Methods, apparatus, and system for a virtual reality device including a display monitor, an adjustable lens, and a focus sensor. The focus sensor may be used to measure a distance between an eye and the display monitor or whether the eye is able to focus images from the display monitor. The user may provide a diopter correction. The VR device may then adjust an optical power of the adjustable lens, based on at least one of the distance or whether the eye is able to focus images from the display monitor. The focus sensor may emit coded electromagnetic radiation and determine a time-of-flight of the coded electromagnetic radiation to determine the distance or whether the eye is able to focus images from the display monitor. The adjustable lens may comprise a flexible lens； the flexible lens may be adjusted with actuators, such as piezoelectric actuators.
