RU2781328C1 - Method for determining optical power of intraocular lens based on personal surgical technique and preoperative data - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to medicine, namely to ophthalmic surgery. To calculate the optical power of the intraocular lens (IOL), a test sample is formed from the IOL implantation data, containing at least ten patient records. The required parameters are: the average radius of curvature of the anterior surface of the cornea (R, mm), the axial length of the eye (AL, mm), the depth of the anterior chamber before surgery (ACD, mm), the optical power of the implanted IOL (P_{IOL_impl}, diopters), the target postoperative refraction ( Ref_target, diopters), postoperative subjective refraction after at least one month (Ref_p/o, diopter), postoperative depth of the anterior chamber - the distance from the anterior surface of the cornea to the anterior surface of the IOL (ACD_p/o, diopter). If available, include parameters: corneal thickness in the central zone (CCT, mm), average curvature of the posterior surface of the cornea (Rz, mm), lens thickness in the central zone (LT, mm), corneal diameter (W, mm), A-constant of the implanted IOL (A_const). According to the test sample data, the optical power of the cornea (P_cor, diopter) is calculated, and the optical power of the eye (P_eye, diopter) and the distance between the second focal point of the cornea and the first focal point of the IOL (N_IOL, mm) are determined by approximating the set of functions. In general, the formula for calculating the IOL has the form

where nwater.moisture is the refractive index of aqueous humor. Using combinations of functions that calculate P_cor, Peye, N_IOL, methods for calculating the optical power of the IOL are formed, which are then used to calculate P_IOL on a test sample. Based on the calculation results, deviations (delta, mm) from the target refraction are calculated for each combination using the formula delta=PIOL-P_{IOL_target}. From the array of calculation formulas, those are selected for which the share of deviations from the target refraction will be no more than ±1 diopter in 85% of cases. After that, the formulas are grouped according to the number and type of parameters included in them for calculation, and in each group for clinical use, the one that has the minimum absolute average value of delta is selected.

EFFECT: application of the invention will improve the accuracy of the calculation of the optical power of the IOL and will provide a breadth of application of the method for any surgical technique and preoperative data.

10 cl, 3 dwg, 6 tbl

P_ИОЛ - P_IOL

P_глаз - P_eye

P_рог - P_cor

N_ИОЛ - N_IOL

n_{вод.влаги} - n_{water.moisture}

Ref_цель - Ref_target

Description

The technical field to which the invention belongs

The invention relates to medicine, namely to ophthalmic surgery, and is intended to determine the optical power of an intraocular lens (IOL) used in the surgical treatment of cataracts in patients who do not have anomalies in the shape and curvature of the cornea. The invention can be used in hardware-software and software-algorithmic complexes for planning an operation to replace the lens with an intraocular lens.

State of the art

The operation to replace the lens is considered, including as a refractive one. Therefore, they seek to minimize the error in calculating the optical power of the IOL (delta, diopter), defined as the difference between postoperative refraction (Ref _{p / o} , diopter) and target refraction (Ref _target , diopter) in the patient. The error of the IOL calculation method should not exceed ±1 diopter in 85% of cases [1]. Among the main reasons for the deviation from the target refraction are: the measurement error of the eye parameters, the choice of a calculation method that is not suitable for the clinical situation, the error in predicting the postoperative position of the IOL, the variety of geometric and optical parameters of the IOL, as well as the surgical technique [2, 3].

Known methods for calculating the optical power of the IOL, Holladay 1, Hoffer Q, Haigis, Holladay II [4-7], allowing to achieve an acceptable error of ±1 diopter in 85% of cases for eyes with standard parameters. The disadvantage of the methods lies in the need to make corrections for a non-standard combination of eye parameters [8].

Known methods are Olsen [9] and Barrett Universal 2 [10], which provide an acceptable calculation error, including with a non-standard combination of eye parameters. Known methods for calculating Kane [11] and Hill-RBF [12]. The Kane method is based on the laws of optics, and includes elements of regression and artificial intelligence. For development, data from thirty thousand cases of IOL implantation were used. The Hill-RBF method is also based on artificial intelligence methods, namely the construction of a neural network using radial basis functions. At least twelve thousand data on IOL implantation were used to train the neural network. The methods have the smallest IOL calculation error compared to previous generations of methods [13, 14]. The disadvantage of these methods is the need to measure the parameters of the eye with optical biometers of certain manufacturers, which, in accordance with the standard for equipping ophthalmological departments [15], significantly limits the breadth of application of the methods on the territory of the Russian Federation.

There is also a known method for calculating SRK/T [16], which includes the use of the laws of paraxial optics with elements of regression analysis, the measurement of eye parameters - the average radius of curvature of the anterior surface of the cornea (R, mm) and the axial length of the eye (AL, mm), and the use of the IOL parameter - A-constants. This method was chosen as a prototype of the proposed solution.

The first disadvantage of this method is that the anatomical features of the structure of the eye are not taken into account. Therefore, the minimum calculation error is achieved when used on eyes longer than 26 mm, and in the range of short (less than 22 mm) and standard (from 22 mm to 26 mm) eye lengths, the use of this prototype method leads to an increase in the calculation error.

The second drawback is associated with the use of the A-constant of the IOL, which indirectly reflects the influence of the design of the optical and haptic parts of the IOL on the position of the lens in the eye. A-constant is a parameter obtained empirically based on postoperative data. The use of the A-constant specified by the IOL manufacturer leads to an increase in the calculation error for eyes whose parameters deviate in magnitude from the average. To reduce the calculation error, it is necessary to calculate a new value of the A-constant based on personal surgical experience and taking into account the type of measuring instruments used (optical or ultrasonic biometer), however, a personalized approach to calculating the A-constant is not widely used in clinical practice.

The technical result of the proposed invention is to achieve an allowable error of ±1 diopter in at least 85% of cases, wide applicability of the method on the territory of the Russian Federation, flexibility and adaptability by taking into account preoperative data, personal surgical equipment, IOL model and manufacturer, using the laws of paraxial optics for the two-component optical system of the eye and regression analysis to evaluate the non-measurable parameters of the optical system.

