A corneal reshaping lens based on big data elliptical model

Abstract

The present invention relates to the technical field of orthokeratology lenses based on big data elliptical models, and in particular to an orthokeratology lens based on a big data elliptical model. The orthokeratology lens based on the big data elliptical model significantly improves the fit between the lens and the cornea by designing a positioning arc area that fits the patient's cornea more closely, thereby improving the wearing comfort and stability of the lens. Compared with the traditional design method based on the average curvature of the junction point, the virtual elliptical model provides a continuously changing curvature calculation of the positioning arc area, so that the lens design is more in line with the actual corneal shape and thus better matches the patient's cornea. In addition, since the design can obtain a preset eccentricity value based on the patient's corneal radius, the optometrist can accurately fit the glasses without additional knowledge or operation, avoiding the problem of inaccurate or low efficiency of orthokeratology lens fitting due to lack of experience of doctors (or optometrists), thereby improving the fitting efficiency, accuracy and wearing comfort of orthokeratology lenses.

Description

Technical Field

[0001] The present invention relates to the technical field of orthokeratology lenses, and in particular to an orthokeratology lens based on a big data elliptical model. Background Art

[0002] Existing orthokeratology lenses are typically designed based on a zonal design, including a base curve zone, a reverse curve zone, a fitting curve zone (positioning curve zone), and a peripheral curve zone. Traditionally, the radius of the positioning curve zone is calculated based on the average corneal curvature of the corneal topography at the junction. This approach can result in insufficient fitting precision in the positioning curve zone, affecting wearing comfort and lens stability, and even potentially causing incorrect orthokeratology.

[0003] In addition, the existing technology requires optometrists to extract multiple parameters from corneal topography data, which increases the time and workload of fitting. The accuracy is also affected by the optometrist's operational stability and technical level when taking the topography, which makes the fitting efficiency, accuracy and wearing comfort of orthokeratology lenses low. Summary of the Invention

[0004] (1) Technical issues to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a corneal reshaping lens based on a big data elliptical model, which solves the technical problems of the existing corneal reshaping lenses in terms of low fitting efficiency, accuracy and wearing comfort.

[0006] (2) Technical solution

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] An embodiment of the present invention provides an orthokeratology lens based on a big data elliptical model. The orthokeratology lens includes a base curve area, a reverse arc area, a first positioning arc area, a second positioning arc area, and a peripheral arc area arranged continuously from the inside to the outside. The base curve area, the reverse arc area, the first positioning arc area, and the second positioning arc area are obtained by the following steps:

[0009] S1. Based on the pre-acquired pupil radius pr, obtain the base arc segment length BCJ of the base arc area;

[0010] S2. Obtain the base curve radius (BCR) of the base curve area based on the previously obtained mean corneal curvature value (FK) of the central 4 mm diameter of the cornea, the patient's actual subjective refraction power (RX), and the overcorrection value (PW).

[0011] S3. Based on the patient's actual subjective refraction power RX, obtain the reversal arc segment length RCJ of the reversal arc;

[0012] S4. Based on the base arc segment length BCJ and the base arc radius BCR, obtain the reversal arc radius RCR of the reversal arc area;

[0013] S5. Based on the base arc segment length BCJ, the reverse arc segment length RCJ, and the previously acquired visible iris diameter HWTW, obtain the positioning arc segment length ACJ1 of the first positioning arc zone and the positioning arc segment length ACJ2 of the second positioning arc zone;

[0014] S6. Based on the average curvature value FK of the central 4mm diameter of the cornea, the corneal radius R0 is obtained. Based on the corneal radius R0, the pre-acquired eccentricity e corresponding to R0, the base arc segment length BCJ and the reversal arc segment length RCJ, according to the elliptical model formula, the positioning arc radius ACR1 of the first positioning arc zone and the positioning arc radius ACR2 of the second positioning arc zone are obtained.

[0015] Preferably, the length of the first positioning arc segment of the first positioning arc area is ACJ1;

[0016] When 12mm≤HWTW<12.8mm, ACJ1=0.8mm;

[0017] When 11.2mm<HWTW<12mm, ACJ1=0.7mm;

[0018] The length of the second positioning arc segment of the second positioning arc zone is ACJ2;

[0019] ACJ2=(HWTW-1.2) / 2-BCJ-RCJ-ACJ1-0.4.

