KR100876854B1 - Corneal shape measuring apparatus and method - Google Patents

Abstract

Disclosed are a corneal shape measuring apparatus and method capable of measuring corneal shape of an eye to be examined and displaying the state of the cornea as a color topographic map. The corneal shape measuring device, the aiming light source for emitting the aiming light for fixing the eye of the eye to be examined; An alignment and focusing light source for injecting a pair of focusing light into the eye; A measurement light source for irradiating the eye with the measurement light having a plurality of plinth ring shapes having the same center; A detector for detecting an image of the measurement light emitted from the measurement light source and reflected from the eye, and an image of the focusing light emitted from the alignment and focusing light source and reflected from the eye; And receiving the signal detected by the detector, comparing the distance between the pair of focusing light and the size of the measurement light of the plinth ring shape to calculate a distance between the corneal shape measuring device and the eye to be examined. And a calculating section for calculating a corneal curvature value from the position and distance of each ring of reflected measurement light.

Description

Apparatus and method for measuring cornea shape

BRIEF DESCRIPTION OF THE DRAWINGS The figure for demonstrating the structure of the conventional corneal shape measuring apparatus.

2 is a view for explaining a focusing error according to the distance between the corneal shape measuring device and the eyeball.

3 is a view for explaining the configuration of the corneal shape measuring apparatus according to an embodiment of the present invention.

4 is a plan view and a side cross-sectional view of a measurement light source used in the corneal shape measuring apparatus according to an embodiment of the present invention.

5 is a view showing a measuring light image of a collimated light, a focusing light and a plinth ring shape obtained in the corneal shape measuring apparatus according to an embodiment of the present invention.

6 is a flow chart showing a corneal shape measuring method according to an embodiment of the present invention.

FIG. 7 is a view illustrating a process of converting height data of a corneal image into three-dimensional coordinates in the corneal shape measuring method according to an embodiment of the present invention. FIG.

8 is a view showing a process of obtaining a corneal curvature value from a three-dimensional corneal shape in the corneal shape measuring method according to an embodiment of the present invention.

9 is a view showing a display screen of corneal data obtained by the corneal shape measuring method according to an embodiment of the present invention.

The present invention relates to a corneal shape measuring apparatus and method, and more particularly, to a corneal shape measuring apparatus and method capable of measuring the corneal shape of the eye to be examined and displaying the state of the cornea as a color topographic map. will be.

The corneal shape measuring device is an ophthalmic and optician-only measuring device for measuring corneal shape before and after surgery of a LASIK operator, or for measuring corneal shape of an eye for accurate prescription of a contact lens. Early corneal shape measuring apparatus, a single ring-shaped light having an infrared wavelength was incident on the cornea, the ring image reflected from the cornea was detected by a CCD camera, and then analyzed to measure the curvature of the cornea. . However, in this case, since only the curvature of the central corneal region can be known, a corneal shape measuring apparatus has been developed that can increase the number of rings and measure even the peripheral region of the cornea. Thus, the shape of the entire cornea can be measured and analyzed. The device is also called the Corneal Topographer. Recently, a corneal topography measuring device capable of measuring not only the curvature of the anterior cornea but also the curvature and thickness of the corneal endothelial (Posterior Cornea) has been developed, and in addition to the method of using multiple reflected ring images, Various corneal shape measurement methods such as an interferometer method using a projected image, a moire lattice method, and a slit scan method using scattered light have been developed. Among them, a method using a plurality of reflected ring images is most widely used, but even in this case, alignment optics and measurement algorithms for calculating and aligning the distance between the measuring device and the eyeball are different from device to device. Repeatability is also different from device to device.

