RU2559287C1 - Method for surgical correction of irregular mixed corneal astigmatism - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: eye cornea is exposed to excimer laser at wavelength 193-222 nm, pulse energy 0.8-2.1 mJ, laser spot diameter 0.5-1.5 mm, pulse length 5-8 nm, and pulse repetition frequency 30-500 Hz. A regular surface is formed in the optical zone, and a surface of a transition zone is formed by removing the corneal segments continually. The regular surface of the optical zone (OZ) is formed as a surface of a hyperbolic paraboloid with a negative constant from minus 0.1 to minus 0.4 in two stages. A concave portion of the surface of the hyperbolic paraboloid lying within the whole OZ is shaped by forming a central zone (CZ) to be removed. The centre of symmetry of the CZ is aligned with the centre of maximum irregularity recognised on an anterior segment analysis chart. A convex portion of the surface of the hyperbolic paraboloid is created by forming the intact CZ. The centre of symmetry of the CZ is aligned with the centre of maximum irregularity recognised on the anterior segment analysis chart, whereas an axis of symmetry of the CZ - with a weak axis of astigmatism. A diameter of the optical zone is specified in accordance with a diameter of the maximum irregularity determined in accordance with an altitude chart on the anterior segment analysis chart. The surface of the transition zone (STZ) is shaped as a portion of a convex outer surface of an annular toroid. An outer edge of the STZ is coupled with an intact corneal segment. An inner edge of the STZ is coupled with an outer edge of the optical surface. A width of the STZ makes 0.04-0.2 exposure diameters.

EFFECT: method enables achieving the high visual functions in the patients with minimising the volume of the corneal tissues to be removed and keeping the physiological corneal conical constant unchanged with less time required for the operation with an excimer laser exposure as precise as possible by performing the one-stage operation.

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Description

The invention relates to ophthalmology and can be used in the correction of irregular mixed corneal astigmatism. The problem of correcting irregular mixed 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, after undergoing operations on the cornea, such as through or layered keratoplasty, it affects about 6.9% 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 problem of correcting incorrect mixed corneal astigmatism one of the urgent problems of ophthalmology.

The well-known "Method for correcting 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 involve the correction of mixed astigmatism, preservation of the physiological conical constant of the cornea after surgery, as well as a decrease in the volume of corneal tissue removed.

The objective of the invention is to develop a method for the surgical correction of irregular mixed 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 errors during re-alignment 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 irregular mixed corneal astigmatism, including the removal of keratotograms and exposure to excimer laser radiation with a wavelength of 193-222 nm, according to the invention, the effect is carried out with an energy in the pulse of 0.8-2.1 mJ, diameter a laser spot 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 by For real layer-by-layer removal of corneal areas, a regular surface of the optical zone (OZ) is formed in the form of a surface of a hyperbolic paraboloid with a negative conical constant from minus 0.1 to minus 0.4 in two stages: first, a concave part of the surface of the hyperbolic paraboloid is formed, which lies within the entire optical zone (OZ), by forming the central zone (CZ) to be removed; the center of symmetry of the center of gravity is combined with the center of the plot of maximum irregularity, determined on the keratotopogram. Next, a convex part of the surface of the hyperbolic paraboloid is formed by the formation of a central brain not subject to influence; the center of symmetry of the center of gravity is combined with the center of the plot of maximum irregularity defined on the keratotopogram, and the axis of symmetry of the center of gravity is combined with the weak axis of astigmatism; the diameter of 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 form the surface of the transition zone (PPZ) in the form of a part of the convex outer surface (NNP) of the annular toroid; the outer edge of the PPP is conjugated to the corneal area not subject to exposure, the inner edge of the second PPP is paired with the outer edge of the optical surface, the width of the PPP is 0.04-0.2 of the diameter of the impact zone.

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: creating a method for surgical correction of incorrect mixed 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, minimize the amount of tissue removed and most accurately trovke excimer laser exposure.

