Visual acuity measurements with pictorial minimum-separable optotypes show preliminary agreement with a four-direction clinical Landolt ring test in adults

This study compared visual acuity measurements obtained with three pictorial minimum-separable optotypes and a four-direction clinical Landolt ring under identical tablet-based conditions. Thirty adults (mean age, 22.6 ± 3.5 years) without ocular disease other than refractive error were tested monocularly without refractive correction at 3 m. The pictorial task required participants to identify which of two side-by-side images contained gaps. Mean logMAR acuities were 0.49 ± 0.32 for the Landolt ring and 0.50 ± 0.31, 0.51 ± 0.32, and 0.50 ± 0.32 for the banana, ice cream, and tree optotypes, respectively; the four conditions did not differ significantly (Friedman χ²(3) = 1.33, P = 0.72). Bland–Altman mean biases (Landolt ring minus pictorial optotype) were − 0.003, − 0.013, and − 0.010 logMAR, with 95% limits of agreement of − 0.16 to 0.16, − 0.17 to 0.14, and − 0.17 to 0.15, respectively. No significant fixed or proportional bias was detected. These findings provide preliminary within-subject agreement data in cooperative adults under the specific 3-m testing conditions and predefined line-pass criteria. They do not establish equivalence with an ISO/DIN Landolt-C standard, clinical interchangeability, measurement reliability, or pediatric screening validity.