WO2005037091A1

WO2005037091A1 - Detector for measuring corneal power, method of measuring corneal power, program which be contained that detector and method of making database for rear side corneal power

Info

Publication number: WO2005037091A1
Application number: PCT/KR2003/002400
Authority: WO
Inventors: Jong-Il Park
Original assignee: A Medical Team Sekwang Medical Foundation
Priority date: 2003-10-15
Filing date: 2003-11-07
Publication date: 2005-04-28
Also published as: KR20030084880A; AU2003277719A1; KR100676276B1

Abstract

The present invention relates to a device for measuring a corneal refractive power, and more specifically, to a device that can draw attentions of the field to a radius of curvature of a corneal posterior surface and provide a background for classifying states of the cornea according to a certain rule. That is, the present invention comprises a device for measuring a radius of curvature of a corneal anterior surface, a device for measuring a radius of curvature of the corneal posterior surface and a calculating means for calculating the corneal refractive power by the dioptrics formula. The present invention further provides a method and a software program for forming a database of the corneal refractive power to perform a cataract operation successfully without a side effect such as the hyperopia.

Description

DETECTOR FOR MEASURING CORNEAL POWER, METHOD OF MEASURING CORNEAL POWER, PROGRAM WHICH BE CONTAINED THAT DETECTOR AND METHOD OF MAKING DATABASE FOR REAR SIDE CORNEAL POWER

TECHNICAL FIELD

The present invention relates to a device and a method for measuring a corneal refractive power. More particularly, it relates to a device and a method for measuring a corneal refractive power and further a software program that will be installed into the device and a method for forming a database of corneal refractive powers of a posterior surface of the cornea. That is, a device for measuring a corneal refractive power according to the present invention comprises a device for measuring a radius of curvature of a corneal anterior surface, a device for measuring a radius of curvature of a corneal posterior surface and a calculating means that calculates the corneal refractive power with a formula, i.e., K = KI + K2, known as a dioptrics formula, where K is a corneal refractive power, KI is a corneal refractive power of a corneal anterior surface and K2 is a corneal refractive power of a corneal posterior surface. KI and K2 can be expressed numerically as follow. KI = (1000 x (n2 - nl)) / rl, K2 = (1000 x (n3 - n2)) / r2, where nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea.

BACKGROUND ART

A cataract operation is usually performed to improve the eyesight by inserting an artificial lens into the eye. An exact corneal refraction power value of a patient should be known before the operation in order to decide a refractive power of the artificial lens that will be used for the operation. There are many different ways to correct the cornea as a Photo

Refractive Keratectomy (PRK), i.e., Excimer Laser Operation, and a Laser In- Situ Keratomileusis (LASIK), for example. After a kerato-refractive surgery, the corneal refractive power can be measured by methods such as a clinical history method using a subjective refraction inspection method or a hard contact lens method. However, it is not easy to measure an accurate corneal refractive power of a patient who has a career of the kerato-refractive surgery before the cataract operation. In addition, more satisfactory result of the cataract operation can be obtained when a previously measured data of the corneal refractive power of the patient is available before the cataract operation. Specially, in case of LASIK, because a sphere surface of the cornea is usually deformed, an actual corneal refractive power value can be obtained only when a corneal refractive power value measured by the subjective refraction method and an auto corneal refraction power value are known. However, because the corneal refractive power data of the patient measured before the LASIK operation is not available in many cases, an accurate corneal refractive power inspection prerequisite for the cataract operation is actually impossible. Therefore, the cataract operation has been performed in the field by deciding the corneal refractive power only with information on the radius of curvature of a corneal anterior surface and a refractive index correction constant, 0.3375, for example. That is, the corneal refractive power has usually been obtained by a correction formula as follows. K_RK = (1000 x 0.3375) / rl, where K is a corneal refractive power and rl is a radius of curvature of a corneal anterior surface that is measured by an auto kerato-refractometer (RK) . Accordingly, many medical devices for a measurement of the corneal refractive power has been manufactured depending on the above formula and a measurement method without any experimental verification or an accurate theoretical ground. According to many clinical data, when the cataract operation is performed only on the basis of the corneal refractive power that is calculated according to the above formula, there may be an error in the calculated corneal refractive power for the patient and which may cause hyperopia after the operation. In spite of the high possibility of the hyperopia after the cataract operation owing to the wrong measurement of corneal refractive power value, the cataract operation has still been frequently performed in the field based only on the corneal refractive power value calculated according to the above formula. Recently, many researchers has been paying their attentions to this matter and many individual ophthalmologists are performing the cataract operation by deciding a little lower corneal refractive power value than an actually measured value of the corneal refractive power. However, this method still has a potential danger of a side effect of the cataract operation because it does not have any consideration or sound ground on a corneal state of the patient .

