Influence of soft contact lens design on clinical performance

A double-masked, randomized study in four parts was conducted to evaluate the effect of varying certain soft contact lens design parameters on clinical performance. The effects of varying back optic zone radius (BOZR) (8.20 to 9.00 mm), back surface design (monocurve, bicurve, aspheric), edge thickness (0.12 to 0.24 mm), and back vertex power (+ 1.00 to -6.00 D) were investigated using test lenses manufactured in a high water content material. In each part of the study, between 20 and 35 volunteer subjects wore a range of lenses which were assessed after > 30 min settling periods. Postblink movement and lens "tightness" as assessed by the push-up test were unaffected by the variation in BOZR. Lenses of flatter BOZR centered lower and more temporally than steeper lenses. Lenses of similar back surface sagittal depth, but differing in terms of back surface design, did not center the same; the monocurve lenses decentered more than bicurve or aspheric lenses. Edge thickness had no significant effect on comfort or lens fit. Plus power lenses resulted in more postblink movement than minus lenses of similar power. The results are discussed in relation to the design and fitting of soft contact lenses.