Retinal damage and laser-induced breakdown produced by ultrashort-pulse lasers

Background: In vivo retinal injury studies using ultrashort-pulse lasers at visible wavelengths for both rabbit and primate eyes have shown that the degree of injury to the retina is not proportional to the pulse energy, especially at suprathreshold levels. In this paper we present results of calculations and measurements for laser-induced breakdown (LIE), bubble generation, and self-focusing within the eye. Methods: We recorded on video and measured the first in vivo LIB and bubble generation thresholds within the vitreous in rabbit and primate eyes, using 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 power pulses. Results: Results of our nonlinear modeling and calculations for self-focusing and LIE within the eye were compared with experimental results. The LIE ED,, bubble threshold for the monkey eye was measured 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 effects were found to be possible for pulsewidths below 1 ps and are probably a contributing factor in femtosecond-pulse LIE in the eye. Conclusions: Based on our measurements for the MVL thresholds and LIB bubble generation thresholds in the monkey eye, we conclude that in the femtosecond pulsewidth regime for visible laser pulses, LIB and self-focusing are contributing factors in the lesion thresholds measured. Our results 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.