The retrobulbar blockade was first described by Herman Knapp in 1884. That same year, Carl Koller reported a case of successful ocular enucleation using cocaine hydrochloride as an anesthetic agent. Years later, Atkinson (1936) described a retrobulbar technique that rapidly became popular; however, the high incidence of complications made this technique obsolete over time. Since then, several anesthesia techniques for ophthalmological surgery have been added to the repertoire of the anesthesiologist.
Modern techniques for retrobulbar blockade have long been considered the gold standard for akinesia and anesthesia in intraocular surgery. However, complications related to this technique, though rare, are devastating and potentially life or sight-threatening. This block has therefore been largely replaced by newer techniques with theoretically less severe complications, such as peribulbar blockade and the Sub-Tenon block, which has a similar profile for anesthesia and akinesia as a retrobulbar blockade. Despite this, some still prefer local anesthesia over regional blocks for certain ocular procedures.[1]
Basic comprehension of orbital anatomy and structural relations is paramount to understanding the mechanism of action and potential complications of the retrobulbar block. As a general approach, the orbital space can be divided into two compartments that freely communicate. The intraconal compartment encloses the orbital fat, ciliary ganglion, ophthalmic artery, several cranial nerves (optic, oculomotor, abducens), and a nasociliary branch of the ophthalmic nerve. The extraconal compartment consists of orbital fat, lacrimal gland, abducens nerve, and the frontal branches of the ophthalmic nerve.
Orbits: Despite the classical description of the orbits as pyramidal in shape, their walls are irregular, curvilinear, and perforated by fissures and foramina at their apex. Orbit height can be around 35 mm at the rims, with an approximately 40 mm width and 42 mm to 54 mm depth from the optic foramen to the orbital rim. For this reason, the use of needles more than 38 mm for the retrobulbar blockade is not advisable. The medial orbital wall is thin from the apex to the base; it is separated from the ethmoid sinus by the lamina papyracea. Perforation of this lamina with a needle may result in an abscess or orbital cellulitis.[2]
Ocular globe: The eyeball is spherical and lies anteriorly in the orbital cavity. It has an axial length of 25 mm, an essential anatomical characteristic to consider when planning a retrobulbar blockade. Myopia increases the anterior to the posterior diameter of the eyeball. Several studies have shown that an axial length of more than 26 mm is associated with a higher risk of ocular globe perforation. The presence of staphylomas (protruding defects of the sclera lined with uveal tissue), which typically lies in the posterior or inferior surface of the ocular globe, is associated with higher perforation risk as well.[3]
Extraocular muscles: Six muscles control ocular globe movements; four of them are the rectus muscles (superior, inferior, lateral, and medial), and the other two are the oblique muscles (inferior and superior). The rectus muscles are inserted anteriorly into the sclera where their tendons join in the intraconal space, forming the Zinn ring that encircles the optic canal. Ample fat-filled space devoid of major anatomical structures is created by the diversion of the medial rectus from the medial orbital wall, making it an ideal area for infiltration.
Motor and sensorial innervation: Motor innervation of the inferior oblique and rectus muscles, with the exemption of the lateral rectus, is provided by the oculomotor nerve. The superior oblique muscle is innervated by the trochlear nerve. This nerve exits the annulus and runs along the muscular surface, making it typically unaffected by inferotemporal blocks. The orbicularis muscle is innervated by the facial nerve, which frequently must be blocked to prevent blinking during surgery. For this reason, a Van Lind block is used at the same time as the retrobulbar block.
Sensorial innervation of the eye is majorly provided by the first branch of the trigeminal nerve (V1) and its branches (frontal, lacrimal, and nasociliary). The peripheral conjunctiva is innervated by the lacrimal and frontal branches of V1. However, these branches run in the extraconal space; thus, the intraconal blockade will not provide any anesthetic effect in these branches. The second branch of the trigeminal nerve (V2) provides only a minor contribution to sensorial innervation through the infraorbital nerve.[4]
Blood supply: The ophthalmic artery provides irrigation to the extraocular muscles and the ocular globe. From its original trajectory entering the orbital space through the optic canal, blood vessel distribution is skewed towards the superior nasal quadrant. Consequently, this is a high-risk area for local anesthetic infiltration and must be avoided.
