Patent ID: 8033664

Claim:
A method of characterizing an eye having astigmatism, said astigmatism being defined by cylinder and axis, said method comprising: (a) measuring said axis for said eye; (b) disposing a target in a line of sight of said eye, the target comprising at least one feature that may be oriented in a desired orientation with respect to said eye; (c) orienting said target such that said at least one feature is oriented either substantially parallel or substantially perpendicular to said axis, respectively; (d) disposing test optics in said line-of-sight between said eye and said target, said test optics being changeable to introduce different amounts of defocus; (e) measuring wavefronts emanating from said eye with a wavefront sensor for different amounts of defocus; and (f) determining a defocus correction, D 1 , based on said wavefront measurements for different amounts of defocus.