DISCLOSURE OF INVENTION

Accordingly, the present invention is directed to a device and a method for measuring a corneal refractive power that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. An object of the present invention is to provide a device for measuring a corneal refractive power, a method for measuring the corneal refractive power, and a software program in order to provide a more accurate value of the corneal refractive power than the prior art. Another object of the present invention is to provide a device and a method for measuring the corneal refractive power that can accurately correct an error in a calculation of a corneal refractive power according to the prior art . Another object of the present invention is to provide an accumulated database that can provide a more credible approximation of the corneal refractive power of each individual patient and can be applied to other patients who have a same or similar state of the cornea. More specifically, the present invention is to provide a device and a method for measuring a corneal refractive power in order to perform a cataract operation more safely with a less side effect when the patient has a career of a kerato-refractive surgery before. Another object of the present invention is to provide a device and a method for measuring a corneal refractive power in which a corneal refractive power can be measured accordingly to an actual state of the cornea of individual patient by classifying the states of the cornea of the patient who has a career of a cornea correction operation before. Another object of the present invention is to provide a device and a method for measuring a corneal refractive power in which a radius of curvature of a corneal posterior surface can be used as a database to understand a corneal state of each individual patient.

The present invention will be described hereinafter more in detail. The present invention provides a device for measuring a corneal refractive power that comprises a device for measuring a radius of curvature of a corneal anterior surface; a device for measuring a radius of curvature of a corneal posterior surface; and a calculating means for calculating the corneal refractive power with formulas as follow: K = KI + K2, KI = (1000 x (n2 - nl)) / rl, K2 = (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is a corneal refractive power of a corneal anterior surface, K2 is a corneal refractive power of a corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea. In the above, the radius of curvature of the corneal anterior surface (rl) may be measured at a plurality of points on a circumference of a designated corneal anterior surface by an auto kerato-refractometer type device, and wherein the radius of curvature of the corneal posterior surface (r2) may be measured by measuring radii of curvature of intersecting points of horizontal and vertical slits in a designated best fit sphere surface by an ORB scanner type device and then using the method of least mean squares. An ORB scanner type device may be selected for measuring both of the radius of curvature of the corneal anterior surface (rl) and the radius of curvature of the corneal posterior surface (r2).

Both an auto kerato-refractometer type device and an ORB scanner type device may be selected for measuring the radius of curvature of the corneal anterior surface (rl) and the ORB scanner type device may be selected for measuring the radius of curvature of the corneal posterior surface (r2). A smaller value between a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the ORB scanner type device and a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato- refractometer (RK) type device, is selected as the corneal refractive power of the corneal anterior surface (KI). In the above, the radius of curvature of the corneal anterior surface (rl) and the radius of curvature of the corneal posterior surface (r2) may be measured at a same corneal sphere region. Diameters of corneal sphere regions for measuring the radii of curvature of corneal anterior and posterior surfaces (rl and r2) may be between 2. 5 mm and 3.5 mm or may be 3 mm. Another aspect of the present invention provides a device for measuring a corneal refractive power that comprises a device for measuring an average radius of curvature of plurality of points on a corneal sphere region; and a calculating means for calculating the corneal refractive power with the average radius of curvature. Another aspect of the present invention provides a device for measuring the corneal refractive power that comprises an auto kerato-refractometer (RK) type device, the auto kerato-refractometer type device obtaining a first corneal refractive power (KRK) by measuring the radius of curvature of the corneal anterior surface (rl) and then inputting the radius of curvature of the corneal anterior surface (rl) into a formula as follow: K_RK = (1000 x 0.3375)) / rl, where KRK is the first corneal refractive power and the rl is the radius of curvature of the corneal anterior surface; and a calculating means, the calculating means obtaining a second corneal refractive power by correcting the first corneal refractive power with a correction formula as follow: K = KRK x 1.114 - n, where K is the second corneal refractive power and n is a correction constant. In the above, the correction constant (n) is an average value of corneal refractive powers of the corneal posterior surface that is obtained by measuring radii of curvature of the corneal posterior surface and then inputting the radii of curvature of the corneal posterior surface into a formula as follow: K2 = (1000 x (n3 - n2)) / r2, where K2 is the corneal refractive power of the corneal posterior surface, n2 is a refractive index of the cornea, n3 is a refractive index of the aqueous humor and r2 is the radius of curvature of the corneal posterior surface. The correction constant (n) may be between 7 and 10. The correction constant may be 7.4 if the first corneal refractive power (KRK) is between 35 diopter and 42 diopter and the correction may be 9 if the first corneal refractive power (KRK) is under 34 diopter. Another aspect of the present invention provides a method for measuring a corneal refractive power that comprises the steps of measuring the radius of curvature of a corneal anterior surface; measuring the radius of curvature of the corneal posterior surface; and calculating the corneal refractive power with formulas as follow: K = KI + K2, KI = (1000 x (n2 - nl)) / rl, K2 = (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is a corneal refractive power of a corneal anterior surface, K2 is a corneal refractive power of a corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea. Another aspect of the present invention provides a software program included in a device for measuring the corneal refractive power that comprises the steps of inputting the radius of curvature of the corneal anterior surface (rl); inputting the radius of curvature of the corneal posterior surface (r2) measured by the ORB scanner type device; and calculating the corneal refractive power with formulas as follow: (a) K = KI + K2, (b) KI = (1000 x (n2 - nl)) / rl, (c) K2 = (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is the corneal refractive power of the corneal anterior surface, K2 is the corneal refractive power of the corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea. In the above, the radius of curvature of the corneal anterior surface

