RU2376965C1 - Method of surgical correction of myopia - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to field of medicine, namely to ophthalmic surgery. Cornea is exposed to pulse radiation of excimer laser with Gauss radial distribution of energy density in transverse ray section in layer-by-layer mode. Exposure is performed by successive reduction of energy density amplitude in centre of pulse symmetry in interval from 175 mJ/sq cm to 100 mJ/sq cm in each of the following pulse series. Parametre of mean square deviation of energy density distribution lies in range from 2.3 mm to 1.8 mm and remains constant during pulse series performing. 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. Ratio of diametre of first curved spherical surface to cornea diametre lies in range from 0.6 to 0.8. Ratio of diametre of second spherical surface to diametre of first spherical surface lies in range from 0.8 to 0.95. Ratio of diametre of third spherical surface to diametre of second spherical surface lies in range from 0.8 to 0.95. Parametres of laser radiation: wave length 193-250 nm, diametre of laser exposure zone from 5 to 9 mm, pulse duration 15-30 ns, pulse repetition rate from 5 to 15 Hz.

EFFECT: method insures reduction of eyes tissue trauma with simultaneous reduction of post-operation complications and volume of removed eye 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 "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 supplement. Translated from English. Moscow, Mir, 1970 , p. 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 are 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 exposure to the cornea by layerwise ablation by pulse radiation of an excimer laser with a radial Gaussian distribution of energy density, the effect is produced by sequentially reducing the amplitude of the energy density in the center of symmetry of the pulse in the range from 175 mJ / sq .cm to 100 mJ / sq. cm in each of the subsequent series of pulses, the parameter of the standard deviation of the energy density distribution lies in the range t is 2.3 mm to 1.8 mm and remains constant throughout the product of a series of pulses, 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 exposure zone is symmetrical with respect to the optical center of symmetry of the cornea;

then form the first concave spherical surface, 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;

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 amplitude of the energy density at the center of symmetry of the pulse in each of the subsequent series of pulses lies in the range from 100 to 175 mJ / cm2 and it cannot be less than 100 mJ / cm2, since this value is the threshold for effective ablation, and more than 175 mJ / sq. cm, since non-linearities of the ablation process arise, which make it difficult to achieve the stated technical problem.

The value of the standard deviation of the energy density distribution (“sigma”) remains constant throughout the series of pulses and is in the range from 2.3 mm to 1.8 mm. It can not 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 larger than 2.3 mm, because a larger diameter of the optical zone is impractical to achieve the claimed technical problem.

The method is illustrated by drawings (Fig.1-3).

Figure 1 is a sequence of decreasing the amplitude of the energy density in the center of symmetry of the pulse. The abscissa shows the distance from the center of the cornea in millimeters. The ordinate axis is the magnitude of the amplitude of the energy density at the center of symmetry of the pulse in mJ / cm2.

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 amplitude of the energy density in the center of symmetry of the pulse in the range from 175 mJ / cm2 to 100 mJ / cm2 in each of the subsequent series of pulses. The parameter "amplitude of the energy density" in this invention is (compared with the prototype) variable, which significantly increases the effectiveness of the proposed method.

In Fig. 1, 1 denotes the initial shape of the energy density distribution curve with an initial amplitude, 2 denotes an intermediate form, and 3 denotes the final shape of an energy density distribution curve with a finite amplitude. During exposure, the amplitude of the energy density distribution becomes smaller while maintaining a constant half-width of the distribution (“sigma”). The decrease in the amplitude from the first series of pulses to the next is performed stepwise. Moreover, inside each series of pulses the value of the amplitude is constant.

In this case, the value of the standard deviation of the energy density distribution (“sigma”) remains constant throughout the series of pulses and is in the range from 2.3 mm to 1.8 mm. 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.

In this case, the value of the parameter of the standard deviation of the energy density distribution (“sigma”) 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. A sequential decrease in the amplitude of the energy density in the center of symmetry of the pulse in each of the subsequent series of pulses with a constant value of the parameter of the standard deviation of the distribution of energy density (sigma) during the whole series of pulses allows, in combination with the other 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 Z., 26 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.08 Sph -4.5 D = 1.0

Vis OS = 0.08 Sph -4.75 D = 1.0

Corneal Thickness: 522 μm

diagnosis: stationary myopia of an average degree of both eyes

The operation in accordance with the proposed invention:

First series of pulses Second series of pulses Third series of pulses Sigma (σ), mm 2.1 2.1 2.1 Amplitude of energy density, (A), mJ / sq.cm 175 165 150 The number of pulses along the stroma of the cornea 220 one hundred one hundred

Condition after surgery (1.5 months):

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

Corneal thickness: 460 microns, the cornea is transparent.

Example 2. Patient M., 28 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.08 Sph -4.0 D = 1.0

Vis OS = 0.08 Sph -4.15 D = 1.0

Corneal Thickness: 532 μm

diagnosis: stationary myopia of an average degree of both eyes. The operation in accordance with the proposed invention:

First series of pulses Second series of pulses Third series of pulses Sigma (σ), mm 2.1 2.1 2.1 Amplitude of energy density, (A), mJ / sq.cm 170 160 155 The number of pulses along the stroma of the cornea 150 150 80

Condition after surgery (5 months):

Visual acuity in the distance: Vis OD = 0.9 Vis OS = 1.0

Corneal thickness: 480 microns, the cornea is transparent.

Minimization of the volume of removed tissue of the eye is achieved by the whole set of technological methods for performing spatial effects 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 in each subsequent layer to create each of the optical surfaces and preserve the integrity of the maximum volume own tissue of the cornea.

Compared with the prototype, the author was able to reduce the volume of removed (ablated) corneal tissue by at least 25%. In addition, by reducing the amplitude of the energy density, a reduction in eye injuries and, thus, a decrease in the likelihood of postoperative complications is achieved.

The whole set of essential distinguishing features of the invention indicated in the claims, including radiation parameters, provide an unambiguous positive solution to the claimed technical problem.

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 treating the cornea by layerwise ablation by pulsed radiation of an excimer laser with a Gaussian radial distribution of energy density in the beam cross section, characterized in that the effect is performed by sequentially reducing the amplitude of the energy density in the center of symmetry of the pulse in the range from 175 to 100 mJ / cm ² in each of the subsequent series of pulses, the parameter of the standard deviation of the energy density distribution lies in the range from 2 , 3 to 1.8 mm and remains constant throughout the product of the series of pulses, each pulse series forms spherical surfaces concave with respect to the initial surface of the cornea, located on one axis, and the exposure zone is symmetrical with respect to the optical center of symmetry of the cornea; then form the first concave spherical surface, 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; 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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