Retinal damage thresholds from single-pulse laser exposures in the visible spectrum

The risks of using lasers, particularly ocular hazards, have called for the definition of exposure limits. Our investigations involved the retinal effects of the laser beam in the visible spectrum and were directed toward verifying the limit values by defining the thresholds of retinal damage in experiments carried out on the rabbit and the monkey. The wavelengths emitted by the experimental set-ups were 593 and 532 nm, the pulse durations were 600 and 40 ns, and the retinal image diameter varied from approximately 30 to 570 microns. A direct ophthalmoscopic observation and a method using fluorescein angiography were employed to detect a pathologic change in the retina. The energy correlates of retinal lesions were statistically analyzed by a method of probit analysis. The results showed that determining funduscopic thresholds is chiefly a function of the investigation technique used and the delay in observation after the exposure. Our results obtained with fluorescein angiography extrapolated to the human eye support the exposure limit established for intrabeam viewing, but not for an extended source laser which corresponds to a probability of damage increasing with the retinal image diameter. The exposure limit related to the experimental retinal spot size of 285 and 570 microns corresponds to damage probabilities of 7% and 32%, respectively.     

Retinal injury thresholds for blue wavelength lasers

The interaction mechanism leading to laser-induced retinal alteration can be thermal or non-thermal, depending upon the wavelength of the laser radiation and the duration of the exposure. To investigate the effect of exposure duration on the interaction mechanism, retinal injury thresholds in the rhesus monkey were experimentally measured for exposure to laser radiation at wavelengths of 441.6, 457.9, 476.5, and 496.5 nm. Exposure durations were 0.1, 1, 5, 16, and 100 s; and 1/e retinal irradiance diameters were 50, 125, and 327 microm. Tissue response was observed via ophthalmoscope 1 h and 48 h post exposure. Thermal and non-thermal damage thresholds were obtained depending upon the exposure duration. These threshold data are in agreement with data previously reported in the literature for 100-s duration exposures, but differences were noted for shorter exposures. The current study yielded an estimated injury threshold for 1-s duration, 327-microm retinal irradiance diameter exposures at 441.6 nm, which is an order of magnitude higher than that previously reported. This study provides evidence that laser-induced retinal damage is primarily induced via thermal mechanisms for exposures shorter than 5 s in duration. Arguments are presented that support an amendment of the thermal hazard function, R(lambda).     

Simultaneous Exposure Using 532 and 860 nm lasers for visible lesion thresholds in the rhesus retina

The growth of commercially available, simultaneous multi-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 ED50 values, and these thresholds at 24 h varied from 5.6 mW to 17 mW total intraocular power.     

The effect of ocular aberrations on retinal laser damage thresholds in the human eye

For the dark-adapted human eye the diffraction limited retinal image is approximately 2.8 microm in diameter for green light, although the estimation of the size of the retinal image resulting from the incidence of a collimated beam on the cornea is problematical and has been estimated to be anywhere from 10 to 30 microm. The resolution of this difference is important for the accurate determination of the retinal hazards of optical sources and for setting safety limits for laser-retinal exposure. Using literature results for the aberrations measured in a population of healthy young adults, beam propagation calculations of retinal images are presented for different pupil diameters. Using the concept of a generalized Strehl ratio, retinal damage thresholds, EDx, are derived for exposures in the thermal confinement regime (exposure times approximately less than 10 micros). The most vulnerable eyes are predicted to be those with pupil sizes 2-3 mm such as would be found under daylight illumination. The results also suggest that populations with particularly small ocular aberrations and correspondingly high visual acuity may be significantly more vulnerable than a "normal" population.     

