No.
It's not okay.
As one of the other comments suggests, it sounds like you're looking for an excuse. I understand bad vision; my vision is lousy, too.
If your vision is poor, then make whatever adjustment is necessary. Maybe, as you suggest, contact lenses or sports glasses. Or use techniques that don't rely as much on sight. True stories:
**When my son wrestled in high school, one wrestler was completely deaf. (The coach communicated with him through sign language.) The guy became an excellent wrestler.
**When my son wrestled in high school, there was a kid from another school who competed in tournaments (in the same weight class). The kid was missing an arm. The kid was lousy as a freshman. By the time the kid was a junior, he was an above-average wrestler.
**My son competes in BJJ and grappling (and MMA, too). Because he competes in the advanced division at under 135 lbs., there often aren't other competitors and he often gets bumped up to the 135-149.9 category. He's 5'2"; many of his competitors are close to 6' tall (in addition to outweighing him). So he's had to develop techniques to deal with guys nearly a foot taller than he is.
The point is: Bad vision is a limitation. So is deafness, missing one arm, or competing against people a foot taller. Those limitations can be overcome. In some cases, they can even be turned into an advantage. (The deaf kid, for instance, learned how to think on his own a lot better than one receiving constant verbal coaching. My son's gotten really good at submissions that taller guys don't see that often, and aren't prepared for.)
It's OK to lose against a person with more skill than you. In fact, that's how you learn and get better. Otherwise, though, it's up to you to figure out how to beat a less-skilled opponent.