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.