Ablation smoothness as a function of excimer laser delivery system

Abstract

Objective: To quantitatively study and compare the ablation profiles of three kinds of excimer laser delivery systems to identify which technology provides the smoothest ablation profile.Setting: Three private practices, one in Canada and two in the United States.Methods: Excimer laser myopic ablations were performed on poly(methyl methacrylate) (PMMA) test blanks in 3.00 diopter increments using a 5 mm optical zone with three kinds of excimer laser delivery systems: (1) iris diaphragm without beamhomogenizing technology (ExciMed, Summit Technologies, Inc.); (2) iris diaphragm with beam homogenizer (20/20, VISX, Inc.); (3) galvanometric scanning (MiniExcimer, LaserSight, Inc.). We used a scanning white-light interferometer (NewView 100, Zygo Corp.) to study three measures of surface smoothness: peak to valley, root mean square average deviation height (RMS), and the arithmetic average deviation from the center line of the data.Results: Using RMS as a measure of surface smoothness in an optical system, the galvanometric scanning delivery system produced ablations approximately three times smoother than the iris diaphragm with beam homogenizer (P = .01), which in turn produced ablations about twice as smooth as the iris diaphragm without beam homogenizer (P = .03).Conclusions: Galvanometric scanning delivery systems provide a significantly smoother ablation profile than iris-diaphragm (variable aperture) systems.