Connective tissue: The Tenon capsule surrounds the ocular globe and extraocular muscles. This dense fibroelastic tissue covers the sclera and forms the episcleral space (Sub-Tenon space). It originates at the sclerocorneal limbus and extends toward the posterior pole of the globe to reach the optic nerve. Local anesthetic injected into Sub-Tenon space diffuses into the retrobulbar space, blocking the extraocular muscles and nerves supplying the globe in this space.
Imaging and contrast spread of retrobulbar block: One small case series comparing gadolinium distribution for the peribulbar vs. retrobulbar block observed that the spread of contrast medium was intense in the intraconal space, laterally greater than medially. Five minutes after injection, contrast surrounded the optic nerve sheath and was visible beyond the optic canal, around the internal carotid artery in its cavernous portion. Contrast remained visible even 90 minutes after injection. At that point, significant intensity was observed within the pterygopalatine fossa.[5]
Physiology applied to anesthesia for ocular surgery: Regional anesthesia techniques for ocular surgery can increase intraocular pressure (IOP). The volume injected in the intraconal, or extraconal compartment generates external compression on the ocular globe, increasing IOP more than 20 mmHg. Additionally, the use of digital pressure to improve local anesthetic spread, control bleeding, or reduce chemosis should be avoided. Digital pressure can increase the IOP up to 400 mmHg[6] and has been associated with bleeding in the anterior chamber. If necessary, a Honan balloon can be used with limited pressure between 20 mmHg to 30 mmHg.
Oculocardiac reflex: The Oculocardiac reflex is mediated by the parasympathetic nervous system. The traction of the extraocular muscles (most commonly the medial rectus muscle) produces direct pressure on the ocular globe, which generates bradycardia, auriculoventricular block, ventricular ectopia, and asystole. The afferent pathway involves the activation of stretching receptors localized in the extraocular muscles. These receptors transmit a signal through the short and long ciliary nerves to a division of the ophthalmic trigeminal nerve, the ciliary ganglion, and subsequently to the Gasser ganglion. Once the signal reaches the trigeminal ganglion, it is conducted to the sensory nucleus of the trigeminal nerve near the fourth ventricle. The signal is then carried by the internuncial nerve fibers to the motor nucleus of the vagus nerve. The efferent branch of the vagus nerve increases parasympathetic inputs to the heart conduction system.[7]
Broad indications exist for the use of retrobulbar blockade. Any intraocular surgery that requires anesthesia and akinesia for less than two hours can be an indication for this block. The most common uses are in cataract surgery, corneal transplant, keratoplasty, vitrectomy, tube shunt placement, enucleation or evisceration of the eyeball, and cyclodestructive procedures.
Absolute
Relative
Sedation
Retrobulbar Block
Peribulbar Block
Sub-Tenon Block
The retrobulbar block is considered an advanced regional anesthesia technique. Thus, it must be performed by trained providers, mostly anesthesiologists, and ophthalmologists. It is helpful to perform with the assistance of a nurse trained in anesthesia to help administer sedation to the patient.
Ophthalmological surgeries are common in the elderly population, who carry a higher incidence of comorbidities. Thus, a thorough preoperative assessment should be conducted, including a history of the present illness, physical exam, and airway assessment. It is essential to review prior test results, especially those that provide information about the length of the ocular globe and coagulation status of the patient (prothrombin time and activated partial thromboplastin time). Likewise, a current list of medications, including analgesics and anticoagulants, should be noted.
Though rates of complications during ophthalmological procedures are low, it is the responsibility of the anesthesiologist to holistically approach the explanation of potential risks and take necessary measures to minimize them. There is no consensus on the management of patients receiving anticoagulation therapy for ophthalmological surgery. However, most physicians follow the American Society of Regional Anesthesia (ASRA) 2018 guidelines for managing anticoagulation or antithrombotic therapy in patients undergoing peripheral regional and neuraxial blocks.[8] The procedure should be delivered in a setting with appropriate resuscitation and monitoring equipment (noninvasive blood pressure, pulse oximetry, capnography, electrocardiography).
