It is more or less normal. Depends on the bunny and is definitely something to ask the vet about. We have several different kinds of bunnies and the flat-faced ones (nethie and holland lop) get these "eye crusties" a lot. The nethie gets them so much that I clear them out for her twice daily, a task her bonded hus-bun used to do. If they get too intense, we have an antibiotic ointment from the vet that we put on her eyes as she sometimes gets a low-grad infection/irritation of her tear ducts that leads to this buildup. This is a side effect of the smooshed face of these breeds--it can lead to tear duct malformation. We monitor this closely and it doesn't change a lot, but when it does, we have medicine for it. If there is a large change in the amount or type of eye crusties, it should be seen by a vet. Also if there is nose runniness like missyscove said, it could be another symptom of an upper respiratory infection.
So to make a long story short, it can be normal or abnormal depending on the bunny and whether there are other URI symptoms.