One of the clearest signs that you might need glasses is the inability to read an actual sign. But there are many other clues that can reveal if your powers of observation are fading. There’s no need for the Sherlock Holmes-style looking glass—eye vision problems are more common than you might think. Roughly 60 percent of the world’s population requires vision correction, according to the Vision Impact Institute.1 That’s a lot of people, but the good news is 80 percent of all visual impairment can be avoided or corrected.2 The key to understanding the clues is fortunately not a mystery. It simply takes understanding the symptoms, said Dr. John Lahr, divisional vice president of EyeMed Provider Relations and medical director.