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

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

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

Answer: (C)

Morgan's norms give typical ranges for smooth vergences at near, used to judge binocular function. For near base-in smooth vergences, the expected values show how much base-in prism you can apply before breaking fusion, how much you need to recover single vision after breaking, and the amount you can sustain in that near-range. The standard set is 13/21/13 prism diopters, meaning a break at about 13 PD BI, a recovery at about 21 PD BI, and a similar near-range reserve of about 13 PD. This is why 13/21/13 is the best answer—it matches the established near BI smooth vergence norms.

Morgan's norms give typical ranges for smooth vergences at near, used to judge binocular function. For near base-in smooth vergences, the expected values show how much base-in prism you can apply before breaking fusion, how much you need to recover single vision after breaking, and the amount you can sustain in that near-range. The standard set is 13/21/13 prism diopters, meaning a break at about 13 PD BI, a recovery at about 21 PD BI, and a similar near-range reserve of about 13 PD. This is why 13/21/13 is the best answer—it matches the established near BI smooth vergence norms.