Background and purpose:The purpose of this study is to determine the impact of melanin on skin response to single 3.8 micron, eight microsecond laser pulses and the difference in lesion formation thresholds for input into laser safety standards. Williams et al., performed a study examining laser tissue interaction from 3.8-micron lasers in lightly pigmented Yorkshire pigs (Sus scrofa domestica). 1 However, studies performed by Eggleston et al comparing pigmented and lightly pigmented skin with human skin found that the Yucatan mini-pig is a superior model for laser skin exposures. 2 Methods: Five Yucatan mini-pigs under general anesthesia were exposed to 3.8 micron laser pulses ranging from 0.8 J/cm 2 to 93 J/cm 2 . Gross examinations were done acutely and 24 hours after laser exposure. Skin biopsies were then collected at various times post exposure, and histologic examinations were conducted. Results: The 24 hour ED 50 was determined to be 4.5 J/cm 2 with fiducial limits of 6.2 and 2.2 J/cm 2 . As deposited energy was increased, the lesion presentation ranged from whitening of the epidermis (4 J/cm 2 ) to whitening with inflammatory centers (14 J/cm 2 ), and at the highest energy levels inflammatory areas were replaced with an epidermal ulcerated central area (>21 J/cm 2 ). Conclusion: Preliminary findings suggest pigmentation or melanin may play a minor role in the mechanism of laser-tissue damage. The ED 50 of Yorkshire pigs was 2.6 J/cm 2 . 3 The ED 50 of the Yucatan mini-pig was found to be 3.6 J/cm 2 , and although it was higher, it is still within the 95% fiducial limits.

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. The author hereby certifies that the use of any copyrighted material in the thesis manuscript entitled: Corneal Injury to Ex-vivo Eyes Exposed to a 3.8 Micron Laserbeyond brief excerpts is with the permission of the copyright owner, and will save and hold harmless the Uniformed Services University of the Health Sciences from any damage that may arise from such copyright violations. Department of Preventive Medicine and BiometricsAs a consequence of the significant expansion of laser use in medicine, industry and research, specific safety standards must be developed that appropriately address eye protection. The purpose of this study is to establish injury thresholds to the cornea for 3.8 µm 8 microsecond laser light pulses and to investigate a possible replacement model to live animal testing. Previous studies of pulsed energy absorption at 3.8 µm were performed using rhesus monkey cornea and were at pulse durations two orders of magnitude different than the 8 microsecond pulses used in this study. Ex-vivo pig eyes were exposed at varying energies and evaluated to establish the statistical threshold for corneal damage. Histologic evaluation was used to determine the extent of damage to the cornea. It is expected that the results will be used to assist in the establishment of safety standards for laser use and offer an alternative to future animal use in establishment of safety standards.

No abstract

No abstract