Abstract
<title>Abstract</title> <p>Background: Uncorrected refractive error remains one of the leading causes of preventable visual impairment among school-aged children, particularly in resource-limited settings where access to standardized vision screening remains challenging. Conventional visual acuity assessment using the Snellen chart requires trained personnel, controlled illumination, and adequate testing space, limiting its feasibility in large-scale school screening programs. This study aimed to develop and validate a portable device for remote visual acuity assessment among school children. Methods: A school-based cross-sectional validation study was conducted among 1,118 children aged 6–16 years in Mysuru and Chamarajanagar districts of Karnataka, India. Visual acuity measured using the developed portable device was compared with the standard Snellen chart, which served as the reference standard. Diagnostic performance was evaluated using sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), overall accuracy, and receiver operating characteristic (ROC) curve analysis. Agreement and reliability were assessed using intraclass correlation coefficients (ICC), Cronbach’s alpha, and Bland–Altman analysis. Results: The portable device demonstrated high diagnostic performance, with sensitivity of 87.2% (95% CI: 81.8–91.4), specificity of 97.2% (95% CI: 96.0–98.2), PPV of 86.8% (95% CI: 81.3–91.2), NPV of 97.3% (95% CI: 96.1–98.3), and overall accuracy of 95.4% (95% CI: 94.0–96.6). The area under the ROC curve was 0.922 (95% CI: 0.894–0.950; p < 0.001), indicating excellent discriminative ability. Agreement-based reliability showed a single-measure ICC of 0.79 and average-measure ICC of 0.93. Bland–Altman analysis demonstrated minimal systematic bias (mean bias: −0.00081 logMAR), with narrow limits of agreement, confirming strong agreement between the portable device and the reference standard. Conclusions: The portable visual acuity device demonstrated excellent diagnostic accuracy, strong reliability, and high agreement with the Snellen chart. The device represents a practical and scalable solution for school-based vision screening and may improve early detection of visual impairment in resource-limited settings.</p>