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

Purpose: To determine the distribution of anesthetic fluid during 3 regional anesthetic techniques routinely used for phacoemulsification. Methods: Patients having routine cataract extraction by phacoemulsification were studied after informed consent had been obtained. B-scan ultrasonography was performed on the eye before administration of the anesthetic agent. Kinetic echography was used to scan the eye during administration of the anesthesia to show the needle position and location of fluid in the orbit during the injection. Ten minutes after injection, another scan was performed to outline the pattern of fluid distribution. Results: In all patients, the needle and the anesthetic fluid were seen on ultrasonography, with sub-Tenon's the most easily seen. in the sub-Tenon's group, fluid tracked behind the globe in the retrobulbar space, appearing as a dark outline during the injection. The fluid around the optic nerve developed a characteristic T sign. In the retrobulbar technique, the needle was less easily identifiable and fluid localized within the cone. The fluid distributed in the intraconal fat. Identification of the peribulbar needle and fluid was also more difficult, the fluid was, however, seen in the extraconal fat. After 10 minutes, fluid was seen within the cone. Conclusion: B-scan ultrasonography was a suitable method of identifying the needle position and the distribution of anesthetic fluid in regional ocular anesthesia. The sub-Tenon's technique appears to be the safest method of introducing anesthetic fluid into the retrobulbar space without the potential complications of sharp-needle techniques.