| optic axes | แกนแสง [ธรณีวิทยา๑๔ ม.ค. ๒๕๔๖] |
| optic axis | (n) in a doubly refracting crystal, the line in the direction of which no double refraction occurs, Example: a crystal may have either one or two optic axes |
| principal axis | (n) a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted, Syn. optic axis, Example: in a normal eye the optic axis is the direction in which objects are seen most distinctly |