Hi. I currently have an O-A visa extension. The visa was obtained in the uk, then extended on re entry to Thailand about 6 months ago. Can anyone tell me in simple terms the difference between an O and an O-A visa / extension. I appreciate that with an O-A I will need medical insurance to get my 2nd extension but what is the actual difference ? Also, I am allowed to apply for an O if I already have an O-A ??