Owner59
Posts: 17033
Joined: 3/14/2006 From: Dirty Jersey Status: offline
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Could the opthamologist/google searcher explain this for us? DARK ADAPTATION Dark adaptation is an independent process during which each eye adjusts from a high-luminance setting to a low-luminance setting. The exact mechanisms are unclear, but they are known to include biochemical, physical, and neural. Both rods and cones contain light-sensitive chemicals called photopigments. The photopigment in the rods is called rhodopsin. There are three different types of cone photopigments that are composed of opsins only slightly different from rhodopsin. Upon exposure to light, photopigments undergo a chemical reaction that converts light energy to electrical activity, initiating visual impulses in the retina that are conducted by nerve fibers from the eye to the brain. The initial chemical reaction is called light adaptation and, in this process, the photopigments are decomposed. Intense light will decompose the photoreceptor pigments rapidly and completely, thus reducing retinal sensitivity to dim light. Regeneration of the photopigments occurs during dark adaptation. The fully dark-adapted eye, in which photopigment regeneration is complete, restores retinal sensitivity to its maximal level. Rods and cones differ markedly, however, in their rate of dark adaptation. Cones attain maximum sensitivity in 5-7 minutes, while rods require 30-45 minutes or longer of absolute darkness to attain maximum sensitivity after exposure to bright light. The cones have a faster rate of photochemical regeneration because they function in greater light than the rods. The cones, however, do not achieve the same level of sensitivity as the rods. The rods slowly adapt to dim illumination, but eventually achieve a much greater sensitivity than the cones. Depending on the preadaptation to light, dark adaptation is about 80% complete within 30 minutes, but it may take hours, or even days, to acquire total dark adaptation. http://www.aoa.org/optometrists/tools-and-resources/clinical-care-publications/aviation-vision/the-eye-and-night-vision
< Message edited by Owner59 -- 3/5/2014 7:26:59 AM >
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