Sub-Tenon's administration of local anaesthetic: a review of the technique

An update on the latest strategies in retinal drug delivery

INTRODUCTION

Retinal drug delivery has witnessed significant advancements in recent years, mainly driven by the prevalence of retinal diseases and the need for more efficient and patient-friendly treatment strategies.

AREAS COVERED

Advancements in nanotechnology have introduced novel drug delivery platforms to improve bioavailability and provide controlled/targeted delivery to specific retinal layers. This review highlights various treatment options for retinal diseases. Additionally, diverse strategies aimed at enhancing delivery of small molecules and antibodies to the posterior segment such as implants, polymeric nanoparticles, liposomes, niosomes, microneedles, iontophoresis and mixed micelles were emphasized. A comprehensive overview of the special technologies currently under clinical trials or already in the clinic was provided.

EXPERT OPINION

Ideally, drug delivery system for treating retinal diseases should be less invasive in nature and exhibit sustained release up to several months. Though topical administration in the form of eye drops offers better patient compliance, its clinical utility is limited by nature of the drug. There is a wide range of delivery platforms available, however, it is not easy to modify any single platform to accommodate all types of drugs. Coordinated efforts between ophthalmologists and drug delivery scientists are necessary while developing therapeutic compounds, right from their inception.

Promising Role of Silk-Based Biomaterials for Ocular-Based Drug Delivery and Tissue Engineering

Silk is a wonderful biopolymer that has a long history of medical applications. Surgical cords and medically authorised human analogues made of silk have a long history of use in management. We describe the use of silk in the treatment of eye diseases in this review by looking at the usage of silk fibroin for eye-related drug delivery applications and medication transfer to the eyes. During this ancient art endeavour, a reduced engineering project that employed silk as a platform for medicine delivery or a cell-filled matrix helped reignite interest. With considerable attention, this study explores the present usage of silk in ocular-based drug delivery. This paper also examines emerging developments with the use of silk as a biopolymer for the treatment of eye ailments. As treatment options for glaucoma, diabetic retinopathy, retinitis pigmentosa, and other retinal diseases and degenerations are developed, the trans-scleral route of drug delivery holds great promise for the selective, sustained-release delivery of these novel therapeutic compounds. We should expect a swarm of silk-inspired materials to enter clinical testing and use on the surface as the secrets of silk are unveiled. This article finishes with a discussion on potential silk power, which adds to better ideas and enhanced ocular medicine delivery.

Long-acting formulation strategies for protein and peptide delivery in the treatment of PSED

The invigoration of protein and peptides in serious eye disease includes age-related macular degeneration, choroidal neovascularization, retinal neovascularization, and diabetic retinopathy. The transportation of macromolecules like aptamers, recombinant proteins, and monoclonal antibodies to the posterior segment of the eye is challenging due to their high molecular weight, rapid degradation, and low solubility. Moreover, it requires frequent administration for prolonged therapy. The long-acting novel formulation strategies are helpful to overcome these issues and provide superior therapy. It avoids frequent administration, improves stability, high retention time, and avoids burst release. This review briefly enlightens posterior segments of eye diseases with their diagnosis techniques and treatments. This article mainly focuses on recent advanced approaches like intravitreal implants and injectables, electrospun injectables, 3D printed drug-loaded implants, nanostructure thin-film polymer devices encapsulated cell technology-based intravitreal implants, injectable and depots, microneedles, PDS with ranibizumab, polymer nanoparticles, inorganic nanoparticles, hydrogels and microparticles for delivering macromolecules in the eye for intended therapy. Furthermore, novel techniques like aptamer, small Interference RNA, and stem cell therapy were also discussed. It is predicted that these systems will make revolutionary changes in treating posterior segment eye diseases in future.

