Techniques of orbital regional anaesthesia

Abstract

1.0–1.5 cm from the apex of the orbit. Local anaesthetics, in blocking concentrations, have to reach an exposed 5–10-mm segment of these motor nerves in the posterior intracone space for conduction block of those nerves and akinesia of their supplied muscles to occur. Retained activity of the superior oblique muscle is frequently seen after intraconal local anaesthetic injection because its motor nerve, the trochlear, runs an extraconal course. There is insufficient space between the lateral rectus muscle and adjacent lateral orbit wall, and between the inferior rectus muscle and adjacent orbit floor, to consider placing injectate in either location without risking injury to the respective muscles. Cornealnd perilimb al conjunctival sensation is mediated via the nasociliary nerve which lies within the cone of muscles; intracone blocks therefore produce anaesthesia of the cornea and the conjunctiva immediately surrounding it. However, the sensation of the peripheral conjunctiva is supplied through the lacrimal, frontal and infraorbital nerves coursing outside the muscle cone [2]; intraoperative pain may be experienced in this area after a solely intracone block [11].