Basically, looking into infrared LED's and a camera with an infrared bandpass filter for tracking eye movements; my concerns are whether there would be any potential negative long term effects from constantly illuminating the eye with low power infrared? TIA A
I would have said that IR is safe, but some studies have suggested otherwise.
This is a vague study on rabbit eyes:
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.
Heat waves are probably infra-red waves. We have these all around us (with great intensity) all the time. A small intensity Infra-red from an LED shall not cause any problem at all even in long terms. Our eyes are evolved to withstand far greater(i.e. around temperature of 45°C) intensities. So, no need to worry.
But since, water is lost from heat waves, do allow subject to blink his eyes frequently.