Fusional convergence in childhood intermittent exotropia

Purpose: To evaluate fusional convergence and associations with control in children with intermittent exotropia (XT). Design: Retrospective case series. Methods: Sixty-four children (median age 7 years) with intermittent XT were identified with measures of angle of deviation, control (using a previously reported 0-to-5-point scale), and fusional convergence at a single examination. Total convergence was defined as the sum of the angle of deviation plus additional convergence in reserve. Mean values were compared with published normals. A fusion reserve ratio was calculated as "convergence reserve divided by angle of deviation." Relationships of control score with total amplitude, reserve, recovery, and fusion reserve ratio were assessed using Spearman rank correlations. Results: Convergence differed from normals in children with intermittent XT: total convergence was higher at distance (33 prism diopters [pd] vs 17 pd, P <.0001) and near (38 pd vs 18 pd, P <.0001) whereas convergence reserve was lower at distance (7 pd vs 17 pd; P <.0001). There was a strong correlation between fusion reserve ratio and control score at distance (R = -0.75, P <.0001) and near (R = -0.66, P <.0001). Conclusions: Children with intermittent XT have subnormal convergence reserves at distance. The fusion reserve ratio correlates well with control and may be useful in grading the severity of intermittent XT.