Oxygen permeability
Encyclopedia
Oxygen permeability 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. Typical values are from 25 to 50. In soft contact lenses, it is dependent on the thickness of the lens and the material of the lens, especially concerning the water content.
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.
Contact lens
A contact lens, or simply contact, is a lens placed on the eye. They are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people use contact lenses worldwide, including 28 to 38 million in the United...
. OP expresses the ability of the lens to let oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
reach the eye by diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
. Another parameter is the transmissibility level (abbreviated DK/t), the Dk per thickness of the lens, and is generally more used. Typical values are from 25 to 50. In soft contact lenses, it is dependent on the thickness of the lens and the material of the lens, especially concerning the water content.
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.