Which statement best describes tear lens related to lens steepness relative to K?

• A. The tear lens magnitude is greater when the lens is steeper than K.
• B. The tear lens magnitude is greater when the lens is flatter than K.
• C. The tear lens magnitude is independent of lens steepness.
• D. The tear lens magnitude is always zero.

Answer: (A)

The tear lens under a gas-permeable lens is the layer of tears that sits between the cornea and the back surface of the lens. Its thickness (magnitude) reflects how much clearance there is between those two surfaces. When the lens is steeper than the cornea (steeper than K), the posterior surface of the lens is more curved than the cornea, which tends to create more central clearance between lens and cornea. That extra clearance means more tear film has to fill the gap, so the tear lens becomes thicker and its magnitude increases. If the lens were flatter than K, the lens would sit closer to the cornea with less central clearance, producing a thinner tear lens. The tear lens is not zero and its size changes with how the lens fits relative to K.