Search

A series of experiments were conducted in vivo using Yucatan miniature pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1319-nm continuous-wave Nd:YAG laser irradiation. Experiments employed exposure durations of 0.25, 1.0, 2.5, and 10 s and beam diameters of ∼0.6 and 1 cm. Thermal imagery data provided a time-dependent surface temperature response from the laser. A damage endpoint of fifty percent probability of a minimally visible effect was used to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of opticalthermal interaction. Resultant trends with respect to exposure duration and beam diameter are compared with current standardized exposure limits for laser safety. Mathematical modeling agreed well with experimental data, predicting that though laser safety standards are sufficient for exposuress, they may become less safe for very long exposures. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JBO.18.12.125002]

Five-axis goniometric stages have been used in laser eye safety research for over forty years. The stages are able to translate in three dimensions and rotate about either eye of a prone-placed subject. This report describes the design, implementation, and operation of a five-axis goniometric stage. The latest design incorporates many ideas from previous versions while adding reliability and functionality improvements, such as a position indicator option. Most notably, the current design merges the rotary and linear portions into a single contained motion system. A manual control box facilitates the operation of the two rotational axes and three linear travel axes. The design criteria for the goniometric portion of the stage nominally called for +/- 15 degrees pitch adjustment and +/1 40 degrees of rotational adjustment. The XY section was designed for 6.5 inches (16.5 cm) of travel in each axis. The height stage section was required to have 8 inches of range with a center of motion approximately 46 inches above the floor., Prepared in cooperation with Air Force Research Laboratory (AFRL), Brooks City-Base, TX. The original document contains color images.

A series of experiments are conducted in vivo using Yucatan mini-pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1940-nm continuous-wave thulium fiber laser irradiation. Experiments employ exposure durations from 10 ms to 10 s and beam diameters of approximately 4.8 to 18 mm. Thermal imagery data provide a time-dependent surface temperature response from the laser. A damage endpoint of minimally visible effect is employed to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of optical-thermal interaction. Results are compared with current exposure limits for laser safety. It is concluded that exposure limits should be based on data representative of large-beam exposures, where effects of radial diffusion are minimized for longer-duration damage thresholds

in this paper we report on our combined measurements of the visible lesion thresholds for porcine skin for wavelengths in the infrared from 810 nm at 44 fs to 1318 nm at pulse durations of 50 ns and 350 microsecond to 1540 nm including pulse durations of 31 ns and 600 microseconds. We also measure thresholds for various spot sizes from less than 1 mm to 5 mm in diameter. All three wavelengths and five pulse durations are used extensively in research and the military. We compare these minimum visible lesion thresholds with ANSI standards set for maximum permissible exposures in the infrared wavelengths. We have measured non-linear effects at the laser-tissue interface for pulse durations below 1 microseconds and determined that damage at these short pulse durations are usually not thermal effects. Damage at the skin surface may include acoustical effects, laser ablation and/or low-density plasma effects, depending on the wavelength and pulse duration. Also the damage effects may be short-lived and disappear within a few days or may last for much longer time periods including permanent discolorations. For femtosecond pulses at 810 nm, damage was almost instant and at 1 hour had an ED50 of 8.2 mJ of pulse energy. After 24 hours, most of the lesions disappeared and the ED50 increased by almost a factor of 3 to 21.3 mJ. There was a similar trend for the 1.318 mu laser for spot sizes of 2 mm and 5 mm where the ED50 was larger after 24 hours. However, for the 1.54 mu laser with a spot size of 5 mm, the ED50 actually decreased by a small amount; from 6.3 Jcm(-2) to 6.1 Jcm(-2) after 24 hours. Thresholds also decreased for the 1314 nm laser at 350 microseconds for spot sizes of 0.7 mm and 1.3 mm diameter after 24 hours. Different results were obtained for the 1540 run laser at 600 microsecond pulse durations where the ED50 decreased for spot sizes 1 mm and below, but increased slightly for the 5 mm diameter spot size from 6.4 Jcm(-2) to 7.4 Jcm(-2)., Prepared in collaboration with the U.S. Air Force Research Laboratory, Brooks City AFB, TX. Presented at the Optical Interactions with Tissue and Cells (18th) held in San Jose, CA on 22-24 Jan 2007. Published in Progress in Biomedical Optics and Imaging, v8 n12, ISSN 1605-744; Proceedings of the SPIE, v6435 paper 64350W, Feb 2007, ISBN 9780819465481. This article is from ADA484275 Conference on Optical Interactions with Tissue and Cells (18th) Held in San Jose, California on January 22-24, 2007

