RU2548518C1 - Method of surgical correction of complicated incorrect myopic corneal astigmatism - Google Patents

Abstract

FIELD: medicine.SUBSTANCE: keratotopogram is made. Then the eye cornea is influenced by the irradiation of an excimer laser with a wave length of 193-222 nm, energy in an impulse of 0.8-21.1 mJ, diameter of a laser spot of 0.5-1.5 mm, pulse duration of 5-8 nsec, pulse repetition rate of 30-500 Hz. A regular surface in the optical zone and surfaces of the transition zone are formed by the successive layer-by-layer removal of the cornea parts. The regular surface of the optical zone (03) is formed in the form of a concave ellipsoid of rotation with a negative conical constant from minus 0.1 to minus 0.4. The optical axis of the ellipsoid is shifted in such a way, that the centre of the optical zone corresponds to the position of the centre of the section of the maximal irregularity on the keratotopogram. The diameter of the optical zone is selected according to the diameter of the section of the maximal irregularity, determined by a map of heights on the keraotopogram. After that surfaces of the transitional zone are formed. The first surface of the transitional zone (STZ), adjacent to the zone, which is not subjected to influence, is formed in the form of a part of a convex external surface (PCES) of a circular toroid. An external edge of the first STZ is connected to the section of the cornea, which is not subjected to influence. The width of STZ constitutes 0.04-0.2 of the influence zone (IZ) diameter. The second STZ is formed in the form of a part of a concave internal surface (PCIS) of a circular toroid, adjacent to the optical zone. The width of the second STZ is equal to the width of the first STZ. An internal edge of the second STZ is connected to the external edge of the optical surface, an external edge - with the internal edge of the first STZ.EFFECT: reduction of the time for carrying out the operation and error in recentring due to carrying out the operation in one stage, reduction of irregularity of the cornea surface with the preservation of physiological conical constant of the cornea and improvement of the patients' visual functions, minimisation of the volume of ablated tissues.3 ex, 14 dwg

Description

The invention relates to ophthalmology and can be used in the correction of complex irregular myopic corneal astigmatism. The problem of correction of complex irregular myopic corneal astigmatism is one of the urgent in ophthalmology.

Wrong corneal astigmatism occurs when the main meridians of the optical surface of the eye are not at right angles or when sections of the same meridian have different refraction. This condition leads to a decrease in uncorrected and corrected visual acuity, ineffectiveness of spectacle correction, the appearance of many pronounced undesirable visual effects and causes significant difficulties in performing visual tasks. Irregular corneal astigmatism is most common with injuries and degenerative diseases of the cornea, it affects about 7.6% of all patients seeking excimer laser vision correction. In addition, eyeglass correction and correction with soft contact lenses in such cases are ineffective. This makes the correction of complex irregular corneal myopic astigmatism one of the urgent problems of ophthalmology.

The well-known "Method of correction of complex irregular myopic astigmatism", patent for the invention of the Russian Federation No. 2137451.

A method for correcting complex irregular myopic astigmatism involves performing keratotopography before surgery, then exposing the cornea to an excimer laser beam with first eliminating the cylindrical component, while the excimer laser beam is offset and set in relation to the center of the cornea in the direction of the cylinder axis by the amount shown by keratotopographic the sample, and then the laser beam is installed in the center of the cornea and an excimer laser is applied to the cornea of the eye with eliminated spherical component.

However, this method has some drawbacks: the presence of two stages of the operation, before each of which the excimer laser action is centered: the stage of photorefractive keratectomy of the cylindrical component with the displacement of the beam of the excimer laser and the stage of photorefractive keratectomy of the spherical component without displacement of the beam of the excimer laser, which increases the time of the operation and the probability bias exposure during the second stage. This method does not imply the preservation of the physiological conical constant of the cornea after surgery, as well as reducing the volume of removed corneal tissue.

The objective of the invention is to develop a method for surgical correction of complex irregular myopic corneal astigmatism, which allows to achieve high visual functions with a minimized volume of removed corneal tissue and less time for surgery with the most accurate alignment of excimer laser exposure.

The technical result achieved by the invention is to reduce the time of the operation and the errors during re-centering due to the operation in one step, reduce the irregularity of the corneal surface while maintaining the physiological conical constant of the cornea and improve the visual functions of patients, as well as minimize the volume of tissue removed.

