Among many other changes in the body as it ages, the lens of the eye stiffens and becomes more yellow over time, causing the eye to filter out light, which in turn disrupts the body's circadian rhythm, or internal clock. The opthalmology researchers, from the University of Kansas School of Medicine, are quoted in the article saying the potential effect on health is "huge". They question the common practice of using blue light-blocking lenses in cataract surgery, which may exacerbate the effect - and recommend older adults spend more time in bright sunlight or under bright artificial light, indoors.
Original Research Paper:
P L Turner, M A Mainster. "Circadian photoreception: ageing and the eye's important role in systemic health." Br J Ophthalmol 2008;92:1439-1444.