Disclosure of invention

This technical result is achieved in that the method for determining the optical power of an intraocular lens based on personal surgical technique and preoperative data, including the use of the laws of paraxial optics and regression analysis, measuring the average radius of curvature of the anterior surface of the cornea (R, mm) and the axial length of the eye (AL, mm),

differs in that

the anatomical features of the structure of the eye are taken into account in the mathematical model of a two-component optical system, to correct the calculation formulas based on a sample of patient data, the regression analysis uses the necessary measured parameters, such as the depth of the anterior chamber before surgery (ACD, mm), the optical power of the implanted IOL (P _{IOL_impl} , diopter), target postoperative refraction (Ref _goal , diopter), postoperative refraction after at least one month (Ref _{p / o} , diopter), postoperative depth of the anterior chamber - the distance from the anterior surface of the cornea to the anterior surface of the IOL (ACD _{p / o} , diopter ), and also optionally use additional parameters, such as the thickness of the cornea in the central zone (CCT, mm), the average curvature of the posterior surface of the cornea (R _c , mm), the thickness of the lens in the central zone (LT, mm), the diameter of the cornea (W, mm), A-constant of the implanted IOL (A _const ). The method is carried out in stages.

At the first stage, a test sample is formed, consisting of at least the required measured parameters of the eye, with a volume of at least ten records.

At the second stage, for each record of the test sample, the following are calculated: the optical power of the cornea P _horn (dptr) i in different ways, the distance between the second main focal point of the cornea and the first main focal point of the IOL - the effective position of the IOL H _eyes (mm) in j ways, the optical power of the eye with IOL P _eyes (dptr) in k ways, and i={1,2}, j=2…M, k=2…2×M, M={2,3}.

At the third stage, the coefficients m of the approximating functions of the effective position of the IOL (H _IOL ) and n approximating functions of the optical power of the eye (P _{eye_IOL} ) are calculated according to the values of the effective positions of the IOL (H _eye ) and the optical power of the eye (P _eye ), respectively, calculated in different ways, where m =(9…M _H )×j and n=(3…M _P )×k, - number of functions, M _H ≤16, M _P ≤5.

At the fourth stage, for each record of the test sample, the optical power of the IOL is calculated by combining the functions obtained at the second and third stages for calculating the optical power of the cornea, the effective position of the IOL, the optical power of the eye: P _{IOL, (t)} (P _{hor (i)} , H _{IOL (m)} , P _{eye_IOL(n)} ), where t=1…i×m×n is the serial number of the combination, i is the serial number of the function for calculating the optical power of the cornea, m is the serial number of the function for calculating the effective position of the IOL, n is the serial number functions for calculating the optical power of the eye.

At the fifth stage, for each column vector of calculated values P _IOL,(t) , a column vector of errors in calculating the optical power of the IOL (delta _(t) , diopter) is calculated:

delta _(t) =P _IOL,(t) - P _{IOL_target} ,

where P _{IOL_target} , diopter - column vector of the optical powers of the IOL, providing the target refraction.

At the sixth stage, for each column vector delta _(t) , the percentage of deviations not exceeding ±1 diopter and the absolute average value of the elements delta ₍ t) are calculated.

At the seventh stage, from the array of functions P _IOL,(t) (P _rog(i) , N _IOL(m) , P _{eye_IOL(n)} ) select those for which the proportion of deviations from the target refraction is no more than ±1 diopter, at least , in 85% of cases.

At the eighth stage, the selected functions are grouped according to the number and type of eye parameters included in the calculation.

At the final stage, from each group for clinical use, a function with the number t is selected, which has the minimum absolute mean value delta _(t) .

There is a variant in which the parameters of the test set are measured either with an optical or ultrasonic biometer and classified according to one of the signs or any combination of them: by age, gender of the patient, manufacturer and model of the implanted IOL, and the value of the measured parameters of the eye.

; оптическую силу ИОЛ, обеспечивающую целевую рефракцию (P_{ИОЛ_цель}, дптр) вычисляют по формуле

.There is a variant in which, at the second stage, the optical power of the IOL, which provides emmetropic refraction (P _{IOL_em} , diopter), is calculated by the formula

; optical power of the IOL, providing the target refraction (P _{IOL_target} , diopter) is calculated by the formula

.

There is also a variant in which, at the second stage, the optical power of the cornea P _horn is calculated by two formulas:

,

,

where CI is the keratometric index, the values of which lie in the range [1.32; 1.35];

,

,

where n _horn \u003d 1.3771 is the refractive index of the cornea,

n _air \u003d 1 - refractive index of air,

n _{water moisture} \u003d 1.3374 - refractive index of aqueous humor.

There is also a variant in which, at the second stage, the effective position of the IOL H _{of the eyes is} calculated by the formulas:

, где

;

, where

;

;

;

,

,

- поправка на фокусные точки роговицы и ИОЛ.where

- correction for the focal points of the cornea and IOL.

There is also a variant in which, at the second stage, the optical power of the eye (P _eye ) is calculated by the formula:

,

,

where P _horn , P _IOL - the optical power of the cornea and IOL, respectively, diopter;

H _eye - effective position of the IOL, mm.

There is also a variant in which, at the third stage, the approximating functions of the effective position of the IOL ( _IOL ) have the form:

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

functions H ₁₀ , ..., H ₁₈ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm).

There is also a variant in which, at the third stage, the effective position of the IOL (N _IOL ) is calculated by the formula:

,

,

where the approximating functions LF, mm - the position of the anterior surface of the IOL relative to the anterior lens capsule, have the form:

;

;

;

;

;

;

;

;

;

;

;

;

;

;

functions LF ₈ , ..., LF ₁₄ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm).

There is also a variant in which, at the third stage, the approximating functions of the optical power of the eye (P _{eye_IOL} ) have the form:

;

;

;

;

,

,

where n _glass. is the refractive index of the vitreous body,

C' - the position of the second main focal point of the combined optical system "cornea - anterior chamber - IOL" relative to the anterior surface of the cornea, is described by a function of the form:

,

,

where either AL or LT or (ACD+LT) is taken as x.

There is also a variant in which, at the fourth stage, the optical power of the IOL is calculated by the formula:

,

,

where P _{eye_IOL} is a function for calculating the optical power of the IOL,

P _horn - function for calculating the optical power of the cornea,

N _IOL - function for calculating the effective position of the IOL

Ref _target - target postoperative refraction, diopter.

