Ultrasonic localization of anesthetic fluid in sub-Tenon's, peribulbar, and retrobulbar techniques

Scleral growth stunting via sub-Tenon injection of cross-linking solutions in live rabbits

BACKGROUND

Scleral cross-linking is a potential method to inhibit axial elongation of the eye, preventing the progression of pathological myopia. Formaldehyde releasers, which are common preservatives found in cosmetics and ophthalmic solutions, have been shown to be not only effective in cross-linking corneal collagen in vitro and in vivo, but also have minimal toxicity effects on the eye. The present study aims to evaluate the efficacy of scleral cross-linking using sodium hydroxymethylglycinate (SMG) to inhibit eye growth using an in vivo rabbit model.

METHODS

A cross-linking solution containing 40 mM SMG was delivered to the sub-Tenon's space behind the equator. The application regimen included a two-quadrant injection performed five times over 2 weeks on New Zealand White rabbits (n=5, group 1), and one-time injection followed for up to 5 days on Dutch-Belted rabbits (n=6, group 2). Group 1 was monitored serially for axial length changes using B-scan ultrasound for 5-6 weeks. Group 2 was injected with a higher viscosity solution formulation. Both groups were evaluated for thermal denaturation temperature changes of the sclera postmortem.

RESULTS

Axial growth was limited by 10%-20% following SMG treatment as compared with the untreated eye. Thermal denaturation analysis showed increased heat resistance of the treated eyes in the areas of injection. Overall, the SMG treatment inhibited eye growth with few side effects from the injections.

CONCLUSIONS

Cross-linking solutions delivered via sub-Tenon injection provide a potential method for limiting axial length growth in progressive myopia and could be used as a potential treatment for myopia.

Comparison of changes in blood pressure in phacoemulsification cataract surgery performed via topical and peribulbar anaesthesia: A cohort study

Background

The purpose of study was to compare the changes in blood pressure in patients undergoing phacoemulsification cataract surgery under topical and peribulbar anaesthesia during preoperative, intraoperative and postoperative period.

Methods

In this prospective cohort study, 240 patients undergoing phacoemulsification were divided into topical (Group 1) and peribulbar (Group 2) equally. Proparacaine 0.5% drops were used for topical anaesthesia, and Inj lignocaine with Inj bupivacaine were used to give peribulbar anaesthesia. Preoperative blood pressure was taken 30 min before surgery with automated sphygmomanometer. Intraoperative blood pressure was taken during phacoemulsification, and postoperative blood pressure was taken 1 h after surgery. Outcomes assessed were systolic, diastolic and mean blood pressure.

Results

Systolic blood pressure in Group 1 was significantly increased in the intraoperative phase, whereas it was significantly decreased in Group 2 in the intraoperative phase. Diastolic and mean blood pressure in Group 1 showed no significant change, whereas in Group 2, both showed significant reduction in intraoperative and postoperative phases.

Conclusion

The increase in intraoperative systolic blood pressure in topical group could be due to discomfort from microscope light, iris manipulation, irrigation and aspiration during surgery. The decrease in intraoperative systolic and diastolic blood pressure in peribulbar group could be due to systemic absorption of local anaesthetic. The mean preoperative systolic blood pressure was also higher in the topical group, which could be due to anxiety or stress under topical anaesthesia. The changes in blood pressure need to be observed so that timely intervention can be made to achieve favourable postoperative outcome.

Sub-Tenon's anaesthesia for modern eye surgery-clinicians' perspective, 30 years after re-introduction

Sub-Tenon's block (STB) is a good technique of local anaesthesia for many types of eye surgery. It has a relatively good risk profile, in that sight- and life-threatening complications appear to be extremely rare. STB has gained popularity in the last three decades, with refinements including different types of blunt metal cannula, plastic cannulae and 'incisionless' approaches. Usage of STB varies significantly across the globe. This narrative review documents the historical evolution of STB techniques, anatomical and physiological considerations, its utility and suitability, complications, explores the current practice and possible future applications.

