John. L Henahan, OD, FAAO
Special to The Citizen
For decades, scientists have looked for explanations as to why certain conditions occur with age, including memory loss, slower reaction time, insomnia and even depression. They have scrupulously investigated such suspects as high cholesterol, obesity, heart disease and an inactive lifestyle.
Now a fascinating body of research supports a largely unrecognized culprit: the aging of the eye, according to Dr. John Henahan an eye doctor at Spectrum Eyecare.
The gradual yellowing of the lens and the narrowing of the pupil that occur with age can 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.
It was not until 2002 that the eye’s role in synchronizing the circadian rhythm became clear when 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. By age 55, blue light tranmission dips by 63 percent, and by age 75, by a massive 83 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.
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. “We believe that it will eventually be shown that cataract surgery results in higher levels of melatonin, and those people likely will sleep better and be less fatigued during the day.
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.
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, says Dr. Henahan. 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 visit Dr. John Henahan at www.SpecEye.com or call 770-487-0667.
