Vision depends on photoreceptor cells (rods and cones) in the retina that convert visible light to signals that are transmitted to the visual cortex of the brain via the optic nerve.
The human retina has approximately 6 million cones and 120 million rods. The outer segments of these photoreceptor cells are damaged by photo-oxidative stress from light exposure and must constantly be regenerated.
The retinal pigment epithelium (RPE) is a pigmented cell layer that lies just below the photoreceptor cells and plays a critical role in the regeneration of photoreceptor outer segments (POS) that make vision possible. Without a healthy RPE, the photoreceptors cannot survive.
A defining characteristic of age-related macular degeneration (AMD) is damage to the retinal pigment epithelium and photoreceptor cells, and associations have been made between cumulative exposure to sunlight and AMD risk.
Here is a sample of studies that have implicated HEV light as a factor in retinal damage that is consistent with the posible development of macular degeneration.
In a study published in Photochemistry and Photobiology, researchers showed that exposing human RPE cells to blue light for up to 48 hours significantly inhibited cell growth and reduced the production of hepatocyte growth factor (HGF), a substance in RPE cells that is associated with cellular growth and survival.
In another study published in Photochemistry and Photobiology, researchers concluded the RPE cell death they were able to créate with blue light exposure was related to the oxidative damage to the mitochondria of RPE cells caused by the HEV rays.
In a study published in Molecular Vision, researchers in Germany concluded that their study of the response of RPE cells to non-lethal exposures of blue light suggests HEV light exposure triggers stress responses at the cellular level that may have implications in the development of macular degeneration.
IS ALL HEV LIGHT HARMFUL?
The potential for eye damage from high-energy visible light depends on the wavelength of light involved. The closer the wavelengths are to the UV spectrum (i.e., the shorter the wavelength of the blue light being emitted), the higher the energy and the greater risk of harmful effects.
For this reason, some people describe shorter-wavelength HEV light (380 to 450 nm) as “bad” blue light and longer wave length HEV light (450 to 500 nm) as “good” blue light. But the rationale for this cutoff may be difficult to defend and more study is needed to determine if such a cutoff between “bad” and “good” blue light exists.
BENEFITS OF BLUE LIGHT EXPOSURE
Exposure to some blue light appears to be necessary for maintenance of the body’s circadian rhythm (24-hour sleep cycle) that is essential for maintaining healthy brain wave activity, hormone production, cell regeneration, and other physiological processes.
Blue light appears to help the body release serotonin, a hormone that reduces sleepiness and contributes to a sense of wellbeing. When blue light is blocked completely, the body reduces production of serotonin and releases melatonin, a hormone that facilitates sleep. Both hormones are vital.
Also, blue light therapy has been proven effective for treating certain mood disorders, such as seasonal affective disorder (SAD).