Eye part clears after treatment (6)
I believe the answer is:
sclera
'eye part' is the definition.
(I know that sclera is a is part of eye)
'clears after treatment' is the wordplay.
'after treatment' indicates anagramming the letters (letters treated or processed in a new way).
'clears' anagrammed gives 'SCLERA'.
(Other definitions for sclera that I've seen before include "Eyeball's outer cover" , "Bit of a looker" , "part of the eye" , "Membrane" , "tissue in the eye" .)