• Kenneth Merhige, MD
• Robert Della Rocca, MD

I.	INTRODUCTION
II.	ANATOMY
III.	RETROBULBAR ANESTHESIA Conventional Technique Alternative Techniques
IV.	PERIBULBAR ANESTHESIA Alternative Techniques Retrobulbar Versus Peribulbar Blocks
V.	MAJOR COMPLICATIONS OF EYE BLOCKS
VI.	TOPICAL ANESTHESIA
VII.	PERILIMBAL (SUBCONJUNCTIVAL) ANESTHESIA
VIII.	EPISCLERAL (SUB-TENON’S) BLOCKS Common Principle Needle Technique Surgical Approach
IX.	USE OF EYE BLOCK FOR POSTOPERATIVE ANALGESIA
X.	LOCAL ANESTHETICS & ADJUVANT AGENTS CONSIDERATIONS Who Should Perform Eye Blocks Perioperative Management
XI.	SUMMARY

INTRODUCTION

Ophthalmic surgery is one of the most frequent surgical procedures requiring anesthesia in developed countries.¹ Perioperative morbidity and mortality rates associated with eye (eg, cataract) surgery are low.^2,3 Nevertheless, because patients with cataracts tend to be older and to have serious comorbidities,^4–9 systematic preoperative evaluation should be performed to consider a patient eligible for surgery.⁹ Anesthetic management may contribute to the success or failure of ophthalmic surgery. A closed-claims analysis by Gild and coworkers¹⁰ found that 30% of eye injury claims associated with anesthesia were characterized by the patient moving during ophthalmic surgery. Clinical strategies to ensure patient immobility are essential, as blindness is the outcome in many cases of eye injury. Most problems occurred during general anesthesia. Quicker patient rehabilitation and fewer complications are the main reasons why many ophthalmic surgeons are choosing local (LA) over general anesthesia.^11–13

In the past, regional anesthesia on the eye typically consisted of retrobulbar anesthesia (RBA), with the surgeon performing the block. Widespread use of the phacoemulsification technique, however, has changed the anesthesia requirements for this technique—total akinesia and lowered intraocular pressure are no longer necessary. Consequently, conventional RBA is used less frequently today, particularly since it carries a greater risk for complications than do the emerging techniques. The newer techniques do not provide akinesia of the globe paralleling that of the retrobulbar block; however, they are useful for anterior segment surgery, especially cataract surgery. Accurate knowledge of anatomy and of various anesthetic techniques are necessary to determine the appropriate block for specific clinical situations. This chapter will review the relevant anatomy of the eye, classic (retro and peribulbar) needle block techniques, emerging anesthesia techniques, and choice of LAs and adjuvant agents.

ANATOMY

The cavity of the orbit has a truncated pyramid shape, with a posterior apex, and a base corresponding to the anterior aperture. The orbit contains mainly adipose tissue, and the globe is suspended in the anterior part. The four rectus muscles of the eye insert anteriorly near the equator of the globe (Figure 21-1). Posteriorly, they insert together at the apex on the tendineus anulus communis of Zinn, through which the optic nerve enters the orbit. The four rectus muscles delineate the retrobulbar cone, which is not sealed by any intermuscular membrane.^14–17 Sensory innervation is supplied by the ophthalmic nerve (first branch of the trigeminal nerve [V]), which passes through the muscular cone (Figure 21-2). The trochlear nerve (IV) provides motor control to the superior oblique muscles, the abducens nerve (VI) to the lateral rectus muscle, and the oculomotor nerve (III) to all other extraocular muscles. All but the trochlear nerve pass through the muscular conus. Injection of LA solution inside the cone will provide anesthesia and akinesia of the globe and the extraocular muscles. Only the motor nerve to the orbicularis muscle of the eyelids has an extraorbital course, coming from the superior branch of the facial nerve (VII). Many major structures are located within the muscular conus and are therefore at risk of needle and injection injury. These include the optic nerve with its meningeal coverings; blood vessels of the orbit; and the autonomic, sensory, and motor innervation of the globe. For this reason, some authors advise that introduction of the needle into the muscular cone be avoided and suggest that needle insertion be limited to the extraconal space.^18,19 However, posterior to the equator of the globe, the extraconal space is only a virtual space, because the rectus muscles are in contact with the bone walls of the orbit.

