Long-term test and retest reliability of clinical vergence testing

Purpose: To establish long-term reliability measures for vergence testing in a control population of adolescents. Methods: Healthy participants between 12 and 17.5 years with normal binocular vision were recruited from 10 clinical sites. Cover test, near point of convergence (NPC), positive and negative fusional vergences, vergence facility (12∆ base-out/3∆ base-in) and vergence jumps (using the Oculomotor Assessment Tool) were performed at the initial visit and repeated at 90 days. The mean and standard deviation were calculated for the overall group for NPC, vergence facility and vergence jumps and by prism dioptre step value for PFV and NFV (1Δ or 2Δ if below 20∆ or 5Δ above 20∆). Agreement was assessed using Bland–Altman plots and 95% limits of agreement (LOA). Results: Ninety-three participants (mean age 14.3 ± 1.7 years, 52% female) were enrolled and 91 (98%) completed the initial and 90-day outcome evaluation. The mean differences were significantly greater than zero for vergence facility (p < 0.05) and the first and second 30 s of vergence jumps (p < 0.01). The 95% LOA were narrow for NPC (±2.5) and negative fusional vergence (±5.9), suggesting good repeatability. LOA were larger for positive fusional vergence (±17.8), vergence facility (±9.8) and vergence jumps (±16.2). Analysis of the positive fusional vergence data indicates that the different step sizes (1∆ or 2∆ vs. 5∆) in the horizontal prism bar contribute to considerably larger variability in these measures. Conclusions: In participants with normal binocular vision and no concussion history, good reliability yielded comparable results 90 days apart for all vergence measures. The results provide values that can be used to interpret the effect of intervention for vergence disorders in clinical practice and research studies. An important outcome of this study is the understanding that 5∆ steps on the typical horizontal prism bar contribute to high variability in positive fusional vergence measures when findings are ≥20∆.