Abstract
Purpose: :
To study mirror symmetry of x–axis coma between left and right eyes in both the anterior corneal surface and the whole eye and its relationship with x–axis shift of the pupil center from the corneal vertex.
Methods: :
Both the left and the right eyes of 176 subjects (aged from 18 to 38 yrs, mean=25.5yr) were tested using a Humphrey Corneal Topographer (Carl Zeiss Medtec, Inc) and a WASCA wavefront analyzer (Carl Zeiss Medtec, Inc) to measure wavefront aberrations in the anterior corneal surface and the whole eye. Zernike aberrations up to 7th order (35 terms) within 6.0 mm pupil area were derived, and the x–axis coma was used for analysis. X–axis shift of the pupil center from the corneal vertex was recorded according to the estimate of pupil center from the Humphrey Corneal Topographer.
Results: :
Positive x–axis coma was found for the left eye with means of 0.16 micron for the anterior corneal surface and 0.04 micron for the whole eye, while negative x–axis coma was observed for the right eye with means of –0.16 (the cornea) and –0.02 microns (the whole eye). The x–axis coma in the left eye was significantly correlated to that in the right eye for either the anterior cornea (r=–0.65, p<0.001) or the whole eye (r=–0.62, p<0.001). The mean x–axis shifts of the pupil center from the corneal vertex were 0.005mm and –0.05mm for the left and the right eyes respectively, and the x–axis coma was significantly correlated to the x–axis shift of the pupil center for both the anterior cornea (r=0.51, p<0.001) and the whole eye (r=0.25, p<0.001).
Conclusions: :
X–axis shift of the pupil center plays an important role in contributing the mirror symmetry of x–axis coma in both the anterior corneal surface and the whole eye.
Keywords: optical properties • cornea: clinical science • cornea: basic science