To determine the relative merits of spherical equivalent refraction (SER) vs axial length (AL) as the primary measure for monitoring childhood myopia progression and predicting adult myopia-related pathology.

Myopia prevalence is rising worldwide, but most patients only reach low-to-moderate myopia. Many guidelines emphasize AL over SER using fixed thresholds to define ``high risk'' (eg, ≥26 mm), yet a large proportion of myopia-related pathology occurs in eyes that never reach those lengths.

We conducted a systematic review and meta-analysis of population-based observational studies (≥200 eyes; PubMed and Embase searched from 1990 to July 2025) reporting AL and/or SER with demographics and/or retinal, cataract, or primary open-angle glaucoma (POAG) outcomes. Random effects meta-analyses with Hartung-Knapp adjustment were performed when k ≥ 3; other results were synthesized descriptively. Risk of bias was assessed with the Newcastle-Ottawa Scale and certainty of evidence with Grading of Recommendations Assessment, Development and Evaluation.

Seventy studies met inclusion criteria. Normal AL varied strongly with age, sex, height, and ethnicity, whereas SER showed much weaker dependence. A small tail of emmetropes reached AL ≥26 mm. Retinal pathology rose steeply with longer AL (odds ratio [OR] 3.85 per +1 mm), implying risk ratio ≈25 at AL 26 mm relative to AL 23.6 mm (pooled gradient), but this long-eye threshold applied to <10% of eyes. SER data, although less frequent, showed consistent retinal risk increases with OR ≈1.5 to 1.8 per –1 diopter and OR 2 to 12 for high myopia. For cataract prevalence, SER-defined moderate/high myopia yielded ORs of 3.09 for nuclear and 4.58 for posterior subcapsular cataract, whereas AL-defined effects were null or modest. For POAG prevalence, AL per +1 mm showed OR 1.37, whereas SER-defined moderate/high myopia showed OR 2.95. Certainty of evidence was moderate for prevalence analyses and lower for incidence and descriptive blocks.

Absolute AL thresholds clearly identify a small tail of very long eyes at high retinal risk, but SER better captures cataract and POAG risk gradients across the myopic range that most patients will reach. SER should be the primary progression and risk metric for monitoring childhood myopia control, with AL used selectively to monitor the minority of children with greater axial elongation.