Meibomian Glands
Specialized sebaceous glands embedded in the eyelids — roughly 30 in the upper lid and 25 in the lower lid of each eye. They open directly onto the lid margin, with no associated hair follicle.
What they produce
Section titled “What they produce”Meibum — an oily secretion specialized for the tear film.
What they do
Section titled “What they do”Meibum forms the outer, oily layer of the tear film. This layer slows the evaporation of tears between blinks; without it, tears would dry within seconds and the eye surface would be constantly damaged.
Why they matter clinically
Section titled “Why they matter clinically”Meibomian gland dysfunction is the leading cause of evaporative dry eye — by far the most common form of dry-eye disease. When meibum is reduced, abnormal, or trapped by blocked ducts, tears evaporate too fast and the eye becomes irritated. A blocked, swollen meibomian gland is the cause of a chalazion — the firm bump that forms on a lid.
Key idea
Section titled “Key idea”The eyelid is essentially a row of specialized sebaceous glands, and their oil is what keeps the eye from drying out between blinks. The lid’s muscle and skin are mostly there to deliver and refresh that oil.