Cindy,
Yes! My eye doctor takes a pen or his finger and moves it up and down, side to side. When the double vision appears I let him know and he makes note of it as to where the position of it is. He then compares it to the previous tests and determines if it has gotten worse. So far, my double vision is on the left side only. However, I am very unique...I find that if I sleep on my right side, my double vision straight ahead is horrible and can take up to 2 hours to correct itself. My MG doctor and eye doctor both are baffled why that is occurring and chalk it up to my individuality.
The key is to find a good eye doctor you like and allow him to monitor your situation continuously and not bounce around to different doctors. He could prescribe prism lenses but the drawbacks would outweigh the benefits, including the heavier weight lenses needed to correct it, causing extra weight resistance on your neck
Hope this helps!

I had a recent eye exam and was prescribed bifocals. I was having mild double vision at the time if I stared to long. Feel it affected my test and I did not get an accurate result. It seems to be a little less than what I needed. Yes the Optometrist did know I had MG at the time. I believe the constant staring at pictures for clarity cause my double vision to start throwing the test off

Hello Cindy:
I have worn tri-focal glasses for many years. I started having double vision and tired eyes about 3 years ago and they did the eye testing without dilation and added prisms. That helped a great deal, although it took a few weeks to get the eyes trained. About a year or so later they reduced the prism strength and I continue to have little issue with double vision. They did determine that looking in certain directions, as Bob3 alluded to, the double vision comes back. Apparently some of the various eye muscles are weakened with MG and will not track correctly all the time. Later in the days, my eyes can get wonky, just due to the many hours of eye muscle strain.
Cheers, Bill Z

Sorry I am late to the party. I have double vision occasionally. My ophthalmologist suggested I put a piece of opaque tape on my lens over the affected eye. I gave it a shot and was amazed with the results.