Table 1.

A Lexicon for Head-Mounted Display Technology in Low Vision Rehabilitation and Vision Enhancement.

Term	Definition	Examples	Advantages for Vision Applications
Electronic visual aids	Any device that provides a digital image to improve visual performance	HMD, closed-circuit television	To provide any digital alteration that improves visual performance such as magnification to improve visual acuity or minification to expand visual fields
Heads-up display	See-through display projected in user’s line of sight that does not move with user; not a form of HMD	Automotive and aviation displays, industrial applications	Limited applications
Augmented reality	Presentation of information to the visual system that does not otherwise exist in the user’s environment	Contour video images	Presentation of visual cues missing from a user’s field of vision; information on potential obstacles in user’s path
Head-mounted display	An electronic visual aid that is worn on the head, often like a pair of glasses or goggles	See various types below	Same functions as electronic visual aids but with improved ergonomics and ease of use since worn on the user’s head
Types of HMD:
Virtual reality	HMD that covers the eyes, occupying the entire visual field	eSight, Oculus Rift	Enhancement of central vision or night vision through image processing
Near-eye display	HMD that projects a see-through image in front of the eye	Epson Moverio, Microsoft Hololens	Expansion of perceived visual field
Retinal projection	HMD that directly project a see-through image onto the user’s retina	Fujitsu Laser Headset, Google Glass	Expansion of perceived visual field
Optical Design
Non-pupil forming display	Display mounted in front of a user’s eyes amplifies image using simple lenses	Epson Moverio, Microsoft Hololens	Easier to design and fabricate than pupil forming displays
Pupil forming display	Use complex sets of lenses to that the image source (camera) can be moved away from the eyes	Fujitsu Laser Headset, Google Glass	Improved ergonomics for retinal projection devices compared to non-pupil forming displays

HMD: head-mounted display