The application of nonlinear optics in ocular biophysics

When laser pulses of high peak powers are incident on tissue, nonlinear processes can be observed as the pulses propagate through the tissue. Some of the processes are relatively benign altering only the amplitude and phase of the pulse but leaving the tissue relatively unchanged. Some of the phenomena are much more destructive, leading to irreversible tissue damage. Some applications of nonlinear responses are already used in medicine. Laser-induced breakdown is routinely used to cut fibrous tissue such as the posterior capsule behind the lens of the eye. Ablative processes can be used in the destruction of gall and kidney stones and the removal of plaque inside arteries. Several dermatological techniques such as tattoo removal and removal of possible melanomas use short pulse lasers that generate nonlinear events. The present study uses concepts of nonlinear optics to help evaluate ultrashort laser exposures and attempts to understand deviation from the trends in minimum visible lesion data seen in the femtosecond to microsecond regime. It is concluded that the application of nonlinear optics in biophysics was essential to fully understand trends seen in laser retinal injury for ultrashort laser pulses. Work is continuing to determine the full extent to which the various phenomena studied affect laser retinal damage and the interplay between nonlinear optical effects and other changes in damage mechanisms