www射-国产免费一级-欧美福利-亚洲成人福利-成人一区在线观看-亚州成人

chinadaily.com.cn
left corner left corner
China Daily Website

Eyes offer clues to ills of old age

Updated: 2012-03-04 07:49
( The New York Times)

Eyes offer clues to ills of old age

For decades, scientists have looked for explanations as to why memory loss, slower reaction time, insomnia and even depression occur with age. They have investigated such suspects as high cholesterol, obesity and an inactive lifestyle.

Now research supports a largely unrecognized culprit: the eye.

As the eyes age, less and less sunlight gets through the pupil and lens to reach cells in the retina that regulate the body's circadian rhythm.

"We believe the effect is huge and that it's just beginning to be recognized as a problem," said Dr. Patricia Turner, an ophthalmologist in Leawood, Kansas, who with her husband, Dr. Martin Mainster, a professor of ophthalmology at the University of Kansas Medical School, has written extensively about the effects of the aging eye on health.

Eyes offer clues to ills of old age

Circadian rhythms are the physiological processes that rally the body in the morning to tackle the day's demands and slow it down at night. This internal clock relies on light. Studies have found that people whose circadian rhythms are out of sync, like shift workers, are at greater risk for ailments like insomnia, heart disease and cancer.

"Evolution has built this beautiful timekeeping mechanism, but the clock is not absolutely perfect and needs to be nudged every day," said Dr. David Berson from Brown University in Providence, Rhode Island.

So-called photoreceptive cells in the retina absorb sunlight and transmit messages to a part of the brain called the suprachiasmatic nucleus (SCN), which governs the internal clock. The SCN adjusts the body by initiating the release of the hormone melatonin in the evening and cortisol in the morning. Melatonin is thought to have many health-promoting functions.

Dr. Berson's team discovered in 2002 that cells in the inner retina had photoreceptors that communicated more directly with the brain and were especially responsive to the blue part of the light spectrum.

In a study published in The British Journal of Ophthalmology, Dr. Mainster and Dr. Turner estimated that by age 45, the photoreceptors of the average adult receive just 50 percent of the light needed to fully stimulate the circadian system. By age 55, it dips to 37 percent, and by age 75, to a mere 17 percent.

Eyes offer clues to ills of old age

"Anything that affects the intensity of light or the wavelength can have important consequences for the synchronization of the circadian rhythm, and that can have effects on all types of physiological processes," Dr. Berson said.

One study, published in the journal Experimental Gerontology, compared how quickly exposure to bright light suppresses melatonin in women in their 20s versus in women in their 50s. The amount of blue light that significantly suppressed melatonin in the younger women had absolutely no effect on melatonin in the older women.

Researchers in Sweden studied patients who had cataract surgery to implant clear intraocular lenses. They found that the incidence of insomnia and daytime sleepiness was significantly reduced.

Dr. Mainster and Dr. Turner believe that with age, people should make an effort to expose themselves to bright sunlight or bright indoor lighting when they cannot get outdoors. Older adults are at particular risk, because they spend more time indoors.

"In modern society, most of the time we live in a controlled environment under artificial lights, which are 1,000 to 10,000 times dimmer than sunlight and the wrong part of the spectrum," Dr. Turner said.

In their own offices, Dr. Mainster and Dr. Turner have installed skylights and extra fluorescent lights to help offset the aging of their own eyes.

The New York Times

 
8.03K
 
...
...
...
主站蜘蛛池模板: 欧美成人免费在线 | 在线观看精品自拍视频 | 免费aⅴ在线 | 欧美日韩精品国产一区在线 | 在线天堂视频 | www.色午夜 | 国产欧美日本在线观看 | 步兵社区在线观看 | 久草免费网站 | avtt亚洲一区中文字幕 | 一级特黄aaa大片 | 91久久国产精品视频 | 欧美成人午夜影院 | 99精品视频在线观看 | 午夜欧美| 亚洲视频免费观看 | 九九精品在线视频 | 在线免费国产 | 国产精品九九视频 | 又粗又爽又色男女乱淫播放男女 | 欧美一级级毛片 | 欧美黄视频网站 | 成人精品国产亚洲欧洲 | 国产精品自拍视频 | 成人免费网站视频 | 国产一区二区三区免费大片天美 | 久久ri精品高清一区二区三区 | 亚洲视频精品在线观看 | 97视频免费播放观看在线视频 | 91香蕉嫩草| 一级特黄aa大片欧美 | 国产精品久久久久久 | 久久99久久99精品免观看 | 特级毛片免费视频播放 | 一级无毛片 | 亚洲m男在线中文字幕 | 国产三a级日本三级日产三级 | 欧美在线二区 | 国产深夜福利视频观看 | 亚洲欧美日产综合在线看 | 欧美日韩a∨毛片一区 |