JPH07318873A - Prescription method and prescription system for multifocal contact lens - Google Patents

Abstract

PURPOSE:To surely provide a multifocal contact lens having a prescribing optimum for a testee by determining the height of a segment line in accordance with the values of both of an optimum near sight value and an optimum far sight value. CONSTITUTION:This method comprises determining the infraduction angle delta of the testee's eyeball at the time of viewing near, installing a photographic means with an elevation angle equal to the infraduction angle delta on the extension line of the visual line, photographing the front image of the eyeball from the direction of 17 and actually measuring the distance to the lower margin 16 of the eyelid from a pupil center 12 from this image. The distance from the pupil center 12 to the lower margin 16 of the eyelid is equal to the distance from the intersected point 15 of the visual line 11 at the time of viewing near and the front surface 14 of the cornea, i.e., the optimum near sight value like in measurement at the time of viewing far by this manner and, therefore, the optimum near sight value HL is determined from the distance from the pupil center 12 to the lower margin 16 of the eyelid. Another method comprises installing the photographic means horizontally on the extension line of a horizontal line 18, photographing the front image of the eyeball from the direction of 19 and determining the infraduction angle delta of the eyeball at the time of viewing near.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prescription method and a prescription system for determining the height of a segment line of an alternating vision type multifocal contact lens.

[0002]

2. Description of the Related Art Multifocal contact lenses are mainly developed for the purpose of correcting the deterioration of the accommodation function of the crystalline lens of the eye in the elderly and providing good visual acuity correction for both far and near. Currently, two types of multifocal contact lenses, a simultaneous vision type and an alternating vision type, are known.

A simultaneous vision type multifocal contact lens is a type in which a light beam from a distance and a light beam from a near distance are simultaneously imaged on the retina, and the wearer unconsciously selects the easier one to adjust on the retina. To focus on. This type of lens generally has a near portion formed in the center of the lens and a distance portion formed in a concentric shape in the peripheral portion.

The alternating vision type multifocal contact lens is designed by using the same principle as the bifocal lens used in the spectacle lens, and as shown in FIG. 6, the correction mainly on the upper part of the lens is suitable for distance vision. A distance portion 61 having a diopter and a near portion 62 having a correction diopter mainly suitable for near vision are formed below the lens. The distance portion 61 and the near portion 62 are divided by a segment line 63.

Further, since a lens of this type is useless when it is rotated during wearing, it is common to apply a prescription called prism ballast in which the thickness and weight below the lens are increased in order to prevent rotation.

In such an alternate vision type lens, good vision cannot be obtained unless the distance portion 61 is used when looking at a distance and the near portion 62 is used when looking at a near distance. Determining the segment line height for the subject's eye is an important point in prescribing this type of multifocal contact lens.

Conventionally, as a prescription method for determining the height of this segment line, "CONTACT LENS P
RACTICE "(ROBERT B. MANELL
Author: FOURTH EDITION, THOMAS B
OOKS 1988) page 800 lines 17-21 and page 804 lines 15-27 are known. In this method, the subject is equipped with a test lens (hereinafter referred to as a trial lens) to check the wearing state of the lens, and when the far vision is maintained under vague lighting, the lower edge of the pupil of the eye lowers the eyelid. Find the distance to the edge,
This is the method of setting it as the height of the segment line.

However, this method has the following drawbacks. That is, it is well known that the size of the human pupil changes depending on the ambient brightness and the psychological state. For this reason, the measurement result changes remarkably depending on the environment at the time of measurement and the psychological state of the subject, which is a disadvantage in that the optimum segment line height for the subject cannot always be obtained. For example, when the subject's pupil is in the smallest state, such as when the measurement is in a very dazzling state or in an extremely tense state, the segment line height is determined based on the measurement value at that time. Once determined, in normal conditions the segment line will cross the pupil even during distance vision,
A light ray from a near distance also forms an image on the retina, which causes a problem that good distance vision cannot be obtained.

As a method of solving this drawback, the following method is generally used in the United States. The method is to obtain the optimum distance vision value, that is, the distance from the intersection of the line of sight and the anterior surface of the cornea at the time of distance vision to the edge of the lower eyelid, and the value obtained by subtracting a predetermined correction value from that value is used as the height of the segment line. is there.

