Sunlight exposure reported to decrease vision deterioration in children
According to a new study, reduced sunlight exposure increases vision deterioration in children. The study was conducted on Danish children with myopia (nearsightedness). The study is particularly relevant to Americans living in the northern regions of the nations where the hours of sunlight in winter are shorter. The findings were published in the February issue of the journal Ophthalmology.
Almost a third of Americans have myopia, which usually appears in childhood and worsens as the eye grows and keeps changing shape until age 20. It is due to either the excessive length of the eyeball or excessive curvature of the cornea. The result is blurred distant vision. A research team led by Dr. Dongmei Cui, an ophthalmologist at Sun Yat-sen University in Guangzhou, China, conducted a study to determine whether increased exposure to sunlight would slow the progression of myopia. The study group comprised more than 200 children aged 8 to 14 years old with myopia in Denmark, where day length ranges from seven hours in winter to almost 18 hours in summer. The investigators looked at changes both in the children’s ability to see and in the shape of their eyes. During the six months with the least daylight, myopia progressed by 0.32 diopters (a measurement of the optical power of a lens and the increment used in eyeglasses prescriptions). In comparison, the children’s vision deteriorated by 0.28 diopters over the sunniest months.
Nearsightedness tends to worsen ass the length of the eyeball increases from front to back. During the winter, the children’s eye length increased by an average of 0.18 millimeters, compared to 0.14 mm over the summer. The investigators did not analyze how much time the children spent outside, just how much they probably did based on the season. They noted that Danish children spend much more time outdoors in summer, and very little in winter, when temperatures hover around freezing for four months.
The researchers noted that past research on myopia in US children deteriorated more during the six months of the school year and less during the six months that include summer. In contrast, another study in Singapore, where days are about the same length all year, found no seasonal difference in the progression of myopia. The researchers of this new study point out that to the best of their knowledge this is the first study to link nearsightedness progression with hours of available daylight. They note that even on overcast days, light from the sun is much more intense than indoor light. Studies on both mammals and birds have found that light exposure plays a role in the development of the eye; animals reared from a young age with frequent exposure to high intensity light may be somewhat protected from myopia. However, no similar effect has been seen with light exposure in adulthood.
Take home message:
As previously mentioned, this study is of more importance to Americans noted in northern regions of the nation, which have a climate and winter sunlight duration similar to Denmark. Another problem linked to decreased sun exposure in the winter is seasonal affective disorder (SAD). It is a mood disorder in which individuals who have normal mental health throughout most of the year experience depressive symptoms in the winter year after year. Indoor light is not very effective for mimicking sun exposure; however, a light box or sun lamp can mimic outdoor sun exposure.