Monocular cues are depth cues that can be perceived with one eye alone. They allow a rich sense of three-dimensional space even when binocular disparity is unavailable.

Relative size, interposition, linear perspective, texture gradient, relative height, relative motion, and light and shadow all supply information about distance. A smaller retinal image of a familiar object is interpreted as farther away. An object that blocks another is seen as closer. Parallel lines appear to converge in the distance. These cues are heavily exploited by painters and by the designers of two-dimensional images that must convey depth.

Monocular cues become especially important at greater distances, where binocular disparity weakens, and for people who lack stereo vision. They operate automatically and in combination, producing a stable perception of layout under ordinary viewing conditions.

Even with one eye closed, the world retains its depth. Monocular cues make that possible.