Chapter 66. Anesthesia for Ophthalmic Surgery

Knowledge of orbital anatomy is required for safe, effective regional anesthesia. The eyes lie within 2 bony cavities of the skull termed orbits. The orbits are pyramidal in shape. Each eye or globe is positioned anteriorly in the orbit and occupies about one-third of the orbit (Fig. 66-1). Each orbit has a volume of approximately 30 mL. The anterior opening of the orbit is approximately 35 mm in height and 45 mm in width. The depth of the orbit varies with race and gender but averages slightly more than 40 mm.

Figure 66-1.

Eye and extraocular muscles, superior view, showing insertion of extraocular muscles. [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]

The average adult globe diameter is 23.5 mm.1 Normal adult globe diameter ranges between 21 and 26 mm. At birth, the diameter is approximately 16 mm but reaches approximately 23 mm by age 3 years. The globe reaches maximum size at puberty.

The transparent cornea occupies the center of the anterior pole of the globe and is approximately 11 to 12 mm in diameter. The cornea, lens, and aqueous humor form the main refractive elements of the eye. The curvature of the cornea contributes approximately one-third of the refractive power. The limbus is the edge of the cornea where it joins the sclera. The sclera is opaque and white, and covers the remaining 80% of the globe. Tendons of the rectus muscles insert into the superficial scleral collagen.

The conjunctiva is a mucous membrane that lines the inner surface of the eyelids and the anterior surface of the globe between the cornea and limbus. The bulbar (posterior) extension of the conjunctiva fuses with the underlying Tenon capsule near the limbus. Tenon capsule continues posteriorly as an incomplete fascial layer composed of collagen fibers and fibroblasts that surrounds the posterior globe and the extraocular muscles (EOMs). Tenon capsule is perforated by the optic nerve sheath and the posterior ciliary vessels and nerves.

The wall of the globe is composed of 3 layers: the sclera, uveal tract, and retina (Fig. 66-2). The middle layer is the uveal tract. It is composed of 3 specialized structures: the iris, ciliary body (located in the anterior uvea), and choroid (located in the posterior uvea). The iris contains dilator and sphincter muscle fibers that control the central aperture, the pupil. Parasympathetic stimulation originating from the cranial nerve (CN) III nucleus contracts iris sphincter fibers, causing pupillary constriction or miosis. Conversely, sympathetic fibers traveling with the ophthalmic division of CN V stimulate iris dilator fibers, dilating the pupil. Directly adjacent and behind the iris is the ciliary body. The ciliary body had 2 primary functions: production of aqueous humor and accommodation. Ciliary muscles within the ciliary body are responsible for fine tuning visual focus by releasing tension on the suspensory fibers or zonules of the lens, increasing the refractive power of the lens. The contraction of ciliary muscles also opens space for increased aqueous drainage.

Figure 66-2.

Anatomy of the eye. [Reprinted from Bruce RA Jr, McGoldrick KE, Oppenheimer P, eds. Anesthesia for Ophthalmology. Birmingham, AL: Aesculapius Publishing; 1982, with permission from Dr Kathryn McGoldrick.]

The posterior part of the uveal tract is a layer of blood vessels and capillaries called the choroid. These vessels nourish the outer portion of the retina, providing oxygen and nutrients. Bleeding from the choroid layer can cause catastrophic intraoperative expulsive hemorrhage.

The retina is a thin, transparent structure that differentiates from the optic cup and constitutes the inner layer of the medioposterior wall of the globe. Photoreceptors of the retinal layer convert light into neural signals, which are processed and carried to the brain via the optic nerve.

The vitreous cavity in the posterior portion of the globe occupies more than 80% of the volume of the globe. The transparent vitreous humor or vitreous contained within this cavity is important in the metabolism of the intraocular tissues; it provides a passageway for metabolites used by the lens, ciliary body, and retina. Although it has a gel-like structure, the vitreous is composed of 99% water. Vitreous adheres to the retina peripherally at the vitreous base, at the disk margin, and onto the posterior margin. Separation of the vitreous from the inner retina proceeds with age and sometimes causes small tears of the retina as it retracts. It is the most common event associated with retinal detachment. Scarring, bleeding, or opacification of the vitreous is treated by its removal, or vitrectomy.

The eyelids are composed of an outer layer of skin, a muscle layer, a cartilaginous tarsal plate, and an inner layer of conjunctiva. The upper eyelid can be raised 15 mm by the action of the levator palpebrae superioris muscle, which is innervated by CN III. The orbicularis oculi muscle, innervated by CN VII (facial), allows tight closure of the eyelids.

The lacrimal gland is located in a shallow depression within the orbital portion of the frontal bone. Tears are formed here by the serous secretion of acinar and myoepithelial cells. Under both reflex and psychogenic stimulation, tears pass from the surface of the eye via the puncta through either the upper or the lower canaliculi to the lacrimal sac and duct and drain into the nasopharynx below the inferior turbinate.

The blood supply to the ocular structures is primarily the ophthalmic artery. The ophthalmic artery is a branch of the internal carotid artery just before the circle of Willis. Venous drainage flows though the superior and inferior ophthalmic veins directly to the cavernous sinus.

The ciliary ganglion provides sensory innervation of the cornea, iris, and ciliary body. Parasympathetic motor fibers originating from the oculomotor nerve synapse in the ciliary ganglion before innervating the sphincter muscle of the iris and the ciliary muscle. Sympathetic motor fibers originating from the carotid plexus travel through the ciliary ganglion to innervate the dilator muscle of the iris.

The CN innervate ocular structures. The optic nerve (CN II) carries the sensory information from the retina. The optic nerve is a special sensory nerve, but it is not a true nerve. Developmentally speaking, both the retina and optic nerve are part of the brain. The optic nerve extends from the retina and enters the cranial cavity through the optic canal (optic foramen). The intraorbital part of the optic nerve is approximately 25 mm long. The optic nerve is enclosed by 3 sheaths that are continuous with the meninges of the brain. These sheaths extend as far as the back of the globe. The thick outer sheath is continuous with the dura mater of the brain and the sclera of the eye. The thin intermediate sheath is continuous with the arachnoid of the brain and is separated from the outer sheath by the subdural space and from the inner sheath by the subarachnoid space. The vascular inner sheath is continuous with the pia mater of the brain and closely invests the optic nerve. The inner sheath sends connective tissue partitions and blood vessels into the nerve. The ventral artery and vein of the retina pierce the dural and arachnoid coverings of the optic nerve approximately 1 cm behind the globe after a short course in the subarachnoid space, penetrate the optic nerve, and run within it to the inner aspect of the retina.

There are 6 EOMs that produce eye movement (Fig. 66-3). Four of these (superior rectus, inferior rectus, medial rectus, and lateral rectus) define the intraorbital cone (Figs. 66-1 and 66-4). Structures within the cone (intraconal space) relevant to providing regional anesthesia include the posterior ciliary (sensory) nerves from the globe, ciliary ganglion, branches of CN III and VI, optic nerve, branches of ophthalmic artery and vein, parasympathetic and sympathetic fibers, adipose tissue, and septae.

Figure 66-3.

Eye and extraocular muscles, frontal view. [Reprinted from Dutton JJ. Atlas of Clinical Surgical Orbital Anatomy. Philadelphia, PA: WB Saunders; 1994, with permission from Elsevier.]

Figure 66-4.

Illustration demonstrating intraconal (retrobulbar) and extraconal (peribulbar) block.

