Work with a twitch in the eye (5)
I believe the answer is:
optic
'the eye' is the definition.
('optic' can be a synonym of 'eye')
'work with a twitch' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'with' means one lot of letters go next to another.
'a twitch' becomes 'tic' (tic is a kind of twitch).
'op'+'tic'='OPTIC'
'in' acts as a link.
(Other definitions for optic that I've seen before include "Bar measure" , "Device for dispensing measures of spirits" , "Spirits dispenser" , "One sees" , "Relating to the eye" .)