HIGH-OXYGEN-TRANSMISSIBILITY SOFT CONTACT-LENSES DO NOT INDUCE LIMBALHYPEREMIA

Purpose. To establish the temporal sequence of limbal hyperaemia in hu mans without contact-lens wear and during conventional and highly oxyg en-permeable soft-contact-lens wear. Methods. Two, 16-h, non-dispensin g clinical studies were conducted, each incorporating 8 h of open eye with normal blinking, followed by 8 h of eye closure during sleep. In the first study. six non-habitual contact-lens wearers did not wear co ntact lenses. In the second study, the same subjects were each randoml y assigned, in a double-masked fashion, to wear a conventional. thin, 38% water, pHEMA soft contact lense (SCL) in one eye and an experiment al high Dk (EHD), 20% water soft contact lens in the other. Limbal red ness (LR) was graded. using a 0-4 scale with decimalised subdivisions: at baseline and after 4, 8 and 16 h. ANOVA was applied to the data, a nd the level for statistical significance was set at p less than or eq ual to 0.005. Results. In the non-wearing eye, LR changes averaged 0.2 +/- 0.2 and 0.4 +/- 0.2 grades at 4 and 16 h, respectively (inferior quadrant). The corresponding values for SCL wear were 1.0 +/- 0.6 and 1.1 +/- 0.6, while for EHD wear they were 0.2 +/- 0.4 and 0.5 +/- 0.5. Both for the normal eye and chose wearing EHD lenses. Increases in LR were significant only during eye closure (p < 0.005). During SCL wear , significant and larger LR increases were seen after 4 h open eye wea r (p < 0.005), with only relatively small further changes being observ ed over the next 12 h. Conclusions. SCL wear induces a marked increase in limbal hyperaemia during open-eye wear, which is not seen either i n the no lens situation or when EHD lenses are worn. The pattern of li mbal hyperaemia for both tie open and closed eyes during EHD lens wear is very similar to that for the no-lens situation. The mechanism wher eby SCL induces excess limbal hyperaemia has not been absolutely estab lished, but it may involve local hypoxia.