Influence of rigid contact lens overall and optic zone diameters on tear pump efficiency.

To determine the effects of contact lens overall diameter on tear pump efficiency, oxygen uptake rates were measured for the open-eye condition and following steady-state periods of static (without blinking) and dynamic (with blinking once every 5 s) contact lens wear of oxygen-impermeable (polymethylmethacrylate) lenses of 5 overall diameters (8.2, 8.5, 8.8, 9.1, and 9.4 mm). The optic zone diameters were 1.4 mm smaller than the overall diameters in each case, while all other parameters remained constant. Differences in corneal oxygen demand following the static and dynamic conditions are a quantitative index of the tear pump efficiency for each lens size on the same cornea, and the differences were found to increase with reduction in lens overall diameter. This indicated that a more efficient tear pump was associated with small diameter designs. In addition, subjects with large palpebral aperture size, relative to lens overall diameter, were found to demonstrate better tear exchange.