Wavelength dependence of ocular damage thresholds in the near-ir to far-ir transition region: proposed revisions to MPES

This report summarizes the results of a series of infrared (IR) laser-induced ocular damage studies conducted over the past decade. The studies examined retinal, lens, and corneal effects of laser exposures in the near-IR to far-IR transition region (wavelengths from 1.3-1.4 mum with exposure durations ranging from Q-switched to continuous wave). The corneal and retinal damage thresholds are tabulated for all pulsewidth regimes, and the wavelength dependence of the IR thresholds is discussed and contrasted to laser safety standard maximum permissible exposure limits. The analysis suggests that the current maximum permissible exposure limits could be beneficially revised to (1) relax the IR limits over wavelength ranges where unusually high safety margins may unintentionally hinder applications of recently developed military and telecommunications laser systems; (2) replace step-function discontinuities in the IR limits by continuously varying analytical functions of wavelength and pulsewidth which more closely follow the trends of the experimental retinal (for point-source laser exposures) and corneal ED50 threshold data; and (3) result in an overall simplification of the permissible exposure limits over the wavelength range from 1.2-2.6 mum. A specific proposal for amending the IR maximum permissible exposure limits over this wavelength range is presented.     

Ultraviolet-induced photochemical damage in ocular tissues

Exposure to ultraviolet (UV) lasers may result in pathology to either the cornea, lens or retina of the primate eye. The particular combination of exposure parameters (wavelength, peak power, pulsewidth, pulse repetition rate, and total energy delivered) determines the primary target tissue(s) in each instance. The effect may be acute or chronic, and the implicated damage mechanism may be categorized as photochemical, photoablative or thermal. This paper summarizes a number of specific cases where UV laser radiation affected one or more of the ocular tissues, describes the nature of the pathologies, and indicates what is known about the damage mechanism in each case. Ranges of exposure parameters where each ocular tissue is the most sensitive are defined. The cornea is most sensitive via a photochemical damge mechanism in the 260- to 280-nm range, where the threshold dose is approximately 5 mJ cm-2. For near-UV wavelengths (320-400 nm), different target molecules absorb the radiation and are susceptible to less efficient photochemical damage mechanism yielding corneal thresholds in the range of 10-100 J cm-2. However, we report acute cataract induction following exposure to a 337-nm nitrogen laser at 1 J cm-2 when the energy is delivered in a 10-ns pulse. Further, with longer pulsewidths (approximately 1 s) of comparable wavelength, retinal lesions were induced when 0.28 J was delivered to the eye. The data suggest that the acute lens effect is the result of a thermal mechanism, whereas the UV-induced retinal lesions result from a photochemical insult to the photoreceptors. Data presented include the action spectra for far- and near-UV-induced ocular damage, the pulsewidth and total energy dependencies of ocular thresholds, cumulative effects of repeated exposures, and repair or recovery rates.     

Retinal damage induced by red diode laser.

Widespread use of compact, low-cost diode lasers (pointers and illuminators) has ushered in an era where large numbers of the general public are accidentally or deliberately exposed to low-power laser radiation. The objectives of this study are both to determine the primate retinal lesion threshold for exposure to 650 nm diode laser radiation and to examine the risks of retinal damage from low-level (sub-threshold) ocular exposures. To this end, the ED50 and ED10 damage thresholds, their fiducial limits, and the slopes of the probability vs. dose curves have been examined in detail. In addition to conventional fundoscopy, exposed eyes were examined by confocal scanning laser ophthalmoscopy, fluorescein angiography, and histopathology at both the light and electron microscopic levels in attempts to discern tissue disruption following exposures below the ophthalmoscopic ED50 threshold dose. These alternative observation techniques did not identify detectable tissue disruption following exposures below the ophthalmoscopic lesion threshold dose.     

Excess risk of head and chest colds among teachers and other school workers

BACKGROUND: Work‐related injuries and illnesses in the educational services sector have not been well studied. This analysis examined whether teachers and other school workers are at higher risk of head/chest cold compared to all other workers in the United States. METHODS: Seven years (1998‐2004) of National Health Interview Survey data on currently employed workers were combined to provide a basis for estimating the incidence proportion of head/chest cold. RESULTS: The adjusted odds ratio for head/chest cold was significantly elevated for teachers and other workers employed at schools compared to all other workers. When examined by month, an excess of increased head/chest cold risk during the school year suggested that a portion of head/chest cold among teachers and other school workers is attributable to their workplace, perhaps due to close contact with students at school. CONCLUSION: Head/chest cold, a surrogate for acute respiratory infection, was more common among school workers during the school year and less common during July than for all other workers in the United States. Targeted training for school workers and students may be beneficial to reduce work‐related exposure to viruses and bacteria that infect the respiratory system.     

