Anatomy

The ciliary ganglion, a parasympathetic ganglion that is 1 to 2 mm in diameter, is located approximately 1 cm anterior to the posterior wall of the orbit between the lateral surface of the optic nerve and the ophthalmic artery (Figure 121-1). Parasympathetic fibers originating in the oculomotor nerve and postganglionic fibers supply the ciliary body and sphincter pupillae muscles. The nasociliary nerve, a branch of the ophthalmic nerve, supplies the sensory innervation of the cornea, iris, and ciliary body via the short ciliary nerves, which are 6 to 10 small filaments accompanying the ciliary arteries.

Terminology

Although the terms retrobulbar and peribulbar identify types of block used in ophthalmologic operations, the terms are often confused and imprecise. Indeed, technically, all orbital blocks are retrobulbar, simply meaning that the block takes place behind the orbit. The more precise and anatomically correct terms are intraconal and extraconal, for retrobulbar and peribulbar, respectively.

Local anesthetic agents

The most commonly used agents are a 1:1 mixture of 2% lidocaine and 0.5% or 0.75% bupivacaine. Adding hyaluronidase to the anesthetic agent, in a typical dose of 3.5 units/mL, ostensibly shortens the time to onset of effect and improves the quality of the block; however, not all clinicians are convinced of the efficacy of hyaluronidase. The addition of epinephrine to the anesthetic agent improves the quality and duration of the block; again, however, its use is controversial in that it may lead to problems related to the retinal vasculature.

An intraconal block primarily involves the ciliary ganglion, ciliary nerves, and cranial nerves II, III, and VI. The classic Atkinson technique (described in Box 121-1, Figure 121-2, A to C) typically uses a 35-mm, 25-gauge, blunt needle inserted to a depth of one third of the distance medially from the outer lower orbital margin. It requires not only deep injection of a local anesthetic agent into the orbit, but also a separate block of the seventh cranial nerve to provide akinesia and anesthesia to the surgical field.