Part of eye is concerning girl (6)
I believe the answer is:
retina
'part of eye' is the definition.
('retina' is part of 'eye')
'concerning girl' is the wordplay.
'concerning' becomes 're'.
'girl' becomes 'tina' (**).
're'+'tina'='RETINA'
'is' is the link.
(Other definitions for retina that I've seen before include "What's behind the humour" , "Eye's membrane" , "Tear in (anag) - part of the eye" , "something that helps conjure up image" , "Sensitive part of eye" .)