Ultrasound detection of iatrogenic injury during peribulbar eye block: a cadaveric study

Background

Ophthalmic eye blocks, such as retrobulbar, peribulbar and sub-Tenon’s, are traditionally conducted “blind”. Complications are rare but potentially devastating. Life-threatening complications include brain stem anesthesia and local anesthetic toxicity, whereas sight-threatening complications include globe perforation, optic nerve damage and ocular muscle damage. Ultrasound permits a view of orbital structures and can be used to guide needle placement. The ultrasound appearances of unintended local anesthetic injection into vital orbital structures have not been documented. This study aimed to record the ultrasound appearances of unintended injection locations.

Methods

The spherical shape of the eyeballs of three soft-fix Thiel embalmed human cadavers were restored using glycerol. Iatrogenic injury in peribulbar block was then simulated through injection of printers’ ink mixed with Thiel embalming fluid. Ultrasound was used to guide the needles and the tips were redirected to lie within the globe, lateral rectus and optic nerve. Ultrasound images were recorded during injection. The orbital cavities were then dissected via a superior approach to record the location and extent of injectate spread.

Results

Real-time globe rupture, ocular muscle injection and optic nerve injection were visible using ultrasound. Characteristic appearances were identified in each case. Dissection confirmed needle and injection placement.

Conclusions

The ultrasound appearance of block complications is important to document and should be an integral part of regional anesthesia training. This study is the first to provide such images for ophthalmic nerve blocks. It offers ophthalmic anesthetists and ophthalmologists the potential to diagnose severe complications rapidly and accurately with a potential impact on patient safety.

Regional Anesthesia for Pediatric Ophthalmic Surgery: A Review of the Literature

Ophthalmic pediatric regional anesthesia has been widely described, but infrequently used. This review summarizes the available evidence supporting the use of conduction anesthesia in pediatric ophthalmic surgery. Key anatomic differences in axial length, intraocular pressure, and available orbital space between young children and adults impact conduct of ophthalmic regional anesthesia. The eye is near adult size at birth and completes its growth rapidly while the orbit does not. This results in significantly diminished extraocular orbital volumes for local anesthetic deposition. Needle-based blocks are categorized by relation of the needle to the extraocular muscle cone (ie, intraconal or extraconal) and in the cannula-based block, by description of the potential space deep to the Tenon capsule. In children, blocks are placed after induction of anesthesia by a pediatric anesthesiologist or ophthalmologist, via anatomic landmarks or under ultrasonography. Ocular conduction anesthesia confers several advantages for eye surgery including analgesia, akinesia, ablation of the oculocardiac reflex, and reduction of postoperative nausea and vomiting. Short (16 mm), blunt-tip needles are preferred because of altered globe-to-orbit ratios in children. Soft-tip cannulae of varying length have been demonstrated as safe in sub-Tenon blockade. Ultrasound technology facilitates direct, real-time visualization of needle position and local anesthetic spread and reduces inadvertent intraconal needle placement. The developing eye is vulnerable to thermal and mechanical insults, so ocular-rated transducers are mandated. The adjuvant hyaluronidase improves ocular akinesia, decreases local anesthetic dosage requirements, and improves initial block success; meanwhile, dexmedetomidine increases local anesthetic potency and prolongs duration of analgesia without an increase in adverse events. Intraconal blockade is a relative contraindication in neonates and infants, retinoblastoma surgery, and in the presence of posterior staphylomas and buphthalmos. Specific considerations include pertinent pediatric ophthalmologic topics, block placement in the syndromic child, and potential adverse effects associated with each technique. Recommendations based on our experience at a busy academic ophthalmologic tertiary referral center are provided.

Second Harmonic Generation Signals in Rabbit Sclera As a Tool for Evaluation of Therapeutic Tissue Cross-linking (TXL) for Myopia

