This is kind of what I tell people on another website about contact lenses and if you can be wearing them and what kind of effect you're going for.
I'm near-sighted really bad. I mean, my perscription is thicker than my dad's perscription and he has thick lenses. Now, there are contacts that I can wear, but my problem is, if I try to put anything within a few inches of my eyeball, my eye automaticly shuts closed. Anything that gets even closer to my eye - light, contact lenses, etc. I shut my eye so fast that the doctor has dialate my pupils to check for glaucoma or any other problems. And I hate eyedrops of any type.
That being said, someone would have to hold my eyelid open by force if I wanted to wear or put something close to my eyes. I've just come to the conclusion that glasses are easier and less of a hastle than contact lenses.
Back to the point. If you're going to the convention to do stuff like go to panels, dances/raves, hang-out with friends, go out to lunch or dinner together, etc. no one is probably going to care if you have contact lenses on or not. I hosted a panel one time at AUSA, and most of my audience were uncostumed males. I was not offended by that in the least.
Now, if you're doing something like cosplay chess, entering the Masquerade/Cosplay Contest, or something like that, and you really want to do contact lenses, then you should go to your eye doctor. If he/she says no to contact lenses, don't use them. If the doctor says yes, talk to him/her about your options. Again, if a doctor says no, you're just going to have to live with it. I'm sorry, but your eye health - present and future - is far more important than wearing something that's "cool" for three days.
And now, I will get off my soapbox.