FIG. 7 is a diagram showing an outline of a method for measuring the optimum distance vision value. Since the normal line of sight passes through the pupil center 71, a line 72 that passes through the pupil center and connects the pupil diameter in actual measurement.
Measurement is performed by regarding the line perpendicular to the line of sight as the line of sight 73.

Since the state in which the examinee keeps his or her line of sight 73 horizontal is in the state of distance vision, if the distance from the center 71 of the pupil to the lower eyelid edge 74 is measured, it is the line of sight 73 and the anterior surface of the cornea 75.
The distance from the intersection point 76 to the lower eyelid edge 74, that is, the optimum distance vision value HF.

The method for measuring the optimum distance vision value HF is to take a frontal image of the eyeball from the direction of 77 using a slit lamp microscope or a steel camera installed at the same height as the center of the pupil,
The method of actually measuring from the image is general.

In addition, the predetermined correction value takes into account the positional deviation of the lens during wear due to the size of the subject's pupil and blinking, etc., and there is a near vision portion on the line of sight at the time of distance vision, or the reverse portion. It is designed to prevent the phenomenon that there is a distance portion on the line of sight during near vision (hereinafter referred to as poor alternating vision). Currently, in the United States, it is an average based on past prescription experience. A value of 1.0 to 1.5 mm is used as this value.

[0014]

However, this method determines the height of the segment line based only on the position of the line of sight during distance vision during wearing, and the movement and posture of the eyeball during near vision. Is not considered at all,
There is a problem that there is a high possibility that good near vision cannot be obtained.

That is, generally, in near vision, not only the eyeball tends to rotate downward, but also the head position tends to tilt forward. Moreover, the amount of head tilt and the downward angle of the eyeball are considerably different from each other. There is. Therefore, when the downward angle of the eyeball is extremely small, the line of sight does not move to the near portion of the lens even in near vision, and poor alternating vision occurs.

In the conventional method, since the height of the segment line is determined based on only the position of the line of sight at the time of distance vision, ignoring such individual differences, the distance vision is guaranteed. There is a problem that the subject cannot guarantee the near vision at all.

As a result, in the past, it was repeated to repeatedly try and remake until an appropriate segment line height was obtained. Therefore, naturally, not only the manufacturing cost becomes high, but also considerable time and labor must be spent before the optimum contact lens can be worn.

Therefore, according to the present invention, the optimum segment line height can be reliably determined in consideration of the individual differences in the head tilt angle and the eyeball downward angle, and it is always possible to obtain good distance vision and near vision. It is an object of the present invention to provide a prescription method and system capable of guaranteeing visual acuity.

[0019]

The prescription method of the present invention is a method for prescribing a multifocal contact lens for determining the height of a segment line of an alternating vision type multifocal contact lens. It is characterized by measuring the visual value and determining the height of the segment line based on both the measured values.

Further, it is characterized in that the optimum near-view value and the optimum far-view value are measured by using photographed images obtained by photographing front images of the eyes during near vision and far vision, respectively.

Further, the optimum near-vision value is measured using a photographed image obtained by installing photographing means on an extension of the line of sight for near vision and photographing a front image of the eyeball during near vision. Or a photographed image obtained by installing a photographing means on an extension line of the line of sight in the case of distance vision to photograph a front image of the eyeball in the case of near vision. A characteristic is that the vertical distance from the center to the lower eyelid edge is measured, and the optimum near-vision value is calculated based on the measured value, the downward angle at near vision and the distance from the center of the pupil to the anterior surface of the cornea. Furthermore, the distance from the center of the pupil to the front surface of the cornea is characterized by using a cross-sectional image of the eyeball.

Further, the prescription system of the present invention comprises a photographing means for photographing at least one of the front image and the sectional image of the eyeball as described above, and the optimum near vision value from the image data inputted from the photographing means. , An optimal distance vision value, at least one of the distance in the vertical direction from the center of the pupil to the lower eyelid edge during near vision and the distance from the center of the pupil to the front surface of the cornea, and the image processing means and the image processing means. It is characterized by comprising an arithmetic means for calculating the height of the segment line based on the measured value.

Further, the image data output from the photographing means is a photographic image, and the image processing means includes image conversion means for digitizing the photographic image and converting it into image data which can be processed by the image processing means. .