The invention is illustrated by the drawings of FIG. 1-17. They show:

FIG. 1 is a frontal section of a 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 - isometric view of the surface 7,

FIG. 5 - the formation of a concave part of the surface 7,

FIG. 6 is an isometric view of the formation of a concave part of the surface 7,

FIG. 7 - alignment of the axes of astigmatism,

FIG. 8 is an isometric view of the concave portion of a hyperbolic paraboloid,

FIG. 9 - the formation of the convex part of the surface 7,

FIG. 10 is an isometric view of the formation of the convex part of the surface 7,

FIG. 11 - the formation of the surface 9 of the transition zone,

FIG. 12 is a top view of the surface 9,

FIG. 13 is an isometric view of the surface 9,

FIG. 14 - frontal section of the surface 9,

FIG. 15 - the formation of a circular zone 35,

FIG. 16 - reduction of the circular zone 36,

FIG. 17 - further reduction of the circular zone 37.

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:

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

Surface 9 of the transition zone;

Transition Zone 10;

By a 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).

They form an optical surface 7 lying within the entire optical zone 8 in the form of a hyperbolic paraboloid. In FIG. 4 is an isometric view of surface 7. The saddle-shaped surface 7 of the hyperbolic paraboloid has a concave part 12 and a convex part 13 (Fig. 4).

The method is as follows.

Initially, the first concave part of the optical surface of the hyperbolic paraboloid is formed, lying within the entire optical zone (OZ), by the formation of a central zone (CZ) 14 to be removed and two symmetric peripheral zones 15 that cannot be removed. In this case, the central lock 14 is limited by two diametrically opposite circular arcs with a radius of the external impact zone 11 and two curved lines that are sections of two symmetric branches of the first hyperbole 16 (Fig. 5).

Mark CZ 14 to be affected. The center of symmetry of the central zone 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), while the axis of symmetry 17, passing through the vertices 18 of the hyperbolas 16, is parallel to the strong axis of astigmatism 19 (Fig. 5 )

An isometric view of the formation of the concave portion of the surface 7 and the position of the central lock 14 to be exposed is shown in FIG. 6.

The peripheral zones 15 during laser irradiation are not removed during the formation of the first corneal layer that changes in shape and each of the subsequent corneal layers that are required to create a surface 7.

In FIG. 5, for convenience of presentation, the case is shown where the strong axis 19 of astigmatism is vertical. In practice, cases with a different arrangement of the axes of astigmatism are possible (not shown in the figure).

With each subsequent layer-by-layer exposure, the area of the central area 14 is reduced by reducing the distance 22 between the vertices 18 of the hyperbolas from a value equal to the diameter of the exposure zone to zero (Fig. 7). All the first hyperbolas have 21 asymptotes in common, while the angle formed by the intersecting asymptotes lies in the range from 6 degrees to 84 degrees.

In FIG. 5, 7, two symmetrical peripheral zones 16 that cannot be removed are not shaded, and the central gate 14 is shaded.

An isometric view of the concave portion of a hyperbolic paraboloid is shown in FIG. 8.

The formation of the optical surface of the hyperbolic paraboloid is continued by the formation of the second convex part of the surface of the hyperbolic paraboloid.

Two symmetric peripheral zones are formed, which are subject to impact 23, and a central zone (CZ) 24, which is not subject to impact (Fig. 9).

In this case, the central lock 24 is limited by two diametrically opposite circular arcs with a radius of the outer impact zone 11 and two curved lines that are sections of two symmetric branches of the second hyperbola 28 (Fig. 9).

CZ 24, which is not subject to influence, is marked out, combining the center of symmetry of the CZ 25 of the central zone 24 with the intersection point of the axis 6 passing through the center of the zone of maximum irregularity with the surface of the cornea, the axis of symmetry 26 passing through the vertices 27 of the second hyperbole 28 is combined with a weak axis of astigmatism 29 (Fig. 9).

The Central zone 24 when the laser exposure is not subjected to removal during the formation of the first changeable shape of the cornea layer and each of the subsequent changeable shape of the layers of the cornea necessary to create a surface 7.

With each subsequent layered exposure, the area of the central area is increased by increasing the distance 30 between the vertices 27 of the hyperbolas 28 from zero to a value equal to the diameter of the impact zone (Fig. 9).

All second hyperbolas have 21 common asymptotes that coincide with the asymptotes of the first hyperbolas.

In FIG. 9, two symmetrical peripheral zones 23 to be removed are shaded, and the central door 24 is not shaded. The spatial totality of all corneal cortex that cannot be removed, in which the area of the subsequent cep is larger than the area of the previous cus, creates a convex part of the optical surface of a hyperbolic paraboloid.

