The conjunctiva is a thin, semi-transparent membrane that covers the exposed white part of the eyeball, known as the anterior sclera and lines the inner surface of the eyelids.

The blood vessels within the conjunctiva deliver blood to the surface of the eye, providing nutritional support and when necessary, substances that help fight infection. These blood vessels are the reason the eye readily becomes red in response to injury or disease.

The conjunctiva also secretes sticky discharge, some of which remains anchored to the eye surface, improving wettability so it is able to support overlying tears. It also thickens the tear film which ensures better lubrication, helping to prevent frictional trauma during eye movements and when blinking.