In the present invention, the optimum distance vision value indicates the distance from the intersection of the line of sight and the front surface of the cornea during distance vision to the edge of the lower eyelid, and the optimum near vision value is the line of sight during near vision. The distance from the intersection with the anterior surface of the cornea to the margin of the lower eyelid is shown. The segment line height refers to the distance from the lower end of the multifocal contact lens, which is in contact with the lower eyelid edge during normal wear, to the segment line on a vertical line passing through the optical center of the multifocal contact lens.

Also in the present invention, the optimum distance vision value is as shown in FIG.
It can be easily obtained by the same measurement method as the conventional one as shown in FIG. However, the optimum near vision value cannot be obtained by the measuring method of FIG. 7 because there are individual differences in the direction of the line of sight during near vision.

FIG. 1 is a diagram showing the outline of the method for measuring the optimum near vision value according to the present invention. Reference numeral 11 is a line of sight for near vision, and usually a line 1 that passes through the pupil center 12 and connects the pupil diameter.
It coincides with the line perpendicular to 3. Line of sight 1 when HL is near vision
1 is the distance from the intersection 15 of 1 and the anterior surface 14 of the cornea to the lower eyelid margin 16, that is, the optimum near vision value.

According to the first measuring method of the present invention, first, the downturn angle δ of the eyeball of the subject at near vision is obtained, and the downturn angle δ of the photographing means (not shown) is set on the extension line of the line of sight 11. It is installed with an elevation angle equal to, and a front image of the eyeball is taken from the 17 direction,
The distance from the pupil center 12 to the lower eyelid margin 16 is measured from the image. According to this method, the distance from the pupil center 12 to the lower eyelid edge 16 is determined from the intersection point 15 of the line of sight 11 and the anterior surface 14 of the cornea in near vision, as in the measurement at the time of distance vision as shown in FIG. 7. Since it becomes equal to the distance to the lower eyelid rim 16, that is, the optimum near vision value, the optimum near vision value HL is obtained from the distance from the pupil center 12 to the lower eyelid rim 16. According to such a first measurement method, since the optimum near vision value is directly obtained from the front image of the eyeball, it is not necessary to use a troublesome calculation formula like the second measurement method described below. There are advantages.

In the second measuring method of the present invention, the photographing means is installed horizontally on the extension of the horizontal line 18, the front image of the eyeball is photographed from the direction of 19, and the eyeball of the subject at near vision is taken. The downturn angle δ is obtained.

In this method, the center of the pupil 1 from the photographed image.
The vertical distance HS from 2 to the lower eyelid margin 16 can be measured. The optimum near vision value HL is obtained from this value and the downturn angle δ and the distance r from the pupil center 12 to the anterior surface of the cornea 14 by the following calculation formula.

That is, if the distance in the vertical direction from the pupil center 12 to the intersection 15 of the line of sight 11 and the front surface of the cornea 14 is ΔK, then ΔK = sin δ × r (1) Therefore, the optimum near vision value HL is obtained by HL = (HS-ΔK) / cosδ = (HS-sinδ × r) / cosδ ... (2).

According to the second measuring method as described above, both the optimum distance-viewing value and the optimum near-viewing value can be obtained without moving the photographing means at all, so that the structure of the photographing means can be simplified. There are advantages.

As the distance r from the center 12 of the pupil to the anterior surface 14 of the cornea, a value of 3.6 mm, which is well known in Gullstrand's simulated eyes (see "Basics of eye optics" by Mototsugu Nishi, published by Kinbara Publishing) is used. And a method of taking a cross-sectional image of the eyeball and obtaining the value based on the actually measured value. The former method is extremely simple, but it is desirable to use the latter method in order to obtain more accurate measurement values in consideration of individual differences.

FIG. 2 is a diagram showing an outline of a method for photographing a cross-sectional image of an eyeball. FIG. 2 is a view of the eyeball viewed from above, and the slit light beam 22 is emitted from the front, that is, the direction on the extension line of the line of sight 21 in the case of distance vision, and the cross-sectional image of the eyeball is photographed from the direction of 23 at the photographing angle θ. From the photographed image, the distance HR from the pupil center 24 in the direction perpendicular to the photographing direction 23 to the intersection point 26 between the line of sight 21 and the anterior surface of the cornea 25 can be measured, so the distance r from the pupil center 24 to the anterior surface of the cornea 26 is r = HR / sin θ (3)

It should be noted that the above description has been made on the premise that all captured images are of the same size in order to avoid complication. However, in reality, it is difficult to accurately obtain a captured image of the same size. Therefore, the above equations (2) and (3) are used.
For the equation, it is necessary to perform the following magnification correction.