Figure 21-1. Insertion of the four rectus muscles of the eye and the two obliques. The muscles insert anteriorly near the equator of the globe. (1) Medial rectus, (2) Lateral rectus, (3) Inferior oblique, (4) Superior oblique, (5) Superior rectus, (6) Inferior rectus.

The scleral portion of the globe is surrounded by Tenons capsule, a fibroelastic layer stretching from the corneal limbus anteriorly to the optic nerve posteriorly. Its proper anatomic name is the facial sheath of the eyeball. It delimits a potential space named the episcleral space (sub-Tenon’s space). This is only a virtual space that expands when fluid is injected into it.

RETROBULBAR ANESTHESIA

Historically, RBA has been the gold standard for anesthesia of the eye and orbit. This technique generally consists of injecting a small volume of LA solution (3-5 mL) inside the muscular cone (Figure 21-3). A facial nerve block is occasionally required to prevent blinking. Because of its extraconal motor control, the superior oblique muscle may frequently remain functional, precluding total akinesia of the globe. The main hazard of RBA is risk of injury to the globe or to one of the anatomic structures in the muscular cone. Near the apex, these structures are packed in a very small space and are fixed by the tendon of Zinn, which prevents them from moving away from a needle.

Conventional Technique

Since its formal description by Atkinson toward the end of the nineteenth century,²⁰ conventional RBA has not changed for decades. The patient is asked to look in the “up-and-in” direction. The needle is introduced through the skin below the inferior lid at the junction between the lateral third and the medial two thirds of the inferior orbital edge (Figure 21-3). The needle is directed to the apex of the orbit ( slightly medially and cephalad) and advanced to a depth of 25-35 mm. Two to 4 mL of LA solution is then injected. An additional facial nerve block is performed to prevent blinking; the technique most frequently used is the Van Lindt block.²¹

Figure 21-2. Sensory innervation of the eye and orbit is supplied by the ophthalmic nerve (first branch of the trigeminal nerve [V]), which passes through the muscular cone.

Figure 21-3. Retrobulbar anesthesia. The needle is introduced through the skin below the inferior lid at the junction between the lateral third and the medial two thirds of the inferior orbital edge.

Figure 21-4. The classic technique of peribulbar anesthesia involves two injections. A: The first injection is inferior and temporal, the needle being introduced at the same site as for an RBA injection, but with a smaller “up-and-in” angle. B: The second injection is superior and nasal between the medial third and the lateral two thirds of the orbital roof edge.

Alternative Techniques

The Atkinson up-and-in position of the gaze was abandoned when Liu and colleagues²² and Unsold and colleagues²³ warned that it increases the risk of optic nerve injury. Indeed, this position places the optic nerve near the path of the needle. Moreover, the optic nerve is stretched and can be injured easily by the needle rather than being pushed aside. Alternative puncture sites and specially designed bent or curved needles have been proposed but have never gained popularity.^24–26 RBA is used less frequently today, at least in part because of its risks of complications.

PERIBULBAR ANESTHESIA

With peribulbar anesthesia, the needle is introduced into the extraconal space.^18,19,27,28 The injected volume of LA (6-12 mL) is larger than that for a retrobulbar injection. This larger volume allows the LA to spread into the whole corpus adiposum of the orbit, including the intraconal space, where the nerves to be blocked are located. Additionally, such a large volume allows anterior spread of LA to the lids to provide a block of the orbicularis muscle and to avoid the need for additional lid block.

Figure 21-5. Site of introduction of the needle for the most frequently used blocks: (1) medial canthus peribulbar anesthesia, (2) lacrimal caruncle, and (3) inferior and temporal peribulbar injections.

