ଅର୍ଥ : In a doubly refracting crystal, the line in the direction of which no double refraction occurs.
ଉଦାହରଣ :
A crystal may have either one or two optic axes.
ଅର୍ଥ : A line that passes through the center of curvature of a lens so that light is neither reflected nor refracted.
ଉଦାହରଣ :
In a normal eye the optic axis is the direction in which objects are seen most distinctly.
ସମକକ୍ଷ : principal axis