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ISSN: 2155-9570
Journal of Clinical & Experimental Ophthalmology
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Efficacy and Performance of Various Local Anesthesia Modalities for Cataract Surgery

Adeela Malik*
Moorfield’s Eye Hospital NHS Foundation Trust, London, UK
Corresponding Author : Adeela Malik, MBBS, BSc (Hons)
Moorfield’s Eye Hospital NHS Foundation Trust
London, UK
E-mail: [email protected]
Received December 23, 2012; Accepted February 01, 2013; Published February 08, 2013
Citation: Malik A (2013) Efficacy and Performance of Various Local Anesthesia Modalities for Cataract Surgery. J Clinic Experiment Ophthalmol S1:007. doi:10.4172/2155-9570.S1-007
Copyright: © 2013 Malik A. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Abstract

The efficacy and performance of various local anesthesia modalities for cataract surgery have been reviewed. A comparative evaluation of these different modalities in terms of akinesia, patient-perceived pain during both anesthesia administration and intraoperative cataract surgery is presented.

Anesthesia requirements, anesthetic agents, and inherent complications of various anesthesia modalities are also discussed, with a description of the clinical procedural details for each modality.

The prevailing practice patterns of anesthesia techniques among refractive surgeons in the United Kingdom and United States are also illustrated.

Keywords
Local anesthesia; Catract surgery; Sub-Tenon; Akinesia
Introduction
Progression in phacoemulsification techniques for cataract surgery[1-4] has also led to inevitable changes in the delivery of accompanying anesthesia from general to local modalities [5-7] i.e. retrobulbar, peribulbar, Sub-Tenon and topical anesthesia. General anesthesia is preferred for complicated intracapsular cataract extraction (ICCE) surgery as this technique involves significant manipulation of the eye, and requires several corneal sutures to provide a watertight wound. Extracapsular cataract surgery [2,8-11] (ECCE) also requires a large corneal incision, but there was a trend towards local anesthesia such as retrobulbar [12-15], which allows quicker patient recovery, and thus facilitated day-case surgery.
With the introduction of the foldable intraocular lens [16] (IOL), phacoemulsification and small-incision surgery has developed [2,16-18]. Initially, this was performed via a scleral tunnel and required sutures, thus retrobulbar and peribulbar anesthesia were preferred [14,19]. With the advent of small, stepped, and self-sealing corneal incisions, very little manipulation is required, and this allowed the use of Sub-Tenon [20-23] and topical anesthesia [14,24-26].
An acceptable anesthesia modality for a cataract surgery implies the correct choice of anesthetic agent, combined with a compatible clinical technique, ensuring patient comfort both during and post surgery. Thus, the choice of an anesthesia modality must be assessed on an individual patient and surgeon basis.
This review discusses the efficacy and performance of the different available local anesthesia modalities for cataract surgery, including anesthesia requirements for patient safety and comfort. Clinical methodologies used for the implementation of varying local anesthesia modalities, with the associated complications, are also discussed with a view to identify an optimum local anesthesia strategy for cataract surgery.
Local Anesthesia Requirements
Akinesia
Many surgeons do not consider akinesia an important requirement for cataract surgery, but some prefer to operate under conditions in which eye movements are blunted if not completely paralyzed. Friedman et al. [27] report that both retrobulbar and peribulbar blocks produce the same degree of akinesia. Comparing retrobulbar and Sub- Tenon techniques, the same survey reports that akinesia was slightly less effective with Sub-Tenon; however, the statistical evidence for this was poor. Topical procedures do not lead to akinesia.
Patient preference (pain experience)
Significant pain during anesthetic administration, intraoperative surgery, or after the cataract procedure, is the major reasons for low patient satisfaction [28]. Perceived pain level thus determines patient’s preference for the anesthesia technique and is an important factor in the selection of an optimum strategy for anesthesia management during cataract surgery. During the anesthesia administration phase, topical anesthesia, unlike injection-type anesthesia modalities, is associated with minimal discomfort. However, with topical anesthesia, the agent blocks trigeminal nerve endings in the cornea and the conjunctiva only [29], leaving the intraocular structures in the anterior segment unanesthetized. Thus, manipulation of the iris or stretching of the ciliary and zonular tissues irritates the ciliary nerves, resulting in discomfort. Although injectable anesthesia provides a higher level of analgesia and akinesia than topical anesthesia, the degree of pain perceived by patients during anesthesia administration and intraoperative surgery varies for retrobulbar, peribulbar, and Sub-Tenon modalities. Patientreported pain for various anesthesia techniques is discussed under “Comparative evaluation of performance of various local anesthesia techniques”.