[0020] Preferably, based on the average curvature value FK of the central 4 mm diameter of the cornea, the corneal radius R0 is obtained according to formula (1);

[0021] Formula (1) is:

[0022]

[0023] Based on the corneal radius R0, the pre-acquired eccentricity e corresponding to the corneal radius R0, the base arc segment length BCJ and the reverse arc segment length RCJ, according to the ellipse model formula (2), the first positioning arc radius of the first positioning arc area is obtained as ACR1;

[0024] Formula (2) is:

[0025]

[0026] Among them, ACS1 is the starting point of the arc length of the first positioning arc zone, and the value of ACS1 is BCJ+RCJ;

[0027] Based on the corneal radius R0, the pre-acquired eccentricity e corresponding to the corneal radius R0, the base arc segment length BCJ and the reverse arc segment length RCJ, according to the ellipse model formula (3), the second positioning arc radius of the second positioning arc area is obtained as ACR2;

[0028] Formula (3) is:

[0029]

[0030] ACS2 is the starting point of the arc length of the second positioning arc zone, and the value of ACS2 is BCJ+RCJ+ACJ1.

[0031] Preferably, the range of the eccentricity e is: 0.18<e<0.93.

[0032] Preferably, the peripheral arc area is obtained by the following steps:

[0033] S7. The peripheral arc segment length PCJ of the peripheral arc zone is a constant. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained.

[0034] Preferably, S1 specifically includes: based on the pre-acquired pupil radius pr, obtaining the base arc segment length BCJ of the base arc area according to formula (4);

[0035] Formula (4) is:

[0036] BCJ = pr + 1.4 mm;

[0037] S2 specifically includes: based on the pre-acquired mean curvature value FK of the central 4mm diameter of the cornea, the patient's actual subjective refraction power RX and the overcorrection value PW, the base curve radius BCR of the base curve area is obtained using formula (4);

[0038] Formula (5) is:

[0039] BCR=337.5 / (FK-RX-PW).

[0040] Preferably, when RX is between -1.00D and -3.00D, PW = 0.75D;

[0041] When RX is between -3.00D and -6.00D, PW=1.00D.

[0042] Preferably, when RX is between -0.25D and -1.00D, RCJ = 0.45mm;

[0043] When RX is between -1.00D and -3.00D, RCJ = 0.5mm;

[0044] When RX is between -3.00D and -6.00D, RCJ = 0.6mm.

[0045] Preferably, S4 specifically includes:

[0046] Based on the base arc segment length BCJ and base arc radius BCR, the reversal arc radius RCR of the reversal arc zone is obtained using formula (6);

[0047] Formula (6) is:

[0048]

[0049] Wherein, b is the first correction coefficient, 0.306<b<4.862.

[0050] Preferably, S7 specifically includes:

[0051] The peripheral arc segment length PCJ of the peripheral arc zone is 0.4 mm. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained using formula (7);

[0052] Formula (7) is:

[0053] PCR=337.5 / SPC+c;

[0054] Among them, SPC is the average corneal curvature corresponding to the length of the peripheral arc segment PCJ in the actual corneal topography, c is the second correction coefficient, 1.625<c<4.663.

[0055] (3) Beneficial effects

[0056] The beneficial effects of the present invention are:

[0057] The orthokeratology lens based on the big data elliptical model of the present invention significantly improves the fit between the lens and the cornea by designing a positioning arc zone that fits the patient's cornea more closely, thereby improving the wearing comfort and stability of the lens. Compared with the traditional design method based on the average curvature of the junction point, the virtual elliptical model provides a continuously changing curvature calculation for the positioning arc zone, so that the lens design is more consistent with the actual corneal shape and thus better matches the patient's cornea. In addition, because the design can obtain a preset eccentricity value based on the patient's corneal radius, the optometrist can accurately fit the glasses without additional knowledge or operation, avoiding the problem of inaccurate or inefficient fitting of orthokeratology lenses due to lack of experience by doctors (or optometrists), thereby improving the fitting efficiency, accuracy and wearing comfort of orthokeratology lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a cross-sectional schematic diagram of the orthokeratology lens of the present invention. DETAILED DESCRIPTION

[0059] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0060] The embodiment of the present invention provides a corneal reshaping lens based on a big data elliptical model, such as Figure 1 As shown, the orthokeratology lens includes a base curve area, a reverse curve area, a first positioning curve area, a second positioning curve area and a peripheral curve area which are arranged continuously from the inside to the outside. The base curve area, the reverse curve area, the first positioning curve area, the second positioning curve area and the peripheral curve area are obtained by the following steps;

[0061] S1. Based on the pre-acquired pupil radius pr, obtain the base arc segment length BCJ of the base arc area;

[0062] S2. Obtain the base curve radius (BCR) of the base curve area based on the previously obtained mean corneal curvature value (FK) of the central 4 mm diameter of the cornea, the patient's actual subjective refraction power (RX), and the overcorrection value (PW).

