Medial canthus episcleral (sub-Tenon) anesthesia imaging

Patient preference and pain-reported outcomes for topical versus subtenon anesthetic for cataract surgery

PURPOSE:

Cataract extraction and lens implantation is the most common surgical procedure performed worldwide, with surgeons opting for either a topical or a subtenon anesthetic in majority of cases. While complication rates and pain scores have been previously examined in a bid to determine which modality was better, patients who have had both eyes operated upon under different techniques have never previously been asked which method they prefer. We undertook this study to fill in this crucial gap in our knowledge.

METHODS:

This is a retrospective study of patients who have undergone bilateral cataract surgery with one eye operated on with topical anesthesia and the other eye with subtenon anesthesia. Patients were identified who had had surgery undertaken in the previous 6 months at Singleton Hospital, Swansea, where both eyes had been operated upon using different anesthetic techniques. Telephone interviews with these patients were performed and their pain scores recorded on a scale from 0 (no pain) to 10 (severe pain) for both eyes, with the patients then being asked which the method of anesthetic they preferred. Statistical analysis of pain scores was compared using Wilcoxon rank-sum testing.

RESULTS:

One hundred and fifty-two patients in total were identified. One hundred and forty-one of the applicable patients participated in the study. Of these, 78 patients received topical anesthesia for their first operation and 63 had subtenon block for their first operation. The mean pain scores reported for surgery with topical anesthesia and subtenon block were 2.30 and 1.38, respectively. The pain data were analyzed using a Wilcoxon signed-rank test, returning a z-score of 4.038. This result therefore suggests that patients experience statistically significantly less pain from cataract surgery when given a subtenon block. Patients expressed a preference for subtenon anesthesia, with 70% preferring subtenon block, 23% preferring topical anesthesia, and 7% having no preference.

CONCLUSIONS:

Patients report less pain with subtenon anesthesia compared with topical anesthesia in cataract surgery, where both eyes were operated upon with different anesthetic techniques. This is the first study in which patients who have had both anesthetic techniques performed independently for cataract surgery have had their pain scores reported and statistically analyzed.

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.

Chemosis Secondary to Anterograde Episcleral (Sub-Tenon) Spread of Local Anesthetic during Retrobulbar Eye Block

Supplemental Digital Content is available in the text.

Anatomy of Tenons capsule

BACKGROUND

  The microscopic and macroscopic anatomy of the anterior and posterior Tenons capsule is described.

METHODS

  An observational anatomic study of twelve orbits of 6 cadavers (mean age 79.5 years) were examined microscopically and 8 orbits of 4 cadavers (mean age 76.8 years) were examined macroscopically. After orbital exenteration, an X-shaped incision was made in the specimens to include the posterior part of the globe. The sections were divided into four parts: superomedial; inferomedial; superolateral; and inferolateral. In the macroscopically examined specimens, the eyelids and globes were removed from the exenterated tissues and the appearance of Tenons capsule was studied.

RESULTS

  In the microscopic study, Tenons capsule covered the sclera beneath the conjunctiva and contained smooth muscle fibres in the anterior area. This anterior fascia, which had a thick appearance, reached the globe equator. From there, the capsule of the orbital fat, which contained no smooth muscle fibres, enveloped the sclera and reached the optic nerve. This was defined as the posterior capsule. In the macroscopic specimens, Tenons capsule had a thick and fibrous white appearance in the anterior area. More posteriorly, the capsule was thinner and more translucent. This thin capsular part was generally larger in the lateral area than in the medial area.

CONCLUSIONS

  Tenons capsule is composed of an anterior thick fibrous tissue comprising the orbital smooth muscle network and the posterior thin fibrous capsule of the orbital fat.

Does sciatic parasacral injection spread to the obturator nerve? An anatomic study

BACKGROUND

The ability of parasacral sciatic nerve block to provide consistent obturator nerve and perineal blockade remains undetermined. In this anatomic work, we assessed the spread of a colored latex mimicking a parasacral injection, and observed the spread to the obturator nerve and sacral nerve roots.

METHODS

Fourteen parasacral injections were performed bilaterally on seven human cadavers. Dissection was performed in two steps. First, the posterior approach confirmed the presence of dye on the sciatic nerve at the level of the piriformis muscle to define the success of the injection. Second, the anterior endopelvic dissection assessed the presence of dye around the pelvic portion of the obturator nerve and on the sacral roots (S1-3). The same score was used for all the nerves, from 0 (total failure) to 3 (total success). For all nerves (sciatic, obturator, sacral roots), a score of 2 or 3 was considered a successful injection.