Blueberry anthocyanins: protection against ageing and light-induced damage in retinal pigment epithelial cells

Retinal pigment epithelium (RPE) cells are vital for retinal health. However, they are susceptible to injury with ageing and exposure to excessive light, including UV (100-380 nm) and visible (380-760 nm) radiation. To evaluate the protective effect of blueberry anthocyanins on RPE cells, in vitro cell models of replicative senescent and light-induced damage were established in the present study. After purification and fractionation, blueberry anthocyanin extracts (BAE) were yielded with total anthocyanin contents of 31·0 (SD 0·5) % and were used in this study. Replicative senescence of RPE cells was induced by repeatedly passaging cells from the fourth passage to the tenth. From the fifth passage, cultured RPE cells began to enter a replicative senescence, exhibiting reduced cell proliferation along with an increase in the number of β-galactosidase-positive cells. RPE cells maintained high cell viability (P < 0·01) and a low (P < 0·01) percentage of β-galactosidase-positive cells when treated with 0·1 μg/ml BAE. In contrast, after exposure to 2500 (SD 500) lx light (420-800 nm) for 12 h, RPE cells in the positive control (light exposure, no BAE treatment) exhibited premature senescence, low (P < 0·01) cell viability and increased (P < 0·01) vascular endothelial growth factor (VEGF) release compared with negative control cells, which were not subjected to light irradiation and BAE exposure. Correspondingly, BAE is beneficial to RPE cells by protecting these cells against light-induced damage through the suppression of ageing and apoptosis as well as the down-regulation of the over-expressed VEGF to normal level. These results demonstrate that BAE is efficacious against senescence and light-induced damage of RPE cells.     

A prospective cohort study of retinal arteriolar narrowing and mortality

The authors examined the relation of narrowed retinal arteriolar diameters, a marker of hypertensive damage, to mortality in a population-based cohort of 4,926 persons aged 43-84 years living in Wisconsin. A computer-assisted method was used to measure retinal vessel diameters from digitized retinal photographs taken at the baseline examination (1988-1990). These measurements were summarized as the retinal arteriole-to-venule ratio (AVR), with a smaller AVR indicating narrower arterioles compared with venules. Its relation to 10-year mortality was analyzed by using Cox proportional hazards models, adjusting for age, gender, blood pressure, diabetes, and other risk factors. No relation was found between smaller AVR and increased mortality. In relation to the largest AVR quartile, the adjusted relative risks of all-cause mortality were 0.93 for the smallest AVR quartile, 0.71 for the second AVR quartile, and 0.80 for the third AVR quartile. Results were largely similar in analyses of cause-specific mortality (vascular disease and non-vascular-disease mortality) and in subgroups stratified by age, gender, and diabetes and hypertension status. These data contrast with recent studies showing a relation between narrowed retinal arterioles and increased cardiovascular risk, suggesting that further research is needed to understand the systemic associations of retinal microvascular changes.     

Ocular injuries from accidental laser exposure

This report presents 29 cases of ocular injury (31 eyes) caused by accidental laser exposure. Twenty-eight eyes were injured during laser adjustment and alignment. Nineteen eyes were damaged by Q-switched lasers at a wavelength of 1064 nm. Macula damage occurred in 25 eyes. During the early phase after injury, there were different degrees of retinal coagulation, edema or hemorrhage in exposed spots and there occurred immediate reduction of visual acuity. Effusion of blood and exudate was absorbed in most injured eyes under treatment lasting several weeks; meanwhile, gray-white scars appeared. Macular holes appeared in seven cases a week after injury, thus extending the course of the injury. Nine cases (10 eyes) were followed-up for 4-10 y, during which time the condition of eight cases (nine eyes) remained stable. The causes of the laser accidents and the relationship between the damage effects and exposure doses were analyzed.     

