Bright lights, ubiquitous in the dental operatory, are necessary tools of the craft. With the expansion of technology in light-cured resin composites, whitening procedures, and the mindfulness to save energy by ‘going green’, we’re seeing a consequent proliferation of sources emitting intense beams of high-energy visible light (HEV). HEV consists of a narrow band of visible light in the shorter wavelengths between 380-500nm (violet to blue). Not only does blue light play a role in illumination of our visual world, it is also responsible for non-visual functions such as circadian rhythms involved in sleep/wake cycles as well as cognitive performance and feelings of well being. But exposure to large amounts of blue light can be extremely harmful to the eye and can reduce acuity and contrast sensitivity. Blue light packs more energy than reds, greens, and yellows and as such penetrates all the way to the back of the eye known as the retina. As a consequence, blue light exposure drives oxidative retinal damage that can lead to age related macular degeneration (AMD)-the leading cause of blindness in the western world. With an increasing number of blue light sources in our daily lives including smartphones, LED televisions, tablets, computer screens, and LED/fluorescent indoor lighting, people are now being bombarded by potentially harmful blue light. For Dentists, the cumulative exposure to HEV can be significant. High powered LED curing lights, LED head-mounted illumination systems, whitening accelerator lamps, and even overhead exam lights, that are now being replaced by the more energy efficient LED/fluorescent models, all lead to increasing amounts of intensely directed blue light exposure in the dentist’s office.
A CAUSE FOR CONCERN
As incandescent bulbs are slowly regulated away, the safety of new forms of efficient lighting i.e. CFLs, LEDs, HIDs are the topic of great debate. Hoping to address the concerns, the European Union convened a multidisciplinary panel of experts, part of the SCENIHR (Scientific Committee on Emerging and Newly Identified Health Risks), which published Health Effects of Artificial Light, March 19, 2012. The report focused primarily on the additional annual exposure to UV rays and HEV individuals will encounter in typical home/office/industrial settings, given average exposure times and proper installation of luminaires. They concluded the effect on most individuals would be the equivalent of a weeklong Mediterranean holiday each year. The burning question: Did we wear our sunscreen, hats, and shades during this imaginary trip on which we’ve incurred real damage?
Epidemiologic research suggests harm from exposure to UV and blue light is cumulative over a lifetime. Some are disproportionately affected due to certain diseases (lupus erythematosus), photosensitizing medications, a lack of natural protective pigments in the lens and retinal tissue, or the gradual buildup of toxic age pigment called drusen, such as occurs in age-related macular degeneration (AMD). Based upon research published in the Journal of the Canadian Dental Association, cyclic intense light exposure, as can occur from reflections off teeth while operating high-powered light curing units, is hazardous to dentists and operatory technicians at exposures as little as six seconds per day. Beyond curing lights, exposure to other sources of HEV is driving excessive production of reactive oxygen species, otherwise known as oxidative stress.
CELLULAR DAMAGE
Over the last few years, several in vitro experimental research studies have revealed the phototoxic effects of exposure to HEV. During acute exposure, mere seconds at the intensity of high-powered LEDs at close range, the result is catastrophic on a microbiologic level. The photoreceptors we need for sight are quickly damaged and shed. Within minutes, this induces a pro-inflammatory immune cascade which further damages mitochondrial DNA and in the worst case, nuclear DNA, activating programmed cell death- apoptosis. The toxic remains are engulfed by RPE cells of the retina. This damage is irreparable. Over time more cellular debris of oxidized lipids and spent vision pigment pile up at the basement membrane of the retina, creating a barrier against effective circulation in the retina. This hypoxic state, in addition to further generation of free radicals, upregulates a molecule called vascular endothelial growth factor (VEGF), This molecule signals the growth of small, leaky blood vessels through the back of the retina. Blindness can ensue.
STAYING SAFE WITH THE BLUE LIGHT
Naturally, effective protection is key and the risks can be mitigated. Keeping aware of the blue light hazard and maintaining vigilance in the use of protective eyewear for everyone in the room will help preserve a lifetime of healthy sight. Several ophthalmic lens manufacturers have recently introduced lenses with specialized coatings that can selectively filter harmful blue light without impacting colour perception. This feature is particularly important in cosmetic dentistry. A new entry in HEV protection is a lens that is infused with natural lens melanin and ocular lens pigments to effectively block harmful HEV and UV light while allowing innocuous light to pass thereby maintaining colour and depth perception. These new lenses can also provide improved visual performance through enhanced visual acuity and contrast. Dental loupe manufacturers will start incorporating these highly protective lenses in the near future. Beyond the external protection of ophthalmic lenses, nutritional supplements containing the three naturally occurring macular pigments (Lutein, Zeaxanthin, and Mesozeaxanthin) act as internal protection by filtering harmful blue light at the retinal level while also neutralizing free radicals. These supplements are safe and do not interact with other medications While a diet rich in green leafy vegetables is a great source of macular carotenoids, most people do not get enough of these important anti-oxidants in a typical North American diet.
Blue light is here to stay and new innovations in energy efficient lighting technology will certainly increase the amount of HEV that we are all exposed to. The challenge is to understand the visual implications and to protect our eyes accordingly. OH
Dr. Kerry Salsberg is an optometrist in private practice in Toronto. His professional focus is macular diseases, ocular nutrition, and preventative eye care. He can be reached at eyeker@gmail.com.
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