Assessing divergence in children with intermittent exotropia

Purpose: To report fusional divergence in children with intermittent exotropia (XT). Methods: We retrospectively studied 32 children with intermittent XT (aged 4 to 13 years) and 38 visually normal non-strabismic children. Fusional divergence break points were measured using a prism bar, starting from a naturally fused state. Distribution of divergence break points was evaluated. Subnormal fusional divergence was defined as below the 5th percentile in visually normal children. In children with intermittent XT, correlations were calculated between divergence break point and control score, angle of deviation, and convergence break point. Results: The distribution of fusional divergence break points in intermittent XT was normal at near but bimodal at distance. Nine percent had subnormal divergence (<10 prism diopters [pd]) at near, and 48% (<6 pd) at distance. There was a moderate correlation between divergence and convergence break points at near (r=0.44; P=.01) but only weak inverse correlations between divergence break point and control score (r=0.29; P=.11) and divergence break point and angle of deviation (r=0.08; P=.68) at near. Conclusions: Most children with intermittent XT have normal near fusional divergence but nearly half have reduced distance fusional divergence. We found the magnitude of near divergence break point correlates with the magnitude of near convergence break point. Measuring divergence may provide useful information about fragility of fusion in patients with intermittent XT. Future studies of fusional divergence are needed to establish whether common measurement methods represent true divergence amplitudes and whether such measures have prognostic significance.