The oculomotor nerve (CN III) is the somatic motor nerve to 4 of the 6 muscles that move the eye and to the levator palpebrae superioris, the muscle that raises the eyelid. The oculomotor nerve was so named because it supplies most of the muscles that move the eye. It also contains parasympathetic fibers to the involuntary muscles that constrict the pupil and change the curvature of the lens (accommodation).

The trochlear nerve (CN IV) has the fewest nerve fibers of any CN, but it has the longest intracranial course. The trochlear nerve enters the orbit through the superior orbital fissure. It then extends superiorly to innervate the superior oblique muscle. This location of the nerve, outside of the muscle cone, delays the abolition of depression and adduction of the globe after retrobulbar block.

The trigeminal nerve (CN V) provides sensory innervation to the skin and conjunctiva of the lower eyelid via that maxillary nerve and to the upper eyelid and conjunctiva via the frontal branch of the ophthalmic nerve. The nasociliary branch of the ophthalmic nerve provides sensory innervation to the medial canthus, lacrimal sac, and canaliculi and sends sensory fibers to the ciliary ganglion.

The abducens nerve (CN VI) passes through the superior orbital fissure to innervate the lateral rectus muscle on its ocular surface. No sympathetic or parasympathetic fibers appear to accompany the motor fibers.

A summary of the function and innervation of the EOMs is given in Table 66-1. A mnemonic that may aid in remembering the motor innervation of the EOM is SO4-LR6. (Superior oblique is innervated by CN IV, lateral rectus by CN VI, all others EOM by CN III.)

Table 66-1 Extraocular Muscles: Innervation and Function

Table 66-1 Extraocular Muscles: Innervation and Function

Muscle

Innervation

Function

Superior rectus

III (oculomotor)

Elevation

Inferior rectus

III (oculomotor)

Depression

Medial rectus

III (oculomotor)

Adduction

Inferior oblique

III (oculomotor)

Elevation, abduction, and medial rotation (intorsion)

Superior oblique

IV (trochlear)

Depression, adduction, and external rotation (extorsion)

Lateral rectus

VI (abducens)

Abduction

Adapted from Snell RS, Lemp MA. Clinical Anatomy of the Eye. 2nd ed. Oxford, UK: Blackwell Science; 1998.2

The facial nerve (CN VII) is a mixed nerve, but it is predominantly motor in function. It was given its name because of large motor branches that spread across the face. The facial nerve exits the skull through the stylomastoid foramen (along with the internal carotid artery) and passes into the substance of the parotid gland, where it divides into 5 branches that supply the muscles of facial expression. The orbicularis oculi muscle, innervated by the zygomatic branch of the facial nerve, allows the patient to close the eyelids tightly. Local anesthetic blockade of the facial nerve can be important in intraocular surgery by eliminating squeezing caused by contraction of the orbicularis oculi.

In the posterior orbit, the optic nerve, ophthalmic artery, and sympathetic fibers from the carotid plexus pass through the optic foramen. Just lateral to the optic foramen is the superior orbital fissure. It is 22 mm long and conducts the lacrimal, frontal, and nasociliary branches of CN III (oculomotor), CN IV (trochlear), CN V (trigeminal), CN VI (abducens), the superior ophthalmic vein, and the sympathetic nerve plexus. The maxillary and pterygoid branches of CN V, a nerve from the pterygopalatine ganglion and the inferior ophthalmic vein, pass through the inferior orbital fissure, which is located just below the superior fissure and extends laterally.

Intraocular Pressure and Anesthesia

Intraocular pressure is the pressure exerted by the contents of the eye upon the cornea and sclera. Normal IOP is 16 ± 5 mm Hg in the sitting position and is generally maintained within this narrow range. IOP undergoes normal minor fluctuations because of changes in body position (+1 mm Hg supine), diurnal rhythm (2-3 mm Hg), blood pressure oscillations (1-2 mm Hg), and respiration (deep inspiration decreases IOP by 5 mm Hg).

Aqueous humor is the major transport system in the eye for oxygen, glucose, proteins, medications, and inflammatory cells. It provides nourishment for the lens and the corneal endothelium. Approximately half of the cornea's oxygen supply comes from aqueous; the remainder comes from diffusion with the air. Drugs may enter the eye with aqueous humor via the cellular pumping action of the ciliary body, but a distinct blood–aqueous barrier prevents high-molecular-weight drugs from entering aqueous from the blood.

Aqueous humor volume is determined by the production and drainage of aqueous. Aqueous humor is formed by the ciliary body, which is the vascular component of the uveal tract located in front of the pars plana and behind the fibers of the suspensory ligament of the lens (Fig. 66-5). The ciliary body is folded over into a series of 80 folds, each 2 to 3 mm, termed processes, which extend to the posterior aspect of the iris. This structure is supplied by a vascular plexus and covered with epithelium that is impervious to proteins and high-molecular-weight substances.

Figure 66-5.

Anatomy of aqueous flow. [Reprinted from Bruce RA Jr, McGoldrick KE, Oppenheimer P, eds. Anesthesia for Ophthalmology. Birmingham, AL: Aesculapius Publishing; 1982, with permission from Dr Kathryn McGoldrick.]

The aqueous flows forward from the suspensory ligament of the lens and passes between the anterior capsule of the lens and posterior surface of the iris through the pupil to the anterior chamber. Flow then proceeds laterally to the meshwork of the trabecula and into the circular canal of Schlemm. This lateral drainage area is termed the angle. Episcleral veins drain aqueous to the venous system. Approximately one-third of the aqueous produced is reabsorbed through the veins in the iris and choroid. The blood vessels of the choroid constitute a large and variable volume in the eye. The sclera is inelastic, and this reduces compliance of the globe; thus, small changes in volume result in large changes in pressure. The volume of the globe is determined principally by the aqueous humor and the blood vessels of the eye, particularly of the choroid.

Clinical measurement of IOP is made indirectly. Commonly used measurement techniques include indentation (Schiotz) and applanation. Goldman applanati on is the "gold standard" for IOP measurement but requires a cooperative, sitting patient. Intraoperatively, a portable applanation tonometer (Tonopen, Reichert Inc., Depew, NY) is often used.

The Schiotz technique uses a plunger activated by a small weight to indent the cornea. The plunger is connected to a lever that points to a number on an arbitrary scale. This number, along with the weight used in the measurement, allows determination of IOP from a nomogram. A small amount of aqueous is forced out of the eye with each indentation. Because of this action and because of the mechanical friction of the tonometer, Schiotz readings decrease as the measurements are repeated. The applanation method exerts graduated pressures to the cornea and results in a more reproducible IOP measurement. In the operating room (OR), the Schiotz tonometer or Tonopen is used. Invasive measurements of IOP are not common because of the risk of eye damage, danger of infection, and likelihood that the measurement itself may alter IOP.

Intraocular pressure should be maintained in as normal a range as possible during intraocular surgery. Increases in IOP interfere with choroidal and retinal blood supply as well as corneal metabolism, potentially causing retinal ischemia and corneal opacification. Severe increases in IOP can lead to choroidal hemorrhage, intraocular bleeding, and expulsion of intraocular contents. Large decreases in IOP (hypotony) increase the risk of retinal detachment, vitreous hemorrhage, and corneal edema.

