The most common complication of the retrobulbar block is hematoma formation, which can be minimized by using a needle shorter than 31 mm or performing a peribulbar approach.
Sudden apnea may happen secondary to unexpected spinal anesthesia—related to injection within the optic nerve sheath.
Additional block of the facial nerve is essential to produce an immobile eye by blocking the orbicularis oculi muscle.
This block is performed more often by ophthalmologists than by anesthesiologists. The combination of retrobulbar anesthesia and block of the orbicularis oculi muscle allows most intraocular surgery to be performed. This regional block is most useful for corneal, anterior chamber, and lens procedures.
Patient Selection. Patients who require retrobulbar (peribulbar) anesthesia are principally older patients who are undergoing ophthalmic operations.
Pharmacologic Choice. If retrobulbar block is used, 2–4 mL of local anesthetic is all that is required to produce adequate retrobulbar anesthesia. Conversely, if the peribulbar approach is chosen (i.e., the needle tip is not purposely inserted through the cone of extraocular muscles), slightly larger volumes—4–6 mL—may be necessary. Almost any of the local anesthetic agents are applicable, with many ophthalmic anesthetists using combinations of bupivacaine and lidocaine.
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 2–3 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. 22.1 ).