I'm at Liverpool University retin-a micro gel da valeant e melora c. saiba mais Vision problems like nearsightedness, farsightedness and astigmatism - collectively known as refractive error - affect about 25% of kids screened by ChildSight, Daniels said. The conditions often develop at ages 11-15 during puberty, when eyes are changing the most, which is why the organization focuses on middle school students.