Technical advances in ophthalmologic surgery have made it possible for many adult patients, even those with multiple chronic conditions, to undergo outpatient eye surgery under regional anesthesia. Regional anesthesia has a lower perioperative morbidity than general anesthesia for ophthalmic surgery.65 If heavy sedation is avoided during regional anesthesia, the already low risks of perioperative problems are reduced further.66 More than 2 million people undergo cataract surgery in the United States every year. At MEEI, about 7000 ophthalmic procedures are performed every year. In adults, most ophthalmic procedures are performed under some form of regional anesthesia, and about 80% of the regional blocks at our institution are performed by anesthesiologists. Patients with a history of orthopnea should be kept upright before and after the procedure and kept supine intraoperatively for the minimum time necessary to reduce the risk of exacerbating congestive heart failure or chronic obstructive pulmonary disease. Patients with a history of mild claustrophobia can often tolerate brief periods of being covered with sterile drapes if they are reassured, lightly sedated, given supplementary air or oxygen, and using clear and suspended drapes if possible so room air and light can enter around the patient's head. Patients who cannot tolerate lying supine or covered for the anticipated duration of the procedure should have their procedure performed at a facility that can provide general anesthesia.
Topical anesthesia involves instillation of local anesthesia eye drops or gel on the surface of the cornea and conjunctiva. Topical anesthesia is appropriate for some uncomplicated procedures in the anterior globe (eg, cataracts, pterygiums) in properly informed and cooperative patients and by surgeons comfortable with these techniques. Topical anesthesia has the lowest rate of eye complications compared with other regional techniques67 and is currently the most popular anesthetic for cataract surgery in the United States.68 The conjunctiva, cornea, iris, and sclera are rapidly anesthetized from absorption of local anesthesia. Tetracaine 0.5%, proparacaine 0.5%, lidocaine 4%, and lidocaine gel 2% to 4% are often used. The advantages of topical anesthesia are that no preprocedural sedation or injections are required, and visual improvement is immediate after lens placement. The duration of analgesia is brief and occasionally requires supplementation with additional topical instillation, or intracameral, subconjunctival, or sub-Tenon injection of local anesthetic.
Eyelid pressure, bright ophthalmic lights, and vision of surgical instruments can be bothersome to some patients. Potential concerns for some surgeons include lack of akinesia, the ability of patients to move their eyelids, a relative lack of IOP control compared with needle blocks or general anesthesia, and the potential requirement of heavy sedation if patients cannot cooperate intraoperatively. Intraoperative comfort may be more reliable with needle-based and sub-Tenon blocks. Interestingly, patients experiencing bilateral cataract extractions who were randomly assigned to topical for 1 eye and retrobulbar block for the other eye preferred the block technique by 71% to 10%.69
Sedation for Nerve Blocks and Ophthalmic Surgery
Sedation before performing needle-based regional anesthesia has several benefits. It can reduce patient anxiety (and sometimes memory) relating to needle insertion near the eye, and it can reduce the pain that is otherwise common during needle blocks. By providing adequate analgesia and sedation, patient cooperation is enhanced, and the risk of movement during the block is reduced. Lastly, sedation and analgesia may keep the patient relax after the block has been placed. At MEEI, a combination of IV midazolam (0-2 mg) and remifentanil (20-60 mcg) appropriate for patient age, weight, and condition are used. Although there is debate over the most appropriate NPO (nothing by mouth) guidelines for patients undergoing eye surgery under regional anesthesia, at our hospital, we use the current ASA NPO guidelines (see Chapter 6).
Because of the risks of oversedation or possible local anesthesia spread to the brain, all patients undergoing sedation or orbital blocks require oximetry, ECG, and blood pressure monitoring. Resuscitation equipment and drugs must be immediately available. As in other situations, the decision to use sedation should be based on need, not routine protocol. For many anxious patients, holding their hands or reassuring words my provide a calming effect. Finally, no amount of sedation, short of general anesthesia, will compensate for inadequate analgesia. Therefore, it may be necessary to remind the surgeon to supplement local anesthesia if it is inadequate initially or decreasingly effective over time.
