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

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 wear is the key idea here. Dk is the material’s inherent oxygen permeability, while Dk/t is that permeability divided by the lens thickness, representing how much oxygen actually reaches the cornea with a given lens. For long wear, the cornea needs a steady oxygen supply to maintain metabolism and minimize hypoxic stress. A higher Dk/t means more oxygen gets through to the cornea, supporting corneal health and reducing edema during extended wear. That’s why the statement about higher Dk/t values aiding corneal health is true. Dk/t matters because it reflects real oxygen delivery, not just material permeability. Dk alone isn’t the same as Dk/t: you can have a highly permeable material (high Dk) but if the lens is thick, the actual oxygen reaching the cornea (Dk/t) may still be limited. Increasing Dk/t can be achieved by using a material with higher Dk or by reducing lens thickness, both of which improve oxygen supply during wear.

Oxygen delivery to the cornea during wear is the key idea here. Dk is the material’s inherent oxygen permeability, while Dk/t is that permeability divided by the lens thickness, representing how much oxygen actually reaches the cornea with a given lens. For long wear, the cornea needs a steady oxygen supply to maintain metabolism and minimize hypoxic stress. A higher Dk/t means more oxygen gets through to the cornea, supporting corneal health and reducing edema during extended wear. That’s why the statement about higher Dk/t values aiding corneal health is true. Dk/t matters because it reflects real oxygen delivery, not just material permeability. Dk alone isn’t the same as Dk/t: you can have a highly permeable material (high Dk) but if the lens is thick, the actual oxygen reaching the cornea (Dk/t) may still be limited. Increasing Dk/t can be achieved by using a material with higher Dk or by reducing lens thickness, both of which improve oxygen supply during wear.