Whereas hypotension, hyperventilation, and hypothermia all decrease IOP, hypoventilation, hypoxia, and venous obstruction increase IOP.3 Hypertension may marginally increase IOP. Endotracheal intubation is another potent stimulus for increasing IOP. External pressure from a face mask, fingers, orbital tumors, contraction of the orbicularis oculi muscle, or retrobulbar hemorrhage also increase IOP.

Many drugs alter the production or drainage of aqueous humor and consequently IOP. Most medications exhibit a "dose–response" relationship with IOP. Initial dosing has minimal effect, a rapid linear response then occurs, leading to a plateau effect, in which increasing dosages have little or no effect on IOP. Most drugs used in anesthesia either have minimal effect on or decrease IOP. Inhalational and intravenous (IV) drugs have the most rapid and pronounced effect. Most sedatives and induction agents (eg, propofol and thiopental) reduce IOP in a dose-related manner.3,4 Narcotics generally cause a small decrease in IOP.3,4 Metoclopramide5 and dexmedetomidine6 do not increase IOP. Ketamine may slightly increase IOP.7 Succinylcholine has been reported to increase IOP 6 to 12 mm Hg,8-14 but straining or coughing raises IOP much more. (See discussion of the use of succinylcholine in the open globe, full stomach scenario in the General Anesthesia section of this chapter.)

The increase IOP observed from succinylcholine has been ascribed to contraction of the EOMs, leading to compression of the globe. But Katz et al10 studied patients undergoing elective enucleation and compared the IOP between the normal eye and diseased eye in which all EOMs were detached. After administration of succinylcholine, both eyes exhibited a precipitous increase in IOP, leading the authors to conclude that EOM contraction does not contribute to the increase in IOP after succinylcholine administration.

Systemic Effects of Ophthalmic Drugs

Some topical ophthalmic medications can have rapid systemic effects. Although topical medications are absorbed slowly from the conjunctival sac, much more rapid absorption can occur via the mucosal surfaces of the nasolacrimal duct. Systemic absorption may be altered in a diseased or postsurgical eye. Systemic absorption may be reduced if the lacrimal duct is compressed until topical absorption from the surface of the eye is complete.

Phenylephrine topical solution is commonly used as a mydriatic (dilates the pupil). There is little increase in mydriasis when solutions with concentrations greater than 5% are used.15 This response is important because significant complications have been reported with 10% phenylephrine. A single drop of this high-concentration solution may contain 5 mg of phenylephrine (100 mg/mL ÷ 20 drops/mL). Complications seen include myocardial infarction, hypertension, reflex bradycardia, and cardiac dysrhythmias.16 Only the 2.5% solution should be used in pediatric patients because excessive absorption can cause hypertension.

Epinephrine 2% topical solution causes a decrease in aqueous secretion and improves outflow, both of which act to reduce IOP in open-angle glaucoma. Complications include hypertension, tachycardia, dysrhythmias, and fainting. Because a single drop of 2% solution contains 0.5 to 1.0 mg of epinephrine, it is reasonable to expect systemic complications to occur. Intraocular epinephrine administered during halothane anesthesia is poorly absorbed and has no significant cardiac effects.17

β-Adrenergic antagonists (eg, timolol) topical solutions are used in the treatment of glaucoma. This class of medication acts to reduce aqueous humor secretion with minimal effects on aqueous outflow. Pupillary size is not affected. Patients may complain of light-headedness, fatigue, and disorientation and may exhibit a general depression of central nervous system (CNS) function. Excessive dosage of β-adrenergic antagonists may lead to cardiovascular dysfunction, including bradycardia, palpitations, syncope, an increase in heart block, and congestive heart failure.18 Rare exacerbations of asthma have been reported.19 Particular caution should be exercised with neonates receiving timolol eye drops because cases of apnea have been reported.20

Apraclonidine is a relatively new α2-adrenergic agonist that has found a role as a topical antiglaucoma medication. Similar to epinephrine, it causes a decrease in aqueous formation and improves aqueous outflow. Systemic absorption may cause significant sedation and drowsiness. Hypotension is a possible complication but has not been reported. Acute withdrawal from long-term therapy may result in rebound hypertension.

Echothiophate iodide is a long-acting topical anticholinesterase drug now rarely used to treat glaucoma. Its duration of action is 4 to 6 weeks. Three weeks after cessation of treatment with echothiophate, plasma cholinesterase activity remains at 50% of normal.21 If a patient receives succinylcholine, a relative overdose of succinylcholine leads to 2 to 3 times the usual duration of action. Careful titration of succinylcholine with use of a peripheral nerve stimulator will avoid prolonged paralysis. The effects of ester local anesthetics (procaine and chloroprocaine) may be significantly prolonged. Amide-type local anesthetics may be a better choice for regional anesthesia.

Topical muscarinic agonists are given to cause prolonged mydriasis. A drop of atropine 1% solution contains 0.2 to 0.5 mg of the drug. One drop of 0.5% scopolamine contains 0.2 mg of the drug. Systemic reactions have been seen in both young and elderly patients after administration of topical ocular atropine or scopolamine. These reactions are manifest by tachycardia, flushing, thirst, and dry skin. Elderly patients may show agitation. CNS excitement and agitation can be treated with incremental doses of 0.15 mg/kg IV of physostigmine.

Acetazolamide (given IV) causes carbonic anhydrase inhibition and interferes with the formation of aqueous humor and lowers IOP. Aside from a metabolic acidosis with depletion of sodium and potassium, long-term therapy may result in dyspepsia. When the drug is given rapidly IV, the patient may exhibit an acute decrease in blood pressure. Caution should be exercised in patients with renal disease, dehydration, and sodium or potassium depletion.

Preoperative Evaluation

See Box 66-1.

Patients coming to the OR for ophthalmologic surgery tend to be very young or very old and have comorbid conditions. Infants often present with apnea of prematurity, bronchopulmonary dysplasia, and patent ductus arteriosus. Congenital glaucoma often is associated with other syndromes. Congenital strabismus may be associated with a myopathy, and if so, malignant hyperthermia precautions should be considered (see Chapter 87). Elderly adults are likely to present with coronary artery disease, valvular heart disease, hypertension, cerebrovascular disease, chronic obstructive pulmonary disease, diabetes, dementia, Parkinson's disease, renal disease, arthritis, osteoporosis, or cancer. Since 1990, the proportion of Medicare patients requiring surgical treatment of chronic eye diseases grew from 13.4% to 45.4%.22 In a study by Kraushar and Turner23 on medical litigation in cataract surgery, failure of proper coordination of preoperative care among anesthesiologists, surgeons, and internists resulted in indemnity findings in 16% of patients. Because most ophthalmic procedures are now performed in outpatients and in free-standing day surgery facilities, obtaining an adequate preoperative evaluation (sometimes requiring additional information from primary care physicians, ophthalmic surgeons, and consultant physicians) can be challenging.

Box 66-1

Box 66-1

Special Concerns in Ophthalmic Anesthesiology

Elderly patients with multiple systemic diseases

Pediatric patients, often premature with congenital syndromes

Patients anxious from loss of vision

Limited access to the airway

Oculocardiac reflex is common with general anesthesia and occasionally seen with blocks

Potential for eye injury with intraoperative movement

Intraocular pressure and anesthetic interactions

Systemic effects of ophthalmic medications

Fortunately, most patients undergoing ophthalmologic procedures are at low risk for major perioperative complications. This may be because there are usually no major perioperative physiologic derangements or blood loss. When general anesthesia is required physiologic changes can occur during induction and emergence. Most of the risk associated with anesthesia relates to patient movement,24 changes in IOP, and postoperative nausea and vomiting (PONV). If these potential problems can be controlled, the morbidity and mortality of ophthalmic surgery will be low25 despite the high-risk population. The anesthesiologist can draw on several sources as guides when performing a preoperative evaluation,26-30 and this topic is covered more extensively elsewhere in this text (see especially Chapters 6, 9, 11, and 13).

