The muscles of the eyelids are divided into 2 components: (1) orbital (responsible for forced closure) and (2) palpebral. The palpebral muscles are further separated into pretarsal (predominantly intermediate fast-twitch fibers responsible for normal blinks) and preseptal muscles. This separation occurs at the upper eyelid fold, located approximately 6–7 mm above the eyelid margin. The superior eyelid fold is formed by collateral insertion of the levator aponeurosis to the skin of the eyelid. Closure of the eyelids is marked by an increase in activity of the orbicularis muscle and inhibition of the levator palpebrae superioris muscle. The balance of tonic orbicularis and active levator activity determines the amount of eyelid opening. For discussion of eyelid abnormalities encountered in neuroophthalmic practice, see Chapter 11. For further discussion of eyelid anatomy, including illustrations, see BCSC Section 7, Oculofacial Plastic and Orbital Surgery.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.