If Cyclops looks into a mirror without his visor- will the beams bounce back and fry him, or will it blast a big hole in his wall??? Get's all pissed off every time he hears Manford Mann's "Blinded by the Light"
More than likely, it'll push him back into the wall, hard enough to knock him out... if it doesn't kill him with the force of impact that would send him crashing through it... Marvel "physics" has been written that way.
(Actually, the theory is that the force beams only act like "light" in our dimension, and that he is shielded to its effects on his own body. Thus, his eyelids don't get blown off or pried open by the beams.)
One of the original premises of the X-Men, besides the fact that their status of being a "new species" of human being making them the targets of bigotry stemming from the fears of mutants conquering humankind. Cyclops needed those ruby quartz visors to stop his optic blasts from causing damage to whatever he cast his gaze to. The Marvel science explained it as the material in those glasses filtering out whatever light frequency those blasts took in our universe.