JP4179606B2 - Photorefractor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photorefractor. More specifically, the present invention relates to a photoreflector for determining whether or not the diopter of an eye to be examined is within a preset range using a photorefractive method.
[0002]
[Prior art]
In the photorefractive method, illumination light is irradiated to the eye to be examined, and the refractive index (diopter) of the eye optical system is obtained from the ratio of reflected light from the fundus in the pupil. Specifically, the reflected light from the fundus that passes through the pupil is photographed with a camera, the ratio of the bright crescent diameter in the pupil in the radial direction of the pupil to the pupil diameter is detected, and the refractive error degree is calculated by the following theoretical formula (1). (For example, refer nonpatent literature 1).
[0003]
R = 1- {eL / 2r (A + L)} (1)
Here, R means the size ratio of the bright crescent in the pupil with respect to the pupil diameter, that is, D / 2r in FIG. D is the length of the bright crescent K in the pupil radial direction, and r is the radius of the pupil of the eye to be examined. A is the diopter (degree of refraction abnormality) of the eye to be examined, and e is the distance from the end 51a of the objective lens 51 of the camera to the illumination light source (strobe) 52. L is the reciprocal of the distance S between the eye to be examined and the objective lens 51 of the camera (L = 1 / S). Note that only one illumination light source 52 is provided.
[0004]
As described above, the ratio R of the bright crescent K varies depending on the degree of refractive error (diopter) A of the eye to be examined if other conditions are constant. That is, the diopter A of the eye to be examined is calculated by the following equation (2) from the bright crescent ratio R measured under a certain condition.
[0005]
A = {eL / 2r (1-R)}-L (2)
FIG. 15 shows an example of the relationship between the bright crescent K ratio R and diopter A thus obtained. In FIG. 15, the horizontal axis represents the diopter A (unit: diopter) of the eye to be examined, and the vertical axis represents the bright crescent ratio R (1.0 is 100%). As illustrated, according to the above formula, a diopter-incapable area I is generated. Crescents occur on both sides of this non-measurable area I, that is, on the positive side and the negative side of the diopter, but the direction in which these crescents appear in the pupil is opposite. In addition, the measurement accuracy decreases greatly as the absolute value of the diopter minus and plus increases.
[0006]
[Non-Patent Document 1]
Hiroshi Uori, “Photo-refraction Method”, Ophthalmology, Kanehara Publishing, 1991, Vol. 33, no. 12
[0007]
[Problems to be solved by the invention]
However, in the above method, since it is necessary to actually obtain the diopter of the eye to be measured accurately, high accuracy is required for detection of the pupil image, and the image processing calculation is complicated.
[0008]
Therefore, when performing a large number of tests in a short period of time, such as when performing eye diopter screening as part of a 3-year-old child health checkup, the work is expensive and the cost for that is high. In diopter screening, for example, a large number of ophthalmic subjects, such as those performed independently by local governments, are classified into normal eyes, follow-up observation eyes, and treatment eyes.
[0009]
The present invention has been made to solve the above-described problems, and does not require high accuracy in detection of the pupil image, and its image processing calculation is easy, and is suitable for screening diopter of the eye to be examined. It aims to provide a simple photorefractor.
[0010]
[Means for Solving the Problems]
The photoreflector of the present invention is
A plurality of illumination light sources that can be selectively lit to illuminate the eye to be examined;
An imaging optical system that has an objective lens and captures illumination light from the illumination light source reflected by the fundus of the eye to be examined;
Position detecting means for detecting a separation distance between the photographing optical system and the eye to be examined;
An image processing arithmetic unit for analyzing a photographed image by the photographing optical system;
An image determination unit,
The plurality of illumination light sources are installed at positions spaced apart from each other in the diameter direction from the end of the objective lens,
The image processing calculation unit detects the generation of bright crescent and the direction of the generated crescent in the pupil based on the captured image,
The image determination unit is configured to determine the diopter class of the eye to be inspected by comparing the detection result with a preset bright crescent direction and presence / absence criteria.
[0011]
With such a configuration, it is determined whether or not the bright crescent of the detected (calculated) eye is generated based on a predetermined criterion, and the direction in which the bright crescent is generated is the same as the preset direction or vice versa. The diopter class of the eye to be inspected can be determined by determining whether or not it occurs in the direction. Therefore, it does not specify an exact diopter value, but only determines the bright crescent for the pupil, for example, whether it is greater than or less than a predetermined reference value and the direction of the crescent, thus detecting the pupil image. Therefore, high accuracy is not required, and the image processing calculation is simple. Such a device facilitates diopter screening. In addition, since a plurality of illumination light sources that can be selectively lit are provided, the eye to be examined can be classified into three or more classes by performing the above determination for each illumination light source.
