Axial elongation as a marker to identify obvious myopic shift in non-myopic eyes of Chinese children.

Objective: Rapid axial elongation in emmetropic eyes may indicate an increased risk of myopia onset. This study aimed to examine the range of axial elongation in non-myopic eyes, to distinguish between those with and without an obvious myopic shift and establish criteria to predict myopia onset within 1 year.

Methods: A total of 1580 non-myopic participants aged 6-10 years with -0.50 D < baseline spherical equivalent (SE) < +2.00 D were included. Eyes with an annual absolute SE change >0.25 and ≤0.25 D were categorised as 'high myopia risk group' and 'low myopia risk group', respectively. Annual axial elongation was calculated and presented as percentiles. The receiver operating characteristic (ROC) curve was used to determine the effectiveness for differentiating between these two groups and for predicting 1-year myopia onset.

Results: Of the 3797 eyes, 1415 (37.3%) were in the low myopia risk group. Depending on age, the median annual axial length (AL) change varied between 0.31 and 0.38 mm/year and 0.15-0.21 mm/year in the high and low myopia risk groups, respectively. Annual AL change was fairly stable across age for all percentiles in both groups, except for the 95th percentile in the high myopia risk group that demonstrated reduced progression with age. The area under the ROC curve (AUC) for axial elongation to differentiate between the two groups was 0.83, with a cut-off >0.20 mm/year being the preferred value to ensure higher sensitivity. Although axial elongation alone was effective in predicting myopia onset (AUC >0.90), combining it with cycloplegic SE increased the AUC (>0.98) for predicting myopia onset.

Conclusions: Annual AL change may serve as a clinically relevant threshold for monitoring pre-myopia risk in children.