My eyes got old when I was in the fifth grade. At the time, it was fun when my brother stood across the room and held up things for me to read and I delightedly claimed that I could see nothing. Nothing! My brother and I were excited by our medical discovery. I was going blind. It was why I was missing things the teacher wrote on the blackboard and why I was having headaches.
My dad picked out my first pair of eyeglasses. Huge 1970s butterfly frames in iridescent purple. I loved them. Who knew my dad – a contractor – had such good fashion sense? Armed in massive purple frames that took up a good 50 percent of my face, I could see again. I could beat the decline of my eyes.
Now, in my 40s, I’m finding my vision is failing again. My 20-20 vision with contact lenses works great when I’m viewing things in the distance; but, for the up-close items (like reading a menu in a restaurant), my eyes are not effective. My optometrist said I needed bifocals and that I was right on schedule for this aging milestone. But, what I wondered, was the schedule and did it affect only my vision? Was the aging of my eyes completely out of my hands or, was there something I could do to slow the march of time?
For decades, scientists have been studying the interesting phenomenon of the effect of blue light (sunlight) on our circadian rhythms. Many of these studies have shown how our environment disrupts the natural cycle of blue light on our retinal cells and causes a variety of diseases. But, Dr. Martin Mainster and Dr. Patricia Turner at University of Kansas School of Medicine believe another culprit is also to blame: our aging eyes. As our eyes age, the pupil narrows and the lens gradually yellows, making it harder for sunlight to get through the lens to the retina. As our pupils narrow and allow in less light, the retina is less able to suppress the production of melatonin and the circadian rhythm is disrupted, which affects the health of older adults.
Melatonin prompts sleep and is responsible for regulating the sleep-wake cycle. Our circadian rhythm sets our internal clock and is responsible for regulating roughly 10 percent of our genes through the hormone melatonin. In 2002, Dr. David Berson of Brown University, made the startling discovery that photoreceptive cells in the retina, called retinal ganglion cells, absorb sunlight and send messages to the suprachiasmatic nucleus, the part of the brain that controls our internal clock by initiating the release of the hormone melatonin in the evening and cortisol in the morning.
Mainster and Turner discovered that by age 45, the average adult’s photoreceptors receive only half of the light needed to fully activate the circadian system. By age 55, it falls to 37% and by age 75, the eye receives just 17% of what the system needs.
In a 2005 study, researchers at University of Surrey compared how quickly blue light suppresses melatonin in women in their 20s versus women in their 50s. The amount of blue light that was effective for women in their 20s had no effect at all on the women in their 50s. Another study by the same team in 2009 looked at the effect on young and older subject’s exposure to blue light. Young subjects were more alert and their mood improved, but there was no effect on older subjects; regardless of the environment, aging clearly had an impact on the amount of blue light reaching retinal cells. Several diseases can be attributed to a disruption to the circadian rhythm, but Mainster and Turner’s findings could be an explanation for many of the health problems that affect the elderly.
The retina is responsible for noting the rise and fall of daylight. At night, when less light enters the retina, the body produces melatonin. In the daytime, the light entering the retina suppresses melatonin. The modern world of light bulbs and screens disrupts the natural rhythm of the body, which was designed to coordinate with the rise and fall of the sun. People are continuously flooded with light even after the sun falls and it is dark. This disruption not only affects sleep, but causes diseases as well.
A 2010 study in PNAS observed two groups of mice; one group was exposed to blue wavelengths at night, while the other group was not. Mice exposed to light at night gained more weight even though both groups of mice consumed the same number of calories. Researchers concluded that excessive exposure to blue light could lead to obesity.
Over the past decade, several other studies have determined that suppressing melatonin by late-night exposure to indoor lighting that mimics blue light contributed to breast cancer. In 2007, the World Health Organization declared shift work a “probable carcinogen as the suppression of melatonin production can disregulate genes involved in tumor development.” People with low melatonin have higher incidence of cancer, diabetes, heart disease and other diseases.
Incandescent bulbs contain more red wavelengths than blue. But, with LEDs and more energy-efficient light bulbs, exposure to blue wavelengths is increasing. Dr. Cajochen and his team at the University of Basel, Switzerland, studied 13 men sitting in front of computers for two weeks; the first week in front of an older fluorescent monitor, the second week in front of LED screens. The LED screens made melatonin rise more slowly and testing scores for memory and cognition were much higher when exposed to blue light.
Dr. George Brainard, a neurologist at Thomas Jefferson University Hospital, in Philadelphia, was one of the first to study light’s effect on hormones. Recently, NASA asked Dr. Brainard to help in designing lighting on the International Space Station that will promote alertness during waking hours and encourage sleep during bedtime hours. Now, Dr. Brainard hopes screens will be designed with wavelengths that adjust according to the hour of the day.
Dr. Mainster and Dr. Turner believe that people should expose themselves to bright sunlight or bright indoor lighting when they cannot get outdoors during the day in the sunshine. Because people spend most of their day indoors in offices with artificial lights that are at the wrong end of the light spectrum, this is especially true as people age.
As for me, well, I am addicted to my laptop. And, when insomnia hits, I am likely to be found playing Sudoku on my iPhone in the dark under the covers. As for my eyes? Well, I just invested in a funky pair of green reading glasses. My dad would be proud.
*Image courtesy of Super Seventies