Evaluation of horizontal fusional vergence in young children with intermittent exotropia using the synoptophore and prism bar

Purpose: The aim of the study was to compare the synoptophore and prism bar for assessing horizontal fusional vergence (HFV) in young children with intermittent exotropia (IXT).

Methods: The research involved ninety-eight subjects with IXT, aged between six and sixteen years. The examination included vision assessment, a cover test, identification of the dominant eye, and measurement of the angle of deviation using a prism bar. The subjects' HFV (positive and negative fusional vergence) was assessed using a horizontal prism bar and synoptophore at both near and far distances. We assessed IXT's control utilizing the Newcastle score for both near and far distances.

Results: The positive fusional vergence (PFV) break points of the synoptophore above those of the prism bar at both near and distance ranges (P < 0.01). There was a statistically significant difference in PFV recovery points for both near (P < 0.01) and distance (P < 0.01). There were no statistically significant changes in the near-negative fusional vergence (NFV) blur and break points as determined by the prism bar and synoptophore. The distance, NFV blur, and break points were larger on the synoptophore compared to the prism bar (P < 0.01).The difference in NFV recovery points was statistically significant at both near (P = 0.05) and distance (P = 0.03).

Conclusion: It is essential to exercise caution when assessing the PFV and NFV in young children with IXT, as the synoptophore and prism bar are not comparable in these kinds of situations.