Sub-Tenon's block with an ultrashort cannula

Abstract

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.