Which pairing correctly associates a DK type with a described trait?

Which pairing correctly associates a DK type with a described trait?

• A. Low-DK — higher oxygen permeability
• B. Low-DK — optical surface wettability and dimensional stability
• C. Hyper-DK — most rigid
• D. High-DK — best scratch resistance

Answer: (B)

The main idea here is how the oxygen-permeability classification (DK) of a gas-permeable lens relates to practical lens traits like how the surface interacts with tear film and how well the optical shape holds up on the eye. Low-DK materials have lower oxygen permeability, but they’re typically associated with a surface that wets more readily and maintains its optical shape stability better in everyday wear. Wettability is about the tear film spreading smoothly across the lens surface, which depends on the surface chemistry and hydrophilicity of the material. Dimensional stability refers to how well the lens preserves its precise optical geometry while in the tear film and under wear conditions. These surface and shape-stability characteristics are more aligned with low-DK materials, whereas higher-DK or hyper-DK materials emphasize oxygen flow and often involve silicone components that can affect surface interactions and hardness differently. The other pairings don’t fit because oxygen permeability (DK) doesn’t determine rigidity or scratch resistance. Hyper-DK lenses aren’t inherently the most rigid, and scratch resistance hinges on the polymer’s hardness and surface properties, not how much oxygen the material allows through.

The main idea here is how the oxygen-permeability classification (DK) of a gas-permeable lens relates to practical lens traits like how the surface interacts with tear film and how well the optical shape holds up on the eye.

Low-DK materials have lower oxygen permeability, but they’re typically associated with a surface that wets more readily and maintains its optical shape stability better in everyday wear. Wettability is about the tear film spreading smoothly across the lens surface, which depends on the surface chemistry and hydrophilicity of the material. Dimensional stability refers to how well the lens preserves its precise optical geometry while in the tear film and under wear conditions. These surface and shape-stability characteristics are more aligned with low-DK materials, whereas higher-DK or hyper-DK materials emphasize oxygen flow and often involve silicone components that can affect surface interactions and hardness differently.

The other pairings don’t fit because oxygen permeability (DK) doesn’t determine rigidity or scratch resistance. Hyper-DK lenses aren’t inherently the most rigid, and scratch resistance hinges on the polymer’s hardness and surface properties, not how much oxygen the material allows through.