Childhood myopia, or nearsightedness, is growing rapidly in the U.S. and around the world. Researchers say kids who spend two hours outside every day, are less likely to develop the condition.

Optometrists are lobbying for more leeway to treat patients — and physicians' groups are pushing back. But it's more than a turf war, both sides say, as they explain why patients' vision is at stake.

The visual problem is usually treated in kids by temporarily covering the other eye with a patch. But that doesn't always work. Research now shows crucial brain rewiring can happen in adulthood, too.