RETINAL EFFECTS OF ULTRASHORT LASER-PULSES IN THE RABBIT EYE

Purpose. To evaluate the effects of ultrashort laser pulses from femto seconds to nanoseconds on the retinas of live rabbit eyes and to deter mine the energy requirements for visible lesion development. Methods. The retinal effects of laser exposures were examined for laser exposur es with pulsewidths ranging from 4 ns to 90 fs, with visible wavelengt hs of 532 nm for durations >5 ps and 580 nm for durations <5 ps. The a uthors examined and scored all laser impact sites in the retina ophtha lmoscopically-with fundus photography and with fluorescein angiography -to identify evidence of visible laser effects. Results. The laser ene rgy required for retinal minimal visible lesions was found to be sligh tly less for pulsewidths <5 ps and varied from 5 mu J at 4 ns to 1.1 m u J at 90 fs for the 1-hour ophthalmoscopic reading. Lesions from high er energy pulses (7 to 120 mu J) were examined at all pulsewidths. For 90-fs high-energy pulse delivery, an increased intensify of retinal l esions and the development of several subretinal hemorrhages were demo nstrated at peak energies of 30 mu J. Fluorescein angiography was foun d to be much more sensitive as an indicator of retinal damage for both femtosecond pulsewidths. Conclusions. The low energies required for v isible lesion production in live rabbit eyes raise new questions surro unding ultrashort pulse propagation in ocular media, energy deposition at the retina, and mechanisms limiting retinal damage from ultrashort laser pulses.