Optical circle

Optic Op"tic ([o^]p"t[i^]k), Optical Op"tic*al ([o^]p"t[i^]*kal), a. [F. optique, Gr. 'optiko`s; akin to 'o`psis sight, 'o`pwpa I have seen, 'o`psomai I shall see, and to 'o`sse the two eyes, 'o`ps face, L. oculus eye. See {Ocular}, {Eye}, and cf. {Canopy}, {Ophthalmia}.] 1. Of, pertaining to, or using vision or sight; as, optical illusions. [WordNet sense 2]

Syn: ocular, optic, visual. [1913 Webster + WordNet 1.5]

The moon, whose orb Through optic glass the Tuscan artist views. --Milton. [1913 Webster]

2. Of or pertaining to the eye; ocular; as, the optic nerves (the first pair of cranial nerves) which are distributed to the retina; the optic (or optical) axis of the eye. See Illust. of {Brain}, and {Eye}. [WordNet sense 3] [1913 Webster]

3. Relating to the science of optics or to devices designed to assist vision; as, optical works; optical equipment. [WordNet sense 1] [1913 Webster +PJC]

{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. [1913 Webster]