Each tarsal plate has vertically placed oil-producing sebaceous glands called Meibomian glands in them, 25 in the upper and 20 in the lower tarsal plate.
Another oil-secreting glands called Meibomian glands are also present in the dense connective tissue plates also known as tarsal plates, which also provide skeletal support and are placed posteriorly in the eyelid.
If these Meibomian gland orifices at the lid margin become plugged or blocked, the contents of the glands (meibum) start getting released into the tarsal plate and surrounding eyelid soft tissue causing an inflammatory reaction.