What is a common modulus value for a silicone/hydrogel lens?

What is a common modulus value for a silicone/hydrogel lens?

• A. <0.3
• B. >0.50
• C. 0.1
• D. 1.0

Answer: (B)

Modulus tells you how stiff a lens material is—the stress needed to bend it a certain amount. Silicone/hydrogel lenses include silicone to boost oxygen permeability, but that addition also makes the material stiffer than traditional hydrogels. Because of this, their typical Young’s modulus is around 0.5 MPa or higher, depending on the exact formulation. So the common modulus value being greater than 0.50 MPa fits with how these lenses behave: they’re stiffer than very soft hydrogels but not every lens sits at the extreme high end. Values well below that would indicate a much softer material, while 1.0 MPa is on the stiffer end and not representative of most daily-wear silicone/hydrogel lenses.

Modulus tells you how stiff a lens material is—the stress needed to bend it a certain amount. Silicone/hydrogel lenses include silicone to boost oxygen permeability, but that addition also makes the material stiffer than traditional hydrogels. Because of this, their typical Young’s modulus is around 0.5 MPa or higher, depending on the exact formulation. So the common modulus value being greater than 0.50 MPa fits with how these lenses behave: they’re stiffer than very soft hydrogels but not every lens sits at the extreme high end. Values well below that would indicate a much softer material, while 1.0 MPa is on the stiffer end and not representative of most daily-wear silicone/hydrogel lenses.