The retinal damage induced by laser photocoagulation increases manifold by the secondary degeneration process whereby tissues adjacent to the primary lesion are destroyed. The neuroprotective effect of immunization by glatiramer acetate (Copolymer-1, Cop-1) in adjuvant was previously demonstrated in models of retina, optic nerve, brain, and spinal cord lesions. The present study tested the neuroprotective ability of Cop-1 to reduce the spread of laser-induced retinal damage. Standard argon laser lesions were created in 72 DA pigmented rats divided into four groups: two Cop-1 treated groups (animals treated seven days before or immediately after the laser session) and two control groups treated respectively by saline or the effective but toxic neuroprotective compound MK-801. The histological and morphological evaluations of the lesions 3, 20, and 60 days after the injury revealed significant reduction in photoreceptor loss of the retinas of the pre-immunized animals. Cop-1 given after the laser injury did not prevent cell loss significantly, while the neuroprotective effect of MK-801 was observed only on the third day after the laser injury. The results show that pre-immunization with Cop-1 is neuroprotective in unmyelinated (gray matter) neural tissue such as the retina. This approach may be of clinical significance in ameliorating laser-induced retinal injuries in humans.

Purpose: To determine funduscopic criteria that will help predict when bridging choroidal neovascular (CNV) complexes will develop after laser retinal trauma and to define early preventive treatment targets. Methods: Ten rhesus monkeys were used and retinal lesions were produced by Nd:YAG exposures (20ns, 1-2mJ, 1064nm, min. spot size) simulating human accidental laser trauma to the central fundus. Funduscopy and fluorescein/ICG angiography were conducted at day 1, 4, and 14, and at 2 and 4 months, and animals terminated for histologic evaluation. Predisposition for bridging fibrovascular complexes was evaluated for single lesions, two small lesions showing coalescing hemorrhages, and multiple lesions involved with large field subretinal and vitreous hemorrhages. Results: Elevated CNVs were present in all single lesions with confined subretinal hemorrhages. All lesion sets that showed initial and small coalescing subretinal hemorrhages formed bridging CNV scars. No bridging CNVs occurred in lesion sets involving a vitreous hemorrhage adjacent to a confined, but small subretinal hemorrhage. In large field subretinal hemorrhages involving multiple laser lesions, complex CNV formation occurred. Extensive secondary photoreceptor losses occurred in confined hemorrhage and CNV zones. Conclusion: Trauma presenting with evidence of coalescing and confined subretinal hemorrhages between two adjacent lesions has a high chance of forming choroidal neovascular bridge complexes between the involved lesions. CNV formation may be related to the long residence time, break down products, and clearance processes of extravasated blood. Removal of trapped blood and curtailing angiogenesis and cellular proliferation may be helpful treatment strategies.

Choroidal perfusion was evaluated following the creation of a laser induced macular hole in a nonhuman primate model. Two Rhesus monkeys underwent macular exposures delivered by a Q-switched Nd:YAG laser. The lesions were evaluated with fluorescein angiography and indocyanine green (ICG) angiography . Each lesion produced vitreous hemorrhage and progressed to a full thickness macular hole. ICG angiography revealed no perfusion of the choriocapillaris beneath the lesion centers. Histopathologic evaluation showed replacement of the choriocapillaris with fibroblasts and connective tissue. Nd:YAG, laser-induced macular holes result in long term impairment of choroidal perfusion at the base of the hole due to choroidal scarring and obliteration of the choriocapillaris.

Purpose: To evaluate long term deficits in human color discrimination induced by accidental laser macular damage and assess potential for recovery of color vision deficits. Methods: Nine laser accident cases (Q-switched Neodymium) presenting initially with confined or vitreous macular hemorrhage were evaluated with the Farnsworth-Munsell 100 Hue test within 2 days to 3 months post exposure. Both total as well as partial errors in the blue/yellow (B/Y) and red/green (R/G) regions were assessed. Independent assessment of axis orientation and complexity were obtained via a Fourier series expansion of error scores. Comparisons of both total and partial B/Y and R/G errors were made with age matched normal subjects, idiopathic and juvenile onset macular holes. Confocal Scanning Laser Ophthalmoscopy and Optical Coherence Tomography characterized the presence of retinal traction, intraretinal scar, macular thickness and macular hole formation. Results: Comparison of exposed and non-exposed age matched individuals were significant (P<.001) for both total and partial errors. In four cases where macular injury ranged from mild scar to macular hole, color discrimination errors achieved normal levels in 1 to 12 months post exposure. A mild tritan axis, dominant B/Y ("blue/yellow") errors, and retinal traction were observed in a macular hole case. At 12 months post exposure, traction about the hole disappeared, and total and partial errors were normal. Where damage involved a greater degree of scarring, retinal traction and multiple injury sites, long term recovery of total and partial error recovery was retarded with complex axis makeup. Single exposures in the paramacula produced tritan axes, while multiple exposures within and external to the macula increased total and partial R/G ("red/green") error scores. Total errors increased when paramacular hole enlargement induced macular traction. Such hole formation produced significant increases in total errors, complex axis formation and increased amplitude in higher Fourier error expansion components. Conclusion: Color discrimination losses reflect the distribution of different cone systems in and about the macula and their selective loss. When secondary damage is minimal, color discrimination deficits recover within 12 months post exposure. When macular scarring and retinal traction are severe, recovery is significantly retarded. Laser induced macular holes may affect color discrimination less when retinal scar and traction are small but may become equivalent with that of idiopathic and juvenile species when scar and traction are severe.

