heck, some people claim to be able to see the difference between 1000 and 1001 frames per second, doesn't mean they can.
The human brain can detect motion at about 30 Hz, the eye can detect maybe up to 60 Hz but the brain can't handle that information.
Most likely this condition has nothing to do with his screen whatsoever (unless it's a really old really bad one) and certainly not with the refresh rate (a low refresh rate can cause headaches, not blurred vision).
What CAN cause eye trouble is poor illumination, having the screen set too bright in relation to the surrounding area.