Temperature increase measurements of multiple 10 ms pulses of 2.01 μm laser light incident on ex-vivo rabbit corneas

2011 Summer.Includes bibliographical references.Current laser safety standards for multiple-pulse lasers are based primarily on modeling and the results of single-pulse studies. Previous thermal effects studies have focused on histological and visible endpoints, with only a few studies examining the actual temperatures achieved. The goal of this research was to probe the actual temperature profile produced by 2.01-micron laser pulses in the cornea. In this study the corneal temperature rise from multiple 2.01-micron Tm:YAG laser pulses was investigated using ex-vivo rabbit eyes. An infrared thermal camera employing microbolometer detectors captured surface temperature rises resulting from laser pulses. Thermal measurements were taken with single 10-ms pulses as well as two-, three-, and four-pulse sequences while holding the total energy delivered constant for the two- through four-pulse train measurements. An average temperature increase of 8.3 degrees C was observed with the single pulse at 2.8 J/cm2/pulse irradiance. For two pulses, an average temperature increase of 10.0 degrees C was observed for 2.7 J/cm2/pulse irradiance. For three pulses, an average temperature increase of 5.8 degrees C was observed for 1.9 J/cm2/pulse irradiance. For four pulses, an average temperature increase of 4.4 degrees C was observed for 1.5 J/cm2/pulse irradiance. A comparison of the data to temperatures required for denaturing proteins and the current laser safety guidelines is presented. It appears that the MPE may be overly conservative by a factor of at least 15. It is recommended that the 2.01-micron laser MPE be investigated to determine if a revision of the standard is warranted