In vivo and in vitro evaluation of the corneal damage induced by 1573 nm laser radiation

This study involved the corneal effects of the laser beam in infrared at 1573 nm. Investigations were directed toward verifying the limit values by defining the thresholds of corneal damage in experiments carried out on the rabbit, and using biochemical techniques, to specify a damage threshold at the cellular level and a better understanding of the cellular steps of the damaging process. Corneal damage thresholds were determined for exposures to 3 ns single pulses using clinical observations and histology. The ED50 obtained with a corneal beam diameter of 400 μm was 26.6 J cm−2. The corresponding radiant exposure, calculated with the 1 mm aperture diameter recommended by standards, was 4.3 J cm−2. This value was still higher than the present 1 J cm−2 exposure limit. In vitro experiments were also carried out on primary keratocytes and HT1080 epithelial cell line. An expanded beam diameter of 3.5 mm was delivered on plates for study of cell proliferation, senescence, and cytotoxicity. The laser beam was expanded to 6 mm on chamber slide systems used for morphological analysis and apoptosis detection. Cells were irradiated with a pulse duration of 3 ns, a repetition rate of 10 Hz, a radiant exposure of 0.395 J cm−2 per pulse on plate, and 0.131 J cm−2 per pulse on chamber slide systems. A number of pulses varying from 13 to 40 on plates, and varying from 10 to 90 on chamber slide systems, led to total doses of 5.1 to 15.9 J cm−2 and 3.9 to 11.8 J cm−2, respectively. The frequency of apoptotic bodies seemed the most suitable criterion capable of revealing the cellular stress induced by laser radiation. The threshold for the appearance of apoptotic bodies in chamber slide systems was the total dose of 3.9 J cm−2.