optic axis

noun Crystallography.

1. (in a crystal exhibiting double refraction) the direction or directions, uniaxial or biaxial, respectively, along which this phenomenon does not occur.

noun

1. the direction in a uniaxial crystal or one of the two directions in a biaxial crystal along which a ray of unpolarized light may pass without undergoing double refraction

n.

1. The line connecting the anterior and the posterior poles of the eye.