Ring doctor's surgery for treatment (3-4)
I believe the answer is:
eye-drop
'treatment' is the definition.
'ring doctor's surgery' is the wordplay.
'ring' becomes 'eye' (both can mean a loop or hole in something).
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'surgery' becomes 'op' (short for operation).
'eye'+'dr'+'op'='EYE-DROP'
'for' is the link.
(Other definitions for eye-drop that I've seen before include "A tear (Shakespeare)" , "A poetical tear?" .)