I have both vaulted and non vaulted. I don't breed specifically for either but not all large round crested birds have vaulted skulls. Silkies as a breed can be very disadvantaged and are , in my opinion not at all genetically designed for free ranging. It is by popular demand that many breeders are breeding them with much bigger crests. I trimmed all of my youngsters crests away from their eyes , this week and it's amazing to watch the personality changes in them. They are now, (with their newfound vision) , much braver and far more adventurous. I've come to the conclusion that whilst many people prefer the appearance of large puffy crests, they fail to link the clumsy , shy charismatic behavior with their limited vision.
Vaulted skull varies in severity, in its mildest form the thin layer of bone will harden and once the feathers grow in , it is difficult to pick them out in the flock. In its severest form the birds will suffer a cerebral hernia,(usually when they are still chicks ) and sadly , die. It's also worth noting that some of these birds will survive until they experience their first extremely hot summer, then they are at risk of cerebral hemorrhage which the first symptoms are ataxia and wryneck .