A group of @ children aged @-@ years scheduled for vitreoretinal surgery who received retrobulbar block were randomly assigned to @ of @ groups : group L ( retrobulbar ropivacaine ) , group LD@ ( ropivacaine plus @ g.kg-@ dexmedetomidine ) , or group LD@ ( ropivacaine plus @ g.kg-@ dexmedetomidine ) .