The cornea is the clear lens that covers the eyeball and focuses light on the retina. Damage to the cornea can result in vision loss or even blindness.
In Sports Medicine, House correctly diagnoses a patient with red eyes and a complaint that they can't remove their contact lenses as having mistakenly tried to touch and remove their cornea instead as the contact lenses were no longer in their eyes.
In Not Cancer, Apple had received a cornea transplant to restore her sight.