1 is a view for explaining the configuration of a conventional corneal shape measuring apparatus, as shown in Figure 1, the conventional corneal shape measuring apparatus, aiming to fix the eye of the eye to be examined (Eye Fixation) Aiming light source 12 for emitting light, measurement light source 14 for irradiating the cornea of the eye 5 to the measurement light (Illumination LED) in the form of a Placido Ring plate having the same center, and the eye ( And a detector 16 such as a CCD camera for detecting an image reflected from the cornea of 5). In Fig. 1, reference numeral 18 denotes a beam splitter mirror for changing the path of the aiming light while maintaining the path of the measurement light. Referring to the operation of the corneal shape measuring device, first, aiming light is irradiated from the aiming light source 12 in order to fix the eye of the eye to be examined 5, and if necessary, the objective lens and the beam splitter mirror 18 are Passes and creates an image of the aiming light in the cornea. In addition, the measuring light in the form of a ply ring ring having the same center is irradiated from the measuring light source 14, and is reflected from the cornea, and the image of the reflected measuring light is partially reflected by the beam splitter mirror 18, and a part is beam splitter. It passes through the mirror 18, the relay lens, and the like, and is detected by the detector 16. At this time, the measuring device is moved up, down, left, and right using an algorithm of an alignment optical system (not shown) until the detected image appears most clearly. In this manner, when the detected image is sharpest, a measurement algorithm can be used to detect the image of each ring, calculate the respective curvature values, and calculate the corneal surface shape therefrom.

As described above, when measuring the shape of the cornea using the reflected ring image, the relative distance between the measurement equipment and the eye must be maintained accurately and precisely, so that accurate measurement values can be repeatedly obtained. FIG. 2 is a view for explaining a focusing error according to the distance between the corneal shape measuring device and the eyeball. As shown in FIG. 2, when the distance between the eye 5 and the measurement light source 14 is not maintained accurately, FIG. (Positioning error) and the size of the image formed on the detector 16 are also different, resulting in a focusing error. In order to eliminate such a focusing error, a method of installing an alignment optical system composed of a plurality of optical devices is known. However, these devices use a large number of optical components, which increases manufacturing costs, and since the optical components must be accurately aligned, the device configuration is also difficult.

In addition, in the corneal shape measuring apparatus, since the accuracy of the measured value varies according to a measurement algorithm that calculates the position and distance of each ring from the image detected by the detector 16, the image is processed more precisely and accurately. It is necessary to develop a measuring algorithm capable of developing the measuring light source. The measuring light in the form of a plinth ring irradiated from the measuring light source 14 is uniform and not only does not give fatigue to the subject even when measuring for a long time, but also the mechanism of the measuring light source 14 The enemy structure must be robust and sophisticated. In addition, the aiming brightness irradiated from the aiming light source 12, it should be clearly visible to fix the eye of the subject, should be reflected from the cornea in a constant shape without scattering.

Accordingly, an object of the present invention is to measure not only the central area of the cornea but also the shape of the entire cornea, including the peripheral area. It is to provide a corneal shape measuring apparatus and method that can be easily represented.

Another object of the present invention is to provide a corneal shape measuring apparatus and method capable of more precisely and accurately measuring corneal shape, and excellent in repeatability of shape measurement.

It is still another object of the present invention to provide a corneal shape measuring apparatus having an alignment optical system capable of reducing focusing error and a measuring algorithm capable of accurately processing a detected image.

In order to achieve the above object, the present invention, the aiming light source for emitting the aiming light for fixing the eye of the eye to be examined; An alignment and focusing light source for injecting a pair of focusing light into the eye; A measurement light source for irradiating the eye with the measurement light having a plurality of plinth ring shapes having the same center; A detector for detecting an image of the measurement light emitted from the measurement light source and reflected from the eye, and an image of the focusing light emitted from the alignment and focusing light source and reflected from the eye; And receiving the signal detected by the detector, comparing the distance between the pair of focusing light and the size of the measurement light of the plinth ring shape to calculate a distance between the corneal shape measuring device and the eye to be examined. Provided is a corneal shape measuring apparatus including a calculating section for calculating a corneal curvature value from the position and distance of each ring of reflected measurement light. In another aspect, the present invention, the step of emitting the aiming light, to fix the eye of the eye to be examined to the aiming light; After emitting a plurality of plinth ring-shaped measurement light and a pair of focusing light having the same center to reflect the measurement light and the focusing light in the cornea of the eye to be examined, the distance between the pair of focusing light and the pludo ring shape Compare the magnitudes of the measured light beams, move the position of the measuring equipment so that the distance between the pair of focusing light beams and the size difference of the light beams of the plinth ring shape is less than or equal to a predetermined value, Positioning; And detecting a region of the measurement light reflected from the cornea of the eye to be examined, and analyzing the measurement light to obtain a corneal curvature value.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail.

