I developed an anal fissure in May 2013. I tried Miralax, lots of water, nifedipine, etc. Finally, a year later in May 2014, I had an LIS. While the procedure was uncomfortable afterwards, it definitely worked. I was discouraged for a while afterwards, growing impatient and thinking that it had not worked.
Everything is different for everyone, but I found the key to be FIBER intake. I scratched the Miralax (it caused burning and diarrhea) and started taking up to 8 fiber pills a day (make sure to work up to that first) and increasing water intake. I tried to make sure that my fiber intake was about 35 grams a day. I trie to use the bathroom first thing in the morning, and not strain (it is better to go in the morning) and immediately use a sitz bath for at least 10 minutes. I learned the hard way that some hemorrhoid wipes only worsen the pain and cause pruritus, so I tried to use sitz bath and soft toilet tissue or baby wipes only. This was the key to the final success and healing. It took about 3 months, but I am finally healed! I get pruritus (itchy bum) every once in a while, but a little vaseline solves that everytime. If you are desperate and considering an LIS or still recovering from one, I hope this helps.
I will never miss my daily fiber intake again. I guess some of us learn the hard way how important fiber is. :)
Good luck!