What does "Dk" refer to in terms of contact lenses?

"Dk" refers to the oxygen permeability of contact lens materials. Specifically, it is a measure that indicates how easily oxygen can pass through a contact lens from the environment to the cornea, which is crucial for maintaining corneal health and preventing hypoxia during lens wear.

The Dk value is determined by the material's diffusivity (D), which indicates how fast oxygen molecules can pass through the lens, and its thickness (k), representing the lens's physical characteristics. A higher Dk value indicates a greater ability for oxygen to reach the cornea, which is particularly important for soft contact lenses worn for extended periods, as eyes need sufficient oxygen to stay healthy and clear.

Understanding the Dk value is essential for eye care professionals when recommending lenses, especially for patients who might have higher oxygen demands due to longer wearing times or specific ocular conditions. The other choices, while related to contact lenses, pertain to different properties: the water content refers to how much moisture is contained within the lens material, transmissibility relates to light passage through the lens, and the Abbe value indicates dispersion of light within the lens material, which affects visual quality.