Spot size and quality of scanning laser correction of higher order wavefront aberrations

PURPOSE: To investigate the effect of laser spot size on the outcome of abe rration correction with scanning laser corneal ablation. METHODS: Numerical simulation of ablation outcome. RESULTS: Correction of wavefront aberrations of Zernike modes from second t o eighth order were simulated. Gaussian and top-hat beams of 0.6 to 2.0-mm full-width-half-maximum, diameters were modeled. The fractional correction and secondary aberration (distortion) were evaluated. Using a distortion/co rrection ratio of less than 0.5 as a cutoff for adequate performance, we fo und that a 2 mm or smaller beam is adequate for spherocylindrical correctio n (Zernike second order), a 1 mm or smaller beam is adequate for correction of up to fourth order Zernike modes, and a 0.6 min or smaller beam is adeq uate for correction of up to sixth order Zernike modes. CONCLUSIONS: Since ocular aberrations above Zernike fourth order are relati vely insignificant 2 current. scanning lasers with a beam diameter of 1 mm, or less are theoretically capable of eliminating most of the higher order aberrations of the eye.