Perceiving by eye (6)
I believe the answer is:
seeing
'perceiving by eye' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for seeing that I've seen before include "Observing - understanding" , "... is believing, it's said" , ". . . . . . is believing, they say" , "Noticing" , "Viewing" .)