An assessment of skin damage caused by near-IR laser exposures is reported. The damage from two distinct laser-tissue temporal regimes is compared at two wavelengths (1.3 microns and 1.5 microns). Skin damage caused by thermal effects from single laser pulses is compared to damage caused by LIB (laser induced breakdown) using histological examinations. Modeling applications are explored to determine crossover points between thermal and photomechanical damage thresholds., Prepared in collaboration with Northrop Grumman, San Antonio, TX. Presented at the Optical Interactions with Tissue and Cells (18th) held in San Jose, CA on 22-24 Jan 2007. Published in Progress in Biomedical Optics and Imaging, v8 n12, ISSN 1605-744; Proceedings of the SPIE, v6435 article 643504, Feb 2007, ISBN 9780819465481. This article is from ADA484275 Conference on Optical Interactions with Tissue and Cells (18th) Held in San Jose, California on January 22-24, 2007

A series of experiments in a new animal model for retinal damage, cynomolgus monkeys (Macaca fascicularis), have been conducted to determine the damage threshold for 12.5-nanosecond laser exposures at 1064 nm. These results provide a direct comparison to threshold values obtained in rhesus monkey (Macaca mulatta), which is the model historically used in establishing retinal maximum permissible exposure (MPE) limits. In this study, the irradiance level of a collimated Gaussian laser beam of 2.5 mm diameter at the cornea was randomly varied to produce a rectangular grid of exposures on the retina. Exposures sites were fundoscopically evaluated at post-irradiance intervals of 1 hour and 24 hours. Probit analysis was performed on dose-response data to obtain probability of response curves. The 50% probability of damage (ED5O) values for 1 and 24 hours post-exposure are 28.5(22.7-38.4) microjoule and 17.0(12.9-21.8) microjoule, respectively. These values compare favorably to data obtained with the rhesus model, 28.7(22.3-39.3) microjoule and 19.1(13.6-24.4) joule, suggesting that the cynomolgus monkey may be a suitable replacement for rhesus monkey in photoacoustic minimum visible lesion threshold studies., Prepared in collaboration with Northrop Grumman, San Antonio, TX. Presented at the Optical Interactions with Tissue and Cells (18th) held in San Jose, CA on 22-24 Jan 2007. Published in Progress in Biomedical Optics and Imaging, v8 n12, ISSN 1605-744; Proceedings of the SPIE, v6435 paper 64350Q, Feb 2007, ISBN 9780819465481. This article is from ADA484275 Conference on Optical Interactions with Tissue and Cells (18th) Held in San Jose, California on January 22-24, 2007

Until reliable nonanimal systems of analysis are available, animal models will be necessary for ocular laser hazard analysis and for evaluating clinical applications. The purpose of this work was to demonstrate the utility of an in vitro system for laser bioeffects by identifying photothermal and photochemical cytotoxicity thresholds for continuous-wave (cw) and mode-locked (ml) laser exposures. Exogenous melanosomes were added to hTERT-RPE1 cells in exposure wells 1 day before laser exposure. Thermal or photochemical laser exposures were delivered to artificially pigmented retinal pigment epithelial (RPE) cultures, with subsequent assay for viability 1 hour after exposure. Beam delivery for the 1-hour photochemical exposures was via a modified culture incubator. The cytoprotective effect of pretreatment with two antioxidants was investigated. Phagocytosis of melanosomes by the RPE cells was efficient, yielding cultures of uniform pigmentation. The damage threshold for the thermal exposure was consistent with published in vivo results. Thresholds for both blue exposures (cw and ml) were identical. Overnight treatment of cells with ascorbic acid (AA) minimized cell death from both cw and ml blue laser exposure, whereas similar treatment with N-acetyl- L-cysteine (NAC) was less effective. The in vitro system described is suitable for measuring meaningful thermal and photochemical laser damage thresholds. The system is also useful in comparative laser bioeffects studies, such as comparisons between cw and ml laser exposures, cells with various degrees of pigmentation, and studies determining the efficacy and mechanisms of treatments altering the response of cells to lasers., Published in Investigative Ophthalmology & Visual Science, v47 n7 p3065-3073, July 2006.

