How does retinal fatigue work? and why?

Question

How does retinal fatigue work? and why?

Answer 1

retinal fatigue and eye fatigue in general can have multiple sources, just to name a few:

watching a computer, tv or any other type of screen for to long (the technology the screen is build has some sort of influence on the amount of fatigue but it can't remove it). the source of fatigue is the fact that when you focus your eyes on something the blink reflex is inhibited and from this your eye surface gets dry

looking at bright light sources, like sunlingh, laser beams, welding sparks and so on. these sources of light oversaturate your light "sensors" from your eyes causing temporal to permanent damage depending on lenght of exposure and intensity

using your eyes in a "wrong" way, like reading in low light and the same also causes fatigue

Answer 2

Actually, the mechanism of retinal fatigue is not very well understood.  Part of it has to do with the firing of rod and cone cells in the retina of the eye that pick up colors; they become "fatigued" after staring at highly contrasted areas and then when you shift your eyes to a white area, they are not prepared to see it as bright enough.  However, it is also thought that the visual cortex of the brain plays a part in the phenomenon.  Studies have shown that neurons in that part of the brain give a weaker response to low-level stimulus after prolonged exposure to a high-contrast one.

The complete picture is probably a combination of the two.