The cornea, the surface film of the eyeball, does not receive oxygen from the bloodstream like the rest of the body does. Instead, its oxygen comes from the air. The oxygen dissolves in the eye's tears and then diffuses along the cornea's surface.The opposite is also true. When the cornea needs to get rid of the waste product carbon dioxide, it releases the gas into the tear film, which then evaporates. You can reference more professional information in this page: http://about.daysoftcontactlenses.com/oxygen-and-your-eyes.aspx?ln=1