What causes a droopy eyelid following the administration of a local anesthetic?

A droopy eyelid, or ptosis, can occur when local anesthetic is inadvertently deposited in the parotid gland. This is commonly associated with the administration of anesthetic agents during procedures such as inferior alveolar nerve blocks. When the anesthetic enters the parotid gland, it can affect the nearby facial nerve (cranial nerve VII), which innervates muscles of facial expression, including those that lift the eyelid. The proximity of the parotid gland to these structures means that local diffusion of the anesthetic can lead to temporary impairment of the eyelid's muscle function, resulting in droopiness.

It’s important to understand the anatomical relationships in the area where local anesthetics are administered. The mistakes that lead to such complications are often related to the technique of injection, emphasizing the need for proper anatomical knowledge during local anesthesia procedures.