[0063] S3. Based on the patient's actual subjective refraction power RX, obtain the reversal arc segment length RCJ of the reversal arc;

[0064] S4. Based on the base arc segment length BCJ and the base arc radius BCR, obtain the reversal arc radius RCR of the reversal arc area;

[0065] S5. Based on the base arc segment length BCJ, the reverse arc segment length RCJ, and the previously acquired visible iris diameter HWTW, obtain the positioning arc segment length ACJ1 of the first positioning arc zone and the positioning arc segment length ACJ2 of the second positioning arc zone;

[0066] S6. Obtain the corneal radius R0 based on the average curvature value FK of the central 4 mm diameter of the cornea. Obtain the positioning arc radius ACR1 of the first positioning arc zone and the positioning arc radius ACR2 of the second positioning arc zone based on the corneal radius R0, the pre-obtained eccentricity e corresponding to R0, the base arc segment length BCJ, and the reverse arc segment length RCJ according to the elliptical model formula.

[0067] S7. The peripheral arc segment length PCJ of the peripheral arc zone is a constant. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained.

[0068] It should be noted that the patient's actual corneal morphology and arc segment data within the visible iris diameter range from the central area to the peripheral area can be measured through the corneal topography, that is, the actual average corneal curvature radius corresponding to each measured width of the entire cornea can be measured based on the patient's corneal topography.

[0069] By designing a positioning arc zone that fits the patient's cornea more closely, the fit between the lens and the cornea is significantly improved, thereby improving wearing comfort and lens stability. Compared to the traditional design method based on the average curvature of the junction point, the virtual elliptical model provides a continuously changing curvature calculation for the positioning arc zone, making the lens design more consistent with the actual corneal shape and thus more compatible with the patient's cornea. In addition, because the design can obtain a preset eccentricity value based on the patient's corneal radius, optometrists can accurately fit glasses without additional knowledge or operation, avoiding the problem of inaccurate or inefficient fitting of orthokeratology lenses due to lack of experience by doctors (or optometrists), thereby improving the fitting efficiency, accuracy and wearing comfort of orthokeratology lenses.

[0070] Preferably, the length of the first positioning arc segment of the first positioning arc zone is ACJ1, when 12mm≤HWTW<12.8mm, ACJ1=0.8mm; when 11.2mm<HWTW<12mm, ACJ1=0.7mm, and the length of the second positioning arc segment of the second positioning arc zone is ACJ2, ACJ2=(HWTW-1.2) / 2-BCJ-RCJ-ACJ1-0.4.

[0071] The corneal radius R0 is obtained based on the average curvature value FK of the central 4 mm diameter of the cornea according to formula (1).

[0072] Formula (1) is:

[0073]

[0074] According to the ellipse model formula (2), the first positioning arc radius of the first positioning arc area is obtained as ACR1, and according to the ellipse model formula (3), the second positioning arc radius of the second positioning arc area is obtained as ACR2.

[0075] Formula (2) is:

[0076]

[0077] ACS1 is the starting point of the arc length of the first positioning arc zone, and the value of ACS1 is BCJ+RCJ.

[0078] Formula (3) is:

[0079]

[0080] ACS2 is the starting point of the arc length of the second positioning arc zone, and the value of ACS2 is BCJ+RCJ+ACJ1.

[0081] It should be noted that a correlation model between corneal radius R0 and eccentricity e was established using big data analysis and machine learning techniques based on a large amount of corneal topography data (over 10,000 samples). Once a patient's corneal radius R0 is determined, this correlation model can be used to quickly calculate or predict the appropriate eccentricity e for the patient. The range of eccentricity e is: 0.18 < e < 0.93.

[0082] Preferably, based on the pre-acquired pupil radius pr, the base arc length BCJ of the base arc zone is obtained according to formula (4). Based on the pre-acquired mean curvature value FK of the central 4 mm diameter of the cornea, the patient's actual subjective refraction power RX, and the overcorrection value PW, the base arc radius BCR of the base arc zone is obtained using formula (5).

[0083] Formula (4) is: BCJ = pr + 1.4 mm.

[0084] Formula (5) is: BCR = 337.5 / (FK-RX-PW).

[0085] When RX is between -1.00D and -3.00D, PW = 0.75D; when RX is between -3.00D and -6.00D, PW = 1.00D. When RX is between -0.25D and -1.00D, RCJ = 0.45mm; when RX is between -1.00D and -3.00D, RCJ = 0.5mm; when RX is between -3.00D and -6.00D, RCJ = 0.6mm.

