What Was the Apostle Paul's "thorn in the flesh"?

Many theories have been advanced by New Testament scholars about the nature of Paul's "thorn in the flesh" he speaks of in 2 Corinthians 12:7. The theories include:  temptation, a chronic eye problem, malaria, migraines, epilepsy, a speech impediment, or even a person, perhaps "Alexander the coppersmith" who paul says did Paul "a great deal of Harm" (2 Timothy 4:14).  In this episode of Religion Today, host Martin Tanner follows the clues and concludes Paul probably had a severe eye problem, which greatly hampered his vision, and which was visible to anyone who looked at Paul's face.  Perhaps Paul had such severe cataracts that he could not see well, and his eyes were visibly cloudy, and obviously diseased.  Paul's physical problem was so severe that he had a permanent physician, Luke, the man who wrote the Gospel of Luke. 

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