Why city children who stay indoors are losing their distance vision
Among children in rural Nepal, nearsightedness affects around 1 percent. In some big Chinese cities the figure reaches 37 percent. Genes matter, but a difference that large points somewhere else: to where childhood is spent. Kids who play outside more are less likely to become myopic, and daylight itself may be doing the protecting.
Myopia means light from far-off objects comes to a focus in front of the retina rather than on it. Nearby things look sharp while distant ones blur. Usually the eyeball has simply grown too long; less often the lens bends light too strongly. It tends to appear in school-age children and gets worse between roughly 8 and 15. It is now the most common eye disorder, estimated to affect 1.5 billion people, about 22 percent of humanity, and rates have been climbing since the 1950s.
Heredity plays a large part. Population studies attribute 60 to 90 percent of the variation in refraction to genetic factors, and people carrying high-risk variants face roughly ten times the usual risk. Yet the variants identified so far explain only a small share of cases, and the rapid rise across the developed world is too quick for genetics alone. Risk also tracks with urban living, close-up work, more years of schooling and higher social class.
The outdoor effect is one of the clearer threads. One hypothesis holds that eyes evolved for bright, varied scenery and develop poorly under dim or fluorescent indoor light. Early evidence suggests long hours of daylight boost the release of dopamine in the retina, which may slow the eyeball's excess growth. The popular idea that reading itself strains the eye has mixed support; the link exists but may not be causal.
Correction is straightforward. Glasses are the simplest and safest option, contact lenses give a wider clear field but raise infection risk, and LASIK and PRK reshape the cornea for good. The stakes rise with severity, since strong myopia increases the chances of retinal detachment, glaucoma, cataracts and macular degeneration.
Source: Myopia