All patients should have a preoperative history and physical examination assessing their medical conditions, ensuring they are appropriately managed for surgery, and given instructions on what medications to take before and on the day of surgery (Table 66-2). For patients having eye surgery (low-risk surgery) with no other medical problems, routine laboratory tests and electrocardiography (ECG) have not been demonstrated to improve outcome,31 and preoperative ECGs are not recommended for asymptomatic patients undergoing low-risk surgery.26 Laboratory tests and ECGs are warranted only if indicated by history and physical examination26,30,31 (Table 66-3; see Chapters 6 and 7). Some of the suggestions drawn from the American Society of Anesthesiologists Task Force on Preoperative Evaluation and Institute for Clinical Systems Improvement are listed in Table 66-2. Of note, for patients without changes in medical history, normal laboratory and ECG results do not need to be repeated if they were performed within the previous 6 months.27

Table 66-2 Preoperative Basic Health Assessment

Table 66-2 Preoperative Basic Health Assessment

General Medical History

Indications for surgery and proposed procedure, including documentation of which eye(s) being operated on

Allergies or other reactions to medications, latex, environmental allergens, or foods

Current medications, doses, timing, and reasons for taking

Prior surgical and anesthesia history

Focused Medical History and Physical Examination (concentrating on)

Functional status (can lie flat without moving, no acute cough)

Cardiac problems

Pulmonary problems

Neurologic problems
Hemostasis problems

Figure 66-6.

Massachusetts Eye and Ear Infirmary (MEEI) preoperative information for patients with pacemakers, implanted cardiac defibrillators, and other implanted electronic devices.

For most eye operations, no electrosurgical device or only battery-operated cautery or bipolar electrosurgical instruments are used. These instruments are very unlikely to interfere with pacemakers or ICDs. There is a very small risk of an active ICD delivering a shock and potentially causing patient movement and eye trauma during eye surgery. One author estimated the risk of a shock being delivered (if patient has never had ventricular tachycardia or fibrillation or recent ICD-delivered electrical therapy) of about 1 in 243,000 cataract cases.57

One author suggests temporarily inactivating all ICDs during eye surgery to eliminate this risk,58 but we believe this risk must be balanced against the risk of inhibiting the device from delivering potentially lifesaving electrical therapy in a timely manner. In a survey of Ophthalmic Anesthesia Society members, 83% left ICDs active during eye surgery with no reports of ICD malfunction or ICD discharge.59 Various device manufacturers report a 6- to 15-second interval between arrhythmia onset and the ICD delivering antiarrhythmic therapy.57 We believe this interval is likely to allow enough time to warn the surgeon of an impending shock if the ECG monitor is vigilantly monitored. At the MEEI, unless there are contraindications (see the following text), we routinely leave ICDs active during eye operations.

If unipolar electrosurgery (eg, Bovie) is required, ICDs should be temporarily disabled (after ensuring a working external defibrillator is immediately available) to prevent inappropriate electrical discharge. These and additional perioperative management recommendations are given in reviews on this subject.54,55 Transcutaneous electrical nerve stimulation units have been reported to cause ICDs to discharge inappropriately,60 so it may be safest to temporarily inactivate ICDs during eye surgery if peripheral nerve stimulators are required. Interestingly, succinylcholine has not been reported to cause ICDs to discharge.54 Temporary inactivation of ICDs should also be considered if within the previous 12 months an ICD delivered a shock or antitachycardia pacing (ATP) if the patient had nonsustained ventricular tachycardia, supraventricular tachycardia, or atrial fibrillation or if a "lead alert" is present. These conditions increase the possibility of an ICD delivering a shock during surgery.

Hypertension is a common problem in elderly patients. Although there is concern that moderate to severe hypertension may increase the risk of perioperative bleeding, CHF, and cerebrovascular events, numerous studies have shown that there is no increased cardiac morbidity for patients with systolic blood pressure below 180 mm Hg and diastolic blood pressure below 110 mm Hg.26,61-63 One study showed no difference in outcome for patients with preoperative hypertension controlled on the day of surgery with medication versus patients whose surgery was cancelled and returned after control of hypertension with oral medications.64

Hypertension can be exacerbated by eye drops containing phenylephrine or epinephrine. At MEEI, we attempt to decrease systolic blood pressure to less than 180 mm Hg and diastolic blood pressure to less than 100 mm Hg before administering these eye drops. If patients with hypertension did not take their prescribed antihypertensive medications on the day of surgery, they are given preoperatively. If patients normally have well-controlled blood pressure but we suspect they are anxious in the hospital setting ("white coat syndrome"), a sedative (eg, midazolam 0.5-2 mg IV), and/or an antihypertensive (eg, labetalol 5-10 mg IV or hydralazine 5-10 mg IV), may be administered. Only if patients have untreated chronic hypertension or normally well-controlled blood pressure unresponsive to medications do we (after consultation with their surgeon) delay their surgery and refer them urgently to an internist.

Regional Anesthesia Techniques

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

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

Figure 66-7.

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.]

Figure 66-8.

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.]

Figure 66-9.

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).

Figure 66-10.

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.

Figure 66-11.

Photo demonstrating "modified" insertion site below lateral canthus. [Photo courtesy of Dr Gabriele Troll.]

Figure 66-12.

Photo demonstrating "modified" insertion site using skull. [Photo courtesy of Dr Gabriele Troll.]

Figure 66-13.

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.]

Figure 66-14.

Illustration of normal globe showing needle angle required to enter the anterior interconal space.

Figure 66-15.

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

Figure 66-16.

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.

Figure 66-17.

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.

Figure 66-18.

Drawing showing the needle entering the extraconal (peribulbar) space.

Figure 66-19.

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.

Figure 66-20.

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 Anesthesia

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

Modified Van Lindt Block

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.

Complications of Regional Techniques

Minor Complications

Oculocardiac Reflex

The oculocardiac reflex (OCR) is commonly observed during eye manipulation. The OCR most commonly presents as sinus bradycardia, but it also may appear as bigeminy, other ectopic beats, nodal rhythms, atrioventricular block, or asystole. These dysrhythmias may persist as long as the stimuli are present, but repeated stimuli often fatigue the reflex. It is more common during general anesthesia than regional anesthesia and more common in children than adults. Alexander109 reported that 90% of patients experienced the OCR during traction of the EOMs.

The afferent pathway of the OCR is via the ciliary ganglion to the ophthalmic division of the trigeminal nerve through the gasserian ganglion to the trigeminal nucleus in the fourth ventricle. The efferent pathway is exclusively through the vagus nerve. The vagus innervation to the abdominal viscera causes nausea and vomiting that can accompany the cardiac manifestations.

Diagnosis of the OCR relies on continuous monitoring of the ECG. Treatment varies based on the severity of the reflex. If the reflex manifests as mild sinus bradycardia or infrequent ectopic beats and the blood pressure remains stable, no treatment may be warranted. If the dysrhythmias become significant, cessation of the surgical stimuli is indicated. Often the procedure may resume after a brief pause. When the OCR is severe, treatment with anticholinergics (glycopyrrolate or atropine) is indicated. Caution must be exercised with large doses of atropine because more severe, prolonged tachydysrhythmias may result.110 Regional block of the orbit is sometimes used to prevent or treat the OCR.

