No agreement between expected phoropter Risley prism and prism bar fusional vergences in a prospective cross-sectional study of African school children

Purpose: To determine the agreement between phoropter Risley prism and prism bar fusional vergence amplitudes in a normative group of school-aged children, aged 8 to 17 years. Method: This prospective cross-sectional study utilized multistage sampling to recruit participants with normal binocular vision. Horizontal fusional vergence amplitudes were measured at distance and near using the phoropter with Risley prisms and the prism bar. Result: The study included 422 normal participants (48.1% male, 51.9% female) with a mean age of 12.39 ± 1.94 years. There were significant differences in the base-in break, base-in recovery, base-out blur, base-out break, and base-out recovery at distance and near between phoropter Risley prism and prism bar fusional vergences (p < 0.05); amplitudes for phoropter Risley prism were higher than that for prism bar. Their mean differences were clinically meaningful except for base-in recovery at distance; however, there was no level of agreement on Bland Altman analysis. Conclusion: Fusional vergence amplitudes measured with the phoropter Risley prism and prism bar should not be considered interchangeable in African schoolchildren.