Are there behavioral causes for myopia?

Question

As an adult, I second guess all of my parents' advice, seeing that most of it was ridiculous, but some of them just might have been true. A large swath of it was connected to eyesight: "Don't watch too much TV or read too many books, you'll ruin your eyes", "Don't watch TV without a lamp on, you'll ruin your eyes", "Don't read lying down on your side", "Don't read books in the morning before you've had at least something to drink, better yet breakfast", "Don't hold the book too close or too far", "Don't wear sunglasses indoors", and probably others I don't remember any more.

They were never specific about what "you'll ruin your eyes" means, but as far as I know, the most usual vision problem in young people is myopia. But myopia's "works" through an anatomical mechanism, by having an eyeball of the wrong length, and I have no idea if any of these behaviors, or another one they failed to specify, can cause the eyeball to grow wrong.

Are there any known behaviors which cause or at least predispose for becoming myopic? Are any of the behaviors listed above connected to poor eyesight? Is it possible to reduce one's chances of becoming myopic by lifestyle and behavior change? If it is possible, does it only work before the process starts, or does it also slow down the progress of already existing myopia?

Answer 1

I think there's a link, but no one can say that this is the cause of myopia

According to American Optometric Association :

• The exact cause of nearsightedness is unknown, but two factors may be primarily responsible for its development: Heredity and Visual Stress

Even though the tendency to develop nearsightedness may be inherited, its actual development may be affected by how a person uses his or her eyes. Individuals who spend considerable time reading, working at a computer, or doing other intense close visual work may be more likely to develop nearsightedness.

Also :

• Some people may experience blurred distance vision only at night. This “night myopia” may be due to the low level of light making it difficult for the eyes to focus properly or the increased pupil size during dark conditions, allowing more peripheral, unfocused light rays to enter the eye.

• People who do an excessive amount of near vision work may experience a false or “pseudo” myopia. Their blurred distance vision is caused by over use of the eyes’ focusing mechanism. After long periods of near work, their eyes are unable to refocus to see clearly in the distance. The symptoms are usually temporary and clear distance vision may return after resting the eyes. However, over time constant visual stress may lead to a permanent reduction in distance vision.

• Symptoms of nearsightedness may also be a sign of variations in blood sugar levels in persons with diabetes or an early indication of a developing cataract.

NSH give us more input about your specifics questions :

One study found that children who read for 30 minutes or more each day were one-and-a-half times more likely to develop myopia than children who didn't read for this period of time. Research has also shown that children who spend time doing outdoor activities, such as playing sports, are less likely to become short-sighted and existing short-sightedness may progress less quickly. It is thought that this protective effect could be associated with the higher light levels outside than inside, and the fact that you are not constantly focusing on near objects. An "everything in moderation" approach is recommended. Although children should be encouraged to read, they should also spend some time away from reading and computer games each day doing outdoor activities.

That being said, since most of studies link this cause of effect on developing eye's, i don't think this could make your myopia worse after you is past 21 years old and your eye's is completely grown.

Answer 2

I think the best known environmental risk factor (to date) for myopia is lack of intense/outdoor light exposure. The pathway for this is reasonably well understood, namely: lack of intense light exposure leads to lowered dopamine, which is necessary to prevent eye growth, which in turn leads to myopia.

This based on relatively recent evidence, but it is of reasonable quality:

• three successful interventional studies (clinical trials) have been conducted first in Taiwan, then in China and again in China (RCT this time); there's a meta-analysis of these which gives the forrest plot below:

• three older cohort studies included in the aforementioned meta-analysis also found an association between light exposure and myopia, and so did a bunch of cross-sectional studies, albeit weakly. The meta-analysis conclusion was "Increased time outdoors is effective in preventing the onset of myopia as well as in slowing the myopic shift in refractive error. But paradoxically, outdoor time was not effective in slowing progression in eyes that were already myopic."

• a prospective longitudinal study (i.e. repeated measures) in Australia using for the first time a wrist-worn light sensor to measure actual light exposure found "modest but statistically significant relationship between objectively measured daily light exposure and axial eye growth (adjusting for potential confounders) indicating that greater average daily light exposure results in less axial growth of the eye in childhood." And concluded that "These findings support the role of light exposure in the documented association between time spent outdoors and childhood myopia." Its findings are consistent with other older studies e.g. one in Denmark that used day length as an approximation for light exposure.

• some animal models support the pathway: in particular a dopamine blocker given to chicken abolished the preventative effect of sunlight on myopia development. Some questions remain in this area though, in particular knock-out mice models insofar did not reproduce the effect.

• High-quality science news sources highlighted the new discoveries: in particular, Nature had featured news story. And if you wonder why all intervention studies in this regard have been conducted in East Asia, Nature has this eye opener on prevalence increase in the region:

• Education, at least in some countries, is correlated with a lack of said outdoors light exposure, but it is a much easier proxy to measure than light exposure. Several article have looked at the interaction between recently discovered genetic risk factors for myopia and education; the latest one seems to be a meta-analysis, whose main finding is reproduced below in graphical form:

The effect appears more significant in Asians than in Europeans.

I should probably mention that education also correlates with near-work exposure, an old favorite hypothesis (advanced centuries ago by Kepler!), but for which direct evidence is weaker.