24 Retrobulbar (Peribulbar) Block
Placement
Anatomy
Sensation to the eye is provided by the ophthalmic nerve through the long and short posterior ciliary nerves. Autonomic innervation is provided by the same nerves, and sympathetic fibers traveling with the arteries and parasympathetic fibers carried by the inferior branch of the oculomotor nerve provide additional autonomic innervation. Because the innervation of the orbicularis oculi muscle is through the facial nerve, blockade of these fibers is required to ensure a quiet eye during ophthalmic operations. The ciliary ganglion, measuring approximately 2 to 3 mm in length, lies deep in the orbit just lateral to the optic nerve and medial to the lateral rectus muscle. From this ganglion, the long and short ciliary nerves extend forward in the orbit. Immediately posterior to the ciliary ganglion, the ophthalmic artery can be found at the lateral side of the optic nerve as it crosses superior to it and passes forward medially (Fig. 24-1).