As used by a publican with vision? (5)
I believe the answer is:
optic
'as' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for optic that I've seen before include "Relating to vision" , "One sees" , "of a viewer?" , "Device for measuring gin etc" , "Of the eye - drinks dispenser" .)