MINNEAPOLIS - Nearly 42% of Americans are now nearsighted – up from 25% 50 years ago. And half the world could be squinting by mid-century. So what causes myopia? Good Question.At the Children’s Museum of Minnesota, few screens are in sight. It’s a welcome tech break in a society glued to their screens.Research shows screen time is having a real-world impact.”We’re seeing a lot more nearsightedness than we did 20, 30 years ago,” said Dr. Andrew Ritter.Ritter is an optometrist at M Health Fairview.”I’ve seen [myopia] in very, very young kids but we tend to see it in school-aged years,” Ritter said.Myopia…