Visual recovery
Rapid vision recovery is highly desirable in cataract surgery and is extremely useful, especially in monocular patients having surgery in the better eye. Modern ophthalmologic surgery is becoming faster and in a typical ophthalmology clinic, an uneventful cataract surgery may take 20 minutes or less; this allows the patient to be discharged with good vision and with an eye patch. Compared with a regional block, topical anesthesia permits early visual rehabilitation, primarily because in this modality only a limited block or no block of the optic nerve is involved.
The overall onset and duration times of the selected anesthetic agent can be adjusted depending on the method of administration, the type of anesthesia, the mixture, and the addition of hyaluronidase (Tables 1-3). Adjustment of the duration of the anesthesia will aid in postoperative recovery and assessment in most cases, but, as in other procedures, children or patients with hearing difficulties are treated under general anesthesia.
Sedation
Administration of an orbital block can result in a great deal of pain; consequently, some clinicians use deep sedation. However, many believe the patient should not be sedated deeply so that he or she remains cooperative. In the UK, the use of sedation decreased from 5.85% in 1996 to 3.9% in 2002/2003 [30,31]. The practice of sedation is, however, not recommended by the Royal College of Anaesthetists [32] and thus should be used to cover only anxiety, not inadequate blocks. Complications of sedation include excessive restlessness, sudden movement, and airway obstruction, which can significantly increase the risk of the surgery [7,28,33]. If the patient is sedated, monitoring is required. The anesthetist should be present and only responsible for that list if the patients have intravenous (IV) sedation. It is considered safer to abandon surgery than to convert to general anesthesia and to continue with general anesthesia only when the patient is fully prepared. “Conscious” sedation, which allows full cooperation of the patient, is recommended [34]. The level of sedation desired, the route of administration, and the choice of drugs commonly used in ophthalmic anesthesia have been reviewed elsewhere [35].
Cost
Literature on the economic evaluation of different systems for cataract surgery and anesthesia is limited, and there is ongoing discussion of the most appropriate methods that can be used [36]. According to a survey reported by Mojon-Azzi and Mojon [37], outpatient surgery is more cost-effective, primarily because there are no costs for overnight stays and lower out-of-pocket expenses. In some European countries (e.g. Holland), the cost savings are estimated at about 20%. The survey also reports that the rate of outpatient cataract surgery in 10 European countries is influenced mainly by acute-bed density, density of practicing physicians, and public expenditure on health [37].
Anesthetic Agents for Local Anesthesia
The choice of a local anesthetic agent is optimal only when the agent’s inherent properties meet the characteristics of the surgical procedure and the requirements of the patient in terms of contraindications and perceived pain. The relative performance, efficacy, and underlying complications of local anesthetic agents, including toxicity, have been discussed extensively in references [22,27,38-47]. The pharmacology and pathogenesis of toxicity of the various agents are also well documented [40,48]. Table 1 lists the properties of popular anesthetic agents. Lidocaine, bupivacaine, and ropivacaine are the most popular traditional agents used for conduction blockades. Levobupivacaine, articaine, and 2-chloroprocaine are recently developed agents. Table 2 lists the typical agents used for various anesthesia techniques and Table 3, the onset time to akinesia for the traditional and newer agents.
The use of hyaluronidase in regional anesthesia is controversial. However, as an adjuvant in retrobulbar and peribulbar anesthesia [7,10,49], it enhances the onset of the block. It also improves the onset and quality of the block in the Sub-Tenon procedure by promoting diffusion to the periorbital and retro-orbital tissue [20,50-52] and alleviating the need for a facial nerve block, which can be painful [42,52]. Hyaluronidase [7] helps to avoid a decrease in retinal circulation and an increase in intraocular pressure (IOP) and to reduce the risk for muscle toxicity from local anesthetic agents.
Intracameral anesthesia (injection into the anterior chamber) is often used as an adjunct to topical anesthesia to enhance the anesthesia and thereby deal with incremental pain that may arise during topical anesthesia alone. Ester-linked benoxinate (oxybuprocaine), amidelinked lidocaine, and ester-linked tetracaine (amethocaine) are the most commonly used topical agents [7] for anesthesia of the cornea and conjunctiva.
