Well....I have never posted this here because I wasn't sure how y'all would respondDoes anyone have a crested SF that seems to have trouble seeing? My crested SF is always behind the pack...always the last one to seek a treat...and has a lot of trouble finding a treat in my hand. He 'whiffs' when trying to get a treat.

I just gave my large-crested girl a "haircut". She is currently 25 weeks old and it was getting so excessive that I was concerned about the issues you state and also about over-head predator vision for whenever they can get back out on range again.
She is also, unfortunately, a crest-to-crest breeding. No vault. Just a pretty large crest.
So...
I had first started with a very conservative cut but then went out and did "the whole 9 yards". But I did leave her a little "tail" of feathers. She has been seeing much better.
BEFORE:
AFTER: