Field of vergence limits.

The binocular visual field is the combined visual field obtained when the eyes are fixating a given point without head movements. The binocular field of fixation is the area within which central bifixation is possible by moving the eyes but not the head. This study introduces a new concept of the binocular field, namely, the vergence limit field, defined as the binocular field of fixation that allows for a specified amount of vergence eye movements at its limits. A newly developed instrument and technique were used to measure this field for a number of normal subjects.