Screen time and related definitions
"Screen time" refers to the amount of time a person spends staring at the digital displays of computers, tablets and smartphones.
According to The Vision Council, 72 percent of American parents report their children routinely engage in more than two hours of screen time per day. And it's very likely most kids actually spend significantly more time staring at screens than their parents think they do.
Why might too much screen time be a problem for kids?
The LED screens of computers and portable digital devices emit a broad spectrum of visible light. Most of these light rays are harmless, but a portion of the light emitted by these screens is relatively high-energy visible light called "blue light."
Blue light has shorter wavelengths and higher energy than other visible light rays. And laboratory research suggests certain bands of blue light may be harmful to the light-sensitive retina of the eye over time.
Blue light also plays an important role in regulating our body's circadian rhythm. This basically is an internal clock that's running in our brain and cycles between alertness and sleepiness at regular intervals over a 24-hour period. It's also called our sleep/wake cycle.
Too much exposure at the wrong time of day can disrupt a person's normal sleep/wake cycle, which can have serious health consequences.
Risks of too much screen time for kids
When talking about the risk of too much screen time for kids, we’re basically talking about the potential harmful effects of too much blue light.
And while it's true that staring at the screens of digital devices adds to the amount of blue light exposure kids get over the course of their lifetime, it's important to point out that the sun emits far more harmful blue light than computers, e-tablets and smartphones. So the blue light exposure from digital devices is an added exposure, over and above the larger amount of blue light exposure a person gets from sunlight.
A second important factor to consider is the timing of the exposure. Blue light exposure from the sun only occurs from sunup to sundown. But blue light exposure from screen time can occur at any hour of the day, including well into the night.
Possible risks from too much screen time for kids can be categorized as immediate or long-term.
Immediate risks
Immediate risks from too much screen time generally occur relatively soon after repeated blue light exposure. Many of these risks are associated with circadian rhythm disruption caused by staring at digital screens well into the night, which can make it much harder to fall asleep at a normal time.
Sleep disruption can be especially problematic for children, leading to daytime drowsiness and poor performance in school because of it. Disruption of the sleep/wake cycle also can eventually lead to weight gain and obesity-related health problems.
Research has shown that people who experience disrupted 24-hour cycles of sleep and activity also are more likely to have mood disorders, lower levels of happiness and greater feelings of loneliness.
Also, an intriguing two-year study of more than 2,500 normal Los Angeles high school students found that teens who reported greater digital device use and screen time during the study were about 10 percent more likely to develop ADHD symptoms by the end of the study period. (The researchers pointed out, however, that this doesn't prove a direct cause-and-effect relationship and more research is needed to fully understand the association between screen time and ADHD symptoms.)
Finally, according to The Vision Council, 30 percent of parents report their children experience at least one of the following symptoms after being exposed to more than two hours of screen time per day:
Headaches
Neck/shoulder pain
Eye strain, dry or irritated eyes
Reduced attention span
Poor behavior
Irritability
Any of these symptoms could potentially affect academic performance and social interactions.
Long-term risks
The simple truth is that the long-term risks of incremental blue light exposure from frequent use of digital devices is not yet known. This is because no previous generation has been exposed to comparable levels blue light from digital devices from childhood on.
It will probably take several decades before the long-term effects of extensive screen time for kids are better understood. But there is already some related research that suggests it may be wise to limit blue light exposure starting at an early age.
For example, researchers in Japan and Switzerland investigated what happened to the retinas of aging eyes from blue light exposure after cataract surgery. In the study, 79 eyes received a clear intraocular lens (IOL) that did not block blue light, and 52 eyes received a yellow IOL that blocked blue light. (Prior to cataract surgery, the retinas of all eyes were protected from blue light by the eye's natural lens that had become clouded by cataracts).
Two years after cataract surgery, none of the eyes that received the yellow IOL that blocked blue light showed any new or worsening signs of macular degeneration (AMD). However, among eyes that received the clear IOL that didn't block any blue light, 15 percent of these eyes showed new or worsening signs of AMD.
The results of this study suggest that the retinas of aging eyes are more susceptible to oxidative damage caused by blue light exposure. If this is true, then it may be prudent and wise to take steps to reduce premature aging of the retina by limiting the amount of blue light exposure the eye receives throughout life.
The greatest benefit may occur when these protective measures are taken during childhood, because this is when the media of the eye (the lens in particular) are exceptionally clear and allow the greatest amount of blue light to reach the retina.
What to do
So then, what can a parent do to prevent harm to their child's eyes (and overall health) from too much screen time?
It's unlikely kids will reduce their use of digital devices. So the answer lies in taking steps to limit the amount of blue light reaching their eyes while they are using these devices.
One solution is to purchase eyeglasses with lenses that reduce the amount of blue light that enters the eyes from computer, e-tablet and smartphone screens. A number of lens manufacturers produce eyeglass lenses that filter blue light.
Another option is to have an anti-reflective coating that blocks blue light applied to the lenses.
A third option is to purchase glasses with photochromic lenses. These sun-sensitive lenses block some blue light indoors and have the added advantage of automatically blocking additional blue light from the sun outdoors without the need for a separate pair of prescription sunglasses.
Yet another option — and the best option for superior protection from harmful blue light from the sun — is a pair of polarized sunglasses for outdoor wear. But what if your child doesn't need prescription glasses? The most convenient option in this case is to purchase a protective blue light filter that can be applied to the surface of your child's digital devices.
Also, remember to use the blue light filtering features on certain devices or multi-platform apps that block blue light.
And, to reduce the risk of your child disrupting his or her sleep/wake cycle, create a "no-screens" rule at least an hour or two before their scheduled bedtime.
Finally, schedule annual eye exams for your child with an eye doctor near you to make sure he/she is seeing as clearly and comfortably as possible. And remember to discuss blue light protection with your doctor at these visits.
This post originally appeared on All About Vision.