[0012]
In the image processing calculation unit,
Let e be the distance in the diameter direction from the end of the objective lens of the illumination light source, L be the reciprocal of the distance between the corresponding eye and the objective lens, r be the radius of the pupil, and A be the corresponding eye The diopter and the diopter between the size ratio of the bright crescent pupil diameter generated by the illumination of each illumination light source and the diopter, calculated by the following equation when R is the size ratio of the bright crescent pupil diameter of the eye. Set the relationship,
R = 1- {eL / 2r (A + L)}
Further, the minimum value of R as a reference value for determining the occurrence of bright crescent, and a reference diopter corresponding to the reference value are set.
The image determination unit can be configured to determine the presence or absence of a bright crescent by comparing the reference value with pixel scanning of the captured image.
[0013]
The image determination unit of the photoreflector can be configured to determine whether the diopter class of the eye to be examined is on the plus side or the minus side with respect to the reference diopter based on the determination result of the presence or absence of bright crescent.
[0014]
The value of R as the reference value is set to zero, and the presence or absence of bright crescents can be determined based on the presence or absence of light detection by pixel scanning of the captured image. When the R value as the reference value is set to a positive value, the scanning line passes through the detection light range during the pixel scanning and the light range corresponding to the reference value. It can be configured to determine whether or not there is a bright crescent by comparing with the reference time.
[0015]
In the image processing calculation unit,
By detecting the positional relationship between the image of the corneal apex reflected light and the bright crescent image of the eye to be examined by pixel scanning of the captured image,
In the image determination unit, a photoreflector configured to determine the appearance direction of a bright crescent in the pupil based on the detection result is preferable.
[0016]
It is preferable that the photographing optical system includes a Purkinje detection light source for irradiating the eye to be examined with detection light along the optical axis of the objective lens.
[0017]
The plurality of illumination light sources are arranged outward from one end of the objective lens, and the same number of corresponding illumination light sources are installed at point-symmetric positions around the illumination light source and the objective lens. And
The image processing calculation unit is configured to determine the appearance direction of the bright crescent in the pupil based on the change in the position where the bright crescent appears when the pair of point symmetric illumination light sources are sequentially turned on. The photoreflector according to claim 1.
[0018]
An attachment member for installing an illumination light source is provided, and the plurality of illumination light sources are installed on the attachment member, and the attachment member is configured to be detachably attached in the vicinity of the photographing optical system. A photorefractor is preferable. This is because the illumination light source can be easily replaced with a different arrangement.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the photoreflector of the present invention will be described with reference to the accompanying drawings.
[0020]
FIG. 1 is a block diagram schematically showing one embodiment of a photoreflector according to the present invention. FIG. 2A is a diagram illustrating a usage state of the handy type photoreflector, and FIG. 2B is a diagram illustrating a usage state of the installation type photoreflector. FIG. 3A is a front view showing the optical head in the photoreflector of FIG. 1, and FIG. 3B is a rear view thereof. 4A is a plan view of the optical head of FIG. 3, and FIG. 4B is a side view thereof.
[0021]
As shown in FIG. 1, the photoreflector 1 includes an optical head 2 that captures an eye E and an analysis device 3 that analyzes an image captured by the optical head 2. The optical head 2 may be of a handy type that is held by hand as shown in FIG. 2A, or may be installed on a gantry 4 as shown in FIG. Regardless of the type, the examiner takes an image while observing the eye E on the monitor screen 9 described later provided in the optical head 2. Then, the examiner operates an analysis device (for example, a personal computer) 3 connected to the optical head 2 to process and calculate the image photographed by the optical head 2 and to examine the eye E based on the processing calculation result. The diopter classification is made.
[0022]
The optical head 2 shown in FIGS. 3 and 4 is of the handy type described above, and includes a holding handle 5 that is held by hand. And the camera 6 which image | photographs a to-be-examined eye, the some illumination light source 7 for illuminating the to-be-examined eye E, and the distance meter for measuring the distance (measurement distance) between the camera 6 and the illumination light source 7, and the to-be-examined eye. 8, a monitor screen 9 for displaying a face including the anterior eye portion of the eye E to be photographed, and a fixation means 10 for the eye to be examined. The illumination light source 7 is a red LED that emits near infrared light. Although not shown, an operation start button, a shooting start button, or the like of the optical head 2 may be installed on the holding handle 5.