Methods to strengthen tissue by introducing chemical bonds (non-enzymatic cross-linking) into structural proteins (fibrillar collagens) for therapy include photochemical cross-linking and tissue cross-linking (TXL) methods. Such methods for inducing mechanical tissue property changes are being employed to the cornea in corneal thinning (mechanically weakened) disorders such as keratoconus as well as the sclera in progressive myopia, where thinning and weakening of the posterior sclera occurs and likely contributes to axial elongation. The primary target proteins for such tissue strengthening are fibrillar collagens which constitute the great majority of dry weight proteins in the cornea and sclera. Fortuitously, fibrillar collagens are the main source of second harmonic generation signals in the tissue extracellular space. Therefore, modifications of the collagen proteins, such as those induced through cross-linking therapies, could potentially be detected and quantitated through the use of second harmonic generation microscopy (SHGM). Monitoring SHGM signals through the use of a laser scanning microscopy system coupled with an infrared excitation light source is an exciting modern imaging method that is enjoying widespread usage in the biomedical sciences. Thus, the present study was undertaken in order to evaluate the use of SHGM microscopy as a means to measure induced cross-linking effects in ex vivo rabbit sclera, following an injection of a chemical cross-linking agent into the sub-Tenon's space (sT), an injection approach that is standard practice for causing ocular anesthesia during ophthalmologic clinical procedures. The chemical cross-linking agent, sodium hydroxymethylglycinate (SMG), is from a class of cosmetic preservatives known as formaldehyde releasing agents (FARs). Scleral changes following reaction with SMG resulted in increases in SHG signals and correlated with shifts in thermal denaturation temperature, a standard method for evaluating induced tissue cross-linking effects.

Evaluation of Therapeutic Tissue Crosslinking (TXL) for Myopia Using Second Harmonic Generation Signal Microscopy in Rabbit Sclera

Purpose

Second harmonic generation signals (SHG) are emitted preferentially from collagenous tissue structures and have been used to evaluate photochemically-induced (CXL) crosslinking changes in the cornea. Since therapeutic tissue crosslinking (TXL) using sodium hydroxymethylglycinate (SMG) of the sclera is a potential treatment for high myopia, we explored the use of SHG microscopy to evaluate the effects.

Methods

Single sub-Tenon's (sT) injections (400 μL) using SMG (40-400 mM) were made at the equatorial 12 o'clock position of the right eye of cadaveric rabbit heads (n = 16 pairs). After 3.5 hours, confocal microscopy (CM) was performed using 860 nm two-photon excitation and 400 to 450 nm emission. Pixel density and fiber bundle "waviness" analyses were performed on the images. Crosslinking effects were confirmed using thermal denaturation (Tm) temperature. Comparison experiments with riboflavin photochemical crosslinking were done.

Results

Therapeutic tissue crosslinking localization studies indicated that crosslinking changes occurred at the site of injection and in adjacent sectors. Second harmonic generation signals revealed large fibrous collagenous bundled structures that displayed various degrees of waviness. Histogram analysis showed a nearly 6-fold signal increase in 400 mM SMG over 40 mM. This corresponded to a ΔTm = 13°C for 400 mM versus ΔTm = 4°C for 40 mM. Waviness analysis indicated increased fiber straightening as a result of SMG CXL.

Conclusions

Second harmonic generation signal intensity and fiber bundle waviness is altered by scleral tissue crosslinking using SMG. These changes provide insights into the macromolecular changes that are induced by therapeutic crosslinking technology and may provide a method to evaluate connective tissue protein changes induced by scleral crosslinking therapies.

Ophthalmic regional blocks: management, challenges, and solutions

In the past decade ophthalmic anesthesia has witnessed a major transformation. The sun has set on the landscape of ophthalmic procedures performed under general anesthesia at in-hospital settings. In its place a new dawn has ushered in the panorama of eye surgeries conducted under regional and topical anesthesia at specialty eye care centers. The impact of the burgeoning geriatric population is that an increasing number of elderly patients will present for eye surgery. In order to accommodate increased patient volumes and simultaneously satisfy administrative initiatives directed at economic frugality, administrators will seek assistance from anesthesia providers in adopting measures that enhance operating room efficiency. The performance of eye blocks in a holding suite meets many of these objectives. Unfortunately, most practicing anesthesiologists resist performing ophthalmic regional blocks because they lack formal training. In future, anesthesiologists will need to block eyes and manage common medical conditions because economic pressures will eliminate routine preoperative testing. This review addresses a variety of topical issues in ophthalmic anesthesia with special emphasis on cannula and needle-based blocks and the new-generation antithrombotic agents. In a constantly evolving arena, the sub-Tenon's block has gained popularity while the deep angulated intraconal (retrobulbar) block has been largely superseded by the shallower extraconal (peribulbar) approach. Improvements in surgical technique have also impacted anesthetic practice. For example, phacoemulsification techniques facilitate the conduct of cataract surgery under topical anesthesia, and suture-free vitrectomy ports may cause venous air embolism during air/fluid exchange. Hyaluronidase is a useful adjuvant because it promotes local anesthetic diffusion and hastens block onset time but it is allergenic. Ultrasound-guided eye blocks afford real-time visualization of needle position and local anesthetic spread. An advantage of sonic guidance is that it may eliminate the hazard of globe perforation by identifying abnormal anatomy, such as staphyloma.

