Eyelashes

Structure and/or Key Feature(s)

Eyelashes are hairs that emerge from the margin of the eyelids, just lateral to the lacrimal papilla (the ciliary part of the eyelid). No eyelashes are present on the margin of either the upper or lower eyelid medial to the lacrimal papilla (lacrimal part of the eyelid). The upper eyelid contains 90-120 eyelashes scattered over five to six rows, while the lower eyelid has 75-80 eyelashes distributed over three to four rows (Aumond and Bitton, 2018).

The eyelashes are similar to hair in the skin. A hair shaft extends distal to the skin, its root is found under the skin, and a bulb is in contact with the dermal papilla. However, unlike hair of the skin, eyelash follicles are shorter and lack the arrector pili muscles responsible for straightening the hair shaft in response to sympathetic stimulation (i.e., producing goose bumps).

Anatomical Relations

Eyelashes are arranged in 2–3 rows along the margin of the eyelid. They are longer, more numerous and curved superiorly on the upper eyelid. They emerge from the skin of the lid margin just anterior to the transition of the conjunctiva (inner eyelid) to skin (external eyelid). The follicles of the eyelashes are closely associated with ciliary sweat glands (palpebral sweat glands or glands of Moll) and the ciliary sebaceous glands (glands of Zeis). These provide lipid-rich secretions that form a film over the cornea and slowing evaporation of the underlying tear fluid.

Function

Eyelashes help protect the eyeball, “brushing away” debris impinging from the external environment. Additionally, eyelashes are sensitive to touch and provide warning that an object is too close to the eye.

List of Clinical Correlates

—Stye (external hordeolum)

—Trichiasis

References

Aumond, S. and Bitton, E. (2018) 'The eyelash follicle features and anomalies: A review', J Optom, 11(4), pp. 211-222.

Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.