The classic technique involves two injections. The first injection is inferior and temporal, the needle being introduced at the same site as for an RBA injection, but with a smaller up-and-in angle. The second injection is superior and nasal between the medial third and the lateral two thirds of the orbital roof edge (Figure 21-4B).

Alternative Techniques

Several alternative techniques of peribulbar anesthesia have been described (Figure 21-5). The most common sites for needle insertion are (1) medial canthus peribulbar anesthesia,²⁹ (2) lacrimal caruncle,^30,31 and (3) inferior and temporal peribulbar injections.^18,19

Clinical Pearls

Whichever technique of peribulbar anesthesia is chosen, several principles apply:

Single-injection vs multiple injection technique. Increasing the injected volume of LA provides sufficient anesthesia. Additional injections are not needed.³² In addition, anatomic distortion following the first injection may increase the risk of complications associated with consecutive injections.³³ As a rule of thumb, a second injection should be performed only as a supplement when the first injection has failed to provide effective anesthesia.

Needle insertion sites. Needle insertion through the superior nasal site should be avoided. At this level, the distance between the orbital roof and the globe is reduced, theoretically increasing the risk of globe perforation. Additionally, the superior oblique muscle maybe injured by the needle. The inferior nasal puncture should be used instead. An alternative site of puncture for peribulbar anesthesia is the medial canthus (see Figure 21-5).²⁹ The needle is introduced at the medial junction of the lids, nasal to the lacrimal caruncle, in a strictly posterior direction to a depth of 15 mm or less. At this level, the space between the orbital wall and the globe is similar in size to that of the inferior and temporal approach and is free from blood vessels. Moreover, myopic staphyloma, an anatomic anomaly that represents a risk factor for perforation, is infrequently encountered on the nasal side of the globe.

Needle insertion depth. Limit needle insertion depth to 25 mm. Posterior to the globe, the rectus muscles are in contact with the orbital walls, so that the extraconal space entirely disappears and becomes virtual. Increasing needle insertion depth would be expected to change a peribulbar to a retrobulbar injection.³⁴ Some “posterior peribulbar blocks” are in fact unintentional retrobulbar injections. This is a plausible explanation for optic nerve injury after an attempted peribulbar injection. Moreover, a long needle fully introduced into the orbit may reach the apex of the orbit, another hazardous area.³⁵ Inserting the needle to a depth of 40 mm has led to performing the injection directly through the optical foramen in 11% of cases.³⁶

Thin needles (25-gauge) are suggested for reducing pain on needle insertion. The use of short-beveled needles may be safer because they may enhance the tactile perception of resistance during needle insertion (intraneural or intramuscular placement). Indeed, on cadavers, more pressure is required with short-bevel needles to perforate the sclera.³⁷ Nevertheless, these are only theoretical considerations, since the complication rate with peribulbar blocks is low.

Use compression to lower intraocular pressure, which increases after injection. Compression has not been shown to enhance the quality of the block. Applying a pressure of 30 mm Hg for 5 to 10 min is usually sufficient.

In all cases, the spread of LA within the corpus adiposum of the orbit remains somewhat unpredictable, leading to the need for more anesthetic to prevent an imperfect block. Depending on the surgeon’s preference for akinesia, additional anesthetic is required in up to half of all cases.^27,28 This poor reproducibility in block efficacy is the main disadvantage of peribulbar anesthesia.¹⁹

Retrobulbar Versus Peribulbar Blocks

Retrobulbar block has been traditionally assumed to be more effective than PBA. However, when a sufficient volume of LA is injected, both blocks have similar success rates.³⁸ There is a sound anatomic explanation for this: the absence of an intermuscular membrane to separate extra-from intraconal compartments results in a similar space for the spread of local anesthetic.^14–17 Therefore, if the effectiveness is similar, it would be logical to use the technique with less risk of complications. Because the retrobulbar block theoretically carries a higher risk of complications (optic nerve injury, brainstem anesthesia, retrobulbar hemorrhage), peribulbar block is deemed preferable to retrobulbar block.