(rl) is measured either by the auto kerato-refractometer (RK) type device or the ORB scanner type device. Both the radius of curvature of the corneal anterior surface measured by the auto kerato-refractometer (RK) type device and the radius of curvature of the corneal anterior surface measured by an ORB scanner type device may be inputted in the step of inputting the radius of curvature of a corneal anterior surface. A smaller value between a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the ORB scanner type device and a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato-refractometer (RK) type device, is selected as the corneal refractive power of the corneal anterior surface (KI) in the step of calculating the corneal refractive power (K) . Another aspect of the present invention provides a software program included in a device for measuring the corneal refractive power that comprises the steps of inputting the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato-refractometer type device; calculating a first corneal refractive power (KRK) with a formula as follow: KRK = (1000 x 0.3775)) / rl, where KRK is the first corneal refractive power and rl is the radius of curvature of the corneal anterior surface; and calculating a second corneal refractive power (K) by correcting the first corneal refractive power with a formula as follow: K = KRK x 1.114 - n, where n is correction constant. In the above, the correction constant (n) is obtained by forming a database of corneal refractive powers of the corneal posterior surface from a sample group of patients and calculating an average value of the corneal refractive power of the corneal posterior surface stored in the database. The database may be classified into first and second groups. The first group corresponds to the corneal refractive power between 35 diopter and 42 diopter measured by thes auto kerato-refractometer type device and the second group corresponds to the corneal refractive power under 34 diopter measured by the auto kerato-refractometer type device. The correction constant for the first group may be between 7 and 8 or may be 7.4. The correction constant for the second group may be 9. The correct constant has a value obtained from the database when a diameter of the corneal sphere region for measuring the corneal refractive power of the corneal posterior surface is between 2. 5mm and 3.5 mm or 3 mm. Another aspect of the present invention provides a method for forming a database of the corneal refractive power of the corneal posterior surface that comprises the steps of forming a group of patients; obtaining the radius of curvature of the corneal posterior surface by the ORB scanner type device,^' and obtaining the corneal refractive power of the corneal posterior surface by the radius of curvature of the corneal posterior surface.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate an embodiment of the present invention and together with the description serve to explain the principles of that invention. In the drawings: FIG. 1 is a flow chart of a method for measuring a corneal refractive power according to the present invention; FIG. 2 is a block diagram of a structure of a device for measuring the corneal refractive power according to the present invention; FIG. 3 is a flow chart of a software program for calculating the corneal refractive power according to the present invention; FIG. 4 is a plan view of the cornea and a corneal sphere region for measuring a radius of curvature of a corneal anterior surface by an auto kerato-refractometer (RK) type device according to present invention; FIG. 5 is a plan view of the cornea and a corneal sphere region for measuring a radius of curvature of a corneal posterior surface by an ORB scanner type device according to the present invention; FIG. 6 is a cross-sectional view of the corneal sphere surface according to the present invention; FIG. 7 is a cross-sectional view illustrating a state of the cornea depending on a radius of curvature measured by the auto kerato-refractometer (RK) and the ORB scanner type devices. FIG. 8 is a graph illustrating a measured result of the corneal refractive power according to the present invention; FIG. 9 is a block diagram illustrating a method for correcting the corneal refractive power according to the prior art and the present invention; FIG. 10 is a flow chart illustrating a method for forming a database to obtain a correction constant; and FIG. 11 is a comparative graph of results of the corneal refractive power according to the prior and the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to illustrated embodiments of the present invention, an example of which is shown in the accompanying drawings. Wherever possible, same reference numbers will be used throughout the drawings to refer to the same parts. FIG. 1 is a flow chart of a method for measuring a corneal refractive power according to the present invention and FIG. 2 is a block diagram of a structure of a device for measuring the corneal refractive power according to the present invention. As shown in figures, a device for measuring a corneal refractive power according to the present invention comprises a device for measuring a radius of curvature of a corneal anterior surface (10-1), a device for measuring a radius of curvature of a corneal posterior surface (20-1) and a calculating means (30-1). FIG. 4 is a plan view of the cornea and a corneal sphere region for measuring a radius of curvature of a corneal anterior surface by an auto kerato-refractometer (RK) type device according to present invention and FIG. 5 is a plan view of the cornea and a corneal sphere region for measuring a radius of curvature of a corneal posterior surface by an ORB scanner type device according to the present invention. As shown in figures, the corneal sphere region is defined on anterior and posterior surfaces of the cornea and the radius of curvature is measured with respect to the corneal sphere region. The corneal refractive power according to the present invention can be measured with a formula as follows that is known as a formula of dioptrics system: K - KI + K2, (1) KI = (1000 x (n2 - nl)) / rl, (2) K2 = (1000 x (n3 - n2)) / r2, where (3) K is the corneal refractive power, KI is a corneal refractive power of a corneal anterior surface, K2 is a corneal refractive power of a corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea. A method for measuring the radius of curvature of the corneal anterior and posterior surfaces according to the present invention will be described more in detail hereinafter with reference to FIG. 4 and FIG. 5. The devices for measuring the radius of curvature of the cornea can be classified into two different types. One is a device for measuring the radius