Comparative assessment of fusional vergences in adults with heterophoria using synoptophore and prism bar

<i>Purpose:</i> The aim of the study was to compare the amplitudes of negative and positive fusional vergences in exophoria and esophoria using a synoptophore and prism bar. <i>Methods</i>: A prospective study was conducted from May to July 2024 among university students. In participants with mild to moderate heterophoria, horizontal fusional vergence amplitudes (blur, break and recovery points) were assessed for distance using prism bar and synoptophore. Consistent testing conditions and standardized procedures were maintained. Data were analyzed using SPSS v26 with the Wilcoxon signed-rank test. <i>p</i> values less than 0.05 were considered as statistically significant. To assess the level of difference between values from synoptophore and prism bar, descriptive statistics was used across heterophoria grades. <i>Results</i>: A total of 60 participants were divided into mild (<10 PD) and moderate (>10-20 PD) exophoria and esophoria groups (<i>n</i> = 15 each). The values obtained from synoptophore yielded consistently higher fusional vergences than prism bar. In mild exophoria, the synoptophore had small, but statistically significant higher negative fusional vergence break point (11.8 ± 1.15 PD) than the prism bar (10.53 ± 1.55 PD, <i>p</i> < .05), as with the positive fusional vergence break (17.27 ± 1.75 PD vs. 15.4 ± 1.71 PD, <i>p</i> < .05). In mild esophoria, the synoptophore had a greater positive fusional vergence break (23.33 ± 1.05 PD) compared to the prism bar (22.33 ± 1.05 PD, <i>p</i> < .05). For moderate deviations, higher values for blur, break and recovery points were seen with the values obtained from synoptophore in both positive and negative fusional vergence. <i>Conclusion</i>: The negative and positive fusional vergences were higher when measured with the synoptophore than the prism bar in both mild and moderate deviations, consistent with earlier research and reinforcing the need for further studies to establish clinical relevance.