Choice of Anesthetic Delivery Techniques in Local Anesthesia
Retrobulbar, Peribulbar, Sub-Tenon and Topical anesthesia are the popular modalities of local anesthesia (LA) [32,53-55]. The regional modalities i.e. retrobulbar, peribulbar, and Sub-Tenon anesthesia depend on injection-delivery of the anesthetic agent, and in some literature these modalities are referred to as intraconal, extraconal, and parabulbar blocks, respectively; but in this paper the former terminology is used exclusively.
Overall, local anesthesia for cataract surgery promises a better procedural safety profile [7,39] and has allowed development of daysurgery cases with quicker patient recovery generally. It is also more economical cost wise.
Substantial information [32] for safe and effective local anesthesia for ophthalmic surgery (intended for practice in the United Kingdom) is contained in joint guidelines issued by the Royal College of Anaesthetists and the Royal College of Ophthalmologists.
With increased popularity of day surgery, general anesthesia is reserved for cases that are unsuitable for local anesthesia: patients (such as a child or a younger adult) intolerant to the local anesthesia procedure, confused patients unable to comply, patients with marked uncontrolled tremor or jerky movements, patients with a history of allergic reaction to local anesthesia, and patients who refused consent for local anesthesia.
Local anesthesia is not free of complications. To reduce complications (discussed under Contraindications), it is essential for the clinician to be fully aware of the procedure (discussed under Local Anesthesia Requirements) involved in the implementation of the various delivery techniques.
Figure 1 illustrates the initial entry/incision and the final/ anesthesia-delivery points for the cannula/needle tip in the various local anesthesia techniques within the orbit. Table 4 lists the relevant procedural details for each technique. The resulting blockade of the various nerves depends on the actual location of the injection as illustrated in Table 5.
Regional anesthesia
Detailed description of clinical techniques of regional anesthesia are described in references [53-55].
Retrobulbar (Intraconal) anesthesia
The retrobulbar procedure achieves good ocular akinesia and analgesia and generally requires an injection of 3.5 mL to 5.0 mL of anesthetic agent into the retrobulbar space [15,43,56,57]. According to Feibel [15], in this technique, a shorter needle (31 mm versus 38 mm) is introduced into the retrobulbar space by having the patient in primary gaze. Precision placement of the needle is essential to avoid complications.
In a survey of members of the American Society of Cataract and Refractive Surgery (ASCRS) [58], the percentage of respondents using retrobulbar anesthesia with some facial block decreased from 76% in 1985 to 9% in 2003; the procedure was used primarily for longer operations in eyes with a less stable anterior chamber.
Peribulbar (Extraconal) anesthesia
The peribulbar technique involves administration of several (up to 4) injections external to the muscle cone and achieves good ocular akinesia and anesthesia [14,19,59]. An audit of peribulbar blockade using short (15.0 mm), medium (25.0 mm), and long (37.5 mm) needles (disregarding the inherent safety aspects of the length of the needles in this particular study for teaching purposes) concluded that the efficacy of peribulbar anesthesia depends on the proximity of the deposition of the local anesthetic solution to the globe or the orbital apex [60]. Consequently, peribulbar anesthesia can be classified as circumocular (Sub-Tenon episcleral), periocular (anterior, superficial), periconal (posterior, deep), and apical (ultra deep). Peribulbar blockade can lead to significant reduction in pulsatile ocular blood flow and IOP, which may be of benefit in certain operations [61].
Sub-Tenon (Parabulbar) anesthesia
Sub-Tenon anesthesia technique [14,20,21,62,63] begins with instillation of topical anesthesia. The Tenon capsule is then dissected, and a blunt cannula is introduced [64] into the Sub-Tenon space to administer the anesthetic agent. This produces anterior segment and conjunctival anesthesia [20,62,63]. Anesthesia sets in rapidly, followed after a few minutes by globe akinesia.
The Tenon capsule is a fascial layer of connective tissue surrounding the globe and extraocular muscles [20]. It is attached anteriorly to the limbus of the eye, extends posteriorly over the surface of the globe, and fuses with the dura surrounding the optic nerve.
The Sub-Tenon technique has been used increasingly for posterior segment eye surgery such as retinal detachment surgery [65,66]. However, the technique requires a certain amount of skill to dissect into the Sub-Tenon space and correctly place the anesthetic agent as well as competence to deal with the increased risk for conjunctival bleeding and chemosis.
