Comparison, within-session repeatability and normative data of three phoria tests

Purpose: Phoria measurements form a routine part of the examination of binocular vision. Various studies have compared different methods of phoria measurement and their repeatability between sessions. However, no studies have accounted for within-session repeatability, and few norms have been available to date. Our aims were to assess the short-term within-session repeatability, the agreement and the comparisons between three phoria tests and the delineation of normative data. Method: The participants comprised 315 refractive corrected participants with a normal binocular vision, with ages between 20 and 80 years. Phoria was measured using three methods: von Graefe (VG), modified Thorington (MT) and Thorighton (TH) procedures. Each measurement was taken 3 consecutive times at far and near. Results: The repeatability between measurements was high (0.87 to 0.96), but the relationship between tests was medium (0.407 to 0.682). About the mean bias, VG show more exo values (0.02 to 0.14 at far and 0.07 to 0.14 at near) and MT and TH similar values (−0.04 to 0.08 at far and −0.1 to 0.03 at near). The best agreement between tests was for TH and MT (LoA = 2.33 at far and LoA = 4.44 at near). Normative data for non-presbyopic were provided. Conclusion: Overall, there is a high agreement between MT and TH. Conversely, VG shows more exo values at near and shows large limits of agreement. We recommend that subjective measurements of phoria can best be quantified once using the MT or TH techniques in free space and the values compared with updated norms.