RU2242201C1 - Surgical method for correcting myopic astigmatism - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: method involves treating eye cornea with ultraviolet pulsating laser radiation having Gauss energy density distribution over beam cross-section. Beam diaphragm is tuned on laser radiation ablation threshold to form round spot of 0.3-1.2 mm diameter and energy of 0.7-1.4 mJ per pulse, pulse duration of 4-7 ns and pulse succession frequency from 100 to 300 Hz. Cornea treatment is concentrated in scanning grid points arranged in equilateral triangles. Treatment points form irregular figure inscribed into en ellipse having its greater axis coincident to weak astigmatism axis. The scanning grid is shifted several times and the treatment is carried out on the following scanning grid having its points between those of the previous one.

EFFECT: enhanced effectiveness in obtaining uniform surface after treatment; shorter operation time.

3 dwg

Description

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

A known method for surgical correction of myopic astigmatism, in which the pulsed radiation of a UV laser with a wavelength of 193 nm, with an intensity distribution having the shape of a truncated iris diaphragm Gaussian distribution, forms a round spot on the cornea with a size of 1-7 mm, the radiation center is initially set at a distance of 0 -2 mm from the center of the optical zone of the eye. Then produce an elliptical scan with a variable angular velocity of the specified spot on the surface of the eye. The angular velocity decreases in areas adjacent to the maximum axis of astigmatism, and increases in areas adjacent to the minimum axis of astigmatism. The major axis of the ellipse coincides with the main axis of astigmatism. 5-20 revolutions per minute are produced for 0.5-5.0 minutes (see RF Patent No. 2192223).

However, this technical solution has significant drawbacks: the presence of a significant number of surface inhomogeneities and a long operation time.

The technical problem solved by this invention is to improve the uniformity of the surface after exposure, reducing the time of operation.

This technical problem is solved by the fact that in the method of surgical correction of myopic astigmatism, which consists in exposing the cornea to the radiation of a UV pulsed laser having a Gaussian distribution of energy density in the beam cross section, according to the invention, the beam is produced by a laser beam diaphragmed by the ablation threshold, forming on the cornea a round spot with a diameter of 0.3-1.2 mm, with an energy per pulse of 0.7-1.4 mJ, a pulse duration of 4-7 ns, a pulse repetition rate of 100 to 300 Hz, The effect on the cornea is performed by the points of the scanning grid formed by equilateral triangles, and the points of influence form a broken figure inscribed in an ellipse, the major axis of which coincides with the weak axis of astigmatism, then the scanning grid is repeatedly shifted, and the effect is made on the points of the next scanning grid, falling between points of previous scan grids.

The set of essential distinguishing features of the invention proposed by the authors is necessary and sufficient for an unambiguous positive solution to the claimed technical problem.

The method is illustrated by the drawings shown in figure 1-figure 3.

Figure 1 shows an example of the distribution of energy density in the area of operation, figure 2 is an example of an operation for myopic astigmatism with an impact zone of 6.0 mm, figure 3 is a view A of figure 2 - nodes of the scanning grid formed by equilateral triangles.

The authors based the following theoretical scheme on the basis of the operation.

The initial form of the cornea is approximated by two parabolas in the directions of astigmatism

Y ₁ (x) = (x ^2/2 · R _1),

where R ₁ and R ₂ are the radii of curvature of the cornea in its center in the directions of astigmatism.

The necessary change in the refraction of the cornea is made by evaporation of the surface layers of the cornea of the desired shape by exposure to an ultraviolet laser beam with a radiation wavelength of 193 nm, forming a round spot on the cornea with a diameter of 0.3-1.2 mm, with an energy per pulse of 0.7-1.4 mJ, pulse duration 4-7 ns, pulse repetition rate from 100 to 300 Hz and with a Gaussian distribution of 1 radiation energy density (Fig. 1), limited by the ablation threshold (formula 2)

W (x) = W ₀ · exp (x ^2/2 · S ^2),

W (x) = 0, for x≥ D,

where D is the beam diameter corresponding to the threshold of corneal ablation;

W ₀ is the energy density in the radiation pulse in the center of the spot;

S is the parameter of the Gaussian distribution.

To ensure the best quality of the obtained surface of the cornea, which leads to less aberrations and higher visual acuity, the action of narrow beams of laser radiation is produced in the nodes of the scanning grid shown in figure 2. A rectangular sector measuring 6.2 × 6.6 mm includes an area of operation with a diameter of 6 mm. Circles of smaller diameter 2 (FIG. 2) indicate the nodes of the scanning grid formed by equilateral triangles 3 (FIG. 3), circles of larger diameter 4 (FIG. 2) indicate the places where the laser beam was exposed during the removal of one layer of the cornea during surgery.

In each horizontal row (FIG. 3, view A), the distance between the centers of the laser beams (nodes of the scanning grid) d is 340 μm. The nodes of each subsequent line are shifted to the right relative to the previous one by a distance d / 2. The shortest distance h between the lines is (formula 3)

Thus, the nodes of the lines described above form equilateral triangles 3 with side d equal to 340 μm, and an equilateral triangle is an elementary fragment of the proposed scanning grid.

