Botox for wrinkles are not supposed to last for an exceptionally long time. It just so happens that the small doses that they are inserted in are supposed to be harmless but effective. Even a minute increase in the dosage can adversely affect the individual but trained professionals have an exact idea of how to inject the serum into your skin to get rid of all the wrinkles.
A doctor once told me that I can wear glasses when the cast is present and once the cast is removed I'll have to leave it alone for a minimum of 6 weeks so that the nasal bones do not shift at any cost. So it is recommended that you wear glasses after 6 weeks.