Head mounted display and low conspicuity pupil illuminator

The present disclosure provides for an optical element useful in an optical device for illuminating the pupil of an eye, particularly for use with a head mountable display that can include eye-tracking. The optical device includes a light source and an optical element that transmits light, where light emitted from the light source is directed by the optical element toward the pupil of the eye, and attributes of the eye can then be detected by an optical sensor such as a camera. The light source can emit infrared light that is not visible to the human eye, so that world view images and/or combined digital images of the head-mountable display are not compromised.