Product Code: ILSC2007_404

Proposed Changes for the Retinal Thermal MPE
Authors:
Bruce Stuck, USAMRD-WRAIR; Brooks City-Base TX USA
Karl Schulmeister, Austrian Research Centers GmbH; Seibersdorf Austria
David Lund, USAMRD-WRAIR; Brooks AFB TX USA
David Sliney, US Army CHPPM; APG MD USA
Presented at ILSC 2007

Recently, a number of new threshold values for retinal thermal damage became available that allow a more complete analysis of the dependence of the threshold on the retinal spot size diameter for different pulse durations. The data originate from non-human primate (NHP) models, excised retinas as well as computer models and compare well with each other. A distinctive dependence of the threshold on laser spot size diameter for different pulse duration is seen which indicates that current (ICNIRP, ANSI and IEC) pulsed laser exposure limits for large spots can be increased. A time dependent amax is proposed which only for the case of long exposure durations has the current value of 100 mrad, but decreases to smaller angles for short exposure durations, effectively increasing the permissible exposure level. The data also indicate that for pulse durations shorter than about 1 µs, bubble (microcavitation) induced damage leads to a lower threshold than the thermally induced threshold. In the nanosecond pulse duration regime, the bubble induced threshold is about a factor of 10 lower than the thermally induced damaged threshold, resulting in the need to lower the MPE values for this condition, which was already indicated by the NHP data of Zuclich et al (JLA 2000).