Mass of rigid contact lenses

Mass should be considered as one of several clinically malleable physical properties of contact lens materials. Lenses with identical posterior surface designs and back vertex powers may have different front surface parameters and thicknesses when manufactured from materials of several refractive indices. Change in anterior surface design affects overall lens volume, which combines with differences in specific gravity to change overall lens weight or mass. Clinical in situ contact lens performance may be affected in many ways by changes in anterior surface profile, volume, and overall mass, although back surface design and effective power is held constant. This study presents methodology for comparing the predicted mass of specific lens designs made from different rigid lens materials. Both theoretical and sample values are presented and discussed. Results suggest that specific gravity by itself may be a good clinical guide to the relative mass of identically designed lenses made of different materials. However, as lens mass can affect lens performance in several ways, it might be worthwhile for the clinician and/or manufacturer to develop methods whereby such calculations were automatically provided in each individual situation.