Yeah, you could lose your eye, but your eye is actually pretty well protected. Get an anatomy book or website and look at how the sinuses and facial bones are arranged.
The bones to the tiop and side of your eye, and the bridge of the nose protect you from most of the blows you are talking about. Your eye socket is made of some big bones; The maxilla (face around the nose), Frontal (forehead), and zygoma (cheek) which are pretty sturdy, but are jointed and can be broken or have joints separate. Then there are several thin bones: Lacrimal, ethmoid, etc more on the inside. These are eggshell-thin bones and are not made to hold much strain.
If you get hit right in the eyeball, forcing it into the socket, you get what is called a blowout fracture, where the floor of the eyesocket blows downward into the maxillary sinus. This is bad, but the fat pad that surrounds the eyeball usually protrudes into the sinus, not the eyeball. If it is severe it can cause enough shift in position to tear or strain the optic nerve. Also, blood and nerve supply can get pinched off.
A crushed eye socket from the side can cause the eyeball to protrude, but they can usually fix it if it doesn't tear the nerve. The problems that arise are that there are often sharp bone fragments that will cut the eye. Even cutting the eyeball open doesn't mean loss of sight, necessarily, but it could. If you damage the lense, focal muscles or the retina where the image forms and the nerves carry it away, yer screwed.
Tearing or detatching the retina, which sits kinda like a sheet on the back of the eye, can mean anything from nothing to losing color sight, to blindness.
Scratching or irritatiing the front of the eye will cause cataracts later, and maybe wavey or screwy vision in that eye.
The eyeball itself rarely pops under pressure, the tissue is pretty tough, nut increasing the pressure inside the eye can damage almost anything in it, depending on where it is applied.
Be careful with the eyes. They are one of the few things surgeons can't nail back together so good.
