International organization for standardization (ISO) method used to assess if the contact lenses are suitable by measuring the oxygen permeability coefficient (Dk) of rigid gas permeable contact lenses up to 100 barrer. Oxygen permeability describes its vital capacity to transport oxygen, with D referring to the material's diffusivity, and k being the solubility of the material. Dk appears in units of 10-11cm2/sec. ml O2/ml × mmHg.