Acceleration of Myopic Shifts in Refraction and Axial Elongation Begins in the Premyopia Stage.

Purpose: To investigate the dependence of age-specific annual changes in refraction and axial elongation on starting refraction (refraction at the first of two yearly examinations). Methods: Children (2259 participants) from the Guangzhou Twin Eye Study, with baseline ages from 7 to 15 years and 12 annual follow-ups, were included. Validation samples were drawn from the Guangzhou Longitudinal Outdoor Activity Study (GOALS). Refractions were categorized into three groups based on starting spherical equivalent (SE): myopia (SE ≤-0.5 D), premyopia (-0.5 < SE ≤ +0.75 D), and hyperopia (SE >+0.75 D). Within each category, we divided data into different bins. Locally estimated scatterplot smoothing (LOWESS) lines were drawn to determine where myopic shifts in refraction and axial elongation begin to accelerate. Results: In the hyperopic category, the annual change in SE was similar across all age groups. In the premyopic category, the annual change in SE increased as the starting SE decreased. Increases were particularly clear before age 12. In the established myopes, the annual change in SE was highest, up to approximately -1.0 D in those under 10 years, but remained relatively stable across all myopic bins at a given age. The LOWESS lines show that the trend of gradual increase in annual change in SE with decreasing starting SE begins at a starting SE of approximately +1.00 D. The trends in axial length were similar. Similar results were seen in the GOALS. Conclusions: Myopia acceleration starts in mild hyperopia. Public health interventions should aim to keep refractions over +1.00 D to delay entry into the premyopic range.