As water content increases, how does soft contact lens rigidity change?

• A. Increases
• B. Decreases
• C. Remains constant
• D. Unrelated

Answer: (B)

Water content acts as a plasticizer in hydrogel polymers. When the lens absorbs more water, the polymer network swells and the chains have more freedom to move, which lowers intermolecular forces that fought stiffness. This increases the free volume and reduces the storage modulus, making the lens more flexible. So, as water content goes up, soft contact lens rigidity decreases. Conversely, lower water content keeps the network tighter and stiffer.