Eye drops that could replace reading glasses for millions of people were approved by the Food and Drug Administration and hit the market this week. The drops, called pilocarpine and marketed as Vuity by Allergan, can sharpen closeup vision for six to 10 hours. They work by using the eye’s existing ability to reduce its pupil size. “Reducing the pupil size expands the depth of field or the depth of focus, and that allows you to focus at different ranges naturally,” George Waring, principal investigator of a clinical trial for the drug involving 750 participants, said. The value proposition is a matter of convenience — wearing reading glasses can be a pain for millions of people, so ditching them is intriguing.