13 – 24 Despite the various modeling approaches comparing the overall predicted performance of laser platforms, an extensive analysis of the impact of individual laser beam characteristics like spot energy, spot diameter, super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice geometry on ablation smoothness is not existing in the literature, to the best of our knowledge. 12 Several mathematical models have been proposed in the recent times, particularly for laser tissue interaction in refractive surgery, in the form of modifications in the Lambert-Beer law. It was concluded that scanning excimer lasers based on flying spot technology created smoother ablations on PMMA plates compared to the older Nidek EC-5000 unit.ĭeviations of Lambert-Beer law affect corneal refractive parameters after refractive surgery. The smoothest surface was obtained in samples produced by Zeiss-Meditec MEL-70 unit (root mean square = 112 ± 23 nm), followed by the Nidek EC-5000 CX (RMS = 153 ± 12 nm), and the Microscan (RMS = 181 ± 11 nm). 8 performed ablations on PMMA plates using four scanning excimer lasers, two with flying spot technology (Zeiss-Meditec MEL-70, and a Russian-made unit, Microscan) and two Nidek models with scanning slit delivery systems and an expanding iris diaphragm (EC-5000 and EC-5000 CX). Ablation smoothness is also influenced by the spot positioning algorithms.

It was concluded that the laser with Scanning spot technology produced smooth ablations even up to −9.00 diopters (D). 7 In a study, ablations were performed on polymethylmethacrylate (PMMA) plates, with four different excimer lasers: VISX-Star, Coherent Schwind Keratom I/II, Chiron Technolas Keracor 117C, and the Nidek EC-5000, to determine and compare the homogeneity and smoothness of the surface.

Smoothness of ablation may also vary with different excimer lasers systems. The temporal and spatial distribution of the laser spots (scan sequence) has shown to affect the surface quality and maximum ablation depth of the ablation profile. This model may improve the quality of results and could be directly applied for improving postoperative surface quality.ĭespite myriad technological advances in this field, laser corneal refractive surgery still presents some challenges in achieving higher ablation smoothness and minimizing the applied energy on the cornea. Theoretically, the proposed model can be used for achieving smoothness with laser systems used for ablation processes at relatively low cost. For given input parameters, proper optimum parameters for minimizing the roughness have been found. Truncating the beam profile increases the roughness in ablation, Gaussian profiles theoretically result in smoother ablations, round spot geometries produce lower roughness in ablation compared to square geometry, triangular lattices theoretically produce lower roughness in ablation compared to the reticular lattice, theoretically modeled beam profiles show lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tends to be lower than on human cornea. The roughness in ablation was determined by the root-mean-square per square root of layer depth. For both, the measured and theoretical beam profiles, two spot geometries (round and square spots) were considered, and two types of lattices (reticular and triangular) were simulated with varying spot overlaps and ablated material (cornea or polymethylmethacrylate ). The intensity beam profile originating from an excimer laser was measured with a beam profiler camera. Given the super Gaussian order, the theoretical beam profile was determined following Lambert-Beer model. The impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice geometry were tested on ablation smoothness.

The purpose of the study was to outline a rigorous simulation model for simulating shot-by-shot ablation process. Controversial opinions exist regarding optimum laser beam characteristics for achieving smoother ablations in laser-based vision correction.

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