principal optic axis

prin·ci·pal op·tic ax·is

a line passing through the center of the lens of a refracting system at right angles to its surface.
Farlex Partner Medical Dictionary © Farlex 2012

prin·ci·pal op·tic ax·is

(prin'si-păl op'tik ak'sis)
A line passing through the center of the lens of a refracting system at right angles to its surface.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012