An isometric view of the formation of the convex part of the surface 7 and the position of the peripheral zones 23 to be affected is shown in FIG. 10.

The sequential creation of a concave and convex part of the surface of the hyperbolic paraboloid leads to the formation of the optical surface of the hyperbolic paraboloid 7, which allows to obtain 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. 11). The surface 9 is formed by rotating the segment 32 of the circle 31, convex towards the optical axis, around the axis 5 of the surface 9 without intersecting the axis 5. The arc of the circle 31 of segment 32 is based on the chord 33 located at an angle of 34 to axis 5 and lying with the axis 5 in one plane (Fig. 11). Top view of surface 9 in FIG. 12. The surface 9 in isometric view is shown in FIG. 13.

The surface 9 is formed by forming a circular zone 35 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.

A frontal section of the surface 9, explaining the formation of the circular zone 35, is shown in Fig. 14. Subsequently, in each layer, the area of the circular zone 35 to be removed is reduced in layers. Positions 36, 37 show the reduction of the circular zone 35. FIG. 15, 16, 17 show a layer-by-layer decrease in the area of circular zones 35, 36, 37 (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 O., 37 years old.

Condition before surgery:

Visual acuity in the distance: Vis OS = 0.1 sph + 1.0 D cyl - 5.0 D ax 0 ° = 0.3 n.k.

Corneal curvature: 46.0 D - 0 °, 40.0 D - 90 °, average - 43.0 D.

Corneal thickness: 554 microns.

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

Condition after surgery:

Visual acuity into the distance: Vis OS = 0.7 sph - 0.5 D cyl - 0.5 D ax 0 ° = 0.9

Corneal curvature: 42.5 D - 0 °, 42.0 D - 90 °, average - 42.25 D.

Example 2: Patient C., 24 years old.

Condition before surgery:

Visual acuity into the distance: Vis OS = 0.05 sph + 2.5 D cyl - 5.25 D ax 0 ° = 0.3

Corneal curvature: 49.0 D - 0 °, 41.25 D - 90 °, average - 45.12 D.

Corneal thickness: 518 microns.

Diagnosis: Stabilized keratoconus of the 1st stage, the state after corneal segment implantation and corneal collagen crosslinking, improper mixed 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 - 1.0 D ax 0 ° = 0.7

Corneal curvature: 41.0 D - 0 °, 40.0 D - 90 °, average - 40.5 D.

Example 3: Patient L., 27 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.1 sph + 3.5 D cyl - 2.5 D ax 0 ° = 0.6

Corneal curvature: 43.0 D - 0 °, 37.0 D - 90 °, average - 40.0 D.

Corneal thickness: 534 microns.

Diagnosis: Improper mixed corneal astigmatism, condition after radial keratotomy. The operation of the PRK in accordance with the proposed invention.

Condition after surgery:

Visual acuity in the distance: Vis OD = 0.8 sph + 1.5 D = 1.0

Corneal curvature: 38.0 D - 0 °, 38.0 D - 90 °, average - 38.0 D.

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 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, provides 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 stated technical problem, the development of a method for one-stage surgical correction of incorrect mixed 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 irregular mixed 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, a laser spot diameter of 0.5-1 , 5 mm, pulse duration of 5-8 ns, 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, a regular surface of the optical they are formed in the form of a surface of a hyperbolic paraboloid with a negative conical constant from minus 0.1 to minus 0.4 in two stages: first, a concave part of the surface of the hyperbolic paraboloid is formed, which lies within the entire optical zone (OP), by the formation to be removed central zone (CZ); the center of symmetry of the centralized zone is combined with the center of the section of maximum irregularity defined on the keratotopogram, then a convex part of the surface of the hyperbolic paraboloid is formed by the formation of an irreplaceable centralized zone; the center of symmetry of the center of gravity is combined with the center of the plot of maximum irregularity defined on the keratotopogram, and the axis of symmetry of the center of gravity is combined with the weak axis of astigmatism; the diameter of 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 form the surface of the transition zone (PPZ) in the form of a part of the convex outer surface (NNP) of the annular toroid; the outer edge of the PPZ is paired with a portion of the cornea that is not subject to exposure, the inner edge of the PPZ is paired with the outer edge of the optical surface, the width of the PPZ is 0.04-0.2 of the diameter of the impact zone.

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