[0023]
The camera 6 includes an optical system 12 having an objective lens 11. The distance meter 8 is an ultrasonic distance meter, and has a transmitter 8a and a receiver 8b. Of course, other known distance meters may be used. The plurality of illumination light sources 7 are aligned at a predetermined distance in the diameter direction of the objective lens 11 from the central axis of the objective lens 11 (the optical axis 12a of the photographing optical system). As shown in FIG. 3A, in this embodiment, four illumination light sources 7 are installed. Among them, one light source 7 a is a distance of 1 mm from the edge of the objective lens 11, the other one light source 7 b is a distance of 4 mm from the edge of the objective lens 11, and the other one light source 7 c is the distance of the objective lens 11. The distance of 12 mm from the end edge and the remaining one light source 7 d are installed at a position of 16 mm from the end edge of the objective lens 11. Although the significance of this distance will be described later, when the reference value for classifying the diopter of the eye E is changed, it may be changed accordingly.
[0024]
Therefore, the distance is not limited. Further, the number of illumination light sources 7 may be increased when the diopter of the eye E is divided into more classes, and may be decreased when divided into fewer classes. For this purpose, it is preferable to provide a mounting plate 18 for installing a plurality of illumination light sources 7. The mounting plate 18 provided with a plurality of illumination light sources 7 is called an illumination light source unit. The attachment plate 18 has an opening through which the objective lens 11 of the camera 6 is exposed, and is detachably attached to the periphery of the objective lens 11. By doing so, it can be replaced with a mounting plate provided with a different number of illumination light sources 7 and a different number of illumination light sources 7 according to user specifications as will be described later.
[0025]
The monitor screen 9 uses a liquid crystal display panel. In this embodiment, the monitor screen 9 is installed on the back surface of the optical head 2, that is, on the surface opposite to the surface on which the objective lens 11 and the illumination light source 7 of the camera are installed. This is for the convenience of the inspector. Of course, you may install in another site | part as needed. The monitor screen 9 continuously displays subjects that are continuously photographed (such as the face of the subject including the eye E). In addition, the distance (measurement distance) between the eye E measured by the distance meter 8 and the objective lens and the fact that the measured distance is within a preset range are displayed. Further, the astigmatism power after inspection, astigmatism axis, eye position abnormality, and the like are displayed.
[0026]
In the case of the handy type optical head, the inspector performs alignment in the X direction and the Y direction between the optical head 2 held in the hand and the eye E while observing the monitor screen 9. Further, the optical head 2 is moved toward and away from the eye E to perform alignment in the Z direction. The Z direction is a direction of a straight line connecting the optical head 2 and the eye E, and is a direction perpendicular to both the XY directions. The alignment in the Z direction is performed by the signal from the distance meter 8 described above.
[0027]
Positioning of the installation type (FIG. 2B) optical head is performed as follows. First, the subject model is installed at a position away from the optical head by a predetermined distance, and an appropriate distance between the optical head and the model is set by a signal from the distance meter 8. During actual inspection, the subject is seated at the set distance from the optical head. Then, the position is adjusted by moving the optical head or the subject only when the predetermined range is deviated while confirming the display by the distance meter. For example, when the appropriate distance is set to 1 m, a deviation of about ± 10 cm has no problem in inspection.
[0028]
The fixation means 10 is for directing the visual axis of the eye E toward the objective lens 11 of the camera, but it is not necessary to strictly match the visual axis with the imaging optical axis 12a. Any device can be used as long as the face of the subject can be directed to the camera 6. Therefore, as the fixation means 10, a visible light LED, an electronic sound generator, or the like that can prompt the subject to gaze at the camera 6 can be adopted.
[0029]
The analysis device 3 determines the diopter class of the eye E to be compared with the processing / calculation unit 14 that performs image processing and various calculations of the image captured by the optical head 2 and a predetermined classification criterion. And input a determination unit 15 for processing, a recording unit 16 for recording processing calculation conditions, processing calculation results, determination results, classification setting criteria, image processing / calculation programs, and a display unit 17 for displaying at least the determination results. The input unit 13 is provided. Of course, the image of the eye E, the processing calculation result, the subject to be verified, the crescent measurement conditions, the determination criteria, and the like may be displayed. Further, the inspection result can be output by an output unit (not shown) such as a printer.
[0030]
Next, diopter classification procedures by the photoreflector 1 will be described. For this classification, it is necessary to determine whether or not a crescent appears, or whether or not the crescent is larger than a predetermined value. That is, there are a method of adopting a crescent size ratio of zero as a criterion and a method of employing a predetermined value of the dimension ratio. Furthermore, it is necessary to determine which side (direction) in the pupil Q the crescent appears. This is because in the eye to be examined having different diopters, the sides appearing with respect to one illumination light source are opposite to each other.
