Ho-rŏp'ter, n.

n. [Gr. ὅρος, boundary, and ὀπτήρ, one who looks, root ὀπ, to see.] (Opt.) The right line drawn through the point of intersection of the two optic axes, and parallel to a line joining the pupils of the two eyes.

Plane of the horopter, the plane in which lies the horopter, and which is perpendicular to the axis of vision. It is the plane at which the optic axes meet, producing single vision, with any given binocular parallax; or it is the limit of distinct vision.