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.

2. An eyeglass. [Obs.] Herbert.

{ Op"tic (?), 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.

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.