This work reports the apparent oxygen transmissibility Dk/t)app of four silicone hydrogel (Si-Hy) contact\udlenses (CLs). A method is described that allows the estimation of the oxygen tension at the lens-cornea\udinterface for closed- and open-eyelids situations combining the instrument oxygen transmissibility (IOT) and\udcorneal parameters such as corneal thickness, corneal permeability, and oxygen flux across the cornea. From\udthese results, the biological oxygen apparent transmissibility (BOAT), equivalent oxygen percentage (EOP),\udpartial pressure, (ptc), of oxygen at the cornea-CL interface and oxygen flux, (jc), were also obtained. This\udmethod allows the evaluation of the physiological environment under the lens using the formulations described\udin previous studies. The oxygen performance of four Si-Hy materials was evaluated using a polarographic\udcell coupled to a permeometer. Measurements of the apparent transmissibility, (Dk/t)app, and permeability,\udDk, were performed in stacks containing from 1 to n repeated lenses and, from the values obtained, the\uderror involved in the measurements in single samples was estimated. It was found that the values of\ud(Dk/t)app and Dk obtained following the two different procedures (stack method and measurement of\udsingle sample) were significantly different from the nominal values given by the manufacturer, particularly\udfor some samples. However, the impact of these differences on the values of the other physiologically relevant\udparameters (BOAT, EOP, ptc, and jc) was not significant. Furthermore, these parameters were similar\udfor the four lenses in spite of the different (Dk/t)app measured. The relationships of (Dk/t)app with the\udremaining physiological parameters were calculated and graphically represented for open and closed-eyelid\udconditions.
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