Ptosis: why is it important and what can it tell you?

To understand the cause of ptosis it is important to review the anatomy of the lid. In facial musculature there are key muscles which function to elevate the eyelid (Tyers, 2018), these include the levator palpebrae superioris (LPS), which is a muscle that originates from the roof of the orbit and fans forwards to fill and insert into the tarsal plate and skin of the eyelid as an aponeurosis (Tyers, 2018). It is the main elevator of the lid (Tyers, 2018) and is innervated by the oculomotor nerve (Tyers, 2018). It has a counterpart known as the Müller's muscle, which is a small muscle attaching to the posterior aspect of LPS and inserts only into the tarsal plate. It is supplied by the sympathetic nervous system and is involved in partial elevation of the upper lid (Snell, 2013). The antagonistic muscles to the elevators are the depressors responsible for closure of the eyelid. This is orbicularis oculi and is innervated by the facial nerve (Bowling, 2016).