The reason bright light helps is due to the way our eyes adjust to day and night. Our vision is received via receptors called cones and rods at the back of our retinas. When you go out at night, you go to what's referred to as your rod vision, your black and white, grainy scale vision. This allows the eye to take as much light as possible and generates an image out of it, but by doing so you lose that fine detail. During the day, cone cells in our eyes give us incredible detail, colour and high definition images. To switch from our rod cells to our cone cells requires a neurotransmitter called retinal dopamine, the release of which is triggered by light. During the day when you go out into the Sunlight, what happens is that dopamine levels go up, turning off the rod pathway so that the dopamine system stops the signal being diffused anymore and allows very fine tuning of the system, and that's what allows us to see fine detail. It's this release of dopamine that appears to be one of the key signals to stop eyes from elongating.
What is this elongation all about? As you get older, your eyeball grows longer and your focus gets shorter. But these days it's a phenomenon happening to more and more children as well. Their eyeballs grow abnormally into an elongated shape causing light rays from the distance to focus in front of the retina rather than on it, resulting in a blurred image. When you look at faraway objects, the lenses of your eyes bend parallel rays of light at an angle so that a sharp image is created on the back of your eye. To look at near objects, the internal lens needs to get rounder to bend the rays at a more acute angle. As you get older, your lens loses flexibility and its ability to curve more. That's why reading gets harder and harder. But when you're myopic, it's the distance that becomes blurry.
Although a well-lit room might feel nice and bright, the reality is it's very dim compared to daylight. A well-lit classroom is usually between around 500 to 1,000 lux, nowhere near bright enough to trigger the amount of dopamine needed. What the eye needs is three hours a day at 40,000 lux. 40,000 lux in Australia would be the equivalent of either a winter's day or a cloudy day. In Europe, that can actually be the intensity you see even in a summer's day.
In China, a three-year trial was carried out, where 40 minutes were added to the school day so the students could be out in bright Sunlight, resulting in a 25% reduction in new cases of myopia. At another trial in Taiwan they had 80 minutes a day and they got 50% protection.
Being afraid of Sun damage is no reason not to give your children outdoor exposure. Even with the standard protection (hats, sunglasses etc) they'll still be getting enough light into their eyes because of the huge difference between indoor and outdoor lighting.
Just another way that the Sun meets our physical needs, when we let it in.
Credit for Picture at Top of Page
Image courtesy of Pixabay: https://pixabay.com/en/wire-rack-head-technology-human-1311162/
 Reference: http://www.abc.net.au/catalyst/stories/4450296.htm