Meibomian glands are large sebaceous glands that are located as
separate gland strands in parallel arrangement within the tarsal
plates of the eyelids. Their oily product, meibum, is secreted
via a holocrine mechanism during which meibocytes are
transformed into the meibum. Following production in the gland
acini, meibum is transported through the ductal system via the
connecting duct and the central duct towards the orifice at the
free eyelid margin close to the inner eyelid border. Meibum is a
complex mixture of various lipids and minor protein components
as well as other components of the meibocytes, which form a
clear liquid at body temperature. It is transported within the
gland by the force of secretory pressure from continuous
secretion and by muscular action of the orbicularis muscle and
Riolans muscles during blinking. After it is delivered onto the
posterior eyelid margin, meibum moves from the posterior eyelid
margin reservoir onto the tear meniscus and is pulled as a thin
layer onto the pre-ocular