The Eyelids

Published on 08/03/2015 by admin

Filed under Opthalmology

Last modified 08/03/2015

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2 The Eyelids

NORMAL ANATOMY

The eyelids protect and maintain the cornea. The structure of both the upper and lower eyelids is similar; each lid consists of two layers or lamellae. The anterior lamella consists of skin and orbicularis muscle, and the posterior lamella of tarsal plate and conjunctiva. The orbital septum extends from the orbital rim to the tarsal plate and separates the preseptal orbicularis muscle from the pre-aponeurotic fat pad. The lid retractors lie deep to this pre-aponeurotic fat pad. The upper lid retractors consist of the levator palpebrae superioris muscle, its aponeurosis and the superior tarsal muscle (Müller’s muscle). The lower lid retractors arise from the sheath of the inferior rectus muscle and are similarly composed of an aponeurosis and smooth muscle (the inferior tarsal muscle).

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Fig. 2.1 Diagrammatic view of the structures of the normal eyelid. The orbicularis muscle can be divided into the pretarsal, the preseptal and orbital parts although these are not separate anatomically. The pretarsal and preseptal parts together form the palpebral section of the orbicularis muscle which is responsible for blinking and facilitates the drainage of tears (see Ch. 20) and the orbital part is responsible for forced lid closure. The grey line is where orbicularis oculi meets the lid margin. This visible line lies anterior to the meibomian gland orifices and posterior to the eyelashes. It is the plane at which the anterior and posterior lamella can be separated during surgery. Removal of the orbicularis muscle exposes the underlying tarsal plates and orbital septum. The levator aponeurosis is the tendon of the levator muscle which inserts between the orbicularis muscle bundles and is responsible for the eyelid skin crease.

EYELID MALPOSITION

All forms of eyelid malposition may be congenital or acquired.

ENTROPION

Entropion is a rotation of the eyelid margin from its normal position towards the globe. The degree of lid laxity needs to be assessed to plan surgical correction.

ECTROPION

Ectropion is a rotation of the eyelid margin from its normal position away from the globe. Eversion of the lid margin results from a combination of factors such as inferior retractor disinsertion and laxity of the horizontal lower lid or of the medial or lateral canthal tendons. These are usually seen as an ageing phenomena but may be related to the floppy eyelid syndrome. Scarring of the anterior lamella of the lid (cicatricial), orbicularis muscle weakness (paralytic) or lumps (mechanical) are the other categories of acquired ectropion.