To determine corneal oxygen consumption with different silicone hydrogel lenses under open and closed eye conditions.
Human eye models were used to assess the relationship between Equivalent Oxygen Percentage (EOP) and lens oxygen transmissibility (Dk/t) with four different silicone hydrogel lenses (Focus NIGHT & DAY, O2Optix, PureVision and Acuvue Advance) in two powers (-3.00DS and +6.00DS) and one conventional thick soft lens (CIBASoft) in one power (+6.00DS). Ten non-habitual contact lens wearers were selected for this study. Cornea and contact lens oxygen uptake rates were conducted under open and closed eye conditions. A Clark-type polarographic oxygen sensor was applied to the unanaesthetized cornea or the anterior surface of the lens. A mathematical model was developed for deriving open eye partial pressures of oxygen (PO2) underneath the lenses from contact lens oxygen uptake rates.
The human eye models relating EOP to lens Dk/t showed higher concentrations of oxygen underneath the lenses with higher Dk/t under open and closed eye conditions (p< 0.05). Measurable differences in PO2 underneath the lenses, derived from the mathematical model, were detected between silicone hydrogel lenses (p> 0.001) for open eye conditions. Subjects wearing lenses that supply higher amounts of oxygen underneath the lenses showed similar oxygen flux as those with lower Dk/t (R2= 0.978). After 5 minutes of eye closure, different levels of contact lens oxygen uptake rates were found between different lens types.
Measuring the contact lens oxygen uptake and deriving the steady state of PO2 under the lens was more discriminating than EOP for open eye conditions. Oxygen flux does not provide a useful way to assess and discriminate corneal oxygenation with different contact lenses on the eye.