Abstract
Thresholds for microcavitation of bovine and porcine melanosomes were previously reported, using single nanosecond (ns) laser pulses in the visible (532 nm) and the near-infrared (NIR) from 1000 to 1319 nm. Here, we report average radiant exposure thresholds for bovine melanosome microcavitation at additional NIR wavelengths up to 1540 nm, which range from ∼0.159 J∕cm2 at 800 nm to 4.5 J∕cm2 at 1540 nm. Melanosome absorption coefficients were also estimated, and decreased with increasing wavelength. These values were compared to retinal pigment epithelium coefficients, and to water absorption, over the same wavelength range. Corneal total intraocular energy retinal damage threshold values were estimated and compared to the previous (2007) and recently changed (2014) maximum permissible exposure (MPE) safe levels. Results provide additional data that support the recent changes to the MPE levels, as well as the first microcavitation data at 1540 nm, a wavelength for which melanosome microcavitation may be an ns-pulse skin damage mechanism.
Highlights
The American National Standards Institute (ANSI) revised the standards for the maximum permissible exposure (MPE) for safe use of lasers under Z136.1.1 The revisions included significant changes to the near-infrared (NIR) spectral region, and to the visible region in the nanosecond time regime
This work supplements and extends our previous study,[2] which presented the first threshold data ever reported in the literature for ns-pulse melanosome microcavitation in the near-IR
We report the first microcavitation threshold data at 1540 nm, a wavelength for which melanosome microcavitation may be a ns-pulse skin damage mechanism
Summary
Our previous study reported NIR thresholds for ns-pulse melanosome microcavitation, which supported the changes made to the safety standards.[2] there is still a need for additional microcavitation data in the ns time regime, in order to support future updates to the ANSI safety standards. Due to the lack of ns-pulse threshold data at other NIR wavelengths of interest, we have expanded this study to determine additional average radiant exposure thresholds for microcavitation of isolated bovine melanosomes using ns laser pulses at wavelengths in the 800 to 1064 nm region, as well as at 1540 nm. Melanosomes are found within both human skin and retinal pigment epithelium (RPE) layers of the eye. They are the main ocular light energy absorbers in the visible and NIR. The formation of small gaseous bubbles around melanosomes in the RPE, a process known as microcavitation, is the threshold-level damage mechanism for ns-pulse ocular exposures.[3,4,5,6]
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