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.
Yucatan Mini-pigs were exposed on their flank to 0.5 milli second 1318 nm pulses of laser light. The ED 50 damage threshold was determined for this laser exposure combination. The skin was assessed for injury immediately, at 1 hour, 24 hours and three days post exposure. Generally, at least 24 hours was required for visible lesions to form. It was found that as the duration between exposure and assessment expanded the injury was more easily visualized. Tissue samples were collected for histology at one hour, 24 hours and three days. Histologic sections will be presented in future work. It was also found that the topical application of mineral oil to the area of interest was found to greatly increase the ease of identification of injuries.
An increasing number of industries, to include military, medicinal, and technological arenas, are using 1.3 micron laser systems for which current skin and eye guidelines are identical. No skin threshold, ED 50 or exposure data are available. The mechanisms of laser-tissue interaction with skin at 1.3 microns are unknown. Together, these facts necessitate increased research to prevent future laser accidents and injuries. This study examines the method of interaction of 1.3 microns laser light with tissue in the Yorkshire pig. Our research addresses laser-tissue interaction through delivery using a Nd:YAG with an intracavity filter producing 1.3 micron light at 0.5 millisecond exposure time and in the range of 137 to 475 J/cm 2 . Laser exposure to Yorkshire pigs was evaluated for dermal lesion development. Lesions were appraised for acute, one-hour and 24-hour post exposure presentation.
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. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited SUPPLEMENTARY NOTESThe original document contains color images. ABSTRACTThe purpose of this study was to compare and contrast the effects of single 3.8-micron laser pulses in an in-vitro and in-vivo model of human skin and to demonstrate the efficacy of in-vitro laser tissue interaction models. The minimum exposure required to produce specific, gross morphologic changes from a four microsecond, pulsed skin exposure for both models was determined. Histologic samples of the tissues were compared to ascertain the effectiveness of the in-vitro models. Eighteen artificial skin equivalents, (in-vitro model), were exposed and compared to exposures made on five Yorkshire pigs. Representative biopsies were taken for histologic evaluation from various locations immediately, one hour, and 24 hours following exposure. The pattern of epithelial changes seen following in-vivo exposure of pig skin was similar to the changes previously observed in human skin equivalents, indicating that the artificial skin equivalents are representative in-vitro models for this particular combination of laser parameters. The author hereby certifies that the use of any copyrighted material in the thesis manuscript entitled:"Comparison of Experimental Models for Predicting Laser Tissue Interaction from 3.8-micron Lasers" beyond 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, which may arise from such copyright violations.
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.
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