December 02, 2014
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BLOG: Blue light - Our world has changed

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When considering photo-oxidative damage of the retina caused from cumulative lifetime exposure to blue light, it is important to think of the source in terms of intensity.

Sunlight is generally our most intense source of blue light exposure (you may recall from physics class the work of Rayleigh regarding light scatter and why the sky is blue), yet the vast majority of sunglasses prescribed and worn throughout history do not protect against blue light.

A report from the Beaver Dam Eye Study published in 2004 looked at sunlight exposure and the 10-year incidence of age-related macular degeneration during the study period. There were 2,764 participants 43 years to 86 years old at the baseline examination conducted from 1988 to 1990. 

One of the outcomes of the study was that subjects exposed to sunlight for more than 5 hours per day while in their teens and 30s were at higher risk for developing AMD over the 10-year study follow-up period than those exposed 2 hours or less per day.

Interestingly, they found that exposure to UV light was not linked to AMD, resulting in their estimation that it was increased exposure to the visible component of sunlight (blue light) that led to the higher incidence of AMD. Importantly, subjects with the highest amount of sun exposure that reported wearing hats and sunglasses at least half the time while exposed did not have a decreased risk of developing early AMD over the 10-year study follow up period. The authors stated that this suggests that wearing sunglasses with UV protection may not provide protection against the development of AMD.

A later report from Beaver Dam looked at “age-period-cohort effect” on the incidence of early AMD. They found that subjects who were born or lived earlier in the last century had a higher incidence of developing early AMD than did those from later in the century. Changes in health care (i.e., better control of hypertension) and changes in lifestyle (less smoking) did not explain the findings. It was uncertain whether other exposures in life (i.e., the flu pandemic of 1918) or period dietary restrictions (i.e., the Great Depression) could explain these birth cohort and period differences. 

The questions these results lead me to ask are: Didn’t society go from a mainly agrarian lifestyle to a more industrial one during the time periods studied? As such, would those born or living earlier in the last century have been exposed to more sunlight? Could this be a reason for the decreased incidence of early AMD in those born later in the century?  

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But look at how our exposure to blue light, even just over the last 10 years has changed.  CRT computer screens, which had longer wavelength emission spectra, started being phased out in 2002 and have essentially disappeared. Sleek flat-panel LED screens have replaced the bulky CRT; however, their spectral emission is much more blue, peaking between 440 nm and 455 nm. The iPhone was introduced in 2007 and the iPad in 2010, yet according to a report from Cisco, these and similar devices will outnumber people on earth in 2014. 

A 2011 study found that we tend to hold electronic screens closer to our eyes than printed material, and, of course, children with short arms hold them even closer. 

I recently visited with a former classmate of mine, Thomas Gosling, OD, who demonstrated a blue light sensor that measures the intensity of light emitted between 400 nm and 450 nm. He explained to me that intensity is proportional to one over the square of the distance a light source is held, (inverse-square law: I~1/d2). So an iPad held at 8 inches by a child actually has about four times the intensity than if the device were held at 16 inches by an adult. It seems to me that this is a critical point to consider regarding the dangers of blue light exposure.

In yet another study from 2010, it was found that kids 8 years to 18 years old were viewing electronic screens an average of 7.5 hours per day. If this study were repeated today and included even younger kids, I have a feeling the number of hours would be even higher. In our school district, some classes are using tablets instead of textbooks.

Essentially, these children are using electronic devices for their social life, entertainment and schoolwork. And, as adults, aren’t we doing the same?

A preponderance of evidence links cumulative lifetime exposure to blue light to risk of AMD development. The amount of blue light coming off of a smart phone or tablet is relatively low; the amount of blue light emitted from a 13-watt CFL bulb (60-watt incandescent equivalent) is much higher, but we do not sit with those 14 inches from our eyes for hours on end. 

One of the greatest unanswered questions in the current blue light conversation is: How much exposure and at what level of radiation will damage occur in humans?

We also know that blue light affects circadian rhythm, which can influence a host of broader health issues. I will explore this further in future posts. For now, thanks for reading.

References:

Bababekova Y, et al. Optom Vis Sci. 2011;88(7):795-797. doi: 10.1097/OPX.0b013e3182198792.

Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2013–2018. http://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/white_paper_c11-520862.html. Posted Feb. 25, 2014. Accessed Dec. 1, 2014.

The Henry J. Kaiser Family Foundation. Generation M2.  Media in the lives of 8- to 18-year-olds. http://kff.org/other/report/generation-m2-media-in-the-lives-of-8-to-18-year-olds/. Posted Jan. 20, 2010. Accessed Dec. 1, 2014.

Klein R, et al. Ophthalmology. 2008;115(9):1460–1467.

Tomany S, et al. Arch Ophthalmol. 2004;122:750-757.