Library · Physiology
Binocular vision
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The two eyes are not in the same spot: they sit side by side, set apart from each other. That is why each one takes in a slightly different view of the same object, and binocular vision, seeing with both eyes, depends on that difference.
Even so we do not see double, and that has a name: fusion, the work the brain does to join the image from one retina with the image from the other and build a single one.
That small difference between the two images, called retinal disparity, is where stereopsis comes from: depth perception, being able to tell what is closer and what is farther away. With one eye there are other clues for judging distance, but stereopsis does not occur.
Picture two photos of the same scene taken one step apart from each other. If one eye drifts out of line, as in strabismus, that partnership breaks down and binocular vision can be lost.
In brief
Because the eyes are set apart from each other, they give two slightly different views of the same object.
Fusion is the neural process that merges those two images into one and makes binocular vision possible.
Stereopsis is the depth perception produced by that disparity, and it does not happen with one eye alone, even though monocular distance cues exist.
Two photos of the same scene taken one step to the right of each other.
If one eye becomes misaligned, as in strabismus, binocular vision can be lost.
Sources (2)
- Webvision, Moran Eye Center, University of Utah Health Sciences CenterThe Perception of Depth, Webvision: The Organization of the Retina and Visual SystemPublished
- National Center for Biotechnology Information, StatPearls PublishingStrabismus, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated