Flexure and residual astigmatism with cellulose acetate buterate (CAB) contact lenses on toric corneas

Thin contact lenses flex on toric corneas, thus changing the residual astigmatism. Our study evaluated the flexure and induced astigmatism of CABCURVE cellulose acetate buterate (CAB) contact lenses on toric corneas and compared the results with those found for polymethyl methacrylate (PMMA) and Polycon lenses. Ten subjects (20 eyes) with corneal toricities ranging from 1.12 to 3.12 D wore six CABCURVE lenses with center thicknesses from 0.10 to 0.20 mm. Flexure and induced residual astigmatism were measured on all corneas with all lenses in a double-masked fashion. We found that all the CABCURVE lenses flexed on the toric corneas and altered residual astigmatism. Both flexure and induced residual astigmatism increased as center thickness decreased, and were greater than with PMMA or Polycon lenses of similar dimensions. These findings should be considered when deciding which lens type to fit on patients with toric corneas.