Brief description of the drawings

The invention is illustrated by illustrative material, where figure 1 shows the scheme for calculating the parameters of the test sample, where P_eyesi,j, is the calculated optical power of the eye, providing emmetropia, where i is the index of the formula for calculating the optical power of the cornea, j is the index of the formula for calculating the distance between the second main focal point of the cornea and the first main focal point of the IOL. In FIG. Figure 2 shows a variant of the scheme for obtaining an array of formulas for calculating the optical power of the IOL, on the basis of which the IOL calculation method is adapted. Block 1 includes data from a test sample - the optical power of the eye, calculated for emmetropia P_eye, the measured depth of the anterior chamber of the ACD_on, the calculated position of the IOL relative to the anterior surface of the lens LF, the measured or calculated optical power of the cornea P_horn. Block 2 demonstrates sets of approximating functions with calculated coefficients. Block 3 contains a set of combinations of functions P_horn,i, P_eye,j, H_IOL,k, where i, j, k - the number of the corresponding calculation formula, providing the calculation of the optical power of the IOL. in fig. 3 shows a diagram for calculating the optical power of the eye P_eye and IOL optical power P_IOL. The numbers indicate the main elements of the calculation scheme: 1 - cornea, 2 - IOL, 3 - lens, 4 - retina. The focal points are marked on the optical axis: the second main focal point of the cornea C_horn, the second main focal point of the eye with implanted IOL C_c', the first main focal point of IOL C_IOL. Axial parameters are indicated: postoperative depth of the anterior chamber ACD_on; ∆+ACD_on (H_eye or H_IOL) is the distance between the second focal point of the cornea and the first focal point of the IOL; CCT - corneal thickness; C' - distance from the anterior surface of the cornea to the second main focal point of the eye with IOL; t_IOL - IOL thickness; ACD - depth of the anterior chamber before surgery; LT - lens thickness; LF - position of the anterior surface of the IOL relative to the anterior surface of the lens capsule; AL - axial length of the eye.

Implementation of the invention

A method for determining the optical power of an intraocular lens based on personal surgical technique and preoperative data, including the use of the laws of paraxial optics and regression analysis, measuring the average radius of curvature of the anterior surface of the cornea (R, mm) and the axial length of the eye (AL, mm),

characterized in that

the anatomical features of the structure of the eye are taken into account in the mathematical model of a two-component optical system, to correct the calculation formulas based on a sample of patient data, the regression analysis uses the necessary measured parameters, such as the depth of the anterior chamber before surgery (ACD, mm), the optical power of the implanted IOL (P _{IOL_impl} , diopter), target postoperative refraction (Ref _goal , diopter), postoperative refraction after at least one month (Ref _{p / o} , diopter), postoperative depth of the anterior chamber - the distance from the anterior surface of the cornea to the anterior surface of the IOL (ACD _{p / o} , diopter ), and also optionally use additional parameters, such as the thickness of the cornea in the central zone (CCT, mm), the average curvature of the posterior surface of the cornea (R _c , mm), the thickness of the lens in the central zone (LT, mm), the diameter of the cornea (W, mm), A-constant of the implanted IOL (A _const ). The method is carried out in stages.

At the first stage, a test sample is formed, with a volume of at least ten records. A smaller number of records will not allow regression analysis for all types of functional dependencies used in the calculation method. Each entry consists of the parameters necessary for the implementation of the method (R, AL, ACD, P _{IOL_impl} , Ref _target , Ref _p/o , ACD _p/o ) and, if available, additional (CCT, R C , LT, _W , A _const ).

At the second stage, for each record of the test sample, according to the available data and given formulas, the following are calculated: the optical power of the cornea P _horn (dptr) i in different ways, the distance between the second main focal point of the cornea and the first main focal point of the IOL - the effective position of the IOL H _eye (mm) j ways, the optical power of the eye with IOL P _eyes (dptr) k ways, and i={1,2}, j=2...M, k=2...2×M, M={2,3}. M=2 if the test sample consists of only the required parameters. The order of calculation of the parameters is carried out according to the scheme in Fig. one.

At the third stage, the methods of regression analysis calculate the coefficients m of the approximating functions of the effective position of the IOL (H _IOL ) and n of the approximating functions of the optical power of the eye (P _{eye_IOL} ) according to the values of the effective positions of the IOL (H _eye ) and optical power of the eye (P _eye ) respectively, where m=(9…M _H )×j and n=(3…M _P )×k, is the number of functions, M _H ≤16, M _P ≤5. The values of M _H and M _P are determined by the number of known parameters of the test set.

At the fourth stage, for each record of the test sample, the optical power of the IOL is calculated by combining the functions obtained at the second and third stages for calculating the optical power of the cornea, the effective position of the IOL, the optical power of the eye: P _{IOL, (t)} (P _{hor (i)} , H _{IOL (m)} , P _{eye_IOL(n)} ), where t=1…i×m×n is the serial number of the combination, i is the serial number of the function for calculating the optical power of the cornea, m is the serial number of the function for calculating the effective position of the IOL, n is the serial number functions for calculating the optical power of the eye. A variant of the formation of an array of formulas for calculating the optical power of the IOL is shown in the diagram of Fig. 2.

At the fifth stage, for each column vector of calculated values P _IOL,(t) , a column vector of errors in calculating the optical power of the IOL (delta _(t) , diopter) is calculated:

delta _(t) =P _IOL,(t) -P _{IOL_target} ,

where P _{IOL_target} , diopter - column vector of the optical powers of the IOL, providing the target refraction.

At the sixth stage, for each column vector delta _(t) , the percentage of deviations not exceeding ±1 diopter and the absolute average value of the elements delta ₍ t) are calculated.

At the seventh stage, from the array of functions P _IOL,(t) (P _rog(i) , N _IOL(m) , P _{eye_IOL(n)} ) select those for which the proportion of deviations from the target refraction is no more than ±1 diopter, at least , in 85% of cases.

At the eighth stage, the selected functions are grouped according to the number and type of eye parameters included in the calculation. At the same time, each group necessarily contains the minimum parameters R and AL required for the calculation. An example of the formation of groups: group I - R, AL, group II - R, AL, ACD, and other options, depending on the presence of additional parameters in the test sample.

At the final stage, from each group for clinical use, a function with the number t is selected, which has the minimum absolute mean value delta _(t) . Thus, for any set of input parameters, a calculation method is obtained.

