The cornea is the transparent tissue at the front of the eye. It has to maintain its optical clarity to allow light and images to properly enter the eye. The cornea partly accomplish this by not having blood vessels criss-crossing it's structure. Without blood vessels and blood carrying oxygen, the cornea gets its oxygen directly from the air. Oxygen permeability pertains to how well a contact lens material allows oxygen to pass through it. This is measured in Dk/t and th