Both human laser accident cases and non-human primate behavioral studies demonstrate the possibility of full visual acuity recovery following foveal laser injury. Current explanations of such recovery require suppositions of complex retinal reorganization dynamics or neural reorganization at higher order visual brain systems. However, recent investigation based on data of retinal photoreceptor and ganglion cell topography and connectivity, suggest that the amount of static inherent plasticity, already exists at the retinal level, may also explain visual acuity recovery in the presence of laser-induced foveal damage. Modeling the off-axis visual acuity while utilizing this data, produces a more gradual fall-off in visual acuity, and supports the notion that visual acuity recovery may reside in the topographical organization of the cones. Moreover, considering the filling-in phenomena, which can conceal the presence of retinal damage from being recognized, together with eye movements, could nullify scotoma, as long as the retinal damage is not too extensive.

In this study reports of laser injuries in all three military services (Air Force, Army and Navy/Marine) are compared. In collecting data for this study laser injury reports provided by Rockwell Laser Industries (RLI), the United States Army Medical Research Detachment of the Walter Reed Army Institute of Research which maintains the Laser Accident and Incident Registry (LAIR), the Food and Drug Administration's Center for Devices and Radiological Health (CDRH), and the three service Safety Centers. We found a total of 29 laser injury reports that met our case definition. Since 1965, when the first injury occurred, there have been 6 Air Force, 15 Army, and 8 Navy/Marine injuries reported. Statistical analysis of data analyzed thus far shows no difference between the services in 8-year risk groupings between 1965-2002.

Recently a review of multiple laser injury and accident databases was initiated. Last year we reported on preliminary findings in this area. This past year the search for laser injury and accident reports was expanded, and a significant number of additional laser incidents were located. The database from the Food and Drug Administration’s Center for Devices and Radiological Health was supplemented with more up to date information and non-medical laser incidents were added. Rockwell Laser Industries database was verified to not contain duplicates from the new information, as was the Army’s Laser Accidents and Incidents Registry. Information from the Federal Aviation Administration regarding laser accidents and incidents were also included. Incidents not resulting in laser specific injuries has been tracked. This information was not included in our previous report. In this study, case reports are used to show gross trends in laser injury, accident and incident reporting. This study is still in progress, and evaluation is incomplete.

In present paper the findings on chromosome mutations, the nature of damage and the repair of the cornea tissue after UV irradiation by excimer lasers at 193, 223 and 248 nm were made. Structural mutations induced by short-pulses UV irradiation were shown to be similar to spontaneous ones by the type, time of formation in the mitotic cycle and location of acentrics. Ten hours after irradiation of the cornea with doses of 0,09 to 1,5 J/cm² the incidence of cells with chromosome aberrations increased linearly with dose and amounted to 11,7% at 248 nm, 5,5% at 223 nm and 2,6% at 193 nm per 1 J/cm². No induced chromosome aberrations occurred 72 hour following irradiation. Within the dose range from 3,0 to 18 J/cm² the cytogenesis effect of radiation was less manifest than that with the doses mentioned above, the frequency of chromosome aberrations being independent of either radiation wavelength or radiation dose and amounted of 2,5 to 3,0%. Thus, large doses of powerful short-pulse UV radiation are safe according to the structural mutation criterion.

