Nearly all teenage males in Taiwan are nearsighted. Better than 8 in 10 teenagers in Beijing, China were found to be nearsighted. Even in the U.S., the rate of nearsightedness (myopia) is 41%, a huge rise from three decades earlier.
One study shows that students who spend 40 more minutes outdoors each days experience a 23% reduction in myopia. [The Wall Street Journal April 20, 2015; PLoS One Nov 5, 2013; Ophthalmologe Aug 26, 2016]
It was Sir Stewart Duke Elder who wrote the encyclopedic Textbook of Ophthalmology who recommended avoidance of indoor activities for children to reduce the risk of nearsightedness in 1935. [Strabismus 2016] Indeed, low vitamin D blood serum levels are associated with a longer eye and a focus point that falls short of the retina, resulting in the ability to see near objects but not distant objects. [European Journal Epidemiology May 2016] A century ago schoolrooms were build with large windows to try to reduce myopia. [Perspectives Public Health Jan 2016] Midday sunlight exposure produces natural vitamin D3 in the skin which is also stored in the liver. Overuse of sunscreen agents also poses a problem. Children should use sunscreen lotion on areas like the nose, feet, face, back of neck, that are more easily sunburned, but not on the entire body.