Three dimensional MRI study: Safety of short versus long needle peribulbar anesthesia

The standard technique of Peribulbar block is to use 25 g 25 mm needle at the junction between the lateral one third and medial two third of the lower orbital rim in the infero-temporal quadrant of the orbit. Theoretically, insertion of longer needles increases the potential of injury to important structure; however, safety of the shorter needle had never been demonstrated. This study describes the anatomy of the orbital structures with magnetic resonance imaging (MRI) using the three-dimensional constructive interference in steady state (3D CISS) sequence to present a morphological basis for needle entry at 12.5 and 25 mm lengths. Statistical comparisons were performed at the 12.5 versus 25 mm depths. Statistical significance was indicated by P < 0.05.