The specified technical result is achieved by the fact that in the method of surgical correction of complex irregular myopic corneal astigmatism, including the removal of a keratotopogram and exposure to an excimer laser with a wavelength of 193-222 nm, according to the invention, the effect is carried out with an energy of 0.8-2.1 mJ per pulse , with a laser spot diameter of 0.5-1.5 mm, a pulse duration of 5-8 ns, a pulse repetition rate of 30-500 Hz on the cornea of the eye with the formation of a regular surface in the optical zone and the surface of the transition zone of put m of sequential layer-by-layer removal of cornea sections, a regular surface of the optical zone (OZ) is formed in the form of a concave ellipsoid of revolution with a negative conical constant from minus 0.1 to minus 0.4, while the optical axis of the ellipsoid is shifted so that the center of the optical zone corresponds to the position the center of the maximum irregularity plot on the keratotopogram, and the diameter of the optical zone is selected in accordance with the diameter of the maximum irregularity plot determined from the height map on the keratotopogram; after that, the surfaces of the transition zone are formed: the first surface of the transition zone (PPZ) adjacent to the zone not to be affected is formed as a part of the convex outer surface (CVP) of the annular toroid; the outer edge of the first PPP is associated with a section of the cornea that is not subject to exposure, the width of the PPP is 0.04-0.2 diameter of the impact zone (SV); the second PPZ adjacent to the optical zone is formed of the same width as the first PPZ, in the form of a part of the concave inner surface (CVP) of the annular toroid, the inner edge of the second PPZ is conjugated with the outer edge of the optical surface, and the outer edge is with the inner edge of the first PPZ .

No need to re-center the excimer laser improves the accuracy of the exposure and reduces the time of the operation.

The decrease in the irregularity of the corneal surface occurs due to the fact that when the optical axis is shifted, the excimer laser action is directed to the maximum irregularity section, and the diameter of the optical zone is selected in accordance with the diameter of the maximum irregularity section, determined from the height map on the keratotogram. After exposure to an excimer laser, the formed optical zone has a regular surface in the form of an ellipsoid with a conical constant from minus 0.1 to minus 0.4, which is equal to the conical constant of the cornea; restoration of visual functions is ensured by the formation of a concave surface within the optical zone; minimization of the volume of tissue removed is ensured by the width of the transition zone of 0.04-0.2 of the diameter of the impact zone.

The set of essential distinguishing features proposed by the authors is necessary and sufficient for an unambiguous positive solution of the technical problem posed: the creation of a method for surgical correction of complex irregular myopic corneal astigmatism in order to reduce the time of surgery, reduce the irregularity of the corneal surface while maintaining the physiological conical constant of the cornea and improve the visual functions of patients, while minimizing the amount of tissue removed and maximizing but precise alignment of excimer laser exposure.

The invention is illustrated by the drawings of FIG. 1-14. They show:

FIG. 1 - frontal section of the radiation exposure zone.

FIG. 2 - frontal section of the location of the optical and transition zones.

FIG. 3 is a top view of the corneal exposure zone.

FIG. 4 - surface formation 7.

FIG. 5 - Location of the weak and strong axis of astigmatism.

FIG. 6 - increase in surface area 7.

FIG. 7 is a view of curved closed asymmetric figures 19.

FIG. 8 - surface formation 8 of the transition zone.

FIG. 9 is a top view of the surface 8.

FIG. 10 is an isometric view of a surface 8.

FIG. 11 is a frontal section of the surface 8.

FIG. 12 - the formation of a circular zone 24.

FIG. 13 - reduction of the circular zone 25.

FIG. 14 - further reduction of the circular zone 26.

The method proposed by the authors is as follows.

The method consists in exposing the cornea of the eye 2 to radiation through the excimer laser 1 by sequential layer-by-layer removal of cornea 3 sections (Fig. 1) 2. Cornea 2 is formed on cornea 2 and cannot be removed. The axis of symmetry 5 passes through the center of the pupil, and the axis 6 passes through the center of the zone of maximum irregularity, determined by the keratotopogram.

In FIG. 2 are presented:

an optical surface 7 lying within the entire optical zone 8;

surface 9 of the transition zone;

transition zone 10.

By part of the surface of the cornea 2 to be removed is meant a portion of the cornea of a certain shape that is exposed to laser radiation 1 and removed as a result of this effect.

By a part of the surface of the cornea that cannot be removed is meant a portion of the cornea of a certain shape that is not exposed to laser radiation and cannot be removed.

By optical surface is meant the interface between two media with different refractive indices, which serves to change the path of the rays when creating a high-quality optical image on the retina of the eye.

By a layer of the cornea is meant a portion of the cornea, the shape of which changes upon a single exposure to a spatially ordered series of laser radiation pulses.

A top view of the exposure zone is shown in FIG. 3. Surfaces 7, 9 are shown in FIG. 1, 2, 3.

