TTT: local light absorption and heat convection versus heat conduction.
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Animals↗
Biomedical subjects
D H Sliney
Publications and source records attributed to D H Sliney.
Do blue light filters confer protection against age-related macular degeneration?
Age-related macular degeneration (AMD) is a major health problem in the developed world accounting for approximately half of all blind registrations. Current treatment options are unsuitable for the majority of patients and therefore the identification of modifiable risk factors that may inform disease prevention programmes is a priority. This review evaluates the long-held belief that blue light exposure has a role in the pathogenesis of AMD. Laboratory evidence has demonstrated that photochemical reactions in the oxygen-rich environment of the outer retina lead to the liberation of cytotoxic reactive oxygen species (ROS). These ROS cause oxidative stress which is known to contribute to the development of AMD. The precise chromopore that may be involved in the pathogenesis of AMD is unclear but the age pigment lipofuscin is a likely candidate. Its aerobic photoreactivity and adverse effects on antioxidant activity combined with its gradual accumulation over time suggests that its in vivo phototoxicity increases with age despite changes in the absorption characteristics of the crystalline lens. Evidence from animal studies confirms blue light's damaging potential but the results are not directly applicable to macular degeneration in humans. Studies of human macular pigment density and the risk of AMD progression following cataract surgery lend further weight to the hypothesis that blue light exposure has a role in the pathogenesis of AMD but the epidemiological evidence is equivocal. On balance the evidences suggests but does not yet confirm that blue light is a risk factor for AMD. Given the socio-economic impact of this disease and urgent need to identify modifiable risk factors, future work should include a large-scale clinical trial to evaluate the effect of blue blocking filters on AMD progression rates.
Animals↗
Photoprotection of the eye - UV radiation and sunglasses.
Although most health scientists now agree that health risks to the skin (e.g., skin cancer) exist from exposure to the ultraviolet radiation in sunlight, a scientific consensus has not really been achieved vis-à-vis sunlight and ocular health. A growing number of scientists warn of hazards to the eye if ultraviolet radiation - and perhaps even shorter wavelength visible radiation also - is not filtered by lenses. Despite a substantial literature on the adverse effects of ultraviolet radiation (UVR) and intense light upon ocular structures, particularly upon the retina, controversy still surrounds the question of whether the levels of natural and man-made light sources are damaging when encountered under normal viewing conditions. Although scientific evidence accumulates to indicate that chronic exposure conditions may accelerate ageing processes in ocular tissues, the quantitative question of "How much is safe?" remains to be answered conclusively.
Environmental Exposure↗
UV doses of Americans.
The UV doses of Americans were never measured, but are needed for assessing the risks of UV-related health effects. We calculated these doses using a novel approach. The Environmental Protection Agency's (EPA) National Human Activity Pattern Survey (NHAPS) recorded the activity profiles of 9386 Americans over 24 months to assess their exposure to environmental pollutants, one of which is UV radiation. NHAPS used randomized telephone interviews to get their previous day's minute-by-minute activities. From NHAPS we extracted only the outdoor-daylight data of the northern and southern indoor workers (95%), stratifying by season, sex and age (0-21, 22-40, 41-59 and 60+ years) to find the average time Americans spend outdoors. Knowing the total daylight time and that while outdoors Americans are exposed to about 30% of the available solar UV (on a horizontal plane), we calculated their percent ambients. The average American's percent ambients are 2.6 and 2.5% for northern and southern females, respectively, and 3.5 and 3.6% for northern and southern males, respectively. Men over 40 years of age have the highest ambients (4%). From their ambients we calculated their annual doses using seasonal averages of UV measurements taken daily for over 2 years by EPA Brewer spectrophotometers located in four quadrants of the United States: Atlanta, GA; Boston, MA; Bozeman, MT and Riverside, CA. The average erythemal UV doses of Americans are about 25,000 J/m2/year, 22,000 for females and 28,000 for males, or 33,000 J/m2/year including a conservative continental U.S. vacation (7800 J/m2). Thus, we can now assess the risks of UV-related health effects for Americans.
Adolescent↗
Retinal image motion during deliberate fixation: implications to laser safety for long duration viewing.
