Five out of every 100 people suffers from an eye condition called Amblyoplia, where one eye can't see as well as the other. But this can be corrected if it's treated before a child reaches the age of seven or eight.
And if you know what to look for, you can save a child from going blind.
One problem is that kids often peek during eye tests, and may get through undetected.
Doctors say in order to have Amblyopia you don't have to have crossed eyes. You can have perfectly straight eyes and be blind in one eye and nobody would know it.
With this condition, one eye has more trouble communicating with the brain than the other. If it isn't treated before age seven, it could cause permanent blindness.
Doctors say this is because the development of the visual system in a child is a lot like concrete hardening. After a critical period, the concrete hardens and there's no time left to fix it.
One patient was given a patch to go over his good eye, forcing his brain to establish a stronger signal in the other.
The challenge is to keep kids wearing their patch.
But a new alternative is also available. Doctors gave some children standard eye dilation drops in the stronger eye, blurring it so the weaker eye had a chance to catch up.
The results were just as good as the patch.
Amblyopia isn't always hereditary.
If you suspect that your child might have this condition, it's wise to have the child seen by a pediatric opthamalogist, especially if you think your child could be getting through screening tests undetected.