Eyelashes

EYELASHES (cilia), hairs located along the anterior border of the free margin of the eyelids. Eyelashes form 2–3–4 rows; on the upper eyelid their number reaches 150–200, on the lower 75–100. The length of the eyelashes is up to 11 mm, the diameter 76–168 µ. Eyelashes belong to the so-called bristle hairs; until puberty, eyelashes are the strongest hairs in humans. With their free edge, eyelashes are directed forward from the eye. Eyelashes have a medullary substance almost throughout their entire length, with the exception of the finest tip. The roots of the eyelashes lie at a depth of 2 mm from the free margin of the eyelids. Near each eyelash, there are 3–4 sebaceous glands (of Zeis); sweat glands open into the hair follicles in the form of peculiarly modified sweat glands of Moll. The average lifespan of eyelashes is 150 days (Donders). Greying (poliosis) of the eyelashes is rare, mainly occurring in endogenous iridocyclitis, vitiligo, trachoma, interstitial keratitis, and others (Gasteiger). Ancient indications that long eyelashes are a sign of scrofula find confirmation in the studies of Tamaoki, who established on extensive material that "eyelashes longer than 6.5 mm are observed in scrofulous children." Trichiasis ("hair disease") is an incorrect position of the eyelashes in which they are directed by their free edge toward the eye. Complete and partial trichiasis are distinguished. The eyelashes in this case touch the cornea and conjunctiva and traumatize them, which sometimes causes photophobia, lacrimation, a sensation of the presence of a foreign body, injection of conjunctival blood vessels, and even keratitis, up to ulceration. In most cases, trichiasis is caused by the development of scar tissue, which pulls the skin of the eyelid backward past its free margin, thereby causing the improper position of the eyelashes. Scars developing after blepharitis, stye, burns, and others usually cause partial trichiasis. Distichiasis is the condition when on the normal margin of the eyelid there are 2 rows of eyelashes, of which one row is located correctly and the other at the posterior border of the eyelid margin and touches the free edges of the eyeball, sometimes causing the same phenomena as trichiasis. Distichiasis represents a congenital anomaly. Treatment for partial involvement consists of periodic epilation with ciliary tweezers, with electrolysis (with novocaine anesthesia) being more radical; in cases of complete trichiasis, surgical intervention is indicated (displacement of the base of the hair bulbs). Phthiriasis palpebrarum is lice infestation of the eyelids, or rather of the eyelashes, on which crab lice (pediculi pubis) are sometimes found, causing itching and the development of blepharitis with prolonged presence. The margins of the eyelids are so speckled with nits that it creates the impression as if they were sprinkled with something black. The crab lice are located in the hair follicles of the eyelashes. Children are affected mainly. For treatment, washing the eyelashes with a sublimate solution (1 : 2,000), yellow mercurial ointment, or red mercurial ointment mixed half-and-half with lanolin is used. Stye — see Hordeolum.