outdoor light and myopia

How Much Outdoor Light Do You Need to Prevent Myopia?

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Updated 12/7/22

If you’ve been reading about the latest findings on why we’re all becoming so nearsighted, then you know that researchers have found a strong link between myopia and outdoor light. They think that outdoor light (possibly even more so than near work) may have the strongest impact on protecting against myopia. However, the simple recommendation of spending more time outdoors is a little ambiguous and not enough information to decide whether following this recommendation was feasible or worthwhile.  As much as I would like to spend my entire day at the beach, in a time-constrained world, I wondered how much and what kind of outdoor light do we need for it to make a difference?

Looking into the distance may also be part of the reason outdoor time prevents myopia
Looking into the distance may also be part of the reason outdoor time prevents myopia

Why outdoor light matters

Why outdoor light matters is still unclear to researchers. There are a few candidate theories, but if the reason is unclear, that means the kind of outdoor light you need is, well, unfortunately, another educated guess. Here are the theories so far:

  • The dopamine theory: Outdoor light triggers retinal dopamine. Animal studies show that when the eye has low levels of dopamine, its’ axial length increases.
  • UV exposure: Being exposed to UV light in the range of 360 nm to 400 nm light may be the part that helps control myopia
  • Vitamin D levels: Vitamin D is believed to help proper eye growth and the body can only produce adequate amounts of Vitamin D levels through physical exposure to the sun’s UVB rays. One study found a correlation between low vitamin D levels and myopia in children.
  • More distance viewing: Being outside causes more frequent distance viewing, as opposed to near work and the closer viewing environment that we have when indoors.
  • Brighter, outdoor light: The higher light levels that are outside are thought to be key – this doesn’t necessarily negate the other theories above. 

How much light and how bright?

Based on the theories above, here are the study recommendations:

  • There was a range of “how much light” recommendations from the studies. On the lower end, I saw that 14 hours outdoors/week could lower the chances of myopia by ⅓. On the higher end, Dr. Ian Morgan, a researcher who specializes in myopia and the environment, has concluded that children need to spend at least 3 hours/day in light levels of at least 10,000 lux to be protected. 
  • 10,000 lux is described as “the level experienced by someone under a shady tree, wearing sunglasses, on a bright summer day.” For comparison, average indoor lighting is about 500 lux. Consequently, sitting by the window with natural outdoor lighting is probably more protective than being indoors without natural light.
  • Despite the fact that the UV exposure may play a role against myopia, it is still recommended that we wear UV protective eyewear and clothing. Since it’s unclear if and how much UV exposure is needed, doctors still recommend protecting against the damaging effects of UV light. However, since many contacts and glasses nowadays include UV protection, they are continuing to investigate the possibility that a different balance may be needed between UV protection and myopia protection. 
  • To get adequate levels of vitamin D (30 ng/mL or more), some experts recommend about 10-15 minutes of sun exposure on your arms and legs without sunscreen between 10a-3pm each day. However, you need to tailor this recommendation for yourself by factoring in sunscreen (which blocks UVB), your skin pigmentation (darker skin needs longer exposure), and where you live in the world. For example, if you live at latitudes 37 degrees north of the equator, there is less UVB exposure resulting in less if any vitamin D production. You may also look into adding more vitamin D rich foods or supplements to your diet.

Most of this research is around outdoor light and its impact on children’s myopia, but it’s probably meaningful to adults who have progressing myopia, too. All in all, 2-3 hours outdoors daily can be a tall order for over-scheduled, over-worked lives – both kids and adults, especially in winter! 

How much time do you and/or your family get to spend outdoors on average? If you’re already fighting myopia in your family, see my other posts on our experiences with myopia control for children and reversing myopia as an adult.

 Resources

How much outdoor light is needed – some different viewpoints

UV light is blocked in contacts and in glasses

Sun protection can still be used outdoors for myopia prevention

Vitamin D, myopia, and sun exposure