Which is better retrobulbar or sub-tenon's capsule local anesthesia?

Subtenon's capsule injection of local anesthia is well known in operations of anterior segment but we are in need for more research in our university to use it in vitreoretinal surgery. Sixty patients received either retrobulbar or subtenon's injection [5 ml of 0.75% ropivacaine] to undergo vitreoretinal surgery. The level of intraoperative pain was evaluated twice using visual analogue scale. Also the [start time] was evaluated in both groups. Local anesthesia in both groups was effective in pain prevention [VAS