Some times my vision get blurred after zazen. It is as if I got very near sighted and it takes about half a hour before my normal vision returns. What can I do about this?

There is nothing strange about this, but it is what happens when we do Zazen. The eyes that perceive the outside world, change their point of focus when sitting Zazen, it becomes closer. And it takes some time after Zazen for the eyes to return to their usual perception. If you add any tension to your focus though, then it takes even longer for your eyes to return to everyday focus. Maybe it is important to learn how to relax and not force the eyes?