Laser fluence compensation of a curved surface

Abstract

A laser system and techniques which compensate for laser fluence drop off or losses of irradiation as an ablating laser beam is traversed on a curved surface (e.g., on corneal tissue). The disclosed ablating laser system and techniques compensate for fluence differentials from pulse-to-pulse by adjusting an appropriate parameter of a laser beam. In the preferred embodiment, the number of pulses imparted in the periphery, the size or shape of the ablating laser beam is adjusted with, e.g., a variable aperture placed in the beam delivery path, by changing a magnification of relay optics in the beam delivery path, or by increasing a number of ablation spots in peripheral portions of an ablation zone as compared with the number of ablation spots in a central portion of the ablation zone. The fluence is compensated for using empirically measured or theoretical fluence correction factors given the angle of the laser beam, size and shape of the ablation spot, etc. In addition to magnification adjustment, the present invention also employs the technique of changing the size of the aperture that is imaged o the eye to provide uniform energy density (i.e., fluence) throughout the entire area of the irradiation site. These techniques are used independently or in conjunction to reshape the curvature of the eye to correct myopia, hyperopia, astigmatism or combinations thereof.