The palpebral conjunctiva is the membrane that forms the underside of the eyelid. The conjunctiva is actually made up of two parts, the palpebral conjunctiva and the bulbar conjunctiva. The conjunctiva is essentially the link between several structures of the frontal portion of the eye. This includes the eyelids; the sclera, which is the thick, external layer of the eye; and the cornea, the front segment of the sclera that controls how much light enters the eye.
The eyelids, also called palpebrae, cover and protect the globe of the eye and consist of skin and muscles for the control of blinking. Eyelids also contain eye lashes, sweat glands, and lacrimal ducts, which produce tears. The interior aspect of the eyelid must be able to cover or close over the globe of the eye without sticking or rubbing the eyeball. The conjunctiva provides a smooth surface that allows the eyelid to glide over the globe for effective covering.
The palpebral conjunctiva also contains openings to lacrimal ducts, which provide moisture to the surface of the eye. This prevents chafing of the globe and can flush out small particles that may get in the eye. Larger amounts of tears that form from these ducts may fill the space of the open eye and spill outward or are drained down into the nose.
The palpebral conjunctiva is vascular and smooth, but the eye can become irritated quickly when small objects get behind the membrane. Sometimes an infection, which is called conjunctivitis, develops. This causes inflammation, drainage and swelling of the eyelid. Infectious conjunctivitis is commonly known as pink eye, which also results in inflammation and redness of the bulbar conjunctiva, giving the appearance of a pink or reddened eye. The condition is contagious, but not all conjunctivitis infections are; some other types may be caused by allergies or environmental irritants.
The palpebral conjunctiva is red because of the many small blood vessels housed in the membrane. This wealth of blood vessels, and the resulting color, means a physician may test for the presence of anemia by checking the palpebral conjunctiva and other mucous membranes, including the gums and nail beds. This is done by turning the eyelid back over a cotton swab to check the color of the underlying tissue. If it appears pale instead of its normal red color, the doctor may consider this as a potential indication of anemia.