Eye blocks

Eye Blocks Anthony Rubin, FRCA

This article describes the anatomy and the techniques of the eye blocks that are used most commonly at the present time. It suggests methods of patient preparation and management that increase the success rate and reduce the incidence of the potential complications of the blocks. Copyright 娀 2000 by W.B. Saunders Company

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he majority of eye surgery, and especially cataract and glaucoma surgery, lends itself to the use of local anesthesia. The patients, being often elderly and with intercurrent disease,1 accept local anesthesia readily. The lack of a need to fast, the reduction in stress response2 and the maintained oxygen saturations, and cardiovascular stability3 and the possibility for diabetics to remain on their normal regimes are all positive advantages. The operations are mostly short, but require good surgical conditions, including a relatively still patient with perfect anesthesia and ideally complete akinesia of the globe and periorbital muscles. These requirements may be met by a variety of block techniques, including peribulbar,4 retrobulbar,5 or combination6 blocks using sharp needles, or by the subtenon’s method7,8 using a blunt cannula. In many parts of the world for phacoemulsification cataract surgery even less invasive methods including topical anesthesia,9 with or without the instillation of local anesthetic into the anterior chamber (intracameral10), or subconjunctival administration of local anesthetic11 seem to be all that is required. However it must be accepted that these methods, while providing superficial anesthesia, do not in any way diminish the movement of the globe. Thus excellent patient cooperation and highly skilled surgery is required.

Contraindications Local anesthesia is indicated unless there are specific contraindications. These include a truly informed preference for a general anesthetic, an inability of the patient to cooperate due to their mental state, failure to obey instructions or to be able to adopt an appropriate position, severe involuntary movements, very rare allergy to local anesthetics, or uncontrolled coughing or sneezing.

Preparation Good counseling and information about what to expect during the procedure allay anxiety and reduce the need for sedation. From Chelsea and Westminster Hospital, London, United Kingdom. Address reprint requests to Anthony Rubin, FRCA, Emeritus consultant Anaesthetist, Chelsea and Westminster Hospital, 42 Menelik Rd, London NW2 3RH, United Kingdom. Copyright 娀 2000 by W.B. Saunders Company 1084-208X/00/0401-0007$10.00/0

Assessment of the patient is usually done by the ophthalmic staff, and problems of general health or special risk factors relating to the eye must be communicated to the anesthetist in good time to allow for relevant investigations, for treatment to get the patient into optimal condition, and to avoid last minute cancellations. The patient should arrive in time to be seen by the anesthetist before the block is undertaken and for consent for the anesthetic to be obtained. All the preoperative information about the eye and general health must be available. It is not considered necessary for the patient to starve because no sedation or minimal sedation only is used and the operation would be cancelled in the very rare event of block failure rather than considering conversion to a general anesthetic. Pulse oximetry, electrocardiogram, and blood pressure recording should be used both where the anesthetic and the surgery are performed.12 Intravenous access must be obtained, and resuscitation drugs and equipment must be available.

Anatomy The globe lies in the front half of the orbit. It is normally 22 to 24 mm in length but in myopic eyes may exceed 30 mm. The longer eye has a thinner sclera and is at greater risk of perforation. The sclera is covered by tenon’s fascia leaving an episcleral or sub-tenon’s space (Fig 1) and then the conjunctiva. Tenon’s fascia is a very thin layer closely applied to the conjunctiva in the elderly. The orbital fat is divided into central and peripheral compartments by the incomplete muscle cone that does not act as a barrier to the passage of local anesthetic (Fig 2). The blood vessels are especially prominent at the apex and in the superonasal quadrant, and although previously described as a suitable site for peribulbar injections, the superonasal compartment should no longer be used. The sensory nerve supply to the central and perilimbal conjunctiva, the iris and ciliary bodies comes from the nasociliary nerves that are within the cone, and the more peripheral conjunctiva from the lacrimal, frontal, and infraorbital nerves, which are in the peripheral compartment. The motor supply is from the 3rd nerve (all the recti except the lateral and the inferior oblique), the 4th nerve (superior oblique), the 5th nerve (levator palpebrae superioris), the 6th nerve (lateral rectus), and the 7th nerve (the orbicularis oculi). All lie within the central space except the 4th and 7th nerves. The orbital floor rises about 5° whereas the roof is horizontal. The temporal (lateral) wall goes in about 45°, whereas the nasal (medial) wall is exactly anteroposterior (Fig 3).

