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We studied oxygen supply to the contact lens covered cornea by means of a complex calculation method. We measured lens thicknesses, both centrally and at a 3mm peripheral location, of a range of optical powers of two different spherical silicone hydrogel contact lens designs (manufactured by Ciba Vision and Bausch & Lomb) and one "traditional" hydrogel. Using the measured values of lens thickness and the nominal oxygen permeabilities of these three plastics, we calculated the oxygen tension level in the tear layer posterior to the contact lens and anterior to the cornea and the oxygen flux through these contact lenses, under both open- and closed-eye conditions. We conclude that variable thicknesses of the silicone hydrogel contact lenses does not significantly affect the oxygen tension in the entrapped tear layer, given their high oxygen diffusion coefficients, under open-eye conditions, and probably only minimally under closed-eye conditions as well.