Is botox for the treatment of blepharospasm?

Yes! In fact, initially, Botox was a drug used by eye doctors for that very purpose. Some very observant people (doctors wives?) noted that the patients getting treated were getting wrinkle reduction. Allergan, saw the potential and turned the Botox into a cosmetic medication.
Absolutely. Works like a charm. This is the first line therapy.
Yes. Botox was originally developed to treat blepharospasm as well as a host of other conditions that cause muscular spasms. My first experience with it many years ago was in treating facial spasms, this was long before we were using it for cosmetic purposes. I still use it for those reasons as well as for my cosmetic patients.