Long-term axial elongation in myopic children wearing DIMS spectacle lenses: an 8-to-10-year observational study

Background/Aim To evaluate the long-term effectiveness of Defocus Incorporated Multiple Segments (DIMS) spectacle lenses in a long-term observational follow-up (>8 years) of an original randomised clinical trial cohort transitioning into late adolescence. Methods This observational post-trial study included 60 young adults (mean age: 19.97±1.64 years) from the original DIMS trial (baseline age: 8–13 years) followed for an average of 9.4±0.3 years. Longitudinal changes in spherical equivalent refraction (SER) and axial length (AL) were analysed using linear mixed-effects models (LMM) to compare rates of change during DIMS versus single vision (SV) wear periods. LMM predictions were benchmarked against an external meta-analysis for untreated Asian children. Results The LMM revealed a significant treatment effect for DIMS on axial elongation (p=0.003), with a predicted 65% cumulative reduction versus modelled SV wear (0.44±0.11 mm vs 1.27±0.11 mm). Conversely, the LMM found no statistically significant effect on SER progression (p=0.83), despite predicting a large, clinically meaningful cumulative difference (DIMS: –0.57±0.32 D vs SV: –2.17±0.37 D). The LMM-predicted elongation for continuous DIMS wear was 76% lower than the external untreated norm. Conclusions DIMS spectacle lens provides sustained slowing of axial elongation through late adolescence, yielding substantial benefits compared with modelled SV wear and external norms. However, this significant biological effect did not translate to a statistically significant refractive error effect in the LMM, possibly due to the low signal-to-noise ratio inherent to long-term autorefraction measurements and the lack of a contemporaneous, untreated single-vision control group. Further research should address this paradox between significant AL control and non-significant SER outcomes in long-term studies.