Administering an eye anaesthetic: principles, techniques, and complications

The trigeminal nerve carries the sensory innervation of the eye and adnexa in three divisions: ophthalmic, maxillary, and mandibular. The sensory fibres of the eye and adnexa are found in the ophthalmic division – with the exception of a portion of the sensory input from the lower lid, which is carried by the maxillary division. Blocking the sensory fibres provides anaesthesia so that no pain is felt. The motor supply of the extraocular muscles and levator palpebrae superioris is carried by the oculomotor (III), trochlear (IV), and abducens (VI) nerves. Paralysing these muscles by blocking their motor supply provides akinesia so that the eye does not move during surgery. The motor supply of the orbicularis oculi, which is responsible for the gentle and forcible closure of the eye, is carried by the facial nerve (VII). Blocking these fibres will provide better surgical exposure. It also reduces the risk of forcing out the ocular contents if the patient tries to close his eyelids forcibly after the surgeon opens the globe. Rationale