The spatial and temporal activation of NF-kB (p65) was monitored in the retina of a transgenic mouse model
(cis-NFkB-EGFP) in vivo after receiving varying grades of laser induced thermal injury in one eye. Baseline images of the
retinas from 26 mice were collected prior to injury and up to five months post-exposure using a Heidelberg Spectralis
HRA confocal scanning laser ophthalmoscope (cSLO) with a spectral domain optical coherence tomographer (SDOCT).
Injured and control eyes were enucleated at discrete time points following laser exposure for cryosectioning to
determine localization of NF-kB dependent enhanced green fluorescent protein (EGFP) reporter gene expression within
the retina using fluorescence microscopy. In addition, EGFP basal expression in brain and retinal tissue from the
cis-NFkB-EGFP was characterized using two-photon imaging. Regions of the retina exposed to threshold and supra-threshold
laser damage evaluated using fluorescence cSLO showed increased EGFP fluorescence localized to the exposed region
for a duration that was dependent upon the degree of injury. Fluorescence microscopy of threshold damage revealed
EGFP localized to the outer nuclear region and retinal pigment epithelial layer. Basal expression of EGFP imaged using
two-photon microscopy was heterogeneously distributed throughout brain tissue and confined to the inner retina. Results
show cis-NF-kB-EGFP reporter mouse can be used for in vivo studies of light induced injury to the retina and possibly
brain injury.
Balb/c wild type mice were used to perform in vivo experiments of laser-induced thermal damage to the retina. A
Heidelberg Spectralis HRA confocal scanning laser ophthalmoscope with a spectral domain optical coherence
tomographer was used to obtain fundus and cross-sectional images of laser induced injury in the retina. Sub-threshold,
threshold, and supra-threshold lesions were observed using optical coherence tomography (OCT), infrared reflectance,
red-free reflectance, fluorescence angiography, and autofluorescence imaging modalities at different time points post-exposure.
Lesions observed using all imaging modalities, except autofluorescence, were not visible immediately after
exposure but did resolve within an hour and grew in size over a 24 hour period. There was a decrease in fundus
autofluorescence at exposure sites immediately following exposure that developed into hyper-fluorescence 24-48 hours
later. OCT images revealed threshold damage that was localized to the RPE but extended into the neural retina over a 24
hour period. Volumetric representations of the mouse retina were created to visualize the extent of damage within the
retina over a 24 hour period. Multimodal imaging provides complementary information regarding damage mechanisms
that may be used to quantify the extent of the damage as well as the effectiveness of treatments without need for
histology.
A study of retinal damage thresholds in non-human primates (NHP) in the near-infrared (NIR) wavelengths of 1110,
1130, 1150, and 1319 nm has recently been reported. The progression of damage in retinal areas that received exposures
below, greater than, and at threshold values for each respective wavelength are compared. Subjects were imaged using
an Adaptive Optics (AO) enhanced Spectral Domain Optical Coherence Tomographer (SD-OCT) a year post laser
exposure to examine damage characteristics and localization. The subject's retinas within the study exhibited a delayed
response to NIR exposures in that many of the lesions that were not visible at the 1-hour observation period continued to
grow in size over the 24-hour period and or became visible. Thermal lensing is believed to play a significant role in the
formation or retinal lesions in the NIR and may explain the delayed response.
Near threshold retinal lesions were created in the eyes of non-human primate (NHP) subjects in the near infrared (NIR)
wavelength range of 1100 to 1319 nm, with 80 to 100 ms laser exposures. Two new in vivo imagining techniques,
Adaptive Optic enhanced-Spectral Domain Optical Coherence Tomography (AO-SDOCT) and Adaptive Optic enhanced
confocal Scanning Laser Ophthalmoscope imagery (AOcSLO) were utilized to pinpoint areas of chronic damage within
the retinal layers resulting from laser exposure. Advantages and limitations of each technology with regard to the study
of laser retinal tissue interaction are highlighted.
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.
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 &mgr;m and 1.5 &mgr;m). 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.
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.1,2 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.
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