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.