Under the optical zone 8 refers to the zone in which the optical surface 7 is formed (Fig. 2, 3).

The impact zone 11 refers to the zone in which the optical surfaces and the surfaces of the transition zone are formed.

Axis 5 is the axis of symmetry of the optical surface of the transition zone 9 and passes through the center of the pupil. Axis 6 is the axis of symmetry of the optical surface 7 and passes through the center of maximum irregularity, determined by the keratotopogram (Fig. 1, 2, 3).

The ellipsoidal concave optical surface 7 and the surface of the transition zone 9 are formed by sequential layer-by-layer removal of cornea sections. There are also sections 4 of the cornea 2, not to be removed, located on the periphery of the cornea.

The method is as follows.

Initially, the first ellipsoidal concave optical surface 7 is formed with a negative conical constant from minus 0.1 to minus 0.4 lying within the entire optical zone 8 by forming a zone 12 that cannot be removed.

Mark the central elliptical zone (CEZ) 13 to be removed (Fig. 4). In FIG. 4-7, zone 12 is not hatched, and zone 13 is hatched.

The center of symmetry of the CEZ is combined with the intersection of the axis 6 passing through the center of the zone of maximum irregularity and the surface of the cornea 2 (Fig. 4), the major axis 14 of the CEZ is combined with the weak axis 15 of astigmatism, and the minor axis 16 of the CEZ is combined with the strong axis 17 of astigmatism ( Fig. 5).

Zone 13 during laser irradiation is removed during the formation of the first corneal layer that changes in shape and each of the subsequent cornea that changes in shape to create a surface 7.

In FIG. 5, for convenience of presentation, the case is shown where the weak axis 15 of astigmatism is horizontal and the strong axis 17 is vertical. In practice, cases with a different arrangement of the axes of astigmatism (not shown) are possible.

With each of the subsequent laser actions, the area of the CEZ 13 increases, and the zone 12 decreases. In this case, zone 12 is formed by a curved closed figure bounded by a circle with the radius of the impact zone 11 and a curved line 18, which is the outer part of the CEZ (Fig. 6). With each subsequent layered exposure, the area of the CEZ 13 to be removed is increased and the area of the zone 12 not to be removed is reduced (Fig. 6).

The area of the CEZ 13 to be removed is increased (Fig. 7). Moreover, due to the mismatch of the axis of symmetry 5 of the surface 9 of the transition zone 10 passing through the center of the pupil and the axis of symmetry 6 of the optical surface 7 passing through the center of maximum irregularity, the curvilinear zone to be removed forms two asymmetric curvilinear closed figures 19, each of which is limited by an arc of a circle with a radius of the impact zone 11 and a curved line 18, which is the outer section of the CEZ 13. In FIG. 7, two asymmetric closed figures 19 are not shaded.

Surface 7 allows you to achieve high visual functions.

Next, form the surface 9 of the transition zone 10, which is the surface of the annular toroid. An annular toroid means a surface formed by the rotation of a circle around an optical axis without intersecting this axis. In the present invention, the surfaces 9 are part of a circular toroid and are formed as part of the convex outer (CVP) surface of the annular toroid (Fig. 9). The surface 9 is formed by rotating the segment 21 of the circle 20, convex towards the optical axis, around the axis 5 of the surface 9 without intersecting the axis 5. The arc of the circle 20 of the segment 21 is based on the chord 22 located at an angle 23 to the axis 5 and lying with the axis 5 in one plane (Fig. 9). Top view of surface 9 in FIG. 10. The surface 9 in isometric view is shown in FIG. eleven.

The surface 9 is formed by forming a circular zone 24 to be removed, limited by a circle with a radius of the impact zone 11, in the range from 0.04 to 0.2 of the diameter of the impact zone. The frontal section of the surface 9, explaining the formation of the circular zone 24, is shown in Fig. 12. Subsequently, in each layer, the area of the circular zone 24 to be removed is reduced in layers. Positions 25, 26 show a decrease in the circular zone 24. Figs 13, 14 show a layer-by-layer decrease in the area of the circular zones 24, 25, 26 (shaded in the figures).

The outer edge of the surface of the transition zone 9 is mated with the portion of the cornea 4, not subject to laser exposure, and the inner edge of the surface of the transition zone 9 is combined with the outer edge of the optical surface 7.

Excimer laser action on the cornea is carried out with the following parameters: excimer laser radiation wavelength of 193-222 nanometers with an energy per pulse of 0.8-2.1 millijoules, with a laser spot diameter of 0.5-1.5 mm, with a pulse duration of 5-8 nanoseconds, pulse repetition rate from 30 to 500 hertz.

