| 摘要 |
In use of laser radiation to ablate corneal tissue, to achieve a sculptured change in curvature of the optically used region of the cornea, a variable magnification (zoom) lens is combined with different sized apertures of an indexible mask to develop a relatively smooth profile for the changed curvature. The zoom-lens settings are varied in the course of cornea exposure through each of the succession of mask apertures. To do this, the range of zoom-lens magnification can always be less than 2:1, yet the zoom-lens system can effectively reduce to insignificance the stepped profiling that is inherent in reliance only upon the indexed aperture technique. Also described are techniques to achieve compensation for delivered flux-density variation as a function of instantaneous zoom-lens setting, and programmable control of the area of delivered flux density in a manner to correct for parabolic or other fall-off in delivered beam intensity as a function of radius outward of the axis of beam delivery. |