Axial parameters for the test set are measured either with an optical or ultrasonic biometer, and corneal parameters with an autorefkeratometer, a keratotopograph, or a biometer. To improve the accuracy of the calculation, the sample is preliminarily classified according to one of the signs or any combination of them: by age, sex of the patient, manufacturer and model of the implanted IOL, and the value of the measured parameters of the eye.

; оптическую силу ИОЛ, обеспечивающую целевую рефракцию (P_{ИОЛ_цель}, дптр) вычисляют по формуле

[18].At the second stage, the optical power of the IOL, providing emmetropic refraction (P _{IOL_em} , diopter), is calculated by the formula:

; optical power of the IOL, providing the target refraction (P _{IOL_target} , diopter) is calculated by the formula

[eighteen].

At the second stage, the optical power of the cornea P _horn is calculated using two formulas [17, 19]:

,

,

where CI is the keratometric index, the values of which lie in the range [1.32; 1.35], and the value for the calculation is chosen by the surgeon;

,

,

where n _horn \u003d 1.3771 is the refractive index of the cornea,

n _air \u003d 1 - refractive index of air,

n _{water moisture} \u003d 1.3374 - refractive index of aqueous humor.

[17], либо через иное соотношение, определенное хирургом на основе персонального опыта.In the absence of the measured parameter R _s , it can be calculated from the known R through the standard Gulstrand relation

[17], or through another ratio determined by the surgeon on the basis of personal experience.

At the second stage, the effective position of the IOL H _{eyes is} calculated by the formulas:

, где

;

, where

;

;

;

,

,

- поправка на фокусные точки роговицы и ИОЛ.where

- correction for the focal points of the cornea and IOL.

, либо другими известными способами [16].The effective position of the IOL H _eye,1 is calculated by the formula proposed in [10]

, or by other known methods [16].

Correction Δ for focal points consists of the sum of the distance from the anterior surface of the cornea to the second main focal point of the cornea (C _horn ) and the distance from the anterior surface of the IOL to the first main focal point of the IOL (C _IOL ) (Fig. 3). The first term was obtained by approximating the second focal lengths calculated from the known parameters of the cornea, and depends on the CCT. To obtain the second term from the known geometric parameters of IOLs of various optical powers [20], the positions of the first main focal point were calculated and an empirical dependence on the axial length AL was obtained.

At the second stage, the optical power of the eye (P _eye ) is calculated according to the formula corresponding to the mathematical model of the two-component optical system of the eye [17]:

,

,

where P _horn , P _IOL - the optical power of the cornea and IOL, respectively, diopter;

H _eye - effective position of the IOL, mm.

To determine the types of functions for approximating the effective position of the IOL (N_IOL) a sample was used consisting of twenty records containing all measured parameters of the eye (R, AL, ACD, LT, W) and the known ACD_on. Regression methods were used to approximate the ACD_on. As a result, dependencies were selected for which the correlation coefficient of the known ACD_on and approximated was at least 0.5:

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

;

functions H ₁₀ , ..., H ₁₈ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm).

The effective position of the IOL (N _IOL ) is also calculated by the formula:

,

,

where LF, mm is the position of the anterior surface of the IOL relative to the anterior lens capsule (Fig. 3).

To determine the types of functions for approximating the effective position of LF, a similar sample was used, consisting of twenty records containing all the measured parameters of the eye (R, AL, ACD, LT, W) and calculated LF _p/o using known ACD _p/o and ACD: LF _{p /o} =ACD _n/o -ACD. Regression methods were used to approximate LF _p/o . As a result, dependencies were selected for which the correlation coefficient of known LF _p/o and approximated ones was at least 0.4:

;

;

;

;

;

;

;

;

;

;

;

;

;

;

functions LF ₈ , ..., LF ₁₄ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm).

To determine the types of functions for approximating the optical power of the eye at stage 3, a sample consisting of twenty records containing known parameters was used: the optical power of the cornea, the optical power of the IOL, which provides emmetropic refraction, and the effective position of the IOL. One of the ways to calculate the optical power of the eye is the calculation formula in terms of the second focal length of the eye f', expressed in terms of the position of the second main focal point [17]:

,

,

where n _glass. is the refractive index of the vitreous body.

Approximation of C' was carried out using regression methods according to the measured parameters of the eye. As a result, a dependence was chosen for which the correlation coefficient of known C' and approximated ones was at least 0.9:

,

,

where either AL or LT or (ACD+LT) is taken as x.

Regression methods for the measured parameters were also used to approximate the optical power of the eye (P _{eye_IOL} ). As a result, two types of dependences were selected, for which the correlation coefficient of the optical powers of the eye calculated at the second stage and the approximated ones was at least 0.95:

;

;

.

.

[17], и с учетом целевой рефракции имеет вид:The final formula for calculating the optical power of the IOL is derived based on the laws of paraxial optics for a two-component optical system

[17] and, taking into account the target refraction, has the form:

,

,

where P _{eye_IOL} - the calculated value of the optical power of the IOL on one of the five functions of approximation of the optical power of the IOL, diopter;

P _horn - the calculated value of the optical power of the cornea according to one of the two calculation functions, diopter;

H _IOL - calculated value of the effective position of the IOL according to one of the thirty-two functions of approximation of the effective position of the IOL, mm;

Ref _target - target postoperative refraction, diopter.

The use of a test sample and the variants of the cornea optical power, the eye optical power, the effective position of the IOL calculated from its data, the introduction of a correction for the focal points of the cornea and the IOL, the use of the functions of approximation of the optical power of the eye and the effective position of the IOL, ensure the achievement of an acceptable error in the calculation of the optical power of the IOL ± 1 diopter in at least 85% of cases, provided that the measurement errors for the required parameters are within acceptable limits corresponding to the measuring instruments used.

The use of the classification of the test sample according to one of the features or any combination of them makes it possible to adapt the method to the personal surgical technique and refuse to use the A-constant of the IOL, which ensures the breadth of the method in the territory of the Russian Federation.

The possibility of using the developed method for determining the optical power of an intraocular lens based on personal surgical technique and preoperative data, as well as the achievement of a technical result, is demonstrated by the data presented below.

The test sample, based on real verified patient data measured by an optical biometer, and consisting of both necessary and additional parameters, is presented in Table 1.

