"lazy eye" Amblyopia is a common problem, weak muscle/imbalance around the eye. Can cause strabismus (cross eye); untreated, can lead to serious eye problems because brain will block out sight from one eye; often treated with patching to force the weak eye to adapt. Good result; rarely surgery.
Turning off vision. The human brain utilized the input of both eyes to aid in depth perception/distance etc. As a child grows, their eyes may have different strength, or weakness in an eye muscle may allow one to line up wrong. The fuzzy or double vision confuses the brain. Over time the brain may begin turning off the input of one eye & keep the best. That process is called amblyopia. If caught early it can be fixed.