Supplementary oxygen can be useful in reducing hypoxemia during preprocedural sedation. But routine use of 100% oxygen by nasal prongs, masks, or other delivery systems during surgery under local anesthesia should be questioned. Although a rare event, there is an increased risk of fire during eye surgery whenever there is an enriched oxygen environment, a heat source (eg, bipolar or battery operated cautery), and a fuel source (eg, facial hair, oxygen tubing, drapes).70-73
Most patients do not require high concentrations of oxygen during eye surgery. Two studies showed that patients who received compressed air under the drapes during cataract surgery had the same oxygen saturation as patients who received 100% oxygen.74,75 If supplementary oxygen is required during the procedure, it should be started at a concentration of 30% if possible72 (ie, oxygen mixed with compressed air in a ratio of 1:8). If oxygen is used in higher concentrations, the surgeon should be alerted to its use and no heat source (eg, cautery) should be used until the oxygen is stopped for a few minutes to minimize the risk of supporting combustion.71
It is possible for CO2 to accumulate under the drapes during eye surgery causing hypercarbia, tachycardia, tachypnea, and restlessness. However, 1 study showed that giving additional oxygen at 2 L/min did not prevent hypercarbia.76 Insufflating fresh gas (eg, compressed air) under the drapes at 10 L/min and using paper drapes helped mitigate this increase in CO2.77 Use of a suction device to remove accumulated CO2 under the drapes has also been successful in decreasing CO2 levels when oxygen was insufflated under the drapes at 2 to 3 L/min.78,79
Retrobulbar (Intraconal) Block and Peribulbar (Extraconal) Block
Retrobulbar block (more precisely defined anatomically as an intraconal block) was first described more than 120 years ago and has been the predominant technique of ophthalmologists and many anesthesiologists for providing regional anesthesia to the orbit during the 20th century and currently. The goal is to inject local anesthetic into (or near) the middle of the muscle cone formed by the 4 recti muscles (the intraconal space) (Figs. 66-1 and 66-4). The local anesthetic spreads from this location to anesthetize the ciliary ganglion (and the sensory nerves that run through it) and motor nerves to the eye. Patient requirements to undergo surgery with sedation and a retrobulbar block are similar to those of topical anesthesia.
Commonly used local anesthetics include lidocaine 2% mixed with bupivacaine 0.75% (in a 1:1 ratio), lidocaine 2% with epinephrine 1:200,000, and chloroprocaine 2%. Lidocaine 4% can be myotoxic and should be avoided.80 Epinephrine in a concentration of 1:200,000 or less can be used if vasoconstriction is desired (eg, during enucleation) or to prolong the effects of lidocaine. Because of the concern that epinephrine could cause tachycardia and inadequate blood flow to the optic nerve in patients with vascular disease, it is best avoided unless specifically indicated. The bulk of evidence suggests that adding the enzyme hyaluronidase increases the speed of onset of ophthalmic blocks and reduces the chance of EOM injuries from local anesthesia.81-83 Hyaluronidase is commonly used in concentrations between 2.5 and 15 U/mL; however, there is evidence that it has effect in concentrations as low as 0.5 to 0.75 U/mL.1,84
Unlike topical anesthesia, a retrobulbar block is effective in anesthetizing the posterior chamber of the eye and causing akinesis. In experienced hands, retrobulbar block has a success rate of more than 90%.85 Retrobulbar block (especially if used with ≤5 mL local anesthesia) may require supplementation with a Van Lint block (a peripheral facial nerve block) if blinking interferes with surgery.