[0086] Preferably, based on the base arc segment length BCJ and the base arc radius BCR, formula (6) is used to obtain the reversal arc radius RCR of the reversal arc zone.

[0087] Formula (6) is: Wherein, b is the first correction coefficient, 0.306<b<4.862, and the value of b is determined according to the condition of the patient's cornea.

[0088] Among them, the peripheral arc segment length PCJ of the peripheral arc zone is 0.4 mm. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained using formula (7);

[0089] Formula (7) is: PCR = 337.5 / SPC + c, where SPC is the average corneal curvature corresponding to the length of the peripheral arc segment PCJ in the actual corneal topography, and c is the second correction coefficient, 1.625 < c < 4.663. The value of c is determined based on the patient's requirements for lens comfort and the morphology of the cornea at this position.

[0090] In summary, in this embodiment, the curvature of the first positioning arc zone and the second positioning arc zone are derived according to the ellipse formula, which is more consistent with the actual cornea. At the same time, in the ellipse formula, since the values ​​of ACS1 and ACS2 are fixed values ​​and not variables, the requirements for existing production equipment are not high. Therefore, the ACR1 and ACR2 derived by the implemented ellipse formula are as close as possible to the actual curvature of the positioning arc cornea, while being more in line with actual production and having a wider application. At the same time, the acquisition of ACR1 and ACR2 minimizes the use of actual corneal topography, so the acquisition of ACR1 and ACR2 is more accurate.

[0091] Example 1

[0092] In this embodiment, taking the glasses fitting condition of the right eye of patient A as an example, the actual refraction power is: RX = -1.75D, the visible iris diameter is: HWTW = 11.8mm, FK = 43.00D, the overcorrection value is: PW = 0.75D, and the pupil radius pr = 1.4mm. The above parameters are all measured based on the actual corneal topography of the patient.

[0093] Among them, R0=337.5 / 43.00=7.85mm; e=0.65;

[0094] BCJ=pr+1.4mm=2.8mm.

[0095] Since RX is between -1.00D and -3.00D, RCJ = 0.5mm.

[0096] Since 11.2mm<HWTW<12mm, ACJ1=0.7mm;

[0097] ACS1=BCJ+RCJ=2.8+0.5=3.3mm;

[0098] ACS2=BCJ+RCJ+ACJ1=2.8+0.5+0.7=4.0mm;

[0099] Therefore, ACR1 = 8.48 mm; ACR2 = 8.82 mm.

[0100] Example 2

[0101] RX = -2.75D;

[0102] PW = 0.75D;

[0103] RCJ = 0.5 mm;

[0104] HWTW=12.2mm;

[0105] ACJ1=0.8mm;

[0106] FK=42.50D;

[0107] R0=337.5 / 42.50=7.94mm;

[0108] e = 0.70;

[0109] pr = 1.5 mm;

[0110] BCJ = pr + 1.4 = 2.9 mm;

[0111] ACS1=BCJ+RCJ=2.9+0.5=3.4mm;

[0112] ACS2=BCJ+RCJ+ACJ1=2.9+0.5+0.8=4.2mm;

[0113] Therefore, ACR1 = 8.72 mm; ACR2 = 9.2 mm.

[0114] In summary, the orthokeratology lens based on the big data elliptical model in this embodiment can obtain accurate fitting parameters, so that the orthokeratology lens is more compatible with the patient's cornea, improving accuracy and wearing comfort.

