Laser: study by confocal and electronic microscopy of retinal damages induced by multiple picosecond pulses

The current laser safety standards do not define the exposure limit values for pulse width less than one nanosecond. It has been hypothesized that one cannot extrapolate from longer pulse widths because the ultrashort pulse contains high peak power and may induce non linear effects. These effects may involve fundamentally different mechanisms of damage particularly for repetitively ultrashort pulses. Most laser safety documents advise the laser user that caution must be used in the evaluation of exposure to repetitively pulsed radiation since they are only limited data on multiple pulse exposure criteria. The empirical multiple pulse formula is based on some data indicating that there is generally a cumulative effect in multiple-pulse exposures. No data exists in the literature concerning the histological effects on the retina of ultrashort pulses delivered with a high repetition rate Jim The aim of this work was to study the evolution of single retinal lesions after exposure to trains of picosecond laser pulses. The experimental approach we have developed corresponded to: 1) observation of 100 μm thick and to characterize lesions by fluorescence microscopy after different specific stainings, 2) epoxy resin embedding of lesion areas for further studies by light and standard electron microscopy. (author)