Smartphone-Based Campbell-Robson Contrast Sensitivity Assessment: Repeatability and Systematic Bias Relative to the Freiburg Acuity and Contrast Test

Purpose: SmartCS is a smartphone-based application developed to assess contrast sensitivity (CS) using a continuous Campbell-Robson grating. This study evaluated the repeatability of SmartCS measurements and their systematic bias relative to the Freiburg Acuity and Contrast Test (FrACT). Methods: Sixty adults underwent near-distance monocular CS assessment using both SmartCS and FrACT under standardized conditions. Intrasession repeatability was evaluated in forty participants who completed two tests on the same day, while intersession repeatability was assessed in twenty participants tested on separate days. Results: SmartCS demonstrated acceptable reliability, although somewhat lower than that of FrACT. SmartCS consistently yielded higher CS values, likely attributable to differences in stimulus presentation. Notably, SmartCS required a significantly shorter testing time, with an average duration of approximately 30 seconds compared with over two minutes for FrACT. Conclusions: The touchscreen-based tracing interface allows rapid and intuitive delineation of the CS profile, offering a more efficient and user-friendly approach. Our results support the reliability of SmartCS, and thus it provides a practical, low-cost alternative for CS assessment in both clinical and remote settings. However, a systematic positive bias relative to FrACT was observed, indicating that SmartCS values are not directly interchangeable with those of optotype-based instruments, and a SmartCS-specific normative dataset will be required before diagnostic use.