Damage from femtosecond mode-locked laser exposure (total exposure times longer than 20 microseconds) is predicted to be mediated by the same thermal mechanism found for continuous wave (CW) laser exposure. Experimentally, this trend holds true when comparing minimum visible lesions (MVL) from 0.25 s mode-locked and CW near-IR exposures in vivo. To further test this hypothesis in an in vitro setting we compared threshold values for cell death at various times post-exposure for mode-locked and CW 810-nm laser exposures. Using an artificially pigmented RPE cell culture system we show that damaging absorption of NIR laser light is directly related to the presence of melanin pigment granules, and that the damage thresholds for mode-locked and CW laser exposures are essentially the same for the pigmented cells. We additionally conclude that the artificially pigmented RPE cell cultures are a reasonable model system for the study of thermal and photomechanical forms of ocular laser tissue damage.

The threshold for laser-induced retinal damage in the rhesus eye was determined for wavelengths between 900 nm and 1300 nm. The laser source was a tunable Optical Parametric Oscillator (OPO) pumped by the 3rd harmonic of a Nd:YAG laser. The laser pulse duration was 3.5 ns. The wavelength dependence of the injury threshold is consistent with the prediction of a model based on the transmission of the preretinal ocular media, absorption in the retinal pigment epithelium, and variation of irradiance diameter resulting from chromatic aberration of the eye optics for wavelengths shorter than 1150 nm but was less consistent for longer wavelengths. The threshold for 24-hour observation was slightly lower than the threshold for 1-hour observation. These data form a basis for reexamination of the currently defined MPEs for wavelengths longer than 1100 nm.

With the advent of future weapons systems that employ high energy lasers, the 1315 nm wavelength will present a new laser safety hazard to the armed forces. Experiments in non-human primates using this wavelength have demonstrated a range of ocular injuries, including corneal, lenticular and retinal lesions, as a function of pulse duration and spot size at the cornea. To improve our understanding of this phenomena, there is a need for a mathematical model that properly predicts these injuries and their dependence on appropriate exposure parameters. This paper describes the use of a finite difference model of laser thermal injury in the cornea and retina. The model was originally developed for use with shorter wavelength laser irradiation, and as such, requires estimation of several key parameters used in the computations. The predictions from the model are compared to the experimental data, and conclusions are drawn regarding the ability of the model to properly follow the published observations at this wavelength.

The measurements on the nonlinear absorption coefficient for the whole retina and separated molecular components have been determined using open-aperture z-scan. Our recent retinal damage studies have shown that the threshold for retinal damage decreases below one nanosecond exposure. Laser-induced breakdown has been implicated in the threshold-level mechanism for damage, and the threshold is reduced below 100 fs where LIB is the damage mechanism. Our hypothesis for this experiment is that non-linear optical properties of the constituents of the retina will affect the absorption coefficient of the retina for ultrashort pulse laser exposure and lower the retinal damage threshold for these exposures. This suggests that nonlinear absorption effects should be considered in the analysis of any data that relate energy deposition rates from laser exposures in tissue to thermal or photomechanical damage mechanisms that explain cell death. We describe the impact of these measurements on retinal damage thresholds and damage mechanisms for various pulse regimes.

Corneal epithelial injury thresholds have been determined for exposures to 1.54 μm infrared radiation having durations from 1 to 100 sec and beam diameters from 0.5 to 7 mm. For 1 sec exposures, measured thresholds range from 12 W/cm² (5 mm diameter beam ) to 67 W/cm² (0.5 mm diameter). For 2 sec exposures, they range from 9 W/cm² (7mm diameter) to 57 W/cm² (0.5 mm diameter). For 10 sec exposures, they range from 3.7 W/cm² (7mm diameter) to 33 W/cm² (0.5 mm diameter). For 100 sec exposures, they are 1.4 W/cm² (7mm diameter) and 3.7 W/cm² (2mm diameter). The dependence of the measured thresholds on laser beam diameter provides strong evidence supporting a critical temperature damage model. These measured thresholds are greater than 10 times the maximum permissible exposure (MPE) in ANSI Z-136.5-2000.

In vitro exposures of explant rabbit corneas to single pulse 1540 nm infrared laser light operating at a pulse width of 0.8 milliseconds resulted in coagulative necrosis of both the corneal epithelium and stroma. Histomorphometric data correlated with increasing tissue radiant exposures. Histologic alterations in the corneal stroma were typical of matrix remodeling within the beam path and reactive to antibodies against matrix metalloproteinase-2. A two-dimensional electrophoretic analysis, using a mini-gel format, was developed to determine if specific corneal protein changes within tissue sections could be detected. Frozen sections taken through the center of the laser lesion were evaluated for proteomic data using tissue isoelectric focusing in the first dimension and polyacrylamide gel electrophoresis in the second dimension. Histomorphometric data describing the extent of the laser lesions were compared to the isoelectric points, molecular weights and relative densities of individual corneal proteins. Increasing radiant exposures of corneal tissues were associated with characteristic histomorphometric and proteomic changes.