и целевую

рефракции, вычисленные варианты оптической силы роговицы:Table 2 contains the calculated values of the optical power of the IOL, providing emmetropic

and target

refractions, calculated variants of the optical power of the cornea:

, где КИ=1,3375 - стандартное значение;P _horn,1 by formula

, where CI=1.3375 - standard value;

P _horn,2 by formula

,

,

;where R _{C is} calculated from the Gulstrand relation

;

, где КИ=1,3282 - вычислено хирургом на основе персонального опыта [19].P _horn,3 is calculated by the formula

, where CI=1.3282 - calculated by the surgeon based on personal experience [19].

The values of the effective position of the IOL were also calculated:

;H _eye,1 according to the formula proposed in [10]:

;

;H _{eye, 2} is taken equal to ACD _{p / o} :

;

;H _eyes,3 are distinguished from H _eyes,2 by adding a correction Δ to the focal points of the cornea and IOL:

;

, где i - номер формулы расчета роговицы, j - номер формулы расчета эффективной позиции ИОЛ.Table 3 presents a set of calculated optical powers of the eye according to the formula

, where i is the number of the formula for calculating the cornea, j is the number of the formula for calculating the effective position of the IOL.

According to H _{eyes, 2} Table 2 approximates the dependence of the effective position of the IOL H _IOL : H ₁ - H ₉ and H ₁₉ - H ₂₅ , and according to H _{eyes, 3} - H ₁₀ - H ₁₈ and H ₂₆ - H ₃₂ . According to P _i,j Table 3 approximate the optical power of the eye (P _eye , diopters).

путем комбинации полученных на втором и третьем этапах функций расчета оптической силы роговицы, эффективной позиции ИОЛ, оптической силы глаза: P_ИОЛ,(t)(P_рог(i), Н_ИОЛ(m), P_{глаз_ИОЛ(n)}), где t=1…i×m×n - порядковый номер комбинации, i - порядковый номер функции расчета оптической силы роговицы, m - порядковый номер функции расчета эффективной позиции ИОЛ, n - порядковый номер функции расчета оптической силы глаза.For each record of the test sample, the optical power of the IOL is calculated by the formula

by combining the functions obtained at the second and third stages for calculating the optical power of the cornea, the effective position _{of the IOL ,} the optical power of the eye: =1…i×m×n - serial number of the combination, i - serial number of the function for calculating the optical power of the cornea, m - serial number of the function for calculating the effective position of the IOL, n - serial number of the function for calculating the optical power of the eye.

For each column vector of calculated values P _IOL,(t) calculate the column vector of errors in the calculation of the optical power of the IOL (delta _(t) , diopter): delta _(t) =P _IOL,(t) -P _{IOL_target} ,. For each column vector delta _(t) calculate the proportion of deviations not exceeding ±1 diopter and the absolute average value of the elements delta _(t) . From the array of functions P _IOL,(t) (P _horn(i) , H _IOL(m) , P _{eye_IOL(n)} ) select those for which the proportion of deviations from the target refraction is no more than ±1 diopter in at least 85% of cases . The selected functions are grouped according to the number and type of eye parameters included in the calculation. In this example, group I is calculated from the parameters (R, AL, CCT, ACD, LT), group II - (R, AL, CCT, ACD), group III - (R, AL). At the final stage, from each group for clinical use, a function with the number t is selected, which has the minimum absolute mean value delta _(t) . The results of the calculation are presented in Table 4. In the example under consideration, the selected functions for calculating the optical power of the IOL are implemented by the following combinations of functions for calculating the optical power of the cornea, the optical power of the eye, and the effective position of the IOL:

combination from group I - F1(R, AL, CCT, ACD, LT):

;

;

;

;

combination from group II - F2(R, AL, CCT, ACD):

;

;

;

;

combination from group III - F3(R, AL):

;

;

;

;

.

.

The obtained formulas are used for calculation according to the data of the control sample presented in Table 5. Table 6 presents the optical power of the target IOL (P _{IOL_target} , diopter), and the comparative results of calculating the optical power of the IOL using the formulas F1-F3, the delta calculated from them, comparison by the fraction of deviations falling within the range of ±1 diopters, and the absolute mean error delta. The level of significance of statistical differences between P _{IOL_target} and the optical power of the IOL calculated by the formulas F1-F3 according to the Mann-Whitney U-test (p) was determined, according to which there are no statistically significant differences between the calculated and target IOL with a significance level of less than 5%, and it means that the desired result of hitting ± 1 diopter was obtained in 85% of cases.

The conducted studies have demonstrated the possibility of carrying out the invention with the achievement of the claimed result.

Table 1. Test set of patient data implanted with a monofocal IOL No. R,
mm CCT,
mm AL,
mm ACD,
mm LT,
mm W,
mm A _const P _{IOL_impl} ,
diopter ref _target ,
diopter Ref _{p / o} ,
diopter ACD _{p / o} , diopter one 7.68 0.575 21.32 2.89 4.41 11.87 118.72 28 0 -0.5 4.12 2 7.71 0.539 22.1 2.40 4.88 12.42 118.72 25 0 0.5 4.31 3 7.50 0.54 22.38 2.32 5.38 11.99 118.72 23 0 0 3.89 four 7.63 0.543 22.53 2.79 4.4 11.52 118.4 22.5 0 0.5 5.56 5 7.75 0.507 22.8 2.87 4.45 11.93 118.72 23 0 0 4.14 6 7.38 0.483 22.81 2.49 5.81 11.71 118.72 21 0 0.75 4.76 7 7.50 0.531 22.84 2.91 5.23 11.56 118.72 21 0 0 5.10 eight 7.72 0.528 23.25 3.16 4.8 12.43 118.4 21.5 0 0 4.81 9 7.79 0.534 23.65 3.04 4.97 12.2 118.72 21 0 0 4.18 ten 7.48 0.526 23.68 3.68 4.72 12.47 118.72 19.5 0 0 5.09 eleven 7.41 0.537 24.75 4.27 3.85 11.46 118.72 19 -2.5 -2.5 4.82 12 7.46 0.472 25.91 3.64 4.47 12.34 118.4 16 -3 -2.5 4.93 13 7.42 0.543 26.18 3.67 3.91 11.45 118.4 fourteen -2.5 -2.5 5.59 fourteen 7.76 0.603 26.45 3.54 3.75 12.44 118.4 fifteen -3 -3 5.40 fifteen 7.73 0.515 27.59 3.78 four 12.73 118.4 13.5 -3 -3 5.87