At our institution, before performing a needle block, we administer a topical anesthetic (proparacaine) and then swab a 10% povidone–iodine solution over the eyelids and around the eye. The solution is allowed to contact the skin for several minutes to provide optimal antibacterial effect. We request patients to look straight ahead during the block (primary gaze position). Looking up and in (the Atkinson position) brings the optic nerve closer to the midline and increases the risk of injury from the needle tip.86
A palpating finger identifies the lower part of the globe and orbital rim. This finger indents the skin and pushes the globe slightly up. The authors prefer a needle length of 7/8 in (23 mm) to reduce the risk of injuring structures that are tightly packed together deep in the orbit (Figs. 66-7 and 66-8). We use an Atkinson needle (blunter than the traditional hypodermic needle to help identify the sclera if inadvertently touched). The needle is inserted, bevel toward the globe, about 1/4 in (6-7 mm) directly below the lateral canthus and above the inferior orbital rim (Fig. 66-9). There is some evidence insertion at this "modified" insertion point instead of the "traditional" insertion point at the junction of the middle and lateral third of the lower eyelid reduces the risk of injury to the inferior rectus and the neurovascular bundle supplying the inferior oblique muscle (Fig. 66-10).1,80
Coronal views of intraconal space just posterior to globe. Note most of inferior-lateral intraconal space just posterior to the globe is adipose tissue. This is a safe area for the tip of a sharp needle to be placed to provide local anesthesia. [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]
Coronal view of intraconal space in the posterior orbit at the level of the annulus of Zinn. Note how tightly packed the intraorbital contents are ("pickle jar" effect). Needles placed deep in the orbit are more likely to injure these vital structures. [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]
Photo of eye with a green circle denoting the recommended "modified" needle insertion point. The red circle denotes the "traditionally" taught insertion point (at the junction of the medial and lateral third of the lower eyelid).
Anterior orbit through the posterior globe (histologic slide). Note how inferior rectus and neurovascular bundle to inferior oblique muscle are very near the junction of the inferolateral third of orbit. (This is the "traditionally" taught insertion point.) To reduce risk of injuring these structures, needles should be inserted further laterally in the orbit. IRM, Inferior rectus muscle NVB, Neurovascular bundle to the inferior oblique muscle. [Adapted by Dr Gary Fanning from photograph in Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier and Dr Gary Fanning.]
The needle is initially directed perpendicular to all planes of the skin (Figs. 66-11 and 66-12). There may be slight resistance as the needle pierces the skin and a slight "pop" after penetration through the orbital septum (Fig. 66-13) several millimeters below the skin. The needle when correctly positioned is only 3 to 4 mm away from the globe, so great care must be taken not to perforate the globe. One of the authors (JB) wiggles the needle several millimeters (parallel to the globe) during insertion to ensure the globe is not encountered by the needle. (If so, the globe would move while wiggling the needle.) After the needle is judged to pass the lowest point of the globe called the inferior equator (for average axial length eyes, about 0.5 in [13 mm] posterior to the cornea), the needle is directed slightly more superiorly and medially, with the intent of entering the anterior intraconal space (Fig. 66-14). Kumar et al1 recommend that the tip of the needle when fully inserted lie in the imaginary vertical plane starting at the limbus (the junction of the cornea and the sclera) and proceeding posteriorly into the orbit (Fig. 66-15). When the tip of the needle is thought to be in the intraconal space, aspirate for signs of blood. If blood is identified, withdraw the needle, apply intermittent digital pressure, and reevaluate the orbit for possible hematoma before attempting to proceed. When using a 7/8- to 1-in needle, 6 to 8 mL of local anesthesia is usually required to obtain a satisfactory block, although some authors use up to 10 mL. If a 1.25-in (32-mm) needle is used, 5 to 7 mL is usually required. Akinesia of EOMs after orbital block usually correlates with adequate analgesia for eye surgery.
Photo demonstrating "modified" insertion site below lateral canthus. [Photo courtesy of Dr Gabriele Troll.]
Photo demonstrating "modified" insertion site using skull. [Photo courtesy of Dr Gabriele Troll.]
Illustration exposing extensive orbital fascia keeping the globe contained within the orbit. When dull needles pass this tissue, one frequently feels a mild "pop." [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]
Illustration of normal globe showing needle angle required to enter the anterior interconal space.
Illustration of the globe with the tip of the needle in plane projecting posteriorly from the limbus.
Patients with long axial length globes are at significantly higher risk of posterior globe perforation if an intraconal block is attempted.87-89 Patients having cataract surgery will have had their axial lengths measured during preoperative ultrasonography. If the axial length is greater than about 26 mm, the patient has a scleral buckle (a band placed around the globe to treat retinal detachment) or enophthalmos (globe recessed in orbit), and the risk is increased of perforating the posterior aspect of the elongated globe when attempting to enter the retrobulbar space. The presence of a staphyloma (an outpouching of the posterior or inferior sclera associated with long axial length eyes detected by ultrasonography) also increases the risk of globe perforation from retrobulbar block90 (Figs. 66-16 and 66-17), For these conditions, other anesthetic techniques should be considered (eg, topical, extraconal block, sub-Tenon block, general anesthesia). If the length of the eye has not been measured, a longer than normal eye can be assumed if the patient wore glasses as a child or young adult to see distant objects (myopia).1,91
A. Normal axial length eye. B. Severely elongated (myopic) eye. C. Eye with a scleral buckle. Intraconal block in severe myopia and prior scleral buckle has an increased risk of globe perforation.
