Elastic modulus of contact lenses
Elastic modulus of contact lenses determines the flexibility of the material. In other words, it says how soft or elastic a lens is. The higher the modulus, the more resistant the lens is to flexing. The lower the modulus, the more comfortable the lens is. The disadvantage of a low modulus is lower resistance during manipulation and shorter longevity of the lens. Elastic modulus is influenced mainly by the material of the contact lenses – the more water lenses contain, the softer the lens is, whereas silicone makes them harder. A compromise exists in the form of the second and third generation of silicone-hydrogel contact lenses (e.g. Acuvue Oasys or Biofinity) that have a low elasticity of modulus.
Soft contact lenses usually have a modulus from approx. 0.4 to 1.4 MPa.