Inattention to nonsuperimposable midline symmetry causes wavefront analysis error

Abstract

Background: The nonsuperimposable mirror-image symmetry of the body (enantiomorphism) is reflected in the wavefront error maps of eyes. Averaging the wavefront errors of right and left eyes has the potential to adversely affect correlations made between wavefront error and visual acuity or other factors. Not only are the results of past studies using Zernike terms suspected of being invalid, there is concern about possible errors in the algorithms used to create customized corneal ablations. Objective: To compare the results of analysis with and without correction for enantiomorphism. Methods: Fourteen TMS-1 corneal topographic maps from 7 patients having with-the-rule astigmatism in both corneas were selected for Zernike decomposition to 45 terms. The maps were distributed among 3 groups: 7 right eye maps, 7 left eye maps, and 7 left eye maps in which the topography was transposed about the vertical axial to correct for enantiomorphism (left eye-corrected). The wavefront error difference between the right and left eyes was compared with the difference between the right eyes and the left eyes in which enantiomorphism was corrected (right eye vs left eye-corrected). The left eye wavefront error was then compared with the left eye wavefront error after correction (left eye vs left eye-corrected). Results: Correcting for enantiomorphism produced a statisticially significant difference in the first 5 radial orders of Zernike terms (P=.02). Of the 45 Zernike terms analyzed, 7 terms were significantly different at the P