RU2376967C1 - Method of surgical correction of myopia - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to ophthalmology and can be applied in myopia correction. Cornea is exposed to excimer laser radiation with Gauss radial distribution of energy density in transverse ray section. Wave length is 193-250 nm, diametre of laser influence zone from 5 to 9 mm, pulse duration 15-30 ns, pulse repetition rate from 5 to 15 Hz. Exposure is performed by successive reduction of mean square deviation of energy density distribution in each of the following pulse series in interval from 2.3 to 1.8 mm. Value of energy density amplitude in centre of pulse symmetry lies in interval from 100 mJ/sq cm to 175mJ/sq cm and remains constant during pulse series carrying out. In each pulse series value of mean square deviation of energy density is constant. Each series of pulses forms curved with respect to initial cornea surface spherical surfaces, located on one axis. Zone of exposure is symmetrical relative to optical centre of cornea symmetry.

EFFECT: method allows to reduce eye tissues trauma with simultaneous reduction of post-operation complications and volume of removed eyes tissues.

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Description

The invention relates to the field of ophthalmic surgery.

A known method of surgical correction of myopia using radiation from a non-scanning excimer laser with a wavelength of λ = 193 nm. Surgical action on the cornea is carried out due to the parameters of the amplitude (A) of the energy density in the center of symmetry of the pulse, the value of the "sigma", the diameter of the ablation zone, and the number of pulses. The parameter “sigma” (σ) means the parameter of the standard deviation of the Gaussian radial distribution of the energy density in the beam cross section (see D. Hudson. Statistics for physicists. 2nd supplemented edition. Translated from English - Moscow, Mir, 1970, pp. 30-32). All these parameters (except the number of pulses) are set in the form of certain quantities and remain unchanged during the operation. Each of the parameters of the effect of excimer laser radiation on the cornea contributes to the result: “sigma” determines the geometry of the spatial effect, the amplitude of the energy density - the intensity of the exposure and partially the geometry, the number of pulses - the final refraction. The main refractive effect is determined by the number of pulses along the stroma of the cornea (see Kachalina GF “Surgical technology of transepithelial photorefractive keratectomy in case of myopia on excimer laser apparatus Profile-500. Abstract of candidate dissertation. Moscow, 2000, pp. 9-14) .

However, this method has significant drawbacks: a sufficient traumatic effect on the tissues of the eye due to the large amount of energy received during the implementation of laser exposure. In addition, in some cases, there is the occurrence of postoperative complications in the form of corneal opacities.

Technical task: to reduce trauma to the tissues of the eye while reducing postoperative complications and the volume of removed eye tissue.

The technical problem is solved in that in the method of surgical correction of myopia, which consists in exposing the cornea by layer-by-layer ablation by pulsed radiation of a non-scanning excimer laser with a Gaussian radial distribution of energy density in the beam cross section, the effect is produced by sequentially decreasing the standard deviation of the energy density distribution in each from subsequent series of pulses in the range from 2.3 mm to 1.8 mm, while the value of the amplitude of the energy density and in the center of symmetry of the pulse lies in the range from 100 mJ / cm ² to 175 mJ / cm ² and remains constant throughout the series of pulses, and inside each series of pulses the value of the standard deviation of the energy density distribution is constant, with each series of pulses forming spherical surfaces concave with respect to the initial surface of the cornea, located on one axis, facing concavity towards the front surface of the cornea, and the area of influence is symmetrical with respect to optically th center of corneal symmetry;

then form the first concave spherical surface, while the ratio of the diameter of the first spherical surface to the diameter of the cornea lies in the range from 0.6 to 0.8;

then form a second concave spherical surface, and the ratio of the diameter of the second spherical surface to the diameter of the first spherical surface lies in the range from 0.8 to 0.95;

then they form a third concave spherical surface, while the ratio of the diameter of the third spherical surface to the diameter of the second spherical surface lies in the range from 0.8 to 0.95, moreover, the surface of the cornea is exposed to radiation from an excimer laser with a wavelength of 193-250 nm, with a diameter of the laser irradiation zone from 5 to 9 mm, pulse duration 15-30 ns, pulse repetition rate from 5 to 15 Hz.

The set of essential distinguishing features proposed by the author is necessary and sufficient for the unique achievement of the task.

