Factors influencing vision with rigid gas permeable alternating bifocals.

This study assessed the fitting and visual performance of a rigid, gas permeable (RGP), monocentric, alternating bifocal. Fourteen presbyopic eyes each wore 24 different lenses consisting of all combinations of 2 diameters, 2 segment heights, 2 prism ballasts, and 3 fitting relations. The influence of parameter selection on visual performance and the usefulness of clinical measurements in predicting visual performance were determined statistically by multivariate logistic regression. Our results showed that prism, segment height, and the fitting relation can influence distance and near visual performance. Lens movement, postblink segment positioning, and return time were the most useful measured predictors of visual performance.