'Trap Queen' Rapper Fetty Wap -- I Didn't Get My Eye Shot Out! That Should Be Obvious (VIDEO)

Now that Fetty Wap is blowing up with his hit "Trap Queen" ... he wants to clear up the biggest rumor about how he lost his left eye, and says the truth is as obvious as the nose on his face.

We got the rapper in NYC after a late night TV appearance ... and just as Fetty was schooling our photog about losing his eye to glaucoma -- Fetty's mom popped up and taught him something he never knew about the eye.

You also gotta hear the Jersey native explain why all that talk about him getting blasted with a shotgun ... makes ZERO sense. Watch ... you will definitely say, "Duh!"