Ultrashort Laser Retinal Damage Threshold Mechanisms

摘要

Ultrashort lasers have been adapted for use in a variety of applications from micromachining of dielectrics to atmospheric spectro- chemistry. These lasers emit almost exclusively in the retinal hazard wavelength regime, making them potential sources for both accidental vision loss, but also candidates for biomedical applications where precise alteration of tissues is an objective. We review the mechanisms for damaging the retina at the threshold for the lowest energy where any change in tissue is barely perceptible. For laser pulses between several picoseconds and ten microseconds, the threshold retinal damage is produced by microbubble formation around melanosomes in the retinal pigmented epithelium. Below one nanosecond both stress-confinement in melanosomes and self-focusing reduce the threshold for damage as measured in corneal radiant exposure, although the mechanism for damage remains unchanged. Below several picoseconds, laser-induced breakdown produces intra-retinal damage, sparing the RPE at threshold levels. These mechanisms have been determined in the past decade and provide an understanding of trends in retinal damage with variation in laser parameters, but also elucidate potential techniques for producing precise alteration to tissues.