Selection of the Local Anesthetic
The selection of local anesthetic is based on drug onset and duration of action. Thus, it is common to find a mixture of short-acting and long-acting drugs (see Table 1). To prevent muscular toxicity induced by local anesthetics, lidocaine should not be used in concentrations higher than 2%.
To decrease the time of onset and facilitate local anesthetic spread through the tissue, some physicians have used hyaluronidase as an adjuvant agent. Hyaluronidase may also decrease the incidence of postoperative strabismus by limiting local anesthetic myotoxicity. A safe dose is 50 IU per milliliter of local anesthetic. Epinephrine has been used to increase the duration of nerve blockade. However, the risk of vasospasm and subsequent retinal ischemia coupled with the increased availability of local anesthetics with long durations of action has limited its use in recent years.[9]
Retrobulbar Technique
Peribulbar Technique
This block requires a second infiltration, as the superior oblique muscle may not receive the effects of the block with just one injection.
Complications of regional anesthesia techniques for eye surgery are rare, though they can put the sight or life of the patient at risk. The incidence of life-threatening events is low at 3.4 per 10,000 cases.[11] Most of these events are associated with a retrobulbar block. Studies have demonstrated that the use of a peribulbar technique with a needle length of less than 31 mm is rarely associated with adverse systemic effects.[12]
Retrobulbar hemorrhage: Retrobulbar hemorrhage has an incidence of 0.04% to 1.7%[13][14] for the retrobulbar blockade and may originate from a venous or arterial source. This complication has been associated with the use of a needle larger than 38 mm.[15] As the needle is advanced further, vascular structures are more compact, thus increasing the risk of vascular puncture. An arterial retrobulbar hemorrhage is characterized by a sudden onset of proptosis, decreased visual acuity, excruciating pain, and increases in intraocular pressure. It is considered a medical emergency and may require lateral canthotomy, cantholysis, or orbital decompression by an ophthalmologist. Retrobulbar hemorrhage with a venous source usually presents with a slower onset, characterized by chemosis and less effect on the intraocular pressure. This complication may improve with external digital pressure and administration of acetazolamide or mannitol.
Ocular globe injury: Ocular globe injury is also a rare complication, with incidence varying from 1 in 12,000[16] retrobulbar blocks to 1 in 16,224[17] for peribulbar blocks. The principal risk factor for this complication is axial ocular length more than 26 mm and the presence of staphyloma in the posterior and inferior pole of the eye. Duker et al. (1991)[14] described that up to 45% of ocular globe perforations are related to an increased axial length and that the retrobulbar block increases the risk of perforation 30-fold. Symptoms of an ocular perforation vary but can be suspected when the patient experiences pain at the injection site and sudden vision loss. Upon physical examination, hypotonia of the ocular globe may be evident, along with poor red reflex and vitreous hemorrhage.[18] When a puncture of the ocular globe is suspected, it is helpful for the operator performing the block to ask the patient to move the eye. If movement is not observed, this may be because the tip of the needle is preventing it from moving.
Optic nerve damage: Optic nerve damage occurring with modern techniques of ophthalmologic blockades is rare. The use of needles more than 31 mm in length has been associated with this complication. According to a study conducted by Unsold et al. (1981)[19] the Atkinson gaze position “upward and inward” exposes the optic nerve, superior orbital vein, ophthalmic artery, and posterior pole of the eye to the tip of the needle, predisposing to puncture, perforation, and infiltration of local anesthetic of the nerve sheath. This can lead to compression and ischemia of the nerve requiring surgical decompression.
