Just posting what Siyuan and I found regarding screen distance and head stabilisation in a sample of 20 studies of fixation. Full results in attached CSV.

• Two reported only ’chin rest’ (of course, this could be shorthand for ‘chin and head rest’; we can’t be sure).
• One reported only ‘head rest’—again, this may include a chin rest too, but it’s unclear.
• Seven reported a chin and (fore)head rest.
• One reported a chin and forehead rest and temple pads
• One reported a chin rest with temple pads (they didn’t mention a forehead rest)
• One used a bite bar (this was the only study we looked at in a non-clinical population; it was from Michele Rucci’s lab). While this is unlikely to be necessary for a clinical population, I think it would be wise for ISCET standards committees to keep in mind the methods used in physiological studies. In fact, I suggest including input from an expert in fixational eye movement physiology to sense-check the guideline development; even though we are only looking to measure deviations from normal (e.g. excessive square-wave jerks, etc), we need to be clear on what ’normal’ is.