A method of operating a wearable heads-up display that in use is worn on a head of a user includes generating an infrared light, scanning the infrared light over an eye of the user, detecting reflections of infrared light from the eye of the user, and extracting test biometric identification data from at least a portion of the detected reflections and corresponding scan orientations. A similarity measure between the test biometric identification data and reference biometric identification data associated with the wearable heads-up display is determined. The user is authenticated based on the similarity measure.