Members have attributed environmental causes of their myopia (spherical defocus) to visual strain from reading books, playing video games, some childhood traumatic event, etc. What causes astigmatism (cylindrical correction)? What may have caused your astigmatism?

The symptom of astigmatism seems to be double-vision (or multiple images). Mine happen to be predominantly double vision in the horizontal direction. Unfortunately I lost my lens prescription to try to correlate this angle with the cylinder angle. How about others here?

Perhaps, another way to ask my question is:
Which cause of myopia also leads to astigmatism and which doesn't?
What caused your myopia and did it also cause astigmatism?
I think my myopia is from strain due to reading too much. I also have astigmatism.