CLINICAL

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A Bolt From the Blue

Shedding light on this spectrum and eye health

CORALIE BARRAU, PARIS, FRANCE

The eyecare industry has spent millions of dollars on educating the public about the dangers of UV light exposure. Given the extensive literature and recent research on blue light and its current prevalence in our daily lives, it’s time the industry focus on providing public education about this spectral range as well.

Here, I present an overview on blue light, its effects on visual and non-visual health and currently available photo-protective ophthalmic products.

Blue light overview

Blue light is a very wide band, from 380 nm to 500 nm. This is the highest energy visible light.

Our eyes are exposed to blue light daily. The highest dose of blue light comes from sunlight, delivering high irradiance levels (up to 100,000 lux at midday in summer) and 30% of blue light within the visible range. However, contrary to UV radiation, blue light is emitted in indoor light environments as well.

Traditional incandescent lamps (warm and yellow lighting) contain less than 5% of blue light. However, new lighting technologies, such as LEDs, may emit higher proportions of blue light than warm and yellow lighting with higher brightness. Current white LEDs combine a blue-pumped LED with a phosphor, emitting at higher wavelengths. Warm white LEDs (used in bedroom or living room lighting) emit less than 10% of blue light, while cold white LEDs (used in smartphone, tablets and computer screens) may emit up to 30% of blue light.

Although the flux emitted by LED lighting is moderate, the luminance may be much higher than traditional incandescent lighting (LEDs have a very small emission surface). LED brightness may induce a high illuminance onto the retina.

Its effects on visual health

Blue light goes deeper than UV into the eye. Specifically, while UV rays are filtered out by the cornea and crystalline lens, blue light reaches the retina.

Blue-light is scientifically recognized as harmful to the retina.¹ Numerous in vitro and in vivo studies provide evidence of the blue light toxicity on the RPE and photoreceptor cells. Cumulative blue light exposure induces photochemical chain reactions, which produce oxidative stress and may progressively and irreversibly alter the retina. Prolonged blue light exposure may cause an accumulation of a noxious photosensitive compound in the photoreceptor outer segments (POS), the all-trans-retinal. This compound is highly sensitive to blue-violet light with a decreasing profile between 400 nm and 450 nm. Its blue photo-activation may induce oxidative stress within the POS.

This stress is normally compensated by retinal antioxidants, but environmental factors (such as tobacco consumption or a poor diet) and age progressively reduce anti-oxidative defenses, thus failing to compensate for the oxidative stress. The POS progressively oxidize, and their renewal into the retinal pigment epithelium (RPE) is more challenging as their membrane components are difficult for the RPE to break down. Thus, intracellular digestion is incomplete and generates an accumulation of residual lipofuscin into the RPE.

Lipofuscin is sensitive to blue-violet light. Its blue photo-activation generates reactive oxygen species. When the amount of oxygen species exceeds the cellular defense capacity, the RPE cells die by apoptosis. Deprived of these support cells, photoreceptors deteriorate, contributing to the loss of vision diagnosed in patients suffering from AMD. In fact, accumulation of lipofuscin in the RPE is a main feature of aging and AMD.

Recent photobiology research, led by Paris Vision Institute and Essilor, has precisely identified the most toxic wavelengths in the blue range on an AMD and aging retinal cell model in sunlight physiological conditions. The 415 nm to 455 nm narrow spectral range, the blue-violet, represents the greatest phototoxic risk to the RPE cells.²

In addition, our eyes’ daily exposure to artificial lighting and LEDs is increasing as they are used in mobile phone and tablet back-lighting and even children’s toy lighting due to their compactness, long lifespan and low energy consumption. The blue light exposure rate is accelerating at increasingly younger ages, and, given the high transparency of their crystalline lens, children are extremely sensitive to blue light retinal exposure.³ In addition, French Agency for Food, Environmental and Occupational Health and Safety (ANSES) experts suggest that certain occupations are at increased risk of exposure, including operators in manufacturing facilities, lighting installers, surgeons and dentists.

Also, our eyes are solicited with moderate-viewing distances during prolonged and repeated exposure time, at several sources at the same. Several health agencies, such as ANSES and the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR), have reviewed the scientific literature on photobiology hazards related to the use of LEDs and conclude that a photochemical blue light risk might exist with prolonged and repeated exposure to some cold white LEDs.³

Its beneficial effects on non-visual health

Blue light at its lowest energies (the blue-turquoise range) is necessary to reset our biological clock and efficiently synchronize our biological rhythm. Blue-turquoise light at 480 nm (±15 nm) positively acts on the retina through the action of a third photoreceptor: melanopsin-containing ganglion cells.

When these ganglion cells are activated by blue-turquoise light, they transmit a nerve signal that runs along the optic nerve and triggers multiple non-visual structures and regulates sleep/wake state (melatonin synthesis), pupil light reflex, cognitive performance, mood, locomotor activity, memory and body temperature.

Protective products

The narrow blue phototoxic range, 415 nm to 455 nm, has been valued in designing a new category of ophthalmic lenses that goes beyond optical correction.

These selective photo-protective ophthalmic lenses filter out UV radiation and significantly attenuate harmful blue-violet light while allowing beneficial blue-turquoise light to pass. This brings a cumulative photo-protection of the retina without disrupting essential visual and non-visual functions of the eye.

Our role

Our eyes are daily and cumulatively exposed to blue light, and the retina is sensitive to chronic day-long, life-time exposure to blue light.

In our digital world, educating and protecting patients from UV and blue-light induced damage is a growing public health issue. OM

Mrs. Barrau is an Optics and Photonics research engineer with Essilor International. E-mail her at barrauc@essilor.fr, or send comments to optometricmanagement@gmail.com.