PHOTODISRUPTION IN THE HUMAN CORNEA AS A FUNCTION OF LASER-PULSE WIDTH

BACKGROUND: We investigated the role of laser pulse width in determini ng fluence thresholds and efficiency for corneal photodisruption. METH ODS: A laser system that delivers a wide range of pulse energies and p ulse widths was used to produce ablations at pulse widths from 100 fem toseconds (fs) to 7 nanoseconds (ns). The laser-induced breakdown flue nce threshold at each pulse width was determined by monitoring individ ual plasma emissions. Using multiple shots, the photodisruption thresh old and cutting depth at each pulse width were determined histological ly. RESULTS: Corneal breakdown thresholds decreased at a faster rate f rom 7 ns to approximately 10 picoseconds (ps), compared to further red uctions in pulse width below 10 ps, where little variation was seen. B reakdown for pulse widths below 10 ps showed little intershot variabil ity, resulting in highly reproducible fluence thresholds. Corneal tiss ue examined histologically showed similar fluence dependency. CONCLUSI ONS: Corneal tissue photodisruption thresholds demonstrate pulse width dependence. At pulse widths less than 10 ps and with fluences near th e breakdown threshold, ablations are maximally precise and efficient. These findings suggest optimal laser parameters for corneal surgery.