Hiya,
i've had this since birth. My mum is convinced it's because I was a forceps delivery and they caight my left eye with the forceps. That's the one that turns inwards now.
I was diagnosed at abotu 4 years old, but mum said it was noticeable since birth. I had to wear glasses full time. It's a weakening in the muscles in one side of the eyeball. My focussing is perfect, it's just that I get double vision when the eye drifts. The glasses fix it perfectly, doesn't look off centre at all.
The good news is, that as I got to a teenager I experimented with not wearing my glasses as much and gradually I managed to strengthen the eye muscles. So nowadays, I don't wear glasses full time. I have them but only use them if I'm tired or doing something that requires a lot of concentration.
Hope this has helped. Anything else let me know. The doctors said they could have operated on me but there was a risk that the operation could cause my eye to turn outwards instead of fixing it, and I think that looks worse so we just went with the glasses. I did have to wear a patch on one eye whilst at home watching telly when I was younger, to strengthen the other eye.
K.xx