pupil swim

Pupil swim is geometric distortion changes in virtual space features as pupils move.

Example @ 0:19/0:41 of this video

Among the most visible pupil swim artifacts are distortions
moving thru what should be renders of fixed text fields.
Eye swim is most obvious during Vestibulo-ocular pupil movements,
compensating for head movements.

Eyebox is the term for small space where lens produces best image.

For e.g. microscope and telescope eyepieces,
eyebox is centered at some distance called eye relief.
Outside that space, resolution and sharpness drop while aberrations increase.
Those aberrations include geometric distortions provoking pupil swim.

Almalence's Digital Lens includes corrections for pupil swim