MAJOR COMPLICATIONS OF EYE BLOCKS

The primary cause of serious complications is needle misplacement. Although patients’ anatomic features may increase the risk of complications, the main risk factor is the lack of training and experience on the part of the physician. However, it should be noted that complications such as retrobulbar hemorrhage may occur with even the most experienced practitioners. Presenting signs, symptoms, and mechanism of common complications are summarized in Tables 21-1 and 21-2).

Central nervous system complications of eye blocks may occur by two different mechanisms:

1. An accidental intraarterial injection may reverse the blood flow in the ophthalmic artery up to the anterior cerebral or the internal carotid artery.⁴⁰ Consequently, injectate volume as small as 4 mL may produce seizures. Symptomatic treatment by maintaining patent airway; providing oxygenation; and abolishing seizure activity with small doses of benzodiazepam, propofol, or barbiturates, is usually adequate and results in a rapid recovery without sequelae.

2. An unintentional injection under the dura mater sheath of the optic nerve or directly through the optic foramen may result in subarachnoid spread of the LA. This causes partial or total brainstem anesthesia.^41–43 Katsev and coworkers³⁶ have shown that the apex of the orbit may be reached with a 40-mm needle in up to 11% of patients.³⁶ Depending on the dose and volume of LA spreading toward the brainstem, a bilateral block; cranial nerve palsy with sympathetic activation, confusion, and restlessness; or total spinal anesthesia with tetra paresis, arterial hypotension, bradycardia, and eventually respiratory arrest can occur. Symptomatic treatment (oxygen, vasopressors, and, if required, tracheal intubation and ventilation) should permit complete recovery after the spinal block wears off (a few hours).

Unintentional globe perforation and rupture is the most devastating complication of eye blocks. It has a poor prognosis, especially when the diagnosis is delayed. The incidence is between 1 in 350 and 7 in 50,000 cases.^44–45 Main risk factors include inadequate experience of the physician and a highly myopic eye (ie, long eyeball).⁴⁶ In a study of 50,000 cases, Edge and Navon⁴⁵ observed that myopic staphyloma was a significant risk factor. This suggests that isolated high myopia may not be a risk factor per se but acts as a confounding factor because myopic staphyloma occurs only in myopic eyes.⁴⁵ Vohra and Good⁴⁶ have observed with B-mode ultrasound that the probability of staphyloma is greater in highly myopic than in slightly myopic eyes. Moreover, staphyloma was more frequently located at the posterior pole of the globe (accounting for perforations after RBA) or in the inferior area of the globe (accounting for perforations after inferior and temporal punctures, both peri-and retrobulbar). As a result, at least in myopic patients and at best in all patients, ultrasound measurement of the axial length of the globe (biometry) should be available. In cases of high myopic eye (axial length greater than 26 mm), a needle block can carry an increased risk of globe perforation. In these cases, a sub-Tenon’s or topical block may be preferable.

Table 21–1.

Signs, Symptoms and Mechanism of Complications of Retrobulbar Anesthesia

Complications	Signs and Symptoms	Mechanism

Ocular

Perforation of globe	Ocular pain, intraocular hemorrhage, restlessness	Direct trauma: Myopic eye, posterior staphyloma, repeated injections

Retrobulbar hemorrhage	Subconjunctival or eyelid ecchymosis, increasing proptosis pain, and/or, increased intraocular pressure	Direct trauma (artery or vein)

Optic nerve damage	Visual loss, optic disc pallor	Direct injury to nerve or blood vessels, vascular occlusion

Systemic

Intraarterial injection	Cardiopulmonary arrest, convulsions	Retrograde flow to internal carotid and access to midbrain structures

Optic nerve sheath injection	Agitation, ptosis, mydriasis dysphagia, dizziness, confusion, contralateral ophthalmoplegia, respiratory depression or cardiac arrest	Subdural or subarachnoid injection

Oculocardiac reflex	Bradycardia, other arrhythmias, asystole	Trigeminal nerve (afferent, arc) to floor of fourth ventricle with efferent arc via vagus nerve