U.S. Air Force Senior Airman Cole Bonack’s, 633rd Aerospace Medicine Squadron Optometry technician, eyes are tested with a phoropter at Langley Air Force Base, Va., Jan. 16, 2015. The Langley Optometry Clinic uses a phoropter, which contains different lenses, to determine a patient’s glasses prescription. (U.S. Air Force photo by Airman 1st Class Areca T. Wilson/Released)