As far as I know there are 4 causes of eye fatigue from CRTs: 1) constantly looking at the same distance. This is the same with LCD and xLED displays, or even paper books; 2) refresh rate 3) intensity of the light emitted (on its own and compared to surrounding environment) 4) particles fired at your face by the magnetic field generated by the CRT

As far as I know, cause 4) has the most impact, dust particles were literally fired at your eyes, and for this reason 20 years ago it was relatively easy to see people with grounded filters mounted to their CRTs (you used to attach the ground wire to the ground contact of the RS232 or parallel port of the PC)