Inter-Examiner Repeatability of Heterophoria Tests

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Relatively few studies have reported on the repeatability of heterophoria (phoria) measurement procedures. The purpose of this study was to assess the inter-examiner repeatability of seven clinical tests of phoria measurement, using correlational and mean difference analyses. Two experienced optometrists performed each of the 7 phoria tests on 72 healthy adult subjects. Subjects ranged in age from 22 to 40 years, had visual acuity correctable to 20/20 in each eye, had no strabismus or amblyopia, and had normal eye health. The seven phoria tests used were: (1) the estimated cover test, (2) the prism-neutralized objective cover test, (3) the prism-neutralized cover test with subjective reporting of target movement, (4) the von Graefe phorometry with continuous target presentation, (5) the von Graefe phorometry with flashed target presentation, (6) the Thorington method, and (7) the modified Thorington method. All tests were performed in the same way by both examiners in random sequence, using standard clinical procedures. Inter-examiner correlations were determined for each test, as well as the mean and standard deviation of the differences between each examiner measurement (in prism diopters) on each subject. The modified Thorington method had the smallest mean difference and standard deviation of all tests and, thus, may be considered the most repeatable. This test also had the highest inter-examiner correlation. The prism-neutralized cover test with subjective reporting of target movement had the second highest correlation and the second lowest 95% limits of agreement, but had the largest mean difference of all tests, von Graefe phorometry methods were the least repeatable of the phoria tests.

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