Drug Delivery to the Posterior Segment of the Eye: Biopharmaceutic and Pharmacokinetic Considerations

The treatment of the posterior-segment ocular diseases, such as age-related eye diseases (AMD) or diabetic retinopathy (DR), present a challenge for ophthalmologists due to the complex anatomy and physiology of the eye. This specialized organ is composed of various static and dynamic barriers that restrict drug delivery into the target site of action. Despite numerous efforts, effective intraocular drug delivery remains unresolved and, therefore, it is highly desirable to improve the current treatments of diseases affecting the posterior cavity. This review article gives an overview of pharmacokinetic and biopharmaceutics aspects for the most commonly-used ocular administration routes (intravitreal, topical, systemic, and periocular), including information of the absorption, distribution, and elimination, as well as the benefits and limitations of each one. This article also encompasses different conventional and novel drug delivery systems designed and developed to improve drug pharmacokinetics intended for the posterior ocular segment treatment.

Point-of-Care Ultrasound in the Evaluation of the Acutely Painful Red Eye

BACKGROUND

Visual loss, ocular pain, and red eye are common presentations to front-line physicians in the emergency department, urgent care centers, or the primary care office. In recent decades, point-of-care ultrasound (POCUS) has been used by clinicians at the bedside in the evaluation and management of a vast array of patients, including those with ocular complaints.

CASE REPORT

A 33-year-old man presented to the emergency department with left eye pain for 4 weeks' duration. The physical examination revealed visual acuity of 20/400 in the affected eye and diffuse conjunctival injection with perilimbal sparing and scleral edema. Using POCUS, he was noted to have diffuse thickening of the globe wall in the symptomatic eye with a thin layer of fluid posterior to the globe in Tenon's space and mild enlargement of the optic nerve sheath diameter. He was ultimately diagnosed with posterior scleritis. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Posterior scleritis carries the potential for significant visual impairment when the diagnosis is missed or delayed. POCUS findings can aid the front-line physician in making the diagnosis of posterior scleritis allowing earlier initiation of appropriate therapy and follow-up.

Sub-Tenon Block: A Learning Curve of 100 Cases

This study measures the learning curve for accomplishing sub-Tenon blocks for ophthalmic surgery applicable to anaesthetists skilled in peribulbar techniques. We defined criteria for a good block in terms of Chemosis, subconjunctival haemorrhage, globe movement and the need for additional peribulbar block. The overall success rate, by our definitions, was 72% and 56% for the two operators. The overall requirement for an additional peribulbar block was 10%). The rate of additional blocks and reduction in globe movement reached a plateau after about 60 procedures for both operators. The rates of Chemosis (6% and 12% overall) and subconjunctival haemorrhage (6% and 12% overall) did not trend with increased experience. The results applied to both a cataract and a vitreo-retinal surgery casemix.

A Review of the Emerging Role of Silk for the Treatment of the Eye

Silk is a remarkable biopolymer with a long history of medical use. Silk fabrications have a robust track record for load-bearing applications, including surgical threads and meshes, which are clinically approved for use in humans. The progression of top-down and bottom-up engineering approaches using silk as the basis of a drug delivery or cell-loaded matrix helped to re-ignite interest in this ancient material. This review comprehensively summarises the current applications of silk for tissue engineering and drug delivery, with specific reference to the eye. Additionally, the review also covers emerging trends for the use of silk as a biologically active biopolymer for the treatment of eye disorders. The review concludes with future capabilities of silk to contribute to advanced, electronically-enhanced ocular drug delivery concepts.

Sub-Tenon's anesthesia for canine cataract surgery

OBJECTIVE

To test a sub-Tenon's anesthesia technique in dogs as an alternative to systemic neuromuscular blockade to aid in canine cataract surgery under general anesthesia.

PROCEDURES

A prospective controlled clinical study was performed involving 12 dogs undergoing bilateral cataract surgery under general anesthesia. One eye was randomly assigned to have phacoemulsification and prosthetic lens implantation performed with sub-Tenon's anesthesia (STA), and the control eye had surgery performed with systemic neuromuscular blockade (NMB). Intraocular pressure (IOP) was measured immediately before and after STA administration. Globe position, globe rotation, pupillary dilation, and vitreal expansion were assessed for both STA and NMB eyes during surgery.

