It has been shown previously that thin polymethyl 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 O2 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 O2 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.
Presented at the Annual Meeting of the American Academy of Optometry, Toronto, Ontario, December, 1986.
Received July 29, 1986; revision received October 16, 1986.
* Optometrist, J.D., M.S., Member of Faculty, F.A.A.O.
Michael G. Harris
Morton D. Sarver Center for Cornea and Contact Lens Research
School of Optometry
University of California, Berkeley
Berkeley, California 94720
© 1987 American Academy of Optometry