Three dimensional MRI study: Safety of short versus long needle peribulbar anesthesia

BACKGROUND

The standard technique of Peribulbar block is to use 25 g 25 mm needle at the junction between the lateral one third and medial two third of the lower orbital rim in the infero-temporal quadrant of the orbit. Theoretically, insertion of longer needles increases the potential of injury to important structure; however, safety of the shorter needle had never been demonstrated. This study describes the anatomy of the orbital structures with magnetic resonance imaging (MRI) using the three-dimensional constructive interference in steady state (3D CISS) sequence to present a morphological basis for needle entry at 12.5 and 25 mm lengths. Statistical comparisons were performed at the 12.5 versus 25 mm depths. Statistical significance was indicated by P < 0.05.

METHOD

Fifty patients free of orbital pathology with normal axial length were selected for MRI with the 3D CISS sequence. Original axial and multiplanar image reconstruction (MPR) images were selected for image interpretation. Orbital structures were identified at 12.5 and 25 mm depths from the orbital rim to compare significant differences in anatomy between the two imaging planes at the expected needle depth and to assess the size of the globe and the orbit.

RESULTS

The cross sectional area of the extraocular muscles were statistically significantly smaller at the 12.5 mm plane (P = 0.001). The area of inferotemporal fat was statistically significantly larger at the 12.5 mm plane (P = 0.033). There was no statistical difference in the inferonasal and superonasal fat areas at different depths (P = 0.34, P = 0.35 respectively). The size of the orbit and globe was significantly larger at 12.5 mm (P = 0.001). There was no difference between depths in the presence or absence of neurovascular bundles and supporting structures including the intramuscular septae.

CONCLUSION

There is a larger structure-free space at a depth of 12.5 mm than at 25 mm. Therefore, the inference is that a needle inserted in the infero-temporal zone to a depth of 12.5 mm is less likely to injure the eyeball or extra-ocular muscles than one advanced to 25 mm.

Anterior segment optical coherence tomography for imaging the sub-Tenon space

In this study, we report the ability of anterior segment optical coherence tomography (AS OCT) in imaging the sub-Tenon space and its clinical application. High-speed AS OCT (Carl Zeiss Meditec, Dublin, Calif., USA) was used to visualize the sub-Tenon space during sub-Tenon injection. The sub-Tenon spaces, Tenon thickness, conjunctiva-Tenon thickness, injecting cannula position in relation to the sub-Tenon space and drug localization/distribution in the sub-Tenon space were analyzed. The sub-Tenon spaces of 12 of 11 patients were visualized with OCT during sub-Tenon injection up to 10-13 mm from the limbus. The mean conjunctiva-Tenon and Tenon thickness were 0.38 ± 0.08 and 0.21 ± 0.07 mm, respectively. The drug was tracked as bright white fluid. There was no conjunctival chemosis, subconjunctival drug or scleral perforation. Anterior segment OCT can be used for imaging the sub-Tenon space, especially during depot injections for confirmation of drug localization.

Sub-Tenon's anesthesia: an update

Sub-Tenon’s block has become the most common technique of orbital regional anesthesia in many centers. It provides effective anesthesia to the orbit with a lower incidence of sight-threatening complications than sharp needle techniques. This article will discuss the relevant anatomy, finer points of sub-Tenon’s block technique, and the evidence supporting its safety.

[Impact of hyaluronidase on anesthetic distribution in retrobulbar region following sub-Tenon anesthesia]

BACKGROUND/AIM

Sub-Tenon's block is nowadays commonly used in ophthalmic surgery because of its safety and efficacy. The aim of this study was to investigate the distribution of the anaesthetic solution with different amounts of hyaluronidase in the retrobulbar space, following an injection into the Sub-Tenon's space.

