Since blue light wavelength make up only a small percentage of the light in white light, any form of light therapy using a high proportion of blue light therefore risks subverting a variety of defensive mechanisms that protect the retina against blue light hazard. These defensive mechanisms include the anatomical positioning and structure of eye and its surrounding features, as well as human posture, which makes it awkward for humans to gaze upwards for long periods of time. Sunnex Biotechnologies, 2008)
The work of David H. Sliney entitled: "Ocular Hazards of Light" presented at the International Lighting in Controlled Environments Workshop states the following risks and hazards to the eye due to lighting: (1) Ultraviolet photochemical injury to cornea (photokeratitis) and lens (cataract) stated at 180mn to 400 nm; (2) thermal injury to the retina of the eye (400nm to 1400nm); (3) blue-light photochemical injury to the retina of the eye (principally 400nm to 550 nm; unless aphakic, 310 to 550 nm); (4) near infrared thermal hazards to the eye lens (approximately 800 nm to 3000 nm); and (5) thermal injury to the eye cornea (approximately 1400 nm to 1mm). (1994) Sliney states that the primary "retinal hazard" due to bright light sources is "photoretinitis, e.g., solar retinitis with an accompanying scotoma which results from staring at the sun." (1994) Sliny states that it is only recently that it has become clear that "photoretinitis results from "a photochemical injury mechanism following exposure of the retina to shorter wavelengths in the visible spectrum, i.e., violet and blue light."(1994) Sliny states that it has been show conclusively that an intense exposure to short-wavelength light, or 'blue light' can cause retinal injury. Sliny specifically states: "The product of the dose-rate and the exposure duration always must result in the same exposure dose (in joules-per-square centimeter at the retina) to produce a threshold injury. Blue-light retinal injury (photoretinitis) can result from viewing either an extremely bright light for a short time, or a less bright light for longer exposure periods. This characteristic of photochemical injury mechanisms is termed reciprocity and helps to distinguish these effects from thermal burns, where heat conduction requires a very intense exposure within seconds to cause a retinal coagulation; otherwise, surrounding tissue conducts the heat away from the retinal image. Injury thresholds for acute injury in experimental animals for both corneal and retinal effects have been corroborated for the human eye from accident data. Occupational safety limits for exposure to UVR and bright light are based upon this knowledge. As with any photochemical injury mechanism, one must consider the action spectrum, which describes the relative effectiveness of different wavelengths in causing a photobiological effect. The action spectrum for photochemical retinal injury peaks at approximately 440 nm." (1994)
Calculation of retinal exposure is also addressed in Sliny's work who states that the knowledge "of the optical parameters of the human eye and from radiometric parameters of a light source" enables the calculation of "irradiances (dose rates) at the retina. (1994) Sliny states that there are two sets of light-measurement quantities and units in the endeavor to define light exposure of the retina: (1) radiometric; and (2) photometric. (1994) Specifically, Sliny states: "Radiometric quantities such as radiance -- used to describe the "brightness" of a source [in W/cm2 sr] and irradiance -- used to describe the irradiance level on a surface [in W/cm2] are particularly useful for hazard analysis. Radiance and luminance are particularly valuable because these quantities describe the source and do not vary with distance. Photometric quantities such as luminance (brightness in cd/cm2 as perceived by a human "standard observer") and illuminance in lux (the "light" falling on a surface) indicate light levels spectrally weighted by the standard photometric visibility curve which peaks at 550 nm for the human eye (Figure 1). To quantify a photochemical effect it is not sufficient to specify the number of photons-per-square-centimeter (photon flux) or the irradiance (W/cm2) since the efficiency of the effect will be highly dependent on wavelength. Generally, shorter-wavelength, higher-energy photons are more efficient." (1994) Sliny goes on to state: "Unfortunately, since the spectral distributions of different light sources vary widely, there is no simple conversion factor between photometric (either photopic or scotopic) and radiometric quantities. This conversion may vary from 15 to 50 lumens/watt (1m/W) for an incandescent source to about 100 1m/W for the sun or a xenon arc, to perhaps 300 to 400 lm/W for a fluorescent source (Sliney and Wolbarsht, 1980;...
Risk Management Unfortunately, it has become necessary to address the issue of falls at the healthcare facility by whom I am employed (Facility A). Recently, there has been a rash of accidents all relating to patients falling. The healthcare facility is concerned not only about the injuries to the patients, but, also about the liability issues. For this reason, the facility has taken steps to assess the risks which pertain to
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A., MD, and Mermin, J. (2012). HIV infection and older Americans: The public health perspective. American Journal of Public Health, 102(8), 1516-1526. Cooperman, N.A., Arnsten, J.H., and Klein, R.S. (2007). Current sexual activity and risky sexual behavior in older men with or at risk for HIV infection. AIDS Education and Prevention, 19(4), 321-33. Hutton, H.E., Lyketsos, C.G., Zenilman, J.M., Thompson, R.E., and Erbelding, E.J. (2004). Depression and HIV risk behaviors among patients
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