Inferior tarsus

At a glance

English

Inferior tarsus

Latin (TA2)

Tarsus inferior

System

Connective tissue

Region

Head

Side

Paired, left and right

About the inferior tarsus

Each eyelid has a skeleton of its own: a firm, curved plate of dense fibrous tissue called the tarsus. It is often described as cartilage, but it contains no true cartilage cells. The inferior tarsus, in the lower lid, is the smaller of the pair. It is a narrow, elliptical strip only about 5 mm high at its centre, roughly half the height of the upper plate, and it follows the curve of the eyeball.

The plate has two margins and two ends. Its lower edge, facing the orbit, is the attached margin; the orbital septum links it to the orbital rim, a fibrous sheet that holds back the orbital fat. Its upper edge, the free or ciliary margin, is thick and straight and lies a little below the lid margin from which the lashes grow. Medially the two plates meet beside the lacrimal lake, and the medial palpebral ligament binds them to the maxilla's frontal process. Laterally the lateral palpebral raphe and ligament anchor their ends on the zygomatic bone.

In front of the plate lie the fibres of orbicularis oculi and the thin skin of the lid; behind it is the conjunctiva, firmly bound to it. A shallow groove on the inner surface near the lid edge, the subtarsal sulcus, often traps small foreign bodies. The inferior tarsal muscle, a thin smooth-muscle sheet, and fibres of the capsulopalpebral fascia attach to its lower edge.

Embedded in the plate and running vertically are the tarsal (meibomian) glands, modified sebaceous glands whose openings line the lid margin. Their oily secretion forms the outer layer of the tear film and slows its evaporation. A blocked gland gives a chalazion, a painless lump in the lid. Laxity of the plate and its ligaments in older age allows the lower lid to turn outwards (ectropion) or inwards (entropion).

Function and supply

Begins at

Medially the medial palpebral ligament ties its end to the maxilla (frontal process); laterally the lateral palpebral ligament ties it to the zygomatic bone.

Ends at

Its lower, orbital margin is attached to the rim of the orbit through the orbital septum and receives the inferior tarsal muscle and capsulopalpebral fascia.

Function

Gives the lower eyelid its shape and stiffness, keeps the lid margin against the eyeball and houses the tarsal glands that oil the tear film.

Nerve supply

Sensation to the lower lid comes mainly from the infraorbital nerve, a branch of the maxillary nerve.

Blood supply

From the inferior palpebral arterial arcade, formed by the medial palpebral branches of the ophthalmic artery and the lateral palpebral branches of the lacrimal artery.