Medscape Medical News
Sari Harrar
August 09, 2024
A surprising therapy is showing promise for chronic pain, vision loss, and muscle recovery, among other conditions.
It’s not a pill, an injection, or surgery.
It’s light.
Yes, light. The thing that appears when you open the curtains, flip a switch, or strike a match.
Light illuminates our world and helps us see. Early human trials suggest it may help us heal in new ways as well.
“Phototherapy is still in its infancy,” said Mohab Ibrahim, MD, PhD, a professor of anesthesiology at the University of Arizona, Tucson, Arizona, who studies the effects of light on chronic pain. “There are so many questions, a lot of things we do not understand yet. But that’s where it gets interesting. What we can conclude is that different colors of light can influence different biological functions.”
This growing field goes by several names. Light therapy. Phototherapy. Photobiomodulation.
It leverages known effects of light on human health — such as skin exposure to ultraviolet light producing vitamin D or blue light’s power to regulate human body clocks — to take light as medicine in surprising new directions.
New Science, Old Idea
The science is young, but the concept of using light to restore health is thousands of years old.
Hippocrates prescribed sunbathing to patients at his medical center on the Greek island of Kos in 400 BC. Florence Nightingale promoted sunshine, along with fresh air, as prerequisites for recovery in hospitals during the Civil War. A Danish doctor, Niels Finsen, won the Nobel Prize in 1903 for developing ultraviolet lamps to treat a tuberculosis-related skin condition. And worried parents of the 1930s sat their babies in front of mercury arc lamps, bought at the drugstore, to discourage rickets.
Today, light therapy is widely used in medicine for newborn jaundice, psoriasis, and seasonal affective disorder and in light-activated treatments for cancers of the esophagus and lungs, as well as for actinic keratosis, a skin condition that can lead to cancer.
But researchers are finding that light may be capable of far more, particularly in conditions with few treatment options or where available drugs have unwanted side effects.
How Red Light Could Restore Vision
When 100 midlife and older adults, aged 53-91, with the dry form of age-related macular degeneration (AMD) were treated with an experimental red-light therapy or a sham therapy, the light treatment group showed signs of improved vision, as measured on a standard eye chart.
Volunteers received the therapy three times a week for 3-5 weeks, every 4 months for 2 years. By the study’s end, 67% of those treated with light could read an additional five letters on the chart, and 20% could read 10 or more. About 7% developed geographic atrophy — the most advanced, vision-threatening stage of dry AMD — compared with 24% in the sham group.
The study, called LIGHTSITE III, was conducted at 10 ophthalmology centers across the United States and published in March in the journal Retina. The device they used — the Valeda Light Delivery System from medical device company LumiThera — is available in Europe and now being reviewed by the US Food and Drug Administration (FDA).
LumiThera’s Valeda Light Delivery System (which is CE Marked in the EU and available in select countries in Latin America, but not cleared by the FDA) is being studied for the treatment of dry AMD and other ocular diseases.
Exposure to red light at the wavelengths used in the study likely revitalizes failing mitochondria — the power plants inside cells — so they produce more energy, the researchers say.
“This is the first therapy for dry AMD that’s actually shown a benefit in improving vision,” said study co-author Richard Rosen, MD, chair of ophthalmology at the Icahn School of Medicine at Mount Sinai and chief of Retinal Services at the New York Eye and Ear Infirmary in New York City. “Supplements called AREDS can reduce progression, and in wet AMD we can improve vision loss with injections. But in dry AMD, none of the treatments studied in the past have improved it.”
AMD develops when the eyes can’t break down natural by-products, which glom together as clumps of protein called drusen. Drusen can lodge under the retina, eventually damaging tissue.
“Retinal epithelial cells, a single layer of cells that cares for the photoreceptors in the eyes, are there for life,” Rosen said. “They have a tremendous capacity to repair themselves, but things [such as aging and smoking] get in the way.”
“I’m proposing,” Rosen said, “that by boosting energy levels in cells [with red light], we’re improving normal repair mechanisms.”
Lab studies support this idea.
In a 2017 mouse study from the University College London Institute of Ophthalmology, London, England, retinal function improved by 25% in old mice exposed to red light. And a 2019 study from the Ophthalmological Research Foundation, Oviedo, Spain, found that exposure to blue light harmed the mitochondria in retina cells, while red light somewhat counteracted the losses.
If cleared by the FDA — which the company anticipated could happen this year — LumiThera’s light delivery device will likely be most useful in the beginning stages of dry AMD, Rosen said. “I think treatment of early dry AMD will be huge.”
Eventually, light therapy may also be valuable in treating or managing glaucoma and diabetic retinopathy.
For now, Rosen recommended that clinicians and consumers with AMD skip over-the-counter (OTC) red-light therapy devices currently on the market.
“We don’t know what kind of light the devices produce,” he said. “The wavelengths can vary. The eyes are delicate. Experimenting on your own may be hazardous to your vision.”
Green Light for Pain Relief
On his way to the pharmacy to pick up pain relievers for a headache, Ibrahim passed Gene C. Reid Park, Tucson, Arizona. Recalling how his brother eased headaches by sitting in his backyard, Ibrahim pulled over.
“Reid Park is probably one of the greenest areas of Tucson,” said Ibrahim, the University of Arizona anesthesiologist, who also serves as medical director of the Comprehensive Center for Pain & Addiction at Banner-University Medical Center Phoenix, Phoenix, Arizona. “I spent a half hour or 40 minutes there, and my headache felt better.”