3 is a view for explaining the configuration of the corneal shape measuring apparatus according to an embodiment of the present invention. As shown in FIG. 3, the corneal shape measuring apparatus according to the present invention includes an aiming light source 30, an alignment and focusing light source 40, a measuring light source 50, a detector 70, and an operation unit 80. The aiming light source 30 emits the aiming light for fixing the eye of the eye 5 to be examined. The aiming light emitted from the aiming light source 30 is focused, or incident on the eye to be examined 5 through the reflection mirror 32, the beam splitter mirror 34, or the like, if necessary. By fixing the line of sight to the aiming light, it is possible to prevent the movement of the eye 5 during measurement.

The alignment and focusing light source 40 is for injecting a pair of focusing beams into the eye 5. The pair of focusing light is for adjusting the distance between the corneal shape measuring device and the eye to be examined 5. Specifically, by detecting the position of a pair of focusing light reflected from the cornea of the eye to be examined 5 to determine the distance between the focusing light, the size of the measurement light emitted from the measurement light source 50, specifically the focusing light The size of the measurement light of the plinth ring shape located closest to is obtained, and the distance between the focusing light and the image size of the measurement light are compared. At this time, the focus, the size difference between the distance and the measurement light image between the light is less than or equal to a predetermined value (threshold value), preferably, the focusing light, the size of the distance and the measurement light images and corneal shape measurement apparatus with the test to be equal between Adjust the distance between the eyes (5). In this way, the distance between the corneal shape measuring device and the eye to be examined 5 can be calculated from the position of the focusing light formed on the cornea of the eye to be examined. The eye 5 may be accurately and repetitively positioned at a distance between the eye 5, that is, at a working distance. The alignment and focusing light source 40 is preferably located obliquely at a predetermined angle with respect to the eye 5, for example, 15 to 25 degrees with respect to the central axis of the eye 5. For example, it may consist of two light sources 40 symmetrically positioned at an angle of 18 degrees. In this way, by using two focusing lights, the distance between the focusing lights and the size of the image of the measuring light can be compared, and the focusing light is incident on the eye 5 by a predetermined angle, thereby focusing on the internal optical system structure. It is easy to irradiate light to the central region of the cornea, and the detection of the focusing light in the detector 70 is also easy. The two focusing lights form a telecentric optical system that illuminates with parallel light, though not completely parallel light, through a lens in the internal optical system. Thus, even when the measuring device is moved, the two focusing lights are illuminated at a constant position and the distance of the two focusing light sources is kept constant. However, the measurement light illuminating the placeholder ring is the light which is directly illuminated to the eye 5 without passing through the lens. Therefore, when the measuring device approaches the eye 5, the measurement light in the shape of a plinth ring becomes large, and when the measuring device moves away from the eye 5, the measuring light also becomes small. By using this difference, when the distance between the focusing light and the size of the image of the measurement light are approximately the same as the critical point, it is determined that the focus position between the measuring device and the eye 5 is measured and measured.

The measurement light source 50 is an illumination system for irradiating the eye 5 with a plurality of Placido Ring-shaped measurement light having the same center, and the measurement light emitted from the measurement light source 50 is examined. It is reflected off the cornea of the eye 5 and is incident on the detector 70. 4 is a plan view and a side cross-sectional view of the measurement light source 50. As shown in FIG. 4, the measurement light source 50 includes a light emitting diode 54 which emits infrared measurement light instead of visible light, and the light emission. An integrating sphere shaped reflector plate 56 reflecting infrared light emitted from the diode 54 and a plurality of thin rings having the same center are formed to reflect the infrared light reflected from the reflector plate 56. It may be made of a ring plate ring 52 that transmits the ring-shaped light. The light emitting diode 54 is surrounded by a donut shape at the edge of the reflecting plate 56. In this way, by making the thickness of the plinth ring thin and using the infrared light emitting diode, the fatigue of the eye can be minimized even when measuring for a long time many times, and by using the principle of the reflector, many circuits and light emitting diodes are used as a whole. Without this, it is possible to irradiate light of a uniform amount of light. Further, the reflecting plate 56 and the plinth ring plate 52 are provided with holes 59 and 59a for aiming light and holes 58 and 58a for passing focusing light, respectively. Therefore, the aiming light is incident to the center of the eye to be examined 5 through the aiming light passing holes 59 and 59a respectively formed at the centers of the reflecting plate 56 and the flash ring plate 52, and the focusing light is Through the focusing light passing holes 58 and 58a formed around the center of the reflecting plate 56 and the plinth ring plate 52, the light enters the center peripheral portion of the eye 5 (see FIG. 5).

