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L. Hoffart, P. Lassonde, F. Légaré, V. François, J.-C. Kieffer, I. Brunette; Femtosecond Laser Ablation Threshold in Epithelial, Stromal and Endothelial Corneal Layers Using a Few Cycle Pulses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):593.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the surface ablation threshold of the corneal epithelial, stromal and endothelial layers using ultra-short laser pulses exposure.
Freshly enucleated slaughterhouse porcine eyes were obtained within 2 hours after death. Surface femtosecond laser ablations were performed on flat corneal mounts. Each corneal layer (epithelium, stroma and endothelium) was tested separately. 7 fs, 30 fs and 100 fs pulses were generated using a Ti:sapphire oscillator/amplifier laser source at 800 nm. Laser spot size was 8 µm and experiments were done on a single shot mode. All measurements were done in triplicata. The ablation threshold was determined by the diameter-regression technique based on the measurement of the damaged tissue area, using a 50x reflection mode optical microscope.
For each corneal layer, the ablation threshold was found to decrease as a function of pulse duration. For 100 fs pulses, the epithelium, stroma and endothelium thresholds were measured at 0.92±0.26 J/cm2, 0.82±0.14 J/cm² and 0.54±0.44 J/cm², respectively. At 30 fs, thresholds of 0.85±0.16 J/cm2, 0.47±0.12 J/cm2 and 0.35±0.26 J/cm2 were measured, while at 7 fs, threshold values were 0.63±0.20 J/cm², 0.30±0.11 J/cm² and 0.10±0.09 J/cm². These results were corroborated by our theoretical model which predicts that the ablation threshold decreases rapidly for pulse durations in the low end of the femtosecond regime. The ablation threshold for corneal epithelium was found to be slightly higher than that of the stroma, which in turn was higher than that of the endothelium.
Surface ablation threshold were shown to rapidly decrease with short pulse durations. This works constitutes a first step towards the investigation of deep corneal layers ablation parameters with ultrashort pulse durations.
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