Being outdoors in a green space may be soothing for lots of reasons, like the quiet or the fresh air. But there’s also sunlight reflected off and shining through greenery. The experience inspired Ibrahim to take a closer look at the effects of green light on chronic pain.
In his 2021 study of 29 people with migraines, participants reported that after daily exposure to green light for 10 weeks, the number of days per month when they had headaches fell from 7.9 to 2.4 for those who had episodic migraines and from 22.3 to 9.4 for those with chronic migraines. In another 2021 study, 21 people with fibromyalgia who had green light therapy for 10 weeks said their average, self-reported pain intensity fell from 8.4 to 4.9 on a 10-point scale used at the University of Arizona’s pain clinic.
Volunteers in both studies got their light therapy at home, switching on green LED lights while they listened to music, read a book, relaxed, or exercised for 1 or 2 hours daily. The lights were within their field of vision, but they did not look directly at them.
Basking in green light for an hour or two a day could significantly help relieve pain from migraines and fibromyalgia, according to University of Arizona research.
Ibrahim now has funding from the US Department of Defense and Department of Veterans Affairs to find out why green light alters pain perception.
“What we know is that the visual system is connected to certain areas of the brain that also modulate pain,” he said. “We are trying to understand the connection.”
Padma Gulur, MD, a professor of anesthesiology and population health and director of Pain Management Strategy and Opioid Surveillance at Duke University, Durham, North Carolina, saw similar results in a 2023 study of 45 people with fibromyalgia. But instead of using a light source, volunteers wore glasses with clear, green, or blue lenses for 4 hours a day.
After 2 weeks, 33% in the green lens group reduced their use of opioids by 10% or more, compared with 11% in the blue lens group and 8% who wore clear lenses. Previous studies have found green light affects levels of the feel-good brain chemical serotonin and stimulates the body’s own opioid system, the authors noted.
“Green light helps your body control and reduce pain,” Gulur said. It “seems to help with pain relief by affecting the body’s natural pain management system. This effect appears to play a crucial role in antinociception — reducing the sensation of pain; antiallodynia — preventing normal, non-painful stimuli from causing pain; and antihyperalgesia — reducing heightened sensitivity to pain.”
Light therapy could help pain patients reduce their dose of opioids or even forgo the drugs altogether, Gulur said. “It is our hope this will become a useful adjuvant therapy to manage pain.”
In the University of Arizona studies, some patients on green-light therapy stopped their medications completely. Even if they didn’t, other benefits appeared. “They had improved quality of life, decreased depression and anxiety, and improved sleep,” Ibrahim said.
But not just any green light or green-tinted glasses will work, both researchers said. “We have found there are specific frequencies of green light that give this benefit,” Gulur said. “OTC products may not be helpful for that reason.”
While Ibrahim said it could be possible for healthcare practitioners and consumers to consult his studies and put together an inexpensive green-light device at home while carefully following the protocol participants used in the studies , it would first be a good idea for patients to talk with their family doctor or a pain specialist.
“A headache is not always just a headache,” Ibrahim said. “It could be some other abnormality that needs diagnosis and treatment. If you have long-lasting pain or pain that’s getting worse, it’s always better to discuss it with your physician.”
Helping Muscles Recover With Red Light
Intense exercise — whether it’s a sprint at the end of a morning run, an extra set of biceps curls, or a weekend of all-day DIY home improvement projects — can temporarily damage muscle, causing soreness, inflammation, and even swelling. Phototherapy with red and near-infrared light is widely used by sports trainers, physical therapists, and athletes to aid in recovery. It may even work better than a trendy plunge in an ice bath, according to a 2019 Texas State University review.
But how does it work? Jamie Ghigiarelli, PhD, professor of Allied Health & Kinesiology at Hofstra University in Hempstead, New York, looked closely at signs of inflammation and muscle damage in 12 athletes to find out.
Study participants overtaxed their muscles with rounds of chin-ups, high-speed sprints, and repeated bench presses. Afterward, they relaxed in a full-body red-light therapy bed or in a similar bed without lights.
The results, published in 2020, showed that blood levels of creatine kinase — an enzyme that’s elevated by muscle damage — were 18% lower 1-3 days after exercising for the light-bed group than for the control group.
“Photobiomodulation seems to help with muscle recovery,” Ghigiarelli said.
Red light at wavelengths from 650 to 820 nm can enter muscle cells, where it is absorbed by mitochondria and boosts their energy production, he said. At the time of his research, some exercise science researchers and athletes thought using light therapy before an event might also increase athletic performance, but according to Ghigiarelli, that use has not panned out.
Handheld red light and near-infrared light devices for muscle recovery are widely available, but it’s important to do your homework before buying one.
“You want to choose a device with the right energy production — the right wavelength of light, the right power — to be safe and effective,” he said.
For details, he recommends consulting a 2019 paper in the Brazilian Journal of Physical Therapy called “Clinical and scientific recommendations for the use of photobiomodulation therapy in exercise performance enhancement and post-exercise recovery: Current evidence and future directions.”
The paper, from the Laboratory of Phototherapy and Innovative Technologies in Health at the Universidade Nove de Julho in Sao Paulo, Brazil, recommends that for small muscle groups like the biceps or triceps, use red-light lasers or LED devices with a wavelength of 640 nm for red light or 950 nm for infrared light, at a power of 50-200 mW per diode for single-probe device types, at a dose of 20-60 J, given 5-10 minutes after exercise.
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