necro81 writes "Researchers at MIT's Media Lab have developed a smartphone app that allows users to measure how poor their vision is (myopia, hyperopia, and astigmatism) and receive a corrective prescription. The user peers through a $2 optical adapter at the screen of a smartphone. The app displays lighted bars, and prompts the user to adjust the display until the bars line up. Repeating this with bars in different locations and orientations allows the vision distortion to be determined to within about 0.4 diopters using a Nexus One. The iPhone 4, with its higher-resolution display, should be able to improve that to 0.28 diopters. This could have broad application in the developing world, where experienced opticians and diagnostic equipment are hard to come by."