The detector 70 is an image of the measurement light emitted from the measurement light source 50 and reflected from the eye 5, and an image of focusing light emitted from the alignment and focusing light source 40 and reflected from the eye 5. Is detected, and the detected image, that is, the detected signal is transmitted to the calculation unit 80. As the detector 70, a conventional charge-coupled device (CCD) camera may be used. The calculation unit 80 functions as a software unit for receiving corneal shape information by receiving a signal (image) detected by the detector 70 and analyzing the signal using an ordinary measurement algorithm. The information analyzed by the calculation unit 80 is displayed on the display unit 82 as needed, and the display unit 82 may display images of the measurement light and the focusing light detected by the detector 70. In addition, corneal shape information calculated by the calculator 80 may be displayed in a color topographical map. The measurement algorithm of the calculation unit 80 calculates a corneal curvature value from the position and distance of each ring of the measurement light reflected by the eye 5, and expresses it as a color (multicolor) topographical map close to the actual corneal shape. To this end, it includes a number of conventional algorithms such as ring detection algorithm, ring discrimination algorithm, compensation algorithm, approximation algorithm, curvature distribution algorithm.

Referring to Figure 3, the operation of the corneal shape measuring apparatus according to the present invention, first, aiming light is emitted from the aiming light source 30, the eye of the eye 5 is fixed to the aiming light. Next, after the measurement light irradiated from the measurement light source 50 and the focusing light irradiated from the alignment and focusing light source 40 are reflected from the cornea of the eye to be examined 5, the beam splitter mirror 34 and the relay lens 36 Is detected by the detector 70. The positions of the aiming light and the focusing light are compared with the position of the measuring light by using the characteristics of the telecentric optical system, and when the center value of the light source, the distance between the light sources, and the distance to the ring meet the set conditions The eye to be examined 5 is positioned at the focus position of the measurement light. That is, in the two-dimensional image obtained by the detector 70, as shown in FIG. 5, aiming light and focusing light appear together with the measurement light in the shape of a plinth ring, and by using these three light sources, After detecting the ring, comparing the distance between the light source and the diameter of the ring, and using a guide that allows the user to easily indicate the measurement distance between the measurement equipment and the eye to be examined, the image when the ring is clearest You can get it. Therefore, if the eye 5 is positioned at the focal position of the measurement light emitted from the measurement light source 50 by moving the measurement device back, left, right, and up and down to conform to this focusing algorithm, the eye 5 and the measurement device The corneal shape is measured while keeping the distance between them constant. Due to the accuracy of this measurement, the distance between the measurement equipment and the eye to be measured is constant at every measurement, thereby improving the measurement repeatability of the system. The two-dimensional image obtained by the detector 70 is transferred to the calculation unit 80 through, for example, a USB terminal, and a general personal computer (PC) in which a measurement algorithm is implemented may be used as the calculation unit 80. have.

6 is a flow chart showing in more detail the corneal shape measuring method according to an embodiment of the present invention. As shown in FIG. 6, the corneal shape measuring method according to the present invention may be largely divided into four parts: a patient management part, an alignment and measurement part, a corneal topographic display part, and a corneal shape analysis and diagnosis part. In the patient management part, the subject's personal information and existing measurement history are managed (S 10), and whether or not the current corneal shape measurement is a new measurement (S 12). It is configured by making a database so that it can be diagnosed by displaying (S40) on a screen. On the other hand, if the current corneal shape measurement is a new measurement, proceed to the alignment and measurement portion, first output the corneal image (S 20), by applying the above-described alignment (focusing) algorithm (S 22), The ring-shaped measuring light is compared and the measuring device is moved to make the lights meet a set condition, that is, to be focused (S 24), and then the measurement is performed (S 30). In this case, it is preferable to display a visual guide on the display screen so that the user can accurately and easily fit the measurement distance, and when the correct measurement distance is reached, a normal measurement algorithm may be automatically performed.