Table 2. Additional calculated test sample data No. P _{IOL_em, diopter} P _{IOL_target} , diopter P _horn,1 , diopter P _horn,2 , diopter P _horn,3 , diopter H _{eye, 1} , mm H _{eye, 2} , mm H _{eye, 3} mm one 28 27.25 43.95 43.40 42.73 4.38 4.12 4.46 2 25 25.75 43.80 43.21 42.60 3.89 4.31 4.64 3 23 23 45.00 44.71 43.76 3.81 3.89 4.21 four 22.5 23.25 44.23 43.75 43.01 4.10 5.56 5.88 5 23 23 43.55 42.89 42.35 4.36 4.14 4.45 6 21 22.125 45.76 45.64 44.50 3.98 4.76 5.07 7 21 21 45.00 44.70 43.76 4.40 5.10 5.41 eight 21.5 21.5 43.75 43.14 42.54 4.46 4.81 5.11 9 21 21 43.32 42.61 42.13 4.54 4.18 4.48 ten 19.5 19.5 45.15 44.89 43.91 5.17 5.09 5.38 eleven 15.25 19 45.55 45.38 44.29 5.76 4.82 5.10 12 11.5 16.75 45.27 45.03 44.02 4.95 4.93 5.19 13 10.25 fourteen 45.52 45.35 44.26 4.98 5.59 5.85 fourteen 10.5 fifteen 43.52 42.87 42.32 4.85 5.40 5.66 fifteen 9 13.5 43.69 43.07 42.49 5.08 5.87 6.09

Table 3. Values of the optical power of the eye P _eye for P _rog,i and H _eye,j No. P _1.1 P _1.2 P _1.3 P _2.1 P _{2.2 P2.3} P _3.1 P _3.2 P _3.3 one 67.92 68.16 67.84 67.42 67.66 67.35 66.82 67.05 66.74 2 65.62 65.27 65.01 65.07 64.73 64.47 64.50 64.16 63.90 3 65.05 64.99 64.74 64.77 64.71 64.47 63.89 63.83 63.59 four 63.68 62.59 62.36 63.23 62.16 61.92 62.55 61.49 61.26 5 63.28 63.45 63.22 62.67 62.84 62.61 62.17 62.34 62.11 6 63.90 63.34 63.12 63.79 63.23 63.01 62.72 62.17 61.96 7 62.89 62.40 62.17 62.61 62.12 61.90 61.73 61.25 61.04 eight 62.11 61.86 61.65 61.54 61.30 61.09 60.99 60.75 60.54 9 61.24 61.48 61.27 60.58 60.81 60.61 60.13 60.36 60.16 ten 61.25 61.30 61.11 61.01 61.06 60.87 60.10 60.15 59.96 eleven 57.81 58.29 58.15 57.65 58.14 58.00 56.63 57.11 56.97 12 54.85 54.85 54.75 54.61 54.62 54.52 53.65 53.66 53.56 13 54.03 53.81 53.73 53.87 53.65 53.56 52.82 52.61 52.53 fourteen 52.36 52.17 52.09 51.74 51.55 51.47 51.21 51.03 50.94 fifteen 51.20 50.96 50.90 50.59 50.37 50.30 50.03 49.81 49.74 * i - number of the formula for calculating the cornea, j - number of the formula for calculating the distance between the second main focal point of the cornea and the first main focal point of the IOL

Table 4. The results of the calculation of the optical power of the IOL using the combined formulas F1-F3, the delta calculated from them, and comparison in terms of the proportion of deviations falling within the range of ±1 D and the absolute mean error delta No. P _IOL (F1),
diopter delta(F1), diopter P _IOL (F2),
diopter delta(F2),
diopter P _IOL (F3),
diopter delta(F3),
diopter one 27.56 0.31 27 0.25 27.85 0.6 2 24.92 0.83 24.78 0.97 25.24 0.51 3 22.77 0.23 22.57 0.43 23.22 0.22 four 23.19 0.06 23.31 0.06 23.37 0.12 5 22.72 0.28 23.19 0.19 23.03 0.03 6 21.67 0.455 20.51 1.615 21.06 1.065 7 21.81 0.81 21.50 0.5 21.62 0.62 eight 21.29 0.21 21.68 0.18 21.37 0.13 9 20.47 0.53 20.57 0.43 20.39 0.61 ten 19.64 0.14 19.01 0.49 18.64 0.86 eleven 19.04 0.04 18.82 0.18 18.42 0.58 12 16.87 0.12 15.76 0.99 15.78 0.97 13 14.7 0.7 13.77 0.23 13.93 0.07 fourteen 16.95 1.95 15.85 0.85 15.97 0.97 fifteen 14.02 0.52 12.24 1.26 12.47 1.03 Wed value 0.48 - 0.59 - 0.56 delta < ±1 diopter 93% 87% 87%

Table 5. Control sample data No. R AL CCT ACD W LT A _const P _{IOL_impl} Ref _target Ref _p/o one 7.25 21.75 0.52 2.18 11.37 4.9 118.72 24 0 -0.75 2 7.89 23.02 0.52 2.9 12 4.53 118.32 22.5 0 0 3 7.75 23.1 0.51 3.19 12.08 4.49 118.72 21.5 0 0.5 four 7.79 23.14 0.59 2.53 11.39 4.51 118.32 22.5 0 -0.75 5 7.44 23.18 0.55 3.4 12.1 4.11 118.72 twenty 0 0 6 7.62 23.41 0.53 2.84 11.24 3.92 118.32 twenty 0 0 7 7.41 23.5 0.52 3.05 12.12 4.42 118.72 19.5 0 0 eight 7.79 23.55 0.51 3.24 12.18 3.53 118.72 21.5 0 0 9 7.9 23.58 0.5 3.04 12.31 4.25 118.32 21 0 -0.5 ten 7.83 23.68 0.6 3.36 12.29 4.35 118.32 21.5 0 -one eleven 7.84 23.74 0.59 3.48 12.19 4.09 118.32 21 0 -0.5 12 7.51 23.77 0.61 3.66 12.18 4.36 118.72 21.5 0 -1.5 13 7.67 23.79 0.55 3.4 12.13 3.85 118.32 21 0 -one fourteen 7.97 23.9 0.56 2.66 12.31 5.21 118.32 21.5 0 -0.5 fifteen 7.29 24.14 0.56 3.16 11.96 4.87 118.72 19 -2.5 -2.5 16 8.15 26.5 0.59 3.34 12.16 four 118.72 16 -one -0.75

