Many age-related medical problems may stem from the aging of the eyes:
It was not until 2002 that the eye’s role in synchronizing the circadian rhythm became clear. It was always believed that the well-known rods and cones, which provide conscious vision, were the eye’s only photoreceptors. But Dr. Berson’s team discovered that cells in the inner retina, called retinal ganglion cells, also had photoreceptors and that these cells communicated more directly with the brain.
These vital cells, it turns out, are especially responsive to the blue part of the light spectrum. Among other implications, that discovery has raised questions about our exposure to energy-efficient light bulbs and electronic gadgets, which largely emit blue light.
But blue light also is the part of the spectrum filtered by the eye’s aging lens. 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.
“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.
Several studies, most in European countries, have shown that the effects are not just theoretical. 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. “What that shows us is that the same amount of light that makes a young person sit up in the morning, feel awake, have better memory retention and be in a better mood has no effect on older people,” Dr. Turner said.
Another study, published in The Journal of Biological Rhythms, found that after exposure to blue light, younger subjects had increased alertness, decreased sleepiness and improved mood, whereas older subjects felt none of these effects.
Researchers in Sweden studied patients who had cataract surgery to remove their clouded lenses and implant clear intraocular lenses. They found that the incidence of insomnia and daytime sleepiness was significantly reduced. Another study found improved reaction time after cataract surgery.
“We believe that it will eventually be shown that cataract surgery results in higher levels of melatonin, and those people will be less likely to have health problems like cancer and heart disease,” Dr. Turner said.