In 1967, when the musical "Hair" opened at the Public Theater in New York, no one thought "Let the Sunshine In" (sung by The 5th Dimension) would become a worldwide chart-topper.

Certainly no one imagined that the song's message could be the prescription for nearsightedness!

But it turns out that kids 14 to 19 and adults 20 to 39 who put down the books, walk away from the computer and TV, and let the sunshine in (their eyes) are far less likely to become nearsighted.

And those with the highest blood levels of lutein — a carotenoid you get from green leafy vegetables and from outdoor time — are the most protected.

The research, published in JAMA Ophthalmology, found that getting outdoors is key to preventing myopia.

We're not sure if it's because of exposure to sunshine (UVB rays) or because you often look at far distances when you're outside.

We do know, however, that lutein is deposited in high quantities in the retina, which contains the macula.

And that nutrient, along with the antioxidant zeaxanthin, plus DHA-omega-3, also offers protection from age-related macular degeneration. That's a double advantage.

We recommend at least 90 minutes of physical activity daily for high-schoolers, as much done outside as possible. It not only benefits their eyes, but it also fights obesity, builds self-confidence and helps them regulate emotions.

Adults should aim for 10,000 steps a day (again, outside if possible!) or equivalent. And everyone should enjoy multiple servings daily of lutein-rich greens, such as kale, spinach, collards, watercress, and basil.