 21 and 22 in synchronization with the frame rate from the video synchronization signal circuit 15, respectively. ) It is input to 23 frame memories 23a and 23b and stored therein. These images are displayed on the display monitor 24 and are subjected to image processing by the arithmetic processing unit 23, and the movement amount and fixation movement amount of the tear fluid layer are calculated as will be described later.

  Next, an operation when measuring symptoms of dry eye in the apparatus configured as described above will be described.

  The light source 1 is turned on to illuminate the cornea of the eye E, and the LED light source 12 is turned on to fix the eye to be examined. With the fixation fixed, the eye to be examined is blinked, and the tear oil layer on the cornea is imaged by the CCD camera 10 after opening the eye.

  FIG. 2 shows a captured image, 2a shows an image of the mask 2, 31 shows an image of the cornea, and 30 shows a tear oil layer. The tear oil layer 30 forms an interference pattern by interference of reflected light on the front surface and the back surface, and extends and moves as shown in FIGS. 2A to 2B after opening the eye. In this embodiment, dry eye symptoms are quantified by formulating the relationship between the amount of movement of the tear fluid layer after blinking and time.

  In order to determine the amount of movement of the tear fluid layer, an image of the tear fluid layer captured by the CCD camera 10 is acquired by the video capture unit 21 and stored in the frame memory 23a. In FIG. 2, A indicates a measurement area having a predetermined size, and the amount of movement Δy in the vertical direction of the image in the measurement area A is obtained.

  FIG. 4 shows how to determine the amount of movement. A measurement area A having a size of xw pixels × yw pixels is set in the start image (image of frame n; corresponding to FIG. 2A) at the time t after opening the eye. Subsequently, at the time point t + 1, the tear fluid layer is imaged and similarly stored in the frame memory 23a as an image of the frame n + 1 (corresponding to the image of FIG. 2B). At this time, the calculation target area B is set as shown on the right side of FIG. The size is set to a size obtained by enlarging −xa pixel, + xa pixel in the X direction, −10 pixel in the Y direction, and + ya pixel so as to cover an assumed movement range of the measurement area A. Is done.

  In order to obtain an image closest to the image in the measurement area A in the calculation target area B, the image in the calculation target area B is sequentially scanned in the x and y directions with the image in the measurement area A, and the correlation is examined. A position where the sum of the difference of values is minimized, that is, a position where the correlation is highest is obtained. If you formulate this,

となる。ｎは画像のフレーム番号であり、撮像される時点でもある。Ｇｎ、Ｇｎ＋１は、それぞれフレームｎ、ｎ＋１の画像の括弧内に示した座標位置での輝度値を示す。ｍｉｎはその最小値を示す。

It becomes. n is the frame number of the image, and is also the time when the image is taken. Gn and Gn + 1 indicate the luminance values at the coordinate positions indicated in parentheses of the images of frames n and n + 1, respectively. min indicates the minimum value.

  In FIG. 4, when an image 41 closest to the image 40 in the measurement area A is obtained at the illustrated position, the tear oil layer has a difference between the y coordinates of both images after the time point n + 1, that is, Δy (n) in the y-axis direction. It has moved in the (vertical direction).

  In this way, a fixed rectangular region (measurement area A) is set in the captured oil layer image, and a rectangular region that most closely matches the oil layer image of the rectangular region is obtained from the oil layer image after a predetermined time by using the correlation method. Thus, the amount of movement in the vertical direction of the oil layer image after a certain time can be obtained.

Thus, when Δy during the development of the tear fluid layer is added over time to obtain the total amount of movement H (t), it becomes as shown by the dotted line in FIG. As shown by the solid line,
H (t) = p [1-exp (−t / λ)]
It can be approximated as an exponential function. Here, p is a constant, t is time, and λ is relaxation time.

  The tear oil layer extends on the cornea after opening, but the extension state can be approximated by an exponential function as described above. Therefore, the tear oil layer is treated as a viscoelastic body, and its extension behavior (oil layer area, oil layer) Change with time) can be analyzed using a rheological model, that is, a Vogt model.

Analyzing the change in the amount of movement of the tear fluid layer in the vertical direction by applying it to the Forked model, the initial stretching speed of the tear fluid layer (time rate of change in the amount of movement of the oil layer at the time of opening mm / sec), that is, the above exponential function First derivative at time t = 0 of H ′ (0) = dH (0) / dt
Ask for.

  In JP-A-11-267102, the image magnification of the opening projected on the tear film surface is obtained, and the curvature radius R of the tear film surface (tear meniscus) along the lower eyelid edge is calculated from this image magnification, A method for evaluating the severity of dry eye from the radius of curvature R is described, and it has been found that this radius of curvature R is used as a value indicating the amount of tear fluid stored on the eye surface with high reliability.

