Chalazion is a lesion caused by occlusion:
– one or more Meibomian glands (deep glands of the eyelid)
– or one or more Zeiss glands (smaller, more superficial sebaceous glands).
Chalazion often appears in the context of fatigue, stress, dusty environments, or when blinking is insufficient (screen, reading, driving). It starts with painless swelling of the eyelid, accompanied by a sensation of a foreign body or itching. The evolution can be brutal: signs of inflammation amplify, pain and signs of superinfection develop.
Styes are generally caused by a staphylococcal infection of the eyelash follicles. It is therefore always located on the edge of the eyelid. In rare cases, it may form in one or more Meibomian glands. This is known as an internal stye.
A stye starts with painful redness, followed by slight swelling. The eye may water, and the person affected may feel a foreign body sensation. In the case of internal styes, the pain is often greater, and the inflammation may even be accompanied by fever or chills.