SURGICAL CORRECTION METHOD FOR TREATING PRESBIOPIA CASES AGGRAVATED WITH MIXED ASTIGMATISM

摘要

FIELD: medicine.;SUBSTANCE: method involves treating eye cornea with excimer laser radiation with optical surfaces and transition zone surface being formed by sequentially layer-by-layer removing cornea segments. Action parameters are wavelength of 193-222 nm pulse power of 0.8-2.1 mJ, laser spot diameter of 0.5-1.5 mm, pulse duration of 5-8 ns, frequency of 30-500 Hz. The first optical surface is concave hyperbolic paraboloid surface is formed in two stages. First, concave hyperbolic paraboloid surface portion arranged within the whole optical zone, is formed by creating central zone to be withdrawn. Central zone symmetry center is made coincide with the optical zone center. Then, convex portion of the hyperbolic paraboloid surface is formed by creating central zone that is not to be acted upon. Central zone symmetry center is made coincide with the optical zone center and its symmetry axis with the weak astigmatism axis. The second optical surface is formed as spherical convex surface which optical axis coincides with the optical zone center. The second optical surface diameter is 0.28-0.55 times as large as the optical zone diameter. The first transition zone surface is formed as a part of convex external surface of annular toroid that is 0.04-0.2 times as wide as the action zone diameter. External transition zone surface edge is coupled with cornea portion that is not to be subjected to treatment. The second transition zone surface is formed as a part of concave internal surface of annular toroid of the same width. Internal edge of the second transition zone surface is coupled with external edge of the first optical surface and external edge of the second transition zone surface is coupled with the internal edge of the first transition zone surface edge.;EFFECT: improved visual function in long and short distance; reduced luminous halation; minimized volume of withdrawn eye tissues.;27 dwg