Orthokeratology (ortho-k) lenses with a smaller, more aspheric treatment zone may impede axial elongation better than lenses with a larger and less aspheric zone, according to research published in Contact Lens and Anterior Eye.
Researchers conducted a retroscopic analysis of 137 children across 2 studies conducted at a single center between 2020 and 2022. Participants were randomized to Euclid (n=42; mean age, 9.93±1.63 years; 22 boys) or DRL lenses (n=28; mean age, 10.63±1.76 years; 14 boys) in 1 study and assigned to CRT lenses (n=67; mean age, 10.02±1.69 years; 30 boys) in the other investigation.
Participants underwent visual acuity, manifest refraction, slit lamp, and corneal topography evaluations at baseline and at follow-up visits conducted at 1 day, 1 week, 2 weeks, 1 month, 3 months, 6 months, 9 months, and 1 year after the initial visit. Axial length (AL) measurements were obtained at baseline, 6 months, and 1 year. Researchers compared AL elongation, maximum relative corneal refractive power change (Ymax) and its corresponding distance from the corneal apex (Xmax), and power exponent among the 3 groups. Polynomial and monomial functions were used to calculate corneal refractive power change.
The 1-year AL elongation was significantly slower among individuals fit with DRL lenses (0.09±0.14 mm) compared with children fit with Euclid (0.26±0.14 mm; P =.002) or CRT lenses (0.32±0.18; P <.0001). The monomial function power exponent was lower for those in the DRL group (F=7.29; P =.0012), indicating that the 5.0 mm back optic zone diameter induced more asphericity than the Euclid and CRT designs with back optic zone diameter of 6.2 mm and 6.0 mm, respectively.
“[T]his study used a unified and repeatable mathematical model to analyze the relative corneal refractive power change post-ortho-k and used it to predict axial elongation across three different ortho-k lens designs,” according to the researchers. “A smaller and more aspheric treatment zone induced by ortho-k lenses may be beneficial for reducing axial elongation in children and adolescents.”
Study limitations include the non uniformity in sample size among groups, a lack of true randomization between the 2 studies, and short study duration.
Zhang Z, Zhou J, Zeng L, Xue F, Zhou X, Chen Z. The effect of corneal power distribution on axial elongation in children using three different orthokeratology lens designs. Cont Lens Anterior Eye. Published online August 22, 2022. doi:10.1016/j.clae.2022.101749