Heterophoria measured with white, dark-grey and dark-red Maddox rods

Abstract.

Background: Heterophoria is defined as a deviation from orthovergence position when no fusional contours are provided. It has been suggested that darkening one eye effects the phoric angle between the two eyes. We tested this assumption by comparing the phoric angles with white, dark-grey and dark-red Maddox rods. Methods: In a first group of 14 subjects horizontal heterophoria was measured with white, dark-grey and dark-red Maddox rods. In a second group of 43 different subjects horizontal heterophoria was measured with white and dark-red Maddox rods. Subjects were asked to continually correct any perceived deviation, using Herschel prisms. Readings were taken after 1 min. Results: Group 1 (n=14): No significant difference between white, dark-grey and dark-red Maddox rods (Friedmann test). Correlation between white and dark-grey Maddox rods r=0.97 (P<0.0001), slope of regression line 0.92 (95% confidence interval 0.78–1.06). Correlation between white and dark-red Maddox rods r=0.94 (P<0.0001), slope of regression line 0.67 (95% confidence interval 0.53–0.82). Group 2 (n=43): No significant difference between white and dark-red Maddox rods (Wilcoxon signed rank tests). Correlation r=0.96 (P<0.0001), slope of regression line 0.95 (95% confidence interval 0.87–1.03). Conclusion: Our study revealed no significant difference and a high correlation among the phoric angles obtained with white, dark-grey and dark-red Maddox rods. The close match suggests that darkening one eye does not effect the phoric angle between the two eyes.