||Because the two eyes are separated laterally by about 6 cm, each eye sees a slightly different view of the world. Visible features lying at different distances from the head are imaged at slightly different positions in each of the two eyes. These small differences in retinal positions, called disparities, are the basis of human stereopsis. In normal observers, features with different disparities appear at different depths. Disparity is, by no means, the only cue to depth. If you close one eye, the visible world does not flatten into a two-dimensional surface, so clearly there are other powerful sources of depth information. Moreover, roughly 5% of the human population has no or very weak stereopsis, yet these stereo-blind individuals function well in natural environments.
For more information, visit