By James M. Stringham, PhD
The dramatic rise in the use of smartphones, tablets, and laptop computers over the past decade has raised concerns about potentially deleterious health effects of this increased “screen time” and associated short-wavelength visible (blue) light exposure. According to a recent report by Nielsen,  the average American adult spends a staggering 11 hours per day staring at screens. For eyecare practitioners, the primary concern, of course, involves the eye. Given the relatively low illuminance of screens, is the threat of blue light something we need to be worried about?
Blue Light Prevalence in Screens
Short-wavelength visible radiation—unlike even shorter-wave ultraviolet—penetrates the anterior ocular media to reach the retina. Because the energy per quantum of light increases with decreasing wavelength, blue light has greater potential to damage the retina via photochemical processes than longer-wavelength lights, such as green or red. Screens—although often appearing a rich white color—actually emit an appreciable amount of blue light. This is due to the technology involved in producing white.
In the case of LED-based devices, for example, a vivid white background is composed of blue light that is either passed through a yellow filter, or mixed with the output of red and green LEDs . In either case, blue is the peak of the overall output of the LED. Although the blue component in an LED is relatively strong, it is not nearly intense enough to produce acute damage in the retina. However, there is potential for long-term, cumulative effects, including cellular damage arising primarily from increased oxidative stress .
Favorable Supplement Response
The potential for damage from blue light in the retina has been met with a favorable adaptation in the eye: a diet-derived, blue-absorbing pigment composed of the dietary carotenoids lutein (L) and zeaxanthin (Z). L and Z are found in relatively high concentrations in leafy-green vegetables  and, along with mesozeaxanthin (MZ), are deposited in rich concentrations in the macular retina (known as macular pigment optical density (MPOD) .
A recent placebo-controlled study determined several benefits associated with increases in MPOD via supplementation with L, Z, and MZ in those with an average daily near-field screen time of roughly eight hours. Versus placebo, those subjects who supplemented 24mg of the macular carotenoids for six months improved significantly in terms of MPOD, number of undesirable sleep symptoms, eye strain, and eye fatigue—the latter three being common patient complaints. An additional benefit included reduced headache frequency.
Although no measures of retinal damage were obtained in the study, it can be safely assumed that, by increasing MPOD, additional protection from oxidative stress and inflammation was conferred by the supplements. Visual performance measures such as contrast sensitivity and visual performance in glare improved significantly; by proxy these functional improvements indicate improved health.
Squinting and Blue Light
The key to these improvements may be reduction of low-level squinting of the eyes over the many hours of screen time. Studies have shown that we are more apt to squint on exposure to blue light,  and long-term squinting has been found to lead to subjective worsening of eye strain, eye fatigue, and headache. Whatever the case may be, it appears that we have a way to help patients improve their daily visual experience—a way that also appears to provide several healthful benefits to the eye.
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Dr. Stringham is a research scientist with Duke University Medical School, Department of Ophthalmology. His research includes the effects of lutein, zeaxanthin, and meso-zeaxanthin on a variety of human physiological, health, and visual performance parameters.