Which Morgan's norms triple corresponds to Distance BI smooth vergences?

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

Answer: (A)

Morgan's norms describe typical smooth vergence responses as a three-part numeric pattern for different viewing conditions. For distance base-in (BI) smooth vergences, the important idea is that the first component is not applicable at that distance (hence a placeholder or dash), while the relevant break and recovery values are the numbers that define the patient’s ability to diverge to maintain single vision when BI prisms are used at distance. In this case, the distance BI smooth vergence norms are represented as a placeholder in the first slot, followed by a break value of about 7 prism diopters and a recovery value of about 4 prism diopters. That’s why the correct triple is blank/7/4. The other options would correspond to different vergence demands (such as other distances or other fusional vergence types) and don’t match the distance BI smooth vergence pattern.