Other Minor Complications

Chemosis is common with both needle blocks and sub-Tenon block. Eyelid bruising is common after needle blocks. Conjunctival hemorrhage is common after sub-Tenon block.

Serious Complications

Serious complications of regional ophthalmic nerve blocks are rare but can be sight and life threatening.111 OPHTS is a modified mnemonic80 that may be useful to help remember serious complications. These complications are optic nerve injury, perforation of the globe, hemorrhage (retrobulbar), toxins (local anesthetics causing EOM dysfunction), and systemic complications (eg, CSF spread, seizures, cardiac arrest). Frequently, these complications are related to needle misplacement. Risk factors for these complications include inadequate knowledge of orbital anatomy, inadequate training, anatomic variations, and uncooperative patients (Tables 66-5 and 66-6).

Table 66-5 Complications of Regional Blocks

Table 66-5 Complications of Regional Blocks

Rare

Sight Threatening

Life Threatening

Optic nerve injury or retinal vascular occlusion

Oversedation

Perforation of globe or detached retina

Brainstem anesthesia

Hemorrhage (retrobulbar)

Seizures

Toxins (myotoxin to EOM)

EOM, extraocular muscle.

Table 66-6 Avoidance of Regional Complications

Table 66-6 Avoidance of Regional Complications

Knowledge of orbital anatomy

Training and supervision under qualified instructor of orbital regional anesthesia techniques

Knowledge of patient's ocular history, eg,

Myopia
Presence of scleral buckle
Multiple eye surgeries (scar tissue?)

Monitoring of oxygen saturation, ECG, and blood pressure

Appropriate peri-block sedation

Fastidious technique

Availability of emergency equipment and medication

ECG, electrocardiography.

Direct optic nerve injury secondary to needle trauma is rare, but when it occurs, it usually results in poor visual outcome or blindness. The usual cause is inadvertent needle insertion or injection into the optic nerve or its sheath with a 1½-in needle during retrobulbar block. It is estimated by Katsev et al112 that up to 20% of the population (those with have short orbits) are at risk of this injury if a 1½-in (38-mm) needle is used in the inferolateral approach. In this study, the optic nerve could not be reached from this approach with needles 1¼ in (32 mm) or less (Fig. 66-21).

Figure 66-21.

Up to 20% of optic nerves are at risk of being injured with 1½-in (38-mm) needles with the traditional inferolateral approach. (The optic nerve extends on average 7 mm anteriorly within the rigid annulus of Zinn and can be injured within this structure by a 38-mm needle if orbit ≤45 mm in an anteroposterior diameter.) [Data from Katsev Drews RC, Rose BT. Anatomic study of retrobulbar needle path length. Ophthalmology. 1989;96:1221.]

Perforation of the globe has been estimated to occur between 1 in 100090 and 1 in 10000113,114 sharp needle eye blocks. Severe loss of vision or blindness usually results. A major risk factor is using a retrobulbar technique in patients with long axial length eyes. (See discussion about this subject in the Retrobulbar [Intraconal] Block and Peribulbar [Extraconal] Block section of this chapter.)

Retrobulbar hemorrhage can result from venous or arterial injury and can cause proptosis and periorbital hematoma. Intermittent manual compression should be instituted and the ophthalmologist consulted. Severe cases require surgical decompression. Visual outcome is usually good after retrobulbar hemorrhage. However, arterial bleeding is more likely to lead to a compressive hematoma sufficient to cause retinal ischemia.

Ocular and orbital muscle injuries are possible. Ptosis can be caused by surgical sutures on the eyelid speculum as well as disruption of the levator aponeurosis from trauma or stretching of the periorbital septum. Strabismus can be seen after injury to the rectus muscle by direct needle trauma, injection into other EOMs, or toxicity from local anesthetics. The risk of postoperative strabismus may be reduced if the lidocaine concentration in block solutions is 2% or less and hyaluronidase is used as an adjuvant for local anesthetics.

Spread of local anesthesia to the CNS can cause life-threatening problems. The reported incidence is 1 in 375 patients when practitioners use 1½-in needles and a retrobulbar injection.115,116 We have not seen this complication at our institution in more than 30,000 patients when a 7/8-in needle was used for an anterior retrobulbar or extraconal block. However, this complication has been reported after peribulbar block.117

Subarachnoid spread of local anesthesia can cause partial or complete brainstem anesthesia.115 Onset usually is within a few minutes but can occur as late as 20 minutes. Signs and symptoms may include restlessness, confusion, apnea, bradycardia, hypotension, sympathetic activation, and on occasion cardiac arrest. Oxygen with bag-mask ventilation to treat apnea may be all that is required to treat milder cases, but vasopressors, intubation, sedation, and prolonged ventilation may be necessary. The possibility of these complications occurring mandates oximetry, ECG, and blood pressure monitoring during and for about 20 minutes after orbital blocks and that resuscitation equipment and medications be immediately available.

Inadvertent intra-arterial injection is rare but can cause retrograde flow of local anesthesia from the ophthalmic artery into the brain. As little as 2 mL can produce seizures. This condition is usually associated with longer retrobulbar needle injections within the muscle cone. Blood should always be attempted to be aspirated before injecting local anesthetic to detect intravascular needle insertion.

General Anesthesia

General anesthesia is used in approximately 35% of the ophthalmic surgery cases at our institution; the most common indications are pediatric strabismus surgery and lengthy retinal surgery (eg, >2-3 h). Indications for general anesthesia also include an inability of the patient to cooperate with monitored anesthesia care (MAC), an inability to achieve ocular anesthesia or akinesia with local anesthesia (eg, patients with multiple previous eye operations with scar tissue), surgical procedure not amenable to regional anesthesia (eg, open globe, coagulopathy), and surgeon or patient preference.

Controversy exists regarding the relative safety of general anesthesia versus regional anesthesia in ophthalmic surgery. Studies reveal no differences between these techniques postoperatively with regard to memory,118 cognitive function,119 and oxygen saturation,120 and the incidences of mortality and major complications are similar.121 Regional anesthesia has been reported to be associated with fewer episodes of intraoperative oxygen desaturation, hemodynamic fluctuation, PONV, and less initial postoperative pain.122 Regional anesthesia for ophthalmic surgery also has been shown to be free of the hormonal stress response associated with general anesthesia.123,124 With these considerations in mind, it seems prudent to avoid general anesthesia if possible in patients with severe cardiovascular or pulmonary disease as well as those who are prone to PONV.

The goals of general anesthesia for ophthalmic surgery include a smooth induction with a stable IOP, avoidance or treatment of severe OCR, maintenance of a motionless field, a smooth emergence, and avoidance of PONV. These goals can be accomplished in a variety of ways using inhalation anesthesia, IV agents, or a combined technique. A remifentanil infusion is a popular adjuvant at our institution. Intermediate-acting muscle relaxants are also frequently used during intraocular surgery (and routinely used by the authors for intraocular surgery) when the slightest patient movement can be disastrous.

An orbital block should be considered intraoperatively during general anesthesia to reduce narcotic requirements perioperatively, reduce the incidence of OCR, reduce the incidence of PONV from narcotics, and control pain in the immediate postoperative period.

