The Collaborative International Dictionary of English v.0.48:

Vision \Vi"sion\, n. [OE. visioun, F. vision, fr. L. visio, from
   videre, visum, to see: akin to Gr. ? to see, ? I know, and E.
   wit. See Wit, v., and cf. Advice, Clairvoyant, Envy,
   Evident, Provide, Revise, Survey, View, Visage,
   Visit.]
   1. The act of seeing external objects; actual sight.
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            Faith here is turned into vision there. --Hammond.
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   2. (Physiol.) The faculty of seeing; sight; one of the five
      senses, by which colors and the physical qualities of
      external objects are appreciated as a result of the
      stimulating action of light on the sensitive retina, an
      expansion of the optic nerve.
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   3. That which is seen; an object of sight. --Shak.
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   4. Especially, that which is seen otherwise than by the
      ordinary sight, or the rational eye; a supernatural,
      prophetic, or imaginary sight; an apparition; a phantom; a
      specter; as, the visions of Isaiah.
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            The baseless fabric of this vision.   --Shak.
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            No dreams, but visions strange.       --Sir P.
                                                  Sidney.
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   5. Hence, something unreal or imaginary; a creation of fancy.
      --Locke.
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   Arc of vision (Astron.), the arc which measures the least
      distance from the sun at which, when the sun is below the
      horizon, a star or planet emerging from his rays becomes
      visible.

   Beatific vision (Theol.), the immediate sight of God in
      heaven.

   Direct vision (Opt.), vision when the image of the object
      falls directly on the yellow spot (see under Yellow);
      also, vision by means of rays which are not deviated from
      their original direction.

   Field of vision, field of view. See under Field.

   Indirect vision (Opt.), vision when the rays of light from
      an object fall upon the peripheral parts of the retina.

   Reflected vision, or Refracted vision, vision by rays
      reflected from mirrors, or refracted by lenses or prisms,
      respectively.

   Vision purple. (Physiol.) See Visual purple, under
      Visual.
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WordNet (r) 3.0 (2006):

field of vision
    n 1: all of the points of the physical environment that can be
         perceived by a stable eye at a given moment [syn: visual
         field, field of vision, field of regard]