Models of Oxygen Performance for the Static, Dynamic and Closed‐lid Wear of Hydrogel Contact Lenses

Contact lenses can restrict the amount of oxygen available to the cornea, often resulting in corneal oedema and visual dysfunction. Predictions of the likely physiological response of the cornea to contact lens wear can be facilitated by developing models of the oxygen performance characteristics of lenses. An equivalent oxygen technique was modified for use in the in vivo human eye; this technique involved equating the corneal oxygen demand following contact lens wear to the demand following exposure to known oxygen levels. A human eye model relating static equivalent oxygen percentages (EOP) to lens oxygen transmissibility (Dk/L) was derived using five hydrogel contact lenses; the discrepancies between this and other models could be explained in terms of the differing criteria upon which they were based. The effect of blinking on the EOP beneath hydrogel lenses was found to be minimal, confirming earlier findings. Attempts to derive an EOP v Dk/L model for hydrogel lens wear under closed‐lid conditions were unsuccessful; individual variations in the supply of oxygen to the cornea under these conditions were thought to contribute to this failure. The validity of similar models was questioned in view of the simplified assumptions which were made.