Refraction and muscular imbalance, as simplified through the use of the ski-optometer

by Daniel Woolf

Movements of Convergence

In order to see an object at a nearby point, the eyes have to converge—a movement affected by a simultaneous and equal contraction of both internal recti. This movement may be combined with a vertical, lateral or oblique parallel movement. Thus, when we wish to look at a near object situated twenty degrees to our right, we first turn both eyes twenty degrees to the right, then converge both equally, turning the left a little more to the right and the right a little back toward the left.

Convergence is governed by a distinct mechanism of the nerves, the source of which has not been determined.