The incidence of conjunctival swelling associated with the Sub- Tenon block is around 39.4% [20,67]. Some of this is attributable to anterior leakage of the injectate, and chemosis is exaggerated if the solution is administered incorrectly into the anterior compartment of Sub-Tenon space or the subconjunctival space. The reported incidence of subconjunctival hemorrhage is 32% to 56% [20,68]. Cauterization of the conjunctival incision is often used to reduce hemorrhage.
Amin et al. [65] suggest the use of a standard IV cannula instead of the Sub-Tenon cannula to puncture the anesthetized and tented conjunctiva to reduce chemosis and subconjunctival hemorrhage, claiming that the “minimal risk” of puncturing the eye is assured because of the clear visibility of the needle tip at all times. Gray and Lucas [21] point out that the needle tip is not clearly visible once under the conjunctiva and in the event of hemorrhage, it would quickly be obscured. Thus, it has no additional safety compared with the peribulbar technique.
Topical anesthesia
For fast recovery and rehabilitation after surgery, cataract patients are often managed under topical anesthesia [69], which can be supplemented with intracameral anesthesia [7,14,25] or oral/IV sedation [24]. One bonus of topical anesthesia, especially in patients who have vision in the operated eye only, is that visual recovery is almost immediate.
Topical anesthesia has also been used with varying degrees of success for combined cataract and glaucoma surgery, trabeculectomy [70], viscocanalostomy, and secondary IOL transplantation.
Topical anesthetic agents [29] block trigeminal nerve endings in the cornea and the conjunctiva only, leaving the intraocular structures in the anterior segment unanesthetized. Thus, manipulation of the iris and stretching of the ciliary and zonular tissues during surgery can irritate the ciliary nerves, resulting in discomfort. For this reason, the addition of intracameral anesthesia as an adjunct is popular [6,14,38,71].
Several methods of topical anesthesia are available, but the use of eyedrops or viscous gels is the most common modalities. Considerations such as corneal epithelial toxicity [72], patient comfort, and patient history of allergies to local anesthetic agents determine the choice of suitable anesthetic eye drops for use in any particular situation. Proparacaine, tetracaine, lidocaine, bupivacaine, or benoxinate anesthetic eye drops (Table 2) into the fornix of the operative eye are used primarily.
High or prolonged doses of local anesthetic agents are toxic to the corneal epithelium, and this prolongs wound healing and causes corneal erosion. Also, repeated administration of drops can cause clouding of the cornea, rendering surgery more difficult. Tetracaine (an ester-type anesthetic agent) is the most irritating of the eye drops listed above and should be avoided in patients allergic to this particular family of anesthetic agents [38]. Proparacaine, although an ester type, does not metabolize to p-aminobenzoate moiety, and thus may be used safely in patients allergic to other ester-type anesthetic agents.
An alternative to eye drops for topical application is the use of viscous lidocaine gel. The gel is often mixed with dilating medications and antibiotic and non-steroidal anti-inflammatory agents. It is reported that 5 mL of lidocaine gel 2% mixed with 4 drops tropicamide, 4 drops cyclopentolate 1%, 4 drops phenylephrine 10%, 10 drops moxifloxacin, and 4 drops ketorolac and applied to the operative eye twice before the surgery typically achieves excellent dilation and anesthesia [38]. However, drug absorption and corneal epithelial safety of this mixture have not been fully investigated.
Intracameral anesthesia
Intracameral anesthesia is a common adjunct to topical anesthesia in phacoemulsification [38]. It probably provides sensory blockage of the iris and ciliary body and thereby relieves discomfort experienced during IOL placement. Intracameral lidocaine alone dilates the pupil well [73], and this is believed to be because of the direct action of lidocaine on the iris, which in turn causes muscle relaxation. Preservative-free lidocaine 1% with epinephrine (0.3cc of 1: 1000) enhances pupillary dilation more than lidocaine 1% alone and thus obviates the need for preoperative dilating drops [74].
Efficacy and Performance of Various Local Anesthesia Modalities
Regional (Injection type) anesthesia
The efficacy of anesthesia partly depends on the ease of irrigation and the spread of the anesthetic agent after injection. A study using magnetic resonance imaging to examine the distribution of local anesthesia solution after combined peribulbar and retrobulbar, superomedial retrobulbar, and Sub-Tenon injection reports that for a combined peribulbar and retrobulbar block [75], a relatively large volume of local anesthetic solution spreads throughout the orbit and a reliable anesthesia is achieved. After superomedial retrobulbar and Sub-Tenon injection, the local anesthetic solution accumulates behind the globe and good analgesia and slight akinesia are achieved with a small volume of anesthetic solution. However, the superomedial approach is not favored because of the close proximity to the cluster of nerves and blood vessels.
