Gas Permeable Contact Lenses – Introduction Practice Test

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Which statement best describes the relation between Dk and corneal health in gas permeable lens materials?

Dk is the material's oxygen permeability; higher Dk/t supports better corneal oxygenation.

Dk describes how easily oxygen can pass through the lens material, while Dk/t represents how much oxygen actually reaches the cornea given the lens thickness. The cornea relies on oxygen from the tear film, so higher oxygen permeability and/or thinner lenses improve corneal oxygenation. In practice, increasing Dk/t means more oxygen gets to the cornea during wear, supporting healthier metabolism, reducing hypoxic stress, and helping maintain clarity and comfort. The idea that Dk is about oxygen permeability and that Dk/t relates to corneal oxygen delivery is why this statement is the best description.

The other interpretations mix up what Dk and Dk/t represent: they are not about lens color, diameter, tear production or turnover, or lens age and shelf life.

Dk is the lens color; Dk/t is the diameter.

Dk is tear production; Dk/t is tear turnover.

Dk is the age of the lens material; Dk/t is the shelf life.