PubMed · 519828
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Y Imbert, J Charleux, J D Grange. 1979. [Visual correction for keratoconus].. https://pubmed.ncbi.nlm.nih.gov/519828/
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The oxygen transmissibility of a contact lens is defined as its oxygen permeability (Dk) divided by its thickness (L). Transmissibility can be obtained from separate measurements of Dk and L, or from a single measurement of oxygen flux through the lens (as for example by the polarographic method). Dk/L of hydrogel contact lenses with optical power measured by the polarographic method was compared with Dk/L calculated from separate measurements of Dk and L. Polarographic sensors of different cathode diameters were used to show the effect of the area over which the flux is measured on the observed Dk/L. Dk/L from oxygen flux measured by the polarographic sensor was found to be a function of the optical power of the lens and cathode diameter. Dk/L calculated from separately determined Dk and L for optically powered lenses was found to be a function of Dk and the choice of L (central or average).
A method is proposed which may prove useful as an aid in the design of non-spherical surfaces with desired multifocal properties. More specifically, if an axially symmetrical surface is described by a polynomial then the coefficients of this polynomial can be found such that optical path lengths between given object and image points are nearly constant over desired portions of the surface. Three examples are given. One of the examples, a 'trifocal' surface, is compared to an aberration-free two-segment concentric bifocal contact lens.
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