Orthokeratology Treatment Zone Diameter May Affect Axial Elongation

A smaller orthokeratology treatment zone diameter may result from treatment with lenses with a smaller back optic zone diameter (BOZD), according to research published in Ophthalmic and Physiological Optics. This change results in less axial elongation during 2 years of treatment, according to the report.

Researchers included 45 pediatric patients with myopia (age range, 6-11 years; myopia, −0.75 to −4.00 diopters [D]) in the double-masked clinical trial and randomly assigned participants to treatment with orthokeratology lenses with a BOZD of 5 or 6 mm (n=22 and n=23, respectively). Study participants underwent cycloplegic examinations at baseline and every 6 months for the 2-year study duration. The team performed subfoveal choroidal thickness (ChT) measurements and corneal topography prior to cycloplegia, axial length measurements after cycloplegia, and subjective refraction before and after cycloplegia, and compared axial elongation and treatment zone characteristics between the 2 groups.  

Orthokeratology treatment zone diameter was significantly smaller among participants treated with the 5 mm BOZD lenses compared with individuals treated with the 6 mm BOZD lenses in the horizontal (2.69 vs 3.84 mm; P <.001) and vertical meridians (2.65 vs 3.42 mm; P <.001), the report shows. This smaller treatment zone created less axial elongation in individuals treated with the 5 mm BOZD lenses compared with the 6 mm BOZD lenses (0.15 vs 0.35 mm; P =.005) at 2 years. 

Significant ChT increases occurred during the 6- and 12-month follow-up visits (P <.001 and P =.004, respectively) among the cohort, and these changes were weakly associated with axial elongation. ChT differences between the 2 treatment groups were not statistically significant (P =.93). Most changes in treatment zone diameter, ChT thickening, and axial elongation occurred during the first 6 months. 

“The efficacy of myopia control using smaller BOZD lenses may likely be affected by the amount of defocus created on the retina, as slower [axial elongation] may result from a greater change in aberrations,” according to the study authors. 

Study limitations include the lack of a spectacle-wearing control group and a small sample size.

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.