The conjunctiva is a thin, transparent membrane underlying the inner lid surfaces and the anterior sclera, and it is important in maintaining a suitable environment for the cornea and as defence against infection and trauma. Conjunctivitis is the inflammation of the conjunctiva and is characterized by dilation of the conjunctival vessels, resulting in hyperaemia and oedema of the conjunctiva, typically with associated discharge. However, visual acuity is usually not affected.