Techniques Techniques should be devised to be as painless as possible. Either transconjunctival or percutaneous approaches may be used but in most cases the transconjunctival route is preferred because it is easy to anesthetize the conjunctiva with topical

Techniques in Regional Anesthesia and Pain Management, Vol 4, No 1 (January), 2000: pp 45-50

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Axis of orbit

Anteroposterior axis of eyeball

Figure available in print only o

~23

o

90 +

Fig 1. Schematic transverse section of the orbit. The dotted line represents the path and depth of penetration of a 30 G sharp disposable needle traversing the medial check ligament and entering the medial compartment of the nasal side of the rectal muscle. (Modified and reprinted with permission from Lippincott Williams and Wilkins.26)

drops, and the globe is immediately visible. Where access is difficult, as in the patient who tends to prevent lid opening or in which there is a narrow palpebral fissure or a sunken eye, there is a place for the percutaneous approach. The eye must be looking straight ahead (in the ‘‘primary gaze’’ position). This allows the optic nerve to remain behind the globe and not to rotate towards the advancing needle.13 For the transconjunctival approach, the conjunctiva is anesthetized with topical drops. Benoxinate 0.4% or Proxymetacaine 0.5% are preferred to amethocaine because they sting less. The lower lid is held open, and an injection of 1 mL of a ‘‘painless

Medial orbital walls

Lateral orbital walls Fig 3. Geometry of the orbits and eyes.

local anesthetic’’ solution (made up by adding 1.5 mL of 2% lignocaine to 13.5 mL of balanced salt solution) made with a 30 swg 1 cm needle. This injection allows for the definitive injection to be made also without pain. All injections should be preceded by aspiration, the needle held firmly, and the injection made as slowly as possible to minimize pain and to reduce the risk if an intravascular injection did occur. All injections should be without resistance. As a general principle, the nearer to the target nerves the local anesthetic is placed, the quicker will be the onset and the greater will be the quality of the anesthesia and akinesia. Thus intraconal (retrobulbar) placement remains the most effective14 but this may have to be balanced against any increased risk of complications.

Local Anesthetic Solutions and Adjuvants

Figure available in print only

Fig 2. Cross section of the orbit 2.6 mm posterior to the hind surface of the globe. Note the proximity of the lateral rectus muscle (lrm) and inferior rectus muscle (irm) to the bony orbit. Note also the connective tissue hammock carrying the superior ophthalmic vein (sov) diagonally across the superior orbit from anteronasal to posterotemporal. slp, levator papebrae superioris muscle; srm, superioris rectus muscle; som, superior oblique muscle; mrm, medial rectus muscle; *connective tissue septa. (Reprinted with permission from Lippincott Williams and Wilkins.27)

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Any of the currently available local anesthetics may be used, but lignocaine or prilocaine are most popular for shorter duration and bupivacaine for longer duration. Very commonly a mixture of lignocaine and bupivacaine is used in the expectation that it will produce rapid onset with long duration.15 High concentrations, eg, 2% lignocaine or 0.75% bupivacaine, are preferred to achieve optimal motor block. Hyaluronidase is often added to the local anesthetic solution to help spread and therefore to improve onset and quality of block.16 It also speeds dissipation of the fluid so that any rise in pressure after the injection is short lived. Long duration of action means prolonged corneal anesthesia and motor block, necessitates postoperative eye padding and leads to a high incidence of diplopia the next day. A balance has to be struck between providing adequate duration of anesthesia for the surgery without these postoperative problems. Postoperative pain is minimal and its prevention is not therefore a reason for prolonging the duration of the block.

