Pinpointing precision: axial length and refraction in paediatric myopia trials-a mixed methods study

Most paediatric myopia intervention trials report two primary outcomes: axial length and cycloplegic autorefraction. Having one single primary outcome would increase trial efficiency, reduce participant burden, and may improve trial retention. This article aims to evaluate precision of axial length and cycloplegic autorefraction and to explore eye care professionals' and young people's views of cycloplegia.

Mixed methods study with meta-analysis of axial length and cycloplegic spherical equivalent measurements reported by paediatric myopia treatment trials; interviews with eye care professionals; engagement/involvement discussion with children and young people.

In the meta-analysis, mean effect size (standard error, SE) was -0.52 (0.12, p < 0.001, 95% confidence interval (CI) -0.76 to -0.29) for axial length and 0.49 (0.11, p < 0.001, CI 0.27 to 0.71) for cycloplegic spherical equivalent refraction. Difference in mean point estimates was 0.033, SE of the difference 0.164 (CI -0.29 to +0.535). With t-statistic (mean difference/SE of mean difference) of 0.20, two-tailed p value was 0.84. Eye care professionals report that children dislike cycloplegia, describing discomfort, distress, and potential refusal to attend follow-up appointments. Children and young people describe pain and discomfort, remember prolonged effects such as blurred vision and light sensitivity, and complain about receiving insufficient information about adverse effects.

Whilst the precision of axial length and cycloplegic autorefraction spherical equivalent measurements is similar, cycloplegic autorefraction requires longer study visits and inflicts more discomfort. In the design of future trials, researchers, funders, and regulators should consider increasing trial efficiency by selecting axial length as primary outcome and removing cycloplegic refraction from follow-up assessments.