Effect of Pupil Size on Wavefront Refraction during Orthokeratology

Abstract

Acknowledgement and DisclosureThis study has been funded by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) 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 30 semi-customized model eyes.Refraction in the central 80º of the visual field was objectively calculated using three different quality metrics criteria: Paraxial curvature matching, minimum Root Mean Square error (minRMS) and the Trough Focus Visual Strehl of the MTF (VSMTF), for 3 and 6 mm pupil diameters. Computed retinal images were subjectively evaluated by three well corrected subjects.Results: The tree metrics predicted significant different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. As for peripheral refraction, all the three metrics predict a more myopic peripheral refraction in the temporal visual field (nasal retina) compared to the nasal visual field, regardless of pupil size. According to our observers the Paraxial metric shows the worst performance for a 3 m pupil. As for the 6 mm pupil, the VSMTF clearly outperforms the Paraxial metric, with the minRMS yielding by far the worst image quality. Conclusions:The present results show that wavefront refraction predicts significant differences in the peripheral refraction pattern depending on the quality metric criteria used. Nevertheless, results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent of pupil size. The results for foveal vision obtained using the VSMTF criteria are more consistent with the reports of fluctuations in visual quality by of ortho-k patients under different light conditions.

Higher order aberrations, refractive error development and myopia control: a review

“…Chen et al 180 found that a larger pupil size during orthokeratology treatment in Chinese children was associated with slower axial eye growth than a smaller pupil, and suggested that this is due to a greater relative peripheral myopic shift. This change in peripheral refraction was confirmed with modelling by Faria-Ribeiro et al, 181 who also demonstrated that onand off-axis HOAs, particularly primary horizontal coma (Z 1 3 ) and primary spherical aberration (Z 0 4 ), also increase with greater pupil size as a result of corneal topographical changes during orthokeratology. This finding may indicate that HOAs influence the myopia control effect of orthokeratology; however, further longitudinal studies that examine the changes in on-and off-axis corneal and total ocular HOAs, pupil size and their association with eye growth before and during orthokeratology are required to provide further insights into a potential role for HOAs in the myopia control effect of orthokeratology.…”

Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology

“…49,50 Chen et al 49 investigated the association between axial elongation and pupil size in 25 children treated with ortho-k and reported an association between slower axial elongation and larger pupil size (compared to the average sample mean). Faria-Ribeiro et al 50 analyzed the influence of pupil sizes from 3 to 6 mm in simulated eye models and suggested that the effectiveness of myopia control may be enhanced in eyes with larger pupils due to increased exposure to peripheral defocus. Therefore, not only the change in corneal optics (e.g., more positive spherical aberration), but the natural pupil size may also influence axial elongation and the extent of myopia control.…”

“…One limitation of our study is that the numbers of children with different refractive errors (low and high myopia, high astigmatism) were not large enough to conduct separate analyses on the association between ocular HOA and axial elongation in different refractive error groups treated with ortho-k. As a result, all subjects were pooled together to provide a general understanding of the association between HOA and axial eye growth with ortho-k treatment. Because emmetropization is a complex, multifactorial process, other possible confounding factors such as pupil size, 49,50 parental myopia, 56 outdoor activities, 57 and living conditions 58 should also be evaluated in future studies (or controlled for with statistical modeling).…”

The Topographical Effect of Optical Zone Diameter in Orthokeratology Contact Lenses in High Myopes

“…Together with peripheral defocus, higher-order aberrations have been associated with myopia control, mainly 4 th -order spherical aberration and coma [22, 23]. Faria-Ribeiro et al described that higher-order aberrations are associated with larger pupil diameters as well as the effect on myopia control, potentially as a result of a larger retinal area exposed to the peripheral myopic defocus [24]. Many studies have shown that higher-order aberrations increase significantly after OrthoK treatment, even in successful fittings [23, 25].…”