Method for surgical correction of presbyopy combined with compound astigmatism with preserving corneal surface asphericity

FIELD: medicine. SUBSTANCE: eye cornea is exposed to an eximer laser light at wave length 193-222 nm, pulse energy 0.8-2.1 mJ, laser spot diameter 0.5-1.5 mm, pulse length 5-8 nm, pulse repetition frequency 30 to 500 Hz. This exposure aiming at a sequential corneal abrasion is combined with forming optical surfaces and transition surfaces. A first optical surface is formed first at two stages in the form of a hyperbolic paraboloid surface. First, a concave portion of the hyperbolic paraboloid surface is formed by limiting a removable centre. The above portion of the paraboloid surface is formed within the entire optical cornea (OC). A centre of central symmetry matches with the OC centre. That is followed by forming a convex portion of the hyperbolic paraboloid surface by limiting a non-exposed centre. A centre of central symmetry matches with the OC centre. An axis of central symmetry matches with a weak axis of astigmatism. A second optical surface is formed as a convex ellipsoid of rotation with a negative conic constant within -0.1 to -0.4. An optical axis of the second optical surface matches with the OC centre. The diameter of the second optical surface is related to the diameter of the OC as a value within the range of 0.85 to 0.95. Then, the transitions surfaces (TS) are formed. The first TS is formed as a portion of a convex outer surface of a first O-toroid. A width of the first TS makes 0.04 to 0.2 diameters of the exposure. The first TS is formed so that its outer border is coupled with the non-exposed cornea. The second TS is formed as a portion of a concave inner surface of a second O-toroid having a width of 0.04 to 0.2 diameters of the exposure. The inner border of the second TS shall be coupled with the outer border of the first optical surface, and its outer border - with the inner border of the first TS. EFFECT: high far and near visual functions with no additional spectacle correction with a decreased light cap and minimised spherical aberration. 27 dwg, 3 ex