Anatomy

The eyelid is a thin tissue that covers the globe and is composed of five layers: skin, subcutaneous tissue, orbicularis oculi muscle, tarsal plate, and conjunctiva. The muscular layer controls lid closure and forms both the medial and lateral canthus; fibers of the orbicularis oculi wrap around the lacrimal system. Nerve supply to the eyelid arises from the temporal and zygomatic branches of the facial nerve. The tarsal plate forms the main body of the lower half of the lid and consists of elastic tissue in a dense matrix of connective tissue. Embedded in the tarsal plate are the meibomian glands, which open into the white line just in front of the conjunctival edge of the lid margin. In the lid margin, the eyelashes are arranged in three irregular rows with their follicles extending obliquely into the tarsal plate.

The lacrimal system begins at the upper and lower puncta as they form the canaliculi. The nasolacrimal duct extends 3 to 5 mm above the level of the medial canthus. It is responsible for tear drainage.7

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