For additional discussion of the developmental anomalies covered in this chapter, see BCSC Section 7, Oculofacial Plastic and Orbital Surgery.
Distichiasis is the aberrant formation of cilia within the tarsus, which causes them to exit the eyelid margin through the orifices of the meibomian glands and results in an extra row of eyelashes. The pathogenesis of distichiasis is thought to be an anomalous formation within the tarsus of a complete pilosebaceous unit rather than just the normal sebaceous (meibomian) gland. Histologically, hair follicles can be seen within the tarsal plate. The tarsus may be rudimentary, and the glands of Moll are often hypertrophic. See BCSC Section 6, Pediatric Ophthalmology and Strabismus, and Section 8, External Disease and Cornea, for additional discussion.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.