Binocular cues are depth cues that depend on the use of both eyes. Because the eyes are separated horizontally, each receives a slightly different view of the world; the visual system exploits that difference to recover depth.

The primary binocular cue is retinal disparity. Nearby objects produce a larger difference between the two retinal images than distant objects. The brain’s disparity-sensitive neurons compute depth from that difference. Convergence—the inward turning of the eyes when fixating a near object—provides a secondary cue, especially at close range. Together these cues support precise depth judgments within a few meters.

Binocular cues are not the only source of depth information. Monocular cues such as relative size, occlusion, and motion parallax work with one eye alone and dominate at greater distances. Yet the fine stereo vision that allows us to thread a needle or catch a ball relies heavily on binocular disparity. People who lack stereo vision from early childhood often develop compensatory reliance on monocular cues and may not notice the deficit until tested.

Three-dimensional movies and virtual-reality displays work by presenting each eye with a slightly different image, artificially recreating the natural binocular cue.