What limits the oxygen permeability in a contact lens that does not contain silicone?

The oxygen permeability of contact lenses that do not contain silicone is primarily influenced by the water content and the center thickness of the lens. High water content can enhance the ability of the lens to allow oxygen to pass through, as water molecules can facilitate gas exchange. However, the center thickness of the lens works inversely; thicker sections of the lens create more resistance to oxygen flow. Therefore, the combination of these two factors—water content, which can promote permeability, and center thickness, which can inhibit it—determines the overall oxygen permeability of non-silicone contact lenses.

This interplay makes the first answer choice particularly relevant and accurate. Other factors such as lens design and curvature or base curve and diameter do contribute to overall lens performance, but they do not directly influence oxygen permeability in the same way that water content and center thickness do.