Acts 9:1 to  

I've had Bible studies on this same topic and for me as one who also has thorns have been led to believe that thorns are soul afflictions.Saul or Paul after conversion must have felt tremendous guilt for persecuting Christians,even though he knew he was forgiven still that is a huge weight to bare...I hope this helps you ...and I hope it's accurate.

also Mary, Paul when He went to the third Heaven many think he had a tormenting demon that effected his flesh; so could be one of many physical issues, but he definitely didn’t receive his full vision back because he had to always have scribes ( luke , john mark ) etc. he signed one epistle with huge letters , in his signature because his vision was so poor and he was old by this time too.