ABSTRACT
Aging causes qualitative and quantitative change in nocturnal sleep. Many studies, including those by Feinberg1 and Bliwise,2 reported decrease of slow-wave sleep (SWS) and sleep ef£ciency during sleep and increase of frequency of waking episodes in older persons. Light in the morning, daytime, and nighttime in—uences sleep-awakening rhythm,3,4 and sleep deterioration, such as poor sleep, frequent awakenings, and dif£culty to fall asleep after awakening at night, is often observed in older people with visual impairment.5 The results of these studies suggest that the quantitative and qualitative change of light entering from an eye to the retina could be one of the reasons of sleep disorder with aging.
