Which vergence type is the primary driver of distance alignment in the absence of activation by accommodation or disparity cues?

• A. Proximal Vergence
• B. Tonic Vergence
• C. Fusional Vergence
• D. Accommodative Vergence

Answer: (B)

Tonic vergence is the resting, cue-independent baseline of the vergence system. It’s the natural alignment the eyes maintain when accommodation is relaxed and there are no disparity cues tugging the eyes to converge or diverge. In the absence of accommodation or disparity signals, this baseline tone is what primarily keeps the eyes in alignment for distant viewing.

Accommodative vergence would come into play if you were focusing up close, since it is driven by the need to accommodate. Fusional vergence relies on binocular disparity to correct misalignment, so it isn’t the driver when there’s no disparity cue. Proximal vergence depends on the perceived closeness of the object, which isn’t a strong motivator for distant targets without cues. Hence, the resting, cue-free baseline—tonic vergence—best explains distance alignment in this scenario.