[0115] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0116] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0117] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0118] In the description of this specification, the terms "one embodiment", "some embodiments", "embodiments", "examples", "specific examples" or "some examples" refer to the specific features, structures, materials or characteristics described in conjunction with the embodiment or example and included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0119] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A corneal reshaping lens based on a big data elliptical model, the corneal reshaping lens comprising a base arc area, a reversal arc area, a first positioning arc area, a second positioning arc area and a peripheral arc area arranged continuously from the inside to the outside, characterized in that: The base arc region, the inversion arc region, the first positioning arc region and the second positioning arc region are obtained by the following steps; S1. Based on the pre-acquired pupil radius pr, obtain the base arc segment length BCJ of the base arc area; S2. Obtaining the base curve radius BCR of the base curve area based on the previously acquired mean curvature value FK of the central 4 mm diameter of the cornea, the patient's actual subjective refraction power RX, and the overcorrection value PW; S3. Obtaining a reversal arc segment length RCJ of the reversal arc based on the actual subjective refraction power RX of the patient; S4. Obtaining a reversal arc radius RCR of the reversal arc region based on the base arc segment length BCJ and the base arc radius BCR; S5. Obtain the positioning arc segment length ACJ1 of the first positioning arc zone and the positioning arc segment length ACJ2 of the second positioning arc zone based on the base arc segment length BCJ, the reverse arc segment length RCJ, and the previously acquired visible iris diameter HWTW; S6. Obtain the corneal radius R0 based on the average curvature value FK of the central 4 mm diameter of the cornea. Obtain the positioning arc radius ACR1 of the first positioning arc zone and the positioning arc radius ACR2 of the second positioning arc zone based on the corneal radius R0, the pre-obtained eccentricity e corresponding to R0, the base arc segment length BCJ, and the reverse arc segment length RCJ according to an elliptical model formula. The S6 specifically includes: obtaining the corneal radius R0 based on the average curvature value FK of the central 4 mm diameter of the cornea according to formula (1); The formula (1) is: ； Based on the corneal radius R0, the pre-acquired eccentricity e corresponding to the corneal radius R0, the base arc segment length BCJ and the reverse arc segment length RCJ, according to the ellipse model formula (2), the first positioning arc radius of the first positioning arc area is obtained as ACR1; The formula (2) is: ； Wherein, ACS1 is the starting point of the arc length of the first positioning arc zone, and the value of ACS1 is BCJ+RCJ; Based on the corneal radius R0, the pre-acquired eccentricity e corresponding to the corneal radius R0, the base arc segment length BCJ and the reverse arc segment length RCJ, according to the ellipse model formula (3), the second positioning arc radius of the second positioning arc area is obtained as ACR2; The formula (3) is: ； Wherein, ACS2 is the starting point of the arc length of the second positioning arc zone, and the value of ACS2 is BCJ+RCJ+ACJ1; The range of the eccentricity e is: 0.18<e<0.

93.

2. The orthokeratology lens based on a big data elliptical model according to claim 1, characterized in that: The length of the first positioning arc segment of the first positioning arc zone is ACJ1; When 12mm≤HWTW<12.8mm, ACJ1=0.8mm; When 11.2mm<HWTW<12mm, ACJ1=0.7mm; The length of the second positioning arc segment of the second positioning arc zone is ACJ2; ACJ2=(HWTW-1.2) / 2-BCJ-RCJ-ACJ1-0.

4.

3. The orthokeratology lens based on a big data elliptical model according to claim 1, characterized in that: The peripheral arc area is obtained by the following steps: S7. The peripheral arc segment length PCJ of the peripheral arc zone is a constant. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained.

4. The orthokeratology lens based on a big data elliptical model according to claim 1, wherein: Said S1 specifically comprises: based on the pupil radius pr obtained in advance, obtaining the base arc segment length BCJ of said base arc area according to formula (4); The formula (4) is: BCJ = pr + 1.4 mm; The S2 specifically includes: based on the pre-acquired mean curvature value FK of the central 4mm diameter of the cornea, the patient's actual subjective refraction power RX and the overcorrection value PW, using formula (5) to obtain the base curve radius BCR of the base curve area; The formula (5) is: BCR=337.5 / (FK-RX-PW).

5. The method for manufacturing orthokeratology lenses based on a big data elliptical model according to claim 4, wherein: When RX is between -1.00D and -3.00D, PW=0.75D; When RX is between -3.00D and -6.00D, PW=1.00D.

6. The orthokeratology lens based on a big data elliptical model according to claim 1, wherein: When RX is between -0.25D and -1.00D, RCJ=0.45mm; When RX is between -1.00D and -3.00D, RCJ=0.5mm; When RX is between -3.00D and -6.00D, RCJ=0.6mm.

7. The orthokeratology lens based on a big data elliptical model according to claim 1, wherein: The S4 specifically includes: Based on the base arc segment length BCJ and the base arc radius BCR, the reversal arc radius RCR of the reversal arc zone is obtained using formula (6); The formula (6) is: RCR= ; Wherein, b is the first correction coefficient, 0.306<b<4.

862.

8. The orthokeratology lens based on a big data elliptical model according to claim 3, characterized in that: The S7 specifically includes: The peripheral arc segment length PCJ of the peripheral arc zone is 0.4 mm. Based on the corneal curvature value corresponding to the peripheral arc segment length PCJ in the actual corneal topography, the peripheral arc radius PCR of the peripheral arc zone is obtained using formula (7); The formula (7) is: PCR=337.5 / SPC+c; Wherein, SPC is the average value of corneal curvature corresponding to the peripheral arc segment length PCJ described in the actual corneal topography, c is the second correction coefficient, 1.625<c<4.663.

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