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

Abstract

PURPOSE: To investigate the effect of laser spot size on the outcome of aberration correction with scanning laser corneal ablation. SETTING: Cleveland Clinic Foundation, Cleveland, Ohio, USA. METHODS: Corrections of wavefront aberrations of Zernike modes from the second to 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. RESULTS: Using a distortion/correction ratio of less than 0.5 as a cutoff for adequate performance, a 2.0 mm or smaller beam was adequate for spherocylindrical correction (Zernike second order), a 1.0 mm or smaller beam was adequate for correction of up to fourth-order Zernike modes, and a 0.6 mm or smaller beam was adequate for correction of up to sixth-order Zernike modes. CONCLUSIONS: Since ocular aberrations above the Zernike fourth order are relatively insignificant in normal eyes, current scanning lasers with a beam diameter of 1.0 mm or less are theoretically capable of eliminating most higher-order aberrations.