This study sought to investigate the agreement between the phoropter Risley and the prism bar prism fusional vergence amplitudes among a normal sample of Ghanaian children aged 8–17 years. This was a school-based study of 2300 children. Of 2300, 116 dropped out and 1712 were excluded because of various visual conditions (amblyopia, strabismus, ocular pathology, etc.) leaving 422 for analysis (203 male, 219 female). Mean age was 12.39 ±1.84 years. There were no significant differences in measurements for males vs. females. Significant differences were found for prism bar fusional vergence amplitudes for base out blur and near and distance, but these were not clinically significant. Base out measures were greater than base in for all measurements as expected. Blur, break and recovery values were significantly greater with Risley vs. prism bar measures and of clinical significance. However, no level agreement was evident on Bland Altman analysis. The authors conclude both forms of prism fusional vergence are not interchangeable. Differences are likely because of gradual increases in prism strength with Risley (1 prism dioptre steps) vs. larger step increments with prism bar measures of 1–5 prism dioptres.
Prism fusional vergence measures for Risley vs prism bar measurements
Reviewed by Fiona Rowe
No agreement between expected phoropter Risley prism and prism bar fusional vergences in a prospective cross-sectional study of African school children.
CONTRIBUTOR
Fiona Rowe (Prof)
Institute of Population Health, University of Liverpool, UK.
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