A type of blepharitis that affects the meibomian glands and meibomian gland orifices. This abnormality can be associated with a spectrum of appearances ranging from meibomian seborrhoea (foaming meibomian gland secretions) and meibomianitis (inflamed meibomian glands), to chalazia. [https://orcid.org/0000-0003-0986-4123]