22.1 Introduction

There are considerably more chapters in this book devoted to lower eyelid surgery. The reason is simple. Surgery on the lower lid can be more complex and fraught with more complications. Although the position of the upper eyelid with respect to the corneoscleral limbus is principally determined by the levator muscle, lower lid position is influenced by the lower lid retractors (capsulopalpebral fascia and the inferior tarsal muscle), the tension along the tarsal plate, integrity of the medial and lateral canthal tendons, and the degree of relative exophthalmos of the globe. Make a change in any of these parameters and the level and shape of the lower lid may be noticeably altered.

Vertical tension in the lower lid is mainly due to the lower lid retractors (Fig. 22-1). The capsulopalpebral fascia (analogous to the levator muscle in the upper eyelid) arises from the inferior rectus muscle and inserts along the lower border of the tarsal plate. Unlike the levator, there are no striated muscle fibers in this structure. The inferior tarsal muscle (analogous to Müller’s muscle) arises from the capsulopalpebral fascia and also inserts into the inferior border of the tarsal plate. Often, the inferior tarsal muscle is no more than scattered smooth muscle fibers within the capsulopalpebral fascia. The lower lid retractors function to depress the level of the lower lid in downgaze. As the inferior rectus contracts when looking down, the pull on the retractors is transmitted to the tarsal plate and the eyelid moves inferiorly to permit unobstructed vision. Surgical release of the lower lid retractors allows the lid margin to rise superiorly on the globe, while tightening them is frequently performed in repair of involutional entropion.

Horizontal tension along the globe is maintained by the tarsus and the medial and lateral canthal tendons and is often referred to as the “tarsoligamentous sling.” These structures become lax with age, necessitating surgical modification in lower eyelid surgery. Reconstruction of the lateral canthus can be difficult, and any variation from the normal position and shape is immediately obvious and often a source of cosmetic dissatisfaction to patients. Surgery on the medial canthal tendon can damage the inferior canaliculus and lacrimal sac, resulting in excessive tearing or dacryocystitis.

The degree of projection of the globe as measured by various exophthalmometry devices is also critical in surgical planning. This situation has classically been compared to the man with a large belly who tightens his belt. The more he tightens his belt, the greater the overhang of his belly. Similarly, when the globe is relatively exophthalmic, surgical horizontal lid tightening may cause the lid margin to slip inferiorly on the globe, resulting in cosmetically objectionable lid retraction. This is often remedied by releasing the lower eyelid retractors and interposing a spacer graft between the cut edge of the retractors and the inferior border of the tarsal plate to effectively lengthen the retractors and add support to the lower eyelid. Hirmand et al found that exophthalmometry readings of 18 or greater anatomically predisposed patients to retraction and developed protocols for surgical correction. I have found that this measurement is important when doing lower eyelid surgery.

Lower lid malposition after eyelid surgery can be conceptualized according to Box 22.1.

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