\Op"tic\, n. [From {Optic}, a.]
1. The organ of sight; an eye.
         The difference is as great between The optics
         seeing, as the object seen.           --Pope.
2. An eyeglass. [Obs.] --Herbert.

\Op"tic\, Optical \Op"tic*al\, a. [F. optique, Gr. ?; akin
to ? sight, ? I have seen, ? I shall see, and to ? the two
eyes, ? face, L. oculus eye. See {Ocular}, {Eye}, and cf.
{Canopy}, {Ophthalmia}.]
1. Of or pertaining to vision or sight.
         The moon, whose orb Through optic glass the Tuscan
         artist views.                         --Milton.
2. Of or pertaining to the eye; ocular; as, the optic nerves
   (the first pair of cranial nerves) which are distributed
   to the retina. See Illust. of {Brain}, and {Eye}.
3. Relating to the science of optics; as, optical works.
{Optic angle} (Opt.), the angle included between the optic
   axes of the two eyes when directed to the same point; --
   sometimes called {binocular parallax}.
{Optic axis}. (Opt.)
   (a) A line drawn through the center of the eye
       perpendicular to its anterior and posterior surfaces.
       In a normal eye it is in the direction of the optic
       axis that objects are most distinctly seen.
   (b) The line in a doubly refracting crystal, in the
       direction of which no double refraction occurs. A
       uniaxial crystal has one such line, a biaxial crystal
       has two.
{Optical circle} (Opt.), a graduated circle used for the
   measurement of angles in optical experiments.
{Optical square}, a surveyor's instrument with reflectors for
   laying off right angles.