A chalazion (also known as meibomian cyst)is a common condition. It is an inflamed swelling in the eyelid caused by a blocked oily duct. The meibomian glands are in the tarsal plates of the eyelids and contain over 25 tiny oily secreting ducts per eyelid which open onto the eyelid margin and secrete oil into the tear film, which helps stop tears evaporate. If just one duct gets blocked, oil accumulates and the body reacts by sending in inflammatory cells which cause a red painful inflamed lump.

Above: Diagram of the eyelids. This shows the location of the meibomian glands in the tarsal plates.

Above: This shows the front view of the tarsal plates. The skin and eyelid muscle are in front of these.