Measurement of SoflensTM posterior curvature with Moiré fringes

The posterior surface curvature of eight Bausch and Lomb SoflensesTM was measured by using a Moiré interference fringe technique. This unique method was used to allow measurement of the curvature variation across the lens surface and to provide new information which may be helpful in understanding difficult fitting problems and improving fitting techniques. Central apical curvature agreed with values published by Bausch and Lomb within 6%. Low negative power lenses became steeper, whereas higher minus power lenses became flatter away from the apex toward the lens periphery. However, none of the lenses tested was a flat in the outer portion of the lens as predicted by hydrodynamic forced-vortex theory which should be applicable for spun-cast fluid lenses. There was also a significant change in curvature, first flattening, then steeping across the lens as it dried out during the course of the measurement.