The military and industry are using 1540 nm laser systems for which current consensus safety standards are misleading. Threshold, ED50, exposure data, along with mechanisms of laser-tissue interaction need to be more accurately determined. Recent studies within our group indicate the Yucatan mini-pig is a more applicable animal model for laser induced skin injury investigators. Laser delivery is accomplished using an Er:Glass system producing 1540 nm of light at millisecond exposure times and in the range of 17 to 77 J/cm(2). Dermal lesion development is evaluated for acute, 1 hour, and 24 hour post exposure presentation. Preliminary data obtained from dermal exposures indicate a difference in ED50 for Yorkshire and Yucatan pigs. In the Yucatan mini-pig erythematous lesions are formed acutely while in the Yorkshire, lesions are seen at 24 hrs. Preliminary data indicates that lesion development occurs at or near the basal layer of the epidermis causing nuclear pyknosis, cellular swelling and loss of cellular detail. Contrary to the theory that water absorption is the primary mechanism of dermal tissue damage observed from 1540 nm laser exposures, skin chromophores appears to play a role in lesion development.

Background and Purpose: The current safety standards for lasers operating in the 1,400- to 2,000-nanometer (nm) wavelength region are based on only a few observations at specific wavelengths. On the basis of experimental results conducted with Yorkshire pigs (Sus scrofa domestics), these standards may not accurately reflect the potential for laser injury when humans are exposed to these wavelengths, It is our belief that one of the damage mechanisms involved in these laser injuries results from energy absorption by skin pigmentation (melanin), and a more highly pigmented animal model, the Yucatan hairless minipig, may be a more suitable subject for laser exposure studies.Methods: Skin specimens were collected from Yorkshire pigs and Yucatan minipigs for histologic examination, and the thickness of the epidermis was measured. Epidermal thickness of human skin also was determined, and a qualitative assessment of the melanin content in the epidermal layers was conducted.Results: Mean +/- SD thicknesses of the Yucatan minipig flank and dorsal neck epidermis were 68 +/- 34 and 68 +/- 25 mu m, respectively. Thicknesses of the Yucatan minipig skin were closely comparable to the thicknesses of human epidermis from the face (68 +/- 26 mu m), neck (65 +/- 24 mu m) and arms (68 +/- 21 mu m), The Yorkshire pig lacks substantial melanin in the epidermis, whereas the skin of the Yucatan minipig is more similar to that of humans.Conclusion: On the basis of epidermal skin thickness measurements and melanin assessment, the flank and dorsal neck of the Yucatan minipig are better suited to laser injury studies than are the Yorkshire pig models of human skin.

Mechanisms of tissue damage are investigated for skin and cornea exposures from 1540 nm ('eye safe') laser single pulses of 0.8 milli-seconds. New skin model data point out the advantages of using the Yucatan mini-pig versus the Yorkshire pig for in-vivo skin laser exposures. Major advantages found include similarities in thickness and melanin content when compared with human skin. Histology from Yucatan mini-pig skin exposures and the calculation of an initial ED50 threshold indicate that the main photon tissue interaction may not be solely due to water absorption. In-vitro corneal equivalents compared well with in-vivo rabbit cornea exposure under similar laser conditions. In-vivo and in-vitro histology show that initial energy deposition leading to damage occurs intrastromally, while epithelial cells show no direct injury due to laser light absorption.

Background and purpose: Light amplification by stimulated emission of radiation (laser) systems operating in the so-called "eye safe" region are gaining widespread use in industry, medicine, and military applications. This research effort was geared to study the effects of laser tissue interaction on human skin by using in vivo porcine skin as an animal model. The goals of the study were to determine the median effective dose (ED50) for 1540-nm laser exposures, to evaluate the Yorkshire pig and the Yucatan mini-pig as animal models for laser exposure, and to characterize laser-induced skin lesions histologically.Methods: A 1540-nm wavelength laser was used to expose multiple sites on the flanks of 10 pigs, using 0.8-ms pulses, ranging from 7 to 96 joules (J)/cm(2). Single pulses were delivered to the flank of Yorkshire and Yucatan pigs in a grid pattern, Exposure sites were evaluated immediately after exposure and at 1 hour and 24 hours for presence of gross lesions. Representative biopsy specimens were collected from lesion sites for histologic evaluation at the 24-hour endpoint.Results: The ED50 for the two breeds differed in the amount of energy required to induce dermal lesions. Grossly, lesions in each breed were well demarcated and pale gray to brightly erythematous. Microscopically, lesions had epidermal layer damage as cellular swelling and nuclear pyknosis, loss of cellular detail, and coagulation necrosis at the dermal layer.Conclusions: Findings suggest the presence of a different mechanism of laser-tissue damage in these two breeds, Photo-thermal mechanism appears to induce the skin lesions in the Yorkshire pig, whereas photo-thermal. and photochemical mechanisms appear to be involved in lesion formation in the Yucatan mini-pig. All data obtained in this study will become part of database used by the American National Standards Institute (ANSI) to recommend laser safety standards for the occupational health and safety programs (OHSP), which will be used by industry and the military to base and update their current OHSP.

We investigate the use of in-vitro corneal equivalents as a replacement model for in-vivo rabbit corneas used in laser damage threshold studies. In-vitro corneal equivalents (CE) were exposed to 0.8 millisecond (ms), 1540 nanometer (nm) single laser light pulses ranging from 124 J/cm(2) to 58 J/cm(2). After exposure, CE's were evaluated opthalmoscopcopically, imaged using confocal microscopy and examined histologically to investigate the mechanisms of laser induced damage. Preliminary results indicate that the 50% damage threshold for CE's, ED50, is approximately 70 J/cm(2) with a 0.5 mm diameter spot size. Additional data points are required to determine a statistically significant ED50. Preliminary exposures of in-vivo rabbit corneas using the same laser parameters as the CE's are also reported. Comparisons between the in-vivo and in-vitro models are presented. Histopathological images from both models show remarkable similarities in the location and extent of damage throughout the full thickness of each tissue. Keywords: laser, corneal equivalent, probit analysis, confocal microscopy, rabbits.

Current safety standards for lasers operating in the 1400 to 10,000 nm wavelength region are based on few observations at specific wavelengths using in vivo models that may not represent an accurate correlation to human integument. Based on experimental results conducted with Yorkshire pigs, these standards may not accurately reflect the potential for laser injury when humans are exposed to these wavelengths. It is our belief that one of the primary damage mechanisms involved in these laser injuries is due to energy absorption by skin pigmentation, or melanin. Qualitatively, Yorkshire pigs lack melanin in their skin when compared to a more highly pigmented animal, such as the Yucatan minipig. It is hypothesized that the Yucatan minipig is a more appropriate model for pigmented human skin. By comparing histologic samples taken from various locations on Yucatan minipigs and Yorkshire pigs, and comparing these to potential locations of skin exposure on humans, we present a discussion for the establishment of more appropriate locations for in vivo laser exposure studies.

We report on preliminary work undertaken to determine ED50 thresholds for both skin and cornea exposure from 1400 to 2000 M1 laser light. Work presented here is focused initially on 1540 nn exposures to both human skin and cornea. Light microscopy and confocal microscopy used to help understand the type of photon-tissue interactions responsible for skin and corneal injury are discussed along with preliminary results from these techniques. Further, we report on in vivo models which are considered to best represent human skin for laser tissue interaction studies. Additionally, in vitro models for corneal exposure are discussed as replacement models for in vivo corneal exposures.