The use of lasers by both the military and civilian community is rapidly expanding. Thus, the potential for and severity of laser eye injury and retinal damage is increasing. Sensitive and accurate methods to evaluate and follow laser retinal damage are needed. The multifocal electroretinogram (mfERG) has the potential to meet these criteria. In this study, the mfERG was used to evaluate changes to retinal function following laser exposure. Landolt C contrast acuity was also measured in the six behaviorally trained Rhesus monkeys. The monkeys then received Nd:YAG laser lesions (1064 nm, 9 ns pulse width) in each eye. One eye received a single foveal lesion of approximately 0.13 mJ total intraocular exposure (TIE) and the other received six parafoveal lesions which varied in TIE from 0.13 to 4 mJ. mfERGs and behavioral data were collected both pre- and post-exposure. mfERGs were recorded using stimuli that contained 103, 241, and 509 hexagons. Landolt C contrast acuity was measured with five sizes of Landolt C (0.33 to 11.15 cycles/degree) of varying contrast. mfERG response densities were sensitive to the functional retinal changes caused by the laser insult. In general, larger lesions showed greater mfERG abnormalities than smaller laser lesions. Deficits in contrast acuity were found to be more severe in the eyes with foveal injuries. Although the mfERG and contrast acuity assess different areas of the visual system, both are sensitive to laser-induced retinal damage and may be complementary tests for laser eye injury triage., Published in Photonic Therapeutics and Diagnostics II, Proceedings of SPIE, v6078, 607837, 2006.

Skin damage thresholds were measured and compared with theoretical predictions using a skin thermal model for near-IR laser pulses at 1318 nm and 1540 nm. For the 1318-nm data, a Q-switched, 50-ns pulse with a spot size of 5 mm was applied to porcine skin and the damage thresholds were determined at 1 hour and 24 hours post-exposure using Probit analysis. The same analysis was conducted for a Q-switched, 30-ns pulse at 1540 nm with a spot size of 5 mm. The Yucatan mini-pig was used as the skin model for human skin due to its similarity to pigmented human skin. The ED50 for these skin exposures at 24 hours post-exposure was 10.5 J/cm2 for the 1318-nm exposures, and 6.1 J/cm2 for the 1540-nm exposures. These results were compared to thermal model predictions. We show that the thermal model fails to account for the ED50 values observed. A brief discussion of the possible causes of this discrepancy is presented. These thresholds are also compared with previously published skin minimum visible lesion (MVL) thresholds and with the ANSI Standard's MPE for 1318-nm lasers at 50 ns and 1540-nm lasers at 30 ns., Published in Optical Interactions with Tissue and Cells XVII, Proceedings of SPIE, V6084, 60840E, 2006.

The reflectance and absorption of the skin plays a vital role in determining how much radiation will be absorbed by human tissue. Any substance covering the skin would change the way radiation is reflected and absorbed and thus the extent of thermal injury. Hairless guinea pigs (cavia porcellus) in vivo were used to evaluate how the minimum visible lesion threshold for single-pulse laser exposure is changed with a topical agent applied to the skin. The ED50 for visible lesions due to an Er: glass laser at 1540-nm with a pulse width of 50-ns was determined, and the results were compared with model predictions using a skin thermal model. The ED50 is compared with the damage threshold of skin coated with a highly absorbing topical cream at 1540 nm to determine its effect on damage pathology and threshold. The ED50 for the guinea pig was then compared to similar studies using Yucatan minipigs and Yorkshire pigs at 1540-nm and nanosecond pulse duration. The damage threshold at 24-hours of a Yorkshire pig for a 2.5-3.5-mm diameter beam for 100 ns was 3.2 Jcm-2; very similar to our ED50 of 3.00 Jcm-2 for the hairless guinea pigs., Published in Optical Interactions with Tissue and Cells XVII, Proceedings of SPIE, v6084, 60840I, 2006.

