Patent ID: 6136012
Filing Date: 2000-10-24
Classification: A61F

Abstract:
An apparatus for use in operating on a cornea of an eye by ablating an optical zone of the cornea with a laser beam for correcting ametropia, the apparatus comprising:input means for inputting data necessary for correcting ametropia;an optical system for directing the laser beam onto the cornea, including:a circular aperture having a variable opening diameter for restricting an irradiation area of the laser beam;a slit aperture, having a variable slit width and a longitudinal axis perpendicular to the slit width, for restricting the irradiation area of the laser beam;a projecting lens for projecting the laser beam passing through the circular aperture and the slit aperture onto the cornea;a moving unit for shifting either the laser beam or the irradiation area of the laser beam or both eccentrically with respect to a center of the optical zone; anda rotator for rotating the laser beam about an optical axis of the optical system;first control means for controlling the optical system to bring the longitudinal axis of the slit aperture into coincidence with a weak principal meridian of an astigmatic axis of the eye,said first control means gradually changing the slit width of the slit aperture so that a position of the cornea closer to the weak principal meridian is ablated more and a position of the cornea farther from the weak principal meridian is ablated less by the laser beam passing through the circular aperture and the slit aperture;second control means for controlling the optical system to bring a longitudinal axis of the laser beam parallel with a strong principal meridian of the astigmatic axis of the eye, the laser beam having a rectangular, slit-like cross-section further limited by the circular aperture,said second control means gradually moving the laser beam eccentrically with respect to the strong principal meridian so that a position of the cornea closer to the strong principal meridian is ablated less and a position of the cornea farther from the strong principal meridian is ablated more by the laser beam passing through the circular aperture and the slit aperture; andcalculating means for allocating a first amount of astigmatism correction to the first control means and a second amount of astigmatism correction to the second control means in accordance with a given standard in cases where the eye has simple myopic astigmatism and mixed astigmatism with a predetermined refractive power to be corrected;whereby the first amount of astigmatism correction is effected by the first control means and the second amount of astigmatism correction is effected by the second control means in accordance with an allocation of the correction amount.