Illustration depicting a myopic eye and an altered angle of approach required to safely enter the anterior intraconal space.
Unfortunately, the anatomic definition of a peribulbar block is imprecise. Some understand it to mean an extraconal block, but the term is sometimes used to denote an anterior retrobulbar block with a needle 1 in or less in length. For the purposes of this discussion, we will use peribulbar to mean extraconal. The goal of a peribulbar block is to insert a needle near and parallel to but not into the intraconal space and deposit enough local anesthesia so it diffuses into the intraconal space (Fig. 66-18). Because there are no discrete septal barriers separating the extraconal from retrobulbar space, adequate volume of local anesthesia injected near the retrobulbar space can diffuse through adipose tissue into the cone and anesthetize the intraconal structures92 (Fig. 66-19). Because the needle tip is farther away from the globe and retrobulbar structures than with a retrobulbar block, an extraconal block may reduce the risk of injury to these structures but at the cost of a slightly lower success rate in providing analgesia and akinesia. Although the reported success rates of 83% to 84% with the extraconal block93,94 are not quite as high as with the retrobulbar technique, it is sufficient to consider performance of this block.
Drawing showing the needle entering the extraconal (peribulbar) space.
Lateral view of the central intraconal space. Mostly composed of adipose tissue in mid orbit, with only few thin septal barriers inhibiting diffusion of local anesthesia. [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]
The insertion site is similar to that of the retrobulbar block. (See the discussion of the retrobulbar technique above.) The needle perforates the skin in the same spot as with the retrobulbar block. It is directed perpendicular to all the planes of the skin and posteriorly below the globe and parallel to the intraconal space but not attempting to enter it. Needles between 7/8 and 1¼ in (23-32 mm) are commonly used for this block. Six to 10 mL of local anesthetic is injected. Extraconal block may be safer for patients with axial length 26 mm or larger, scleral buckle, or severe enophthalmos. When this block was initially described,95 one needle was placed in the inferolateral orbit and a second one in the superior orbit. Most practitioners now routinely use a single inferolateral extraconal injection because evidence has shown that 1 injection is likely to be as effective as 2.96,97
If retrobulbar or peribulbar block does not produce global akinesia (and analgesia) after 5 to 10 minutes, it may be repeated once, preferably with a slightly lower volume of local anesthesia. Multiple repeat injection of local anesthesia should be avoided.
Median Orbital Block and Superior Orbital Blocks
If a retrobulbar or peribulbar block is inadequate in blocking the medial rectus or the superior oblique muscles, practitioners may supplement the block by performing a median orbital (extraconal) block.1,98 The space between the medial rectus muscle and the medial orbital wall is primarily filled with adipose tissue and is the target area for this block. After topical anesthesia and 5% Betadine ophthalmic solutions are applied, a ½- to 1-in (25- to 30-g) blunt needle is inserted between the caruncle and the medial canthus (Fig. 66-20). The needle is aimed at the medial orbital wall and gently advanced until the wall is just touched.
Arrow 1 indicates the entry point for a median orbital block. Arrow 2 indicates the site of dissection for a sub-Tenon (episcleral) block. Arrow 3 indicates the entry point below the lateral canthus and above the inferior orbital rim for inferotemporal intraconal and extraconal block. [Modified from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]
The wall here (lamina papyracea) is extremely thin and can be easily perforated if too much force is applied. After gently touching the wall, the needle is withdrawn 1 to 2 mm and redirected parallel to both the orbital wall and floor. To avoid injury to the medial rectus muscle, the needle must be close to the wall but not subperiosteal. To avoid injury to the optic nerve, the needle should be no longer than 1 in in length, and its shoulder should be no deeper than the plane of the iris. Two to 4 mL of local anesthesia and a compression device after the block are commonly used.
