Determination of the oxygen permeability (Dk) of contact lenses with a fiber-optic luminescent sensor system

An optical sensing system, alternative to current electrochemical techniques, has been developed for determining the oxygen permeability (Dk) of rigid gas-permeable contact lenses. The novel sensor is based on kinetic measurements of the oxygen partial pressure inside a chamber sealed by the sample contact lens, where a thin luminescent O2-sensitive film is placed. The standard equation for calculating the Dk value of the lens material has been adapted to the optical technique and a fitting procedure of the sensor response has been developed to achieve the maximum accuracy and precision. Unlike the electrochemical techniques, the optical sensor is unaffected by the contact lens thickness and the lens edge and boundary effects. Therefore, the latter does not require lengthy measuring procedures for extracting the actual Dk values. The optical sensor system has been applied to oxygen permeability determinations of commercial contact lenses of nominal Dk values equal to 17 and 36 ANSI units of 10−11 cm3 cm/s cm2 mmHg.