The Ideal Excimer Beam for Refractive Surgery

PURPOSE: To identify essential considerations for the optimal excimer laser beam for refractive laser surgery and further to determine specific beam parameters fulfilling the essential requirements. METHODS: Starting with the fundamental laser tissue interaction, the various parameters defining the laser beam are analyzed and optimal values for each are evaluated. RESULTS: Gaussian beams generally produce smoother ablated surfaces than "flat top" beams. Optimal ablation efficiency for a Gaussian profile occurs at a peak laser fluence of approximately 450 mJ/cm2. To treat realistic optical aberrations the Gaussian spot size should be < 0.9 mm. The laser repetition rate for such a beam can be multiple hundred hertz without causing thermal damage if a "flying spot" strategy is used. Accurate treatment under such conditions requires both high-fidelity laser spot placement and high-performance eye tracking. CONCLUSIONS: Surgical systems using the characteristics defined in this study should yield excellent treatment outcomes.