[0031]
First, as described above, the eye to be examined is photographed by the optical head 2 when the measurement distance is within a preset range. This photographing is performed by illumination from each illumination light source 7. Information on the type of captured image corresponding to the number of illumination light sources 7 is sent to the analysis device 3. The analysis device 3 scans the pixels of the image to detect the presence / absence and direction of the crescent. FIG. 5 shows the light detection status by this scanning. FIG. 5 shows a case where a crescent size ratio of zero is adopted as a classification criterion (related to FIGS. 7 and 8). In this case, the method is divided into a case where corneal apex reflected light (hereinafter referred to as a Purkinje image) P can be used and a case where it cannot be used.
[0032]
FIG. 5A shows a case where the Purkinje image P can be used, and FIG. 5B shows a case where the Purkinje image P cannot be used. In the figure, reference numerals A1 to A3 and B1 to B3 denote scanning lines, respectively.
[0033]
In FIG. 5A, when only the Purkinje image P is detected by scanning even though the illumination light source 7 is turned on (symbol A1 in FIG. 5A), it is determined that no crescent appears. Is done. When the Purkinje image P and other light are detected, it is determined that the crescent K appears. Which side of the pupil Q appears in the pupil Q can be determined from the relative positional relationship with the Purkinje image P.
[0034]
In this case, when the crescent K appears on the same side as the illumination light source 7 with respect to the Purkinje image P (symbol A2 in FIG. 5A), the diopter of the eye to be examined is on the minus side, and the illumination light source When it appears on the opposite side of 7 (symbol A3 in FIG. 5A), it is the plus side.
[0035]
The Purkinje image P and the crescent K can be easily distinguished by using a light source (purkinje detection light source 19, see FIG. 1) different from the illumination light source 7 described above. For example, a light source having a much smaller light quantity than the illumination light source 7 is used for Purkinje image detection. This is because the Crescent cannot be detected by the Purkinje detection light source 19 having a small amount of light. The detection light from the Purkinje detection light source 19 is applied to the anterior eye portion of the eye to be examined from the front through the objective lens 11. In addition, if the illumination light source 7 is blinked, the Purkinje image P and the crescent K can be more clearly identified.
[0036]
Under the condition that no Purkinje image is generated, a mounting plate 28 on which the illumination light source 7 is arranged is used as shown in FIG. The mounting plate 28 is provided with the illumination light source 7 shown in FIG. 3A being point-symmetrically (on the opposite side) with respect to the objective lens 11. That is, illumination light sources 7a, 7b, 7c, and 7d are installed at respective points spaced 1 mm, 4 mm, 12 mm, and 16 mm to the right from the right edge of the objective lens 11, and 1 mm from the left edge of the objective lens 11 to the left. Illumination light sources 7e, 7f, 7g, and 7h are installed at respective points separated by 4 mm, 12 mm, and 16 mm. In FIG. 5B, the illumination light sources 7a and 7e are arranged on both sides of the objective lens 11 at the lowermost stage.
[0037]
Under the condition that no Purkinje image is generated (FIG. 5B), when any of the illumination light sources 7 is turned on and no light is detected by scanning (reference numeral B1 in FIG. 5B), the crescent Can be determined not to appear. On the other hand, when light is detected, it can be determined that the crescent K1 has appeared. In order to determine which side in the pupil Q the crescent K is located, the illumination light source that is currently lit is turned off, and the illumination light source at the point target position with the objective lens interposed therebetween is turned on. For example, 7a is turned off and 7e is turned on. Then, the original crescent K1 disappears, and a new crescent K2 is generated on the opposite side of the pupil Q. By doing so, it can be determined on which side of the pupil Q the crescent appears. Also in this case, whether the diopter of the eye to be examined is positive or negative is determined by the change in the position of the crescent K accompanying the change of the illumination light source. That is, when the crescent K is displaced in the same direction as the change direction of the illumination light source 7 (reference numeral B2 in FIG. 5B), the diopter of the eye to be examined is negative, and the change direction of the illumination light source 7 is When displaced in the opposite direction (symbol B3 in FIG. 5B) is the plus side.
[0038]
On the other hand, the recording unit 16 records electronic information about the relationship between the diopter A and the crescent size ratio R shown in FIG. That is, the relationship between the diopter A obtained by calculation and the dimensional ratio R of the crescent according to the following theoretical formula (1) described in the section of the prior art. The horizontal axis represents the diopter A, and the vertical axis represents the crescent ratio R.
[0039]
R = 1- {eL / 2r (A + L)} (1)
e is the distance from the end 11 a of the objective lens 11 to the illumination light source 7. L is the reciprocal of the separation distance (measurement distance) S between the eye to be examined and the objective lens 11 (L = 1 / S). In the present embodiment, there are four illumination light sources 7a, 7b, 7c, 7d as shown in FIG. 3A, so that there are four types of distance e of 1 mm, 4 mm, 12 mm, and 16 mm as described above. The above-described measurement distance S is also set in the recording unit 16, and therefore its reciprocal L is also set. Further, as described above, the reference pupil diameter 2r is also set in advance.