Retrobulbar Block Traditionally, retrobulbar injections were made deep into the orbit, but it is now accepted that the injection should be ANTHONY RUBIN

shallow using a needle ideally of 2.5 cm length and certainly not longer than 3.1 cm to avoid damage to the optic nerve17 and to reduce the risk of hemorrhage from the concentration of large vessels grouped at the tapering apex of the orbit. The entry point, avoiding obvious conjunctival vessels, should be as far temporal (lateral) in the inferior conjunctival fornix as possible. This allows the needle to miss the inferior oblique muscle. The initial direction of a 25 or 27 swg needle should be tangential to the globe, then pass below it and once past the equator, gauged by the axial length of the globe, allowed to go upwards and inwards to enter the central space just behind the globe (Fig 4). It is difficult to be dogmatic as to the exact volume to be injected. The orbital fat varies in compliance and as a rule the injection may continue as long as the intraocular pressure does not rise excessively. A rise in intraocular pressure whether due to volume injected or hemorrhage necessitates immediate cessation of the injection and the application of pressure to try to dissipate the volume. Usually 3 to 5 mL will be adequate, but in the presence of low pressure additional volume may be administered. The retrobulbar injection should produce anesthesia with the possible exception of the peripheral conjunctiva, and akinesia with the possible exception of the superior oblique and the orbicularis oculi muscles. After this injection, the rapid onset means that an assessment may be made after about 2 minutes. Additional injections may be necessary to correct deficiencies in the block. Unless there is virtually no akinesia, in which case the retrobulbar injection should be repeated, these are usually made in the peripheral (extracone, peribulbar) compartment.

Fig 5. Peribulbar injection. (Reprinted with permission.28)

Inferotemporal Peribulbar Block The first injection may be made deliberately outside the cone. The technique is similar to an inferotemporal retrobulbar

injection, but the needle, after going tangentially and below the globe, does not go upwards and inwards and so remains extraconal (Fig 5). The depth to which it is inserted is also a matter of personal preference but the more shallow it is placed the more likely is the need for more local anesthetic or more injections. Usually, about 5 mL of local anesthetic is administered but the same volume considerations apply as to a retrobulbar injection. The assessment of the akinesia dictates the need for further injections. If there is significant deficiency, the first injection should be repeated in the inferotemporal region. If there is deficiency in the block of the medial rectus or the orbicularis oculi, a nasal peribulbar injection is indicated.

Nasal Peribulbar Block

Fig 4. Retrobulbar injection. (Reprinted with permission.28) EYE BLOCKS

This injection is made with the same needle between the caruncle and the medial canthus and passing directly backwards parallel to the medial orbital wall18 (Fig 6). The resistance of the medial orbital septum is usually felt and once it has been pierced, and after negative aspiration, an injection of 3 to 5 mL is made. Some of the solution remains deep to the septum in the peripheral compartment and complements the peribulbar block. Some comes forwards through openings above and below the septum (Fig 7) to fill the lids and block the terminal branches of the facial nerve to the orbicularis oculi muscle. A technique has been described in which the nasal injection is used as the primary and hopefully sole injection.19,20 A larger volume (6 to 8 mL) is used but if full akinesia is required a further injection is required in up to 50% of patients.

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Figure available in print only

Figure available in print only

Fig 6. Medial pericone block. (Reprinted with permission from Gimbel Educational Services.)

Fig 8. Superotemporal pericone block. (Reprinted with permission from Gimbel Educational Services.)

Superotemporal Injection Occasionally, if there is a deficiency of the block of the superior rectus or levator palpebrae superioris muscles, a superotemporal injection may be used. This is performed transcutaneously through the closed upper lid just below the superior orbital margin level with the lateral limbus (lateral edge of the iris). There may be relatively little space between the globe and the orbital roof and so great care must be taken to direct the needle up towards the orbital roof and the advancing of it no more than 2 cm parallel to the roof (Fig 8). Usually, only about 3 mL is required.

Subtenon’s Block In the last few years, continuing concern over the rare but serious complications of sharp needle blocks has led to increasing interest and use of subtenon’s block.7,8,21,22 After topical anesthesia and the application of betadine, the conjunctiva is picked up in the inferonasal quadrant with nontoothed

Supraobital notch Lacrimal gland

Superior oblique muscle

Lateral check ligament

forceps, and a small incision made in it with squint scissors (Fig 9). Usually, the tenon’s fascia layer will be opened as well and bare sclera seen. Blunt dissection with the scissors may be performed to open a space around the globe towards the central space behind the globe. A blunt lacrimal or disposable subtenon’s cannula is passed along this track and about 5 mL of solution injected (Fig 10). The solution should remain mostly behind the eye and not come back out through the incision or produce much chemosis. There will be rapid onset of anesthesia and akinesia that is comparable with retrobulbar block.22 However, the akinesia may not be complete unless a further 2 to 3 mL of solution is administered.

