Dilated eye after having a black eye?!

It sounds like the muscle that controls whether your pupil is small or large (dilated) got damaged with the trauma of an elbow to your eye. It is also possible that you could still be having some inflammation and swelling going on in your eye, that you can't see from the outside that is causing that muscle not to work properly.

The iris sphincter muscle is responsible to contrict your pupil and make it smaller. This is the muscle that sounds to be problematic in your case, because your pupil is unable to be smaller.
The iris dilator muscle is responsible to allow your pupil to dilate and make it larger.
The iris is the colored portion of your eye.
The pupil is the black circle in the center of the iris.

Either way, I would suggest you go see an eye doctor (optometrist) to check it out. There's other things that could potentially have been damaged in your eye that you cannot see or feel, and it certainly isn't a bad idea to get that checked out. And if your eye still is inflammed on the inside, you may need some drops to help tone down the inflammation so the rest of your eye can heal -- especially if it has already been one week.

I am an optometry intern.