Citation: Webber AL, Mandall TR, Molloy DT, Lister LJ, Birch EE. Worth 4 Dot App for determining size and depth of suppression. Trans Vis Sci Tech. 2020;9(4):9, https://doi.org/10. 1167/tvst.9.4.9 Purpose: To describe and evaluate an iOS application suppression test, Worth 4 Dot App (W4DApp), which was designed and developed to assess size and depth of suppression.Methods: Characteristics of sensory fusion were evaluated in 25 participants (age 12-69 years) with normal (n = 6) and abnormal (n = 19) binocular vision. Suppression zone size and classification of fusion were determined by W4DApp and by flashlight Worth 4 Dot (W4D) responses from 33 cm to 6 m. Measures of suppression depth were compared between the W4DApp, the flashlight W4D with neutral density filter bar and the dichoptic letters contrast balance index test.Results: There was high agreement in classification of fusion between the W4DApp method and that derived from flashlight W4D responses from 33 cm to 6 m (α = 0.817). There were no significant differences in success rates or in reliability between the W4DApp or the flashlight W4D methods for determining suppression zone size. W4DApp suppression zone size strongly correlated to that determined with the flashlight W4D (rho = 0.964, P < 0.001). W4DApp depth of suppression measures showed significantly higher success rates (χ 2 = 5.128, P = 0.043) and reliability (intraclass correlation analysis = 0.901) but no significant correlation to the depth of suppression calculated by flashlight W4D and neutral density bar (rho = 0.301, P = 0.399) or contrast balance index (rho = −0.018, P = 0.958). Conclusions:The W4DApp has potential clinical benefit in measuring suppression zone size; however, further modifications are required to improve validity of suppression depth measures.Translational Relevance: W4DApp iOS application will be a convenient tool for clinical determination of suppression characteristics.