I think it's difficult for any of us to take guesses Bec - but I do know that even if you have the same genetic makeup/eye issues, things can vary widely over the years. My (identical) twin and I were born with a squint and short-sightedness (and related 'lazy eye' developed).

However, whilst her brain has continued to have the 'lazy eye' input switched off (back in those days, they were less proactive with surgery), mine 'switched on' with the lazy eye in my teenage years, causing eye strain which worsened the squint (although as the dystonia kicked in at that point, it's hard to say after that).

It could just be a growth issue - sometimes squint surgeries do need redoing (for various reasons). I'd bring it up with the Opth., but from what I remember Spency doesn't have major fluctuating tone, so it's maybe more likely to be a growth issue.

Also, some parents don't actually notice that their child has an intermittent squint until they start reading/doing close-up work - seems to be more obvious after the muscles have been working hard (talking NT children here).

HTH and good luck,
Swift
PS just found this link: http://www.patient.co.uk/showdoc/23068827 - could even 'just' mean that he needs glasses.