In comparing hydrogel and silicone hydrogel lenses, which statement accurately describes Dk changes with increasing water content?

In comparing hydrogel and silicone hydrogel lenses, which statement accurately describes Dk changes with increasing water content?

• A. Hydrogel Dk increases; Silicone hydrogel Dk increases
• B. Hydrogel Dk decreases; Silicone hydrogel Dk increases
• C. Hydrogel Dk increases; Silicone hydrogel Dk decreases
• D. Hydrogel Dk decreases; Silicone hydrogel Dk decreases

Answer: (C)

Oxygen permeability (Dk) in contact lenses is determined by how the material conducts oxygen and how water content influences that conduction. In conventional hydrogels, adding water creates more pathways for O2 diffusion because the polymer matrix is water-rich, so higher water content tends to raise Dk. In silicone hydrogels, the oxygen-permeating property mainly comes from the silicone component. Increasing water content dilutes the silicone phase and disrupts the continuous silicone pathways, leading to a lower Dk despite the overall high permeability of these lenses. Therefore, hydrogel Dk rises with more water, while silicone hydrogel Dk falls with more water.

Oxygen permeability (Dk) in contact lenses is determined by how the material conducts oxygen and how water content influences that conduction. In conventional hydrogels, adding water creates more pathways for O2 diffusion because the polymer matrix is water-rich, so higher water content tends to raise Dk. In silicone hydrogels, the oxygen-permeating property mainly comes from the silicone component. Increasing water content dilutes the silicone phase and disrupts the continuous silicone pathways, leading to a lower Dk despite the overall high permeability of these lenses. Therefore, hydrogel Dk rises with more water, while silicone hydrogel Dk falls with more water.