Person in theatre who performs surgery using rubber and ruler (5,6)
I believe the answer is:
opera singer
'person in theatre who performs' is the definition.
'surgery using rubber and ruler' is the wordplay.
'surgery' becomes 'op' (short for operation).
'using rubber' becomes 'erasing'.
'and' is a charade indicator (letters next to each other).
'ruler' becomes 'er' (abbreviation for Elizabeth Regina).
'op'+'erasing'+'er'='OPERA-SINGER'
(Other definitions for opera singer that I've seen before include "La Scala artiste" , "Stage performer" , "diva" , "Prima donna" , "Butt perhaps" .)