Table 6 summarizes the effectiveness of various regional anesthesia modalities in terms of akinesia, patient-reported pain during anesthetic administration, patient-reported intraoperative pain, and visual recovery. The results show that retrobulbar and peribulbar procedures produce equally good akinesia, and Sub-Tenon procedures produce slightly less akinesia, but the supporting evidence for this is insufficient.
Peribulbar anesthesia is the local anesthesia of choice in complex cataract cases that need total akinesia or iris manipulation. It provides superior akinesia and anesthesia, and in well-trained hands, there is an extremely low risk for globe penetration. However, the inherently largevolume injection requirements for peribulbar lead to relatively higher chemosis in peribulbar anesthesia than in retrobulbar anesthesia.
Table 6 also indicates that visual recovery after topical anesthesia compared with retrobulbar, peribulbar, and Sub-Tenon is relatively a lot quicker.
Topical anesthesia
Topical anesthesia has been demonstrated to be a safe and effective alternative to retrobulbar and peribulbar procedures, but it does not provide akinesia and may even give inadequate sensory blockade for the iris and ciliary body [38]. Consequently, it is used for short surgeries and in cooperative patients with low to medium anxiety. A significant number of surgeons consider that for routine small-incision cataract surgery, ocular anesthesia with a topical anesthetic agent is sufficient [14,38,76].
A comparative clinical trial of topical anesthetic agents in cataract surgery [77] suggests that lidocaine gel is a better agent than bupivacaine or benoxinate drops. However, bupivacaine drops are effective in providing deep topical anesthesia. Also, the reported verbal pain score (VPS) during surgery for lidocaine gel, bupivacaine, and benoxinate drops was 1.6, 4.1, and 7.1, respectively (using an arbitrary pain scale of 0 to 10 where zero represents no pain and a score of 10, high pain). The VPS during application of the agent was 2.97, 1.53, and 1.03, respectively.
Several studies have compared the relative performance of topical anesthesia and regional blocks. One shows that although the topical route is well tolerated, there is greater overall satisfaction and less immediate and post-procedure pain with Sub-Tenon blockade [78]. Another concludes that patient comfort and surgery-related complications did not differ between topical anesthesia and peribulbar anesthesia and that in view of the minimally invasive character of topical anesthesia compared with that of peribulbar anesthesia, the use of topical anesthesia for routine cataract surgery is justified [79].
A study comparing topical anesthesia and retrobulbar anesthesia [80] reports that phacoemulsification with topical anesthesia is more painful than retrobulbar anesthesia, and that in hypertonic patients and younger patients more susceptible to pain, topical anesthesia should be avoided or used in conjunction with sedation. Yet, another study [81] suggests that topical anesthesia is justified as a means of improving safety without causing discomfort to the patient even in complicated cataract surgery cases. The Royal College of Anaesthetists [32] recommends the presence of an anesthetist only when a sharpneedle block or sedation is undertaken.
Intracameral anesthesia
Intracameral anesthesia has several advantages: injuries to ocular tissue or life-threatening systemic side-effects are minimal, the vision is restored instantly after the operation, the undesirable cosmetic sideeffects are avoided, the technique is economical, and there is no need for an anesthetist to be present. The efficacy of intracameral anesthesia with regard to possible retinal and corneal endothelial toxicity is discussed in a report by the American Academy of Ophthalmology [38,82]. Some of the papers clearly indicate the efficacy of intracameral anesthesia, whereas others fail to support this conclusion. However, the report concludes that as topical anesthesia alone is effective, intracameral anesthesia should be reserved to deal with incremental pain arising during the procedure.
Short-term studies of the safety of intracameral anesthesia indicate that preservative-free lidocaine 1% is well tolerated by the corneal endothelium, whereas higher concentrations are toxic [38]. Although short-term studies indicate safety, the long-term effects are not known.
