Which statement about Dk and long-wear wear is true?

• A. Higher Dk/t values support corneal health during long wear
• B. Dk/t has no effect on corneal health
• C. Lower Dk/t is better for oxygen permeability
• D. Dk is the same as Dk/t

Answer: (A)

Oxygen delivery to the cornea during lens wear is the main idea here. Dk is the material’s inherent oxygen permeability, while Dk/t is the oxygen transmissibility that also includes the lens thickness (and tear layer). In practice, a higher Dk/t means more oxygen can reach the cornea, which helps maintain corneal health during long wear and reduces hypoxic stress. The other statements conflict with how these measures work: Dk/t does affect corneal health, so saying it has no effect isn’t accurate;

lower Dk/t would actually reduce oxygen delivery, not improve it; and Dk is not the same as Dk/t—Dk is a property of the material, while Dk/t reflects actual oxygen delivery taking thickness into account.