Wednesday, August 1, 2012

Visual Clarity and Comfort

by NASA's Marshall Space Flight Center
Visual Clarity and Comfort
Article by Yifer

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Sunglasses of particular shapes may be in vogue as a fashion accessory. Fashion trends can also draw on the "cool" image of sunglasses.This can be true for people with severe visual impairment, such as the blind, who may wear sunglasses to avoid making others uncomfortable. The assumption is that it may be more comfortable for another person not to see the hidden eyes rather than see abnormal eyes or eyes which seem to look in the wrong direction. People may also wear sunglasses to hide dilated or contracted pupils, bloodshot eyes due to drug use, recent physical abuse (such as a black eye), exophthalmos (bulging eyes), a cataract, or eyes which jerk uncontrollably.Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations.Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.The lenses of polarised sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces such as water. They are popular among fishermen because they allow wearers to see into water when normally only glare would be seen.The most widespread protection is against ultraviolet radiation, which can cause short-term and long-term ocular problems such as photokeratitis, snow blindness, cataracts, pterygium, and various forms of eye cancer. Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV; for adequate protection, experts recommend sunglasses that reflect or filter out 99-100 % of UVA and UVB light, with wavelengths up to 400 nm. Sunglasses which meet this requirement are often labeled as "UV400." This is slightly more protection than the widely used standard of the European Union (see below), which requires that 95 % of the radiation up to only 380 nm must be reflected or filtered out. Sunglasses are not sufficient to protect the eyes against permanent harm from looking directly at the Sun, even during a solar eclipse.More recently, high-energy visible light (HEV) has been implicated as a cause of age-related macular degeneration;[10] before, debates had already existed as to whether "blue blocking" or amber tinted lenses may have a protective effect. Some manufacturers already design to block blue light; the insurance company Suva, which covers most Swiss employees, asked eye experts around Charlotte Rem

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