Retinal toxicity can occur because of posterior diffusion of local anesthesia to the retina, and a temporary loss of light perception has been reported after intracameral anesthesia [38]. Several in vitro studies suggest that both lidocaine and bupivacaine may be toxic to the retina; therefore, a minimal concentration of local anesthesia must be used [38]. Although the toxic effects of the commonly available topical anesthetic agents on the corneal epithelium have been studied extensively [29], their effect on corneal endothelium as part of intracameral anesthesia administration is not fully understood. Preservative-free lidocaine 1% in doses of 0.1 to 0.5 mL is not associated with corneal endothelial toxicity [38], but higher concentrations may be toxic. Compared with lidocaine, intracameral bupivacaine is not well studied, but it may be more toxic to corneal endothelium than lidocaine 1%. Thus, preservative-free lidocaine 1% has been suggested as the local anesthesia of choice for intracameral anesthesia [38].
A study in rabbits shows that the preservative benzalkonium chloride (at a concentration of 0.025% to 0.05%) in commercially available anesthetic agents may cause irreversible damage to corneal tissues [29]. Injecting unpreserved lidocaine hydrochloric acid 4% into the anterior chamber over a period of several days [72] produced significant corneal thickening and opacification in rabbit models.
Exposure time to the agent and the preservative in the agent are important in determining the effect of lidocaine. However, a brief exposure (typically equal to that needed for uneventful foldable IOL implantation) to unpreserved lidocaine is considered unlikely to injure the corneal endothelium.
Several incidents of visual sensations (ranging from a mere perception of glow to perception of real objects) have been reported during surgery under topical anesthesia procedures [83]. Many patients find this an unexpected and disturbing experience, but this fear may be reduced with adequate patient counseling.
Comparative Evaluation of Performance of Various Local Anesthesia Modalities
Patient-reported pain
Large heterogeneity normally exists [27] in the contents, design, and outcomes of most of the studies related to randomized trials in regional anesthesia management strategies for cataract surgery. This was confirmed by Friedman et al. [27] during data collection (using a systematic literature search using PubMed and Cochrane Collaboration’s database (Central)) for the synthesis of the findings of various trials. Consequently in these cases the scientific justification for the meta-analysis is not always met.
The authors then concluded that under such circumstances the unconventional consensus-type approach to grade the outcomes based on the methodology proposed by Garbutt et al. [84] is more appropriate. Malik et al. [1] have discussed the scope and limitations of meta-analysis for trial results complicated by large heterogeneity and concluded that the difficulty may be partially overcome using relatively large number of randomized clinical trials of various local anesthesia procedures. The rationale is that a larger number of studies and larger number of patients per study would reduce bias in statistical modeling and also overcome the problem of any shortfall in the number of degrees of freedom.
The assessment of pain scores described in the following sections of this report is based on the analysis of the data collected and reported by Friedman et al. [27].
The outcome of a recent meta-analysis report [85], comparing pain scores of topical anesthesia against regional anesthesia is consistent with these findings.
 
Patient-perceived pain during anesthesia administration
Figure 2 shows the quantitative grading of the patient-perceived pain during anesthesia administration for various modalities. The results show that among the injection types, the perceived pain is least with the Sub-Tenon approach, and that overall the application of anesthesia by injection is relatively more painful than that by topical means. The vertical scale represents mean pain level within an arbitrary scale 0 to 10, where zero score represents no pain, 1 to 2 mild pain, 3 to 5 moderate pain, and a score of more than 5 severe pain. Some uncertainty however remains due to the restricted availability of the data for Sub-Tenon and topical anesthesia
Patient-perceived pain during intraoperative surgery
Figure 3 illustrates the patient perceived pain during intraoperative surgery. The illustrated qualitative outcome is based on the global plot of perceived pain constructed by Malik et al. [1] using the data reported by Friedman et al. [27]. Here the quantitative grading of the results was not possible due to limited data available. However, the qualitative results of Figure 3 indicate that the patient-perceived pain during intraoperative surgery is greater with topical anesthesia than that with injection blocks. For the injection types, pain is less with the Sub-Tenon procedure than with retrobulbar and peribulbar procedures.
Patient-perceived pain due to various anesthetic agents
Pain experienced during surgery for different types of topical anesthetic agents such as lidocaine gel 2%, bupivacaine 5% drops, and benoxinate 0.4% drops has been reported as 1.6, 4.1, and 7.1, respectively [77]. The scores represent the verbal judgment of patients soon after the surgery using pain scores between 0-10 (where zero represents no pain and 10, high pain).