RESULTS

Sub-Tenon's anesthesia produced a globe position suitable for cataract surgery with the degree of vitreal expansion not significantly different to control NMB eyes. STA produced greater anterior globe displacement than NMB in all cases. STA had no significant effect on IOP.

CONCLUSION

Sub-Tenon's anesthesia was an effective alternative to systemic neuromuscular blockade for canine cataract surgery and may be beneficial for surgical exposure in deep orbited breeds.

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.

Posterior drug delivery via periocular route: challenges and opportunities

Drug delivery to the posterior segment via the periocular route is a promising route for delivery of a range of formulations. In this review, we have highlighted the challenges and opportunities of posterior segment drug delivery via the periocular route. Consequently, we have discussed different types of periocular routes, physiological barriers that limit effective drug delivery, practical challenges regarding patient compliance and acceptability and recent advances in developing innovative strategies to enhance periocular drug delivery. We conclude with a perspective on how we envisage the importance of understanding complex barrier functions so as to continue to develop innovative drug-delivery systems.

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.

Sub-Tenon's injection in equine cadaver eyes: MRI visualization of anesthetic fluid distribution and comparison of two different volumes

OBJECTIVE

To compare the localization and distribution of two different anesthetic fluid volumes around equine cadaver eyes to determine an appropriate volume for a single sub-Tenon's injection in horses.

PROCEDURE

A single sub-Tenon's injection of 2% lidocaine was performed in 10 equine cadaver heads (20 eyes) using two different volumes (7 mL on one side and 10 mL on the opposite side). The posterior circular distribution of the anesthetic was quantified in sagittal, dorsal, and transverse MRI (T2W-TSE) sequences and evaluated independently by three board-certified radiologists. The distribution of the two fluid volumes was compared via a paired Student's t-test. The interobserver reliability was evaluated via a Kruskal-Wallis test.

RESULTS

Extension of the injection fluid was observed along the dorsal and temporal quadrants of the globe within the subconjunctival space, the anterior and posterior sub-Tenon's space, and into the muscle sheaths along the extraocular muscles. Accumulation of anesthetic fluid directly surrounding the optic nerve was detected in three of 20 cadaver eyes. Circular distribution of the 7 and 10 mL anesthetic volumes was not significantly different (P = 0.849). More retrograde leakage of the anesthetic was observed using the 10 mL volume. Evaluation of interobserver reliability revealed no significant differences between observers (P = 0.21-0.92).

CONCLUSIONS

Sub-Tenon's anesthesia can have potential as an alternative to retrobulbar anesthesia for ophthalmic surgeries in equines. A 7- to 10-mL injection volume should be appropriate based on the results of this study. The distribution of the anesthetic solution in live tissues, the clinical effects, and the potential for complications will have to be evaluated in vivo.

Effects of peribulbar anesthesia (sub-Tenon injection of a local anesthetic) on akinesia of extraocular muscles, mydriasis, and intraoperative and postoperative analgesia in dogs undergoing phacoemulsification

OBJECTIVE

To evaluate the effects of peribulbar anesthesia (sub-Tenon injection of lidocaine hydrochloride) on akinesia of extraocular muscles, mydriasis, and intraoperative and postoperative analgesia in dogs undergoing phacoemulsification.

ANIMALS

14 Beagles with ophthalmically normal eyes.

PROCEDURES

A blinded randomized controlled trial was performed. Dogs were anesthetized and assigned to 2 treatments: concurrent sub-Tenon injection of 2% lidocaine hydrochloride solution (2 mL) and IV injection of saline (0.9% NaCl) solution (0.02 mL/kg; lidocaine group [n = 7]) or concurrent sub-Tenon injection of saline solution (2 mL) and IV injection of 0.2 mg of atracurium/kg (0.02 mL/kg; control group [7]). Pupils were dilated by topical application of a combined tropicamide and phenylephrine ophthalmic solution. Ten minutes after the injections, pupil diameter was measured and phacoemulsification was performed. End-tidal isoflurane concentration was used to evaluate intraoperative pain. Subjective pain scores were recorded during the postoperative period.

