Is there a botox treatment for controlling the eye muscles affecting astigmatism?

No. Astigmatism is caused by an irregularity in the cornea or lens of the eye which causes images to be out of focus. Imagine having slush on your window or a ding in the glass-changing the thickness of the glass won't let you see any better. Astigmatism is not correctable by any muscle manipulation. See a good optometrist to determine if contact lenses or special glasses can improve your vision.
Spasm. Botox can be used around the eyes to treat muscle spasm, counterbalance the muscles that align the eyes (strabismus) or for cosmetic purposes. It cannot be used to treat astigmatism.