Which type of vergence is clinically measured as a distance phoria?

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

Answer: (B)

The resting baseline of eye alignment—tonic vergence—determines what we measure as a distance phoria. At distance, accommodation is minimal, so the eyes rely on this baseline vergence to stay aligned without extra focusing or near cues. A distance phoria reflects that inherent, resting alignment rather than the effort to fuse or accommodate. Accommodative vergence depends on focusing depth and is negligible at distance; proximal vergence is driven by perceived closeness and is a near-task cue; fusional vergence is the active adjustment used to maintain single vision when disparities occur, which isn’t what a distance phoria test isolates. So the distance phoria primarily represents tonic vergence.