That is, when a front image or a cross-sectional image of an eyeball is photographed, the subject is fitted with a trial lens whose accurate dimension (for example, diameter) is known in advance, and the dimension of the trial lens on the photographed image is adjusted. By actually measuring
A magnification correction value is obtained. If the actual diameter of the trial lens is LT and the actual measurement value obtained from the captured image is LR, the magnification correction value Y is Y = LT / LR. By using this value and correcting equations (2) and (3) as follows, a correct measurement value can be obtained.

HL = (HS × Y-sin δ × r) / co
sδ ... (2 ′) r = (HR × Y) / sin θ ... (3 ′) Next, a method for obtaining the downward angle of the eyeball during near vision will be described.

FIG. 3 is a diagram showing an outline of the first method for measuring the downward angle of the eyeball in the near vision, in which the scale 32 is vertically placed in front of the subject 31 with a predetermined measurement distance N. It is installed on the scale, and the zero scale of the scale is matched with the line of sight for distance vision. Next, by moving the line of sight to the optimum near vision and having the subject read the scale of the scale that can be read best at that time, the downward angle of the optimum near vision can be obtained.

When the scale scale is a normal length scale and the scale scale read at the time of optimum near vision is X, the downturn angle δ is δ = tan ^-1 (X / N). You can ask.

FIG. 4 is a diagram showing the outline of the second method of measuring the downward angle of the eyeball in near vision. Instead of the scale of FIG. 3, an arc-shaped protractor having a radius N and having an angle scale is shown. 41
Is an example using. In this case, as a photographing means in which the value read by the subject directly becomes the downward rotation angle of the eye during optimal near vision, photography using a slit lamp microscope is generally used.
It is also possible to shoot directly using a video camera, CCD camera, still camera, polaroid camera, or the like.

As a method of obtaining a measured value from a photographed image, a method is used in which an image observed by a slit lamp microscope is photographed and a scale is applied to the photograph to perform actual measurement, or the photographed image is digitized and input to an image processing apparatus. There is a method of obtaining a measured value by image processing.

According to the latter method, it is possible to realize a prescription system in which a necessary prescription value can be automatically obtained only by capturing a necessary eyeball image.

FIG. 5 is a schematic view showing an example of the prescription system of the present invention, and 51 is a photographing means for photographing necessary images such as a frontal image and a cross-sectional image of an eyeball, which are a video camera and a CCD camera. , A camera such as a still camera or a polaroid camera, or a slit lamp microscope equipped with these cameras for imaging the observation image. When measuring the optimum near vision value with the first measurement method, a means for moving the photographing means to the extension line of the line of sight during near vision is included, and the downward angle of the eyeball is further adjusted regardless of the measurement method. The measuring means as shown in FIG. 3 or FIG. 4 for measuring is also included. Reference numeral 52 converts the image data obtained by the image capturing means into image data that can be digitized and processed by a known image processing technique using an image conversion element such as an image sensor when the captured image is analog data such as a still picture. This is not necessary when the photographing means is an image converting means and the photographing means uses an electronic camera such as a video camera or a CCD camera, and the photographed image to be output is already digitized image data.

Reference numeral 53 denotes an image processing means for actually measuring a necessary measurement value from the input image data by using a known image processing technique. When the optimum near vision value is measured by the first measuring method. Is the optimum distance vision value and the optimum near vision value,
When the second measurement method is used, the optimum distance vision value, the vertical distance from the pupil center to the lower eyelid edge in near vision, and the distance from the pupil center to the anterior corneal surface are obtained. Also, if necessary, regardless of the measuring method, dimensions such as the diameter of the trial lens for calculating the correction value of the photographing magnification are actually measured. The image processing means 53 is composed of a computer such as a personal computer having a built-in image processing program obtained by converting a known image processing technique into a computer program.

