monocular

Monocular describes anything related to a single eye or suitable for use with one eye. The term derives from Latin unus ("one") and oculus ("eye"), and is commonly contrasted with binocular, which involves both eyes. In biology and perception, monocular vision refers to vision produced by one eye. Many birds and some fish have eyes placed laterally, yielding broad monocular fields with limited overlap; humans have binocular overlap but can rely on monocular cues for depth perception when one eye is closed. Depth from monocular vision relies on cues such as motion parallax, relative size, perspective, occlusion, texture gradient, and shading, enabling depth judgments even without two-eyed disparity.

A monocular is a compact, single-lens optical instrument used for viewing at a distance; essentially a small telescope for one eye. It typically provides magnification from about 2x to 10x, and is favored for portability and quick use in outdoor observation, surveillance, or astronomy. It differs from a binocular telescope in size and field of view.

In medical contexts, monocular refers to functions or conditions involving only one eye, such as monocular vision loss, monocular diplopia, or monocular blindness. Clinically, assessments may distinguish monocular from binocular deficits to determine contributions of eye health and brain processing to visual function.