Eyelid Anatomy Surface (Anatomy and Skin)

    The appearance of the 'eye' is largely determined by the shape of the palpebral fissure and its position relative to the globe. This aperture between the upper and lower eyelid margins measures 28—30 mm horizontally and 10—12 mm vertically. The upper lid covers up to 2 mm of the upper cornea, with the lower lid typically crossing at the level of the lower corneoscleral limbus. The point of maximum lid margin concavity differs in the two lids: in the upper lid it is medial to the pupil and in the lower it is lateral (Fig. 5-1).

    The skin of the eyelid is the thinnest in the body, being less than 1 mm thick, with sparse underlying subcutaneous fat. This relative absence of a padding fat layer predisposes to the characteristic fine wrinkles that appear with age in the mobile preseptal skin. The skin is also prone to stretching and further thinning by the repetitive forces resulting from too much eyelid rubbing or excess tension following surgical over-resection.

    The lid margins are 2 mm wide, with the posterior margin being sharp and applied to the globe. The anterior margin is rounded and holds the eyelashes. The grey line, visible along the middle of each lid margin and formed by the gap between the pretarsal tissue and the underlying tarsal plate, marks the junction of the skin and conjunctiva. The Meibomian glands that contribute to the tear film, reside within the substance of the tarsal plate giving rise to openings just behind the grey line. The apocrine sweat glands of Moll and the specialized sebaceous glands of Zeis are found just anterior to the grey line in association with the lash follicles. Eccrine sweat glands and conventional sebaceous glands are found throughout the eyelid skin, although the sebaceous glands are more numerous on the medial half, contributing to the skin's smoother and oilier texture medially.

Figure 5-1
Eyelid surface anatomy.

    The skin crease of the upper eyelid typically overlies the superior border of the tarsus and is referred to as the supratarsal skin crease. Fascial bands from the underlying pretarsal extension of the levator palpebrae pass through the orbicularis oculi muscle and insert into the pretarsal dermis, maximal near the lash line passing up to the level of the crease (Fig. 5-2). The preseptal skin superior to the crease is comparatively non-adherent and mobile with a degree of laxity to allow movement of the lid. This relatively lax skin hangs over the supratarsal crease to create the supra¬tarsal fold. In the oriental eyelid, the supratarsal skin crease is less well-defined and lower set on the upper lid due to the low insertion of the levator aponeurosis closer to the lashes.

    In the lower eyelid, fibrous bands from the capsulo-palpebral fascia also pass through the orbicularis muscle and insert into the skin to create the infratarsal skin crease. This extends as an oblique line 5 mm from the lid margin medially and 7 mm laterally, that is less well defined than its counterpart in the upper lid and becomes less visible as aging progresses.







Figure 5-2 Sagittal section of the eyelids.