Known image processing will be briefly described.
The digitized image data is composed of a set of points having a value corresponding to the brightness or color of the shooting location.
For example, since the pupil is photographed as a black circle, the number of black points on the vertical or horizontal line passing through the center of the pupil in the image data is counted. Since the number of points per 1 mm is determined by the resolution peculiar to the photographing means or the image conversion element, the diameter of the pupil can be obtained from the number of black points.
The image processing means 53 stores in advance the points to be counted, that is, the average brightness or color of the pupil, cornea, eyelid, etc., and is programmed so as to count the corresponding points. A desired actual measurement value can be obtained from

Reference numeral 54 denotes a calculation means, which is based on the actual measurement value input from the image processing means and the downward angle of the eyeball at near vision input separately and the actual size of the trial lens if necessary. The measurement value is calculated using the above-described calculation formula, and the height of the segment line is calculated using a predetermined correction value. The calculation means 54 can be configured by incorporating a desired calculation program in a computer such as a personal computer that constitutes the image processing means 53.

In determining the height of the segment line, it is necessary to add a predetermined correction value in consideration of the size of the pupil and the positional deviation of the lens during wearing so as not to cause defective alternating vision. The value obtained by adding the correction value to the optimum near vision value becomes the position of the segment line, that is, the height.

This correction value has the same meaning as the correction value described in the description of the prior art. That is, when the correction value is not added, the line of sight during near vision passes on the segment line, resulting in poor alternating vision. Therefore, in order to ensure good near vision, a certain correction value is added so that the line of sight at near vision passes through the near portion of the multifocal contact lens, and most of the pupil area is used for near vision. It must be prescribed so that it is covered by the department.

Factors for determining such a correction value are mainly the size (diameter) of the pupil of the subject, the positional deviation of the lens during wearing (lens movement due to blinking, insufficient lens ballast lens). However, if the focus is placed on the stable state of the lens, the size of the pupil becomes a decisive factor. Regarding the size of the pupil, it is said from the results of past ophthalmological research that the diameter of a young person is 4 to 6 mm and that of an elderly person is 2 to 4 mm in a normal state. The multifocal contact lens to which the present invention is applied is intended for elderly people in their 40s or older, who are generally said to have a deterioration in the accommodation function of the crystalline lens of the eye. It is reasonable to assume that the diameter is about 2 to 4 mm.

When the pupil of the subject has a diameter of 2 mm and the correction value is set to 1 mm, the pupil is completely covered by the near portion of the lens at the time of near vision, resulting in a very good near distance. You can get sight. When the correction value is 0.5 mm, about 80% of the apparent pupil is covered by the near portion of the lens, and the remaining about 20% is covered by the distance portion. Correction value is 1
Compared with the case of mm, the amount of light from the near object that forms an image on the retina is reduced by about 20%, but it can be expected that substantially good near vision can be obtained at this level. Further, in the case of a subject with a large pupil, it is necessary to increase the correction value accordingly. Therefore, the correction value is adjusted within the range of 0.5 to 2 mm. Further, considering the positional deviation of the lens during wearing, a larger correction value may be required depending on the subject.
Therefore, it is desirable to adjust and determine the correction value within the range of 0.5 to 2.5 mm.

The prescription method and the prescription system of the present invention can be applied to the prescription of any contact lens as long as it is an alternating vision type multifocal contact lens, and it is sold under the name of "Tangent streak". It is suitable for a non-jumping alternating vision type multifocal contact lens as described in JP-A-62-283312.

[0051]

[Examples] From the subjects in their 40s to 60s wishing to wear alternating vision type multifocal contact lenses, 10 subjects were selected with the consent of the subject, and a jumpless alternating vision type The prescription according to the present invention was carried out using a multifocal contact lens (trade name: Tangent Streak, manufactured by Seiko Epson Contact Lens Co., Ltd.). To ensure that each subject actually wears it and confirms whether or not good corrected vision was obtained, the corrective power and corneal shape suitable for each subject are used in the same manner as for normal contact lens prescriptions. Although a prescription such as a base curve according to the above was also performed, it is not directly related to the present invention, and therefore the description of prescription results other than the prescription for determining the height of the segment line is omitted.

