Comparative analysis of Modified Thorington to the prism cover, von Graefe and Maddox rod tests

Background: Heterophoria measurement is important in the evaluation of binocular vision. There are many different methods of heterophoria measurement. There are various methods of heterophoria measurements, and studies have compared different methods, some reporting little difference between the methods while others reported that measures can be significantly different.Aim: The purpose of this study was to compare heterophoria measurements obtained using four clinical methods, that is, the modified Thorington test (MTT) on the Bernell Muscle Imbalance Measure (MIM) with those obtained from the prism cover test (PCT), Von Graefe test (VGT) and Maddox rod test (MRT), and thereby to establish their interchangeability.Setting: The study was performed at an optometric clinic within a South African university.Methods: Dissociated near horizontal heterophoria was measured on a sample of 30 optometry students (ages 19–25 years) using the PCT, VGT, MRT and MTT. Three measurements for each of the four tests per participant were obtained, and thereafter the means were applied in analysis of the results. Agreement between paired tests was assessed using Bland–Altman plots.Results: The means for near or proximal heterophoria obtained using the four tests were −2.63 ± 1.9Δ, −2.90 ± 1.7Δ, −3.37 ± 2.0Δ and −2.47 ± 1.9Δ, with a strong correlation for each pair (p = 0.00) (minus signs indicate exophoria [XOP]). Among the different combinations of tests, the MTT and PCT showed the best agreement, although the reliability was good for all four tests.Conclusion: The measurement of near heterophoria can best be quantified either using the MTT or PCT because they showed the greatest level of agreement.