How do I know what the correct size of the glasses is for me?

Within each AmblyoPlay Box, standard-sized glasses come included. They are OK for everyone above the age of 5. Admittedly, they will be a bit oversized, but it is better to have a wider visual field covered. If you need smaller glasses instead (if your child is younger), you can either write a note in the order that we should replace the standard glasses with smaller ones, or you can purchase smaller glasses so that you have both at your disposal. You can add Smaller Glasses here: https://www.amblyoplay.com/product/small-amblyoplay-glasses/