What is "horopter"

Horopter \Ho*rop"ter\, n. [Gr. ? boundary + ? one who looks.] (Opt.) The line or surface in which are situated all the points which are seen single while the point of sight, or the adjustment of the eyes, remains unchanged.

The sum of all the points which are seen single, while the point of sight remains unchanged, is called the horopter.
--J. Le Conte.

n. For any system of binocular vision, the '''horopter''' is a three-dimensional curve which contains all points from which the light will converge into a single image.

In studies of binocular vision the horopter is the locus of points in space have the same disparity as fixation. This can be defined theoretically as the points in space which project on corresponding points in the two retinas, that is, on anatomically identical points. The horopter can be measured empirically in which it is defined using some criterion.