Tuesday, April 14, 2015

Seeing The Light…On Myopia

Posted By Michael D. Shaw @ HealthDigestNews.com

A friend of mine loves telling the story of the quintessential teacher’s pet—a grammar school classmate of his in New York City. As he tells it, while the rest of the kids went out for recess, this particular boy usually stayed inside, peering at a book. At one point, the teacher admonished him to go outside and play with the rest of the class. He politely refused, and even asked if there were some assignment she could give him, for extra credit.
“Jimmy,” she said. “You already have an A-plus in every subject. You don’t need any extra credit. But, if you don’t go out right now, I’ll see that you lose some credit, and then you won’t have A-pluses anymore.” With that, the boy ran out, and even became a star athlete in high school. Back then, you see, it was normal, nay obligatory, for kids to play outside.
Fast forward to the present. For a variety of reasons—ranging from security concerns to the lure of cyber entertainment—children are spending far less time outdoors. And, these days, there is a much higher incidence of myopia.
Myopia, also known as nearsightedness or shortsightedness, is a condition in which the visual images come to a focus in front of the retina, either because of defects in the refractive media of the eye, or an elongated eyeball. The result is defective (blurry) vision of distant objects.
According to an article from 2009 entitled “Increased Prevalence of Myopia in the United States Between 1971–1972 and 1999–2004,” which appeared in Archives of Ophthalmology, “[T]he estimated prevalence of myopia in persons aged 12 to 54 years was significantly higher in 1999–2004 than in 1971–1972 (41.6% vs 25.0%, respectively).” Not that this problem is limited to the US or the Western world.
PhD geneticist and nifty science journo Elie Dolgin compiled the facts and figures in a recent Nature article: The growth in myopia is most pronounced in east Asia. Sixty years ago, 10–20% of the Chinese population was nearsighted. Today in China, up to 90% of teenagers and young adults have the condition. Dolgin reports that an incredible 96.5% of 19-year-old men in Seoul suffer from myopia.
In a widely publicized “Captain Obvious” comment, Dr. Padmaja Sankaridurg—leader of the myopia program at the Brien Holden Vision Institute in Sydney, Australia—warns us: “We are going down the path of having a myopia epidemic.” Although most instances of myopia can be corrected with lenses or surgery, in severe cases, complications can ensue, with blindness as a rare but not unknown consequence.
OK. What’s causing this epidemic, and what can we do about it?
Traditionally, myopia has been blamed on too much close work, and this explanation dates back to astronomer/mathematician Johannes Kepler (1571–1630) lamenting his own condition—if not earlier. Numerous studies have correlated increased incidence of myopia with more years of schooling, and within those results, the higher achievers were even more prone to the affliction. However, this devotion to scholarly pursuits might be a marker, rather than the true cause.
In an assiduously documented 2013 article called “Time outdoors and the prevention of myopia,” published in Experimental Eye Research, the authors identify 19 studies, dating from 1993–2013, which demonstrate the premise implied in their title.
A likely mechanism of the protective effect of time outdoors involves light-stimulated release of dopamine from the retina, since increased dopamine release appears to inhibit increased axial elongation, which is the structural basis of myopia. Animal experiments have replicated the protective effects of bright light against the development of myopia under laboratory conditions, and have shown that the effect is, at least in part, mediated by dopamine, since the D2-dopamine antagonist spiperone reduces the protective effect.
As to how bright the light, and how much time is required for the myopia-protective effect, noted researcher Ian G. Morgan posits that children need to spend around three hours per day under light levels of at least 10,000 lux. (1 lux = 1 lumen per square meter). 10,000 lux is said to approximate the level experienced by someone under a shady tree, wearing sunglasses, on a bright summer day. Compare this to a typical classroom or office at around 500 lux.

I guess that teacher from the beginning of this piece was onto something.

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