# Optical changes and axial elongation in children wearing orthokeratology lenses of smaller back optic zone diameter: a systematic review and meta-analysis

## TL;DR

This study finds that orthokeratology lenses with smaller back optic zone diameters reduce eye growth in children compared to conventional lenses.

## Contribution

The study systematically reviews and meta-analyzes the impact of smaller back optic zone diameter lenses on axial elongation and optical aberrations in children.

## Key findings

- Smaller BOZD lenses reduce axial elongation by 0.07-0.14 mm over 6-24 months compared to conventional lenses.
- Smaller BOZD lenses increase higher-order aberrations like spherical aberration and coma.
- The effect may be due to reduced treatment zone diameter and increased optical aberrations.

## Abstract

To evaluate the effect of orthokeratology lenses (Ortho-K) with smaller back optic zone diameters (BOZD) on axial elongation and ocular higher-order aberrations in children and adolescents.

PubMed, the Cochrane Library, Embase, CNKI, and Web of Science databases were comprehensively searched for relevant studies. The Cochrane risk-of-bias tool and the Newcastle-Ottawa Scale were used to assess the risk of bias in the included studies. RevMan 5.4 was applied for meta-analysis, and STATA 17.0 was employed for meta-regression, sensitivity analysis, and publication bias assessment. This study was registered at PROSPERO (registration number CRD42024538742).

Seventeen studies were included, comprising nine RCTs and eight cohort studies, with 1,548 participants in the smaller BOZD group and 1,570 in the conventional BOZD group. Meta-analysis shows that the smaller BOZD group has a lower axial elongation than the conventional BOZD group at 6 months, 12 months, and 24 months following Ortho-K treatment, with reductions of −0.07 mm (95% CI [−0.09, −0.04] P < 0.00001), −0.12 mm (95% CI [−0.13, −0.10] P < 0.00001), and −0.14 mm (95% CI [−0.19, −0.08]; P < 0.00001), respectively. Furthermore, compared to the conventional BOZD group, the smaller BOZD group result in a smaller treatment zone diameter (TZD) (MD: −0.49; 95% CI [−0.62, −0.36] P < 0.00001) and increased root mean square (RMS) higher-order aberrations (MD: 0.20; 95% CI [0.16–0.24]; P < 0.00001), RMS spherical aberration (MD: 0.17; 95% CI [0.12–0.21]; P < 0.00001) and RMS coma (MD = 0.10, 95% CI [0.02–0.18]; P < 0.0001) in children.

Our meta-analysis revealed that Ortho-K lenses with smaller BOZD exhibited less axial elongation in children compared with conventional Ortho-K lenses. This effect may be related to the reduction of TZD and the increase of higher-order aberrations (HOAs) caused by the smaller BOZD design.