Oxygen permeability

Oxygen permeability (OP) is a parameter of a contact lens. OP expresses the ability of the lens to let oxygen reach the eye by diffusion. Another parameter is the transmissibility level (abbreviated DK/t), the Dk per thickness of the lens, and is generally more used. In soft contact lenses, it is dependent on the thickness of the lens and the material of the lens, especially concerning the water content.

Typical values for hydrogel contact lenses are from 25 to 50. For example, Nelfilcon A has a Dk value of 26, and the Omafilcon A has a Dk of 25. However, one of the particular benefits of silicone hydrogel is high oxygen permeability. For example, the dk value of Lotrafilcon B is 110 and Comfilcon A is 128, twice more than the hydrogel lenses. The earliest models of soft contact lenses had a level of oxygen permeability of around 6–8 Dk/t.^[1]

D being diffusivity (cm²/sec)--a measure of how fast the oxygen moves through the material. Note, different sources may use different units: contact package inserts often use cm²/sec, while academic papers may use other values for distance such as mm²/sec.

k being the solubility (ml O²/ml of material x mm Hg)--a measure of how much oxygen is contained in the material. Once again, various sources may use units of different sizes. Do not assume that they're the same unless specified by the source.

External links

• Oxygen Permeability of Contact Lenses Materials
• Dk values (See page 4)

1. "Oxygen permeability". lenses-contact.co.uk.