Abstract: An optical adapter system for a smart-phone has a lens and a light transmission guide within a housing. The adapter lens is located at the distal end of the housing in optical alignment with the smart-phone's camera lens, and the light transmission guide extends from one end that is adjacent to the smart-phone's light source toward the distal end of the housing and directs light outside of the housing to the subject being imaged. The optical adapter is preferably used in combination with the smart-phone as an ophthalmic examination tool and can be used with a computer program that runs on the smart-phone's processor. The computer program can be calibrated for use with the particular optical adapter and can be used to control the smart-phone's imaging system, such as varying the intensity of the light source, and can determine a refractive error in a patient's eye.