METHODS

In this experimental study, 40 pig cadaver heads were used (80 eyeballs). The material was divided into four groups (of 20 eyeballs each). Each group was administered 4.5 ml of a mixture of 2% lignocaine, 0.5% bupivacaine, and 0.5 ml of Indian ink, with different amounts of hyaluronidase--15 IU/ml, 75 IU/ml, 150 IU/ml, except the control one. Samples of retrobulbar tissue were analysed using the standard histopathological procedure. After that, they were also analysed using the Adobe Photoshop program (Windows, USA). The retrobulbar space was divided into eight zones by four perpendicular lines, which crossed in the centre of the optic nerve. The presence of ink in fat and muscle tissues and in the sheath of the optic nerve was observed.

RESULTS

The presence of the local anaesthetic solution was significantly higher in inferonasal and superonasal quadrants of the fat and muscle tissues (p < 0.01). The distribution in optic nerve sheath is similar in each quadrant. Distribution of local anesthetic in each zone of the muscle tissue (I-VIII) was strongly influenced by the amount of hyaluronidase added. In the fat tissue, the distribution of local anesthetic under the influence of hyaluronidase was significantly higher (p < 0.05) in the areas which were distant from the place of injection (I-IV). The distribution in the optic nerve sheath is significantly higher (p < 0.01) in the group with 150 IU/ml of hyaluronidase.

CONCLUSIONS

Following a sub-Tenon block local anaesthetic was present in the retrobulbar space in a high percentage of the cases. The presence of local anaesthetic solution in retrobulbar space depends on the amount of hyaluronidase previously added to the local anaesthetic.

Retrobulbar hemorrhage after sub-Tenon's anesthesia

We present a case of retrobulbar hemorrhage complicating sub-Tenon's anesthesia in a patient receiving oral anticoagulants. To our knowledge, this has been described only once in the literature.

The effect of hyaluronidase on ultrasound-measured dispersal of local anaesthetic following sub-Tenon injection

PURPOSE

To determine by B-scan ultrasonography if the addition of hyaluronidase affects the dispersal of anaesthetic fluid after sub-Tenon's injection.

DESIGN

Single-centre prospective randomised double-blind study.

MATERIALS AND METHODS

We performed a trial in 19 patients who were randomised to receive 5 ml of lidocaine 2% alone, or with hyaluronidase 15 IU/ml. A pre-anaesthetic B-scan ultrasound was performed followed by a standard infero-nasal sub-Tenon's injection. Further B-scan ultrasound studies were performed at 1, 3, and 5 min recording depth of local anaesthetic fluid. Data was analysed with Fisher's exact test and Student's t-test where appropriate. Results were considered significant when P<0.05.

RESULTS

The maximum depth of local anaesthetic was significantly less in the hyaluronidase group than the control group at 3 and 5 min (0.79 vs1.65 mm, P-value 0.01 and 0.43 vs1.52 mm, P-value 0.002 respectively). There were no statistically significant differences in the akinesia, pain and surgical satisfaction scores between the two groups.

CONCLUSIONS

The addition of hyaluronidase significantly augments the dispersal of local anaesthetic fluid, as measured by B-scan ultrasonography.

Death potentially secondary to sub-Tenon's block

An 82-year-old ASA 2 patient underwent routine sub-Tenon's block for cataract surgery. One minute after injection of the local anaesthetic, the patient had a generalised tonic-clonic seizure and developed refractory ventricular fibrillation; subsequent resuscitation was unsuccessful. With no evidence for intravascular injection, the lack of structural brain abnormalities, and the most striking feature on post mortem examination being severe triple vessel coronary artery disease, it was concluded that this was primarily cardiac in origin; however, the possibility of brainstem anaesthesia should also be considered.

Retrobulbar Alcohol Injection for Orbital Pain Relief Under Difficult Circumstances: A Case Report

Introduction: A case is presented of a patient with severe and chronic pain in the orbital region, which was relieved by retrobulbar injection of absolute alcohol. The management of chronic pain in the orbital region has received little attention and the literature is reviewed. Clinical Picture: A 52-year-old man with adenoid cystic carcinoma of the maxillary sinus was suffering from severe pain, especially in the left orbital region. There was also pain from ocular exposure and compression caused by the tumour. Magnetic resonance imaging (MRI) revealed spread of tumour to both orbits, particularly on the left. Multiple debulking surgery and various treatment modalities offered no relief from his pain. Treatment: A single retrobulbar injection of 2 mL of absolute alcohol, was placed into the putative orbital apex. Outcome: As a consequence of the injection, he had complete resolution of his pain in the 6 months prior to his death. Discussion: Retrobulbar injection of alcohol offers effective pain relief in certain specific conditions characterised by chronic orbital pain when other treatments do not help. Conclusion: We have demonstrated that the retrobulbar technique still has a place in our armamentarium. Key words: Ocular pain, Orbital pain, Orbital pain management, Retrobulbar alcohol injection

