ABSTRACT It has been shown previously that thin poly‐methyl methacrylate (PMMA), cellulose acetate butyrate (CAB), and Polycon I contact lenses flex on toric corneas. We investigated the flexure and induced residual astigmatism of two gas permeable contact lens materials, Paraperm 02 and Boston II, and compared the results with those of other materials. Six subjects (12 eyes) with corneal toricities ranging from 1.75 to 3.25 D wore five Paraperm 02 lenses and five Boston II lenses with center thicknesses ranging from 0.10 to 0.20 mm. Flexure and induced residual astigmatism were measured on all corneas wearing all lenses in a double‐masked fashion. All lenses studied showed flexure and induced residual astigmatism, which increased as center thickness decreased. For both lens types, lenses thinner than 0.15 mm flexed significantly more than thicker lenses. This critical center thickness should be considered when fitting these lens types on toric corneas.
Harris et al. (1987) studied this question.