In recent years, scientists working at the intersection of two historically well-developed fields, retinal physiology and circadian biology, upended the conventional view of retinal organization with the confirmation of a nonvisual ocular photoreceptor system.
The fact that the eye has functions beyond image perception holds the potential to explain why a significant proportion of patients with progressive degenerative ocular disease suffer from sleep disturbances. An understanding of these non-rod/non-cone photoreceptors might also explain seasonal affective disorder (SAD), jet lag and depression in the blind. It has the potential to influence intraocular lens selection for cataract patients. “The shocker is, you don’t need rods and cones to synchronize your circadian clock to the local light-dark cycle,” said Russell N. Van Gelder, MD, PhD. “There’s this whole other photoreceptive system lurking in the retina entraining your circadian system.” Dr. Van Gelder is professor and chairman of ophthalmology at the University of Washington in Seattle.
The Eye Is a Camera, and Clock, Too
The notion of a parallel ocular universe began more than 80 years ago with the observation that blind mice continued to show pupil constriction in response to light.1 Over time, researchers at about a dozen labs worldwide pursued the idea that the circadian and classical visual systems process light information in different ways.
http://www.visionmonday.com/latest-news/article/after-daylight-savings-time-more-darkness-may-mean-more-vision-problems-new-survey-says/
After Daylight Savings Time, More Darkness May Mean More Vision Problems, New Survey Says
By Staff
Monday, November 05, 2007 12:40 AM
JACKSONVILLE, Fla.—With most U.S. residents having set their clocks back over the weekend to mark the end of Daylight Savings Time, a new survey indicates that nearly one-third of all drivers say they have trouble seeing while driving at night.
According to “Shedding Light on Driving in the Dark,” a nationwide survey of 515 vision-corrected American--sponsored by Road & Travel magazine and Vistakon’s Acuvue contact lenses--32 percent of drivers say they have difficulty seeing all or most of the time while driving in the dark. More than one-fourth (26 percent) report trouble seeing signs or exits; 20 percent acknowledge difficulty seeing animals or pedestrians, while 20 percent also have difficulty seeing turns in the road. Twenty-two percent also report problems in judging distance while driving in the dark.
Survey respondents complained of eyestrain (38 percent), dry or tired eyes (34 percent), fatigue (25 percent), headaches (19 percent), inability to focus (18 percent) and double or blurred vision (15 percent) while driving in the dark. Sixty-one percent say headlights from oncoming traffic or from cars behind them are particularly bothersome, while 48 percent report experiencing glare or light sensitivity while driving in the dark.
And although 73 percent of these drivers say they believe correcting their vision problems would improve their ability to drive in low-light conditions, only 27 percent have talked to an eyecare professional about treatment options.
“Any vision problem left uncorrected or under-corrected can result in tragic consequences for drivers, passengers, and pedestrians,” noted Elise Brisco, OD, of Los Angeles. “A comprehensive eye exam will include testing to diagnose potential problems and determine the correct form of treatment, such as a new pair of glasses or contact lenses.”
http://abcnews.go.com/Health/story?id=117902
Darkness Disturbs Sleep of the Blind
B O S T O N, Oct. 11
By Melissa Schorr
For the 200,000 Americans who are completely blind, darkness is a constant, but sleep is often disturbed.
Without light cues that the rest of us rely on to synchronize our body clocks, as many as half of these blind people may have difficulty getting sleep schedules in step with a 24-hour cycle and may suffer sleep disorders as a result, researchers say.
But a new study shows that a daily dose of melatonin may be able to help reset a blind person’s unregulated body clock to a daily schedule, making it easier to rise and shine. The research, from a team of doctors at Oregon Health Sciences University in Portland, is in the Oct. 12 issue of the New England Journal of Medicine.
According to Dr. Alfred Lewy, a co-author of the study, this finding can also be applied to those with sight who experience shift changes at jobs, jet lag, daylight-saving time adjustment problems, winter depression and the “Monday Blues.”
Melatonin Revisited Melatonin is a hormone produced every evening by the brain’s pineal gland. Apparently, the chemical helps facilitate the onset of sleep. Darkness serves as a cue for the body to secrete melatonin into the blood stream and light serves to suppress it. Melatonin production also drops with age, possibly causing the elderly to get less sleep.
In recent years, melatonin has been hailed as a “wonder drug,” with proponents claiming it could be used for everything from fighting aging to improving one’s sex drive, without evidence from human studies, Lewy says. Because melatonin is a naturally occurring hormone, companies sell it as an over-the-counter dietary supplement — without any regulation by the Food and Drug Administration or thorough testing of any potential health claims.
“This study cuts through all the hype and spurious claims for melatonin a few years ago, and establishes its main use in humans: to help people with body clock disorders,” Lewy says.
Out of Step Scientists have known for some time that most people’s body clocks are naturally out of sync with the Earth’s 24-hour light and darkness cycle. When human subjects are placed in windowless rooms without any time cues, most people naturally drift into a a sleep-and-wake cycle that is approximately 25 to 26 hours long. Scientists do not know why humans evolved to have a 25-hour cycle rather than a 24-hour one.
A person living in this “natural,” 25-hour windowless world would rotate through the 24-hour sleep cycle every 24 days, and by the 11th day, approximately, would be sleeping only during daytime hours. If such a person were returned to the regular world, he or she would have trouble getting back in step and would be groggy.
People with normal vision can use light, transmitted through the retina to the brain’s internal clock, to reset their internal schedule to the Earth’s 24-hour rotation. Light also allows them to eventually readjust to minor changes in time, such as the switch to or from daylight-saving time or flying from one time zone to a destination in another.
Blind people, however, lack this visual cue, leaving them more susceptible to fall into a 25-hour rhythm that eventually disrupts a daily sleep schedule. Melatonin has been believed to act as a replacement for the light cues.
For those with sight who also need to readjust their body clocks, such as for jet lag or a shift change, using melatonin shortly before sleep may work as well, Lewy says.
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