Which statement correctly describes the modulus of hydrogel lenses compared with SiHy lenses?

Which statement correctly describes the modulus of hydrogel lenses compared with SiHy lenses?

• A. Hydrogels lower; SiHy higher
• B. Hydrogels higher; SiHy lower
• C. Both equal
• D. Both higher

Answer: (A)

Modulus is about stiffness: a lower modulus means a softer, more flexible lens, while a higher modulus means a stiffer one. Hydrogels are highly water-rich polymers with a flexible network, so they tend to have a relatively low modulus. Silicone hydrogel lenses, which include siloxane structures to boost oxygen permeability, form a tougher polymer network and are therefore stiffer, giving them a higher modulus than conventional hydrogels. So, hydrogel lenses have a lower modulus and silicone hydrogel lenses have a higher modulus.

Modulus is about stiffness: a lower modulus means a softer, more flexible lens, while a higher modulus means a stiffer one. Hydrogels are highly water-rich polymers with a flexible network, so they tend to have a relatively low modulus. Silicone hydrogel lenses, which include siloxane structures to boost oxygen permeability, form a tougher polymer network and are therefore stiffer, giving them a higher modulus than conventional hydrogels. So, hydrogel lenses have a lower modulus and silicone hydrogel lenses have a higher modulus.