How repeatable are measures of heterophoria? Implications for clinical practice

Purpose: Heterophoria measurement is a common clinical technique used in the diagnosis of binocular vision anomalies, the most common of which is convergence insufficiency (CI). The purpose of this study was to assess the intra- and inter-examiner variability of four clinical tests of heterophoria measurements. Methods: Distance and near heterophorias of 20 visually-normal adults were measured using four different techniques (alternating prism cover test, von Graefe, Howell Card and Maddox Rod) on different days, by two separate examiners using standardized instructions and clinical techniques. Results: The Howell Card had the best inter-examiner agreement at both distance (95% limits of agreement = ±1.57 prism diopters (PD)) and near (95% LOA = ±1.91 PD). Intra-examiner agreement was also best for the distance Howell Card (95% LOA = ±1.63 PD) and near (95% LOA = ±2.41 PD). Conclusions: Howell Card is the most repeatable test both between examiners and over time.