Consideration of phantom phenomena during tonometry measurement with contact lens

Imparting a local high pressure to cornea with a damage by various accidents should be definitely avoided from the viewpoint of protecting eyes. For such eyes, medical doctors purposely utilize a contact lens for protecting eyes during internal pressure measurement. While attaching contact lens increases the total stiffness due to additional equivalent stiffness coming from contact lens, the tonometer provides us with a smaller pressure under near-sighted contact lens than that without any contact lens. Furthermore, the displacement of cornea under far-sighted contact lens is more than that without any contact lens. We discuss why such unexpected behaviors happen and how we can explain the physics. We also discuss how to convert the internal pressure with contact lens to that without contact lens.