[0040]
Note that since the measurement distance S is set in the analysis device 3, it is necessary to make the actual measurement distance substantially coincide with the set measurement distance S when the eye to be examined is photographed by the optical head 2. For this purpose, as described above, the distance meter 8 detects that the actual measurement distance is within a predetermined range centered on the set measurement distance S and performs imaging. Therefore, the image may be transmitted to the analysis device 3 only when the distance meter 8 performs the above detection. Further, since the reference pupil diameter 2r is also set in advance, the actual pupil diameter of the eye to be examined at the time of imaging needs to be within a predetermined range centered on the set value 2r. Therefore, at the time of shooting, the lighting of the shooting environment is set to a predetermined value so as not to change.
[0041]
From the above conditions, a curve showing the relationship between the diopter A and the crescent size ratio R is obtained by the above equation (1). This is shown in the graph of FIG. Curves C1 and C2 are calculated values for one light source 7a (e = 1 mm), curves C3 and C4 are calculated values for the other light source 7b (e = 4 mm), and curves C5 and C6 are Of the remaining light source, the calculated value is for the light source 7c (e = 12 mm), and the curve C7 and the curve C8 are the calculated values for the remaining light source 7d (e = 16 mm). As described above, two light-symmetrical curves with respect to the asymptotic line G in the drawing are shown for each of the light sources 7a, 7b, 7c, and 7d. This means that a crescent appears in the opposite direction of the pupil Q in the subject's eye with different diopters for one light source. The calculated points are plotted on each curve in the figure.
[0042]
Further, the diopter serving as a criterion for diopter classification is set in the recording unit 16. This reference diopter has a character set according to the specification from the user. For example, in this embodiment, as shown in FIG. 7, the reference diopter (the determination diopter, the diopter enclosed in parentheses in FIG. 7) is set to −2, 0, +2, and +3. In the determination unit 15, as shown in FIG. 8, a subject whose diopter A is A ≦ −2 or + 3 ≦ A requires treatment, and −2 <A <−0.75 or + 2 ≦ A < In the case of +3, the follow-up observation is performed, and further, it is determined that the eye to be examined that is −0.75 ≦ A <+2 is normal.
[0043]
A specific determination procedure in the determination unit 15 will be described. The determination unit 15 sets the crescent size ratio R = 0 as the threshold (determination point) J for the determination. That is, the classification is performed by determining whether or not a crescent appears with respect to illumination by one light source. In other words, it is an on / off determination.
[0044]
Further details will be described with reference to FIG. The calculation result by the processing calculation unit 14 is placed on several curves C1, C2, C3, C4, C5, C6, C7, C8, or not on the curve by any illumination light source (R ≦ 0), which corresponds to a point between the point M and the point N in the figure (an unmeasurable range). If 0 ≦ R for the light source 7a (curve C1), it is determined that −0.75 ≦ A. A crescent appears in the opposite direction to the light source 7a (curve C2), and it is determined that A ≦ −1.25 if 0 ≦ R. It is determined that 0 ≦ A if 0 ≦ R for the other light source 7b (curve C3). For the same light source 7b, a crescent appears in the opposite direction (curve C4), and if 0 ≦ R, it is determined that A ≦ −2. It is determined that + 2 ≦ A if 0 ≦ R for one of the remaining light sources 7c (curve C5). A crescent appears in the opposite direction to the light source 7c (curve C6), and A ≦ −4 is determined as 0 ≦ R. If the remaining light source 7d (curve C7) is 0 ≦ R, it is determined that + 3 ≦ A. For the same light source 7d, a crescent appears in the opposite direction (curve C8), and if 0 ≦ R, it is determined that A ≦ −5. Based on these determinations or a combination thereof, the above-described classification (FIG. 8) is performed. These determination results and classification are recorded in the recording unit 16 in association with the client information and displayed on the display unit 17.
[0045]
The above diopter classification depends on the user's specifications, but the curve C calculated by the above equation (1) passes the determination diopter of the above specifications (the diopter enclosed in parentheses in FIG. 7) and Each value of e and 2r is set so that the determination point J of the dimensional ratio of the crescent corresponding to the determination diopter on the curve can be clearly set (as described above, for example, R = 0). On the optical head 2, the installation position of each light source 7 is determined, the detection range of the distance meter 8 is set, and the illumination intensity of the shooting environment is set.
[0046]
Accordingly, if the user's specification changes, the values of e and 2r in the recording unit are changed, and an appropriate discrimination point J is reset at the same time as these changes (for example, R = 0.25 described later). . Accordingly, various set values on the optical head 2 are changed. Specifically, the storage medium for the arithmetic program is replaced, and the mounting plate 18 for the illumination light source is replaced. It should be noted that the detection range of the distance meter 8, that is, the setting of the measurement distance S is not changed as much as possible, and it is dealt with by changing other parameters (e, r, J). This is because it is desired to fix the measurement distance S in consideration of the usability of the apparatus 1 and compatibility with other inspections. However, the measurement distance S is not excluded and can be easily changed.
