What are the Morgan's norms for Distance BI smooth vergences?

• A. -----/7/4
• B. 9/19/10
• C. 13/21/13
• D. 17/21/11

Answer: (A)

Morgan's norms give the typical fusional vergence limits at distance and near, telling you how much divergence or convergence a person can maintain before diplopia appears and how well they recover after the prism is removed. For distance base-in (BI) smooth vergences, the expected values are a break around 7 prism diopters and a recovery around 4 prism diopters. The dash before the numbers indicates there isn’t a blur value reported for this measure in this norm set, since smooth BI vergence testing focuses on break and recovery rather than a separate blur threshold. So the standard presentation is a dash for blur, then 7 for break, and 4 for recovery. The other reported sets would imply much larger ranges than Morgan's norms indicate for distance BI, which is why they don’t fit.