High IOP and pain levels

I am not able to monitor my own IOP but wondered what levels of pain are experienced by people who do. For instance at what level would you first notice physical signs that your pressure was raised and what are the first signs? At what level would you experience mild, moderate or severe pain? I have had pain behind my eye at pressure of only 25 but my doctor doubts that pain is experienced at this level. I would be interested to hear the thoughts of people who can monitor their pressure when they have a headache.

Gayle