Visual experiences during cataract surgery: what anaesthesia providers should know

Recently published literature shows that most patients experience a variety of visual sensations during cataract surgery under local anaesthesia. Most patients (80-100%) retain at least some light perception in the operated eye and many also experience a variety of other visual sensations during cataract surgery under regional ophthalmic anaesthesia (retrobulbar, peribulbar and sub-Tenon's blocks) or topical anaesthesia. The visual sensations experienced include perception of movements, flashes, colours, changes in brightness, or the sight of surgical instruments, the surgeon's hands or fingers, or even the surgeon. These findings are clinically significant because 3-16.2% of patients who had cataract surgery under either regional or topical anaesthesia were frightened by their intraoperative visual experience. Fear and anxiety may cause some patients to become uncooperative during the surgery and may also induce a sympathetic stress response that might cause hypertension, tachycardia with myocardial ischaemia, hyperventilation or an acute panic attack. These effects are especially undesirable as the majority of cataract patients are elderly and have concurrent medical problems. Besides increasing the risk of intraoperative complications, a frightening visual experience may decrease patient satisfaction. Appropriate preoperative counselling has been shown to be effective in reducing the patients' fear. As most patients retain some visual function during cataract surgery under local anaesthesia, anaesthesia providers should be mindful of this phenomenon and offer appropriate preoperative information and counselling to their patients.

A review of sub-Tenon's block

The place of sub-Tenon's block in ophthalmic surgery is now established. This block was introduced into clinical practice in the early 1990s as a simple, safe and effective technique. Since then, techniques have evolved, newer cannulae have been introduced and many complications, both minor as well as major, have been reported. This review deals with the recent developments in sub-Tenon's block.

Retrobulbar hemorrhage after sub-Tenon's anesthesia

We present a case of retrobulbar hemorrhage from uneventful, infranasal, sub-Tenon's anesthesia before cataract surgery. To our knowledge, this is the first report of such a complication.

Peribulbar anesthesia: a percutaneous single injection technique with a small volume of anesthetic

We evaluated the efficacy and safety of a single injection technique with a small volume of anesthetic for ocular peribulbar anesthesia. We included 857 patients undergoing various ophthalmic procedures. Anesthesia consisted of a medial percutaneous injection of 5-6.5 mL of 2% lidocaine. At 2 min 85.6% of the patients had a motor block of at least 50% and at 5 min 78.6% had a motor block >80%. After 5 min 100% of the patients had adequate surgical anesthesia. There were no serious block-related complications. The described technique is a simple and satisfactory alternative to the classical techniques.

L’anesthésie topique en chirurgie de la cataracte ambulatoire de l’adulte sans anesthésiste présent

To review the local anesthesia environment in France in adult out-patient cataract surgery. The author considers the presence or absence of an anesthesiologist in the operating room. The report shows that in many circumstances there is no need for an anesthesiologist if the following criteria are respected: the adult is fully informed, in rather good health, with no acute risk factors, and surgery is performed by a senior surgeon in a certified operating room. In France, a move toward more flexible regulations is expected, with a new cooperation between ophthalmologists and anesthesiologists that will lead to a new true risk/benefit/obligation ratio. Respect of the individual and safety remain crucial requirements making systematic generalizations impossible.

Effect of the Honan intraocular pressure reducer in sub-Tenon's anesthesia

PURPOSE

To ascertain whether the Honan intraocular pressure reducer (HIPR) has an effect on the preoperative intraocular pressure (IOP), surgeon's assessment of anesthesia, and patients' analgesic experience when sub-Tenon's anesthesia is used for routine cataract surgery.

SETTING

Princess Alexandra Eye Pavilion, Edinburgh, Scotland.

