The lenses in our eyes yellow as we age. Does this affect the light-mediated regulation of our body clocks? Could it explain any age-related dysfunction?

Mike Speciner
Acton, Mass.

Indeed, it could. The progressive browning of tissue in the eye can end up “acting like yellow-tinted sunglasses,” says Elizabeth R. Gaillard of Northern Illinois University. Moreover, the eye’s lenses thicken and the pupils shrink with age, further limiting how much light reaches the retina, notes Mariana Figueiro of Rensselaer Polytechnic Institute’s Lighting Research Center. Such physical changes “can mute the light-dark signal sent to the body’s master clock, presumably contributing to major sleep disturbances in seniors,” says Figueiro. —J. Raloff