Quick Facts
The tarsus is the firm framework of connective tissue that gives shape to the lower eyelid (Dorland, 2011).
Related parts of the anatomy
Structure and/or Key Feature(s)
The superior eyelid contains a thin, elongated plate of tough collagenous tissue called the superior tarsal plate. It is convex shaped to conform to the anterior surface of the eyeball. It has an inferior, free, straight ciliary border adjacent to the hair follicles of the eyelashes, and a superior, convex orbital border that is attached to the orbital septum (palpebral fascia). The superior tarsus is the larger of the two tarsal plates, measuring approximately 2.5 cm long and 10 mm high (Standring, 2016).
Anatomical Relations
The free ciliary margins of the tarsal plates end approximately 2 mm from the margin of the eyelid and runs parallel to it.
The orbital margins of the tarsal plates are bound to margins of the orbital septum and to the palpebral ligaments on each side. The medial palpebral (canthic) ligament passes from the medial ends of both tarsal plates and insets into the anterior lacrimal crest and the frontal process of the maxilla bone that forms part of the medial wall of the orbit. As it inserts into the tarsal plates, the ligament splits to surround the lacrimal canaliculi. The lateral palpebral ligament, on the other hand, is poorly developed. It extends from the lateral edges of the tarsal plates to the zygomatic bone that forms part of the orbital margin.
Superficial to the superior tarsal plate is a thin layer of muscle, the palpebral portion of the orbicularis oculi and small blood vessels of the marginal arterial arcade. Deep to the plate is a thin layer of connective tissue and a layer of the conjunctiva.
A smooth muscle, the superior tarsal muscle, attaches to the superior margin of the superior plate. Additionally, the deep fibers from the aponeurosis of levator palpebrae superioris extend and attach to the anterior surface of the superior tarsus. Thus, both the superior tarsal and levator palpebrae superioris muscles work to raise the eyelid.
Function
The superior and inferior tarsal plates provide support to the eyelids and determine the shape of the lid.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series: Elsevier Limited.
