Tarsal glands

The tarsal glands (a.k.a. the meibomian glands) are specialized modified sebaceous glands located within the tarsal plates of the eyelids, between the tarsi and the palpebral conjunctiva. On eversion of the eyelids, they appear through the conjunctiva as parallel yellowish lines resembling strings of pearls.

The tarsal glands are arranged vertically within grooves on the inner surfaces of the tarsal plates and extend throughout their length. Consequently, they are longer and more numerous in the upper eyelid than in the lower eyelid, with approximately 50 glands in the upper lid and 25 in the lower lid. Their ducts open onto the posterior margin of the eyelid through minute openings situated behind the eyelashes.

Histological architecture of glands

Each tarsal gland consists of a long central duct with numerous lateral acini, resembling a branched sebaceous gland. Histologically, the ducts are lined by stratified cuboidal epithelium, while the secretory acini contain lipid producing sebaceous cells known as meibocytes. These cells release their secretion by holocrine secretion, in which entire cells disintegrate to discharge their lipid contents into the duct system.

Function

The oily secretion produced by these glands, known as meibum, forms the outer lipid layer of the tear film. This lipid layer reduces tear evaporation, prevents spillage of tears over the eyelid margin, and contributes to tear film stability and smooth lubrication of the ocular surface.

Clinical correlate

Obstruction of a tarsal gland may lead to formation of a chalazion, while dysfunction of the glands is commonly associated with blepharitis and evaporative dry eye disease.