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M. Chhabra, J. M. Prausnitz, C. J. Radke; A Novel Single-Lens Polarographic Cell to Measure Oxygen Permeability (Dk) of Hypertransmissible Soft Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5420.
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To measure oxygen permeability (Dk) of hypertransmissible (above 100 barrer) soft contact lenses.
The polarographic technique was used to ascertain oxygen permeability of hypertransmissible lenses. This approach utilizes an electrolytic cell with a curved electrode assembly, a gold cathode (working electrode) at the center and silver anode surrounding it. The contact lens is saturated with phosphate buffer saline (PBS) for at least 24 hrs. The presoaked lens is placed atop the electrode, and fastened by the lens holder onto the electrode assembly. During the experiment, the lens is kept saturated by contact with a stirred buffer solution in the cell. Steady-state current is recorded at different stirring speeds at physiological temperature (35oC) to determine the oxygen permeability (Dk) through the soft contact lenses. Common defects encountered with conventional polarographic cells were taken into account.
Unlike conventional polarographic and coulometric methods, where a range of lens thicknesses is demanded for determining precise oxygen permeabilities of soft contact lenses, the current apparatus requires only a single-lens thickness. This is accomplished by minimizing or completely eliminating deficiencies in the current apparatus including edge effects, boundary-layer resistances, and lens desiccation. We measure reliable oxygen permeabilities of hypertransmissible soft contact lenses (above 100 barrer). Nine commercial contact lenses were tested ranging in permeability from 9 to 180 barrer. These single-lens oxygen permeabilities are in excellent agreement with those claimed by the commercial manufacturers.
The new single-lens permeameter is reliable, efficient, and economical for measuring the oxygen permeability of commercial soft contact lenses. The single-lens method also offers potential as an international standard for measuring the oxygen permeability of soft contact lens up to 250 barrer.
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