Amblyopia, common referred to as lazy eye, is an eye whose vision is diminished. As a result, the brain begins to favor the "good" eye; it ignores the vision from the lazy eye. As a result, vision in the lazy eye progressively worsens and could lead to blindness in the lazy eye. Early detection is crucial. Once the diagnosis is made, the lazy eye can be strengthened either by patching the "good" eye, thereby forcing the brain to use the lazy eye or through the use of corrective lens or glasses. If detected early, the brain will adapt and vision will improve. If not caught by about 7 years old, the vision learning centers in the brain do not mature. Therefore, the weaker "lazy" eye stays with diminished vision forever. Simply put, if you don't use it, you lose it.
A recent multi-study review showed that with treatment, vision gains are significantly greater in children that were between 3 and 7 years old than those that were between 7 and 13 years old. The younger a child is diagnosed and treated, the greater the vision gain. However, it is interesting to note that the multi-study review also revealed that there are some vision gains with treatment beyond age 7.