Comparison of phoropter and trial frame-based von Graefe heterophoria measures in non-presbyopic participants

Background: There are several clinical techniques for the subjective measurement of heterophoria. In South Africa, von Graefe (VG) is a commonly used technique to quantify heterophoria using the phoropter.Purpose: The purpose of the study was to investigate the agreement of VG heterophoria measurement using the phoropter and a trial frame.Setting: The study was conducted at an Optometry Clinic, University of Limpopo, South Africa.Methods: Both distance and near horizontal and vertical heterophoria VG measurements were performed on 88 visually-normal university students using the phoropter and trial frame. The handheld rotary prism was used on the trial frame. The 95% limits of agreement in prism diopters were compared using the Bland-Altman statistical test.Results: For distance horizontal heterophoria, the VG means were 0.39 exophoria ± 2.0Δ and 0.38 exophoria ± 1.8Δ with the phoropter and trial frame respectively. The means for near horizontal heterophoria were 3.69 exophoria ± 3.3Δ and 4.13 exophoria ± 3.27Δ with the phoropter and trial frame. For the vertical heterophoria at distance, the means and standard deviations were 0.18 hyperphoria ± 0.74 and 0.13 hyperphoria ± 0.07Δ, while at near vision they were 0.03 hyperphoria ± 0.71 and 0.07 hyperphoria ± 0.71Δ, respectively.Conclusion: Measurement of VG heterophoria testing using the phoropter and trial frame showed a high level of agreement for both distance and near vision performed through the phoropter and a trial frame. For clinical and research purposes, the phoropter and trial frame can be used interchangeably for measuring heterophoria.