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

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

Answer: (B)

Morgan's norms give typical reference values for how much horizontal vergence a person can sustain smoothly, including distance base-out (BO) movements. When you test distance BO smooth vergence, you’re looking at how far the eyes can converge to maintain single vision as base-out prisms are introduced, and how much recovery is possible once the prisms are reduced.

The standard reference for distance BO smooth vergences is about 9 prism diopters to break, with a total vergence range around 19 prism diopters and a recovery near 10 prism diopters. The notation 9/19/10 captures these three aspects: the break point, the overall vergence range, and the recovery. This is why that option is the best match for Morgan’s norms of distance BO smooth vergences.

For context, near values are typically higher (e.g., around 13/21/13), reflecting greater vergence demand at close distances. Individual variation exists, but these figures serve as useful benchmarks when evaluating binocular function.