Could there be any effects from low powered infrared being used to track eye movements long term?
I would have said that IR is safe, but some studies have suggested otherwise.

This is a vague study on rabbit eyes:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3116568/

https://academic.oup.com/annweh/article-abstract/35/1/1/170395

So there may be a dosimetric exposure limit of some kind that you have to aim for. LED's are very controllable. I'm amazed that they talk about cataracts with a chemically soft, non -ionizing wavelength like IR, because we get IR all day from the sun. If you control the levels to be less than a sunny day, you may find that you can use equivalent of 1hr of sun exposure to run many hours of eye tracking. the figures are a matter of research.