The author has done a lot of work, allowing to determine the intervals of the main parameters. The value of the standard deviation of the energy density distribution ("sigma") in each of the subsequent series of pulses lies in the range from 2.3 mm to 1.8 mm, and it cannot be less than 1.8 mm, because the diameter of the formed optical zone becomes less than the diameter of the central optical zone and cannot be more than 2.3 mm, because a larger diameter of the optical zone is impractical to achieve the claimed technical problem.

The value of the amplitude of the energy density at the center of symmetry of the pulse remains constant throughout the series of pulses and lies in the range from 100 to 175 mJ / cm ² . It cannot be less than 100 mJ / cm ² , since this value is an effective threshold for ablation, and more than 175 mJ / cm ² , since non-linearities of the ablation process arise, which make it difficult to achieve the stated technical problem.

The method is illustrated by drawings in Fig.1-3.

Figure 1 is a sequence of decreasing the standard deviation of the energy density distribution ("sigma"). The abscissa shows the distance from the center of the cornea in millimeters. The ordinate axis is the value of the energy density of the laser beam in mJ / cm ² .

Figure 2 is a top view of the impact zone. The coordinate axes show the distance in millimeters from the optical center of the cornea.

Figure 3 is a frontal section of the resulting surface. The horizontal axis represents the distance in millimeters from the optical center of the cornea.

The method is as follows.

A method of surgical correction of myopia consists in acting on the cornea by layerwise ablation by pulsed radiation of a non-scanning excimer laser with a radial Gaussian distribution of the energy density in the beam cross section. The optical axis of the laser radiation is combined with the optical center of the cornea.

The impact is produced by successively decreasing the standard deviation of the energy density distribution ("sigma") in each of the subsequent series of pulses in the range from 2.3 mm to 1.8 mm. The parameter "sigma" - the magnitude of the standard deviation of the distribution of energy density - in this invention is (compared with the prototype) variable, which greatly increases the effectiveness of the proposed method.

In Fig. 1, 1 denotes the initial shape of the energy density distribution curve, 2 denotes an intermediate form, and 3 denotes the final shape of the energy density distribution curve. During exposure, the shape of the energy density distribution curve becomes more pointed while maintaining a constant amplitude. The decrease in the "sigma" from the first series of pulses to the next is performed stepwise. Moreover, within each series of pulses the value of the "sigma" value is constant.

The value of the amplitude of the energy density in the center of symmetry of the pulse lies in the range from 100 mJ / cm ² to 175 mJ / cm ² and remains constant throughout the series of pulses. Each series of pulses forms concave spherical surfaces facing concavity towards the front surface of the cornea. The exposure zone is symmetrical with respect to the optical center of symmetry of the cornea.

The formation of surfaces under the influence of laser radiation is presented in figure 2 and figure 3. 3, reference numeral 4 denotes the initial surface of the cornea.

First form the first concave spherical surface (Figure 2, 1, Figure 3, 1), while the ratio of the diameter of the first concave spherical surface to the diameter of the cornea lies in the range from 0.6 to 0.8.

Next, a second concave spherical surface is formed (FIG. 2, position 2, FIG. 3, position 2), and the ratio of the diameter of the second spherical surface to the diameter of the first spherical surface lies in the range from 0.8 to 0.95.

Then form a third concave spherical surface (Figure 2, position 3, Figure 3, position 3), while the ratio of the diameter of the third spherical surface to the diameter of the second spherical surface lies in the range from 0.8 to 0.95.

The value of the amplitude of the energy density in the center of symmetry of the pulse lies in the range from 100 mJ / cm ² to 175 mJ / cm ² and remains constant throughout the series of pulses.

The impact on the surface of the cornea is produced by radiation of an excimer laser with a wavelength of 193-250 nm, with a diameter of the laser irradiation zone from 5 to 9 mm, a pulse duration of 15-30 ns, and a pulse repetition rate of 5 to 15 Hz.

All surfaces obtained by these methods are concave with respect to the original front surface of the cornea. The degree of concavity uniquely determines the optical power of the surface. The optical power of each of the surfaces formed in accordance with the claims is constant, but varies from surface to surface, with the central segment having a minimum optical power with respect to the original surface of the cornea. The value of this value is calculated in advance before the operation in order to provide the patient with normal, proportional refraction (emmetropia) in the central optical zone. The number of pulses required for the formation of each of the surfaces is constant, but different for each of them. The sequential decrease in the parameter of the standard deviation of the energy density distribution (sigma) in each of the subsequent series of pulses with a constant value of the amplitude of the energy density in the center of symmetry of the pulse during the whole series of pulses allows, in combination with the remaining parameters indicated in the characterizing part of the claims, to unambiguously solve the claimed technical task.

