Ewan G Kemp
Entropion refers to any form of inverted lid margin.
The normal physiological position of the upper and lower eyelid margin is dependent on the relationship between the anterior and posterior lid lamellae (Figures 4.1 and 4.2). These are tightly bound together at the lid margin but elsewhere slippage can occur to cause either an entropion or ectropion. The lamella structure of the lids imparts rigidity and movement which has been well documented by Mustarde. The lids are opened by the lid retractors. In the upper lid these are mainly the levator muscle with its aponeurosis and Muller's muscle. In the lower lid they are fascial expansions from the inferior rectus muscle with some associated slips of smooth muscle. The lids are closed by the palpebral orbicularis muscle (Figure 4.3). In involutional entropion all the tissues become lax. In the lower lid, the retractors no longer hold the lower border of the tarsus downwards. The fascial extensions which form the skin crease become lax allowing the pre-septal muscle to move upwards over the pre-tarsal muscle and the lid inverts. In the upper lid, laxity leads to some sagging of the anterior lamella with reduction of the skin crease. The increased size of the tarsus gives more stability and the lid margin rarely inverts.
The stability of the lid margin is dependent on the interdigitation of the cilia, connective tissue and the muscle of Riolan on the anterior part of the terminal tarsus. The
orifices of between 25 and 35 meibomian lands open on the upper lid margin compared to between 15 and 25 in the lower lid. These glands produce the oily layer of the tear film. The lash follicles also have smaller glands: the glands of Zeiss which are sebaceous, and the glands of Moll which are apocrine. They both deposit their fluid directly into the lash follicles. In entropion not only lashes abraid the cornea but undiluted secretion from the tarsal plate glands also cause irritation. If the keratinising process present at the mouths of the glands increases through disease it can cause a physical corneal abrasion. The hostile corneal environment is initially visible as a superficial punctate keratitis, which if allowed to progress will cause a full-thickness stromal defect which can perforate or scar. Entropion is classified as:
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