Optical changes and visual performance with orthokeratology

Abstract

Orthokeratology has undergone drastic changes since first described in the early 1960s. The original orthokeratology procedure involved a series of lenses to flatten the central cornea and was plagued by variable results. The introduction of highly oxygen‐permeable lens materials that can be worn overnight, corneal topography, and reverse‐geometry lens designs revolutionised this procedure. Modern overnight orthokeratology causes rapid, reliable, and reversible reductions in refractive error. With modern designs, patients can wear lenses overnight, remove them in the morning, and see clearly throughout the day without the need for daytime refractive correction. Modern reverse‐geometry lens designs cause central corneal flattening and mid‐peripheral corneal steepening that provides clear foveal vision while simultaneously causing a myopic shift in peripheral retinal defocus. The peripheral myopic retinal defocus caused by orthokeratology is hypothesised to be responsible for reductions in myopia progression in children fitted with these lenses. This paper reviews the changes in orthokeratology lens design that led to the reverse‐geometry orthokeratology lenses that are used today and the optical changes these lenses produce. The optical changes reviewed include changes in refractive error and their time course, high‐ and low‐contrast visual acuity changes, changes in higher‐order aberrations and visual quality metrics, changes in accommodation, and changes in peripheral defocus caused by orthokeratology. The use of orthokeratology for myopia control in children is also reviewed, as are hypothesised connections between orthokeratology‐induced myopic peripheral defocus and slowed myopia progression in children, and safety and complications associated with lens wear. A better understanding of the ocular and optical changes that occur with orthokeratology will be beneficial to both clinicians and patients in making informed decisions regarding the utilisation of orthokeratology. Future research directions with this lens modality are also discussed.

The Combined Effect of Low-dose Atropine with Orthokeratology in Pediatric Myopia Control: Review of the Current Treatment Status for Myopia

“…Chen et al [61] described a statistically significant rise in spherical aberrations (0.05 ± 0.6 to 0.19 ± 0.13 µm) and coma aberrations (0.12 ± 0.19 to 0.36 ± 0.23 µm). Other authors found similar results and conclusions [49,[66][67][68][69]. Some authors related this increase in aberrations with the decrease in the corneal thickness [70] with contact lens use of approximately 20 µm [61], although Guo et al [71] did not consider these significant changes after seven years of follow-up, coinciding with other studies that did not find changes in the endothelial cell density [72,73].…”

“…This also provides freedom for participation in sports activities. A new study [49] reviewed different works on the effects of OK, reporting a better quality of life and satisfaction with vision by patients who completed a visual scale. Findings have shown orthokeratology to be effective in slowing axial elongation.…”

Higher order aberrations and axial elongation in combined 0.01% atropine with orthokeratology for myopia control

“…Following overnight reshaping of the anterior corneal surface from a prolate to an oblate shape, the eye exhibits a significant decrease in spherical refractive error and an increase in corneal and total ocular higher order aberrations (HOA's). 2 The most notable changes in the HOA profile are a positive shift in primary spherical aberration 3 and variations in horizontal and vertical coma related to treatment zone centration, 4 which result in an increase in higher order root mean square error values (HO RMS) that typically stabilises after one to four weeks of lens wear. 5 Since HOA's cannot be corrected with a conventional sphero-cylindrical refraction they may potentially influence eye growth through a vision-dependent mechanism by altering retinal image quality, or providing a directional cue through variations in optical vergence across the pupil.…”

“…However, the exact optical mechanism underlying the myopia control effect of orthokeratology remains unclear. Following overnight reshaping of the anterior corneal surface from a prolate to an oblate shape, the eye exhibits a significant decrease in spherical refractive error and an increase in corneal and total ocular higher order aberrations (HOA’s) 2 . The most notable changes in the HOA profile are a positive shift in primary spherical aberration 3 and variations in horizontal and vertical coma related to treatment zone centration, 4 which result in an increase in higher order root mean square error values (HO RMS) that typically stabilises after one to four weeks of lens wear 5 .…”

Looking and seeing beyond 2020

“…While it is now well accepted that overnight orthokeratology treatment significantly slows myopia progression in children, the underlying optical mechanism remains unclear. Nti and Berntsen review the optics of modern overnight reverse geometry orthokeratology lens designs including their effects on accommodation, peripheral refraction and on axis higher order aberrations. Lau et al also report on the change in the higher order aberration profile by modifying the Jessen factor in paediatric orthokeratology for myopia control.…”