[0047]
In this way, when the diopter value to be classified is given, the position of the illumination light source, the R value as the discrimination point J, etc. are changed so that it can be clearly discriminated accordingly. Point J can be set arbitrarily. Therefore, it is only necessary to determine a discrimination point J that can clearly discriminate the classification diopter value in the specification.
[0048]
Next, as described above, a case where the determination point J of the R value is a positive value, for example, 0.25 will be described. In this case, classification cannot be performed simply by determining whether or not a crescent appears. In this case, for example, a mounting plate 38 shown in FIG. 9 is used. Three illumination light sources 27 are installed on the mounting plate 38. Among them, one light source 27a is a distance of 1 mm from the right edge of the objective lens 11, the other one light source 27b is a distance of 7mm from the left edge of the objective lens 11, and the remaining one light source 27c is 9 mm from the right edge of the objective lens 11. It is installed at a distance of. This distance can be changed no matter how the discrimination point J is a positive numerical value. Moreover, the reason why only one illumination light source 27b is installed on the opposite side (left side) is that the distance between the selected illumination light sources is simply too small to arrange three illumination light sources on the same side. .
[0049]
The reason why the illumination light source arrangement is set is that the determination diopter of the diopter class (the diopter enclosed in parentheses in FIG. 10) is set to A = −2, −1, +2, and +3, respectively. For this purpose, the reference pupil diameter r is also set again, and electronic information (corresponding to FIG. 7) regarding the relationship between the diopter A and the crescent size ratio R for diopter classification is replaced. . FIG. 10 shows the relationship between the diopter A calculated by the above theoretical formula (1) and the dimensional ratio R of the crescent. As in FIG. 7, the horizontal axis represents the diopter A, and the vertical axis represents the crescent ratio R.
[0050]
In FIG. 10, a curve C11 and a curve C12 are calculated values for one light source 27a (e = 1 mm), a curve C13 and a curve C14 are calculated values for another light source 27b (e = 7 mm), and a curve C15 Curve C16 is the calculated value for the remaining light source 27c (e = 9 mm). For each light source, a crescent appears in the direction opposite to the pupil Q in the eye to be examined having a different diopter. Speaking of the curves in FIG. 10, they are C12 for C11, C14 for C13, and C16 for C15 across the asymptote G. This is the same as in FIG.
[0051]
Further, as described above, values of −2, −1, +2, and +3 are set in the recording unit 16 as the reference diopter classification for diopter classification according to user specifications. And in the determination part 15, as shown in FIG. 11, the subject whose diopter A is A <=-2 or +3 <= A needs a treatment, respectively, and -2 <A <=-1 or 2 <= A < In the case of 3, the follow-up observation is performed, and further, it is determined that the eye to be examined for which -1 <A <2 is normal.
[0052]
A specific determination procedure in the determination unit 15 will be described. As shown in FIG. 10, the determination unit 15 sets a determination point J (R = 0.25) as a threshold for the above determination. Then, the classification is performed by determining whether the calculated value of R is 0.25 or less (less than) or more than 0.25 (or more) for illumination by one light source. In other words, it is an on / off determination. The calculation result by the processing calculation unit 14 is on a number of curves C11, C12, C13, C14, C15, C16, or does not satisfy 0.25 ≦ R by any illumination light source. Between the M point and the N point (a non-measurable range). It is determined that A ≦ −2 when 0.25 ≦ R with respect to the light source 27a (curve C11). A crescent appears in the opposite direction to the light source 27a (curve C12), and 0.25 ≦ R is determined as −1 ≦ A. When 0.25 ≦ R for the other light source 27b (curve C13), it is determined that + 2 ≦ A. If the remaining light source 27c (curve C14) is 0.25 ≦ R, it is determined that + 3 ≦ A. Based on these determinations or combinations thereof, the above-described classification is performed.
[0053]
The analysis device 3 scans the pixels of the image to detect the size ratio and direction of the crescent. FIG. 12 shows the detection status of light by this scanning. In this case, the method is divided into the case where the aforementioned Purkinje image P can be used and the case where it cannot be used to determine the direction of the crescent. FIG. 12A shows a case where the Purkinje image P can be used, and FIG. 12B shows a case where the Purkinje image P cannot be used.
