Which is NOT a main type of vergence?

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

Answer: (C)

Vergence is driven by several distinct inputs that keep the eyes aligned. Tonic vergence is the baseline eye posture the system settles into in the absence of visual cues. Proximal vergence is triggered by the awareness that a target is at a near distance, prompting a preemptive adjustment even before disparity appears. Fusional vergence is the disparity-driven adjustment that realigns the eyes when images are misaligned, maintaining single vision. Accommodative vergence, tied to focusing on near objects via the accommodative-convergence reflex, is another well-established contributor, though not always listed as a separate option in every question. Eccentric vergence does not belong to this standard set of main vergence types. It’s not considered a primary driver of vergence in clinical classifications, so it’s the best answer for what is not a main type.