Precise targeting of retinal structures including retinal pigment epithelial cells, feeder vessels, ganglion cells, photoreceptors, and other cells important for light transduction may enable earlier disease intervention with laser therapies and advanced methods for vision studies. A novel imaging system based upon scanning laser ophthalmoscopy (SLO) with adaptive optics (AO) and active image stabilization was designed, developed, and tested in humans and animals. An additional port allows delivery of aberration-corrected therapeutic/stimulus laser sources. The system design includes simultaneous presentation of non-AO, wide-field (tilde 40 deg) and AO, high-magnification (1-2 deg) retinal scans easily positioned anywhere on the retina in a drag-and-drop manner. The AO optical design achieves an error of <0.45 waves (at 800 nm) over plus or minus 6 deg on the retina. A MEMS-based deformable mirror (Boston Micromachines Inc.) is used for wave-front correction. The third generation retinal tracking system achieves a bandwidth of greater than 1 kHz allowing acquisition of stabilized AO images with an accuracy of tilde 10 micrometers. Normal adult human volunteers and animals with previously-placed lesions (cynomolgus monkeys) were tested to optimize the tracking instrumentation and to characterize AO imaging performance. Ultrafast laser pulses were delivered to monkeys to characterize the ability to precisely place lesions and stimulus beams. Other advanced features such as real-time image averaging, automatic highresolution mosaic generation, and automatic blink detection and tracking re-lock were also tested. The system has the potential to become an important tool to clinicians and researchers for early detection and treatment of retinal diseases., Presented at the SPIE BiOS 2006 Advanced Biomedical and Clinical and Diagnostic Systems Conference (4th) held in San Jose, CA on 21-26 January 2006. Published in the Proceedings of the SPIE BiOS 2006 Advanced Biomedical and Clinical and Diagnostic Systems (4th), January 2006.

Er:glass lasers have been in operation with both long pulses (hundreds of microseconds) and Q-switched pulses (50 to 100 ns) for more than 35 yr. The ocular hazards of this laser were reported early, and it was determined that damage to the eye from the 1.54-microns wavelength occurred mainly in the cornea where light from this wavelength is highly absorbed. Research on skin hazards has been reported only in the past few years because of limited pulse energies from these lasers. Currently, however, with pulse energies in the hundreds of joules, these lasers may be hazardous to the skin in addition to being eye hazards. We report our minimum visible lesion (MVL) threshold measurements for two different pulse durations and three different spot sizes for the 1.54-microns wavelength using porcine skin as an in vivo model. We also compare our measurements to results from our model, based on the heat transfer equation and the rate process equation. Our MVL-ED50 thresholds for the long pulse (600 microsecs) at 24 h postexposure were measured to be 20, 8.1, and 7.4 J cm2 for spot diameters of 0.7, 1.0, and 5 mm, respectively. Q-switched laser pulses of 31 ns had lower ED50 (estimated dose for a 50% probability of laser-induced damage) thresholds of 6.1 J cm(2) for a 5-mm-diam, top-hat spatial profile laser pulse., Published in Journal of Biomedical Optics, v11 n2 p024001-1-024001-8 March/April 2006.