The use of lasers in the infrared region between 1200-1400 nm has steadily increased in various industrial and commercial applications. However, there are few studies documenting damage thresholds for the skin in this region, and current laser safety standards are based on limited data. This study has determined preliminary skin damage thresholds for the Effective Dose for 50% probability (ED50) of a Minimum Visible Lesion (MVL) with laser exposure at 1314nm and 0.35 ms pulse width. An in-vivo pigmented animal model, Yucatan mini-pig (Sus scrofa domestica), was used in this study. The type and extent of tissue damage in the porcine skin was determined through histopathologic examination, and the findings are discussed. Finally, the results of this study were compared to other literature as well as to the existing ANSI Z136.1 (2000) standard for safe use of lasers.

The current laser safety standard for skin exposures, ANSI Z136.1, was based on a limited number of data points for various beam sizes at a few specific wavelengths. To help refine this standard, we explore the existence of a relationship between beam spot size and the ED50 lesion threshold values. In the first phase of this study we analyzed the spot size dependence of the skin lesion thresholds from previously documented experiments. We utilized the thermal skin model to predict damage thresholds and compared these with those presented in this paper. We report the results of this analysis , which we used to design an experiment to determine the true spot-size dependency of skin laser damage thresholds. The data collected in this first phase is discussed and compared to the existing ANSI Z136.1 (2000) laser safety standard.

For more than 10 years there have been discussions regarding the unexplainable significant variation of the ED50 attained with small changes in wavelength, found in the experimental results reported by the USAMRD-WRAIR. Previous studies showed that the probit analysis that was used to estimate the ED₅₀ occasionally yield unreliable results in the special case of data gathered in dose-respond laser-tissue experiment. A reanalysis the data of the USAMRD-WRAIR revealed significant subject’s dissimilarity that was not considered in the first analysis. However, though both the subjects dissimilarity and the potential of unreliable probit’s estimates could contribute to the spectral ED₅₀ variation, no satisfying analysis and expiation of spectral ED₅₀ has yet been suggested. A new analysis method that inherently incorporates physical and statistical models will be presented. This method enables the identification of the laser damage mechanism and suggests a new spectral ED₅₀. The method can, then, also disclose questionable data sections, which neither complies with the data majority nor follows physical causality.

The U.S. Dept. of Defense (DOD) is currently developing and testing a number of High Energy Laser (HEL) weapons systems. DOD range safety officers now face the challenge of designing safe methods of testing HEL's on DOD ranges. In particular, safety officers need to ensure that diffuse and specular reflections from HEL system targets, as well as direct beam paths, are contained within DOD boundaries. If both the laser source and the target are moving, as they are for the Airborne Laser (ABL), a complex series of calculations is required and manual calculations are impractical. Over the past 5 years, the Optical Radiation Branch of the Air Force Research Laboratory (AFRL/HEDO), the ABL System Program Office, Logicon-RDA, and Northrup-Grumman, have worked together to develop a computer model called teh Laser Range Safety Tool (LRST), specifically designed for HEL reflection hazard analyses. The code, which is still under development, is currently tailored to support the ABL program. AFRL/HEDO has led an LRST Validation and Verification (V&V) effort since 1998, in order to determine if code predictions are accurate. This paper summarizes LRST V&V efforts to date including: i) comparison of code results with laboratory measurements of reflected laser energy and with reflection measurements made during actual HEL field tests, and ii) validation of LRST's hazard zone computations.

The US Food and Drug Administration, Center of Devices and Radiological Health issued Laser Notice 50 in July 2001. This Notice is a preliminary step that FDA has taken to harmonize US regulations for laser products (21 Code of Federal Regulations) with the IEC (International Electrotechnical Commission) standards for Safety of Laser Products. The paper discusses rationale for the changes and describes some of the implementation issues, including comparisons between the current standards. The impact on the regulated industry and the user community is that the same laser hazard classification scheme is used and that engineered safety features are consistentin the world markets.

Sunglasses are widely sold for visual comfort in bright sunlight and for cosmetic purposes. Few people select sunglasses with any thought of protection of their eyes and vision. Nevertheless, standards organizations attempt to provide certain optical requirements to minimize risk from excessive UV exposure. Many sunglass manufacturers claim certain benefits of UV protection. However, these standards focus on the spectral properties of the filter lenses and generally ignore the frame. Recent research has shown that the design of the sunglass frame plays an important role in solar protection of the eyes.