Extubation and emergence from general anesthesia require special attention after eye surgery. Deep extubation (deep enough to prevent straining when the endotracheal tube is removed) but ensuring adequate spontaneous ventilation after extubation is frequently used after eye surgery to reduce the of increased IOP or damage to delicate surgical repairs. There is a small possibility of aspiration from deep extubation because airway reflexes have not yet completely returned. Patients having recently ingested food or liquids and patients with compromised airways are not good candidates for deep extubation. When awake extubation is indicated, judicious use of adjuvant medications such as lidocaine and narcotics (eg, remifentanil infusion) may decrease straining on the endotracheal tube during emergence.

Open Globe, Full Stomach

Succinylcholine causes an increase in IOP by 6 to 12 mm Hg within 1 to 4 minutes after its IV use; 7 to 10 minutes later, the IOP usually returns to baseline.8,125 There has been concern that use of succinylcholine in patients with open globe injuries could further damage the globe because of this increase in IOP. The history of this controversy has been reviewed by Vachon et al.126 Several large retrospective studies do not link the use of succinylcholine to further eye injury in this scenario.127,128 Although the increase in IOP associated with succinylcholine is not insignificant, that associated with coughing and straining is 3 or 4 times greater (ie, to ∼40 mm Hg), indicating that many other factors in addition to succinylcholine can influence the quality of anesthetic care. Direct pressure on the eye (from the mask or fingers) can also increase IOP and should be avoided. Efforts to quickly obtain good intubating conditions and prevent bucking and straining in the open globe scenario are much more important for reducing the risk of extrusion of eye contents than the avoidance of succinylcholine.

The most appropriate airway management of patients with an open globe and full stomach should be determined after assessing the likelihood of a difficult intubation and the viability of the eye. An algorithm has been proposed for this scenario.129 If the intubation is judged to be difficult but the eye is viable, succinylcholine (after pretreatment with a small dose of a nondepolarizing muscle relaxant, eg, 0.3-0.5 mg of rocuronium in adults) is an appropriate option. If the patient is likely to be an easy intubation, a short- to intermediate-acting nondepolarizing agent, administered in greater-than-normal doses, such as 0.6 to 1.2 mg/kg of rocuronium, has proven effective.130-132 The use of propofol has been shown to improve intubating conditions if rocuronium is used.130 IV lidocaine and narcotic may also reduce the risk of straining and bucking. A fiberoptic intubation should be used if the eye is nonviable and the intubation is judged to be difficult.

Small "self-taming" doses of succinylcholine,133,134 some nondepolarizing muscle relaxants,135 and diazepam14 have not been show to be effective in blocking the succinylcholine-induced increase in IOP. If small amounts of a nondepolarizing relaxant (eg, rocuronium) are used to block the succinylcholine-induced increase in IOP, 1.5 mg/kg of succinylcholine should then be used to achieve paralysis, waiting 60 to 90 seconds to ensure good-quality intubating conditions.

Potentially serious complications can occur if nitrous oxide (N2O) is provided as part of the anesthetic regimen and the surgeon administers an intravitreal gas. Several cases of blindness have been reported from the use of N2O in patients undergoing general anesthesia weeks after injection of 2 medical gases, sulfur hexafluoride (SF6) and octafluoropropane (C3F8) into the vitreous cavity (eg, for the treatment of retinal detachment.)136,137 N2O enters the intraocular gas bubble much more rapidly than SF6 and C3F8 exits. If N2O is used after the injection of these gases, the injected gas bubble can expand up to 3 times its original volume. To prevent this complication, all patients undergoing general anesthesia should be asked about recent eye surgery. Small residual bubbles of SF6 and C3F8 have been observed in the vitreous as long as 3 and 10 weeks, respectively, after injection. To provide a margin of safety, N2O should not be used for patients who had intravitreal injections of SF6 within the last 30 days or C3F8 within the last 90 days. If N2O is used during retinal surgery, the ophthalmologist should be informed and the N2O should be discontinued at least 15 to 20 minutes before the injection of a gas into the vitreous cavity.138

Anesthesia for Pediatric Ophthalmology

Anesthesia for pediatric ophthalmology encompasses a diverse group of patients and procedures. It has been said that pediatric ophthalmic anesthesiology can be considered a separate subspecialty.139 Patients range from newborns with medical problems associated with prematurity to children with congenital syndromes to healthy adolescents. Many of the ophthalmic procedures performed in adults with MAC require general anesthesia in the pediatric population.

Measurement of IOP in awake children is difficult because of their lack of cooperation and frequently requires general anesthesia. IOP is affected by most anesthetic drugs and practices such as laryngoscopy and intubation. Therefore, most ophthalmologists prefer to measure IOP before a deep level of anesthesia has been reached and intubation has been performed. It is our practice to allow measurement of IOP soon after induction of anesthesia and before instrumentation of the airway has taken place. This is accomplished by positioning the mask and hand of the anesthesiologist so the ophthalmologist has unobstructed access to the eye. Instillation of topical anesthetic drops into the eye may allow earlier IOP measurement than otherwise possible. If necessary, the mask can be removed to allow IOP measurement and then replaced. If further examination is required (eg, ultrasonography, gonioscopy), either the trachea is intubated or an laryngeal mask airway (LMA) is inserted.

Measurement of IOP in the pediatric patient is performed to diagnose glaucoma or to follow the efficacy of therapy. Congenital glaucoma can be associated with several systemic syndromes (eg, rubella, oculocerebrorenal [Lowe] syndrome). In addition, Sturge-Weber syndrome or congenital capillary hemangioma may affect the skin of the face, neck, mucous membranes, meninges, and choroid plexus. These patients frequently have seizure disorders. If the affected areas include the distribution of the fifth CN, glaucoma is commonly found. Children with Sturge-Weber syndrome come to the OR for frequent examinations under anesthesia to follow the efficacy of surgical and medical interventions. Good rapport and appropriate use of premedicants allow a smooth induction of anesthesia and the most accurate measurement of IOP.

Strabismus surgery is the most common type of ophthalmic surgery performed in children. Several studies have reported the incidence of PONV as greater than 50%.140,141 Several different anesthetic techniques and antiemetic regimens have been used in an attempt to decrease this high incidence of nausea and vomiting. Wachta et al140 showed that patients anesthetized solely with propofol after halothane induction had an incidence of emesis in the first 24 hours of 23% compared with 50% in those who received halothane, N2O, and droperidol. All patients in all groups received opioids for pain relief, a technique that undoubtedly contributed to the high incidence of PONV. The OCR is frequently elicited during strabismus surgery by traction on the EOMs.109

At MEEI, patients at moderate to high risk of PONV receive a 5HT3 antagonist (eg, ondansetron) and dexamethasone (Decadron) unless contraindicated. For strabismus surgery, pain is minimized with nonopiate analgesics, most commonly 0.5 to 1 mg/kg IV of ketorolac (maximum pediatric dose, 15 mg IV). Patients with congenital strabismus may have a higher risk than the general population of developing malignant hyperthermia, and this risk should be factored into anesthetic management. (See Chapter 87 for a full discussion of malignant hyperthermia.)

Nasolacrimal duct probing for obstruction is another common procedure performed in pediatric ophthalmic patients. Successful relief of obstruction diminishes after the first year of life, so many of these patients are infants. Use of an LMA provides the surgeon with unobstructed access to the patient and protects the airway from the fluorescein dye that is injected into the nasolacrimal duct.

