Purpose. It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology,
might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical
quality after orthokeratology, using ray tracing software for different pupil sizes.
Methods. Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography
changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the
visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean
square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm
pupil diameters.
Results. The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the
Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts
only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and
VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm.
Conclusions. The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent
on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF
criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more
significant under low illumination levels.This study has been funded by FEDER through the COMPETE Program and
by the Portuguese Foundation for Science and Technology (FCT) in the
framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/
098392/2008, and the Strategic Project PEST-C/FIS/UI607/2011. Dr.
Navarro acknowledges funding by the Spanish Ministery of Economy and
Competivity, grant FIS2014-58303-P. The authors have no proprietary
interests in the methods and devices described in this manuscript
