Visual Convergence

Visual convergence is the process by which the eyes rotate inward toward the nose in order to align the fovea to enable focusing on a close object. Vergence eye movements are the only disconjugate (meaning that the eyes move in different directions) movements in the visual system. Convergence allows for perception of objects at varying distances and can be voluntary or reflexive. The brain is able to judge distance based upon the angle of convergence allowing for depth perception (Gregory 1990). Convergence is usually measured by instructing a patient to keep a target in focus while it moves toward their nose. The test ends when diplopia (or double vision) occurs and the near point of convergence (NPC) is measured (Miller and Newman 1999). Convergence is a skill that develops in the third month of infancy and shows deterioration (seen in the slowing of velocity and the onset of movement of convergence resulting in diplopia or double vision) with age (Leigh and Zee 1999). Common...