Some monitors do have pwm backlights which flicker extremely fast, and can worsen eyestrain or cause headaches for some. I've seen it even on monitors that advertise being flicker free.
The problem is if their PWM is too slow, to the point where we actually see the flicker directly, or just barely indirectly (e.g. by seeing a "slideshow effect" when you move a finger back and front against the lit-up display).
Concensus among opticians and ophthalmologists is however still that the main cause for eye strain is focusing your eyes at a short distance for an extended period of time.
Concensus among opticians and ophthalmologists is however still that the main cause for eye strain is focusing your eyes at a short distance for an extended period of time.