In general, the last muscle to be rendered akinetic with a retrobulbar anesthetic block is:

B i.e. Superior Oblique In retrobulbar block, a good sign of correct needle placement is the onset of ptosis during the injection. This may be used as the end point to limit the injection volume. This volume should block all the relevant sensory nerves and the motor nerves to all structures, except perhaps the orbicularis oculi and the superior obliqueQ, which are out side the muscle cone. Orbicularis oculi can be blocked by nasal peribulbar injection.