How do I know if a wasp has stung me in the eye?

I would think that it would result in pain.  "When in doubt, get it checked out" (which is similar to the saying of potentially spoiled food that "when in doubt, throw it out").

Please talk with your doctor if believing that a bug sting occurred, especially near or on the eye.

Would you ask if you were bitten by a dog if it ran up to you, then ran the other way?

It will definitely hurt

You will have trouble seeing and you will feel uncomfortable.

If a wasp had stung you in your eye, you wouldn't have wonder if a wasp had stung you in your eye. Your eye would immediately hurt so badly that you would have no doubt that you had been stung.

If you can see out of the eye, you probably were not stung.

You'd know.  A wasp can sting you in the eyelid.  It would swell up and be extremely painful.  A wasp cannot sting you in the eyeball.  The hard surround of your eye is too hard for the wasp's stinger to penetrate.

you wouldn't be able to see

You would feel pain and be unable to see out of the eye for a while.