The interaction mechanism leading to laser-induced retinal alteration can be thermal or non-thermal, depending upon the wavelength of the laser radiation and the duration of the exposure. To investigate the effect of exposure duration on the interaction mechanism, retinal injury thresholds in the rhesus monkey were experimentally measured for exposure to laser radiation at wavelengths of 441.6, 457.9, 476.5, and 496.5 nm. Exposure durations were 0.1, 1, 5, 16, and 100 s; and 1/e retinal irradiance diameters were 50, 125, and 327 μm. Tissue response was observed via ophthalmoscope 1 h and 48 h post exposure. Thermal and non-thermal damage thresholds were obtained depending upon the exposure duration. These threshold data are in agreement with data previously reported in the literature for 100-s duration exposures, but differences were noted for shorter exposures. The current study yielded an estimated injury threshold for 1-s duration, 327-μm retinal irradiance diameter exposures at 441.6 nm, which is an order of magnitude higher than that previously reported. This study provides evidence that laser-induced retinal damage is primarily induced via thermal mechanisms for exposures shorter than 5 s in duration. Arguments are presented that support an amendment of the thermal hazard function, R(λ).
* U.S. Army Medical Research Detachment, Walter Reed Army Institute of Research, 7965 Dave Erwin Drive, Brooks City-Base, TX 78235-5108; † Northrop Grumman IT, 4241 Woodcock Drive, Suite B100, San Antonio, TX 78228.
For correspondence or reprints contact: D. J. Lund, USAMRD-WRAIR, 7965 Dave Erwin Drive, Brooks City-Base, TX 78235-5108, or email at firstname.lastname@example.org.
(Manuscript received 27 July 2005; revised manuscript received 22 September 2005, accepted 26 December 2005)