Rigid contact lens area and corneal oxygenation

The corneal area covered by a rigid contact lens under static conditions was calculated for various combinations of lens and corneal diameters. The lens was then assumed to move to various positions on the cornea to find the lens overlap of the corneal area originally covered by the lens. For most clinically practical dimensions, when the contact lens moves to the corneal limbus, a small area of lens overlap remains. This corneal area receives no direct exposure to the external atmosphere and must derive its oxygen via a tear-pumping action by the lens. A method for the calculation of this area is presented. The model is used to explain the appearance of central corneal clouding (CCC), the function of the contact lens peripheral curve, and a possible mechanism for corneal oxygenation during extended wear.