The second measuring method of the present invention was used as the measuring method of the optimum near vision value. That is, the subject is fitted with a trial lens having a diameter of 9 mm and a correction power of 0, and a slit lamp microscope installed horizontally at the same position as the eye level of the subject is used to image the observation image. First, a front image of the eyeball is photographed with the video camera and a photographing means equipped with a scale 32 as shown in FIG. 3 for determining the downward angle of the eyeball, while the line of sight is kept in the distance vision, that is, in the horizontal state. Then, have the subject move his or her line of sight to a position that is most suitable for near vision for the subject, and read the scale of the scale that can be read best at that time, and in that state, in front of the eyeball in near vision. The picture was taken. Finally,
The line of sight was returned to the horizontal direction again, and the head was rotated horizontally until the target object, which was placed on the side of the slit lamp microscope and separated by a predetermined distance, was in front of the slit lamp microscope. A cross-sectional image of the eyeball was photographed by irradiating a slit light beam from a light source. If the distance from the slit lamp microscope to the eyeball, that is, the shooting distance and the distance from the slit lamp microscope to the target object are determined in advance, a cross-sectional image with a predetermined shooting angle can be obtained.

Each image thus photographed is inputted to an image processing means comprising a personal computer having an image processing program built-in, and a diameter of the trial lens on the image, an optimum distance vision value, and a pupil center at near vision are inputted. The vertical distance from the eyelid to the lower eyelid and the distance from the pupil center in the direction perpendicular to the imaging direction to the intersection of the line of sight and the anterior surface of the cornea were obtained. In the personal computer that constitutes the image processing means, the downward angle of the eyeball obtained from the scale of the scale read by each subject is input, and each measurement value obtained by the image processing program is stored in advance. Based on the actual diameter of the trial lens, the shooting angle of the cross-sectional image, and the correction value, the height of the segment line was obtained using the built-in calculation program.

As the correction value, 1.3 mm, which is used as a value having the smallest possibility of prescription failure in the conventional prescription method, is added to the optimum near vision value, and the inverse value is set. When the difference between the optimum distance vision value and the segment line height is less than 1 mm, the segregant line height is set to be corrected to an intermediate value between the optimum distance vision value and the optimum near vision value. did.

Table 1 shows the results of prescribing the heights of the segment lines for 10 subjects in this manner.

For comparison, a conventional prescription method, that is, only the optimum distance vision value was measured using the same contact lens as that used in the present example for 10 same subjects, and Prescription was performed with the value obtained by subtracting the predetermined correction value as the height of the segment line. Lenses made based on both prescriptions were worn and compared. The correction value was 1.3 mm as in this example. The prescription results are also shown in Table 1.

[0057]

[Table 1]

As is clear from Table 1, in the conventional prescription method, the subject C has a line of sight in the near vision passing over the segment line, and the subject F has a line of sight in the near vision with the segment line. Since it is lower than that, complete replacement vision failure will occur. Further, in the case of the subjects B and H, the difference between the height of the segment line and the optimum near vision value is only 2 mm and 1 mm, respectively, and it is determined that there is a high possibility of near vision failure. When he was actually worn, he complained of poor near vision.

In the conventional prescription method, the height of the segment line must be prescribed while the optimum near vision value is completely unknown. Therefore, these subjects B, C, F and H are once displayed. It is a waste to make a lens based on the prescription result of 1 and have it actually worn, then check the degree of poor near vision and adjust the segment line height based on experience and can and remake the lens. Work is required.

On the other hand, according to the prescription method of the present invention, it is possible to prescribe the optimum segment line height to the subject from the beginning. From the results of Table 1, in the case of the subjects B, C, and H, the difference between the segment line height and the optimum distance-viewing value and the optimum near-viewing value is 0.6 to
Although it is only about 0.7 mm, it is 0.5 as described above.
If there is a difference of not less than mm, it can be judged that good distance and near vision can be guaranteed, which is not perfect but almost satisfactory. In fact, subjects B, C and H did not point out any problems.

Further, in the case of the examinee F, the difference between the height of the segment line and the optimum far-sighted value and optimum near-sightedness value was only 0.4 mm, and it was judged that prescription was impossible. In this way, the subject with a significantly small difference between the optimum distance vision value and the optimum near vision value does not move his or her line of sight during near vision,
He is a person who tends to tilt his head forward and cannot adapt to alternating vision type multifocal contact lenses.
The most appropriate countermeasure is to wear a simultaneous vision type multifocal contact lens on such a subject. However, according to the prescription method of the present invention, such a subject is preliminarily examined. It is also possible to check, and after trying the lens many times, it is necessary to remake it, it is judged that it is not adaptable, wasteful work and the situation where the subject is mentally seriously damaged Can be prevented.

[0062]

According to the invention of claim 1 or 2, the height of the segment line is determined on the basis of both the optimum near-viewing value and the optimum far-viewing value, which is optimal for the subject. It is possible to reliably provide a multifocal contact lens having a prescription.