Precise targeting of retinal structures including retinal pigment epithelial cells, feeder vessels, ganglion cells, photoreceptors, and other cells important for light transduction may enable earlier disease intervention with laser therapies and advanced methods for vision studies. A novel imaging system based upon scanning laser ophthalmoscopy (SLO) with adaptive optics (AO) and active image stabilization was designed, developed, and tested in humans and animals. An additional port allows delivery of aberration-corrected therapeutic/stimulus laser sources. The system design includes simultaneous presentation of non-AO, wide-field (approx. 40 deg) and AO, high-magnification (1-2 deg) retinal scans easily positioned anywhere on the retina in a drag-and-drop manner. The AO optical design achieves an error of <0.45 waves (at 800 nm) over +/- 6 deg on the retina. A MEMS-based deformable mirror (Boston Micromachines Inc.) is used for wave-front correction. The third generation retinal tracking system achieves a bandwidth of greater than 1 kHz allowing acquisition of stabilized AO images with an accuracy of approx. 10 micron. Normal adult human volunteers and animals with previously-placed lesions (cynomolgus monkeys) were tested to optimize the tracking instrumentation and to characterize AO imaging performance. Ultrafast laser pulses were delivered to monkeys to characterize the ability to precisely place lesions and stimulus beams. Other advanced features such as real-time image averaging, automatic high resolution mosaic generation, and automatic blink detection and tracking re-lock were also tested. The system has the potential to become an important tool to clinicians and researchers for early detection and treatment of retinal diseases., Published in Ophthalmic Technologies XVI, SPIE Proceedings v6138 article 61381, Feb 2006. Prepared in collaboration with Physical Sciences Inc., Andover MA; Northrop Grumman Corporation, San Antonio TX; and Department of Opthalmology, Duke University Medical Center, Durham, NC.

The growth of commercially available, simultaneous muiti-wavelength laser systems has increased the likelihood of possible ocular hazard. For example, many systems utilize frequency multiplying methods to produce combinations of visible, near-infrared, and ultraviolet wavelengths. Unfortunately, very little data exists to substantiate the current methods for estimating hazards from simultaneous lasing. To properly assess the retinal hazards from these wavelengths, the retinal effects of 10-s laser irradiation from 532 and 860 nm were determined in non-human primates for four different relative dosage combinations of these wavelengths. This pair of wavelengths represents the typical problem of a visible-wavelength laser combined with an in-band, infrared wavelength that is not as well focused at the retina - a situation difficult to address. To add confidence to the experimental results obtained, a theoretical thermodynamic model was developed to predict the minimal damage threshold for simultaneous wavelengths at 1 h post exposure. The new model calculations and the data obtained are compared with results from one currently accepted method of predicting relative exposure limits from multi-wavelength systems. In addition, the current ANSI-Z136-2000 standard was used to compute the combined MPEs for comparison with measured visible lesion thresholds. A total of 12 eyes were exposed using four different ratios of power levels (532/860 power rations) to determine the contribution to the damage levels from each wavelength. The experimental data were analyzed using probit analysis at both 1-h and 24-h post exposure to determine the minimum-visible-lesion (MVL) thresholds at ED^ values, and these thresholds at 24 h varied from 5.6 mW to 17 mW total intraocular power., Published in Health Physics, v90 n3 p241-249, March 2006. Prepared in collaboration with Northrop Grumman, San Antonio, TX, Fort Hays State University, Hays, KS and U. S. Army Medical Research Detachment, Walter Reed Army Institute of Research, Brooks AFB, TX.

Terawatt (TW) lasers have become commonplace since the development of the chirped-pulse amplification method using Ti:sapphire and Nd:glass laser rods. We have measured the minimum visible lesion (MVL) thresholds for porcine1 (Yucatan minipig) skin using TW laser pulses. Our system produced laser pulses at 810 nm and sub-50 femtoseconds. These 1-2 TW laser pulses created multiple self-focusing (SF) filaments during propagation and were directed on the flanks of mini-pigs under anesthesia. We measured the pulse energies necessary to determine the ED50 skin damage thresholds., The original document contains color images. Pub. in Lasers in Surgery and Medicine, v37, p59-63, 2005.

Applications of ultrashort pulse laser systems have increased dramatically in the past several years. Retinal exposure to these laser pulses can produce visible lesions with pulse energies of less than 1 microjoule (microJ) per pulse. Our research has found a reduction in the energy required for retinal damage as pulse duration is decreased from the nanosecond (ns) to femtosecond (fs) regime. With this data, new laser safety standards are being proposed to reduce the dangers and uncertainties when working around these lasers., The original document contains color images. All DTIC reproductions will be in black and white.