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BLOG: Changes in the blue light conversation – digital screens, retinal damage
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Last week’s blog addressed how the blue light discussion has progressed from fringe to more mainstream, with topics including age-related macular degeneration, sleep disruption and digital eye strain, and product ads including nutritional supplements, lens materials and coatings, and lighting.
This second part will address digital screens and retinal damage.
Digital screens
Our worlds are now dominated by handheld digital screens, with one statistic I recently saw stating that app usage is now greater than TV usage (Khalaf).
The predominant wavelengths emitted from these LED backlit screens are blue (400 nm to 500 nm). Continuing this conversation, the topic of blue light can be broken into three categories: retinal damage, sleep disruption and digital eye strain.
In discussing digital screens, in particular their safety, these same three concerns can be addressed. Starting with retinal damage, a question we must ask is: Where are our patients getting information on screen safety?
Retinal damage
A recent New York Post headline read: “Staring at screens all day may not fry your eyes after all.” The story covered a recent paper that appeared in the journal Eye (O’Hagan, et al). The researchers looked at the amount of blue light the eye is exposed to while outdoors on a clear or cloudy day vs. the amount of blue light received from low-energy lightbulbs and digital screens such as computers, tablets and smart phones. Compared to a proposed safe exposure limit as set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), blue light exposure on a clear day in June was around 10% of the ICNIRP safe limit and on a cloudy day in December it was around 3% of the limit. The blue light emitted from digital devices and energy-efficient bulbs was less than these natural exposures.
The lead author of the study stated: “Even under extreme long-term viewing conditions, none of the low-energy lightbulbs, computers, tablets and mobile phones we assessed suggested cause for concern for public health.” The study team concluded: “Even considering that people may stare at computer screens for hours in the course of work or play, it is not likely to damage their retinas.”
However, not mentioned in this New York Post story are the facts around the ICNIRP guidelines. The first page of the guidelines states: “There is a paucity of data for long-term chronic exposure” (referring to wavelengths from 380 nm to 1 mm). “Therefore, the guidelines are based on the dataset of threshold data for short delay (up to 48 hours) onset of damage.” Later in the guidelines it is states: “For experimental injury threshold determination, incrementing individual exposures are each evaluated by ophthalmoscopy or other methods of examination and rated on a binary scale as lesion or no lesion.”
The guidelines use an effective dose of radiation resulting in a 50% probability for damage, listed as ED-50. If a retinal lesion is observed 1 hour after exposure, it will have a higher ED-50 than if the lesion is first observed 24 hours after exposure. For ophthalmoscopically visible lesions, 24 hours is the endpoint the guidelines use. For photochemically induced retinal injury, the endpoint is 48 hours.
In other words, the ICNIRP Guidelines were developed to determine at what wavelength and intensity acute ocular damage would occur. Acute damage, producing an ophthalmoscopically visible lesion after 24 hours occurs from sources such as arc welders, lasers or starring at the sun. The guidelines were not developed to determine the wavelength, intensity and chronic duration of exposure at which damage would occur. To my knowledge, there are no human studies to demonstrate this. So while I am not questioning the accuracy of O’Hagan and colleagues’ findings, I am asking how it can be concluded from a study using current ICNIRP guidelines that all digital screens regardless of size, intensity, proximity or duration of exposure are safe for the human eye.
On the other hand, there are recently published studies using in vitro and in vivo models demonstrating retinal damage by simulating chronic LED light exposure at commonly encountered domestic lighting levels. In an in vitro model (Chamorro, et al.) using human retinal pigment epithelium cells, results showed a 75% to 99% decrease in cellular viability, a 66% to 89% increase in cellular apoptosis, an increase in reactive oxygen species production and DNA damage.
In an in vivo model (Shang, et al.) using rats, functional, histological and biochemical retinal damage was present as early as 9 days after exposure.
As clinicians, patients put their trust in our recommendations, including advice on safe digital screen usage. All opinions in this conversation are valuable, but we must remember to look at the complete picture, considering all research available.
Next week, we will take a look at what is being said in the mainstream media regarding digital screens and sleep.
References:
Chamorro E, et al. Photochem Photobiol. 2013;89:468-473. doi:10.1111/j.1751-1097.2012.01237.x.
International Commission on Non-Ionizing Radiation Protection. ICNIRP guidelines on limits of exposure to incoherent visible and infrared radiation. Health Physics. 2013;105(1):7496. doi:10.1097/HP.0b013e318289a611.
Khalaf S. Flurry Insights. September 30, 2015. http://flurrymobile.tumblr.com/post/128773968605/the-cable-industry-faces-the-perfect-storm-apps
O’Hagan JB, et al. Eye. 2016;30(2):230-233. doi: 10.1038/eye.2015.261.
Reuters. Staring at screens all day might not fry your eyes after all. New York Post. January 29, 2016. http://nypost.com/2016/01/29/staring-at-screens-all-day-might-not-fry-your-eyes-after-all/
Shang YM, et al. Environ Health Perspect. 2014;122:269-276. doi:10.1289/ehp.1307294.