Relationships between fusional convergence, suppression depth, and exotropia control in intermittent exotropia

Purpose: To assess the correlation between the contribution rates of fusional convergence from the dominant and non-dominant eye and suppression depth and exotropia control. Study design: Cross-sectional prospective study. Methods: The fusional convergence of 25 participants with intermittent exotropia (mean age 10.8 ± 3.4; range 6-18 years) was measured with an eye-tracking system. The contribution rate was defined based on the amplitude of fusional convergence during refusion relative to the exo-deviation angle. The suppression depth was assessed, and exotropia control was evaluated using the intermittent exotropia Office Control Score. We analyzed the correlations between the contribution rate from the dominant and non-dominant eyes and the suppression depth or control score. Results: There was a negative correlation between the dominant eye's contribution rate and the suppression depth in both eyes (r =  -0.85, 95% confidence interval [CI]: -0.97 to - 0.20 in the fixated dominant eye and r =  -0.91, 95%CI: -0.95 to - 0.40 in the fixated non-dominant eye). There was a negative correlation between the dominant eye's contribution rate and the control score at a 4-meter distance (r =  -0.53, 95%CI: -0.76 to - 0.17). Conclusion: Suppression in intermittent exotropia patients could affect the fusional convergence in the dominant eye.