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Clinical highs and lows of Dk/t

In the first of a two-part series, Professor Noel Brennan and Dr Philip Morgan look at the latest terminology and theories about oxygenation of the cornea through silicone hydrogel lenses

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Part 1 - Has oxygen run out of puff?

Although silicone hydrogel (SiH) contact lenses have fallen short of their original goal, solving the continuous wear-infectious keratitis problem, they undeniably provide a superior environment than hydrogels by promoting normal corneal metabolic activity. While there is consensus on this benefit, it is less clear how high we have to go in terms of oxygen transmissibility (Dk/t) within the SiH category to achieve an optimal physiological result. (For simplicity, units of 10-9(cm/sec)(mlO2/ml.mmHg) are omitted where Dk/t values are given in the text.) Theoretical modelling backed up by equivalent oxygen percentage (EOP)-based empirical data suggests that there will be little difference between any of the SiH lenses.1-6 However, some authors argue that one should expect continuing benefits by increasing Dk/t within the SiH range.7-9

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