[0054]
In FIG. 12A, when only the Purkinje image P is detected by scanning even though the illumination light source 27 is turned on (symbol A1 in FIG. 12A), it is determined that no crescent appears. Is done. When the Purkinje image P and other light are detected, it is determined that the crescent K appears. It can be determined from the position with respect to the Purkinje image P, as described above, which side of the pupil K appears. In this case, when the crescent appears on the same side as the illumination light source 27 with respect to the Purkinje image P (symbol A2 in FIG. 12A), the diopter of the eye to be examined is on the minus side, and the illumination light source 27 Appears on the opposite side (symbol A3 in FIG. 12A) is the plus side. As described above, the Purkinje image P and the Crescent K can be easily distinguished by using a Purkinje detection light source different from the illumination light source 27 in combination.
[0055]
Next, it is determined as follows whether the size ratio of the crescent is greater than or less than the threshold value J (R = 0.25). The scanning time T2 required to pass the detection crescent range on the scanning line where the crescent is detected by scanning is compared with the scanning time (reference time or threshold time) T0 corresponding to R = 0.25. If T2 <T0, it is determined that there is no crescent, and if T2 ≧ T0, it is determined that the crescent has appeared (reference signs A2 and A3 in FIG. 12A).
[0056]
In this illumination light source arrangement, the same light source array cannot be further arranged symmetrically with respect to the objective lens. Therefore, the direction of the crescent cannot be determined without using the Purkinje image. However, in the case of a light source arrangement in which the same light source array can be arranged point-symmetrically, the Purkinje image as described above with reference to FIG. 5B is used even if the discrimination point J is a positive numerical value. The direction of the crescent when it cannot be used can be determined. That is, as shown in FIG. 12B, the crescent is detected for each illumination by alternately lighting the illumination light sources at the same distance on both sides of the objective lens 11. Then, the position of the crescent is determined by the scanning time T1 and the position of the scanning line in the figure, and the position of the crescent XY coordinates is determined.
[0057]
FIG. 13 shows another optical head 42. The optical head 42 is different from the optical head 2 in the mounting plate 48 of the illumination light source. Twelve illumination light sources are installed on the mounting plate 48. Among these, eight light sources (referred to as one light source group) 47a, 47b, 47c, 47d, 47e, 47f, 47g, and 47h arranged in the left-right direction are the same as those of the optical head 2 in FIG. . In addition, eight illumination light sources (referred to as the other light source group) 47j, 47k, 47m, 47n, 47p, 47q, 47r, 47s are in a direction (vertical direction) perpendicular to the arrangement line of the one light source group. It is arranged on the straight line. As shown in the figure, the distance from the edge of the objective lens 11 of the other light source group is the same as that of the one light source group, and is 1 mm, 4 mm, 12 mm, and 16 mm, respectively. In other words, the illumination light sources arranged in the left-right arrangement and the illumination light sources arranged in the upper-lower arrangement are in a positional relationship that they are rotated by 90 ° with respect to the objective lens 11.
[0058]
Thus, by providing two light source groups having the same distance from the edge of the objective lens 11 and orthogonal to each other, the astigmatic axis of the eye to be examined can be measured by a known method. It is not limited to the above value of the separation distance. In short, it is only necessary that the corresponding light sources of the two light source groups orthogonal to each other are installed at the same distance from the edge of the objective lens 11.
[0059]
【The invention's effect】
According to the photoreflector of the present invention, high accuracy is not required for detection of the image of the pupil, the image processing calculation is easy, and it is suitable for screening the diopter of the eye to be examined.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing an embodiment of a photoreflector according to the present invention.
FIG. 2 (a) is a diagram showing a usage state of a handy type photoreflector, and FIG. 2 (b) is a diagram showing a usage state of an installation type photoreflector.
3A is a front view showing an optical head in the photoreflector of FIG. 1, and FIG. 3B is a rear view thereof.
4A is a plan view of the optical head of FIG. 3, and FIG. 4B is a side view thereof.
5A is a diagram for explaining detection of the crescent by the illumination light source arrangement position of FIG. 3A, and FIG. 5B is a diagram for explaining the detection of the crescent by the illumination light source arrangement position of FIG. It is a figure to do.
6 is a front view showing another example of a mounting plate for an illumination light source in the photoreflector of FIG. 1. FIG.
7 is a graph for explaining processing by the analysis device in the photoreflector of FIG. 1; FIG.
8 is a diagram showing an example of diopter classification criteria by the photoreflector of FIG. 1; FIG.
9 is a front view showing still another example of an illumination light source mounting plate in the photoreflector of FIG. 1. FIG.
10 is a graph for explaining processing performed by the analysis device based on an image obtained from the illumination light source arrangement position of FIG. 9;
11 is a diagram illustrating an example of a diopter classification criterion based on an image obtained from the illumination light source arrangement position of FIG. 9;
12A is a diagram for explaining the detection of the crescent by the illumination light source arrangement position of FIG. 9, and FIG. 12B is a diagram for explaining the detection of the crescent when the Purkinje image cannot be used. It is.
