I've spent my entire martial arts career - striking and grappling - with crappy eyesight and no contact lenses (really contemplating seeing if contacts are a possibility for me once I go back to BJJ).
Anyway - it's not a major problem and you shouldn't hesitate to try out BJJ if your eyesight isn't great. It's not really an impediment at all when rolling or drilling technique. Stuff's pretty blurry for me, but thankfully my eyesight isn't so compromised that I can't see where an oppoent's gi is to take a collar grip, for instance. If yours is really bad, then you may have to adapt accordingly. As mentioned above, there's an awful lot you can do on feel alone.
Some general pointers:
- if you choose to wear your glasses when observing technique (I often don't, just kinda depends on my familiarity with what's being drilled that day), find a safe spot in the gym to put them when you take them off. Put them in the same spot every time, don't let anybody else touch them if at all possible. Last thing you need is somebody crushing your glasses when rolling carelessly. Staggering around trying to find them when you're exhausted sucks too.
- Don't be afraid to ask your coach questions. If your glasses were off and you think you missed a small detail watching the demonstration of a technique, ask about it. Your technique shouldn't/doesn't have to suffer because of your eyesight. Don't be afraid to move closer or around whoever's demonstrating to get the angle you need - just don't block others if you can avoid it.
- Get in the habit of memorizing gi color/belt color combinations of your classmates before you take your glasses off. For me, I cannot see faces at a distance. If there's somebody I really want to partner up with/roll against (or somebody I don't want to roll against for whatever reason) this memorization is how I identify people in addition to their basic size and shape. No gi...uh...good luck?
- Going off the last point: your teammates will probably make fun of you for being "blind." If it's good-hearted, just let it slide. For instance: I can't tell if someone is making eye contact with me from across the mat if they'd like to roll. Folks have to wave their arms and yell at me to get me to notice them. Laugh it off.