Stress wave amplitudes during laser surgery of the cornea

Purpose: To determine the stress wave amplitudes generated during photoablation of the cornea using an argon fluoride excimer laser. Design: Experimental study using porcine eyes. Methods: Profiles of the stress wave amplitudes and enucleated human eyes along the axis of symmetry of porcine eyes and enucleated human eyes were measured using a miniature piezoelectric transducer. The ablation parameters, fluence, and ablation diameters were varied within the range of clinical application. Main Outcome Measures: Stress wave amplitudes generated during photoablation. Results: The stress waves pass through a pressure focus located in the posterior lens and anterior vitreous, where amplitudes of up to 100 atm were measured with a 6-mm or larger ablation zone. Posterior to this focus, the stress wave amplitudes rapidly decrease to less than 10 atm at the retinal site. Small diameter excimer laser spots (≤1.5 mm) produce a declining stress wave with no pressure focus at the lens and anterior vitreous. Conclusions: Stress waves may be potentially hazardous to anterior structures of the human eye, including the corneal endothelium, lens and anterior vitreous face. They peak at the lens and vitreous with a broad beam, but not with small spot laser ablation. At posterior retinal and subretinal structures, they may be considered harmless.