Now a fascinating body of research supports a largely unrecognized culprit: the aging of the eye.
The gradual yellowing of the lens and the narrowing of the pupil that occur with age disturb the body’s circadian rhythm, contributing to a range of health problems, these studies suggest. As the eyes age, less and less sunlight gets through the lens to reach key cells in the retina that regulate the body’s circadian rhythm, its internal clock.
“We believe the effect is huge and that it’s just beginning to be recognized as a problem,” said Dr. Patricia Turner, an ophthalmologist in Leawood, Kansas.
Circadian rhythms rally the body in the morning to tackle the day’s demands and slow it down at night, allowing the body to rest and repair. This internal clock relies on light to function properly.
The body has a beautiful timekeeping mechanism, “but the clock is not absolutely perfect and needs to be nudged every day,” said Dr. David Berson, who studies how the eye communicates with the brain.
So-called photoreceptive cells in the retina absorb sunlight and transmit messages to a part of the brain which governs the internal clock. The brain adjusts the body to the environment by initiating the release of the hormone melatonin in the evening and cortisol in the morning.
Melatonin is thought to have many health-promoting functions, and studies have shown that people with low melatonin secretion, have a higher incidence of many illnesses including cancer, diabetes and heart disease.
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 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. Blue light 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. A 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.
Because of these light-filtering changes, Dr. Mainster and Dr. Turner believe that with age, people should make an effort to expose themselves to bright sunlight or bright indoor lighting when they cannot get outdoors. Older adults are at particular risk, because they spend more time indoors.
“In modern society, most of the time we live in a controlled environment under artificial lights, which are 1,000 to 10,000 times dimmer than sunlight and the wrong part of the spectrum,” Dr. Turner said.
In their own offices, Dr. Mainster and Dr. Turner have installed skylights and extra fluorescent lights to help offset the aging of their own eyes.
Should this research lead to earlier extraction of yellowing lenses? Historically during an eye exam, we have waited until a patient’s vision is impaired. Follow up studies are needed but may indicate that people as young as their 50’s might benefit from having the lens inside the eye removed and replaced with a clear implant lens. It may also suggest a need for eye drops that slightly dilate the pupil in people with very small pupils.
If you or would like to learn more, please contact Dr. John Henahan here, or call us at 770-487-0667.