When an infant or young child presents with poor vision but normal ocular structures, electroretinography can help differentiate among retinal disorders. This procedure is generally performed in a completely dark laboratory and requires a period of approximately 20 minutes for the retina to dark-adapt. General anesthesia or sedation is required because the child usually is not able to cooperate for the examination. Before beginning the procedure, the anesthesiologist must become familiar with the location of the various pieces of equipment and power outlets and be completely satisfied with the setup.

Retinopathy of prematurity, previously called retrolental fibroplasia, is a condition usually associated with prematurity. Although a disease of complex etiologies, it is believed to be primarily related to hyperoxic periods during neonatal intensive care. Nonetheless, full-term infants can have this condition, as can premature infants who have never received oxygen therapy. After initial examination in the intensive care unit, the child may come to the OR for multiple examinations under anesthesia and vitreoretinal procedures such as scleral buckling or vitrectomy. The care of ex–premature infants is complex and must start with a thorough history and physical examination. Important historical data include gestational age at birth, birth weight, duration of intubation and ventilation, history of apneic episodes and other breathing disorders, and history of heart and other congenital anomalies.142 Hyaline membrane disease occurs in 60% to 80% of infants born at less than 28 weeks of gestation. Hyaline membrane disease may progress to the chronic pulmonary disease of prematurity called bronchopulmonary dysplasia. Although bronchopulmonary dysplasia improves with growth and development, these children should be considered at risk for increased airway reactivity.

If an inhalation induction is chosen, IV or inhalation anesthesia can be used for maintenance. Intravenous access is rapidly secured so the amount of inhalational agent can be decreased and muscle relaxant administered. For intraocular surgery, a motionless field is critical. For this reason, the authors believe it is prudent to supplement an adequate depth of anesthesia with muscle paralysis during the intraocular portion of the procedure. Conservative amounts of opioids, most commonly fentanyl, are administered. Although extubation should be the goal at the conclusion of surgery, the endotracheal tube should be left in place until the child meets criteria for extubation.

In 1982, anesthesiologists were alerted to the occurrence of postoperative apnea in ex–premature infants recovering from minor surgical procedures after general anesthesia.143 When these infants are no longer at risk is not always adequately defined144; however, the incidence of apnea is known to be strongly related to gestational age and postconceptual age. Most hospitals have guidelines to admit infants younger than 54 to 60 weeks postconceptual age for overnight monitoring. It is especially important in pediatric patients to calculate the maximum amount of local anesthetic allowable to avoid toxicity, to know if local anesthesia solutions contain epinephrine, and to remind the surgeon of these dosages. The recommended safe maximal doses of commonly used local anesthetics in ophthalmology are as follows: lidocaine: 7 mg/kg with epinephrine (maximum dose, 500 mg) or 4.5 mg/kg without epinephrine (maximum dose, 300 mg) and bupivacaine: 2.5 mg/kg (maximum dose, 175 mg). When isoflurane is used, up to 3 mcg/kg epinephrine is acceptable. These dosages of epinephrine are conservative and can be repeated after 10 minutes if no untoward effects are observed.

Ophthalmic Procedures

Strabismus

Strabismus means ocular misalignment or deviation of one eye relative to the visual axis of the other. Although most strabismus is caused by refractive errors or muscle imbalance, rare causes include retinoblastoma or other serious ocular defects and neurologic disease. Left untreated, about 50% of children with strabismus have some visual loss because of amblyopia. A detailed nomenclature has evolved to describe the various patterns of strabismus. Whereas the prefix eso- denotes deviation nasally, exo- denotes temporal deviation. The suffix -phoria describes the tendency of one eye to turn inward or outward when covered, and -tropia describes manifest inward or outward deviation of the eye.

The surgical correction of strabismus is a repositioning of the EOMs. To strengthen a muscle, a resection is performed. To weaken a muscle, a recession is performed. In severe cases, a resection may be performed on one muscle and a recession on the opposing muscle. Because visual maturation occurs by age 5 years, strabismus correction usually is attempted early in childhood. If left uncorrected, amblyopia (partial or complete loss of vision in 1 eye caused by conditions that affects normal development) can occur. Adjustable sutures are sometimes used to improve the chances of alignment with a single operation. The adjustment is performed in the immediate postoperative period when the patient is fully awake and able to focus.

Pediatric patients undergoing strabismus surgery require general anesthesia. Some adult patients do well with a regional technique and IV sedation. Most patients prefer general anesthesia and have a satisfactory result with propofol, remifentanil, 5HT3 antagonists, or dexamethasone and nonopiates for pain.

Cornea

Keratoplasty

Penetrating keratoplasty refers to surgical replacement of the entire cornea with donor tissue. Donor tissue that comes from the patient is called an autograft. Tissue that comes from another person is called an allograft. The indications for this procedure are many; corneal opacity, keratoconus, infection, and scarring are a few. Lamellar keratoplasty replaces only a portion of the cornea. Endothelial keratoplasty replaces Descemet membrane and endothelium, and deep anterior keratoplasty replaces the top 90% of the cornea. Either regional or general anesthesia may be appropriate for these procedures. The importance of suppressing coughing when the anterior chamber is open cannot be overemphasized.

Pterygium

A pterygium is a benign growth of conjunctiva and fibrovascular tissue that has invaded the superficial cornea. Excision is indicated when vision becomes impaired, the lesion causes irritation, or the lesion becomes cosmetically significant. Topical or injection anesthesia, with or without IV sedation, is satisfactory for removal.

Radial Keratotomy

Radical keratotomy is the surgical procedure used to correct myopia. Recall that the cornea contributes approximately 30% of the refractive element of vision. Under topical anesthesia, a series of incisions is made in the cornea in a spoke-like manner, causing a positive diopter change in vision. The indications and rationale for radical keratotomy remain controversial. Typically, these procedures are performed with topical anesthesia only.

Cataracts

Cataracts are a common cause of visual impairment in older individuals. The pathogenesis of cataracts is multifactorial but results in opacity of the lens. Small incision extracapsular cataract extraction, also known as phacoemulsification, is the preferred method of modern cataract extraction. The procedure is performed through a small (3-4 mm) incision and is usually less traumatic to the corneal endothelium than older techniques. The nucleus of the lens is fragmented by an ultrasonic needle and then aspirated. Residual cortical material is then removed. Removal of the lens with an intact posterior capsule provides for better positioning of an intraocular lens implant. Intracapsular cataract extraction (ICCE) is an older technique that completely removes the lens with the capsule through a much larger (12 mm) incision. ICCE is sometimes required with very dense cataracts and in areas of the world where modern ophthalmology equipment is not available. Cataract extraction can be performed with topical anesthesia or with retrobulbar, peribulbar, or sub-Tenon block.

Glaucoma

Altered circulation of aqueous humor can produce an increase in IOP, termed ocular hypertension. Glaucoma refers to ocular hypertension with associated optic neuropathy and visual field loss. Glaucoma is commonly associated with an increase in outflow resistance.

Acute angle-closure glaucoma is one of the leading causes of blindness in the United States. It occurs when there is a sudden occlusion of the drainage angle because of papillary block. This occlusion often is associated with a patient with a narrow anatomic angle hyperopic, a pupil dilated by atropinergic compounds, or an iris propelled anteriorly. Often the patient has a history of an episode of coughing or straining.

