RU2196499C2 - Method for predicting full myopia correction in performing excimer laser photorefraction keratectomy - Google Patents

Abstract

FIELD: medicine. SUBSTANCE: method involves measuring myopia degree before operation to match averaged maximum correction value to before operation myopia and determine myopia value to be corrected. The correction value is adjusted by varying it in inverse proportion to the before operation myopia magnitude by 0.15 diopters when varying the before operation myopia magnitude by 1 diopter and depending on age of patient having stable myopia by 0.05 diopters when patient age changes by 1 year. Myopia value to be corrected is determined from formula M_cor = M_ref+K-[(W^*0,05)+(M $\genfrac{}{}{0ex}{}{\text{*}}{\text{ref}}$ 0,15)]. EFFECT: high accuracy of the method.

Description

 The invention relates to medicine, namely to ophthalmology, and can be used to predict the complete correction of myopia during excimer laser photorefractive keratectomy operation on the Profile-500 installation.

 A known method for predicting the complete correction of myopia during excimer laser photorefractive keratectomy surgery (See Instructions for medical use BT2.900.000MP "Installation excimer laser ophthalmic surgery with program control UELO-O 193-01" Profile-500 "p. 18), which consists in measuring the value of preoperative myopia, depending on which and on the patient's age, the average maximum value of the correction for preoperative myopia is selected and the corrected myopia is determined.

 However, in practice, when determining at the preparatory stage before the excimer laser photorefractive keratectomy, the magnitude of the correction to preoperative myopia does not take into account the mathematical dependence of the correction on the magnitude of the preoperative myopia and the patient's age. Therefore, an approximate value of corrected myopia is obtained. The magnitude of the error can vary widely depending on the experience of the surgeon and on the accumulated statistical data on the postoperative results of the patients operated on by him.

 The present invention solves the problem of predicting the complete correction of myopia during excimer laser photorefractive keratectomy. The technical result obtained in this case consists in the possibility of the most accurate determination of the optimal value of corrected myopia, which ensures complete correction of the myopia in the patient after the operation.

 This is ensured by accurate preoperative calculation of the magnitude of corrected myopia. The use of a clear mathematical dependence of the averaged maximum correction value on the preoperative myopia and the patient's age, expressed by the formula defining this dependence, makes it possible to increase the predictability of the refractive effect achieved as a result of the operation and, accordingly, the efficiency of excimer laser photorefractive keratectomy, to obtain high functional results, and to avoid unpredictable refraction and complicated course of the postoperative period.

The specified technical result is achieved by the fact that in the method for predicting the complete correction of myopia during excimer laser photorefractive keratectomy, which consists in measuring the magnitude of preoperative myopia, depending on which and on the age of the patient, the average maximum correction value for preoperative myopia is selected, and determining the magnitude of corrected myopia, specify the correction value, for which they change it inversely with the magnitude of preoperative myopia by 0.15 diopters with a change in s pre-operative myopia of 1 diopter and age of the patient with a stable 0.05 diopters myopia when changing the patient's age 1 year, and myopia correctable value determined by the formula
M _cor = M _ref + K - [(W • 0.05) + (M _ref • 0.15)],
where M _core - the value of corrected myopia;
M _ref - the magnitude of preoperative myopia detected refractometrically in cycloplegia;
K is the averaged maximum value of the correction for preoperative myopia;
W is the age of the patient with stable myopia;
0,05 - the coefficient of change of amendment depending on the age of the patient, corresponding to a change in the patient's age by 1 year;
0.15 - coefficient of change in correction depending on the magnitude of preoperative myopia, corresponding to a change in the magnitude of preoperative myopia by 1 diopter.

 A method for predicting the complete correction of myopia during excimer laser photorefractive keratectomy surgery is as follows.

 A complete examination of the patient is carried out according to the generally accepted scheme. Based on refractometric data under cycloplegia conditions (Canon RK-5 keratorefractometer, measurement within 3 mm of the optical zone), the magnitude of the preoperative myopia of the patient’s eye is determined by spheroequivalent.