of curvature of the corneal anterior surface and the other is a device for measuring the radius of curvature of the corneal posterior surface. The auto kerato-refractometer (RK) is one of the device for measuring the radius of curvature of the corneal anterior surface and the ORB scanner, i.e., a corneal topography analyzer, is one of the device for measuring the radius of curvature of the corneal posterior surface. In an embodiment of the present invention, one of the auto kerato-refractometer (RK) and the ORB scanner or both of them are selected as the device for measuring the radius of curvature of the corneal anterior surface. The ORB scanner is selected as the device for measuring the radius of curvature of the corneal posterior surface. As shown in FIG. 4, the corneal sphere region 200 having a certain radius from a center point 110 of the cornea is defined on the corneal anterior surface 100 and plurality of points is defined on a circumference of the corneal sphere region 200. The auto kerato-refractometer (RK) measures the radius of curvature of the corneal anterior surface by measuring the radius of curvature of the plurality of points and making an average of them. Meanwhile, as shown in FIG. 5, the corneal sphere region for measuring the radius of curvature of the corneal posterior surface is defined on the corneal posterior surface and is set as a best fit sphere (BFS). A plurality of horizontal and vertical slits 222 and 221 is defined on the best fit sphere (BFS) and a plurality of intersecting points is formed by the crossing horizontal and vertical slits. The ORB scanner obtains the radius of curvature of the corneal posterior surface by measuring the radius of curvature of the plurality of points and then making an average of them. FIG. 6 is a cross-sectional view of the corneal sphere surface according to the present invention. As shown in the figure, the auto kerato-refractometer (RK) obtains information on the radius of curvature of the corneal anterior surface along the circumference of the corneal sphere region while the ORB scanner obtains information on the radius of curvature of a center area of the corneal posterior surface. FIG. 7 is a cross-sectional view illustrating a state of the cornea depending on a radius of curvature measured by the auto kerato-refractometer (RK) and the ORB scanner type devices. If the radius of curvature of the corneal anterior surface (ΓRK) is smaller than the radius of curvature of the corneal posterior surface (Γ_ORB). the cornea in the corneal sphere region will be a projected type cornea as shown in (a) of FIG. 7. If the ΓRK is same as the Γ_ORB, the cornea in the corneal sphere region will be a normal type cornea as shown in (b) of FIG. 7. If the ΓRK is bigger than the ΓORB, the corneal in the corneal sphere region will be a depressed type cornea. As stated above, the radii of curvature of the corneal anterior and posterior surfaces can be measured either by the auto kerato-refractometer (RK) or the ORB scanner. The corneal refractive power according to the present invention can be obtained by the dioptrics formula. The auto kerato- refractometer (RK) and the ORB scanner can be selectively used for measuring the radius of curvature depending on the state of the cornea. In the formula, KI is the corneal refractive power of the corneal front surface and the K2 is the corneal refractive power of the corneal posterior surface. The corneal refractive power KI can be obtained from the radius of curvature of the corneal anterior surface (rl) measured either by the auto kerato-refractometer (RK) or the ORB scanner. If the corneal refractive power of the corneal anterior surface is obtained from the radius of curvature of the corneal anterior surface that is measured by the auto kerato-refractometer (RK) , the corneal refractive power is defined as a Kl(RK). If the corneal refractive power of the corneal anterior surface is obtained from the radius of curvature of the corneal anterior surface that is measured by the ORB scanner, the corneal refractive power of the corneal anterior surface is defined as Kl(ORB). If the corneal refractive power of the corneal posterior surface is obtained from the radius of curvature of the corneal posterior surface that is measured by the ORB scanner, the corneal refractive power of the corneal posterior surface is defined as K2(0RB). Accordingly, the formula (1) can be expressed as follow: K = KKRK) + K2(0RB) or K = Kl(ORB) + K2(0RB) The corneal refractive powers Kl(RK) and Kl(ORB) usually has a different value depending on the state of the cornea. Therefore, it is preferable to select a smaller value among those corneal refractive powers as the corneal refractive power of the corneal anterior surface (KI) for the formula (1). That is, if the state of the cornea is the projected type, the Kl(RK) is selected and if the state of the corneal is the depressed type, the Kl(ORB) is selected. When the state of the cornea is the normal type, both of the Kl(RK) and Kl(ORB) can be used for KI in the formula (1). FIG. 8 is a graph illustrating a measured result of the corneal refractive power according to the present invention. The graph is obtained from a group of cataract patients. In the graph, method 1 shows a measured corneal refractive power when the Kl(RK) is selected for the formula (2) and method 2 shows a measured corneal refractive power when the Kl(ORB) is selected for the formula (1). In the graph, the bar type graph shows the corneal refractive power of the corneal anterior surface measured before an cataract operation and the lowest curve shows a real corneal refractive power of the corneal front surface. Numbers of the horizontal axis are classifying numbers of the cataract patients. The closer to the real curve, the more accurate result will be provided in the graph. As shown in the graph, if the cornea is a projected type, the Kl(RK) provides a more accurate result as in a range from 2 to 8 and if the cornea is the depressed type, the Kl(ORB) provides a more accurate result as in range 1, 5 and 7 of the horizontal axis. The corneal sphere region for measuring the radius of curvature of the corneal anterior surface is coincides with the corneal sphere region for measuring the radius of curvature of the corneal posterior surface so that more credible results can be acquired. A diameter of the corneal sphere region may be between 2. 