Amblyopia, commonly called lazy eye, is a condition in children when vision does not develop properly in one eye. If it’s left untreated, a child's vision will never develop correctly in that eye. Vision impairment becomes permanent because as the child’s brain matures, it will "ignore" the image coming from the poorly seeing eye.
"A study was conducted among high school students in California who were identified by their teachers as "poor readers." The study found that only 17% had deficient visual acuity (20/40 or worse in one eye), but 80% were weak in at least one of the following visual skills: binocular fusion ranges at near, accomodative facility, & convergence near point. Stated another way, 80% of the students passed the visual acuity testing, but only 20% had adequate visual skills." ~uniteforsight.org