The Howell phoria card, a new modification of the Prentice design, has no previously published validity or reliability data. The purpose of this study was to compare the interexaminer repeatability of the Howell phoria card with established tests.
Experienced optometrists measured the near heterophoria of 72 subjects. Heterophoria was measured in a pseudo-random order using five standardized procedures: (1) Howell phoria card continuous presentation, (2) Howell phoria card flashed presentation, (3) free-space von Graefe method, 4) Bernell Muscle Imbalance Measure (MIM) card continuous presentation, and (5) MIM card flashed presentation.
The von Graefe method and the Howell phoria card flashed presentation found significantly less exophoric results than the MIM card. There was no consistent tendency for different examiners to find more exo- or more esophoric results with the phoria measurement techniques used in this study (p = 0.28). Both the Howell phoria card continuous presentation and the MIM card had significantly less variability in interexaminer differences than the Howell phoria card flashed presentation and the von Graefe method (p < 0.05).
Results from this study suggest that the Howell phoria card used in a continuous presentation method has an interexaminer repeatability that is not significantly different from the MIM card but greater than the von Graefe method.