Ametropia, commonly referred to as refractive error, is one of the leading causes of preventable visual impairment worldwide and remains a significant public health concern among school-aged children. This study investigated the effect of ametropia on the academic performance of secondary school students in Owerri Municipal Local Government Area (LGA), Imo State, Nigeria. A descriptive cross-sectional study design was adopted, involving 350 students aged 10–18 years who were randomly selected using a stratified sampling technique from two secondary schools within the municipality. Visual acuity assessment was conducted using the Snellen chart, pinhole test, and occlusion method, while academic performance data were obtained from official school records. Findings revealed that 75.71% of the students had normal visual acuity, whereas 24.29% presented with reduced visual acuity attributable to ametropia. Statistical analysis demonstrated a significant association between visual acuity status and academic performance (p < 0.05). Students with normal visual acuity performed significantly better academically compared to their counterparts with reduced visual acuity. These findings underscore the negative impact of uncorrected ametropia on educational achievement among secondary school children. The study highlights the importance of early detection, routine school vision screening programs, and prompt optical correction to prevent avoidable academic setbacks. Strengthening school-based eye health services within Owerri Municipal LGA and similar settings may contribute significantly to improved educational outcomes and overall child development.