RETINAL DAMAGE AND LASER-INDUCED BREAKDOWN PRODUCED BY ULTRASHORT-PULSE LASERS

Background: In vivo retinal injury studies using ultrashort-pulse lase rs at visible wavelengths for both rabbit and primate eyes have shown that the degree of injury to the retina is not proportional to the pul se energy, especially at suprathreshold levels. In this paper we prese nt results of calculations and measurements for laser-induced breakdow n (LIE), bubble generation, and self-focusing within the eye. Methods: We recorded on video and measured the first in vivo LIB and bubble ge neration thresholds within the vitreous in rabbit and primate eyes, us ing external optics and femtosecond pulses. These thresholds were then compared with calculations from our LIE model, and calculations were made for self-focusing effects within the vitreous for the high peak p ower pulses. Results: Results of our nonlinear modeling and calculatio ns for self-focusing and LIE within the eye were compared with experim ental results. The LIE ED,, bubble threshold for the monkey eye was me asured and found to be 0.56 mu J at 120 fs, compared with the minimum visible lesion (MVL) threshold of 0.43 mu J at 90 fs. Self-focusing ef fects were found to be possible for pulsewidths below 1 ps and are pro bably a contributing factor in femtosecond-pulse LIE in the eye. Concl usions: Based on our measurements for the MVL thresholds and LIB bubbl e generation thresholds in the monkey eye, we conclude that in the fem tosecond pulsewidth regime for visible laser pulses, LIB and self-focu sing are contributing factors in the lesion thresholds measured. Our r esults may also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-fs laser pulses even at 100 mu J of energy.