Author's Reply.

We thank Drs. Naduvilath and Sankaridurg for their interest in our article “Comparison between estimated and measured myopia progression in Hong Kong children without myopia control intervention”. They emphasise the utility of the BHVI myopia calculator as a tool to illustrate the progressive nature of myopia and the benefits of myopia control treatments to patients and parents. We agree with them, as stated in our original paper; “The graphical representation of myopia progression with and without an intervention can be a useful educational tool for eye care practitioners when discussing myopia management with patients and adult caregivers.” We also agree with Naduvilath and Sankaridurg that to estimate future myopia progression in diverse populations (i.e., not Asian or Caucasian children), different longitudinal childhood refractive error datasets would be required, including myopic children wearing single vision corrections. However, as noted in our original paper, future prospective data collection of myopic children wearing single vision corrections may not be considered ethical; “...given the mounting evidence supporting early intervention for progressive myopia in children to prevent ocular complications later in life it may not be ethically justifiable to conduct longterm prospective studies of myopic children wearing singlevision distance spectacles, particularly in Asian countries.” The authors present an analysis of one year follow up data of 526 children corrected with single vision lenses (BHVI data on file) to validate the “without management” option for Asian children in the BHVI calculator. It is not stated whether these 526 children are also included in the sample of 4504 myopic eyes included in the calculator's “without management” estimates for Asian children. Nonetheless, this analysis confirms the results from our study that; “... on average, the estimated SER data obtained from the BHVI Myopia Calculator using the baseline refraction, sex and ethnicity of Hong Kong children wearing singlevision distance spectacles was in close agreement with the measured cycloplegic subjective and objective refraction data over 1 and 2 years of followup (mean differences <0.25 D).” The authors advocate for the use of the 95% prediction interval to study and monitor the refractive progression of individual eyes. While the 95% confidence interval is provided graphically in the BHVI calculator, the 95% prediction interval is not, and it cannot be calculated without knowledge of the sample characteristics used within the calculator (e.g., baseline ages and refractive errors, and myopia progression) for each age group and baseline refractive error combination. Despite the much wider 95% prediction intervals provided by the authors compared to 95% confidence intervals we extracted from the BHVI calculator (~3x wider for both the 1and 2year followup data), the authors analysis highlights that individual refractive progression data for children (~10%– 14%) can still fall outside the 95% prediction interval. Ultimately, this analysis supports the original conclusion drawn from our study that “the progression data for a standard singlevision correction (the ‘without management’ option) used in the BHVI Myopia Calculator may not provide an accurate estimate of the extent of myopia progression for all children...”.