Aspheric orthokeratology (ortho-k) lenses may result in a more aspheric treatment zone and produce greater relative corneal refractive power and peripheral refractive error changes than ortho-k lenses with a spherical design, according to research published in Contact Lens and Anterior Eye. These changes may possibly allow the lens to demonstrate greater myopia control efficacy, the report suggests.
Researchers included 62 children with myopia in the controlled, single-masked trial and randomized them to treatment with aspheric (n=33; mean age, 9.43 years; 19 boys) or spherical ortho-k lenses (n=29; mean age, 9.62 years; 15 boys). Study participants underwent relative corneal refraction assessments for the 8 mm central cornea along the horizontal and vertical axes and corneal peripheral refraction measurements along the 10°, 20°, and 30° nasal and temporal retina during 1-day, 1-week, and 1- and 3-month follow-up visits. The investigators compared corneal refractive power and peripheral refractive error changes between the 2 cohorts.
“[T]he asphericity of the corneal optical surface after treatment is linked with [corneal refractive power] and its spatial distribution; moreover, it may impact the relative peripheral refraction,” the study authors note. “Theoretically, the change in the corneal optical surface may depend on the lens design and the corneal response. However, whether an ortho-k lens with an aspheric base curve could induce a more aspheric treatment zone remains unknown.”
Individuals treated with the aspheric lens designs demonstrated greater corneal refractive power changes (2.08 vs 1.32 diopters [D]; P <.001) and relative peripheral refractive error changes (-1.82 vs -0.98 D; P <.001) compared with patients fit with the spherical design. Patients undergoing aspheric lens treatment exhibited a hyperopic shift in relative corneal peripheral refraction at all locations along the horizontal and vertical meridians and myopic shifts in relative peripheral refraction at all locations, according to the report.
“The peripheral shape in the aspherical base curve is steeper than that in the spherical base curve,” according to the researchers. “Therefore, the aspheric base curve could produce a sharper decline in the central refractive power after lens wearing, causing a more aspheric treatment zone in the [aspheric base curve] group. The asphericity of the treatment zone has been linked with myopia control effects.”
Study limitations include failure to assess astigmatism set orthogonally at 90° and 180° meridians and oblique astigmatism, and homogeneity among the cohort that may limit globalization of the research findings.
Disclosure: This research was supported by Eyebright. Please see the original reference for a full list of disclosures.
Liu T, Ma W, Wang J, et al. The effects of base curve aspheric orthokeratology lenses on corneal topography and peripheral refraction: a randomized prospective trial. Cont Lens Anterior Eye. Published online January 20, 2023. doi:10.1016/j.clae.2023.101814