In the zone of operation of the required diameter, the points of influence form a broken figure inscribed in ellipse 5. The major axis of the ellipse coincides with the weak axis of astigmatism. If the major axis of the ellipse exceeds the diameter of the optical zone, then it is cut off by the diameter of the optical zone. Next, the scan grid is repeatedly shifted, while the effect is produced on the points of the next scan grid that fall between the points of previous grids. The number of shifts of the scan grid is determined by the calculation of the data of the operated eye of the patient.

The cylindrical lens resulting from the operation consists of a set of microlenses with an optical power of about - 0.3 Dptr. In turn, each microlens consists of a set of flat layers of elliptical shape. The area of the layers decreases in the vertical direction. As a result of exposure to N pulses, the scanning grid is filled and one flat layer of the cornea is removed. As a result of the evaporation of the corneal tissues, the surface of the cornea will be obtained, described by the equation (formula 3), which in general is not a parabola equation

Preparation for surgery for the correction of myopic astigmatism, carried out by the proposed method, involves a refractive diagnosis of the patient’s eye, which includes the determination of subjective refraction, visual acuity, ophthalmometry, echobiometry, corneometry, and computer keratotopography.

The effect of laser radiation on the cornea of the patient’s eye is produced by the points of the scanning grid proposed by the authors, formed by equilateral triangles, according to the described algorithm. The initial data for the calculation are the initial refraction of the cornea, the thickness of the cornea, the desired change in refraction, the diameter of the zone of influence, the dependence of the thickness of the removed layer on the energy density at this point.

In the postoperative period, the patient is prescribed the installation 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 N., 24 years old, diagnosis: high myopia, complex myopic astigmatism of the middle degree of the left eye.

Visual acuity: OS = 0.01 sph-9.5 D cyl-3.0 D ax 164 = 0.7. Refractometry: 164 ° = -9.5 D, 74 ° = -12.5 D. Ophthalmometry: 164 ° = 42.25 D, 74 ° = 45.25 D. Corneometry in the center = 547 μm.

The operation was performed according to the method proposed by the authors.

After 7 days during the examination:

Visual acuity: OS = 0.7. Refractometry: 164 ° = -0.25 D, 74 ° = -0.5 D. Ophthalmometry: 164 ° = 33 D, 74 ° = 33.25 D.

Conclusion: As a result of the operation, it was possible to completely correct the myopic and astigmatic components of eye refraction and achieve maximum visual functions.

Example 2

Patient 0., 26 years old, diagnosis: simple myopic astigmatism of a high degree of the left eye.

Visual acuity: OS = 0.05 cyl-5.5 D ax 90 = 0.6. Refractometry: 180 ° = -5.0 D, 90 ° = -0.25 D. Ophthalmometry: 180 ° = 44.50 D, 90 ° = 39.0 D. Corneometry in the center = 522 μm.

The operation was performed according to the method proposed by the authors.

After 10 days during the examination:

Visual acuity: OS = 0.5 cyl-0.75 ah 92 ° = 0.7. Refractometry: 2 ° = -0.75 D, 92 ° = + 0.25 D. Ophthalmometry: 2 ° = 39.75 D, 92 ° = 38.75 D.

Conclusion: Astigmatism was completely corrected without changing the refraction of the eye in the opposite meridian.

Example 3

Patient E., 18 years old, diagnosis: mild myopia, complex myopic astigmatism of a weak degree of the left eye.

Visual acuity: OS = 0.1 sph-1.5 D cyl-1.75 D ax 170 ° = 1.0. Refractometry: 80 ° = -3.25 D, 170 ° = -1.5 D. Ophthalmometry: 80 ° = 42.75 D, 170 ° = 41.00 D. Corneometry in the center = 501 μm.

The operation was performed according to the method proposed by the authors.

After 7 days during the examination:

Visual acuity: OS = 1.0. Refractometry: 79 ° = 0.0 D, 169 ° = -0.25 D. Ophthalmometry: 79 ° = 39.50 D, 169 ° = 39.75 D.

Conclusion: High postoperative visual acuity was the result of a complete correction of myopia and astigmatism.

Using the method of the operation proposed by the authors allows to improve the uniformity of the surface after exposure, to reduce the operation time.

Claims (1)

A method of surgical correction of myopic astigmatism, which consists in exposing the eye cornea to UV-pulsed laser radiation having a Gaussian distribution of the energy density in the beam cross section, characterized in that the beam is produced by a laser beam diaphragmed by the ablation threshold and forming a round spot on the cornea with a diameter of 0, 3-1.2 mm, with an energy per pulse of 0.7-1.4 mJ, a pulse duration of 4-7 ns, a pulse repetition rate of 100 to 300 Hz, and the impact on the cornea am of the scan grid formed by equilateral triangles, and the impact points form a broken figure inscribed in an ellipse, the major axis of which coincides with the weak axis of astigmatism, then the scan grid is repeatedly shifted, while the action is performed on the points of the next scan grid falling between the points of previous scan grids .

Images