The proposed method is characterized by the following clinical examples.

Example 1: Patient C., 32 years old.

Condition before surgery:

Visual acuity in the distance: Vis OS = 0.1 sph-1,0 D cyl-4,5 D ax 0 ° = 0.4 n.k.

Corneal curvature: 46.5D-0 °, 42.0D-90 °, average 44.25 D.

Corneal thickness: 527 microns.

Diagnosis: Complicated irregular myopic corneal astigmatism, scar after penetrating wound of the cornea. The operation of the PRK in accordance with the proposed invention.

Condition after surgery:

Visual acuity in the distance: Vis OS = 0.7 sph-0.5 D = 0.9.

Corneal curvature: 41.0D-0 °, 41.0D-90 °, average - 41.0D.

Example 2: Patient K., 34 years old.

Condition before surgery:

Visual acuity into the distance: Vis OS = 0.05 sph - 3.5D cyl - 5.25D ax 0 ° = 0.3.

Corneal curvature: 48.0D-0 °, 42.75D-90 °, average - 45.37D.

Corneal thickness: 518 microns.

Diagnosis: Stabilized keratoconus of the 1st stage, the condition after crosslinking of corneal collagen, complex irregular myopic corneal astigmatism. The operation of the PRK in accordance with the proposed invention.

Condition after surgery:

Visual acuity in the distance: Vis OS = 0.6 cyl - 0.75D ax 0 ° == 0.8.

Corneal curvature: 40.75D-0 °, 40.0D-90 °, average - 40.37D.

Example 3: Patient A., 36 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.1 sph - 2.0D cyl - 4.25D ax 0 ° = 0.6.

Corneal curvature: 45.0D-0 °, 40.75D-90 °, average - 42.8D.

Corneal thickness: 564 microns.

Diagnosis: Condition after end-to-end keratoplasty for stage 4 keratoconus, complex irregular myopic corneal astigmatism. The operation LASIK in accordance with the proposed invention.

Condition after surgery:

Visual acuity in the distance: Vis OD = 0.7 sph - 0.5 D = 1.0.

Corneal curvature: 39.0D-0 °, 39.0D-90 °, average - 39.0D.

Carrying out the operation in one step allows to reduce the time of the operation and to reduce the error associated with the re-centering of the radiation of the excimer laser.

The presence of the surface 7 with a negative conical constant from minus 0.1 to minus 0.4 ensures the restoration of visual functions while maintaining the physiological conical constant of the cornea.

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 the techniques of removing and not removing curved shapes in each layer of the cornea with each exposure and the logically necessary combination of these techniques in each subsequent layer to create an optical surface 7, surface transition zone 9 and preservation of the integrity of the surface 4 on the periphery of the cornea.

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.

The use of the invention in FBSU MNTK "Eye Microsurgery" them. Acad. S.N. Fedorova made it possible to confirm an unambiguous positive solution to the claimed technical problem, the development of a method for one-stage surgical correction of complex irregular myopic corneal astigmatism to ensure high visual functions while maintaining the physiological conical constant of the cornea and at the same time minimizing the volume of removed eye tissue.

Claims (1)

A method for correcting complex irregular myopic corneal astigmatism, including applying an excimer laser with a wavelength of 193-222 nm to the cornea of the eye, characterized in that the exposure is carried out with an energy of 0.8-2.1 mJ per pulse, 0.5- laser diameter 1.5 mm, a pulse duration of 5-8 ns, a pulse repetition rate of 30-500 Hz on the cornea of the eye with the formation of a regular surface in the optical zone and the surface of the transition zone by sequential layer-by-layer removal of cornea, the regular surface is about of the optical zone (OZ) is formed in the form of a concave ellipsoid of revolution with a negative conical constant from minus 0.1 to minus 0.4, while the optical axis of the ellipsoid is displaced so that the center of the optical zone corresponds to the position of the center of the maximum irregularity section on the keratotogram, and the diameter the optical zone is selected in accordance with the diameter of the section of maximum irregularity, determined by the height map on the keratotopogram; after that, the surfaces of the transition zone are formed: the first surface of the transition zone (PPZ) adjacent to the zone not to be affected is formed as a part of the convex outer surface (CVP) of the annular toroid; the outer edge of the first PPP is associated with a section of the cornea that is not subject to exposure, the width of the PPP is 0.04-0.2 diameter of the impact zone (SV); the second PPZ adjacent to the optical zone is formed of the same width as the first PPZ, in the form of a part of the concave inner surface (CVP) of the annular toroid, the inner edge of the second PPZ is conjugated with the outer edge of the optical surface, and the outer edge is with the inner edge of the first PPZ .

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