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In studies of binocular vision the horopter is the locus of points in space that yield single vision. This can be defined theoretically as the points in space which are imaged on corresponding points in the two retinas, that is, on anatomically identical points. An alternative definition is that it is the locus of points in space which make the same angles at the two eyes with the fixation lines. More usually it is defined empirically using some criterion. == History of the term == The horopter was first discovered in the eleventh century by Ibn al-Haytham, known to the west as "Alhazen". He built on the binocular vision work of Ptolemy and discovered that objects lying on a horizontal line passing through the fixation point resulted in single images, while objects a reasonable distance from this line resulted in double images.〔 It was only later that this line was described as a circular plane surrounding the viewer's head. The term ''horopter'' was introduced by Franciscus Aguilonius in the second of his six books in optics in 1613. In 1818, Gerhard Vieth argued from geometry that the horopter must be a circle passing through the fixation-point and the centers of the lenses of the two eyes. A few years later Johannes Müller made a similar conclusion for the horizontal plane containing the fixation point, although he did expect the horopter to be a surface in space (i.e., not restricted to the horizontal plane). The theoretical/geometrical horopter in the horizontal plane became known as the ''Vieth-Müller circle''. Howarth〔 later clarified that the geometrical horopter in the fixation plane is not a complete circle, but only its larger arc ranging from one nodal point (center of the eye lens) to the other. In 1838, Charles Wheatstone invented the stereoscope, allowing him to explore the empirical horopter.〔〔 He found that there were many points in space that yielded single vision; this is very different from the theoretical horopter, and subsequent authors have similarly found that the empirical horopter deviates from the form expected on the basis of simple geometry. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Horopter」の詳細全文を読む スポンサード リンク
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