I've had an individual approach me about eye strain which he believes is caused because he were wares contact lenses and safety glasses. I have given him the usual advice of ensure is safety glasses are clean, try if different type, go to your optician etc. However, I am curious if there has been any research done on this matter? I would like to go back to the workforce and if possible put this "myth" to bed if possible.

The “myth” is that wearing glasses can permanently damage your eyes, not that eye strain exists. It might be possible that wearing safety glasses over contact lenses causes eyestrain (the muscles that focus the eye having to work extra hard and like any muscle they get tired)
This is of course not an excuse not to wear your safety glasses. Instead the matter should be referred to an optician who can recommend appropriate action.
You cannot expect staff to wear eyes protection which causes them discomfort.