Wavelength dependence of ocular damage thresholds in the near-IR to far-IR transition region (proposed revisions to MPEs)

We have previously reported on unique aspects of the laser-tissue interactions associated with penetrating laser wavelengths in the near-IR to far-IR transition region. Retinal, lens, and corneal effects have been described following 1.3-1.4 μm laser exposures with exposure durations ranging from cw to sub-millisecond. The puslewidth range studied has now been extended down to the nanosecond regime using a Q-switched, 1.319-μm, Nd:YAG laser. This paper presents the Q-switched data and discusses the wavelength dependence of the IR thresholds across all pulsewidth regimes. The corneal and retinal thresholds are contrasted to laser safety standard maximum permissible exposure (MPE) limits and changes suggested to the existing MPEs with the objectives of: (1) relaxing the standards over wavelength ranges where unusually high safety margins may unnecessarily hinder applications of recently developed military and telecommunications laser systems and; (2) replacing step-function discontinuities in the MPEs by more gradually changing functions of wavelength which follow the trends of the retinal and corneal ED₅₀ threshold data. Based on these considerations, revisions to laser safety standard MPEs are proposed over the wavelength range from 1.15 μm to 2.6 μm.