RESULTS

Akinesia was induced and maintained throughout the surgery in all eyes. Mean ± SD pupil diameter was significantly greater in the lidocaine group (13.7 ± 0.7 mm) than in the control group (12.2 ± 0.8 mm). Isoflurane requirements were significantly lower in the lidocaine group than the control group. However, postoperative pain scores were not significantly different between the groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Sub-Tenon injection of lidocaine was an effective method for inducing akinesia of extraocular muscles, mydriasis, and intraoperative analgesia for phacoemulsification in dogs. Therefore, this could be another option for surgical field exposure and pain management during phacoemulsification in dogs.

A sub-Tenon's capsule injection of lidocaine induces extraocular muscle akinesia and mydriasis in dogs

The effect of local anaesthetic on the extraocular muscles was investigated in dogs by injecting lidocaine into the space between Tenon's capsule and the sclera. A cross-over design was used with both eyes from five Beagle dogs randomly injected, under general anaesthesia, with 1 mL of 2% lidocaine (1 mL-lidocaine group), 2 mL of 2% lidocaine (2 mL-lidocaine group) or 2 mL of normal saline (control group). Each eye was assigned to all treatments with a minimum 14 day interval between injections. Changes in eye position, pupil diameter, and intraocular pressure (IOP) were evaluated during the procedure. All eyes in the 2 mL-lidocaine group exhibited akinesia and mydriasis (pupil diameter >10mm) with an onset time of 6.5 ± 4.9 and 4.2 ± 4.3 min, respectively. In the 1 mL-lidocaine group, akinesia was induced in nine eyes and mydriasis occurred in seven eyes at 10.7 ± 5.8 and 5.4 ± 2.4 min after the injection, respectively. No changes in eye position or pupil diameter were observed in the control group. Akinesia was maintained for 44.3 ± 26.7 min in the 1 mL-lidocaine group and for 88.5 ± 17.2 min in the 2 mL-lidocaine group. Duration of mydriasis was 51.7 ± 28.9 min in the 1 mL-lidocaine group and 82.9 ± 15.6 min in the 2 mL-lidocaine group. Marked chemosis and sub-conjunctival haemorrhage occurred in 16/30 and 15/30 eyes, respectively. No significant change in IOP was observed between the mean pre- and post-injection values in all groups. These results suggest that a sub-Tenon's injection of 2 mL of 2% lidocaine provided effective extraocular muscle akinesia and mydriasis in dogs.

Hyaluronidase in sub-Tenon's anesthesia for phacoemulsification, a double-blind randomized clinical trial

AIM

To investigate the effect of hyaluronidase use on the quality of sub-Tenon's anaesthesia for phacoemulsification.

METHODS

This was a randomized, double-blind clinical trial which was conducted at Nikookari Eye Hospital for 5 months. Forty-two eyes of candidates for phacoemulsification under sub-Tenon's anaesthesia were randomly allocated to two equal groups and received either 2 mL of lidocaine 2% solution with (LH), or without (L) addition of hyaluronidase (150IU/mL). Akinesia was assessed 15 minutes after sub-Tenon's injection. Patients and surgeon's satisfaction, as well as the postoperative pain (the visual analogue scale, VAS) were investigated after operation. The contingency tables (including the Chi-square or Fisher's exact tests, when appropriate) and parametric analysis (the independent samples t test) were used for statistical analysis.

RESULTS

Complete akinesia (33.3% vs 4.8%, P=0.04), as well as the patients (85.7% vs 57.1%, P=0.04) and surgeon's satisfaction (87.5% vs 52.4%, P=0.02) were significantly more frequent in LH than in L group. The mean VAS was significantly lower in the same group (1.90±1.45 vs 3.00±1.55, P=0.04).

