Oxygen permeability

Oxygen permeability describes the amount of oxygen that is able to pass through the contact lens to reach the eye. Its value is expressed in Dk/t. The earliest models of soft contact lenses had a level of oxygen permeability of around 6-8 Dk/t. Today’s silicone hydrogel lenses feature oxygen permeability levels of around 150 Dk/t.

A high oxygen permeability ensures that your cornea will receive a lot of oxygen, which it needs to keep your eyes as healthy as possible. Hydrogel lenses generally feature a higher water content and low oxygen permeability, whereas silicone hydrogel lenses have a high oxygen permeability and relatively lower water content. When it comes to choosing between a lot of water or a lot of oxygen, there really isn’t a right answer. It all depends on your needs and your eyes.

• Read more about certain lens properties and their advantages and disadvantages

Oxygen permeability and types of lenses

Hydrogel lenses use water in the lens to transport oxygen. Therefore, a higher water content means a greater level of oxygen permeability, with a maximum Dk/t of around 40. In silicone-hydrogel lenses, oxygen is not transported by water, but rather through silicone molecule chains. The silicone molecules in these types of lenses can have an oxygen permeability of more than 100 Dk/t.

On our website, we use an industry standard number showing oxygen permeability in relation to thickness of the lens (t) -- shown as (Dk/t). Most manufacturers provide a (Dk/t), which is why we've chosen to use it for all our products. However, your box of lenses may only show the (Dk) value. This just means that your box is showing the base value.