Prevention of Complications General Principles Good rapport with the patient and painless techniques reduce the need for sedation with its attendant risks, and also minimize rises in blood pressure associated with pain or stress. The aim should be for a relaxed patient but who remains alert and cooperative. There is no place for sedation to cover inadequate blocks.

Medial check ligament

Lateral Arcuate expansion

Inferior oblique muscle

Fig 7. Hernial orifices within the connective tissue diaphragm situated just anterior to the globe equator.

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Medial

Fig 9. Conjunctival incision in inferonasal quadrant. ANTHONY RUBIN

Fig 10. Sub-Tenon’s anesthesia.

Prevention of ‘‘Retrobulbar’’ Hemorrhage

Prevention of Other Complications

The incidence should be reduced by using needles no longer than 31 mm and no bigger than 25 swg, and by applying pressure after needle removal. Less vascular compartments such as the inferotemporal, nasal, and superotemporal should be used. The superonasal area, which has many end arteries of the ophthalmic system, should no longer be used.

Optic nerve damage may result from deep injections. Tamponade of the retinal vessels within the nerve, or the small vessels supplying the nerve, may result from a large injected volume or as a result of hemorrhage. Systemic toxicity of local anesthetic is related to the total dose, the speed of injection, the vascularity of site of injection, the drug used, and addition or not of adrenaline. Amounts used in ophthalmology are relatively small, but close to toxic levels have been reported. It is desirable to aspirate before and during injection, to use a slow rate of injection, to use the minimum effective dose, to maintain verbal contact with the patient, and to monitor the patient continuously. Allergy to local anesthetics or hyaluronidase are very rare. A history should be sought in all cases, and the relevant drugs avoided as necessary. The oculocardiac reflex is very rare with local anesthesia, although vasovagal reactions may arise with an incidence of less than 1%.

Prevention of Globe Penetration and Perforation The axial length of the globe must be known, and special care must be taken of long eyes that may have thinner sclerae and could have staphylomata. Previous retinal detachment surgery may also add to the hazard. Good patient cooperation and easy access to the conjunctival fornix is required. Peribulbar blocks have not been shown to be safer than retrobulbar blocks.23 Neither are blunt needles safer, whereas they hurt more and are likely to cause more damage if penetration occurs.24,25

Prevention of Brainstem Anesthesia The patient should be asked to look straight ahead to keep the optic nerve behind the eye and not rotated towards the needle.13 Short needles, no longer than 31 mm, should be used.17 Monitoring, drugs, and equipment to provide respiratory support and cardiovascular resuscitation must be available.

Prevention of Prolonged or Permanent Muscle Palsy Excessive local anesthetic concentrations, eg, 4% lignocaine, should be avoided. Injection into muscles is avoided by anatomical knowledge and suitable needle sites. The inferior oblique will not be damaged if the inferotemporal needle is inserted as far temporally (laterally) as possible. EYE BLOCKS

References 1. McKibbin M: The pre-operative assessment and investigation of ophthalmic patients. Eye 10:138-140, 1996 2. Barker JP, Vafidis GC, Robinson PN: The metabolic and hormonal response to cataract surgery. Anaesthesia 48:488-491, 1993 3. Campbell DNC, Lim M, Kerr Muir G: A prospective randomised study of local versus general anaesthesia for cataract surgery. Anaesthesia 48:422-428, 1993 4. Davis DB, Mandel MR: Posterior peribulbar anesthesia: An alternative to retrobulbar anesthesia. J Cataract Refract Surg 12:182-184, 1986 5. Hamilton RC: Regional anaesthesia of the eye. Curr Opin Anaesthesiol 3:740-744, 1990