5 mm and 3.5 mm and desirably it may be 3 mm. As stated above, the ORB scanner is selected as the device for measuring the radius of curvature of the corneal posterior surface. The ORB scanner defines the best fit sphere (BFS) on the corneal posterior surface and then defines a plurality of horizontal and vertical slits in the best fit sphere (BFS). The ORB scanner subsequently measures the radius of curvature of the intersecting points of the horizontal and vertical slits and then produces an average value of the radius of curvature of the points. Though the ORB scanner is selected for measuring the radius of curvature of the corneal posterior surface in the present invention, any other device for measuring the radius of curvature of the corneal posterior surface can be substituted for the ORB scanner . A method for measuring the corneal refractive power according to the present invention will be described more in detail hereinafter with reference to figures attached. FIG. 3 is a flow chart of a software program for calculating the corneal refractive power according to the present invention. The method for measuring the corneal refractive power of the present invention comprises three steps. The first step is for measuring the radius of curvature of the corneal anterior surface, the second step is for measuring the radius of curvature of the corneal posterior surface and the third step is for calculating the corneal refractive power with the measured radii of curvature of the corneal anterior and posterior surfaces. In addition, the method can be divided into three different methods. In the first method, the radius of curvature of the corneal anterior surface is measured by the auto kerato-refractometer (RK) type device in the first step and the radius of curvature of the corneal posterior surface is measured by the ORB scanner type device in the second step. The auto kerato-refractometer (RK) type device obtains the radius of curvature of the corneal anterior surface by defining the corneal sphere region on the corneal anterior surface and then measuring the plurality of points along the circumference of the corneal sphere region. The ORB scanner type device obtains the radius of curvature of the corneal posterior surface by defining the best fit sphere (BFS) on the corneal posterior surface, forming a plurality of horizontal and vertical slits in the best fit sphere (BFS) and then measuring the plurality of intersecting points of the horizontal and vertical slits. A final value of the radius of curvature of the corneal posterior surface can be obtained by the method of least mean squares in the ORB scanner type device. In the second method, the ORB scanner type device measures both the radii of curvature of the corneal anterior and posterior surfaces. The corneal refractive power obtained by the first and second methods is more accurate than the corneal refractive power obtained by a clinical history method. In the third method, the radius of curvature of the corneal anterior surface is measured by both the auto kerato-refractometer (RK) type device and the ORB scanner type device in the first step and the radius of curvature of the corneal posterior surface is measured by the ORB scanner type device in the second step. The corneal refractive power (K) is calculated by the formula (1) in the third step. That is, two corneal refractive powers (KI) are obtained respectively with the radii of curvature of the anterior surface measured by the auto kerato-refractometer (RK) type device and the ORB scanner type device and a smaller corneal refractive power (KI) between the two is selected for the formula (1). The third method can provide a more accurate corneal refractive power (K) by considering an individual state of the cornea. FIG. 11 is a comparative graph of results of the corneal refractive power of cataract patients according to the prior and the present invention. FIG. 11 shows a real corneal refractive power, a corneal refractive power measured by the typical arts and the corneal refractive power measured by the present invention. In FIG. 11, the bar type graph shows the real corneal refractive power measured before the cataract operation and the highest curve shows the corneal refractive power measured by the typical arts. The closer to the real corneal refractive power, the more accurate the result in the graph. It is more desirable for the measured corneal refractive power to be little bit lower than the real corneal refractive power. The highest curve is the result of the measured corneal refractive power by the conventional auto kerato- refractometer (RK) and it shows a great deviation from the real corneal refractive power. Accordingly, a measurement of the corneal refractive power according to the prior art may increase the possibility of the side effect such as a hyperopia after the cataract operation. However, as shown in the figure, the method 1 and 2 of the present invention provides a very close value of the corneal refractive power to the real value of the corneal refractive power. Though it is not shown in the figure, the third method of the present invention can provide a more accurate result by considering the individual state of the cornea by taking the smaller value among the two corneal refractive powers (KI) measured by two different type of measuring device as stated before. FIG. 9 is a block diagram illustrating a method for correcting the corneal refractive power according to the prior art and the present invention and FIG. 10 is a flow chart illustrating a method for forming a database to obtain a correction constant. A method for correcting the corneal refractive power measured by the prior art will be described hereinafter with reference to the figures attached. A first corneal refractive power (KRK) is obtained by measuring only the radius of curvature of the corneal anterior surface (rl) and then inputting the radius of curvature (rl) into a formula as follow: KRK = (1000 x 0.3375) / rl, where (4) KRK is the corneal refractive power measured by the auto kerato- refractometer (RK) type device and the rl is the radius of curvature of the corneal anterior surface. A second corneal refractive power (K) can be obtained by inputting the first corneal refractive power (KRK) into a formula as follow: K = KRK x 1.114 - n, where (5) K is the second corneal refractive power and n is a correction constant. The device for correcting the corneal refractive power comprises the auto kerato-refractometer (RK) type device for measuring the radius of the curvature and a calculating means for correcting the corneal refractive power with the correction formula. The correction constant (n) can be decided as follow. A sample group of patients is defined and the radii of curvature of the corneal posterior surface (r2) of the group are measured. The measured radius of curvature (r2) is put into the formula (2) in order to calculate the corneal refractive power (K2). The correction constant (n) is finally obtained by taking an average value of those corneal refractive powers (K2) . If the sample group is formed with the patients who have careers of the LASIK