Although some practitioners perform a superior orbital block lateral to the supraorbital notch to anesthetize the superomedial orbit, the authors are concerned that in this location, the globe is close to the orbit, the superior orbit is more vascular than the inferior and medial orbit, and the trochlear nerve and apparatus are in the vicinity. All of these structures are susceptible to needle injury.
Sub-Tenon block is accomplished by injecting local anesthetic into the episcleral space (the space between the sclera and the overlying sub-Tenon capsule) via needle or cannula.1 The conjunctiva is fused several millimeters posterior to the limbus with the underlying sub-Tenon capsule. If the conjunctiva is lifted off the sclera posterior to this fusion, the sub-Tenon capsule is also elevated, allowing insertion of local anesthesia between the scleral and the now exposed episcleral space (Fig. 66-20).
The principles of sub-Tenon block were described in the late 1800s. Modern cannula-based sub-Tenon block was developed as a method to potentially avoid complications of sharp needle blocks, including globe perforation, EOM injury, and retrobulbar hemorrhage. It has become very popular in Great Britain, and many European and Asian countries. Sub-Tenon block has been reported to have a lower rate of sight-threatening complications versus needle blocks, but it is important to be aware that most of the same complications that can occur with sharp needle blocks have also been reported with sub-Tenon block.99-102
The technique is most often performed in the inferomedial quadrant. After sterile preparation, application of topical anesthetic drops or gel to the surface of the globe, and topical application of 5% Betadine solution to the conjunctiva, the conjunctiva is grasped 3 to 5 mm from the limbus, and blunt Westcott scissors are used to create an opening in the conjunctiva and Tenon capsule to access the episcleral space. Specially designed blunt, often curved cannulas are advanced into the episcleral space, and the local anesthesia mixture is injected. Three to 5 mL of local anesthesia is commonly used. Three mL of local anesthesia provides analgesia to the globe and 5 mL will spread to the EOMs and provide akinesia.
Chemosis (subconjunctival spread of local anesthesia) and conjunctival hemorrhage are more common with sub-Tenon block than with needle blocks. Sub-Tenon block is contraindicated in patients with a prior scleral buckling (preventing posterior spread of anesthetic) or local infection and should be used with caution with glaucoma surgery (can interfere with lifting flap), highly myopic eyes (can perforate thin sclera or posterior staphyloma), previous pterygium repairs (can damage repair), or prior vitreoretinal surgery. Sub-Tenon block is also frequently used intraoperatively by ophthalmologists as a supplement to poor-quality or receding regional anesthesia blocks.103
Needle-based sub-Tenon block has been described by Ripart et al104 and Mouvellon et al.105
When paralysis of the orbicularis oculi is necessary to prevent squinting during eye surgery, a modified Van Lindt block can be performed.106 The orbicularis oculi is innervated by the superior branch of the facial nerve. This nerve can be blocked by inserting a needle 1 cm lateral to the lateral junction of the superior and inferior orbital rims. Two to 4 mL of anesthetic is injected just lateral to both the superolateral and inferolateral orbital rim. One should avoid injections into the eyelids because this is painful and frequently causes a hematoma.
Regional Postoperative Analgesia
Postoperative pain is usually minimal after cataract surgery, and patients are usually instructed to take acetaminophen for postoperative analgesia. Severe pain after cataract surgery is abnormal and should prompt urgent consultation with an ophthalmologist because it may indicate infection or increased IOP. Postoperative pain is greater after posterior segment surgery. Inadequate pain relief can lead to nausea, vomiting, crying, and restlessness in children as well as hematoma formation, prolonged recovery, hospital admission, and reduced patient satisfaction. Use of opioids to treat pain also can lead to nausea and vomiting, resulting in admission or surgical complications. For these reasons, if general anesthesia is required, consideration should be given to administration of sub-Tenon, retrobulbar, or peribulbar anesthesia after induction or before emergence to provide analgesia in the immediate postoperative period. Some centers advocate the use of indwelling catheters to relieve postoperative pain,107,108 but life-threatening complications have been reported from this practice (usually related to catheter migration); for this reason, this technique has not gained wide acceptance.