> One of the observations that you had to account for was why the older grad students/professors had this "vibration".

Microsaccade amplitude is correlated with uncorrected myopia, actually. If you have visual blur it seems fixational eye movements have higher amplitude. (Proper corrective lenses generally remove this effect).

Of course, if someone has astigmatism, often it won't be properly corrected looking far right or left, too. I'm guessing this is the effect you measured.

https://iovs.arvojournals.org/article.aspx?articleid=2281647