In addition, it is possible to confirm in advance the subjects whose eye movements are extremely small in the distance vision and the near vision and cannot be applied to the alternating vision type multifocal contact lens, and it is possible to use them as in the conventional case. As a result, it is possible to prevent the useless work of making a decision of non-adaptation after repeating the work of remaking many times.

According to the third aspect of the present invention, the optimum near vision value can be directly measured without using a complicated calculation formula.

According to the invention described in claim 4, it is possible to obtain the optimum near vision value by the photographing means having a simple structure.

According to the invention of claim 6, the same effect as that of the invention of claim 1 or 2 can be obtained, and
It is possible to automatically obtain the optimum prescription value for the subject simply by capturing the necessary eyeball image.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a method for measuring an optimum near vision value according to the present invention.

FIG. 2 is a diagram showing an outline of a method for capturing a cross-sectional image of an eyeball of the present invention.

FIG. 3 is a diagram showing an outline of the first method of measuring the downward angle of the eyeball during near vision according to the present invention.

FIG. 4 is a diagram showing the outline of a second method of measuring the downward angle of the eyeball during near vision according to the present invention.

FIG. 5 is a schematic view showing an example of a prescription system of the present invention.

FIG. 6 is a diagram showing the design principle of an alternating vision type multifocal contact lens.

FIG. 7 is a diagram showing an outline of a conventional method for measuring an optimum distance vision value.

[Explanation of symbols]

 11 Line of sight 12 Center of pupil 13 Line passing through center of pupil and connecting pupil diameter 14 Front of cornea 15 Intersection of line of sight and front of cornea 16 Lower eyelid edge 17 Photographing direction 18 Horizontal line 19 Photographing direction 21 Far vision 22 Slit ray 23 Photographing Direction 24 Pupil center 25 Corneal front face 26 Intersection point of line of sight and corneal front face 31 Examinee 32 Scale 41 Examinee 42 Protractor 51 Imaging means 52 Image converting means 53 Image processing means 54 Computing means 61 Distance portion 62 Near-distance portion 63 Segment line 71 Center of pupil 72 Line passing through the center of pupil and connecting pupil diameter 73 Line of sight 74 Lower eyelid edge 75 Front of cornea 76 Intersection of line of sight and front of cornea 77 Shooting direction

Claims (7)

[Claims] 1. A method of prescribing a multifocal contact lens for determining the height of a segment line of an alternating vision type multifocal contact lens, wherein optimum near vision value and optimum far vision value are measured, and both measured values are measured. A method for prescribing a multifocal contact lens, characterized in that the height of a segment line is determined based on this. 2. The optimum near-view value and the optimum far-view value are measured using photographed images obtained by photographing front images of the eyes during near vision and far vision, respectively. Item 2. A method for prescribing a multifocal contact lens according to Item 1. 3. The optimum near vision value is measured using a captured image obtained by installing a photographing means on an extension of the line of sight during near vision and photographing a front image of the eyeball during near vision. The method for prescribing a multifocal contact lens according to claim 2, wherein: 4. A photographed image obtained by installing a photographing means on an extension line of the line of sight for distance vision to photograph a frontal image of the eyeball for near vision and to lower the center of the pupil for near vision. The vertical distance to the eyelid edge is measured, and the optimum near vision value is calculated based on the measured value, the downward angle of the near vision and the distance from the pupil center to the anterior surface of the cornea. Item 3. A method for prescribing a multifocal contact lens according to item 2. 5. The distance from the center of the pupil to the anterior surface of the cornea is measured using a cross-sectional image of an eyeball.
A method for prescribing the described multifocal contact lens. 6. A photographing means for photographing at least one of the front image and the cross-sectional image of the eyeball according to claim 2, an optimum near vision value from image data input from the photographing means, Input from the image processing unit and the image processing unit that measures at least one of the optimum distance vision value, the vertical distance from the pupil center to the lower eyelid edge in near vision, and the distance from the pupil center to the front surface of the cornea. A prescription system for a multifocal contact lens, comprising a calculation means for calculating the height of a segment line based on an actual measurement value. 7. The image data output from the photographing means is a photographic image, and the image data includes an image conversion means for converting the photographic image into image data which can be processed by the image processing means. A prescription system for a multifocal contact lens according to claim 6.