Part of eye in centre of head behind ears, perhaps (6)
I believe the answer is:
cornea
'part of eye' is the definition.
(I know this)
'centre of head behind ears perhaps' is the wordplay.
'centre of' says to take the centre.
'behind' means one lot of letters go next to another.
'ears perhaps' becomes 'corn' (several ears of corn).
The middle letters of 'head' are 'ea'.
'ea' put after 'corn' is 'CORNEA'.
'in' acts as a link.
(Other definitions for cornea that I've seen before include "It covers the eye" , "Eyeball membrane" , "Front covering of eye" , "transplantable part" , "Outer covering of the eye" .)