Surgical procedure overcoming twitching of the eye (5)
I believe the answer is:
optic
'of the eye' is the definition.
(I've seen this before)
'surgical procedure overcoming twitching' is the wordplay.
'surgical procedure' becomes 'op' (short for operation).
'overcoming' is a charade indicator (letters next to each other) (some letters are written over others).
'twitching' becomes 'tic' (tic is a kind of twitching).
'op'+'tic'='OPTIC'
(Other definitions for optic that I've seen before include "Of sight or the eye" , "Like a sort of nerve" , "Relating to sight" , "Spirit measuring device" , "Device for dispensing measures of spirits" .)