An arcus is a condition in which the eyelashes grow backward instead of downward or upward, which can irritate the corneal tissue and cause damage to the eye, or in more severe cases, even inversion of the lid. Patients themselves can observe the condition of an impingement or entropion in well-lit conditions. If the number of impingements is small, such as one or several, and they are small and short and downy, then an ophthalmologist will need to examine them under a slit lamp magnifying glass to diagnose them. In addition, patients with impingement often have conscious symptoms such as photophobia, tearing, and foreign body sensation. A past medical history of trachoma, blepharitis, trauma, and scarring of the skin may also help in the diagnosis.