\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.