eyelid

The eyelid is the mobile tissue that covers the eye, protecting the ocular surface and aiding with lubrication.  The eyelids have two distinct layers. The outer layer contains the surface skin and muscles (that function to close the eyes).  The inner layer contains the tarsal plate – this is a thick layer with a consistency of cartilage that gives the lid its integrity.  Eyelashes run along the lid margin and serve to protect the eye from foreign bodies Also running along the lid margin is a row of excretory pores called the meibomian glands. These glands produce oil which is an important component of the tear film. If these pores clog up, the oil can back up and turn into a chalazion. At the inner margin of the eyelids, near the nose, are two drainage holes called the punctum (see puncta).  These punctum drain excess tears into the nose via the nasolacrimal duct. With nasolacrimal duct obstruction, this drainage is blocked and leads to watery eyes. Tears are produced continuously by cells embedded in the eyelid and the surface of the conjunctiva of the eyeball itself. Extra “reflexive tearing” is produced by the lacrimal gland which is located underneath the upper eyelid.