Objective This study aims to investigate the associations of axial length to corneal radius of curvature (AL/CRC) ratio with refractive error and to determine the effect of AL/CRC ratio on hyperopia reserve and myopia assessment among Chinese preschoolers. Methods This was a retrospective cross-sectional study that evaluated subjects aged 4–6 years. AL and CRC were obtained using a non-contact ocular biometer. Correlation analysis was performed to explore the associations of AL/CRC ratio with spherical equivalent refractive error (SER). The accuracy of AL/CRC ratio for hyperopia reserve and myopia assessment was analysed using cycloplegic refraction by drawing receiver operating characteristic (ROC) curves. Results The analysis included 1024 participants (537 boys, 52.4%). The mean AL/CRC ratios in hyperopes, emmetropes and myopes were 2.90±0.06, 2.95±0.05 and 3.08±0.07, respectively. The SER was found to be more strongly correlated with AL/CRC ratio (ρ=−0.66, p<0.001) than either AL or CRC alone (ρ=−0.52, p<0.001; ρ=−0.03, p=0.33, respectively). AL/CRC was correlated with SER in hyperopes (ρ=−0.54, p<0.001), emmetropes (ρ=−0.33, p<0.001) and myopes (r=−0.67, p<0.001). For low hyperopia reserve assessment, the area under the ROC curves of AL/CRC ratio was 0.861 (95% CI 0.829 to 0.892), the optimal cut-off value of the AL/CRC ratio was ≥2.955. For myopia assessment, the area under the ROC curves of AL/CRC ratio was 0.954 (95% CI 0.925 to 0.982), the optimal cut-off value of the AL/CRC ratio was ≥2.975. Conclusions The SER showed a better correlation with AL/CRC ratio than either AL or CRC alone, especially in myopes, among children aged 4–6 years. These findings indicate that when cycloplegic refraction is unavailable, AL/CRC ratio could be used as an alternative indicator for identifying low hyperopia reserve and myopia among preschoolers, helping clinicians and parents screen children with low hyperopia reserve before primary school in a timely manner.

Objectives To examine the ocular biometric parameters and predict the annual growth rate of the physiological axial length (AL) in Chinese preschool children aged 4–6 years old. Methods This retrospective cross-sectional study included 1090 kindergarten students (1090 right eyes) between the ages of 4 and 6 years from Pinggu and Chaoyang District, Beijing. Dioptre values were ascertained following cycloplegic autorefraction. Predicted AL was obtained through the application of the Gaussian process regression model as an optimisation technique. Subsequently, the annual growth rate of physiological AL for non-myopic preschool children (n=1061) was computed via the backward difference method. Results In total, 85.4% of preschool children (931 individuals) had hyperopic refractive status in the 4–6 years age group, while only 2.7% (29 individuals) showed myopia. Boys had longer AL, larger AL-to-corneal radius ratio, deeper anterior chamber depth and lower lens power. The average physiological axial growth for boys and girls ranged from 0.050 mm/year to 0.165 mm/year and 0.063 mm/year to 0.168 mm/year, respectively. As age increased, the physiological AL growth in non-myopic cases decreased. Additionally, as hyperopic spherical equivalent refraction error lessened, the physiological AL growth component slowed down. Conclusions In preschool children, refractive development predominantly exhibits mild hyperopia. The concept of physiological AL provides valuable insights into the complexities of ocular development.

Objectives: To investigate seasonal variations in the effect of controlling myopia progression using orthokeratology (Ortho-K) in Chinese myopic children. Methods: One hundred sixteen myopic children aged 7 to 12 years who completed 1 year of Ortho-K treatment. Based on initial time wearing Ortho-K, subjects were classified as four groups: spring group (March–May), summer group (June–August), autumn group (September–November), and winter group (December–February). Axial length (AL) was measured every 3 months for 1 year by partial coherence interferometer. Axial elongation over time and between groups was compared. Results: The effect of myopia control using Ortho-K was influenced by seasonal variation. After adjusting study groups (type of Ortho-K), age, AL, spherical equivalent refractive error (SER), and ocular parameters at the baseline, the mean axial elongation over 1 year wearing Ortho-K was 0.33±0.08 mm for spring group, 0.30±0.10 mm for summer group, 0.21±0.08 mm for autumn group, and 0.22±0.09 mm for winter group (P<0.001). Statistically significantly higher mean axial elongation was observed in winter months than that in summer (0.09±0.06 mm vs. 0.05±0.05 mm, P<0.001). Conclusions: In general, axial elongation in myopic children receiving Ortho-K in summer months was approximately 56% of that in winter. Initial time wearing Ortho-K in autumn/winter months, the effect of myopia control is better than in spring/summer. Our results indicated that seasonal variation should be taken into account in studies related to Ortho-K.