Reliability of two dissociating tests of phoria in artificially created phoria in normal adults.

Background: The ability of physical therapists (PTs) to accurately identify and reliably measure phoria/tropia is critical in the differential diagnosis of individuals with acute vestibular syndrome and concussion/mild traumatic brain injury.

Objectives: To determine if PTs may reliably measure phoria and to determine the reliability of two dissociating tests of phoria, the prism neutralized Maddox rod test and modified Thorington method, in normal adults with artificially created phoria.

Methods: Thirty adults (mean age 24.87 ± 4.74 years) were randomly assigned to wear trial lenses (1, 2, 4, or 6 pd prism left, plain glass right) to create phoria. In sitting and supine, phoria was measured using prism neutralized Maddox rod test and modified Thorington method. Mean, SD, and range of first neutral endpoint were calculated for each examiner. Percentage of trials in agreement (≤ 2 and 4 pd); comparisons within the linear mixed effects regression model; and inter-rater reliability between examiners was calculated with the intra-class correlation coefficient (ICC).

Results: Participants underwent 20 measurements by each examiner. Trial agreement between examiners was 74% (range 13%-100%) in horizontal and 91% (range 63%-100%) in vertical plane. Maddox rod test had significantly different means between two examiners ( < .05). Modified Thorington test had no significant difference. The Maddox rod test had a significant examiner main effect, examiner 2 always scored lower. Inter-rater correlation coefficient for each test was significant at level of  < .01 (ICC ≥ 0.67 ≤ 0.94) except for modified Thorington test in supine, horizontal plane with  < .05 (ICC ≥ 0.38).

Conclusion: PTs may reliably measure artificially created phorias using prism neutralized Maddox rod test and modified Thorington method.