every one sees something which is very close as double.

There is a limit to the convergence of our muscles. We don't normally focus on objects which are so close to our eyes.

And yes, using one eye muscle can lead to fatigue of other muscles. That is why straining your eyes can lead to ptosis.

I was fortunate to reach a brilliant ophthalmologist who realized that I need three sets of eye-glasses so that I will need to do as little accommodation as possible.

I have one mutlifocal which is good for most distances, as long as I don't have to focus for long. I have one for reading, which is adjusted to the distance I use when I read and I have one for long distance (such as when seeing a movie).

This trick led to significant improvement in my visual abilities.