FIG. 13 is a front view showing another example of the optical head in the photoreflector of the present invention.
FIG. 14 is a diagram showing the principle of a photorefractive method.
FIG. 15 is a graph for explaining a method for measuring diopter of an eye to be examined by a photorefractive method.
[Explanation of symbols]
1 Photorefractor
2 Optical head
3 Analysis device
4 frame
5 Holding handle
6 Camera
7, 7a-7h Illumination light source
8 Distance meter
9 Monitor screen
10 Fixation means
11 Objective lens
12 Optical system
13 Input section
14 Processing operation part
15 judgment part
16 Recording section
17 Display
18 Mounting plate
22 Optical head
27a-27f Illumination light source
28 Mounting plate
38 Mounting plate
42 Optical head
47a-47h, 47j, 47k Illumination light source
47m, 47n, 47p, 47q Illumination light source
48 Mounting plate
A diopter (refractive index)
A1-A3, B1-B3 scanning lines
B Crescent string
Curve in C1-C8 graph
Curves in C11-C16 graph
D Crescent dimensions
E Eye to be examined
e Distance from the edge of the objective lens to the illumination light source
G asymptote
J discrimination point
K, K1, K2 (bright) Crescent
P Purkinje statue
Q pupil
R Crescent dimension ratio
r Pupil radius
S Measuring distance
Time taken for the T0 scan line to pass through the crescent light
T1 Time required to detect a crescent of one scanning line.
Scanning time required to pass the T2 detection crescent

Claims (8)

A plurality of illumination light sources that can be selectively lit to illuminate the eye to be examined;
An imaging optical system that has an objective lens and captures illumination light from the illumination light source reflected by the fundus of the eye to be examined;
Position detecting means for detecting a separation distance between the photographing optical system and the eye to be examined;
An image processing arithmetic unit for analyzing a photographed image by the photographing optical system;
An image determination unit,
The plurality of illumination light sources are installed at positions spaced apart from each other in the diameter direction from the end of the objective lens,
The image processing calculation unit detects the generation of bright crescent and the direction of the generated crescent in the pupil based on the captured image,
A photorefractor in which the image determination unit is configured to perform diopter class determination of an eye to be inspected by comparing the detection result with a preset bright crescent direction and a presence / absence criterion. In the image processing calculation unit,
Let e be the distance in the diameter direction from the end of the objective lens of the illumination light source, L be the reciprocal of the distance between the corresponding eye and the objective lens, r be the radius of the pupil, and A be the corresponding eye The diopter and the diopter between the size ratio of the bright crescent pupil diameter generated by the illumination of each illumination light source and the diopter, calculated by the following equation when R is the size ratio of the bright crescent pupil diameter of the eye. Relationship is set,
R = 1- {eL / 2r (A + L)}
Furthermore, the minimum value of R as a reference value for determining the occurrence of bright crescent, and a reference diopter corresponding to the reference value are set.
The photoreflector according to claim 1, wherein the image determination unit is configured to determine the presence or absence of a bright crescent by comparing with the reference value by pixel scanning of a captured image. 3. The photoreflector according to claim 2, wherein the image determination unit is configured to determine whether the diopter class of the eye to be examined is a plus side or a minus side with respect to the reference diopter based on a judgment result of presence or absence of bright crescent. Lactor. 4. The photoreflector according to claim 2, wherein the R value as the reference value is zero, and the presence or absence of a bright crescent is determined based on the presence or absence of light detection by pixel scanning of a captured image. In the image processing calculation unit,
By detecting the positional relationship between the image of the corneal apex reflected light and the bright crescent image of the eye to be examined by pixel scanning of the captured image,
The photoreflector according to claim 1, wherein the image determination unit is configured to determine an appearance direction of a bright crescent in the pupil based on the detection result. 6. The photoreflector according to claim 5, wherein the photographing optical system has a Purkinje detection light source for irradiating the eye to be examined with detection light along the optical axis of the objective lens. The plurality of illumination light sources are arranged outward from one end of the objective lens, and the same number of corresponding illumination light sources are installed at point-symmetric positions around the illumination light source and the objective lens. And
The image processing calculation unit is configured to determine an appearance direction of a bright crescent in the pupil based on a change in a position where the bright crescent appears when a pair of point-symmetric illumination light sources are sequentially turned on. The photoreflector according to claim 1. An attachment member for installing an illumination light source is provided, and the plurality of illumination light sources are installed on the attachment member, and the attachment member is configured to be detachably attached in the vicinity of the photographing optical system. The photorefractor according to claim 1.

Images