Stereopsie

Stereopsie, or stereopsis in English, is the perception of depth that arises from binocular disparity. When both eyes view a scene, each eye receives a slightly different image; the brain fuses these two views to produce a single, three‑dimensional percept. The primary cue for stereopsis is binocular disparity—the spatial offset between corresponding retinal points for objects at different depths. The brain combines disparity information with signals from vergence (eye alignment) and accommodation to generate depth perception. While many depth cues—perspective, shading, motion parallax—assist depth perception, stereo depth relies on accurate binocular correspondence.

Development and measurement: Stereopsie begins to develop in infancy with the establishment of stable binocular alignment and continues to refine into childhood. Normal stereoacuity in healthy adults is typically in the range of about 20 to 60 arcseconds, with variation among individuals. Clinically, stereoacuity is assessed with tests such as the Titmus or Randot tests, the TNO test, or random-dot stereograms. Values are reported in arcseconds; smaller values denote finer depth resolution.

Clinical significance: Reduced or absent stereopsie signals binocular vision disorders such as strabismus, anisometropia, or amblyopia, and may accompany ocular pathology or aging. Treatment focuses on restoring binocular input and alignment and may include vision therapy, occlusion (patching), refractive correction, prisms, or surgery in selected cases. Even when stereopsis is diminished, other depth cues remain functional and useful for daily tasks.

History: The concept has historical roots in Wheatstone's 1838 stereoscope, which demonstrated depth perception from two slightly different images. Later work, including Bela Julesz's random-dot stereograms, helped delineate the neural processing of stereopsis.