Pressure transients occurring inside the eyeball as a consequence of excimer laser ablation of the cornea were measured at various distances along the optical axis, on enucleated porcine eyes. Positive (compressive) pressure spikes up to 90 bars were observed, lasting 100 ns, and developing, as they propagated in the eyeball, satellite rarefaction pulses with negative pressure as high as -40 bar. Such rarefaction wavefronts can trigger the formation of cavitation bubbles, in both the anterior and posterior chamber, depending on the ablation geometry. The potential risks associated with these photoacoustic phenomena, particularly for retina and corneal endothelium, are outlined.

These preliminary results indicate this approach is effective in reducing hyperopia, while its predictability has still to be proved in a larger treatment group with longer follow-up. A cautious approach to this technique is still advisable, especially for higher hyperopic corrections, in view of the large best corrected visual acuity loss seen in two eyes at six months.