Comparison of subjective heterophoria testing with a phoropter and trial frame

Purpose. Subjective measurement of the oculomotor deviation at both distance and near is a standard test in optometric practice. A number of procedures are available to the practitioner, and previous studies have demonstrated differences in the repeatability of many of the techniques. However, it is unclear whether testing the subject through a phoropter or in free space (trial frame) will alter the oculomotor deviation. Methods. Distance and near heterophoria was measured in 60 visually normal subjects between 20 and 34 years of age using the Von Graefe (VG), Maddox Rod (MR), and Modified Thorington (MT) procedures. The deviation was assessed for viewing distances of 6 m and 0.40 m using both a phoropter and trial frame. To examine the repeatability of each technique, the deviation was measured on two separate occasions for each procedure, with the two sessions being separated by at least 24 hours. Results. The mean vertical deviations at both distance and near were extremely close to orthophoria, and only minimal variation was observed. However, the MR procedure, when used with a trial frame, gave the best repeatability for measuring vertical deviations both at distance and near. Regarding horizontal deviations, the repeatability was better for all three procedures when using a trial frame compared with the phoropter. The best repeatability at distance and near was observed when the MT and MR techniques, respectively, were used with the trial frame. Consistent with previous reports, the VG procedure had poor repeatability, especially when used with the phoropter, and the mean findings showed a greater exo deviation when compared with the other two techniques. Conclusions. Testing oculomotor deviations in free space provides a more repeatable response than when using a phoropter. Accordingly, we recommend that subjective measurements of heterophoria in the clinical setting can best be quantified using either the MR or MT techniques in free space.