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4.1. Technology of Visualization 55
• Eye relief and exit pupil. Eye relief is the distance of the eye from the
nearest component of the HMD. This is shown in Figure 4.5. The size
of the eye relief is often dependent on whether the user is required to
keep his eyeglasses on, as this requires extra space between the HMD
and the eye. An eye relief of 25 mm is usually accepted to be the
minimum for use with eyeglasses. If the HMD is focusable such that
eyeglasses do not need to be worn then the eye relief can be less. The
exit pupil is the area where the eye can be placed in order to see the
full display. If the eye is outside the exit pupil then ...