For almost two decades already medical researchers have been studying the effects of laser light with various wavelengths on different organs and systems of humans and animals. In early studies it was shown that 670-nm light exposure helped reduce oxidative damage in models of neurotoxicity, optic nerve transection, accelerate wound healing, and restore tissue damage in models of Parkinson’s disease, multiple sclerosis, and methanol-induced retinal toxicity.
Since we have long learned to control our light environment, our rod and cone function goes down with age. With artificial lighting humans are rarely dark-adapted, hence cone function becomes critical. Dark adaptometry is a known biomarker of age-related macular degeneration (AMD). Today, age-related macular degeneration is a great eye health problem affecting as many as appoximately 50 million of the world population, leading to blindness in people over 65.
That is why the need to improve this condition in a progressively aging population is critical. However, therapeutic options for AMD are limited.
No wonder that many researchers look for new methods of physical therapy of this serious pathology. From time to time medical and scientific journals publish papers devoted to the newest investigations in this field.
One of early publications in the Photomedicine and Laser Surgery journal made in 2007 tells about the positive effects of low-level laser therapy (LLLT) in patients with age-related macular degeneration (AMD) and cataracts.
A semiconductor laser diode (780 nm, 7.5 mW, 292 Hz, continuous emission) was used for transconjunctival irradiation of the macula for 40 sec (0.3 J/cm2) with a total dose of 1.2 J/cm2 . It resulted in a significant visual activity for 3-36 mo after treatment.
In 2012 The Journal of Neuroinflammation published an article telling about 670-nm light treatmant of retinas in rats with induced macular degeneration. The aim of the investigation was to see if that treatment would reduce the propagation of complement in a light-induced model of atrophic age-related macular degeneration, as complement activation was associated with the pathogenesis of AMD.
The experimental animals were pretreated with 9 J/cm2 670-nm light for 3 minutes daily over 5 days. Following light damage, which induced a kind of atrophic age-related macular degeneration, their degenerating retinas pretreated with 670-nm light demonstrated reduced lipid peroxidation and complement propagation. This research showed that 670-nm light pretreatment lessened oxidative damage to photoreceptors and reduced inflammation.
The authors of the article concluded that 670-nm light irradiation might be used to control detrimental propagation of inflammatory responses in retinal degenerations including atrophic AMD and serve as a potentially perspective method of non-invasive anti-inflammatory therapy.
As the studies in this direction continued, it was suggested that the application of red light with a wavelength of 670 nm changed the course of aged decline improving visual functions in patients with intermediate AMD by 12 months.
An article published in 2020 in the Journal of Clinical Medicine describes the effects of 670 nm light in humans with healthy aging and age-related macular degeneration. The researchers treated the eyes of the people under study with 670 nm light daily in the morning for 2 minutes during 12 months.
The source of light was a hand-held device in the form of a tube, 8,7 cm long and with a 2,5 cm diamter. It produced diffuse red light in the range of 650-700 nm, emitting energy equivalent to 40 mW/cm2 or 4.8J/ cm2 (in 120 s) at its viewing aperture. It comprised 9 light-emitting diodes (LED) covered by a diffuser for patient comfort and tolerance. The other end of the device was closed with a push-button switch activated by the power application, the light source.
Patients with intermediate AMD (iAMD) and people aged 55 years or above with normal retina took part in the investigation. All their visual functions and retinal imaging at baseline, 1, 3, 6, and 12 months were assessed as well as the results of the rod and cone function tests.
The study showed that 670 nm photobiomodulation did not have any positive effect on either the visual function parameters or outer retinal structures in the eyes of people with AMD over a period of 12 months. There was no difference in changes in visual function and structure between healthy eyes and iAMD. In healthy aged people, exposed to 670 nm light, rod function (rod-recovery time) improved as well as the scotopic thresholds increased by 12 months, while no positive effect was observed in the disease group.
One of the main limitations of those clinic studies was the lack of a mechanism to verify whether the device light output remained constant over the trial.
As for the dosing of the light therapy, some researchers evaluated the impact of three wavelengths of light, 590 nm, 670 nm and 790 nm on eyes with early and intermediate AMD. While both 670 and 790 nm are red and infrared wavelengths and their effects might be complimentary, the effect of 590 nm light (yellow) on the retina is not clear. Still, the researchers claimed that AMD eyes subjected to a treatment course of 3 weeks had shown improvement in visual acuity, contrast sensitivity, while the drusen volume and central drusen thickness remained stable.
The most recent publication in the Nature journal has evoked a new interest in the laser treatment of eye diseases. The authors prove that repeated 3 min morning (8-9 AM) exposures of aged (37-70years) human retina to 670 nm light significantly improve for one week their cone receptor function resulting in better color contrast detection.
It is important to point out that the time of exposure is critical, as 670 nm light is only effective in the morning (8-9 AM).
The researchers show that energy as low as 8 mW/cm2 (opposed to 40 mW/cm2 used in previous studies) is enough to obtain significant improvement in the quality of life of eldery people.
It is demostrated that daily exposures to 670 nm light over weeks in aged humans have a positive impact on the rod and cone function.
All these investigations demonstrate that this kind of therapy works not only in animal models including normal aging and induced pathology but also in humans. Still, the age window, dosing, timing of intervention need to be investigated further. For the time being, nobody knows how much exposure is needed and how long its influence lasts.
No less important is the question of the device design generating the energy of the required parameters. To make the 670nm light therapy available for the general public the laser light generator should have an affordable price.
One of the lead researchers in this field, Professor Glen Jeffery (UCL Institute of Ophthalmology) is confident that “The technology is simple and very safe; the energy delivered by 670nm long wave light is not that much greater than that found in natural environmental light… In the near future, a once a week three-minute exposure to deep red light could be done while making a coffee, or on the commute listening to a podcast, and such a simple addition could transform eye care and vision around the world.”