Schirmer's test is one of the tests used by eye doctors to determine whether you have dry eye syndrome. It's very simple - paper strips are inserted into the lower eyelid and the eyes are closed for 5 minutes. The amount of moisture (longitudinally along the strip) is then measured. Wikipedia adds that sometimes a local anesthetic is used so that the eyes don't tear due merely to the irritation of the paper.
Determining dry eye syndrome is also determined through anecdotal reporting of chronic dry eyes, chronic need of eyedrops, and a clinical exam.
Related condition: dry eyes.