operations, the above correction formula will be more useful to the patient who has experienced the LASIK operation when the real corneal refractive power is not available. According to the present invention, a relatively accurate corneal refractive power can be provided only by the auto kerato-refractometer (RK) without the expensive ORB scanner type device. The correction formula (5) can be obtained as follows. KRK = (1000 x 0.3375) / rl, and then KRK x [1000 x (n2-nl)] / [1000 x 0.3375] = [1000 x(n2-nl)] / rl = KI, and then KRK x [(1000 x 0.376) / (1000 x 0.3375)] = KI, where nl is a refractive index of the air and has a value of 1, and n2 is a refractive index of the cornea and has a value of 1.376. so, KI = KRK x 1.114. If the corneal refractive power of the corneal anterior surface (KI) is put into the formula (1), the correction formula (5) is obtained. If the sample group is formed with the patients having the LASIK career, the correction constant is between 7 and 10. However, the idea of the present invention can be applied not only to the sample group of the patients having the LASIK operation but also to other sample group of patients having any other operation career. In addition, a more credible result can be obtained by changing the correction constant according to the states of the cornea of the sample group. That is, if the corneal refraction power KRK is between 35 diopters and 42 diopters, it is desirable to correct the corneal refractive power KRK with the correction constant value of 7.4. The correction constant may be 9 if the corneal refractive power KRK is under 34 diopters. The reason for using a different correction constant above is that the corneal refractive power shows a great difference depending on a degree of a deformation of the cornea. It is desirable to make the corneal sphere region for measuring the radius of curvature of the corneal posterior surface by the ORB scanner same as the corneal sphere region for measuring the radius of curvature of the corneal anterior surface in order to increase the credibility of the calculated corneal refractive power (K). A diameter of the corneal sphere region is desirably between 2.5 and 3.5 mm and more desirably is 3mm. The present invention stated above can be applied to the conventional device by adding a software program to the conventional device. The software program of the present invention comprises a first step of input of the rl, a second step of input of r2 and a third step of calculation. The measured radius of curvature of the corneal anterior surface (rl) is inputted in the first step and the measured radius of curvature of the corneal posterior surface (r2) is inputted in the second step. The software program will be included in a measuring system that comprises the devices for measuring the radii of curvature of the corneal anterior and posterior surfaces. The corneal refractive power (K) is calculated in the third step with the formula (1), (2) and (3). The radius of curvature of the corneal anterior surface (rl) is measured either by the auto kerato-refractometer (RK) type device or the ORB scanner type device and the radius of curvature of the corneal posterior surface (r2) is measured by the ORB scanner type device. A proper corneal refractive power of the corneal anterior surface should be chosen from the corneal refractive powers measured by both of the above devices depending on the state of the cornea. However, it is enough to select a smaller value as the corneal refractive power of the corneal anterior surface (KI) without considering the state of the cornea in the present invention. The credible result of this can be verified in FIG. 11. The idea of the present invention can be embodied only by adding a correction program to the usual auto kerato-refractometer (RK) type device. The present invention further provides a device for measuring the corneal refractive power having a software program. More specifically, the software program comprises a step of inputting a radius of curvature of a corneal anterior surface (rl) measured by an auto kerato-refractometer type device, a step of calculating a first corneal refractive power (KRK) with a formula as follow: KRK = (1000 x 0.3775)) / rl, where K is the first corneal refractive power and rl is the radius of curvature of the corneal anterior surface, and a step of calculating a second corneal refractive power (K) by correcting the first corneal refractive power with a formula as follow: K = KRK x 1.114 - n, where n is correction constant. The correction constant (n) is obtained by forming a database of corneal refractive powers of a corneal posterior surface from a sample group of patients and calculating an average value of the corneal refractive power of the corneal posterior surface stored in the database. The database maybe classified into many different groups depending on the corneal refractive power measured by the auto kerato-refractometer (RK) type device. It is desirable to make a first group correspond to the corneal refractive power between 35 diopter and 42 diopter and the second group correspond to the corneal refractive power under 34 diopter. The correction constant for the first group is usually between 7 and 8, and it is experimentally desirable for the correction constant to have a value of 7.4. Undoubtedly, the correction constant may be vary as the size of the same group becomes bigger. Meanwhile, the experimentally verified value of the correction constant is 9 and this value may vary as the size of the sample group becomes bigger. The correction constant is also dependent on a position of the selected corneal sphere region for a measurement. The correction constant is obtained from the database when a diameter of the corneal sphere region for measuring the corneal refractive power of the corneal posterior surface is between 2. 5 and 3.5 mm. It is more desirable for the correct constant to have a value obtained from the database when a diameter of a corneal sphere region for measuring the corneal refractive power of the corneal posterior surface is 3 mm. The present invention further provides a method for forming a database of a corneal refractive power of a corneal posterior surface comprising the steps of forming a group of same patients, obtaining a radius of curvature of a corneal posterior surface by an ORB scanner type device, and obtaining the corneal refractive power of the corneal posterior surface by the radius of curvature of the corneal posterior surface. It will be apparent to those skilled in the art that various modifications and variation can be made in the system and method for the electronic commerce without departing from the spirit or scope of the present invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

