Estimation of Oxygen Flux through SiH Lenses under Open & Closed Eye Conditions

Percy Lazon, Brien Holden, Donna La Hood, Robert Terry, Klaus Ehrmann

Purpose:
To determine corneal oxygen consumption with different silicone hydrogel lenses under open and closed eye conditions.

Methods:
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.

Results:
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.

Conclusions:
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.