Impact of age on human non-visual responses to light
Ageing is associated with increased disturbances in the timing, duration, and quality of sleep. These disruptions may reflect changes in the circadian timing system and/or the sleep homeostat which are both necessary to produce consolidated sleep at an appropriate time. In addition, it is possible that age-related alterations in the detection and transmission of the photic signal responsible for synchronizing the circadian clock may play a role. Ageing is accompanied by many changes within the eye including alterations in pupil size, lens transmission, and number of photoreceptors. The observed increase in ocular lens density with age will diminish the transmission of short wavelength blue light to which the circadian system has been shown to be most sensitive, and may contribute, in part, to the observed increase in sleep disturbances in older people. We were the first group to test the hypothesis that non-visual responses to blue light would be impaired in older individuals. Our research has demonstrated that whilst acute non-visual effects of blue light are impaired with age, the light resetting effect appears unaltered. Future research should work towards optimizing the light environment for older people to promote good quality sleep and daytime functioning.