Fig. 5. Error at 30 degrees off-axis for spherical power polycarbonate lenses. The heavy solid line shows the residual error for optimally designed lenses at an average eyewire distance. Other plots are errors for eyewire distances 4 mm longer or shorter than the design values and errors for the same eyewire distances, but with base curves 1.00 D flatter than ideal. Flattening the base curve by 1.00 D actually improves the off-axis performance of the lens fit 4 mm too far from the eye.