This helps one to see wine son overlooked (6)
I believe the answer is:
retina
'this helps one to see' is the definition.
(I've seen this before)
'wine son overlooked' is the wordplay.
'wine' becomes 'retsina' (type of Greek wine).
'son' becomes 's'.
'overlooked' is a deletion indicator.
'retsina' with 's' removed is 'RETINA'.
(Other definitions for retina that I've seen before include "Light-receptive part of eye" , "Light-sensitive eye lining" , "Sensitive part of eye" , "Membrane in eye, sensitive to light" , "Viewer's part" .)