Just to offer a different perspective on this:
I'm an adult who has undergone the squint correction surgery about 6 months ago. I had it done for cosmetic reasons only as my eye was getting my down and affecting my confidence. It is a pretty simple procedure, afterwards they let you rest for a few hours and then you go home, with eye drops. Follow up appt to check all is well about a week later. It's painful for the first few days, but not unduly so - more really irritating, like when you have an eyelash stuck in your eye. The eye is puffy and sore, and I took paracetamol for a few days to help me sleep at night, not in the day. After that there is no pain, but they eye itself will be red for anything up to six weeks, this is normal.
For me it was too late to do anything about the vision in that eye, it is pretty bad. Can't read with it and if I was dependent on it I would be crashing into things when walking around etc! It's really important to try and get your DC's squinting eye to work just as hard as their good eye, as if it is not used the brain will start to disregard it and they eye will not develop vision as it should. Then the window for the brain to recognize and use the 'bad' eye in conjunction with the good eye is gone, and nothing can be done to improve the vision, or make the two work together. A bit like the speech learning window, kids need to learn to talk by a certain age or they never will, that kind of thing.
So, yeah - it's great you are getting it sorted. It's a pain not having binocular vision, and also being treated like a weirdo because one of your eyes is pointing the other way. People can be so insensitive, and it affects you a lot when you make others uncomfortable, it's horrible. As a child I wouldn't wear the patches and said I didn't want glasses or an operation at the age of 6 or 7. So my mum just went with that. I wish she had seen the long term and made me wear the patches, to be honest. I am still sad that she took the words of a child over medical advice. Too soft
Good luck with your sons appointment, I'm sure it will go fine!