On the relationship between soft contact lens oxygen transmissibility and induced limbal hyperaemia

The relationship between induced limbal hyperaemia and lens oxygen transmissibility was investigated in a series of clinical studies in which subjects wore a range of soft contact lenses for eight hours each. Data representing the degree of limbal hyperaemia induced in each case was extracted and subjected to non linear regression analysis with hyperaemia as dependent, and oxygen transmissibility as independent variables. Strong, statistically significant associations were found, particularly when oxygen transmissibility in a 12 mm diameter annular zone at the lens periphery was considered. Best fitting functions were of an inverse form for nasal (r2=0.86, P=0.008) and temporal (r2=0.81, P=0.014) quadrants and a logarithmic form for superior (r2=0.87, P=0.007) and inferior (r2=0. 97, P< 0.005) quadrants. These findings provide support for an hypoxic theory of soft contact lens induced limbal hyperaemia. Estimates based on the logarithmic model suggest a 95% confidence interval for the peripheral oxygen transmissibility required to avoid limbal hyperaemia of 56-274 x 10(-9) (cm s-1) (mlO2 ml-1 x mm Hg).