I'd say I had it about 6-8 weeks. It was painful but not horrible.
At about week 6, it was really driving me crazy and I asked the doc what could be done to make it stop. He said he could pop out my eye and shoot cortisone behind it. HAHA Well, It didn't hurt quite that bad.
The vision problems to me wasn't as bad as was the pain. Ask for some pain meds for him if he's hurting. Not super strong ones, but at least ones that will give him a break from the pain for a few hours. You use and move your eyes the whole time you're awake. I mean, you can't help it. It hurts each time you move it so becomes quite annoying after a couple weeks. You just want it to go away for awhile.
I also had an MRI to rule out anything worse. My vision came back to the way it was before. I mean, it wasn't permanent. Good luck.