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

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

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

Answer: (C)

Morgan's norms describe how much smooth vergence a person can maintain at distance and near, giving typical three-number patterns for each type of vergence. For near base-in (BI) smooth vergences, the standard reference is 13/21/13. The larger middle value reflects the break point where diplopia occurs as the eyes converge further. The outer values, both about 13, correspond to the recovery and blur thresholds, which are close to each other at near. This pattern matches the normative data used to interpret near BI vergence ranges, so 13/21/13 is the appropriate triple. The other options don’t align with these near BI norms, which is why they’re not the correct match.

Morgan's norms describe how much smooth vergence a person can maintain at distance and near, giving typical three-number patterns for each type of vergence. For near base-in (BI) smooth vergences, the standard reference is 13/21/13. The larger middle value reflects the break point where diplopia occurs as the eyes converge further. The outer values, both about 13, correspond to the recovery and blur thresholds, which are close to each other at near. This pattern matches the normative data used to interpret near BI vergence ranges, so 13/21/13 is the appropriate triple. The other options don’t align with these near BI norms, which is why they’re not the correct match.