A comparison of near-dissociated heterophoria tests in free space

Background: Many clinical techniques exist to quantify the magnitude of heterophoria in free space. In this article, we determine the agreement between the modified Thorington test and three different tests for dissociated heterophoria at near distance in free space. Methods: The modified Thorington, Maddox rod, von Graefe and alternate cover tests were performed on 49 university students at near distance in free space. The 95% limits of agreement between the modified Thorington and other tests were compared in pairs by using the Bland-Altman statistical test. Results: While the Maddox rod-modified Thorington pair showed narrow 95% limit range (2.5 to -3.34^Δ) between each other compared to the von Graefe-modified Thorington (4.2 to -3.15^Δ) and alternate cover test-modified Thorington pairs (4.52 to -2.77^Δ), none of the three tests showed good agreement with the modified Thorington test. Conclusion: The modified Thorington test cannot be interchanged with the other three near tests for heterophoria in free space. The accuracy in the measurement and the different methods of dissociation may play a crucial role in comparisons of the different tests for heterophoria.