Extraocular muscle injury: The mechanism of extraocular muscle injury seems related to direct injection of local anesthetic into the muscle, high volume of local anesthetic, and direct local anesthetic toxicity. The direct local anesthetic injection has been reported more commonly occurring in the inferior rectus, with strabismus, ptosis, and diplopia as principal signs. Ptosis can be a normal finding up to 24 hours after ocular surgery, though the persistence of other signs raises the suspicion of muscular or even nerve damage. Delayed recovery of more than six weeks may be related to permanent damage in up to 25% of cases.[10] The volume injected with retrobulbar block should not exceed 5 mL in the intraconal compartment. Most authors suggest a safe dose is between 3 mL to 4 mL of local anesthetic. A high concentration of local anesthetic can cause direct toxicity, which is why concentrations of lidocaine higher than 2% are not recommended.[20]
Central spread of the local anesthetic and brain stem anesthesia: Fortunately, this life-threatening complication has a reported incidence as low as 0.3% to 0.8% of cases.[21][22] The exact mechanism of the central spread of local anesthetic and brain stem anesthesia is a matter of debate. Some authors conclude central spread is due to the direct puncture of the optic nerve sheath that communicates with the subarachnoid space.[23] Others suggest that puncture of a vascular structure and retrograde flow may place the local anesthetic in contact with encephalic structures. Symptoms of this complication usually start between 10 to 15 minutes after local anesthetic injection and may initially manifest as tinnitus, amaurosis, slurred speech, tremors, agitation, and seizures. Within a few minutes, patients can present with respiratory depression and alterations in cardiac rhythm (bradycardia, asystole). Symptoms last approximately 2 to 3 hours, though during this period, the patient will require intensive care unit observation and ventilatory support.
For many years, the retrobulbar block was considered the "gold standard" technique for ocular anesthesia. However, its use has declined since the introduction of newer techniques with similar efficacy in anesthesia and akinesia, yet lower rates of complications. The physician must recognize the potential usefulness of the retrobulbar block and its advantages in generating faster pain relief and akinesia over other techniques. Equally important is an understanding of the basic anatomy of the orbital space, to facilitate comprehension of the risks associated with any regional anesthesia technique.
The retrobulbar block is a regional anesthesia technique long considered the “gold standard” for ophthalmological surgery. Though complications associated with this technique occur at a relatively low incidence, they can be sight or life-threatening, contributing to extended and expensive treatments and even medical support in the intensive care unit (ICU). While acknowledging the potential usefulness of this technique, it is imperative for physicians to recognize the associated complications and be prepared to react. The use of retrobulbar blockade must be discussed preoperatively with both the surgeon and patient to rule out potential risk factors, such as local anesthetic allergies, staphyloma, axial eye length more than 26 mm, presence of nystagmus, coagulopathy or anticoagulant medications, and to improve patient safety and surgical outcomes. [Level 2]
[1] | Nouvellon E,Cuvillon P,Ripart J, Regional anesthesia and eye surgery. Anesthesiology. 2010 Nov; [PubMed PMID: 20938330] |
[2] | Jaichandran V, Ophthalmic regional anaesthesia: A review and update. Indian journal of anaesthesia. 2013 Jan; [PubMed PMID: 23716759] |
[3] | Kels BD,Grzybowski A,Grant-Kels JM, Human ocular anatomy. Clinics in dermatology. 2015 Mar-Apr; [PubMed PMID: 25704934] |
[4] | Turvey TA,Golden BA, Orbital anatomy for the surgeon. Oral and maxillofacial surgery clinics of North America. 2012 Nov; [PubMed PMID: 23107426] |