 Empirically, depending on the magnitude of preoperative myopia and on the age of the patient, an average maximum magnitude of correction for preoperative myopia is selected. Based on the statistical data and depending on the features of the individual technique used by the surgeon for performing the operation, the magnitude of the correction for preoperative myopia is 2.35. Identify the patient's age (full years) with stable myopia. Myopia stabilization, i.e. the cessation of its progression occurs, as a rule, no earlier than 18 years and therefore from this age they perform an excimer laser photorefractive keratectomy operation.

 The obtained values are substituted into the formula and the optimal magnitude of corrected myopia is calculated.

 Transepithelial excimer laser photorefractive keratectomy is performed and visual acuity after surgery is determined.

 Example 1. Patient B., 18 years old. Diagnosis: Mild myopia OD.

Visual acuity: 0.1 sph - 2.0 = 1.0
Refractometry: sph - 2.0 D.

M _core = 2.0 + 2.35 - [(18 • 0.05) + (2.0 • 0.15)] = 3.15
Estimated corrected myopia M _cor = 3.15 D.

The transepithelial excimer laser photorefractive keratectomy operation was performed at an energy of 250 mJ / cm ² .

 After one month during the control examination, visual acuity = 1.0.

 On the keratotopogram - throughout the ablation zone, a uniform, smoothly changing refractive ability of the cornea.

 Example 2. Patient K., 30 years old. Diagnosis: High myopia, astigmatism OS.

Visual acuity: 0.03 sph - 12.5 cul - 1.0 ax 4 ^o = 0.8
Refractometry: sph - 12.0 cul - 2.0 ax 6 ^o
spheroequivalent = 13.0 D.

M _core = 13.0 + 2.35 - [(30 • 0.05) + (13.0 • 0.15)] = 11.9
Estimated corrected myopia M _cor = 11.9 D.

The transepithelial excimer laser photorefractive keratectomy operation was performed at an energy of 230 mJ / cm ² .

 After one month during the control examination, visual acuity = 0.8.

 On the keratotopogram - throughout the ablation zone, a uniform, smoothly changing refractive ability of the cornea.

 Example 3. Patient U., 45 years old. Diagnosis: moderate myopia, astigmatism OS.

Visual acuity: 0.04 sph - 5.0 cul - 1.5 ax 7 ^o = 0.9
Refractometry: sph - 4.0 cul - 3.0 ax 6 ^o
spheroequivalent = 6.0 D.

M _cor = 6.0 + 2.35 - [(45 • 0.05) + (6.0 • 0.15)] = 5.2
Estimated corrected myopia M _cor = 5.2 D.

The transepithelial excimer laser photorefractive keratectomy operation was performed at an energy of 230 mJ / cm ² .

 After one month during the control examination, visual acuity = 0.8.

 On the keratotopogram - throughout the ablation zone, a uniform, smoothly changing refractive ability of the cornea.

Claims (1)

A method for predicting the complete correction of myopia during excimer laser photorefractive keratectomy, which consists in measuring the magnitude of preoperative myopia, depending on which and on the age of the patient select the average maximum value of the correction for preoperative myopia, and determining the magnitude of corrected myopia, characterized in that they specify the magnitude of the correction, for which change it inversely with the magnitude of preoperative myopia by 0.15 diopters when changing the magnitude of preoperative myopia by 1 diopt iju and the age of the patient with a stable 0.05 diopters myopia when changing the patient's age 1 year, and myopia correctable value determined by the formula
M _cor = M _ref + K - [(W • 0.05) + (M _ref • 0.15)],
where M _core - the value of corrected myopia;
M _ref - the magnitude of preoperative myopia detected refractometrically in cycloplegia;
K is the averaged maximum value of the correction for preoperative myopia;
W is the age of the patient with stable myopia;
0,05 - the coefficient of change of amendment depending on the age of the patient, corresponding to a change in the patient's age by 1 year;
0.15 - coefficient of change in correction depending on the magnitude of preoperative myopia, corresponding to a change in the magnitude of preoperative myopia by 1 diopter.