Retinal Damage and Laser-Induced Breakdown Produced by Ultrashort-Pulse Lasers

摘要

In vivo retinal injury studies using ultrashort-pulse lasers at visiblewavelengths for both rabbit and primate eyes have been completed, and the results are presented herein for laser-induced breakdown (LIB) and bubble generation. Results of previous measurements for the millimum visible lesion (MVL) threshold doses for both primate and rabbit eyes were reported earlier for pulsewidths from 4 nanoseconds (ns) to as low as 90 femtoseconds (fs). We have recorded on video the first in vivo LIB in vitreous using both albino (New Zealand white) and pigmented (Dutch-belted) rabbit and rhesus monkey eyes with 580-nanometer (nm), 120-fs pulses. We believe the phenomena responsible for bubble generation to be LIB because of the extremely high irradiances within the focused beam and because of the very low absorption properties of the vitreous humor. The laser-generated LIB-ED(50) bubble threshold for the monkey eye was 0.56 uJ at 120 fs. Results of our nonlinear modeling and calculations for self-focusing within the eye and for LIB thresholds are presented and are compared with our experimental results. Data is presented which show that LIB thresholds cannot be reached with MVL-ED(50) doses until the pulsewidth drops to <600 fs and the retinal image diameter is close to 10 micrometers (um). Self-focusing and LIB are the two nonlinear effects shown to affect the visible lesion thresholds, and our results also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-uJ, 100-fs laser pulses.