High-oxygen-transmissibility soft contact lenses do not induce limbal hyperaemia

To establish the temporal sequence of limbal hyperaemia in humans without contact-lens wear and during conventional and highly oxygen-permeable soft-contact-lens wear.

Two, 16-h, non-dispensing 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 contact lenses. In the second study, the same subjects were each randomly assigned, in a double-masked fashion, to wear a conventional, thin, 38% water, pHEMA soft contact lens (SCL) in one eye and an experimental high Dk (EHD), 20%-water soft contact lens in the other. Limbal redness (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, and the level for statistical significance was set at p < or = 0.005.

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 those 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 wear (p < 0.005), with only relatively small further changes being observed over the next 12 h.

SCL wear induces a marked increase in limbal hyperaemia during open-eye wear, which is not seen either in the no lens situation or when EHD lenses are worn. The pattern of limbal hyperaemia for both the open and closed eyes during EHD lens wear is very similar to that for the no-lens situation. The mechanism whereby SCL induces excess limbal hyperaemia has not been absolutely established, but it may involve local hypoxia.