Jeffrey W. Oliver

Histological and modeling study of skin thermal injury to 2.0 μm laser irradiation

Qualitative and quantitative gross histopathologic studies of skin damage were performed at 48 hours after irradiation with a 2.0 µm thulium CW laser to determine the mechanisms of laser effects in the skin under various exposure conditions.

Trends in retinal damage thresholds from 100-millisecond near-infrared laser radiation exposures: A study at 1,110, 1,130, 1,150, and 1,319 nm

Retinal damage thresholds from 100‐millisecond exposures to laser radiation for wavelengths between 1,100 and 1,350 nm have never previously been established. We sought to determine the retinal damage threshold for 100‐millisecond exposures of near‐infrared (NIR) laser radiation wavelengths at 1,110, 1,130, 1,150, and 1,319 nm. These data were then used to create trends for retinal damage thresholds over the 1,100–1,350 nm NIR region based upon linear absorption of laser radiation in ocular media and chromatic dispersion of the eye.

Infrared skin damage thresholds from 1940-nm continuous-wave laser exposures

Abstract. 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 optical-thermal 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 exposures <10  s, they may become less safe for very long exposures.

Variation of fluorescence in tissue with temperature.

Previous studies demonstrated a decrease in fluorescence intensity as tissue temperature increased. In vitro samples were increased from room temperature and in vivo canine liver from body temperature. This study investigated variations in fluorescence intensity with temperatures starting at 14°C and compared in vivo and in vitro results for consistency.

High-Resolution In Vivo Imaging of Regimes of Laser Damage to the Primate Retina

Purpose. To investigate fundamental mechanisms of regimes of laser induced damage to the retina and the morphological changes associated with the damage response. Methods. Varying grades of photothermal, photochemical, and photomechanical retinal laser damage were produced in eyes of eight cynomolgus monkeys. An adaptive optics confocal scanning laser ophthalmoscope and spectral domain optical coherence tomographer were combined to simultaneously collect complementary in vivo images of retinal laser damage during and following exposure. Baseline color fundus photography was performed to complement high-resolution imaging. Monkeys were perfused with 10% buffered formalin and eyes were enucleated for histological analysis. Results. Laser energies for visible retinal damage in this study were consistent with previously reported damage thresholds. Lesions were identified in OCT images that were not visible in direct ophthalmoscopic examination or fundus photos. Unique diagnostic characteristics, specific to each damage regime, were identified and associated with shape and localization of lesions to specific retinal layers. Previously undocumented retinal healing response to blue continuous wave laser exposure was recorded through a novel experimental methodology. Conclusion. This study revealed increased sensitivity of lesion detection and improved specificity to the laser of origin utilizing high-resolution imaging when compared to traditional ophthalmic imaging techniques in the retina.

Effect of laser thermal injury on Langerhans cells in mouse and hairless guinea pig epidermis.

To examine the effect of laser thermal injury on Langerhans cells (LC) within the epidermis, the dorsal skin of mice and hairless guinea pigs was exposed to varying levels of laser irradiation using a thulium laser at a wavelength of 2.0 μm. At 6, 24 and 48 h post irradiation, animals were euthanized, skin samples prepared for histology and the epidermis obtained and stained by major histocompatibility complex‐II staining (mice) or ATPase assay (hairless guinea pigs) for the enumeration of LC. Mouse skin exhibited histological evidence of thermal damage at 24 h post irradiation at even the lowest dose (0.14 W) and decreases in the numbers of epidermal LC were observed at all doses and decreases were proportional to dose. In contrast, hairless guinea pig skin only showed consistent histological evidence of thermal damage at the highest dose of irradiation (0.70 W) at 24 and 48 h post irradiation and exhibited a statistically significant decrease in numbers of epidermal LC only at this dose. Thus, epidermal LC depletion occurred in the skin of both mice and hairless guinea pigs in response to laser treatment and the magnitude of depletion directly correlated with the extent of thermal damage both within and between species.

Porcine skin ED50 damage thresholds for 1214 nm laser irradiation

A series of experiments were conducted in vivo on porcine skin to determine the ED50 damage thresholds for 1214 nm continuous wave laser irradiation. These results provide new information for refinement of Maximum Permissible Exposure (MPE). The study employed exposure durations of 1 sec, 3 sec, and 10 seconds with nominal spot diameters of 6 mm, 8 mm and 10 mm and as a function of laser power. The effect of each irradiation was evaluated acutely, one hour after exposure, and 24 hours post exposure. Probit analysis was conducted to estimate the dose for 50% probability of laser-induced damage (ED50); Damage was defined as persistent redness at the site of irradiation for the pig skin after 24 hours. The results indicated that Maximum Permissible Exposure (MPE) limits should be lowered for the laser beam diameters larger than 6 mm.

Porcine skin damage thresholds for 0.6 to 9.5 cm beam diameters from 1070-nm continuous-wave infrared laser radiation.

Abstract. There is an increasing use of high-power fiber lasers in manufacturing and telecommunications industries operating in the infrared spectrum between 1000 and 2000 nm, which are advertised to provide as much as 10 kW continuous output power at 1070 nm. Safety standards have traditionally been based on experimental and modeling investigations with scant data available for these wavelengths. A series of studies using 1070-nm infrared lasers to determine the minimum visible lesion damage thresholds in skin using the Yucatan miniature pig (Sus scrofa domestica) for a range of beam diameters (0.6, 1.1, 1.9, 2.4, 4.7, and 9.5 cm) and a range of exposure durations (10 ms to 10 s) is presented. Experimental peak temperatures associated with each damage threshold were measured using thermal imaging. Peak temperatures at damage threshold for the 10-s exposures were ∼10°C lower than those at shorter exposures. The lowest and highest experimental minimum visible lesion damage thresholds were found to have peak radiant exposures of 19 and 432  J/cm2 for the beam diameter-exposure duration pairs of 2.4 cm, 25 ms and 0.6 cm, 10 s, respectively. Thresholds for beam diameters >2.5  cm had a weak to no effect on threshold radiant exposure levels for exposure times ≤0.25  s, but may have a larger effect on thresholds for exposures ≥10  s.

Confocal Imaging of Thermal Lensing Induced by Near-IR Laser Radiation in an Artificial Eye

A custom confocal imaging system was built and used to record a probe beams spatiotemporal response to a thermal lens induced by a near-IR laser radiation source in a water-filled artificial eye. The IR laser radiation input power levels were varied between 150 and 890 mW at wavelengths of 1110, 1130, 1150 and 1318 nm in order to determine the strength of the resulting thermal lens as a function of time, input power, and wavelength. A high-frame-rate camera captured the probe beams logarithmic excitation and exponential decay caused by the thermal lens (supplemental video data are provided). Data showed that for equivalent input powers and beam geometries, thermal lensing was strongest for the 1150-nm laser radiation wavelength followed by 1130, 1318 and 1110 nm.

Method for measuring ocular aberrations induced by thermal lensing in vivo

An adaptive optics imaging system was used to qualitatively observe the types of aberrations induced by an infrared laser in a rhesus eye. Thermal lensing was induced with an infrared laser radiation wavelength of 1150-nm. The adaptive optics system tracked the temporal response of the aberrations at a frequency of 30 Hz for continuous-wave exposures. Results are compared against thermal lensing aberrations induced in an artificial eye.