SURGICAL METHOD FOR CORRECTING PRESBYOPIA COMBINED WITH SIMPLE HYPERMETROPIC ASTIGMATISM

摘要

FIELD: medicine. ^ SUBSTANCE: method involves exposing cornea to excimer laser radiation with optical surfaces and optical transition zone surfaces being formed by means of sequential layer-by-layer removal of cornea areas. The first optical surface is built as convex surface belonging to the whole optical zone. The zone is built as irremovable internal central segment formed by two parallel chords and circle having its diameter equal to treatment zone diameter. Internal central segment symmetry center is superposed with the optical zone center. Internal central segment symmetry axis aligned in parallel to the chords is superposed with the strong astigmatism axis. The second optical surface is built as convex spherical surface. Its optical axis coincides with the optical zone center. Ratio between its diameter and optical zone diameter belongs to interval from 0.28 to 0.55. The first surface of the transition zone is built as a portion of convex external surface of the first ring-shaped toroid being 0.04-0.2 times as large as the treatment zone diameter. External boundary of the first transition zone surface has smooth interface to untreatable cornea portion. The second surface of the transition zone of the same width is formed as a portion of the concave external surface of the second ring-shaped toroid. Internal boundary of the second transition zone surface has smooth interface to external boundary of the first optical surface, the external one being conjugated with the internal boundary of the first transition zone surface. Treatment parameters are as follows. Wavelength is 193-222 nm large, impulse power is equal to 0.8-2.1 mJ, laser spot diameter is 0.5-1.5 mm large, pulse duration is equal to 5-8 ns, pulse succession frequency is 30-500 Hz. ^ EFFECT: improved vision function in near and far zone; minimized removed eye tissues volume. ^ 22 dwg