Alterations in Peripheral Refraction are Most Significant Just Before the Onset of Myopia: Evidence from Multispectral Refraction Topography

This study aims to explore the characteristics of retinal defocus values (RDVs) during refractive development of Chinese children. In this cross-sectional study, 2125 children (2125 right eyes) aged 4-15 years were included and divided into several groups according to spherical equivalent (SE) or axial length (AL). Ocular biological parameters including AL, central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT) and corneal curvature were detected, and multispectral refractive tomography (MRT) was used to measure total retinal defocus values (TRDV), RDVs of 0°-15°/15°-30°/30°-45° concentric annulus area (RDV-15/30/45), RDVs of the superior, nasal, inferior and temporal fan-shaped region (RDV-S/N/I/T). CCT and ACD increased while LT decreased with myopia progression. As diopter descended, almost all RDVs gradually inclined to hyperopic defocus; however, the superior retina demonstrated consistent myopic defocus across different dioptric states. RDV-45 and RDV-T changed most obviously among RDV-15/30/45 and RDV-S/N/I/T, respectively. Importantly, hyperopic shift of RDVs was most pronounced between the emmetropia and low myopia group, and also when AL was approximately 23 mm. Additionally, difference between superior and inferior RDVs also peaks in early myopia. The rapid changes and longitudinal inequality of RDVs are most significant just before 23 mm of AL, this condition may have important predictive value for the occurrence of myopia. Additionally, defocus of the temporal retina showed the greatest variation in dioptric development, suggesting that nasal visual information may affect refractive outcomes.