「暗い所で本を読むと目が悪くなる」は言い過ぎ。近視とはっきり関係していたのは"外遊び"だった

Many parents say, "Don't read in the dark! It will hurt your eyes." Is that true? Reading in dim light can make your eyes tired, but they get better after rest.

Eye doctors say it does not damage your eyes. Nearsightedness, or myopia, is more clearly related to not playing outside enough. Scientists are still checking if room light matters too. Playing outside may help protect your eyes.

Many of us were told that reading in dim light would ruin our eyesight. However, the American Academy of Ophthalmology says that reading in the dark does not damage the eyes. It can cause tired eyes, dryness or headaches, but these are temporary. Most myopia happens when the eyeball grows slightly too long from front to back. This change is usually permanent, so it is different from tiredness.

In a 2015 study in China, about 1,900 first-grade children were followed for three years. In schools that added 40 minutes of outdoor activity each day, about 30 percent of children developed myopia, compared with about 40 percent in other schools. Whether indoor light levels also matter is still being studied.

Everyone has heard "Don't read in the dark or you'll ruin your eyes," yet there is little evidence that it harms the eyes. Dim light makes the pupils widen and the focusing muscles work harder, and close reading makes people blink less, so temporary eye strain, dryness and headaches can occur.

The American Academy of Ophthalmology states that reading in dim light does not harm the eyes, and a 2007 BMJ article on medical myths found no support for permanent damage. Myopia is different: most cases arise when the eyeball becomes slightly too long, so that distant images focus in front of the retina, a structural change that usually cannot be reversed. Besides genetics, environment matters.

In a 2015 randomized trial in Guangzhou, China, involving about 1,900 first-graders, schools that added 40 minutes of daily outdoor activity saw about 30 percent of children develop myopia over three years, compared with about 40 percent in other schools. Long hours of near work are also linked to myopia, but only modestly. Light itself may be the key. In one Chinese study, fewer children developed myopia after their classrooms were made brighter. Bright outdoor light may also slow the eye's growth.