When you go to the optometrist, you’re asked to read symbols off a chart through a large metal device filled with lenses known as a phoropter. As you read, the optometrist switches lenses, asking you which brings the symbols into focus. Is it better now? Click. How about now? Click. The purpose is to find an array of lenses that alters the way light hits our retinas so that we may see with greater clarity.