With the easy attainability of hand-held laser devices and the burgeoning light emitting diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with quantifying the effect of head and eye movements on the distribution of energy over the retina. This experiment describes target motion over the retina as a result of head and eye movements during a deliberate fixation task. Volunteers deliberately fixated, with (fettered) and without (unfettered) head and chin rest support, on LEDs that subtended a 0.1 min of arc visual angle. A Dual Purkinje Image Eyetracker measured eye position during each 100-s fixation trial. The data showed an elliptical retinal energy distribution, oriented on the temporal/ nasal retinal axis, with a major axis 1.5 times greater than the minor. The average half-maximum diameter for the major axis was 40 microm for the fettered and 107 microm for the unfettered condition. The retinal area illuminated from head and eye movements showed a positive linear relationship with time. Peak retinal radiant exposure at 100 s was reduced by a factor of 10 as a result of eye movements and by a factor of 30 as a result of head and eye movements. Although the net result was a reduction in radiant exposure from a "no-movement" baseline, the distribution of energy over the retina was well within the 200 microm foveal boundary. The data suggest that the laser permissible exposure limits for long term viewing of a small continuous wave source include a factor that adjusts for this reduction in retinal radiant exposure with time.
Adult↗
Optical radiation safety considerations for ocular glucose monitoring.
The potential for noninvasive detection of blood glucose is an area of intense academic and commercial research and a subject of keen interest in the diabetic and healthcare communities. A number of techniques are under investigation that attempt to infer blood glucose levels from measurements of optical signals. Frequently, these techniques are based on laser sources that may, under certain circumstances, be capable of inducing ocular injury. This article provides an overview of ocular damage mechanisms and the international standards for laser exposure limits that have been developed. The application of relevant standards to specific implementations of lasers in optical glucose sensing is presented. In addition, the concept of risk versus benefit for consideration of new medical devices is also discussed.
Animals↗
Geometrical assessment of ocular exposure to environmental UV radiation--implications for ophthalmic epidemiology.
Epidemiological studies of the influence of environmental ultraviolet radiation (UVR) in the development of cataract, pterygium, droplet keratopathies and age-related macular degeneration have produced inconsistent findings. The lack of consistent results may be due largely to either incomplete or erroneous estimates of outdoor UV exposure dose. Geometrical factors dominate the determination of UVR exposure of the eye. The degree of lid opening limits ocular exposure to only those rays entering at angles near the horizon. Clouds redistribute overhead UVR to the horizon sky. Mountains, trees and building shield the eye from direct sky exposure. Most ground surfaces reflect little UVR. The result is that the highest UVR exposure occurs during light overcast where the horizon is visible and ground surface reflection is high. By contrast, exposure in a high mountain valley with green foliage results in a much lower ocular dose. Other findings of these studies show that retinal exposure to light and UVR in daylight occurs largely in the superior retina.
Animals↗
Intercomparison of effective erythemal irradiance measurements from two types of broad-band instruments during June 1995.
The biologically effective global solar ultraviolet radiation (UVR) measurements from a multiband UVR monitor and a conventional broadband UVR monitor are compared. The measurements were performed during the varied weather conditions of June 1995. We compared the daily total exposures measured by both instruments, as well as the ratio of the measured doses throughout the course of each day. The daily total exposures agreed within approximately 11% throughout the month. The ratio between the measured doses held at 1.12 between 0900 and 1700 h (solar zenith angles approximately 16-52 degrees). The ratio decreased from 1.12 to 0.90 during the next 90 min outside that period (solar zenith angles approximately 52-72 degrees) and decreased further beyond that point. Spectral response and cosine response mismatch between the instruments are discussed as the possible cause of discrepancies between the measured doses. Implications for erythemal irradiance monitoring and suggestions for further study are discussed.
Erythema↗
Optical radiation safety of medical light sources.
The phototoxicity of medical ultraviolet (UV) sources used in dermatology has long been recognized. Less obvious are potential hazards to the eye and skin from many other optical sources-both to the patient and to the health-care worker. To assess potential hazards, one must consider not only the optical and radiometric parameters of the optical source in question but also the geometrical exposure factors. This knowledge is required to accurately determine the irradiances (dose rates) to exposed tissues. Both photochemically and thermally induced damage are possible from intense light sources used in medicine and surgery; however, thermal injury is rare unless the light source is pulsed or nearly in contact with tissue. Generally, photochemical interaction mechanisms are most pronounced at short wavelengths (UV) where photon energies are greatest, and also will be most readily observed for lengthy exposure durations.
