Retinal effects of ultrashort laser pulses in the rabbit eye.

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Abstract

PURPOSE: To evaluate the effects of ultrashort laser pulses from femtoseconds to nanoseconds on the retinas of live rabbit eyes and to determine the energy requirements for visible lesion development. METHODS: The retinal effects of laser exposures were examined for laser exposures with pulsewidths ranging from 4 ns to 90 fs, with visible wavelengths of 532 nm for durations > 5 ps and 580 nm for durations < 5 ps. The authors examined and scored all laser impact sites in the retina ophthalmoscopically--with fundus photography and with fluorescein angiography--to identify evidence of visible laser effects. RESULTS: The laser energy required for retinal minimal visible lesions was found to be slightly less for pulsewidths < 5 ps and varied from 5 microJ at 4 ns to 1.1 microJ at 90 fs for the 1-hour ophthalmoscopic reading. Lesions from higher energy pulses (7 to 120 microJ) were examined at all pulsewidths. For 90-fs high-energy pulse delivery, an increased intensity of retinal lesions and the development of several subretinal hemorrhages were demonstrated at peak energies of 30 microJ. Fluorescein angiography was found to be much more sensitive as an indicator of retinal damage for both femtosecond pulsewidths. CONCLUSIONS: The low energies required for visible lesion production in live rabbit eyes raise new questions surrounding ultrashort pulse propagation in ocular media, energy deposition at the retina, and mechanisms limiting retinal damage from ultrashort laser pulses.