When it comes to double vision,Most MGer's dont' get relief from Mestinon .
Prednisone will help the fastest, with in a few weeks. Other immuno suppressants such as Imuran, Cell-cept, CycloSporine..etc. will take a few months to see the difference, and it's also very common for it to take up to a good year to see full effects of those drugs.
For the most part, the meds for this disease, is not something that's a quick fix. Unfortuanately it can take a few years to really work out what cocktail of meds work best for your body.
This is why it's known as the snowflake disease, cause we're all so different and react so differently to treatments. Too many things play into it.
Best of wishes.
In the mean time, there is the prism and tape to help while you're getting situated.
Love Lizzie