Why This Article Matters
Summary
This retrospective cohort study evaluated interocular differences in axial length (AL) growth and spherical equivalent refraction (SER) progression in 246 children aged 8–14 years with myopic anisometropia (≥1.00 D). Of these, 116 wore HAL spectacles and 130 wore single-vision (SP) spectacles for 12 months. Linear mixed-effects models were used to account for within-participant inter-eye correlation and relevant baseline covariates. In the SP group, refractive anisometropia decreased modestly over 1 year (adjusted mean difference, −0.13 ± 0.04 D; p<0.001), with greater axial elongation in the less myopic than in the more myopic eye (0.34 vs 0.28 mm; adjusted inter-eye difference, 0.06 ± 0.01 mm; p<0.001). HAL wear was associated with less myopic progression and less axial elongation than SP wear in both eyes, with a greater 1-year axial treatment difference in the less myopic eyes. Within the HAL group, a small increase in interocular AL difference was observed (0.04 ± 0.01 mm; p=0.003), while refractive anisometropia remained stable (0.00 ± 0.04 D; p=0.963). In the subgroup with intermediate follow-up, axial elongation under HAL treatment was lower during months 0–6 than during months 6–12 in both eyes.
Commentary
Limitations
The retrospective, non-randomized design leaves the HAL-versus-SP comparison vulnerable to selection bias and residual confounding. Refractive outcomes were based on non-cycloplegic subjective refraction, and baseline anisometropia was generally mild (median 1.25 D), limiting generalizability to more severe cases. Ocular dominance, accommodative/vergence function, near work, and outdoor exposure were not systematically recorded. The interval-specific analysis also involved a smaller subgroup (53 SP and 70 HAL participants), with visits between months 4 and 8 normalized to 6-month equivalents, so the temporal findings warrant caution.
Clinical relevance
The findings provide reassuring evidence that binocular HAL wear can reduce myopia progression in children with myopic anisometropia while maintaining stable refractive anisometropia over 12 months. However, the small increase in interocular AL difference and the retrospective design mean that these results should support, rather than definitively establish, clinical practice. Monitoring both axial length and refractive anisometropia remains appropriate.
Comparison with existing evidence
The modest reduction in anisometropia with SP wear differs from several earlier reports of little or no change but is partially consistent with Wang et al. (2024). Greater axial control in the less myopic eye under HAL treatment is consistent with Yu et al. (2024), whereas Zhai et al. (2024) did not find a significant interocular difference after 1 year. The stronger axial control during the first 6 months also resembles findings from Yu et al., although Bao et al. did not observe the same temporal pattern in a different refractive range. Baseline refractive severity and study design may therefore influence the apparent interocular and time-dependent response.
Unanswered questions
Prospective, ideally randomized studies with longer follow-up are needed to determine whether the small increase in axial asymmetry under HAL wear translates into clinically meaningful refractive anisometropia. Future studies should include broader anisometropia severity and standardized measures of accommodative function, vergence, sensory ocular dominance, near-work behavior, and outdoor exposure.
Key Take-Home Messages
- HAL spectacles were associated with less axial elongation and less myopic progression than single-vision spectacles in both eyes over 12 months. - Refractive anisometropia remained stable with HAL wear over 12 months, despite a small increase in interocular axial-length difference. - The less myopic eyes showed greater axial suppression over 12 months under HAL treatment; the biological basis of this differential response remains uncertain. - In the subgroup analysis, axial elongation under HAL treatment was lower during the first 6 months than during months 6–12; this time-dependent pattern requires prospective confirmation.
Conflict of Interest Statement
The author declares no conflict of interest related to this article.
Strengths
A major strength is the paired interocular analysis, comparing the more and less myopic eyes within the same child and thereby reducing confounding from participant-level characteristics shared by fellow eyes. The linear mixed-effects models appropriately account for inter-eye correlation and relevant covariates, and the cohort is relatively large for this specific clinical phenotype.