title: Visual acuity, lens flexure, and residual astigmatism of keratoconic eyes as a function of back optic zone radius of rigid lenses.
abstract: The purpose of this study was to determine whether the visual acuity of keratoconic eyes was affected by alteration of back optic zone radii (BOZRs) of rigid gas permeable lenses (RGP) contact lenses. Visual acuity, spherical and sphero-cylindrical over-refraction and keratometry of the front surface of the RGP lenses of nine keratoconic eyes were measured. The BOZR of the five lenses varied from steeper to flatter than that habitually worn by the subjects. The steepest lenses produced significantly greater lens flexure and residual astigmatism (P < 0.002) and worse high and low contrast visual acuity with the spherical over-refraction (P < 0.05). There was no statistical difference in visual acuity across the range of BOZR when a sphero-cylindrical over-refraction was applied. Thus reduced visual acuity in keratoconus with steep lenses is likely due to uncorrected residual astigmatism from a combination of several possible sources.
authors.forename: L
authors.initials: L
authors.lastname: Sorbara
authors.forename: T
authors.initials: T
authors.lastname: Chong
authors.forename: D
authors.initials: D
authors.lastname: Fonn