A chalazion is a cyst caused by a blocked meibomian gland in the eyelid. These cysts can develop on either the upper or lower eyelids. Meibomian glands in the eyelid produce oils, which help keep the eyes moist. If a gland becomes blocked, the oil builds up into a cyst and gets inflamed, which can form a lump in the eyelid. The lump can become irritated, red, occasionally infected and on occasion lead to swelling of the whole eyelid. If traditional treatments have not been successful or if there is a large or problematic cyst which remains for a time it is possible to perform surgery to remove it and to speed up healing of the cyst.