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6. Loots JH, Koorts AS, Venter JA: Peribulbar anesthesia. A prospective statistical analysis of the efficacy and predictability of bupivacaine and a lignocaine/bupivacaine mixture. J Cataract Refract Surg 19:72-76, 1993 7. Stevens JD: A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon’s infiltration. Br J Ophthalmol 76:670-674, 1992 8. Bergman L, Berglin L, Algreve PV: Limbal sub-Tenon’s administration of retrobulbar anesthesia using a blunt irrigating cannula. Ophthalmic Surg Lasers 27:106-112, 1996 9. Grabow HB: Topical anaesthesia for cataract surgery. Eur J Implant Ref Surg 5:20-24, 1993 10. Masket S, Gokmen F: Efficacy and safety of intracameral lidocaine as a supplement to topical anesthesia. J Cataract Refract Surg 24:956-960, 1998 11. Petersen WC, Yanoff M: Subconjunctical anesthesia: An alternative to retrobulbar and peribulbar techniques. Ophthalmic Surg 22:199-201, 1991 12. Report of the Joint Working Party on Anaesthesia in Ophthalmic Surgery. Royal College of Anaesthetists and College of Ophthalmologists, March 1993 13. Unsold R, Stanley JA, Degroot J: The CT-topography of retrobulbar anesthesia. Anatomic-clinical correlation of complications and a suggestion of a modified technique. Graefes Arch Clin Exp Ophthalmol 217:125-136, 1981 14. Hamilton RC, Gimbel HV, Strunin I: Regional anaesthesia for 12,000 cataract extraction and intraocular lens implantation procedures. Can J Anaesth 35:615-623, 1988 15. Sarvela PJ, Paloheimo MPJ, Nikki PH: Comparison of ph-adjusted bupivacaine 0.75% and a mixture of bupivacaine 0.75% and lidocaine 2% both with hyaluronidase, in day-case cataract surgery under regional anesthesia. Anesth Analg 79:35-39, 1994

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16. Nicoll JMV, Treuren T, Acharya PA: Retrobulbar anesthesia: The role of hyaluronidase. Anesth Analg 65:1324-1328, 1986 17. Katsev DA, Drews RC, Rose BT: An anatomic study of retrobulbar needle path length. Ophthalmology 96:1221-1224, 1989 18. Hustead RF, Hamilton RC, Loken RG: Periocular local anesthesia: Medial orbital as an alternative to superior nasal injection. J Cataract Refract Surg 20:197-201, 1994 19. Brahma AK, Pemberton CJ, Ayeko M: Single medial injection peribulbar anaesthesia using prilocaine. Anaesthesia 49:1003-1005, 1994 20. Ripart J, Lefrant J-Y, Lalourcey L: Medial canthus (Caruncle) single injection periocular anesthesia. Anesth Analg 83:1234-1238, 1996 21. Kapran Z, Uyar M, Eltutar K: One quadrant sub-Tenon’s capsule anesthesia in anterior segment surgery. Eur J Ophthalmol 6:131-136, 1996 22. Khoo B-K, Lim T-H, Yong V: Sub-Tenon’s versus retrobulbar anesthesia for cataract surgery. Ophthalmic Surg Lasers 27:773-777, 1996 23. Hay A, Flynn HW Jr, Hoffman JI: Needle penetration of the globe during retrobulbar and peribulbar injections. Ophthalmology 98:1017-1024, 1991 24. Grizzard WS, Kirk NM, Pavan PR: Perforating ocular injuries caused by anesthesia personnel. Ophthalmology 98:1011-1016, 1991 25. Vivian AJ, Canning CR: Scleral perforation with retrobulbar needles. Eur J Implant Ref Surgery 5:39-41, 1993 26. Donaxas MT, Anderson RL (eds): Clinical Orbital Anatomy. Baltimore, MD, Williams and Wilkins, 1984, p 232 27. Koorneef L, Grizzard WS: Ophthalmic anesthesia, in Reinecke RD (ed): Ophthalmology Annual. New York, NY, Raven Press, 1989, pp 265-294 28. Wildsmith JAW, Armitage EN: Principles and Practice of Regional Anaesthesia. Edinburgh, London, Churchill Livingstone, 1993, pp 217, 219

ANTHONY RUBIN