Spherical Equivalent Percentile Curves in a Portuguese School-Aged Population

<b>Bacground/Objectives</b>: This study aimed to develop age- and sex-specific spherical equivalent (SE) percentile curves and estimate the prevalence of refractive errors (REs) in Portuguese schoolchildren aged 6-17 years. <b>Methods</b>: A cross-sectional study was conducted in three schools in Lisbon, including 2205 children (mean age = 9.3 ± 2.6 years; 49.3% boys). Vision was assessed using non-cycloplegic static retinoscopy (chosen due to feasibility in school settings) and visual acuity tests. SE percentile curves (P5-P95) were generated by age and sex. SE values and RE distribution (hyperopia, emmetropia, and myopia) were compared across four age groups (6-8, 9-11, 12-14, and 15-17 years). <b>Results</b>: SE values decreased significantly with age (<i>p</i> < 0.001). Median SE ranged from +0.50 D (6-8 years) to 0.00 D (15-17 years), with no sex differences. Hyperopia predominated in younger children (60.6% at 6-8 years), whereas myopia increased in older ages (32.2% at 15-17 years). <b>Conclusions</b>: This study presents the first SE percentile curves for Portuguese schoolchildren, providing a practical, age-specific reference for vision screening. The progressive shift from hyperopia to myopia highlights the importance of early detection and monitoring to prevent visual impairment.