CONCLUSION

Addition of hyaluronidase to lidocaine solution for sub-Tenon's anesthesia significantly improves the ocular akinesia, enhances the intra-operative patients and surgeons' satisfaction, and attenuates the postoperative pain.

Adverse events associated with regional ophthalmic anaesthesia in an Australian teaching hospital

This study prospectively audited 3339 peribulbar and 2688 sub-Tenon's eye blocks in an Australian teaching hospital with regard to the occurrence of adverse events. Complications were classified into three groups: ocular complications directly due to the eye block technique, systemic medical complications possibly associated with block technique and adverse events which were unlikely to have been associated with block technique. Five serious ocular complications were associated with peribulbar block compared to none with sub-Tenon's block (P = 0.07).

[Sub-tenon block for ocular globe anesthesia: a review]

Sub-Tenon anesthesia is an effective, well-tolerated technique for surgery in the anterior or posterior compartments of the eye. The advantages of this block are comparable to those of peribulbar and retrobulbar anesthesia and complications are minimal. Sub-Tenon anesthesia provides better analgesia than akinesia. Most studies suggest that sub-Tenon anesthesia is a good technique to choose, given that potential adverse effects are fewer than for other regional blocks and analgesia and akinesia are superior.

Sub-Tenon's ropivacaine block for pain relief after primary strabismus surgery

PURPOSE

Pain is the main cause of patient distress/dissatisfaction after strabismus surgery. The aim of the study was to evaluate the effect of sub-Tenon's block with ropivacaine at the end of strabismus surgery on post-operative pain.

METHODS

A prospective trial was conducted in 79 patients (age 1.0-65 years) scheduled for outpatient primary strabismus surgery with fixed sutures under general anesthesia (GA) at a major tertiary hospital. Half the patients were randomly allocated to receive sub-Tenon's block with ropivacaine 0.2% at conclusion of the operation. Primary outcome measures were visual analog scale (VAS) scores at arrival to the post-anesthesia care unit (PACU), at discharge 3 hr later, 12-16 hr post-operatively, and 24 hr post-operatively. Supplemental analgesia requirements and patient satisfaction were recorded as well. Data were presented as median (range). Mann-Whitney test, Pearson chi(2)-test or Fisher's exact test was used for statistical analysis; p <or= 0.05 was considered significant.

RESULTS

There were no between-group differences in median VAS scores at arrival to the PACU and at discharge, with a borderline difference at 24 hr post-operatively (p = 0.06). At 12-16 hr post-operatively, the median score was 0.0 (range 0-5) in the study group and 4.0 (range 0-6) in the controls (p < 0.001). The lower VAS score in the study group was associated with a lower rate of supplemental analgesia use (21.9% versus 57.9%, p = 0.001), fewer doses of supplemental analgesia (10 doses versus 35, p = 0.03), and higher patient satisfaction (p < 0.001).

CONCLUSIONS

Sub-Tenon's block with ropivacaine 0.2% at the completion of outpatient primary strabismus surgery with fixed sutures under GA reduces pain 12-16 hr post-operatively and analgesia requirements 4-23 hr post-operatively.

[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.

Hyaluronidase reduces local anaesthetic volumes for sub-Tenon’s anaesthesia

BACKGROUND

Volumes of local anaesthetics for sub-Tenon's anaesthesia vary. Lower volumes produce less akinesia, whereas higher volumes increase chemosis and intra-ocular pressures. Hyaluronidase is often added to local anaesthetics to improve akinesia without increasing the volume of the injection, but this is controversial. This randomized, sequential allocation study examines the addition of hyaluronidase on the minimum local anaesthetic volume (MLAV) required for a sub-Tenon's block.

METHODS

Sixty-two patients having sub-Tenon's blocks for cataract surgery were randomized into two groups. The control group (n=31) received 2% w/v lidocaine and the study group (n=31) received 2% w/v lidocaine with hyaluronidase 15 IU ml(-1). Using parallel up-down sequential allocation from a 4 ml starting volume, the volumes in both groups were changed using a testing interval of 1 ml according to the quality of globe akinesia. The median effective local anaesthetic volume (MLAV) was calculated for both groups using probit regression.