Table 6. The results of calculating the optical power of the IOL on the control sample using the combined formulas F1-F3, the delta calculated from them, comparison of the proportion of deviations falling within the range of ±1 D and the absolute mean error delta, assessment of the significance of the level of statistical differences No. P _{IOL_goal} ,
diopter delta
(P _{IOL_target} ),
diopter F1,
diopter delta
(F1)
diopter F2,
diopter delta
(F2)
diopter F3,
diopter delta
(F3)
diopter one 22.875 1.125 24.17 1.295 22.63 0.245 24.12 1.245 2 22.5 0 22.59 0.09 23.27 0.77 22.96 0.46 3 22.25 0.75 21.66 0.59 22.42 0.17 22.02 0.23 four 21.375 1.125 22.23 0.855 21.97 0.595 22.08 0.705 5 twenty 0 19.76 0.24 20.35 0.35 20.12 0.12 6 twenty 0 21.23 1.23 20.24 0.24 20.32 0.32 7 19.5 0 18.58 0.92 18.73 0.77 18.85 0.65 eight 21.5 0 21.61 0.11 21.09 0.41 20.72 0.78 9 20.25 0.75 21.03 0.78 21.46 1.21 21.16 0.91 ten twenty 1.5 20.26 0.26 20.96 0.96 20.49 0.49 eleven 20.25 0.75 20.1 0.15 20.89 0.64 20.35 0.1 12 19.25 2.25 18.63 0.62 18.87 0.38 18.51 0.74 13 19.5 1.5 19.28 0.22 19.62 0.12 19.32 0.18 fourteen 20.75 0.75 20.4 0.35 20.45 0.3 20.45 0.3 fifteen 19 0 19.96 0.96 19.46 0.46 19.7 0.7 16 16.375 0.375 15.85 0.525 14.9 1.475 14.93 1.445 Wed value 0.68 * 0.57 * 0.57 * 0.59 delta < ±1 diopter 69% 88% 88% 88% * Based on the Mann-Whitney U-test, with a probability of at least 95%, there were no statistically significant differences between the calculated and target optical power of the IOL

LITERATURE

1. Gale R. P. et al. Benchmark standards for refractive outcomes after NHS cataract surgery // Eye. - 2009. - T. 23. - No. 1. - S. 149-152.

2. Kulikov A. N., Kokareva E. V., Dzilikhov A. A. Effective position of the lens. Review // Ophthalmosurgery. - 2018. - no. 1. - S. 92-97.

3. Manaenkova G. E. Errors in the calculation of the optical power of the IOL in non-standard clinical situations. Literature review // Ophthalmology. - 2022. - T. 19. - No. 1. - S. 46-52.

4 Holladay J. T. et al. A three-part system for refining intraocular lens power calculations // Journal of Cataract & Refractive Surgery. - 1988. - T. 14. - No. 1. - S. 17-24.

5. Hoffer K. J. The Hoffer Q formula: a comparison of theoretic and regression formulas // Journal of Cataract & Refractive Surgery. - 1993. - T. 19. - No. 6. - S. 700-712.

6. Haigis W. The Haigis formula. In: Shammas H, editor. Intraocular Lens Power Calculations. Thorifare, NJ, Slack; 2004. p. 41-57.

7. Hoffer K. J. Clinical results using the Holladay 2 intraocular lens power formula // Journal of Cataract & Refractive Surgery. - 2000. - T. 26. - No. 8. - S. 1233-1237.

8. Zakharova I. A., Isakova I. A. Analysis of refractive results of IOL calculation depending on the biometric features of the eyes // Modern technologies in ophthalmology. - 2019. - no. 5. - S. 28-32.

9. Olsen T. Calculation of intraocular lens power: a review // Acta Ophthalmologica Scandinavica. - 2007. - T. 85. - No. 5. - S. 472-485.

10. Barrett G. D. An improved universal theoretical formula for intraocular lens power prediction // Journal of Cataract & Refractive Surgery. - 1993. - T. 19. - No. 6. - S. 713-720.

11. Kane Formula. [Electronic resource] Access mode: https://www.iolformula.com/about/

12. Hill-RBF Calculator Version 3.0. [Electronic resource] Access mode: https://www.rbfcalculator.com/online/index.html

13. Darcy K. et al. Assessment of the accuracy of new and updated intraocular lens power calculation formulas in 10 930 eyes from the UK National Health Service // Journal of Cataract & Refractive Surgery. - 2020. - T. 46. - No. 1. - S. 2-7.

14 Savini G. et al. Comparison of 13 formulas for IOL power calculation with measurements from partial coherence interferometry // British Journal of Ophthalmology. - 2021. - T. 105. - No. 4. - S. 484-489.

15. Order of the Ministry of Health of Russia dated November 12, 2012 No. 902n “On approval of the Procedure for providing medical care to the adult population in diseases of the eye, adnexa and orbit” (Registered in the Ministry of Justice of Russia on December 13, 2012 No. 26116). Russian newspaper, special issue, No. 78/1, 04/11/2013

16. Retzlaff J. A., Sanders D. R., Kraff M. C. Development of the SRK/T intraocular lens implant power calculation formula // Journal of Cataract & Refractive Surgery. - 1990. - T. 16. - No. 3. - S. 333-340.

17. German, I. Physics of the human body / I. German // Dolgoprudny: Intellect Publishing House, 2011. - 992 p.

18. Olsen, T. Calculation of intraocular lens power: a review / T. Olsen // Acta Ophthalmol. Scand. - 2007. - Vol. 85. - P. 472-485.

19. Zhezheleva L. V. Personalized algorithm for calculating the optical power of intraocular lenses in patients with cataracts after previous radial keratotomy: dis. - Institute of advanced training Feder. medical biol. agencies of Russia, 2017

20. Patent No. 2339341 RF, IPC A 61 F 2/16. Intraocular lens / Hong S., Xie J., Wang St. J. N., Stanley D., Caracelle M., Simpson M. J., Zhang S.; applicant and patent holder Alcon, Inc. - No. 2006140808/14; dec. 04/04/2006; publ. November 27, 2008, Bull. No. 33. - 18 p.

