Development and human factors evaluation of a true three-dimensional display: A stereoscopic retinal scanned light display that provides accurate focus cues to ocular accommodation

Current state-of-the-art 3D displays rely primarily on the presentation of stereoscopic and vergence (angle between lines of sight of two eyes) cues to convey depth information, but generate conflicting cues to accommodation (eye focus), leading to eye fatigue and headaches in many users and rendering such displays unusable for extended viewing. In response to this shortcoming, I have designed and constructed a prototype "True 3D" display, a new variant of retinal scanning laser display that has the capability to present variable focus cues to accommodation, to better match the vergence demands generated by stereoscopic imagery. A pixel-modulated laser beam is raster-scanned onto the retina, while its focus is dynamically adjusted with a deformable membrane mirror (DMM), to create full-color high-resolution multi-focal images, in which the viewing distance of displayed objects can be shifted throughout the full range of human accommodation (6.25 cm to optical infinity). As under natural viewing conditions, objects at different distances in a scene are at different focal distances. A viewer can naturally shift accommodation to bring different objects into focus. In addition to developing the display, I have conducted a number of interrelated studies to assess the interaction of accommodation with this new display (across a variety of configurations and stages of development) and a range of other scanned light displays. Prior to this research, the accommodation response to retinal scanned light displays was not known. A key finding is that the diameter of the scanning beam plays a primary role in determining the accommodation response to the display. When the diameter of the scanned laser beam is large (>2 mm), accommodation operates under a closed feedback-loop and accurately follows DMM-induced changes in image focus. When the diameter is small (<2 mm), the depth of focus of the display increases and accommodation is partially open-looped, resulting in increased variability of accommodation (both between and within subjects), while proximal accommodation cues lead to an increased average accommodation response. The suitability of large and small beam diameters for different applications and the potential of this technology are discussed.