Needle blocks of the eye

Published on 07/02/2015 by admin

Filed under Anesthesiology

Last modified 22/04/2025

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Needle blocks of the eye

Michael P. Hosking, MD

In most cases, anesthesia for cataract surgery is performed using regional techniques; in the United States, 50% of patients have retrobulbar blocks, 25% have peribulbar blocks, and the remaining patients receive topically applied anesthetic agents, sub-Tenon blocks, or inhalation agents. Increasingly, these regional blocks are performed by the ophthalmologist; however, whether the block is performed by the surgeon or the anesthesiologist, anesthesiologists must be cognizant of the technique and its side effects.

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.

Types of eye blocks

Intraconal block

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.

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Figures 121-2 A to C, Administering the intraconal block. See Box 121-1 for further explanation of technique shown. (Images courtesy of eyerounds.org.)

In the past 2 decades, major changes have taken place in the performance of intraconal blocks. The position of the eye in Atkinson blocks has been supplanted by a forward-looking position. Based on cadaver and other data, the length, bevel, position, and size of the needle, as well as the amount of anesthetic agent injected, have all been revised. To reduce the incidence of needle-related complications, the current recommended needle sizes for performing either an intraconal or extraconal block are no longer than 2.5 cm, and as short as 1.5 cm, and 25 gauge. More often than not, sharp, beveled, narrow-gauge needles have replaced the blunt dull needles used more commonly in the past.

Complications

Retrobulbar hemorrhage

The most common complication, retrobulbar hemorrhage, occurs secondary to puncture of the vessels within the retrobulbar space. It is characterized by simultaneous appearance of an excellent motor block of the globe, closing of the upper lid, proptosis, and a palpable increase in intraocular pressure. Many retrobulbar hemorrhages are minimal or even subclinical, and, on rare occasion, surgery may be continued; however, because of the significant risk of repeat hemorrhage, with its devastating complications, surgery often must be postponed.

Oculocardiac reflex

An oculocardiac reflex (see Chapter 38) manifested by bradycardia, arrhythmias, and even periods of cardiac asystole—may occur acutely with block placement or expanding retrobulbar hemorrhage. The latter may happen some hours after a retrobulbar hemorrhage as additional blood extravasates. The reflex is trigeminal-vagal via the ciliary branch of the ophthalmic division of the trigeminal nerve. If an arrhythmia develops, surgical manipulation should be stopped and intravenous atropine (0.007 mg/kg) given.