METHOD

Forty-five eyes of 45 patients having routine phacoemulsification cataract surgery were randomized to receive 10 minutes of ocular compression using the HIPR or no compression after administration of sub-Tenon's anesthesia. The IOP was measured immediately before and immediately and 10 minutes after sub-Tenon's anesthesia administration using a standard technique. One surgeon who was masked to the randomization process performed all injections and completed a questionnaire on aspects of the anesthetic block. Patients scored their level of analgesia during surgery.

RESULTS

The mean rise in IOP immediately after administration of sub-Tenon's anesthesia was 1.39 mm Hg +/- 3.91 (SD) (95% confidence interval +0.22 to 2.57; P =.021). In the 22 patients who received compression, there was a mean IOP reduction of 4.20 +/- 2.74 mm Hg at 10 minutes. The mean difference between the compression and no-compression groups at 10 minutes was 4.99 mm Hg (P<.0001). There was no difference in the surgeon's scores for any aspect of the sub-Tenon's anesthesia (P>.05). All patients reported good levels of analgesia.

CONCLUSIONS

There was a significant reduction in IOP after compression using the HIPR. However, the rise in IOP after administration of sub-Tenon's anesthesia was small and the use of the HIPR did not make a significant difference in the effectiveness of the anesthesia to the surgeon or patients.

Sub-Tenon's block with an ultrashort cannula

PURPOSE

To evaluate the effectiveness and safety of an orbital block using an ultrashort, wide-bore blunt metal cannula to inject local anesthetic agents into the anterior sub-Tenon's space.

SETTING

Department of Ophthalmology, North Riding Infirmary, Middlesbrough, United Kingdom.

METHODS

Fifty-nine consecutive patients having routine phacoemulsification with intraocular lens implantation were studied. Five milliliters of lidocaine 2% with adrenaline 1:200000 and hyaluronidase 150 units was injected into the anterior sub-Tenon's space in the inferonasal quadrant via a 16-gauge, short (0.6 cm), blunt metal cannula. Horizontal and vertical movements were assessed before injection and 2, 4, and 6 minutes after injection (also at 8 and 10 minutes if akinesia was inadequate). The movements were scored from 0 (no movement) to 3 (full movement). Incyclotorsion and lid movements were assessed at the same intervals. In the first 15 patients, B-scan ultrasonography was performed before, during, and 2 minutes after the injection. If the aggregate akinesia score was higher than 4 at 6 minutes, a supplementary injection was given. Pain during the injection and surgery was assessed using a 10-point verbal rating score. The incidence, severity, and quadrant of chemosis and conjunctival hemorrhage were noted.

RESULTS

Forty-eight patients (81.35%) had an aggregate akinesia score lower than 4 at 2 minutes and 58 (98.30%) at 4 minutes. One patient had an akinesia score higher than 4 at 6 minutes and required supplementary injection. Incyclotorsion was present in 42 patients (72.88%) at 2 minutes and in 19 (32.20%) at 4 minutes. Lid opening (levator function) was present in 33 patients (55.93%) at 2 minutes and in 19 (32.20%) at 4 minutes. Lid closure (orbicularis function) was present in 34 patients (57.62%) at 2 minutes and in 18 (30.50%) at 4 minutes. One patient required a supplementary injection at 10 minutes. Ultrasonography showed the injection caused rapid opening of sub-Tenon's space, with fluid spreading around the optic nerve. No pain on injection occurred in 67.79% of patients; 17 (28.81%) had a verbal rating score of 1, 1 (1.69%) had a score of 3, and 1 had a score of 5. No patient reported pain during surgery. A minor degree of chemosis and conjunctival hemorrhage occurred in 43 patients and 37 patients, respectively. Moderate chemosis occurred in 15 cases and severe chemosis in 1 case.

CONCLUSIONS

Effective and predictable ocular anesthesia can be achieved using a blunt, ultrashort cannula for sub-Tenon's block. The technique greatly reduces the risks for globe perforation, muscle damage, and other serious complications.

Localization of local anesthetic solution by magnetic resonance imaging

PURPOSE

The aim of this study was to examine the distribution of local anesthetic solution by magnetic resonance imaging (MRI) after combined peribulbar and retrobulbar, superomedial retrobulbar, and sub-Tenon's injection in relation to clinical akinesia.

DESIGN

Randomized clinical trial.

PARTICIPANTS

Fifteen patients scheduled for cataract surgery, 5 patients in each group.

