Score doubled, perfect in one faculty? (6-6)
I believe the answer is:
twenty-twenty
'perfect in one faculty?' is the definition.
(20-20 vision is perfect vision)
'score doubled' is the wordplay.
'score' becomes 'twenty' (synonyms).
'doubled' shows that letters should be duplicated.
'twenty' duplicated is 'TWENTY-TWENTY'.
(Other definitions for twenty-twenty that I've seen before include "Denoting normal vision" , "Perfect vision" , "Normal (as of five days ago?)" , "Normal eyesight" .)