Vision is usually managed, correctly, I think, by gently 'plucking' the muff feathering just below the eyes. Judges will usually look to make sure that the bird is question can see. But they don't want to see a bird's mangled, awkwardly cut crest. Plucking hurts for a second, like eyebrows for humans. The correct way one should do this is by 'tweezing' (with the index finger and thumb) the feathers just below the eyes (be very careful not to go to low) and quickly, (gently but firmly) pluck. If done the right way, the bird might twitch for a second, then it would be done. I know my judge likes to see feathers managed like this. Many will usually look for it in a Silkie, considering so many have trouble seeing. I hear that not plucking is an easy way to lose points, if the bird is so obviously unable to see.
Feathers in this case shouldn't bleed. I've done it several times and have seen it done and none of the times has any bird drawn blood. I've heard this is a popular practice.