  Therefore, the tear meniscus radius of curvature R (mm) is measured for each eye to be examined, and the relationship between the tear initial velocity H ′ (0) of the tear fluid layer is examined, and H ′ ( A significant positive linear correlation of [H ′ (0) = m × R−n] is recognized between 0) and R, where m and n are constants.

  From this, it can be seen that the tear oil layer stretches while exhibiting a behavior that can be approximated to the vault elastic body of the Forked model after opening, and that the initial stretching speed increases in proportion to the increase in the tear fluid storage amount. Therefore, in the present invention, the time change rate of the amount of movement of the tear fluid layer in the vertical direction at the time of opening (t = 0) is calculated, and this is used as a value indicating the amount of tear fluid stored in the eye to be examined. Use the quantification value to determine severity.

  In this way, in the present embodiment, attention is paid to the moving amount of the image shading pattern in the designated area, and therefore, it can be quantified even in a moderate dry eye state of grades 2 and 3.

  Here, since the measurement time for measuring the amount of movement of the tear fluid layer is about 5 to 10 seconds after opening the eye, the amount of movement of the tear fluid layer is disturbed when the subject's eye moves, including microscopic movements of the fixation. This is not the case with the Forked model. Therefore, as will be described below, the fixation fine movement is measured by the CCD camera 14, and the fixation movement amount is reflected in the oil film movement amount and calculated.

  Since the fixation light source 12 is turned on during measurement, the CCD camera 14 has a bright spot 50 by the fixation light source 12 projected onto the anterior eye portion (cornea) 51 of the eye to be examined, as shown in FIG. Imaged. The image of the CCD camera 14 is captured as a still image by the video capture unit 22 in synchronization with the image of the tear oil layer from the CCD camera 10 in accordance with the frame rate from the video synchronization signal circuit 15, and is captured in the frame memory 23b. It is input and stored there.

  When the eye to be examined moves, such as fixation fixation fine movement, the reflection direction of the luminescent spot 50 changes, so the position of the luminescent spot 50 is also moved by the movement of the eye to be examined. The arithmetic processing unit 23 obtains the center coordinates of the bright spot 50 in the frame memory 23b, and the amount of movement of the center position of the bright spot between the n and (n + 1) frames due to the movement of the eye to be examined in the horizontal and vertical directions. (Δ (n) xs, Δ (n) ys) is obtained and added to the above equation 1 to calculate the following equation. And

に従い、輝度値の差の総和が最小になる画像位置を求め、固視移動量に起因する涙液油層の移動量の補正を行う。そして、この補正された涙液油層の移動量の経時変化Ｈ（ｔ）を求め、その時間ｔ＝０における時間変化率を求めて、これを被検眼に貯留する涙液量を示す値とする。

Accordingly, the image position where the sum of the differences in luminance values is minimized is obtained, and the movement amount of the tear fluid layer due to the fixation movement amount is corrected. Then, a time-dependent change H (t) of the corrected amount of movement of the tear fluid layer is obtained, a time change rate at time t = 0 is obtained, and this is a value indicating the amount of tear fluid stored in the eye to be examined. .

  As a result, even if there is a fixation movement, the movement amount of the tear oil layer can be calculated by correcting the movement amount. It can be quantified with good quality.

It is the block diagram which showed schematic structure of the ophthalmic measurement apparatus of this invention. It is explanatory drawing which showed extension of the tear fluid layer. It is explanatory drawing which showed the fixation luminescent point projected on a cornea. It is explanatory drawing which showed the process of calculating | requiring the movement amount of a tear fluid layer. It is the diagram which showed the time-dependent change of the moving amount | distance of a tear fluid layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 14 CCD camera 12 Fixation light source 15 Video synchronous signal circuit 21, 22 Video capture unit 23 Arithmetic processing part 23a, 23b Frame memory 30 Tear oil layer 50 Fixation bright spot

Claims (3)

An optical system that projects illumination light onto the tear fluid layer on the eye cornea;
An oil layer imaging means for receiving reflected light from the tear fluid layer and imaging the tear fluid layer;
An arithmetic processing means for processing the image of the taken tear film and calculating the amount of movement of the tear film on the cornea;
Detection means for detecting the amount of fixation movement of the eye to be examined,
Based on the detected amount of fixation movement, the amount of movement of the tear fluid layer is corrected, and the time change rate of the corrected amount of movement of the tear fluid layer is determined to indicate the amount of tear fluid stored in the eye to be examined. An ophthalmologic measuring apparatus characterized by that.   The detection means is an imaging means provided separately from the oil layer imaging means, and is constituted by a fixation imaging means for capturing a reflected image of a bright spot projected on the anterior eye portion of the eye to be examined. Item 4. The ophthalmologic measurement apparatus according to Item 1.   The ophthalmic measurement apparatus according to claim 2, wherein the oil layer imaging unit and the fixation imaging unit capture a tear oil layer and a bright spot reflection image at the same frame rate, respectively.

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