Both of my twin boys had surgery for Strabismus, one at the age of 3 and the other at 4.
They are both slightly far-sighted. We figured glasses might help them. I couldn't get them to wear glasses. The glasses didn't make enough of a difference for them to keep them on. It was horrible, but I'm still glad we tried.
I had heard of vision-therapy and something about prisms (I can't recall if the prisms were related to the therapy or not - my boys are now 9). The research I had done with vision therapy (again this was over 5 years ago), didn't seem too promising.
Here's what I can offer from the surgical stand point: The first twin to receive surgery had his left eye crossing in. The doctor will wait until you've had a few visits with the eye remaining in the same position. They will not do surgery if the eye is still turning in. You probably already know that. Anyway, when Twin A had his surgery they did a muscle in each eye to correct his vision. The surgery didn't take long, but waiting for him to wake took a few hours. When he woke, his eyes were blood red and when he cried he had red tears, broke my heart. The tears were only upon waking. Once he ate a popsicle we were allowed to leave. We had eye ointment and drops that we needed to give him. Since it was August when his surgery was done, he had to wear very dark sunglasses. By that evening, his sight was getting back to normal (we discovered he could count when he told us he saw two spiders - there was only one). His eyes were red for a few days, but cleared up quickly and he was fine by the next morning. We had to chase him down to wear his sunglasses when he wanted to go outside.
Now, Twin B's surgery. His eye took almost a year to settle. Twin B's right eye was turning in. When his surgery was done, they only did the muscle in one eye. He recovered just as quickly as his brother. However, he seems to have moments where his eye gets lazy sometimes. It's not constant and it's not always noticeable, but we are making another doctor appointment.
If you go with surgery I'd ask about doing the muscles in both eyes. It seemed to work well and seems to hold up over the years.
If you try vision therapy and don't mind, I would love to hear how it goes. I think you can contact me through this list.
Good luck and I'm looking forward on reading the answers you receive.