Choose to be in charge of vision (5)
I believe the answer is:
optic
'of vision' is the definition.
(I've seen this before)
'choose to be in charge' is the wordplay.
'choose' becomes 'opt' (I've seen this before).
'to be in charge' becomes 'ic'.
'opt'+'ic'='OPTIC'
(Other definitions for optic that I've seen before include "Pertaining to sight" , "Device for measuring out spirits" , "Spirits dispenser" , "Visual" , "of a viewer?" .)