As Polarbear says - how much the child chooses to wear the glasses is probably quite telling.
My DD doesn't have double vision, and has excellent normal vision. Her glasses are primarly for visual processing issues (prisms). We were told she would likely need them for a year or two. She wore them VERY reliably for a good 6 months to a year. Nearly 18 months later she's much more variable with them.
A couple of months ago, when she was going through a period of not bothering to wear them much she was doing timez attack and really struggling. She wondered off, came back with her glasses and it was really quite shocking to me the difference it made to her as I had the impression no longer needed them that much (you can't hear a noticeable difference when she reads aloud most days for example, though sometimes you can).
