Flexure of rigid contact lenses on toric corneas as a function of base curve fitting relationship.

This study examined flexure of contact lenses while varying the base curve corneal relationship. Identical 9.5 mm lens designs of Polycon I, Polycon II and PMMA and Polycon I 9.0 mm lenses were fitted to corneas with toricities of between 0.75 and 5.00 D. It was found that the amount and direction of the flexure were determined by the base curve fitting relationship. As lenses were fitted steeper than K, with-the-rule flexure occurred, and flatter than K, against-the-rule flexure. If the upper lid covers the superior portion of the lens, an against-the-rule flexure component is usually introduced.