Akinesia due to various anesthetic modalities
An extent of akinesia produced [27,86] after implementation of various anesthesia modalities is shown in Table 6. The results show that both RB and PB produce equally good akinesia. Addition of hyaluronidase appears to increase the effectiveness of these blocks in producing akinesia, but the use of hyaluronidase in procedures other than RB is controversial (see also section- Anesthetic Agents for Local Anesthesia).
Comparisation [27] between RB and ST procedures show that akinesia is slightly less effective in ST procedures, but there is insufficient evidence to support this conclusion.
Practice patterns among cataract surgeons in the United Kingdom and the United States
Figure 4 illustrates the trend in the use of various local anesthetic techniques in the US from 1995 to 2003. These results of the practicepattern survey of American Society Cataract Refractory Surgery (ASCRS) members [58] clearly indicate that from 1998 to 2003, there was a significant decline in the use of retrobulbar anesthesia procedures and an increase in topical procedures. The results also indicate a renewed interest in Sub-Tenon techniques. The survey also suggests that the use of topical anesthesia varied according to the surgical volume: In 2003, it was 38% for institutions with 1 to 5 procedures a month and 76% for institutions with more than 75 procedures a month.
A 2002 European survey [87] comparing anesthesia techniques and practices internationally suggested that peribulbar block was the most frequently used technique and that topical anesthesia was used by a sizeable minority of surgeons only. However, the American survey [58] is considered more thorough and is also more widely accepted.
Table 7 lists the findings of UK-based studies (The British Ophthalmological Surveillance Unit) [30,31], illustrating the changing trend in anesthesia techniques over the period 1996 to 2002/2003. The results show that local anesthesia techniques were more popular than general anesthesia.
Figures 5 and 6 illustrate the relative change in the practice of various anesthesia techniques from 1995 to 2003 in the United States and from 1996 to 2003 in the UK. In both countries, there was a decline in the use of retrobulbar and peribulbar injection techniques, with Sub- Tenon and topical techniques gaining popularity.
Contraindications
The contraindications [32] to various modalities are listed in Table 8.
Complications of Local Anesthesia Techniques
Safety considerations
Safety considerations concern the inherent safety of the anesthetic agent and the technique used. A UK-based survey concludes that potentially life-threatening complications exist with all techniques except topical/intracameral local anesthesia [30]. This suggests that an anesthetist must be present [32] to deal with adverse events when intraocular surgery is performed. Another UK-based survey [31] showed that in 1996, an anesthetist was present for 84% of the cases monitored and IV access was established in 60% of these cases. The UKbased survey [30] also showed that from 2002 to 2003, potentially sightthreatening complications were mostly associated with retrobulbar and peribulbar techniques.
Orbital hemorrhage
Orbital hemorrhage can be reduced by avoiding injection into the apex (vascular area), using fine, short needles (25-gauge and 25 mm needles) [32,42,64,88-90]. Fanning [56] discussed a choice of needles for use in orbital regional anesthesia. The use of needles longer than 31 mm is not recommended. The use of retrobulbar and peribulbar anesthesia is decreasing primarily because of the increased risk and severity of complications such as globe perforation and retrobulbar hemorrhage, especially as other modalities have been found to be as effective. Delivery of the anesthetic agent with a blunt needle, such as that used in Sub-Tenon delivery, reduces this risk substantially.
Globe perforation
Globe perforation is a rare complication, more likely to occur in myopic eyes (which are thinner and longer), especially when carrying out retrobulbar and peribulbar blocks [32,42,91]. The reported incidence of globe perforation ranges from 0 in 2,000 to 1 in 16,224 for peribulbar procedures [92], 3 in 4,000 for retrobulbar, and 1 in 12,000 for a mixture of peribulbar and retrobulbar procedures [17]. A significant proportion of globe penetrations are not detected during administration of the anesthetic agent but are noticed following the development of hypotony, poor red reflex, and vitreous hemorrhage during surgery [42].
During delivery of the anesthetic agent, patients are often asked to move their eyes from side to side to ensure that no contact with the globe has occurred. The risk with this is that a patient will move his or her head instead and in doing so run the risk of deepening the depth of penetration.
The complication rate of globe perforation can be reduced by correct knowledge of anatomy (especially if previous ocular surgery that may alter the anatomy has occurred), patient cooperation, and the use of blunt needles. Although perforation is less likely with blunt needles, in the event of a perforation, more trauma is involved [39].
