Eyelashes are arranged in rows along the edge of each eyelid and typically curve outward. Their main function is to prevent dust and debris from entering the eye. As a person ages, the eyelashes tend to become finer and less abundant.
An abnormal direction of lash growth can be attributed to eyelid injury or, more frequently, an infection. In cases of severe blepharitis (inflammation of the eyelid margins), the lash roots can be damaged. Trachoma, an infectious condition causing scarring, may result in trichiasis, where the lashes turn inward and rub against the cornea (the clear front dome of the eyeball).