The proposed invention is characterized by the following clinical examples.

Example 1. Patient Sh., 26 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.06 Sph-8.0 D = 1.0

Vis OS = 0.06 Sph-8.0 D = 1.0

Corneal Thickness: 514 μm

Diagnosis: high degree stationary myopia

The operation was carried out in accordance with the proposed invention (see table 1).

Table 1

First series of pulses Second series of pulses Third series of pulses Sigma (σ), mm 2.3 2.15 2.0 The amplitude of the energy density, (A), mJ / cm ² 175 175 175 The number of pulses along the stroma of the cornea 200 200 133

Condition after surgery (1 year):

Visual acuity in the distance: Vis OD = 1.0 Vis OS = 1.0

Corneal thickness: 460 microns, the cornea is transparent.

Example 2. Patient S., 19 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.08 Sph-7.5 D = 0.8

Vis OS = 0.006 Sph-8.0 D = 0.8

Corneal Thickness: 500 μm

Diagnosis: high degree stationary myopia. The operation was performed in accordance with the proposed invention (see table 2).

table 2

First series of pulses Second series of pulses Third series of pulses Sigma (σ), mm 2.1 2.0 1.8 The amplitude of the energy density, (A), mJ / cm ² 150 150 150 The number of pulses along the stroma of the cornea 200 160 80

Condition after surgery (9 months):

Visual acuity in the distance: Vis OD = 0.9 Vis OS = 0.8

Corneal thickness: 440 microns, weak subepithelial opalescence.

Minimization of the volume of removed eye tissues is achieved by the whole set of technological methods for performing laser irradiation on the cornea of the eye by simultaneously combining all removal techniques with each exposure and the logically necessary combination of these techniques and their parameters to create each of the optical surfaces and preserve the integrity of the maximum volume of their own corneal tissues.

Compared with the prototype, the author was able to reduce the volume of removed (ablated) corneal tissue by at least 30%. Since the negative response of the cornea to the laser irradiation is directly proportional to the volume of ablated tissue, the use of the invention allows to reduce the likelihood of postoperative complications.

A sequential change in the parameter of the standard deviation of the Gaussian radial distribution of the beam energy density (sigma) is made by tuning the Profile-500 laser unit, which does not require a change in its design.

Using the proposed invention on the “Profile-500” installation made it possible to confirm an unambiguous positive solution to the claimed technical problem: developing a method for surgical correction of myopia - reducing trauma to eye tissues while reducing postoperative complications, reducing the volume of removed eye tissues.

Claims (1)

A method of surgical correction of myopia, which consists in applying a non-scanning excimer laser with a Gaussian radial distribution of energy density in the beam cross section by pulsed ablation by pulsed radiation, characterized in that the effect is performed by sequentially reducing the standard deviation of the energy density distribution in each of the following series of pulses in the range from 2.3 to 1.8 mm, while the amplitude of the energy density in the center of symmetry mpulsa lies in the range from 100 to 175 mJ / cm ² and is kept constant during the duration of the pulse series; inside each series of pulses, the value of the standard deviation of the energy density distribution is constant; moreover, each series of pulses forms spherical surfaces concave with respect to the initial surface of the cornea, located on one axis, and the impact zone is symmetrical with respect to the optical center of symmetry of the cornea; initially form the first concave spherical surface, the ratio of the diameter of the first concave spherical surface to the diameter of the cornea lies in the range from 0.6 to 0.8; then form a second concave spherical surface, and the ratio of the diameter of the second spherical surface to the diameter of the first spherical surface is in the range from 0.8 to 0.95; then they form a third concave spherical surface, while the ratio of the diameter of the third spherical surface to the diameter of the second spherical surface lies in the range from 0.8 to 0.95, and the impact on the surface of the cornea is produced by radiation of an excimer laser with a wavelength of 193-250 nm, with a diameter zones of laser exposure from 5 to 9 mm, pulse duration 15-30 ns, pulse repetition rate from 5 to 15 Hz.

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