What kind of doctor do we need to see for a developmental vision evaluation?

He's been wearing glasses since he was two, and has some strabismus. We've been to five different pediatric opthmalogists in three states since then, and several other optometrists. We've gotten many different diagnoses (it seems he never fits in any of their boxes), but the overall impression is that his glasses are correcting his problems well enough that it shouldn't be affecting him functionally. I think he's just *really* good at compensating over short periods, and making the doctors think it's less of a problem than it is. So I'm not sure where else we would take him to get evaluated for that.