The break point during smooth vergences represents the limit of which vergences?

• A. Limit of fusional vergence only
• B. Limit of accommodative vergence only
• C. Limit of accommodative and fusional vergence
• D. Limit of proximal vergence only

Answer: (C)

The break point in smooth vergence testing shows the limit of the vergence system to maintain a single image as demand increases. It reflects the combined capacity of accommodative vergence (how accommodation drives convergence via the AC/A link) and fusional vergence (the disparity-driven adjustment to maintain fusion). When either component can no longer supply enough vergence to keep images aligned, diplopia occurs, marking the break. Proximal vergence isn’t the limiting factor in this context, so the breakpoint specifically represents the limits of accommodative and fusional vergence together.