The Lacrimal System

Abstract

The lacrimal system is made up of both the lacrimal secretory system and the nasolacrimal drainage system. The secretory system consists of the glands that make up the tear film (the lacrimal gland, the accessory glands of Krause and Wolfring, and the meibomian glands). The nasolacrimal drainage system consists of the puncta, canaliculi, lacrimal sac, and nasolacrimal duct. These two systems provide for the production and maintenance of the precorneal tear film as well as the drainage of tears from the eye. The normal functioning of these two systems is essential for proper optical refraction, preservation of corneal integrity, and ocular comfort. The physiology of tear production and distribution requires normal eyelid anatomy and mobility. Blinking spreads the tears vertically over the ocular surface. It also adds two important components to the tear film: lipid from the meibomian glands and mucin from the conjunctival goblet cells. The horizontal flow of tears to the medial canthus is along the tear meniscus at the eyelid margin. This requires normal contour and eyelid apposition to the globe and an adequately functioning orbicularis pump mechanism. Both of these functions can be compromised by horizontal and vertical eyelid laxity or by eyelid margin deformities. The lacrimal gland begins in embryologic development as epithelial buds arising from the conjunctiva of the superior temporal fornix. Canalization of the epithelial buds to form ducts begins in utero, but full development of the gland does not occur until three to four years postnatal. The lacrimal gland provides the principal aqueous secretory component of the tear film. It is located just behind the superolateral orbital rim within a depression in the lateral aspect of the orbital roof (the lacrimal gland fossa). The gland’s convex/concave shape reflects its location between the roof of the orbit and the globe. The gland is divided into a larger orbital lobe and a smaller palpebral lobe by the lateral horn of the levator aponeurosis. The orbital lobe lies behind the orbital septum and immediately above the lateral horn of levator.