[5] | Almeida DR,Belliveau MJ,Enright T,Islam O,El-Defrawy SR,Gale J, Anatomic distribution of gadolinium contrast medium by high-resolution magnetic resonance imaging after peribulbar and retrobulbar injections. Archives of ophthalmology (Chicago, Ill. : 1960). 2012 Jun; [PubMed PMID: 22801836] |
[6] | Ernest JT,Goldstick TK,Stein MA,Zheutlin JD, Ocular massage before cataract surgery. Transactions of the American Ophthalmological Society. 1985; [PubMed PMID: 3832527] |
[7] | Alexander JP, Reflex disturbances of cardiac rhythm during ophthalmic surgery. The British journal of ophthalmology. 1975 Sep; [PubMed PMID: 54191] |
[8] | Horlocker TT,Vandermeuelen E,Kopp SL,Gogarten W,Leffert LR,Benzon HT, Regional Anesthesia in the Patient Receiving Antithrombotic or Thrombolytic Therapy: American Society of Regional Anesthesia and Pain Medicine Evidence-Based Guidelines (Fourth Edition). Regional anesthesia and pain medicine. 2018 Apr; [PubMed PMID: 29561531] |
[9] | Kallio H,Rosenberg PH, Advances in ophthalmic regional anaesthesia. Best practice [PubMed PMID: 15966494] |
[10] | Kumar CM,Dowd TC, Complications of ophthalmic regional blocks: their treatment and prevention. Ophthalmologica. Journal international d'ophtalmologie. International journal of ophthalmology. Zeitschrift fur Augenheilkunde. 2006; [PubMed PMID: 16491028] |
[11] | Eke T,Thompson JR, The National Survey of Local Anaesthesia for Ocular Surgery. II. Safety profiles of local anaesthesia techniques. Eye (London, England). 1999 Apr; [PubMed PMID: 10450381] |
[12] | Faccenda KA,Finucane BT, Complications of regional anaesthesia Incidence and prevention. Drug safety. 2001; [PubMed PMID: 11368250] |
[13] | Hamilton RC,Gimbel HV,Strunin L, Regional anaesthesia for 12,000 cataract extraction and intraocular lens implantation procedures. Canadian journal of anaesthesia = Journal canadien d'anesthesie. 1988 Nov; [PubMed PMID: 3203455] |
[14] | Edge KR,Nicoll JM, Retrobulbar hemorrhage after 12,500 retrobulbar blocks. Anesthesia and analgesia. 1993 May; [PubMed PMID: 8484501] |
[15] | Katsev DA,Drews RC,Rose BT, An anatomic study of retrobulbar needle path length. Ophthalmology. 1989 Aug; [PubMed PMID: 2797726] |
[16] | Duker JS,Belmont JB,Benson WE,Brooks HL Jr,Brown GC,Federman JL,Fischer DH,Tasman WS, Inadvertent globe perforation during retrobulbar and peribulbar anesthesia. Patient characteristics, surgical management, and visual outcome. Ophthalmology. 1991 Apr; [PubMed PMID: 2052307] |
[17] | Ripart J,Lefrant JY,L'Hermite J,Borzli F,Nouvellon E,Fabbro-Peray P,Dadure C,Jaussaud A,Dupeyron G,de la Coussaye JE,Eledjam JJ, Caruncle single injection episcleral (Sub-tenon) anesthesia for cataract surgery: mepivacaine versus a lidocaine-bupivacaine mixture. Anesthesia and analgesia. 2000 Jul; [PubMed PMID: 10866895] |
[18] | Schneider ME,Milstein DE,Oyakawa RT,Ober RR,Campo R, Ocular perforation from a retrobulbar injection. American journal of ophthalmology. 1988 Jul 15; [PubMed PMID: 3394766] |
[19] | Unsöld R,Stanley JA,DeGroot J, The CT-topography of retrobulbar anesthesia. Anatomic-clinical correlation of complications and suggestion of a modified technique. Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie. Albrecht von Graefe's archive for clinical and experimental ophthalmology. 1981; [PubMed PMID: 6912767] |
[20] | Hamilton RC, Retrobulbar block revisited and revised. Journal of cataract and refractive surgery. 1996 Nov; [PubMed PMID: 8972364] |
[21] | Nicoll JM,Acharya PA,Ahlen K,Baguneid S,Edge KR, Central nervous system complications after 6000 retrobulbar blocks. Anesthesia and analgesia. 1987 Dec; [PubMed PMID: 3688501] |
[22] | Hamilton RC, Brain-stem anesthesia as a complication of regional anesthesia for ophthalmic surgery. Canadian journal of ophthalmology. Journal canadien d'ophtalmologie. 1992 Dec; [PubMed PMID: 1490240] |
[23] | Drysdale DB, Experimental subdural retrobulbar injection of anesthetic. Annals of ophthalmology. 1984 Aug; [PubMed PMID: 6497217] |