Normal AC/A ratio is?

Normal AC/A ratio is?

• A. 3:1
• B. 5:1
• C. 4:1
• D. 2:1

Answer: (C)

AC/A ratio shows how accommodation triggers convergence. It quantifies the amount of convergence the eyes use for a given amount of focusing effort, expressed as prism diopters of convergence per diopter of accommodation. The normal value is about four prism diopters of convergence for each diopter of accommodation, meaning when you focus enough to see something near (one diopter of accommodation), the eyes should converge by roughly four prism diopters to maintain single binocular vision. This coupling is a standard reference in clinical practice, so at typical near demands (around three diopters of accommodation), you’d expect about twelve prism diopters of convergence. While there’s a range cited in literature, four to one is the classic, textbook value. That’s why the normal AC/A ratio is four to one.

AC/A ratio shows how accommodation triggers convergence. It quantifies the amount of convergence the eyes use for a given amount of focusing effort, expressed as prism diopters of convergence per diopter of accommodation. The normal value is about four prism diopters of convergence for each diopter of accommodation, meaning when you focus enough to see something near (one diopter of accommodation), the eyes should converge by roughly four prism diopters to maintain single binocular vision. This coupling is a standard reference in clinical practice, so at typical near demands (around three diopters of accommodation), you’d expect about twelve prism diopters of convergence. While there’s a range cited in literature, four to one is the classic, textbook value. That’s why the normal AC/A ratio is four to one.