Looking at the measurement portion (S 30) in detail, first, to store the corneal image during measurement, to detect the ring reflected from the cornea, and then to distinguish each ring by numbering each ring starting from the center of the ring, An image processing process is performed (S 310). The measuring ring-shaped measurement light irradiated from the measurement light source is reflected from the cornea, and its shape varies depending on the shape of the cornea. Therefore, it is necessary to properly detect the ring region reflected, so that the corneal curvature at that point can be obtained accurately. In order to detect the ring-shaped measurement light, a method of obtaining the center of the collimated light, drawing a profile line from the center to each meridian, and then obtaining each point where the gray level becomes the maximum is used. In the image processing process (S 310), a point that is not the actual ring area may be detected due to eyebrows or other noise signals among the points where the gray level is maximum. In this case, since the ring numbers to be stored in order from the center are mixed, it is necessary to rearrange the detected rings according to each ring number. To do this, you can reorder each ring to match the number by rescanning the rings in order from the center, eliminating the points where the rings of the same number are not connected in succession, and setting the index by the frequency of each ring. .

Next, by applying a compensation algorithm (S 320), after compensating for curvature error, system error, etc., generated due to poor ring division, the measured value of each ring is stored. The measurement value of each ring is determined by a preset value and a relational expression, and system error and the like are eliminated. For example, in order to quantify the ring image error, the length of the ring is obtained for each angle, and then approximated to a Fourier Series of appropriate order using a least square method. At this time, the reflected image of the circle of radius R is approximated to the Fourier series, so the remaining terms minus the constant term can be viewed as system error. In order to apply the compensation algorithm, for the standard model eye having a radius of curvature of -15D, -7D, 0D, + 7D, and + 15D, the coefficient of error is obtained for each ring in the same manner as above. Where the constant term is the average of the image. For all model eyes, the amplitude coefficients of the image mean and the error of each ring are stored, and a straight line representing the relationship between the image average of the ring and the amplitude coefficient of the error is obtained and stored as the least square root.

In order to approximate the measured value of the ring thus compensated for by a continuous curve, a Klein algorithm is applied to calculate height data of each point of the cornea (S330). Specifically, the coordinates of the actual cornea are obtained by connecting a continuous curve in the previous ring by using a Taylor polynomial to the point where the incidence slope of the placemat ring and the angle of reflection reflected by the cornea become the same. The point thus obtained becomes the height data of the cornea. Then, based on this, the above operation is repeated to obtain the inclination of the incident image with a different image length. This can be repeated for all rings to obtain height data for the entire cornea. The height data coordinates z and y calculated as described above are approximated by three-dimensional coordinates to obtain a three-dimensional shape of the cornea (S 340). Specifically, a Zernike polynomial that converts the calculated height data coordinates (z, y) into three-dimensional coordinates, and approximates the three-dimensional coordinates with a least square, as shown in FIG. By obtaining the coefficient of, the Zernnik polynomial representing the three-dimensional shape of the cornea can be obtained.

Using the approximated three-dimensional shape data, information such as curvature values for each point of the cornea can be calculated (S 32), and the corneal topographic map can be expressed by mapping the calculated curvature values to values of a predetermined color. (S 40). Specifically, as shown in FIG. 8, the Zernik polynomial, that is, the first derivative and the second derivative are determined at one point z1 and y1 of the three-dimensional cornea shape, and the curvature value at that point is obtained. Can be obtained. In the same manner, the curvature value can be obtained at each point of the entire cornea. The curvature value of each point obtained in this way is matched with the color value determined on the standard color palette, and the corneal topography is displayed. As described above, the corneal topographic map display unit displays various topographic maps suitable for the corneal characteristics using the data of each point calculated through the measurement algorithm (S40). Such corneal topographic maps include refractive maps, height maps, and three-dimensional corneal topographic maps (3D), in addition to sagittal maps and tangential maps that can be calculated from FIG. 8. Cornea map, Fourier map (Fourier map), Zernike map (Zernike map) and the like can be exemplified. 9 is a diagram illustrating an example of a corneal topographical display screen obtained in this manner.

