U.S. Air Force Staff Sgt. Iolanda Johnson, 633rd Aerospace Medicine Squadron ophthalmic technician, looks through a phoropter at the U.S. Air Force Hospital Langley optometry clinic at Langley Air Force Base, Va., Dec. 19, 2013. Ophthalmic technicians use the phoropter during eye examinations to measure patients' error and determine their eyeglass prescription. Johnson hails from Fayetteville, N.C. (U.S. Air Force photo by Senior Airman Jason J. Brown/Released)