Method for surgical correction of irregular mixed corneal astigmatism

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. 17 dwg, 3 ex