lol. see i think it all has to do w/ the person. i have one friend that gets all squinty eyed, another that gets crazy glowing red eyes, and i really get about inbetween, my eyes are slightly red, usually not noticeable, and sometimes i get slightly squinty eyed. dont really thing it has to do w/ tolerance as much as your eyes being more used to it. your veins will adapt after a long time using. today tho me and my friend vaped, then put a blunt in a maglite and put it in two liter made into a drainer and he looked crazy as fuck and he's been smoking bout 3-4 yrs