How to tell if I have staph in my eye?

See doctor. If you are talking about conjunctivitis, which is an infection of the lining of the eye, you should see your doctor; they will be able to diagnose whether it is likely bacterial (one-sided, purulent discharge), viral, or allergic. If he deems it bacterial, the antibiotics given should cover staph. If you are talking about inside the eye itself, you definitely need to see your ophthalmologist.