The onset of chronic open-angle glaucoma is insidious. Although peripheral vision is gradually lost in the early stages of the disease, the angle is found open and the trabecula appears to operate normally. Chronic open-angle glaucoma may be congenital or associated with a familial diathesis or increasing age.

Goniotomy is a procedure performed to treat infantile glaucoma. A superficial incision is made in the trabecular meshwork to improve outflow of aqueous humor from the anterior chamber. Infants and children require general anesthesia for this procedure.

Trabeculectomy is the most commonly performed filtering procedure in adults. A block of limbal tissue is removed beneath a scleral flap, permitting outflow of aqueous. Antimetabolites, such as mitomycin, can be injected intraoperatively to help prevent surgical failures secondary to scarring.

Many different tubes or shunts have been used to divert aqueous (eg, Molteno valve). These implants are generally reserved for patients who have not responded to other management. Implants in current use have a plastic tube placed in the anterior chamber connected to a plate placed posterior to the limbus.

Iridectomy usually is performed with an yttrium-aluminum-garnet laser at 1064 nm; however, an incisional iridectomy occasionally is required. Iridectomy is the definitive treatment for angle-closure glaucoma.

Anesthesia for glaucoma surgery in adults usually is performed with a retrobulbar or peribulbar injection and, if needed, a facial nerve block.

Vitreoretinal Surgery

Vitrectomy refers to surgical extraction of the contents of the vitreous chamber and replacement with a physiologic solution. An anterior segment vitrectomy is performed for vitreous loss during cataract surgery and for late anterior segment vitreous complications. A posterior segment vitrectomy is indicated for removal of an intraocular foreign body, management of complicated retinal detachments with intraocular membranes, removal of media opacities, and alleviation of vitreous traction on the retina.

General anesthesia was traditionally used for vitreoretinal surgery. However, using regional anesthesia with MAC is now common and has many advantages over general anesthesia.145 After a regional block, the OCR usually is absent. The rapid recovery associated with MAC allows early prone positioning in the recovery room after posterior chamber gas injection. Patient comfort is increased because of less nausea and vomiting and diminution of postoperative pain. Unfortunately, MAC is not suitable for long procedures. Procedures lasting longer than 2 or 3 hours exceed the tolerance of most patients to lie supine and motionless. If necessary, a retrobulbar or peribulbar block can be supplemented during surgery with a sub-Tenon injection using a blunt, 19-gauge needle.

General anesthesia is appropriate for longer cases. It is a useful technique when communication with the patient is difficult or for patients who cannot lie supine or motionless. General anesthesia has some disadvantages. An increase in IOP from straining risks retinal repairs and expulsion of intraocular contents when the globe is open. The OCR is much more common during general anesthesia than regional anesthesia, frequently requiring anticholinergic treatment. After general anesthesia, patients require more systemic postoperative analgesics and antiemetics. Somnolence, pain, and nausea may delay the proper positioning of patients postoperatively.

After general anesthesia is administered, use of long-acting retrobulbar blockade has significant advantages. Retrobulbar block with 0.75% bupivacaine greatly reduces the need for parenteral analgesics within the first 24 hours after surgery.146 In a prospective double-blinded study of patients receiving general anesthesia with or without retrobulbar block with 0.5% bupivacaine, the group receiving the bupivacaine had significantly less pain and nausea postoperatively.147 Alternatively, under direct vision, a blunt 19-gauge cannula can be used to directly inject the anesthetic agent into the episcleral space via a sub-Tenon approach. This technique minimizes the risk of scleral perforation.

The dangers of N2O use during surgery when intravitreal gas is administered and for several weeks to months thereafter are reviewed in the General Anesthesia section of this chapter. A similar hazard exists with air transport of patients. Because the aircraft cabin is pressurized to an altitude of approximately 2000 m above sea level, the gas bubble will expand, resulting in elevated IOP. Therefore, patients should avoid air travel for similar periods of time after injection of these intravitreal gases.148

Oculoplastic Surgery

All of the following oculoplastic procedures can be performed with regional anesthesia on adult patients.

Ectropion Repair

An ectropion results from excess, loose eyelid tissue or scarring that causes the margin of the eyelid to turn outward away from the globe (eversion). Repair consists of excising excess tissue and tightening the remaining eyelid or releasing the related scar tissue.

Entropion Repair

An entropion usually is caused by senile or involutional changes, primarily in the lower eyelids, resulting in weakening of the eyelid retractor muscles and horizontal laxity. The eyelid margin is turned inward toward the globe (inversion). The goal of surgical repair is to increase the tension of the retractor muscles (eg, by reattaching them) and tighten any horizontal laxity.

Ptosis Repair

Ptosis is a congenital or acquired drooping of the eyelid. Most often it is repaired by shortening or reattaching the levator palpebrae aponeurosis. When levator function is inadequate, the upper eyelid can be suspended from the frontalis by a sling of fascia lata.

Blepharoplasty

Blepharoplasty is any plastic surgery of the eyelids, usually to remove redundant tissue. The procedure is performed to remove visual field obstruction and for cosmesis.

Dacryocystorhinostomy

Dacryocystorhinostomy is the creation of a communication between the lacrimal sac and the nasal cavity to allow for tear drainage. A Jones tube is sometimes used to bypass the canaliculi and form a conjunctivorhinostomy. Nasolacrimal duct probing is performed in children with congenital nasolacrimal duct obstruction. The duct is probed with a wire, then dye is injected into the duct and aspirated from the nasal cavity to test the patency of the duct. Silicon tubes can be inserted to act as stents.

Orbital Surgery

Most orbital surgery requires general anesthesia unless the procedure is limited to the anterior orbit and does not involve the bones of the orbit.

Orbitotomy

An orbitotomy is performed to gain surgical access to the orbit. Approaches include transconjunctival, transseptal, and transperiosteal. Indications for orbitotomy include tumor, abscess, foreign body, and orbital fractures.

Orbital Decompression

Orbital decompression is indicated for correction of exophthalmos resulting from Graves disease. Access to the orbit is obtained by either a transconjunctival or transperiosteal approach. Some surgeons use a coronal incision with reflection of the scalp anteriorly to the level of the orbit. Cases can be long (≥4 h), and blood loss can be large enough to require transfusion.

Acknowledgments: The authors would like to thank Dr Roberto Pineda for his assistance in reviewing and updating information about ophthalmic procedures; Dr Gary Fanning, Dr Jonathan Dutton, and Dr Gabriele Troll for their generous lending of personal photographs and drawings; Mr Peter Goldberg for assistance with photographic material; and Ms Elizabeth Kiernan and Ms Viviana Silva-Kong for their assistance with the preparation of figures used in this chapter.

Key References

Hamilton RC. A discourse on the complications of retrobulbar and peribulbar blockade. Can J Ophthalmol. 2000;35:363.
Katsev DA, Drews RC, Rose BT. Anatomic study of retrobulbar needle path length. Ophthalmology. 1989;96:1221.
Kumar C, Dodds C, Fanning G. Pharmocolgy for regional ophthalmic anaesthesia. In: Kumar C, Dodds C, Fanning G, eds. Ophthalmic Anaesthesia. Lisse, The Netherlands: Swets & Zeitlinger; 2002.
Schein OD, Katz, J, Bass EB, et al. The value of routine preoperative medical testing before cataract surgery. N Engl J Med. 2000;342:168.
Snell RS, Lemp MA. Clinical Anatomy of the Eye. 2nd ed. Oxford, UK: Blackwell Science; 1998.

References