I do not have terrible vision, but I do have glasses for reading road signs at night. I do not have contacts. I never wear my glasses on coasters, but I imagine the ride might be more enjoyable if I could actually see what was going on around me. Will they fall off?
I've never had a problem wearing my glasses on coasters. Usually, I put a strap on, and I tighten it when I get up to the station. With that on, there's absolutely no way they'll fall off. I did, however, ride Millennium Force twice with my glasses on, and no strap, and they stayed on. My second ride (in the front car), I had to reach up to push them on further (just precautionary), but they never flew up and away. Just buy an adjustable glasses strap that can be tightened, and away you go! (I'm much more worried about losing my contacts on a ride...the wind can just whip them out.)
I wear my glasses on coasters, no strap unless the park REQUIRES it. This includes strapless (ooh, sounds kinky) rides on Millennium Force, Phantom's Revenge, Flight of Fear, HyperSonic, S:UE, and so on.
As long as your glasses fit properly, the safest place for them is right on your face -- you know where they are, and they won't slip out of a pocket mid-ride...
I won't ride without my glasses. Furthermore, for safety reasons, if I didn't need to wear glasses, I'd invest in some form of protective eyewear...sunglasses, goggles, whatever...for roller coasting. I've scraped enough debris off my glasses over the years to be convinced of that requirement. I used to always use a neck cord until a ride on a Rock-O-Plane where the cord went over my head and caught under my chin, pulling the glasses loose. Since then, I don't bother with the strap unless the park requires one.
I have to agree with Rideman - I think it's not only safer, but a better ride experience with glasses. My wife lost a contact on MF at Coastermania from the wind causing her eyes to water (this was the second time she's lost one on a coaster). After a trip back to the Breakers to get her glasses, she is now a convert. And the only ride I have ever ridden that even threatened knocking my glasses off was Mean Streak when it was at it's meanest, 1994. ------------- Without upstops, airtime would have a whole new meaning.
I wear a strap that I keep not so tight, just a little tight. Too tight makes 'em feel like they're going to pop apart or something. The glasses I usually wear fit loose, so the strap is kept to where I can't take off my glasses without loosening it. If they were going to fly off, I would have noticed, since there is room for them to move around on my face, and they haven't done this on any ride including MF. My old glasses almost flew off me once early last season in Myrtle Beach, but you should excpect that if you do not take care of your specs and keep the fit up to date.
I would ride with sunglasses or something if I didn't have to wear 'scripts (I am blind, I would not be able to ride without my glasses:(), I've scraped crazy things off my glasses, too, and heard pings and such. I still get stuff in on occassion.
Well, I was riding Medusa with a friend. I had my glasses attached with Croakies (a glasses strap), he didn't. I didn't lose my glasses, he did. Luckily his were not prescription sunglasses and he just bought an overpriced replacement pair at the park. I leave the strap loose until I'm about ready to board the train, then I tighten it (not too tight). Chiller could be a problem, and definitely Medusa. I suppose there are people out there who have ridden these coasters and nothing happened to their glasses, but it may also depend on how big the frames are (they'd catch more air), and how tightly they fit you. Better safe than sorry. Walmart (and a lot of other stores) sell them (with their sunglasses) and they're very inexpensive. Have fun.