Cornea: The clear front window of the eye, which transmits and focuses light into the eye. The cornea is more than a protective film; it is a fairly complex structure that has five layers. SLIDESHOW Pink Eye (Conjunctivitis) Symptoms, Causes, Treatments See Slideshow From Eye Health Resources Eye Care When You Have Graves' Eye DiseaseFinding the Care You Need for MS Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19