Comparison of near heterophoria tests under varying conditions on an adult sample

Purpose: This study compared the near phoria measurement using the Bernell muscle balance card with and without prism neutralization, using both trial frame and phoropter correction, and compared with the conventional Maddox rod method. Methods: Forty young normal Chinese adults had their near phoria measured with trial frame correction using the conventional muscle balance card method (method 1). Any deviation was compensated with a prism bar as an alternative approach (method 2). The conventional Maddox rod method (method 3) was also carried out for comparison. These three methods were repeated with phoropter correction and considered as methods 4, 5 and 6. Results: The phorias obtained from these six methods were not significantly different from each other (repeated measures ANOVA, p > 0.05). More than half of the subjects were exophoric. Although the difference in phoria was not significant, phoria measurement using phoropter correction yielded a greater coefficient of variation. Conclusions: Near phoria measurement using the muscle balance card conducted with trial frame correction was less variable, and was also more natural and similar to a real reading situation. The use of prism for compensation did not affect the phoria results. Exophoria seems to be more common than esophoria in young Chinese adults.