RESULTS

The groups were similar for age, sex, and ocular axial length. The MLAV in the hyaluronidase group was 2.6 ml [95% confidence interval (CI), 2.1-3.l] and 6.4 ml (95% CI, 5.1-8.1) in the control group (P<0.002).

CONCLUSIONS

Hyaluronidase permits a significant 2.4-fold (95% CI, 1.8-3.4) reduction in MLAV for sub-Tenon's anaesthesia.

Preoperative Sub–Tenon’s Capsule Injection of Ropivacaine in Conjunction with General Anesthesia in Retinal Detachment Surgery

OBJECTIVE

To evaluate the effects of preoperative sub-Tenon's capsule injection of ropivacaine on intraoperative hemodynamics, postoperative pain, nausea, and recovery in patients undergoing scleral buckling surgery under general anesthesia (GA).

DESIGN

Randomized double-masked controlled clinical trial.

PARTICIPANTS

Ninety-eight patients with primary rhegmatogenous retinal detachment undergoing scleral buckling surgery under GA.

METHODS

Random allocation to either preoperative sub-Tenon's capsule injection of 3 ml of 0.75% ropivacaine or sub-Tenon's capsule injection of 3 ml of saline (controls) immediately before a scleral buckling procedure under GA. Intraoperative monitoring of hemodynamic parameters, need of analgesia with sevoflurane and alfentanil, time in the recovery unit, measurements of pain and nausea on the visual analog scale (VAS) up to 12 hours postoperatively, and consumption of analgesics and antiemetics was recorded.

MAIN OUTCOME MEASURES

Intraoperative systolic blood pressure (BP); bradycardia; minimum alveolar concentration (MAC) of sevoflurane; maximum postoperative VAS scores of pain and nausea; time in recovery unit; and total need of alfentanil, ketobemidone, dextropropoxyphene, and dixyrazine.

RESULTS

Ninety-seven patients were analyzed (48 in the ropivacaine group and 49 controls). A significantly lower intraoperative systolic BP (104+/-6 vs. 112+/-7 mmHg; P = 0.004), less need of sevoflurane (1.33+/-0.19 vs. 1.56+/-0.23; P = 0.03), and shorter time in the recovery unit (67+/-9 vs. 76+/-16 minutes; P = 0.01) were observed in the ropivacaine group. Maximum VAS pain scores were 50+/-21 in the control group and 36+/-25 in the ropivacaine group (P = 0.05), with a significantly lower consumption of opioids (ketobemidone) in the ropivacaine group (3.6+/-3.5 vs. 1.3+/-2.0 mg). No significant difference was observed regarding nausea or need of dixyrazine or dextropropoxyphene postoperatively.

CONCLUSIONS

Preoperative sub-Tenon's capsule injection of ropivacaine in scleral buckling surgery under GA lowers the intraoperative systolic BP, reduces the amount of inhalable sevoflurane needed, and enhances postoperative vigilance through reduction of pain and need of opioids.

Novel approaches to retinal drug delivery

Research into treatment modalities affecting vision is rapidly progressing due to the high incidence of diseases such as diabetic macular edema, proliferative vitreoretinopathy, wet and dry age-related macular degeneration and cytomegalovirus retinitis. The unique anatomy and physiology of eye offers many challenges to developing effective retinal drug delivery systems. Historically, drugs have been administered to the eye as liquid drops instilled in the cul-de-sac. However retinal drug delivery is a challenging area. The transport of molecules between the vitreous/retina and systemic circulation is restricted by the blood-retinal barrier, which is made up of retinal pigment epithelium and endothelial cells of the retinal blood vessels. An increase in the understanding of drug absorption mechanisms into the retina from local and systemic administration has led to the development of various drug delivery systems, such as biodegradable and non-biodegradable implants, microspheres, nanoparticles and liposomes, gels and transporter-targeted prodrugs. Such diversity in approaches is an indication that there is still a need for an optimized noninvasive or minimally invasive drug delivery system to the eye. A number of large molecular weight compounds (i.e., oligonucleotides, RNA aptamers, peptides and monoclonal antibodies) have been and continue to be introduced as new therapeutic entities. However, for high molecular weight polar compounds the mechanism of epithelial transport is primarily through the tight junctions in the retinal pigment epithelium, as these agents undergo limited transcellular diffusion. Delivery and administration of these new drugs in a safe and effective manner is still a major challenge facing pharmaceutical scientists. In this review article, the authors discuss various drug delivery strategies, devices and challenges associated with drug delivery to the retina.

