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J. P. Wood, G. Chidlow, V. Previn, M. Plunkett, R. Casson; Nanosecond Laser Pulses for Retinal Treatment. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4797. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate an exciting new approach to retinal laser treatment using nanosecond laser pulses. Also to determine which laser pulse parameters produce the greatest therapeutic range for RPE treatment without causing collateral damage. Different 532nm nanosecond laser beam profiles and pulsing techniques were compared with the effects produced by millisecond laser pulses.
Porcine explants were used, with neuro-retina in place for laser treatment. The calcein-AM live cell assay was used to visualise RPE samples and light microscopy for retinal samples. The following 532nm lasers were used:1. FD-YAG, 3ns pulse duration, speckle beam profile2. FD-YAG, 3ns pulse duration, gaussian beam profile3. Quasi-CW laser, 100ms & 10ms pulse durations, flat top profile.4. CW laser , 100ms & 10ms pulse durations, flat top profile.Threshold levels were determined by image analysis and therapeutic range ratio defined as minimum visible effect threshold versus minimum RPE kill threshold within the laser spot diameter.
Both of the 3ns lasers produced much lower RPE kill thresholds than the CW or Quasi-CW lasers due to thermal confinement resulting from the temporal confinement of energy within nanosecond pulses. The 3ns laser with the speckle beam profile produced lower RPE kill thresholds than the 3ns laser with a gaussian beam profile due to the additional spatial confinement of energy. Using nanosecond pulses the visible effect threshold was found to be largely coincident with the RPE cell membrane rupture threshold. A therapeutic range ratio greater than 6:1 was achieved using nanosecond laser 1 while producing no discernable neuro-retinal damage.
Nanosecond laser pulses can provide a very wide therapeutic range of energies in which RPE treatment can be performed, without damage to the neuro-retina, using energy levels approximately 200 times less than CW or Quasi-CW photocoagulators. Nanosecond laser pulses with a fine speckle beam profile were found to be the most effective and produced a therapeutic range greater than 6:1 which to our knowledge is wider than previously reported. These results may have important implications for the treatment of early age-related macular degeneration and diabetic macular edema.
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