Referring back to FIG. 6, in the final stage of corneal shape analysis and diagnosis, in addition to the data of each point calculated through the measurement algorithm, the shape of the cornea is used by using indices calculated through various topographic maps. The contact lens is prescribed to the most suitable (S 50), and if necessary, by comparing the value of the actual contact lens and the shape of the cornea, and calculating the height difference between the cornea and the contact lens, the suitability of the contact lens virtually Can be verified In addition, through the shape of the cornea, each index value (indices) can be numerically digitized so that pathological symptoms such as corneal stools and keratoconus can be easily understood, and the numerical value can be used for automatic diagnosis. This automatic diagnosis function, along with the subjective judgment of the doctor about the lesion, can help diagnose the lesion.

As described above, the corneal shape measuring apparatus according to the present invention enables the prescription of a contact lens that exactly fits the cornea of the subject, and provides accurate information about the cornea during LASIK, as well as quantifying the corneal shape data. By automatically diagnosing corneal abnormalities, it can help doctors determine disease. In addition, the corneal shape measuring apparatus according to the present invention, by irradiating the light of the plinth ring measurement light of a uniform amount of light, to minimize the fatigue of the eye, and improve the sharpness of the image reflected from the cornea, it is possible to easily detect and distinguish the ring have.

Claims (7)

An aiming light source emitting an aiming light to fix an eye of an eye to be examined; An alignment and focusing light source for injecting a pair of focusing light into the eye, wherein the distance between the focusing light remains constant even if the distance between the eye and the corneal shape measuring device changes; A measurement light source for irradiating the eye with the measurement light having a plurality of plinth ring shapes having the same center; A detector for detecting an image of the measurement light emitted from the measurement light source and reflected from the eye, and an image of the focusing light emitted from the alignment and focusing light source and reflected from the eye; And Receiving the signal detected by the detector, comparing the distance between the pair of focusing light and the size of the image of the measurement ring-shaped measurement light, to calculate the distance between the corneal shape measuring device and the eye to And a calculation unit configured to adjust a distance between the corneal shape measuring device and the eye to be examined, and calculating a corneal curvature value from an image of each ring of the measurement light reflected by the eye. The apparatus of claim 1, wherein the alignment and focusing light sources comprise two light sources symmetrically positioned at an angle of 15 to 25 degrees with respect to a central axis of the eye to be examined. According to claim 1, wherein the measurement light source, Light emitting diode for emitting infrared measurement light; An integrating sphere-shaped reflector reflecting infrared light emitted from the light emitting diode; And a plinth ring plate having a plurality of rings having the same center and transmitting infrared light reflected by the concave mirror to ring-shaped light. 4. The collimator of claim 3, wherein the reflecting plate and the plinth ring plate are provided with holes for aiming light and focusing light, respectively. And the focusing light is incident on the eye through the focusing light passing hole formed around the center of the reflecting plate and the plinth ring plate. The method of claim 1, wherein the information analyzed by the calculation unit is displayed on a display unit, and the display unit may display images of the measurement light and the focusing light detected by the detector, and the corneal shape information calculated by the calculation unit may be displayed. Corneal shape measuring device that is displayed in a color topographic map. Emitting the aiming light to fix the eye of the eye to the aiming light; Even if the distance between the eye and the corneal shape measuring device is changed, a pair of focusing light in which the distance between the focusing light is kept constant and a plurality of flashlight ring-shaped measuring light having the same center are emitted, and the measurement light is emitted from the cornea of the eye. And after reflecting focusing light, comparing the distance between the pair of focusing light and the size of the image of the measurement light of the plinth ring shape, and comparing the distance between the pair of focusing light and the measurement light of the plinth ring shape. Moving the position of the measurement equipment so that the difference in size is equal to or less than a predetermined value, such that the eye is placed at a focus position of the measurement light; And Detecting an image of the measurement light reflected from the cornea of the eye, and analyzing the image of the measurement light to obtain a corneal curvature value. The method of claim 6, further comprising displaying the corneal curvature using an index value and performing an automatic diagnosis through the numerical value.

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