Smoothness of ablation on acrylic by four different excimer lasers

PURPOSE: There are many different excimer laser devices available for photo ablative refractive surgery. Smoothness of ablation may vary with different excimer lasers systems. METHODS: Ablations were performed on polymethylmethacrylate (PMMA) plates o f 8 x 4 x 0.5 cm, with four different excimer lasers: VISX-Star, Coherent S chwind Keratom I/II, Chiron Technolas Keracor 117C (Plano Scan), and the Ni dek EC-5000, to determine and compare the homogeneity and smoothness of the surface. Ten -3.00 D samples, ten -6.00 D samples, and ten -9.00 D samples were ablated with each laser. The PMMA discs were examined with optical mi croscopy, documented by photographs, and each sample was measured quantitat ively using a Hommel-Werkel rugosimeter. We used the same PMMA material thr oughout. RESULTS: Statistically significant differences in smoothness were found bet ween the Chiron Technolas 117C and the VISX-Star, Nidek and VISX-Star, and Coherent Schwind and VISX-Star in the homogeneities achieved by ablating -3 .00 D. Ablations of -6.00 D resulted in homogeneities that were statistical ly significantly different: Chiron Technolas 117C with the other three devi ces, the Nidek EC-5000 with the VISX-Star, and the Coherent-Schwind with th e VISX-Star. In the ablations for -9.00 D, statistically significant differ ences in homogeneity were found between the Chiron Technolas 117C and Nidek , between the Chiron and VISX-Star, between the Coherent Schwind and VISX-S tar, and between the Nidek and VISX-Star. The laser with the scanning spot system was smoother. CONCLUSION: Scanning spot technology produced smooth ablations even up to - 9.00 D.