Complications of ophthalmic regional blocks: their treatment and prevention

Complications following ophthalmic regional anaesthesia are rare but are reported during both needle (intraconal and extraconal blocks) and blunt cannula (sub-Tenon's block) techniques. At present there is no perfect technique of ophthalmic regional anaesthesia. This article reports on the complications, treatment and prevention of commonly used ophthalmic regional blocks. Thorough knowledge of the measures required to deal with complications when they occur are of paramount importance for safe clinical practice.

A comparison of infero-nasal and infero-temporal sub-Tenon's block

BACKGROUND AND OBJECTIVE

Sub-Tenon's block is usually delivered by the infero-nasal (IN) approach, but occasionally this may not be possible. The infero-temporal (IT) approach has been described, but data is not available on its efficacy.

METHODS

One hundred patients undergoing cataract extraction were randomized to receive an IN or IT sub-Tenon's injection of lidocaine 2% with hyaluronidase 15 IU mL-1. Akinesia was assessed using the Brahma scale at 0, 2, 4, 6 and 8 min. Injection, intraoperative and postoperative pain scores (verbal analogue score, 0-10) were noted, along with the incidence of sub-conjunctival haemorrhage and chemosis.

RESULTS

There were no differences in patient characteristics data, or mean volume of administered local anaesthetic solution (3.3 (SD = 0.4) mL). There were no significant differences between groups in terms of onset of akinesia. Mean akinesia scores at 2, 4, 6 and 8 min were 2.7, 1.1, 0.4 and 0.2 for Group IN, compared to 2.2, 0.9, 0.8 and 0.3 for Group IT. Chemosis occurred in 14 patients in Group IN, compared to 22 in Group IT (P = 0.21).A sub-conjunctival haemorrhage was noted in 14 patients in Group IN and 19 patients in Group IT (P = 0.52). No patients required supplementary injections. Mean pain scores for the injection, intraoperatively and postoperatively were 0.9, 0 and 0 for Group IN, compared to 1.1, 0 and 0 for group IT. The surgeons scored all the blocks as 'good' except for one patient in each group.

CONCLUSIONS

The IT approach provides an equally rapid onset of block, without a significant increase in complications.

Periocular routes for retinal drug delivery

Despite numerous scientific efforts, delivery of therapeutic amounts of a drug to the retina remains a challenge. This challenge is compounded if chronic therapy is desired. The inability or inefficiency of topical and systemic routes for retinal delivery of existing drugs is now widely accepted. Although the intravitreal route offers high local concentrations in the vitreous and, hence, retina, these advantages are offset by side effects, such as cataracts, endophthalmitis and retinal detachment, following repeated intravitreal injections, or intravitreal placement of sustained-release implants. As discussed in this review, periocular routes, including subconjunctival, sub-tenon, retrobulbar, peribulbar and posterior juxtascleral routes, potentially offer a more promising alternative for enhanced drug delivery to the retina compared with topical and systemic routes. Periocular routes exploit the permeability of sclera for retinal drug delivery, and they are particularly useful for administering sustained-release systems of potent drugs. This review discusses the various periocular routes with respect to their anatomical location, pharmacokinetics, safety and mechanisms of drug delivery. In the coming years, several innovations in absorption enhancement, drug delivery systems and drug administration devices are anticipated for improving retinal drug delivery via periocular routes.

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.