Eyelashes rubbing against the eye is not always trichiasis: a plea for distinguishing trichiasis from entropion

According to Webster’s dictionary, the noun trichiasis derives from Greek (trix or trich = hair + iasis = medical condition) and was first used in English in 1661. We have always taught our ophthalmology residents that trichiasis is a disorder of eyelash direction. Unlike normal eyelashes that emerge from their follicles and curve outward away from the eye, trichiatic lashes are misdirected and bend toward the eye, coming into contact with the ocular surface. In addition, the quality of trichiatic lashes is often different from normal lashes, being thick and stiff. In trichiasis, by definition, the position of the lid margin is normal [ 1 , 2 ]. Therefore, if eyelashes are touching the eye because the lid margin is distorted and inverted, the condition is an entropion, not trichiasis. Trichiasis and entropion should also be distinguished from distichiasis (also from the Greek di = double + stichos = row), a congenital or acquired condition characterised by an extra row of eyelashes emerging from meibomian gland orifices [ 3 ].