The measured optical density of various laser eye protection samples is presented as a function of irradiance using femtosecond laser pulses. We show that the protective quality of some eyewear degrades as irradiance increases. In previous studies this problem has been demonstrated for samples irradiated by nanosecond pulses, but the current study shows that some modern laser eye protection seems to be robust except for the irradiance level possible with ultrashort laser pulse exposure. We discuss the most likely saturation mechanisms in this pulse duration regime and its relevance to laser safety.

A new technique is described where laser safety glasses are based on optical distortion of the phase of the laser transmitted through the safety glasses. The glass contains an absorber at the laser wavelength, which heats the glass and therefore changes its index of reflection. The uniqueness of the concept presented is the layout of the absorber and its dependence on the transverse dimensions of the safety glass. Because the absorption varies across the glass, the absorbed power varies and therefore the change in index of refraction also varies. This variation in the optical property causes distortion and a reduction of "coherence" of the laser beam. By combining the phase distortion with absorption, the laser safety glasses can be designed to protect the retina at low intensities and once the phase distortion becomes important at intermediate intensities, it dominates at all higher intensities. These Phase Distortion Safety Glasses are designed to protect the retina from quasi cw lasers at all wavelengths - the near UV, visible, and near IR and the visible light transmission is equal to three percent. Once the threshold is reached the phase distortion will never allow the retina to be damaged no matter how high the laser intensity. These glasses also allow the operator to see the laser beam that is being protected against.

Currently there are no universally accepted functional diagnostics and treatments for laser eye injury. The multifocal electroretinogram (MERG) determines the function of several areas of the retina simultaneously. The objective of this research is to determine if the MERG is sensitive enough to provide a functional assessment of retinal laser lesions that correlates to established contrast sensitivity/visual acuity tests currently in use. The Visual-Evoked Response Imaging System (VERIS) Clinic^TM, a MERG system with continuous visualization of the fundus, was used to record from normal rhesus monkeys. The MERG mapping of the rhesus monkeys was localized to the macula and centered on the foveal region. The recordings yielded three waveforms for each of the 103-recorded responses. A difference was seen in all of the waveform mean amplitudes with the human normal values being one and one-half times as large for the first, twice as large for the second and four times as large for the third waveform. This may be due to a much lower number of subjects for recording (5 Rhesus versus 48 human recordings) or the monkey retina may, in fact, produce lower amplitude retinal responses. This on-going project is expanding research to include the functional assessment of laser retinal injury through the use of the MERG with the intent of correlating the function to currently used behavioral metrics of the visual system.

INTRODUCTION: The amount of visual disruption experienced by individuals exposed to a visible laser source at levels, which are below that, which will damage the cornea or retina will depend on laser exposure parameters and task demands. Previous work has evaluated the effects of wavelength, duration, ambient light level, and target variables. One factor that has not received attention is monocular vs. binocular exposure. Whether the exposure is monocular or binocular may alter pupil dynamics, eyelid closure, and ultimately affect visual performance. METHODS: In this study 10 males and females were exposed to 0.1 and 3.0 sec laser flashes while tracking a dynamic target at 0.28 deg/sec through a scope that was capable of selecting binocular or monocular viewing. Bright (430 nits) and dawn/dusk (4.3 nits) ambient light conditions were simulated using ND filters. A collimated 514.5 nm argon laser beam produced corneal radiant exposures of 0.16 and 1.0 mJ/cm2 for the 0.1 and 3.0 sec conditions respectively. For each flash trial total time off target and maximum absolute error scores were calculated. Eye response (changes in pupil diameter) was assessed by evaluation of videotape from an IR eye camera. Tracking error scores (total time off target) were calculated for each flash trial. RESULTS: Analysis of variance results for the total time off target scores found all three main factors (light level, exposure duration, and monocular/binocular to be significant. Earlier studies have previously shown dawn/dusk flash exposures be more disruptive than bright light trials. Also three sec exposures were more disruptive than one sec exposures. Finally, monocular exposures produced significantly higher error scores than did binocular exposures. For the pupil diameters the post-flash diameters were significantly smaller that the pre-flash diameters and monocular diameters larger that binocular pupil sizes. SUMMARY: The Total Time Off Target error scores for the monocular viewing condition were significantly higher than the binocular viewing condition supporting bilateral summation contributions to binocular tracking. Pupil recovery diameters were approximately 84% of baseline for monocular viewing regardless of ambient light level and flash duration. Binocular viewing conditions yielded an average 75% pupil recovery. Continuing analysis of the pupil data precludes us from making a more definitive statement.