RU2192220C1 - Surgical method for correcting myopia - Google Patents

Abstract

FIELD: medicine. SUBSTANCE: method involves applying refraction diagnostic techniques and laser radiation parameter calculation to produce cornea shape enabling optimum refraction conditions. Laser radiation is sent via forming system giving way for producing radiation beam creating circular spot on the cornea which size is equal to 1.0-7.0 mm. Radiation center is first set to 0-2.0 mm from the optical zone of the eye. Then, circular scanning with constant angular velocity of the mentioned spot movement over the cornea surface is carried out. Scanning circle radius belongs to an interval from 0 to 2 mm. 5 to 20 revolutions are performed within 0.5-5.0 min. EFFECT: enhanced effectiveness of treatment; improved vision function. 4 dwg _

Description

 The invention relates to ophthalmology and is intended for the correction of myopia.

 There is a method of surgical treatment of myopia with pulsed UV-laser radiation with a wavelength of 193 nm, with an intensity distribution in the form of a truncated Gaussian distribution, in which, by layer-by-layer evaporation of the cornea, a change in the curvature of the cornea is performed (see AS 2022544).

 The disadvantage of this method is the lack of accuracy of operations for the correction of myopia.

 The technical problem solved by this invention is to increase the accuracy of surgical correction of myopia.

 This technical problem is solved in that in the method of surgical correction of myopia, which consists in exposing the cornea to the radiation of a UV laser having a Gaussian distribution of the energy density in the beam cross section, according to the invention, the effect is produced by laser radiation forming a circular spot on the cornea with a diameter of 1.0 -7.0 mm, the center of which is initially set at a distance of 0-2.0 mm from the center of the optical zone of the eye, after which a circular scan is performed with a constant angular velocity of the indicated spot p about the surface of the cornea, scanning is performed around a circle whose radius lies in the range of 0-2.0 mm, and from 5 to 20 revolutions is performed for 1 min, the exposure time is 0.5-5.0 min.

 The method is illustrated in figures 1 to 4.

 Figure 1 shows an example of the distribution of energy density in the area of operation; figure 2. - layer evaporated from the surface of the cornea (shaded); figure 3 and 4 - the process of conducting the operation.

 The method is as follows.

 Initially, refractive diagnostics are performed, which includes the determination of subjective refraction, visual acuity, echobiometry, corneometry, ophthalmometry, and computer keratotopography.

 The refractive problem is determined (the magnitude of the change in refraction, taking into account the anomaly of refraction, the anatomical features of the organ of vision and the age of the patient).

 The optimal solution to the refraction problem is calculated by varying the parameters of the laser radiation (energy density, Gaussian distribution parameter, trajectory and diameter, angular velocity, number of laser radiation pulses) to obtain the shape of the cornea that provides optimal refraction.

The necessary change in the refraction of the cornea (change in its radius of curvature in the optical zone) is made by evaporation of the surface layers of the cornea of the desired shape by exposure to pulsed ultraviolet laser radiation with a laser pulse duration of 5-50 ns, a radiation wavelength of 0.19-0.25 microns, and a repetition rate radiation pulses 1-30 Hz, with a truncated Gaussian distribution of the radiation energy density in the operation area (formula 1)
W (x) = W ₀ • exp (-x ^2/2 • S ²⁾ at | x | <D and
W (x) = 0 for x≥D (Fig. 1), (1)
where D is the diameter of the optical zone;
W ₀ is the energy density in the radiation pulse in the center of the spot;
S - Gaussian distribution parameter
in the optical zone with a diameter of 3 mm <d <8 mm, the energy density in the radiation pulse in the center of the spot is 120 <W ₀ <500 mJ / cm ² and with an individual choice of the parameters W ₀ and S of this distribution for each operation, the number of radiation pulses in a series of 100 2000.

The initial shape of the cornea is approximated by a parabola
Y (x) = (x ^2/2 • R)
(figure 2, curve 1), (2)
where R is the radius of curvature of the cornea in its center.

As a result of the action of N radiation pulses moving along the surface of the cornea with a constant angular velocity ω (φ), with a truncated Gaussian energy distribution (formula 1), characterized by the parameters W ₀ and S, due to the evaporation of the corneal tissues, the corneal surface described by equation (3 )
Y ₀ (x) = f (x, N, S, W ₀ , ω (φ)
(figure 2, curve 2), (3)
generally not a parabola equation.

N, S, W ₀ , ω (φ) are chosen such that this equation in the optical zone is the least different from the equation of the parabola with the desired radius of curvature R, which leads to lower aberrations and, therefore, to higher visual acuity. In view of the great mathematical complexity, the problem is solved using a computer. The initial data for the calculation are the initial refraction of the cornea, its thickness, the desired change in refraction, the diameter of the exposure zone, the law of photoablation of the cornea (the dependence of the thickness of the removed layer on the energy density at a given point).