As mentioned before, the present invention have the following advantages in the field. According to the present invention, devices, methods and software programs are provided to obtain a more credible corneal refractive power of a cataract patent than the prior art by the dioptrics formula. Besides, the present invention points out an error of a conventional method for measuring the corneal refractive power that has been repeated in the field and provides a theoretical background for correcting the corneal refractive power. The present invention make it possible to form a data base for estimating a corneal state of an individual patient and apply it to patients having a similar corneal state. Above all, the present invention greatly reduces the possibility of a side effect of the cataract operation when the patient has a career of a LASIK operation. The present invention further provides a more proper way of measuring the corneal refractive power by classifying patients into several group having similar corneal state and then considering the corneal state of the patient before an cataract operation. The present invention pays an attention to an importance of a radius of curvature of a corneal posterior surface and utilizes it for understating the individual state of each patient. To support above technical idea according to the present invention, a software is additionally provided.

Claims

1. A device for measuring a corneal refractive power, comprising: a device for measuring a radius of curvature of a corneal anterior surface; a device for measuring a radius of curvature of a corneal posterior surface; and a calculating means for calculating the corneal refractive power with , formulas as follow: K = KI + K2, KI = (1000 x (n2 - nl)) / rl, K2 = (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is a corneal refractive power of a corneal anterior surface, K2 is a corneal refractive power of a corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea.

2. The device according to claim 1, wherein the radius of curvature of the corneal anterior surface (rl) is measured at a plurality of points on a circumference of a designated corneal anterior surface by an auto kerato- refractometer type device, and wherein the radius of curvature of the corneal posterior surface (r2) is measured by measuring radii of curvature of intersecting points of horizontal and vertical slits in a designated best fit sphere surface by an ORB scanner type device and then using the method of least mean squares.

3. The device according to claim 1, wherein an ORB scanner type device is selected for measuring both of the radius of curvature of the corneal anterior surface (rl) and the radius of curvature of the corneal posterior surface (r2).

4. The device according to claim 1, wherein both an auto kerato- refractometer type device and an ORB scanner type device are selected for measuring the radius of curvature of the corneal anterior surface (rl) and the ORB scanner type device is selected for measuring the radius of curvature of the corneal posterior surface (r2), and wherein a smaller value between a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the ORB scanner type device and a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato-refractometer (RK) type device, is selected as the corneal refractive power of the corneal anterior surface (KI).

5. The device according to claim 1,2, 3 or 4, wherein the radius of curvature of the corneal anterior surface (rl) and the radius of curvature of the corneal posterior surface (r2) are measured at a same corneal sphere region.

6. The device according to claim 1,2,3 or 4, wherein diameters of corneal sphere regions for measuring the radii of curvature of corneal anterior and posterior surfaces (rl and r2) are between 2. 5 mm and 3.5 mm.

7. The device according to claim 1,2,3 or 4, wherein diameters of corneal sphere regions for measuring the radii of curvature of corneal anterior and posterior surfaces (rl and r2) are 3 mm.

8. A device for measuring a corneal refractive power, comprising: a device for measuring an average radius of curvature of plurality of points on a corneal sphere region; and a calculating means for calculating the corneal refractive power with the average radius of curvature.

9. The device according to claim 8, wherein the device is an ORB scanner type device in which the corneal sphere region is set as a best fit sphere (BFS), a plurality of horizontal and vertical slits are defined on the best fit sphere

(BFS) and then the average radius of curvature is calculated by applying the method of least mean squares to radii of curvatures of intersecting points of the horizontal and vertical slits.

10. The device according to claim 9, wherein a diameter of the best fit sphere (BFS) is 3 mm.

11. A device for measuring a corneal refractive power, comprising: an auto kerato-refractometer type device, the auto kerato-refractometer type device obtaining a first corneal refractive power (KRK) by measuring a radius of curvature of a corneal anterior surface (rl) and then inputting the radius of curvature of the corneal anterior surface (rl) into a formula as follow: KRK = (1000 x 0.3375)) / rl, where KRK is the first corneal refractive power and the rl is the radius of curvature of the corneal anterior surface; and a calculating means, the calculating means obtaining a second corneal refractive power by correcting the first corneal refractive power with a correction formula as follow: K = KRK x 1.114 - n, where K is the second corneal refractive power and n is a correction constant.

12. The device according to claim 11, wherein the correction constant (n) is an average value of corneal refractive powers of the corneal posterior surface that is obtained by measuring radii of curvature of the corneal posterior surface and then inputting the radii of curvature of the corneal posterior surface into a formula as follow: K2 = (1000 x (n3 - n2)) / r2, where K2 is the corneal refractive power of the corneal posterior surface, n2 is a refractive index of the cornea, n3 is a refractive index of the aqueous humor and r2 is the radius of curvature of the corneal posterior surface.

13. The device according to claim 11, wherein the correction constant is between 7 and 10.

14. The device according to claim 11, wherein the correction constant is 7.4 if the first corneal refractive power (KRK) is between 35 diopter and 42 diopter and the correction is 9 if the first corneal refractive power is under 34 diopter.

15. The device according to claim 11, 12, 13 or 14, wherein a diameter of a corneal sphere region for measuring the radius of curvature of the corneal anterior surface is between 2.5 mm and 3. 5 mm.

16. The device according to claim 11, 12, 13 or 14, wherein a diameter of a corneal sphere region for measuring the radius of curvature of a corneal anterior surface is 3mm.