Claims (73)

1. A method for determining the optical power of an intraocular lens based on personal surgical technique and preoperative data, including using the laws of paraxial optics and regression analysis, measurement of the average radius of curvature of the anterior surface of the cornea (R, mm) and the axial length of the eye (AL, mm), characterized in that anatomical features of the structure of the eye are taken into account in the mathematical model of a two-component optical system, to correct the calculation formulas based on a sample of patient data, the regression analysis uses the necessary measured parameters, such as the depth of the anterior chamber before surgery (ACD, mm), optical power of the implanted intraocular lens (IOL) (P _{IOL_impl} , diopters), target postoperative refraction (Ref _target , diopters), postoperative refraction after at least one month (Ref _{p / o} , diopters), postoperative depth of the anterior chamber - the distance from the anterior surface of the cornea to the anterior surface of the IOL (ACD _{p / o} , diopters), and also optionally use additional parameters, such as the thickness of the cornea in the central zone (CCT, mm), the average curvature of the posterior surface of the cornea ( _Rc , mm), the thickness of the lens in the central zone (LT, mm), the diameter of the cornea (W, mm) , A-constant of the implanted IOL (A _const ), and the method is carried out in stages: (1) form a test sample consisting of at least the required measured parameters of the eye, with a volume of at least ten records; (2) for each record of the test sample, the following are calculated: the optical power of the IOL providing emmetropic refraction (P _{IOL_em} , diopter), the optical power of the IOL providing the target refraction (P _{IOL_target} , diopter), the optical power of the cornea P _horn (dptr) i in different ways, the distance between the second main focal point of the cornea and the first main focal point of the IOL is the effective position of the IOL H _eyes (mm) in j ways, the optical power of the eye with IOL P _eyes (dptr) in k ways, with i = {1,2}, j = 2 ...M, k =2...2×M, M = {2,3}; (3) calculate the coefficients m of the approximating functions of the effective position of the IOL (H _IOL ) and n approximating functions of the optical power of the eye (P _{eye_IOL} ) according to the values of the effective position of the IOL (H _eye ) and optical power of the eye (P _eye ) calculated in different ways, respectively, where m =(9…M _H )× j and n =(3...M _P )× k , is the number of functions, M _H ≤16, M _P ≤5; (4) for each record of the test sample, the optical power of the IOL is calculated by combining the functions obtained at stages (2) and (3) for calculating the optical power of the cornea, the effective position of the IOL, the optical power of the eye: P _{IOL,( t )} (P _{horn( i )} , N _{IOL( m )} , P _{eye_IOL( n )} ), where t =1.. i × m × n is the ordinal number of the combination, i is the ordinal number of the function for calculating the optical power of the cornea, m is the ordinal number of the function for calculating the effective position of the IOL, n is the ordinal number of the function for calculating the optical power of the eye; (5) for each column vector of calculated values P _{IOL,( t )} calculate the column vector of errors in the calculation of the optical power of the IOL (delta _{( t )} , diopter): delta _{( t )} =P _{IOL,( t )} -P _{IOL_target} , where P _{IOL_target} , diopter is the column vector of optical powers of the IOL, providing the target refraction; (6) for each column vector delta _{( t )} calculate the proportion of deviations not exceeding ±1 diopter and the absolute average value of the elements of delta _{( t )} ; (7) from the array of functions P _{IOL,( t )} (P _{horn( i )} , N _{IOL( m )} , P _{eye_IOL( n )} ) select those for which the proportion of deviations from the target refraction is no more than ±1 diopter, at least in 85% of cases; (8) the selected functions are grouped according to the number and type of eye parameters included in the calculation; (9) from each group, for clinical use, select the function number t that has the minimum absolute mean delta _{( t )} . 2. The method according to claim 1, characterized in that in step (1) the parameters of the test sample are measured either with an optical or ultrasonic biometer and classified according to one of the features or any combination of them: by age, gender of the patient, manufacturer and model of the implanted IOL, the value of the measured parameters of the eye. 3. The method according to claim 1, characterized in that the optical power of the IOL, providing emmetropic refraction (P _{IOL_em} , diopter), is calculated by the formula

; the optical power of the IOL, providing the target refraction (P _{IOL_target} , diopter), is calculated by the formula

. 4. The method according to claim 1, characterized in that in step (2) the optical power of the cornea P _horn is calculated by two formulas:

, where CI is the keratometric index, the values of which lie in the range [1.32; 1.35];

, where n _horn \u003d 1.3771 is the refractive index of the cornea; n _air =1 - refractive index of air; n _{water moisture} \u003d 1.3374 - the refractive index of aqueous humor. 5. The method according to claim 1, characterized in that in step (2) the effective position of the IOL H _{eyes is} calculated by the formulas:

, where

;

;

, where

- correction for the focal points of the cornea and IOL. 6. The method according to claim 1, characterized in that in step (2) the optical power of the eye (P _eye ) is calculated by the formula:

, where P _horn , P _IOL - the optical power of the cornea and IOL, respectively, diopter; H _eye is the effective position of the IOL, mm. 7. The method according to claim 1, characterized in that at step (3) the approximating functions of the effective position of the IOL (N _IOL ) have the form:

;

;

;

;

;

;

;

;

; functions H ₁₀ , ..., H ₁₈ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm). 8. The method according to claim 1, characterized in that in step (3) the effective position of the IOL (N _IOL ) is calculated by the formula:

, where the approximating functions for LF (mm) are the positions of the anterior surface of the IOL relative to the anterior lens capsule, have the form:

;

;

;

;

;

;

; functions LF ₈ , ..., LF ₁₄ differ from those listed above by adding a correction for the focal points of the cornea and IOL (Δ, mm). 9. The method according to claim 1, characterized in that at step (3) the approximating functions of the optical power of the eye (P _{eye_IOL} ) have the form:

;

;

, where n _glass. is the refractive index of the vitreous body, С' - position of the second main focal point of the combined optical system "cornea - anterior chamber - IOL" relative to the anterior surface of the cornea, which is described by the function of the form:

, where either AL or LT or (ACD+LT) is taken as x. 10. The method according to claim 1, characterized in that the optical power of the IOL is calculated by the formula:

, where P _{eye_IOL} is a function for calculating the optical power of the IOL, P _horn is a function for calculating the optical power of the cornea, N _IOL - function for calculating the effective position of the IOL, Ref _target - target postoperative refraction, diopter.

Images