Evaluation of a workplace cardiovascular health promotion programme in the Republic of Ireland

This paper describes a comprehensive evaluation of the organizational impact of a workplace health promotion programme, in the context of a framework devised by Nutbeam in 1998. The Happy Heart at Work programme, sponsored by the Irish Heart Foundation, has been in existence for 10 years and aims to promote a healthy lifestyle through specially devised modular materials. A postal census survey of 785 valid registered sites expressing any level of initial interest in the programme yielded a 40% response rate (n = 311). Of these, 194 (63%) were currently active and 114 were not. Active organizations were less likely to be Irish owned (54.5% versus 71.4%, p < 0.05), and more likely to operate in shifts (72.3% versus 51.1%, p < 0.05) or to have an occupational physician amongst the staff (36.9% versus 31%). Programme impact within active organizations, based on pre-defined Health Promoting Workplace parameters, was documented. There was agreement in the questionnaire responses that participating organizations promote a smoke-free environment (mean rating on five-point scale = 4.42), employee health and well-being (4.21) and good nutritional practice (4.11). Triangulation of research methods, including a telephone survey of gatekeepers from within organizations (n = 18), focus groups with participant employees (n = 42) and a review of the staff opinions of the facilitating organization on the programme, all showed strong concordance with respect to the strengths and weaknesses of Happy Heart at Work. The programme was felt to help improve employees' lifestyle habits and morale, as well as the company's public image. The main drawbacks of the programme were its relatively low profile, even in actively participating organizations, and the fact that it was not seen to be independently sustainable without intensive and ongoing support.     

Ultraviolet Lamps for Room Air Disinfection

Studies of the efectiveness of upper air ultra violet (UV) radiation against artificially generated bacterial aerosols were conducted in a laboratory test room with an 8 foot 6 Inch ceiling; the room was ventilated with six air changes per hour (ch/hr). At or below the five-foot level in the room, reflected UV radiation ranged from 0.02; to 2.6μw/sq cm, in the upper portion of the room, direct UV radiation ranged from about 10 to 150μw/sq cm. The test organism was late-log-phase Serratia marcescens in aerosols with single viable cells per particle; count median diameters (CMD) of 2.7μ and 5.2μ were generated With the 2.7μ and 5.2μ CMD aerosols, equivalent added! sanitary ventilation of 39 ch/hr and 18 ch/hr were produced, respectively; these values are meaningful improvements in sanitary ventilation.     

Evaluation of erythemal UV effective irradiance from UV lamp exposure and the application in shield metal arc welding processing

Ultraviolet radiation (UVR) exposure is known to cause potential effects such as erythema in skin. For UV-induced erythema (sunburn), the action spectrum from the Commission Internationale de l'Eclairage, International Commission on Illumination (CIE) was adopted. Erythemal UV effects from UVR lamp exposure were investigated with commercial spectroradiometry devices in this research. Three kinds of portable UV germicidal lamps with broadband UVA (BB UVA, 350-400 nm), broadband UVB (BB UVB, 280-350 nm), and narrowband UVC (NB UVC, 254 nm) wavelengths served as the UVR emission sources. An action spectrum expresses the effectiveness of radiation for assessing the hazard of UVR in the erythemal action spectrum from 250-400 nm. The UV Index (UVI) is an irradiance scale computed by multiplying the CIE erythemal irradiance integral in milliwatts per square meter by 0.04 m mW. A comprehensive approach to detecting erythemal UVR magnitude was developed to monitor the effective exposure from UV lamps. The erythemal UVR measurement was established and the exposure assessment was applied to monitor erythemal UVR magnitude from shield metal arc welding (SMAW) processing. From this study, the erythemal UVR exposures were assessed and evaluated with environmental solar simulation of the UVI exposure.     