 The operation is performed as follows: laser radiation (not shown) is passed through a forming system (not shown), which allows to receive a radiation beam on the cornea 3 of the patient’s eyes, forming a circular spot 4, the center of which is initially set at a distance of 0-2.0 mm from the center of the optical zone of the eye 5, moving along a circular path 6 (figure 3), after which a circular scan is made around circle 6 with a constant angular velocity ω (φ) of the indicated spot 4 on the surface of the cornea 3, and from 5 to 20 revolutions per 1 min t chenie 0.5-5.0 min (Figure 4).

 Under local anesthesia (Dicainum solution 1%), the calculated number of laser pulses is applied to the cornea of the operated eye, the deviations of which from the optical axis of radiation are controlled by the surgeon using an operating microscope.

 In the postoperative period, the patient is prescribed instillation of eye drops: antibiotics (for example, 0.25% chloramphenicol solution) for 7-10 days 4-6 times a day. From the 3rd day for 2-3 months. topical corticosteroids are prescribed (for example, dexamethasone 0.1%) according to the scheme (from six instillations per day to a single instillation at the end of the term).

Example 1
Patient R., 20 years old, diagnosis: High degree myopia of the right eye.

Visual acuity: OD = 0.05 sph-6.25 D = 0.9. Refractometry: 180 ^° = -6.25D, 90 ^° = -6.25D. Ophthalmometry: 180 ^o = 41.0 D, 90 ^o = 41.0 D. Corneometry in the center = 554 microns.

An operation was carried out according to the invention according to the invention with an energy of 220 mJ / cm ² , a frequency of 10 Hz, a pulse duration of 15 ns, an impact diameter of 6.8 mm, a residual thickness of the cornea in the center = 316 μm, exposure time 1 min. After surgery, a solution of chloramphenicol was instilled, an aseptic dressing was applied.

After 10 days during the examination:
Visual acuity: OS = 0.8 sph-0.25 D = 0.9. Refractometry: 180 ^o = -0.25D, 90 ^o = -0.25D. Ophthalmometry: 180 ^o = 35.0 D, 90 ^o = 35.0 D.

 Conclusion: As a result of the operation, it was possible to achieve a complete correction of myopia and planned visual acuity.

Example 2
Patient R., 49 years old, diagnosis: High degree myopia of the left eye.

Visual acuity: OD = 0.05 sph-12.50 D = 0.7. Refractometry: 175 ^o = -12.25 D, 85 ^o = -12.50 D. Ophthalmometry: 175 ^o = 44.25 D, 85 ^o = 44.0 D. Corneometry in the center = 586 μm.

The operation is carried out according to the technology according to the invention with an energy of 230 mJ / cm ² . with a frequency of 10 Hz, a pulse duration of 15 ns, an impact diameter of 6.5 mm, a residual thickness of the cornea in the center = 310 μm, an exposure time of 1.5 min. After surgery, a solution of chloramphenicol was instilled, an aseptic dressing was applied.

After 14 days during the examination:
Visual acuity: OS = 0.5 sph-1.00 D = 0.7. Refractometry: 1 ^o = -1.00 D. 91 ^o = -1.00 D. Ophthalmometry: 1 ^o = 33.75 D, 90 ^o = 33.50 D.

 Conclusion: After the operation, the desired mild myopic refraction of the eye and high visual functions were obtained.

Example 3
Patient Z. 19 years old, diagnosis: Myopia of a weak degree of the right eye.

Visual acuity: OD = 0.1 sph-2.0 D = 1.0. Refractometry: 180 ^o = -2.0 D. 90 ⁰ = -2.00 D. Ophthalmometry: 180 ^o = 41.50 D, 90 ^o = 41.50 D. Corneometry in the center = 504 microns.

An operation was carried out according to the invention according to the invention with an energy of 250 mJ / cm ² , a frequency of 10 Hz, a pulse duration of 15 ns, an impact diameter of 6.9 mm, a residual thickness of the cornea in the center = 415 μm, an exposure time of 40 s. After surgery, a solution of chloramphenicol was instilled, an aseptic dressing was applied.

After 7 days during the examination:
Visual acuity: OS = 1.0. Refractometry: 180 ^o = -0.25 D, 90 ^o = -0.25 D. Ophthalmometry: 180 ^o = 39.50 D, 90 ^o = 39.50 D.

 Conclusion: The obtained emmetropic refraction made it possible to increase uncorrected visual acuity to the level of visual acuity with correction before surgery.

Claims (1)

 A method of surgical correction of myopia, which consists in exposing the cornea to the radiation of a UV laser having a Gaussian distribution of energy density in the beam cross section, characterized in that the effect is produced by laser radiation forming a circular spot on the cornea with a diameter of 1.0-7.0 mm, the center of which is initially set at a distance of 0-2.0 mm from the center of the optical zone of the eye, after which a circular scan is performed with a constant angular velocity of the indicated spot along the surface of the cornea, scanning odyat circumferentially whose radius lies in the range of 0-2.0 mm and produced from 5 to 20 rev / min, the exposure time of 0.5-5.0 min.

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