Oxygen permeability (OP) is a parameter of a

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

that expresses the ability of the lens to let

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

reach the eye by

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

. In soft contact lenses, it is dependent on the thickness of the lens and the material of the lens, especially concerning the water content. Because of this dependence on thickness, transmissibility level (abbreviated ''Dk''/''t''), the ''Dk'' per thickness of the lens, is more commonly used. The earliest models of soft contact lenses, based on

hydrogel A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...

material, had a level of oxygen permeability of around 6–8 ''Dk''/''t''.

Polymacon Polymacon is a non-proprietary (i.e., generic) term for a hydrophilic polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many ...

, the material used in the first

contact lenses Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

in some countries in the 1960s and approved by the

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

in the U.S. in 1971, has a ''Dk'' of 9 . These days, typical values of oxygen permeability for hydrogel contact lenses range from 25 to 50. For example, Nelfilcon A has a ''Dk'' value of 26, and the Omafilcon A has a ''Dk'' of 25. While those numbers are typical of hydrogel contact lenses, many contact lenses are made of

silicone hydrogel A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...

, which has a much higher oxygen permeability. For example, the ''Dk'' value of Lotrafilcon B and Comfilcon A, two silicone hydrogels, is 110 and 128, respectively. These values are more than twice the values of oxygen permeability for hydrogel materials. ''D'' being

diffusivity Diffusivity is a rate of diffusion, a measure of the rate at which particles or heat or fluids can spread. It is measured differently for different mediums. Diffusivity may refer to: *Thermal diffusivity, diffusivity of heat *Diffusivity of mass: ...

(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 × 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.

References

External links

Oxygen Permeability of Contact Lenses MaterialsColored Eye Contacts

Dk values
(See page 4) Contact lenses {{optics-stub