Damage thresholds of skin irradiated by ultraviolet lasers

The effects of pulsed radiation on animal models were studied. Erythemic responses to laser radiation were observed macroscopically and were examined histologically by both light and electron microscopy. Based on statistical analysis of the biological data presented in this study, skin damage thresholds were calculated for short pulses with lasers at wavelengths of 265 nm and 308 nm.     

微波对体外培养视网膜神经细胞损伤的光镜与电镜观察

为了探讨２４５０ＭＨｚ微波对眼底的损伤，采用体外培养视网膜神经细胞，按微波强度分为３组进行微波辐照１ｈ，进行光镜和透射电镜观察。结果表明，３０ｍＷ／ｃｍ＾２微波辐照可使视网膜神经细胞发生凋亡，６０ｍＷ／ｃｍ＾２微波辐照可导致细胞坏死。可见，微波可损伤体外培养的视网膜神经细胞，诱发细胞凋亡，随着微波辐照强度的增大，损伤程度加重。     

Ozone-related fluorescent compounds in mouse liver and lung

Groups of ten female, weanling mice were fed a basal, vitamin E-deficient diet or a basal diet supplemented with RRR-alpha-tocopheryl acetate for 14 months. During the last month one group from each dietary regimen was exposed for 30-60 min/day to 1.5 ppm ozone (25 hr total ozone exposure) and the remaining groups to control ambient air. The liver and lung tissues were homogenized and extracted with 2:1 chloroform:methanol and water. The water-soluble and organic solvent-soluble fluorescent materials were separated on Sephadex G-25 and LH-20 columns, respectively. Excitation and emission wavelengths for the eluting fractions were determined by continuous emission scans from 250 to 600 nm for each excitation wavelength between 250 and 500 nm (in increments of 25 nm). Ozone exposure did not effect the concentration of any of the fluorescent materials examined in the lung, but it resulted in a significant increase in two of four water-soluble compounds in the liver with excitation wavelength maxima/emission wavelength maxima of 270 nm/310 nm and 275 nm/350 nm (smaller molecular weight material) suggesting in vivo lipid oxidation.     

Time course and spacial distribution of UV effects on human skin in organ culture

Apoptosis plays an important role in eliminating cells from populations when cells have been exposed to UV irradiation and damaged. Studies of cells in culture have provided some details of the mechanisms involved when stress response genes act after exposure to UV irradiation and other environmental stresses. However, little is known about the responses of intact sections of human skin growing in organ culture to UV irradiation. In the work reported here, it was found that the response of organ-cultured human skin after exposure to UV irradiation is different than the response of cultured cells. At wavelengths below 300 nm, the action spectrum obtained from organ-cultured skin samples showed a lower sensitivity than that observed at 300 nm, indicating that the overlying stratum corneum and upper epidermal cell layers had probably caused a selective absorption of incident UV radiation at some wavelengths. At 3 hours after UV irradiation, p53 was phosphorylated at Ser 15 and Ser 46, and accumulated in the cell nuclei, notably after exposure to 280-320 nm wavelengths. Accumulations of Bax, active Caspase-3 and cleaved PARP were detected in apoptotic cells at 24 hours post-exposure, along with a reduction of Bcl-2 levels, notably after exposure to 300-365 nm light. This difference in apoptotic responses may result from the characteristics of the different irradiation wavelengths used, and from details in the skin's structure. The data obtained in this study using an organ-culture system utilized direct measurements of the biological effects of different wavelengths of UV lights.     

Reducing occupation-based disparities related to tobacco: roles for occupational health and organized labor

BACKGROUND: Persistent and growing occupation-based disparities related to tobacco pose a serious public health challenge. Tobacco exacts a disproportionate toll on individuals employed in working class occupations, due to higher prevalence of smoking and exposure to secondhand smoke among these workers compared to others. METHODS: We provide an overview of recent advances that may help to reduce these disparities, including research findings on a successful social contextual intervention model that integrates smoking cessation and occupational health and safety, and a new national effort to link labor unions and tobacco control organizations around their shared interest in reducing tobacco's threat to workers' health. CONCLUSIONS: Implications of these efforts for future research and action are discussed.