Thank you for your thoughts an links. I will ask a few more questions and see about finding an MD.
I know many people hesitate about asking too questions, but I might suggest asking the optometrist more about what exactly the concern is.I am guessing it is likely this issue:
http://www.geteyesmart.org/eyesmart/diseases/amblyopia.cfm
"When a child has refractive, or anisometropic, amblyopia, it means he or she has a different amount of refractive error in each eye. When this is the case, the brain will use the better-seeing eye and essentially "turn off" vision from the weaker eye."
Although MDs likely have more training, optometrists are trained to deal with the issue, this page from the American Optometric Society
http://www.aoa.org/x4699.xml
links to their "Clinical Practice Guidelines: Care of Patient with Amblyopia" which has a table giving the potential difference between the eyes which could cause a problem and in "Table 2 Potentially Amblyopiogenic Refractive Errors" it lists a difference in astigmatism of ">1.50 D" as a possible problem.
I'd ask if he is going to switch fairly soon to a full correction. I would ask him more about the issue to see his level of experience with it. Obviously its always safest to get a second opinion and see an ophthalmologist as the MD above suggested, you could even ask if he thinks that is needed. You can decide whether you agree if he says no, or can always get a second opinion anyway.
It could be true it could be false. My feeling is the optom is not a physician not a MD not have the training to do something that will be very traumatic for your child.
My strong suggestion would be to hold off on the glasses and take the child to a pediatric ophthalmologist. Ask your pediatrician for a referral or if in USA find one near you at www.geteyesmart.com
JCH MD