The vitreous is what its name says - it doesn’t flow. Its prime job is to hold the retina in place. That said, people have viterectomies and see perfectly well after. But it isn’t a procedure to be taken lightly. The biggest danger with any eye injury is infection. Most of the eye is not well served with bloodflow, and infections can be hard to manage. A random injury will heal, but infection may lead to permanent damage.
Needing glasses after an injury could mean anything. However just a refractive problem is unlikely. The eye maintains its shape due to the pressure of the aqueous humour. This is essentially water, but it does contain a few dissolved nutrients. The aqueous constantly flows in the front part of the eye, (ie in front of the vitreous) being produced behind the iris, flowing through the iris opening, and is drained by a circle of tiny drain passages circling the edge of the cornea. The flow is controlled and maintains the pressure in the eye, and thus the shape. Pressure variations are a problem. Too low and the eye can deflate, too high and the blood flow through the retina is impaired. It is the latter that is the really dangerous condition. Just perforating the eyeball with a needle won’t cause loss of pressure. Aspirating aqueous humour with a syringe and needle can do done to reduce pressure for a short while.
Just perforating the eyeball, as noted above, is a routine procedure to inject things. It is no more injurious that a simple injection into anywhere else. There are a range of conditions that need to be treated by injections into the eyeball. So long as it is done with antiseptic care, there is no unreasonable risk of problems.
I was bitten in the eye by a rat snake ~20 years ago ( hit me open-mouthed, sort of like a spiky projectile rather than an actual biting motion ). Went through my eyelid which alarmingly bled like a stuck pig for a several seconds and into the eyeball underneath.
About half my sclera turned red-black for a week or so, which led to the short-lived work nickname of ‘snake-eye’ ;). Otherwise zero side effects. Healed up quickly and had no impact on my vision.
Just for the participation points, I once got something lodged in my cornea that had to be removed with a needle. They numbed my eye first, then held it open with a thing like in A Clockwork Orange. They also had my head stabilized so I wouldn’t react by turning it involuntarily. So I got to watch a needle come down and prod my eye. Didn’t feel a thing, but watched the whole thing. They didn’t give me anything to relax me, either, so I have a perfectly clear memory of the whole thing.
It might not flow like water but I can say from personal experience it does move about a bit. When I was eight I was struck in the right eye by one of those suction cup toy arrows. I don’t know if the retina detached or not* but I remember everything going dark in that eye as my buddies led/dragged me home so there had to be vitreous hemorrhage.
What I got for treatment was lying in a hospital bed forever (it felt like) with both eyes bandaged to minimize movement. My main memory of the time is a nurse feeding me commenting, “You’re the only one in the whole ward (shove) who’s eating his sweet potatoes (shove).” That’s 'cause I can’t see it coming, ya dumb bunny!
Anyway, to get to the point, I wound up with a permanent floater in that eye. It isn’t the kinda transparent ones in the wiki article illustration (I get those too, once in a while) but rather, a dark spot with blurry edges. The center of the spot varies in size from small and dense to larger and not so dense. It tends to hang around the 4 o’clock position, luckily nowhere near the fovea, but since it’s distinct and unique I can track it.
Over a period of time (like weeks) it can move further from its usual spot or a bit closer, higher or lower and, like the classic floaters, does follow rapid motions of my eye. My WAG is that, while the vitreous humor is a gel it does circulate within the eye. I would assume like everything else in the body, it does (if slowly) get renewed and is not permanently sealed inside the eye like some kind of organic snow globe. Can any opthalmologists out there verify this?
*Doubtful because this was before there were lasers available to tack it back into place.
When I was a kid, I shot at a porcelain electric fence insulator with a BB gun. It bounced straight back and struck my eyelid. I must have been in the middle of a blink because for a short period, maybe an hour, I saw nothing but white from that eye. There was no permanent damage. I was incredibly lucky.