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

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

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

Answer: (D)

Morgan's norms give reference values for how the eyes should vergence at near in specific directions. For near base-out smooth vergences, the normative triplet describes how much convergence the eyes can produce before fusion is disrupted (the break point), how much convergence remains after re-establishing fusion (the recovery), and the overall near vergence capability in that direction. The pattern should show break greater than recovery, with a plausible total range. The triple 17/21/11 fits this: a break around 17 prism diopters, a recovery around 11 prism diopters, and an overall near BO range about 21 prism diopters. The other options either mix the values in a way that doesn’t match the expected relationship (recovery greater than break) or omit a necessary component, so they don’t align with Morgan's norms for near BO smooth vergences.

Morgan's norms give reference values for how the eyes should vergence at near in specific directions. For near base-out smooth vergences, the normative triplet describes how much convergence the eyes can produce before fusion is disrupted (the break point), how much convergence remains after re-establishing fusion (the recovery), and the overall near vergence capability in that direction. The pattern should show break greater than recovery, with a plausible total range. The triple 17/21/11 fits this: a break around 17 prism diopters, a recovery around 11 prism diopters, and an overall near BO range about 21 prism diopters. The other options either mix the values in a way that doesn’t match the expected relationship (recovery greater than break) or omit a necessary component, so they don’t align with Morgan's norms for near BO smooth vergences.