METHODS

Five patients received combined peribulbar and retrobulbar anesthesia, 5 patients received superomedial retrobulbar injection, and 5 patients had sub-Tenon's injection, all with a combination of bupivacaine 0.75%, lidocaine 2%, and hyaluronidase. The MRI scans were performed before the injection and up to 35 minutes after the injection.

RESULTS AND CONCLUSIONS

Reliable anesthesia is achieved using a combined peribulbar and retrobulbar block and a relatively great volume of local anesthetic solution, which spreads throughout the orbit, as evidenced by MRI. After superomedial retrobulbar and sub-Tenon's injection, the local anesthetic solution accumulates behind the globe. Sub-Tenon's injection gives good analgesia and slight akinesia with a very small volume. Superomedial retrobulbar injection and combined peribulbar and retrobulbar block provide a similar degree of exophthalmos, which seems to be the result of the volume injected behind the globe.

Ultrasonic localization of anaesthetic fluid using sub-Tenon's cannulae of three different lengths

PURPOSE

To study the distribution of anaesthetic fluid during sub-Tenon's block by B-scan ultrasonography using cannulae of three different lengths.

METHODS

A total of 30 patients undergoing routine phacoemulsification and lens implantation were studied after informed consent had been obtained. Ages ranged from 60 to 92 years and globe axial lengths from 21.50 to 27.00 mm. All were given a sub-Tenon's block and the patients were classified into three groups in which either a long, intermediate, or short cannula was used. B-scan ultrasonography was performed before administration of the anaesthetic agent, during injection, and 2 min after completion of the injection.

RESULTS

In all patients the optic nerve was identified. During the injection, anaesthetic fluid could be seen tracking behind the globe and opening up the posterior sub-Tenon's space (the previously described 'T'-sign). After 2 min very little or no fluid was seen, suggesting that it had dispersed into the surrounding tissues. There was no discernible difference in the distribution of fluid or in the quality of the block in the three groups.

CONCLUSIONS

B-scan ultrasonography can reliably identify the distribution of anaesthetic fluid during sub-Tenon's block. Anaesthetic agents can be successfully delivered into the sub-Tenon's space by long, intermediate, or short cannulae.

Subjective visual experience during phacoemulsification cataract surgery under sub-Tenon's block

In a prospective survey, 121 patients received sub-Tenon's block and were interviewed on the same day after their phacoemulsification cataract surgery regarding their visual experience in the operated eye during surgery. Majority of patients (81%) reported that they could see some light during surgery and various colours were seen by 56%. Movements of various descriptions were also reported by 40% of patients. The majority of patients (93%) found the visual experience acceptable but 4% thought it to be unpleasant and 3% found it frightening. Patients undergoing phacoemulsification surgery under sub-Tenon's block experience a variety of visual sensations and some patients may be frightened. All patients should receive appropriate preoperative warning.

Complications after sub-Tenon's eye block

IMPLICATIONS

The use of blunt instead of sharp needles for ophthalmic local anesthesia techniques has reduced the incidence of injury to intra-orbital structures. This case review of complications from blunt needle sub-Tenon's block suggests that sight-threatening or even life-threatening complications can still occur.

Anesthetic dose and analgesic effects of sub-Tenon's anesthesia in cataract surgery

PURPOSE

To compare the analgesic effects of different doses of sub-Tenon's anesthesia in cataract surgery by assessing patient response to visceral stimulus.

SETTING

Inouye Eye Hospital, Tokyo, Japan.

METHODS

A prospective study was done of 1019 eyes of 1019 patients having phacoemulsification and posterior chamber intraocular lens implantation. They received a 1.0 mL (391 eyes), 2.0 mL (366 eyes), or 3.0 mL (262 eyes) anesthetic infiltration into the sub-Tenon's space. Pain scores were recorded when the anterior chamber was irrigated with an acetylcholine chloride solution to attain miosis after lens implantation.

RESULTS

The distribution of pain scores was significantly different among the 3 groups (P < .0001, Kruskal-Wallis test). Multiple comparison revealed that the 3.0 mL anesthetic infiltration offered significantly higher analgesic effects than the 2 lower doses. The 3.0 mL sub-Tenon's anesthesia effectively blocked the visceral stimulus.

CONCLUSION

For cataract surgery, 3 mL is the optimal dose of anesthetic solution in sub-Tenon's anesthesia.