An Introduction to Binocular Vision & Stereopsis. Why 2 Eyes are better than 1!

Abstract Purpose In visual normals, covering one eye does not markedly alter central vision. However, having two eyes confers at least 2 advantages. 1. Binocular Summation: performance is generally better on tasks when both eyes are open; and 2. Stereopsis: the recovery of information about depth that results from disparity in the retinal images in the right & left eyes. Indeed stereopsis is usually considered to be the ultimate in binocular co‐operation. Methods The precise value of stereopsis remains somewhat controversial. Good stereopsis is highly valued by those who enjoy it and its loss due to trauma/pathology has a major negative impact. However, a significant minority of the population (>5%, many of whom have strabismus and/or amblyopia) have never had clinically measurable stereopsis and they appear to behave little different from visual normals in everyday tasks. If stereopsis is so valuable, why does its absence seemingly have so few consequences? Results Here we examine the many facets of this conundrum, highlighting how, for example, many of those apparently without stereopsis when tested with standard clinical tests may in fact be capable of extracting depth‐from‐disparity information in lab‐based testing. It also emerges that those with reduced/absent stereopsis do exhibit differences relative to normals on fine motor tasks. And, when asked, these individuals often report avoidance of, or poor performance in, tasks relying upon good stereopsis. Conclusion As well as introducing the symposium presentations, this talk will summarise the recent research literature on the importance of binocular vision & stereopsis. This shows that, as in visual normals, 2 eyes are better than 1 in seemingly stereo‐deficient individuals, but the binocular advantage is reduced.