Ultrasound-guided ophthalmic regional anesthesia

Abstract

Ultrasound-guided ophthalmic regional anesthesia is evolving beyond simple visualization of the anatomy. Recent research emphasizes the imprecision of needle tip location without ultrasound and the key role of imaging local anesthetic dispersion. There is ongoing debate in the literature regarding the utility of routine ultrasound for eye blocks.

A randomised controlled trial of periconal eye blockade with or without ultrasound guidance

“…The standard needle length for extraconal injection is 25 mm , but long needles could increase the rate of complications . Ultrasound is used by ophthalmologists as a diagnostic tool, but infrequently as an aid to ophthalmic regional anaesthesia when it might reduce damage caused by needles to the globe and optic nerve . In some images, the needle abutted the globe, consistent with previous research .…”

“…The onset of 3–5 ml of local anaesthetic injected behind the globe is rapid, but the needle may damage nearby structures including the globe and the optic nerve, and could induce brainstem anaesthesia . Retrobulbar anaesthesia has been progressively replaced by other anaesthetic methods, including the peribulbar technique that places 6–12 ml of local anaesthetic outside the muscle cone . The periconal or posterior peribulbar variant uses a needle 25 mm long, longer than that used in other peribulbar techniques but shorter than the needle used in retrobulbar anaesthesia .…”

Ultrasound-assisted periconal ocular blockade in rabbits

“…; Benhamou & Ripart ). In contrast to other regional blocks in which US guidance is used to facilitate the positioning of a needle tip close to nerve trunks, avoiding vascular structures, the primary goal of sonographic‐assisted ophthalmic regional anesthesia is to avoid trauma to the globe and optic nerve (Gayer & Kumar ). Using real‐time direct visualization of the needle and its progress through the orbit, practitioners may ensure against misadventures with the needle (Gayer & Kumar ).…”

“…The optic nerve is located at the bottom of the display (Byrne & Green ). Nevertheless, the optic nerve is less echogenic than the orbital fat tending to create an acoustic shadowing and is often not distinctly delineated (Gayer & Kumar ).…”

“…However, there are few reports about ophthalmologic blocks assisted by ultrasound. The eye is easily accessible, its geometry and surrounding elements are relatively straightforward, and the tissue contents of the orbit lack gas‐filled or bony structures, making this an ideal area for ultrasonic image (Gayer & Kumar ). Ultrasonography may improve the safety of ophthalmic regional blocks, particularly by reducing the incidence of globe perforation or penetration associated with the needle‐based techniques; techniques that may be necessary as topical anesthesia does not provide complete akinesia.…”