Diagnostic Imaging↗
Ocular exposure to environmental light and ultraviolet--the impact of lid opening and sky conditions.
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Adult↗
Evolving issues in laser safety.
The approach to laser safety has come a long way since the 1960s when the first guidelines were issued by defense research organizations in the US and the UK, and then by the American Conference of Governmental Industrial Hygienists. Although the search for 'eye-safe' numbers continues in a few laboratories, this work is almost exclusively centered on deriving retinal thresholds for ultra-short (sub-nanosecond) lasers. Setting limits in this temporal region has been difficult, since there are conflicting data sets and there is a limited amount of data to extrapolate to other spectral regions. In the standards arena, the concentrated efforts have been in terms of product classification and attempts to resolve the eternal question of 'how safe is safe?'. Recent efforts to revise safety standards have not always taken into account the historical rationale for the maximum permissible exposures and forget that safety factors were already factored into the limits and further safety factors are quite unnecessary. Finally, the study of accidents raises the question of whether our approach to eye protection and enclosures are adequate and whether separate standards and guidance is needed for different applications.
Equipment Design↗
Laser safety.
Safety has always been an important aspect of any laser application in surgery and medicine. In any review of the laser surgery literature, several issues continue to dominate. These issues include: wearing eye protectors, dealing with the plume of vaporized tissue, and controlling potential fire hazards. No one denies that lasers can pose a serious hazard to the eye, but the decision to wear eye protectors in all procedures has been frequently questioned. The degree of effort needed to minimize the very serious risk from chronic breathing of vaporized tissue also requires judgment. Aside from a few eye injuries from a laser beam exposure, most serious accidental injuries (and even deaths) reported to date from the laser beam itself can be traced to the ignition of surgical drapes and airway tubes.
Humans↗
UV radiation ocular exposure dosimetry.
There is currently some degree of controversy as to the magnitude of cataract and other ocular diseases related to human lifetime exposure to UV radiation (UVR). Concerns about the depletion of stratospheric ozone and the related increase in terrestrial UVR exposure have emphasized the importance of resolving this controversy. A careful study of ocular exposure to environmental sunlight demonstrates that it is not simple to determine accurately the level of solar UVR exposure of the human eye. Past attempts to measure or calculate UVR exposure of the eye have generally relied on the measurement of ambient UVR in sunlight with global monitors. Unfortunately, such attempts have seldom assessed properly the large role of ground reflection, the horizon sky contribution, the degree of lid opening and the extreme lateral component of UVR incident on the eye. A series of recent ocular dosimetry studies are described which have considered all of these factors. In addition, the value of different types of eye protection is shown to vary widely depending on the frame design. The dosimetry studies can be confirmed by a biological dosimeter--the human cornea. Because the action spectrum and threshold for human photokeratitis are well defined, the living cornea can serve as a biological dosimeter for ocular exposure.
Cornea↗
New stroboscopic light source for intraoperative retinal fluorescein angiography.
We tested a new stroboscopic light source for intraoperative fluorescein angiography. A pulsed xenon light source and narrow-band interference filters are coupled to a 20-gauge endoilluminator and a 35-mm camera mounted on a surgical microscope. The system was tested with good success in a patient undergoing penetrating keratoplasty. An 18- to 22-microJ flash of 2 milliseconds' duration is achieved, which is well below the safety threshold level. This new stroboscopic light source provides a flash of sufficient light intensity to perform high-resolution, high-contrast fluorescein angiography during operations for the removal of opacified media.
Aged↗
Epidemiological studies of sunlight and cataract: the critical factor of ultraviolet exposure geometry.
Despite the large body of laboratory evidence that ultraviolet radiation (UVR) is cataractogenic, epidemiological studies of the relationship between age-related cataract and chronic UVR exposure have provided apparently conflicting results. An explanation for these conflicting results could be related to errors in dosimetry. Failure to account for the biophysical, physiological and behavioral factors, as well as ground reflectance, which determine the level of UVR exposure of the lens can lead to completely wrong assignments of lifetime exposure. It is argued that by overlooking these factors, past epidemiological studies of UVR and cataract could readily be expected to produce conflicting results.
Cataract↗
Recovery from pulsed-dye laser retinal injury.
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Adult↗