RESULTS

Eleven of 14 injections were considered successful parasacral injections. The three failed injections were excluded from further analysis. One was intravascular and two (same cadaver) in the gluteal muscles were too superficial. Of the 11 successful injections, 9 (82%) were scored as providing the spread of latex to both the obturator nerve and to the sacral roots.

CONCLUSION

We conclude from this anatomical study that successful parasacral injection consistently spreads to the pelvic portion of the obturator nerve and to the sacral roots. Therefore, parasacral block should theoretically provide obturator and perineal blockade, and eliminate the need for systematic separate obturator nerve block. These results must be confirmed by further clinical studies.

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.

An audit of peribulbar blockade using 15 mm, 25 mm and 37.5 mm needles, and sub-Tenon's injection*

The efficacy of peribulbar anaesthesia performed with short, medium and long needles, with sub-Tenon's injection as a control, was audited. Two hundred patients undergoing cataract surgery underwent peribulbar injection using 25G needles of the following lengths: 15 mm, 25 mm or 37.5 mm. Sub-Tenon's injections were performed with a curved 25-mm sub-Tenon anaesthesia cannula. The injection technique, ocular akinesia and analgesia scoring system, and supplementary injection protocols were standardised. After initial injections of local anaesthetic via the sub-Tenon's cannula or with 37.5 mm, 25 mm and 15 mm needles, supplementation was required in one (2%), 13 (26%), 22 (44%) and 32 (64%) of patients, respectively; the total number of supplementary injections required were 1, 16, 35 and 47, respectively. It is concluded that the efficacy of peribulbar anaesthesia depends upon the proximity of the deposition of local anaesthetic solution either to the globe or orbital apex. These data justify the classification of peribulbar anaesthesia into: circum-ocular (sub-Tenon's, episcleral), peri-ocular (anterior, superficial); peri-conal (posterior, deep) and apical (ultra-deep) for teaching purposes.

Altered globe dimensions of axial myopia as risk factors for penetrating ocular injury during peribulbar anaesthesia

We measured the range of equatorial horizontal widths (EHW) in axially myopic eyes and identified the sites of staphyloma using B scan echography. One hundred eyes in 50 patients were studied. The axial lengths (ALs) were sorted into five groups of increasing severity of myopia. The group mean AL, group mean EHW and the ratio of EHW/AL was calculated for each range. The results suggest that the increase in the AL in an axially myopic eye is associated with an increase in the EHW. However, this increase in the group mean EHW is relatively small (2.3 mm) compared with the increase mean AL (8.2 mm) across the entire range. The ratio of EHW/AL decreased with an increase in the group mean AL. Therefore, the increase in EHW in an axially myopic eye is unlikely to be a significant risk factor for inadvertent ocular injury for peribulbar injections if a careful single medial canthal approach is used. There was high incidence of staphylomas in eyes with AL > 29 mm, most were inferior to the posterior pole of the globe, and there were none at the equator.

Caruncle single injection episcleral (Sub-tenon) anesthesia for cataract surgery: mepivacaine versus a lidocaine-bupivacaine mixture

We compared the quality of anesthesia provided by mepivacaine 2% or a mixture of lidocaine 2%-bupivacaine 0.5%, both with hyaluronidase, in caruncle single-injection episcleral (sub-Tenon) anesthesia. Sixty patients undergoing cataract surgery were included in this randomized, double-blinded study. The time to the onset of blockade, maximal akinesia, need for supplemental injection, and time to recovery were recorded. With mepivacaine, the time to onset was slightly shorter, and the akinesia score higher, than with the mixture. Although statistically significant, these differences are small. With mepivacaine, the time to recovery was shorter. We conclude that the reproducible short duration of the block may be an advantage in outpatient surgery.

IMPLICATIONS

We compared the classic mixture of lidocaine 2% plus bupivacaine 0.5% to mepivacaine 2% for caruncle episcleral (sub-Tenon) anesthesia for cataract surgery. Mepivacaine provided a more efficient block with a quicker onset and a quicker recovery. However, these differences were very small and were of little clinical interest.