Systemic adverse events
Systemic risk [32] such as brainstem anesthesia can occur with local anesthesia. For this reason, the patient must be monitored carefully after administration of the anesthesia and also during surgery. Symptoms such as drowsiness and loss of or confused verbal contact often suggest brainstem anesthesia, which can lead to respiratory and cardiac arrest [32]. The onset usually occurs within 8 to 10 minutes of local anesthesia delivery. Resuscitation equipment and personnel trained to use it must be available. The oculocardiac reflex—episodes of bradycardia provoked by eye surgery or eye manipulation—is blocked when the ciliary ganglion is anesthetized. The oculocardiac reflex is rare with local anesthesia because blockade of the ciliary ganglion ablates the afferent oculocardiac reflex [39], but rapid distension of the tissues by volume or hemorrhage can occasionally provoke it.
Death can result from local anesthesia as a consequence of spread of the anesthetic agent along the optic nerve sheath or intra-arterial injection of the anesthetic solution with retrograde flow, giving rise to systemic toxicity that causes brainstem anesthesia [39,42]. This is more likely to occur with retrobulbar anesthesia (0.1% to 0.3%); it rarely occurs with peribulbar and short needles, as they avoid the cone of the extraocular muscles. This risk is also reduced if short needles are used in primary gaze to avoid rotation of the needle toward the nerve [14], which reduces the incidence of direct trauma to the optic nerve. In the UK during the period 2002 to 2003, 7 of 8 reported neurological complications (consistent with brainstem) were due to retrobulbar and peribulbar anesthesia [30].
A study of the management of cataract in a predominantly elderly female population exhibiting significant systemic illness and coexisting advanced cataract, presenting for surgery in a typical public hospital in New Zealand, reported adverse intraoperative events of only 5% [93].
Allergy
The adverse effects of some common drugs used in cataract surgery have been studied [32,40,42,94,95]. Toxicity (arising because of overdose or intravascular injection) and allergic or vasovagal reactions are the most common complications associated with local anesthesia and can lead to systemic complications [31].
There have been several case reports of allergy from use of local anesthesia or proparacaine eyedrops [96,97]. Although crosssensitization between proparacaine and other related topical ophthalmologic anesthetic agents, such as tetracaine, is a rare occurrence, some studies [97] suggest that allergic sensitization and possible cross-reaction to topical anesthetic agents in ophthalmologists is an occupational hazard.
The development of amide local anesthetic agents have effectively reduced allergic reactions, and amides are now considered rare allergens; only about 1% alleged reactions are believed to be caused by a truly immune-mediated process [40]. Hyaluronidase, an additive used to promote the onset and quality of the block, may rarely cause allergic reactions [98,99].
Other complications
Persistent diplopia (overall incidence 0.25%), lasting over a month and due to direct damage to the inferior rectus muscle, can occur as a result of the retrobulbar technique [100,101]. Muscle palsy (diplopia and ptosis) can be prevented by not using high concentrations of local anesthesia, which can become both neurotoxic and myotoxic. Facial nerve blocks can lead to dysphagia or respiratory obstruction [42] from spread of the anesthesia to the glossopharyngeal nerve and should be used only in the presence of severe blepharospasm. Adjuvant IV anesthetic agents for the reduction of pain are normally associated with an increase in medical events [102].
The incidence of perioperative myocardial ischemia in elderly patients having cataract surgery is significantly less under local anesthesia than general anesthesia [103]. High or prolonged doses of local anesthesia are toxic to the corneal epithelium; this prolongs wound healing and causes corneal erosion. Repeated administration of topical local anesthetic agents frequently sting and occasionally cause temporary clouding of the cornea, rendering surgery difficult [41,42].
Conclusion
Patient safety and comfort, combined with anesthesia efficacy, and the surgeon’s expertise, are all important factors in determining the overall usefulness of various anesthetic techniques in cataract surgery. In local anesthesia, the trend from sharp needle to blunt needle, and topical treatments, has improved the safety profile of anesthesia delivery. Both modalities appear acceptable for patient comfort during anesthesia delivery and intraoperative surgery. However, consideration of contraindications, and the desired duration of anesthesia for the accomplishment of set surgical objectives determine the choice between these 2 modalities. Other modalities have their place, and should be considered if the surgery is complicated, likely to be of prolonged duration, or especially if the patient is intolerant of local or topical procedures.
There is a need for more randomized clinical trials of various local anesthesia procedures in cataract surgery in order to facilitate the statistical methods of meta-analysis, and thus establish convincingly the relative merits, and efficacy of these procedures.
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