17. A method for measuring a corneal refractive power, comprising: measuring a radius of curvature of a corneal anterior surface; measuring a radius of curvature of a corneal posterior surface; and calculating the corneal refractive power with formulas as follow: K = KI + K2, KI = (1000 x (n2 - nl)) / rl, K2 = (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is a corneal refractive power of a corneal anterior surface, K2 is a corneal refractive power of a corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea.

18. The method according to claim 17, wherein the radius of curvature of the corneal anterior surface (rl) is measured at a plurality of points on a circumference of a designated corneal anterior surface by an auto kerato- refractometer type device, and wherein the radius of curvature of the corneal posterior surface (r2) is measured by measuring radii of curvature of intersecting points of horizontal and vertical slits in a designated best fit sphere surface by an ORB scanner type device and then using the method of least mean squares.

19. The method according to claim 17, wherein an ORB scanner type device is selected for measuring both the radius of curvature of the corneal anterior surface (rl) and the radius of curvature of the corneal posterior surface (r2).

20. The method according to claim 17, wherein both an auto kerato- refractometer type device and an ORB scanner type device are selected for measuring the radius of curvature of the corneal anterior surface (rl) and the ORB scanner type device is selected for measuring the radius of curvature of the corneal posterior surface (r2), and wherein a smaller value between a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the ORB scanner type device and a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato-refractometer (RK) type device, is selected as the corneal refractive power of the corneal anterior surface (KI) .

21. The method according to claim 17, 18, 19 or 20, wherein diameters of corneal sphere regions for measuring the radii of curvature of corneal anterior and posterior surfaces (rl and r2) are between 2. 5 mm and 3.5 mm.

22. The method according to claim 17, 18, 19 or 20, wherein diameters of corneal sphere regions for measuring the radii of curvature of corneal anterior and posterior surfaces (rl and r2) are 3 mm.

23. A software program included in a device for measuring a corneal refractive power, comprising steps of : inputting a radius of curvature of a corneal anterior surface (rl); inputting a radius of curvature of a corneal posterior surface measured by the ORB scanner type device (r2); and calculating the corneal refractive power with formulas as follow: (a) K = KI + K2, (b) KI = (1000 x (n2 - nl)) / rl, (c) K2 - (1000 x (n3 - n2)) / r2, where K is the corneal refractive power, KI is a corneal refractive power of the corneal anterior surface, K2 is a corneal refractive power of the corneal posterior surface, nl, n2 and n3 are refractive indices of the air, the cornea and the aqueous humor, respectively and rl and r2 are radii of curvature respectively of anterior and posterior surfaces of the cornea.

24. The program according to claim 23, wherein the radius of curvature of the corneal front surface (rl) is measured either by an auto kerato- refractometer (RK) type device or an ORB scanner type device.

25. The program according to claim 23, wherein both a radius of curvature of the corneal anterior surface (rl) measured by an auto kerato- refractometer (RK) type device and a radius of curvature of the corneal anterior surface measured by an ORB scanner type device are inputted in the step of inputting the radius of curvature of a corneal anterior surface, and wherein a smaller value between a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the ORB scanner type device and a corneal refractive power of the corneal anterior surface that is calculated with the radius of curvature of the corneal anterior surface (rl) measured by the auto kerato-refractometer (RK) type device, is selected as the corneal refractive power of the corneal anterior surface (KI) in the step of calculating the corneal refractive power (K).

26. A program included in a device for measuring a corneal refractive power, comprising: inputting a radius of curvature of a corneal anterior surface (rl) measured by an auto kerato-refractometer type device; calculating a first corneal refractive power (KRK) with a formula as follow: KRK = (1000 x 0.3775)) / rl, where KRK is the first corneal refractive power and rl is the radius of curvature of the corneal anterior surface; and calculating a second corneal refractive power (K) by correcting the first corneal refractive power with a formula as follow: K = KRK x 1.114 - n, where n is correction constant.

27. The program according to claim 26, wherein the correction constant (n) is obtained by forming a database of corneal refractive powers of a corneal posterior surface from a sample group of patients and calculating an average value of the corneal refractive power of the corneal posterior surface stored in the database.

28. The program according to claim 27, wherein the database is classified into first and second groups, the first group corresponding to the corneal refractive power between 35 diopter and 42 diopter measured by an auto kerato-refractometer type device and the second group corresponding to the corneal refractive power under 34 diopter measured by the auto kerato- refractometer type device.

29. The program according to claim 28, wherein the correction constant for the first group is between 7 and 8.

30. The program according to claim 28, wherein the correction constant for the first group is 7.4.

31. The program according to claim 28, wherein the correction constant for the second group is 9.

32. The program according to claim 27, wherein the correct constant has a value obtained from the database when a diameter of a corneal sphere region for measuring the corneal refractive power of the corneal posterior surface is between 2. 5mm and 3.5 mm.

33. The program according to claim 27, wherein the correct constant has a value obtained from the database when a diameter of a corneal sphere region for measuring the corneal refractive power of the corneal posterior surface is 3 mm.

34. A method for forming a database of a corneal refractive power of a corneal posterior surface, comprising-' forming a group of same patients; obtaining a radius of curvature of a corneal posterior surface by an ORB scanner type device,^' and obtaining the corneal refractive power of the corneal posterior surface by the radius of curvature of the corneal posterior surface.