Orthokeratology Design Demonstrates Superiority in Impeding Axial Elongation

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.