Poles and axes of eyeball

The eyeball has two poles - anterior pole and posterior pole. Both poles are connected via the optic axis, which is an imaginary line passing through the centers of the cornea and lens.

The eyeball can be described using one more axis - the visual axis, which is an imaginary line connecting the object being looked at (fixation point) to the fovea centralis of the retina.

Additionally, meridian is any great circle passing through both poles of the eyeball. And finally, the equator is an imaginary circle perpendicular to the optic axis that lies midway between the anterior and posterior poles.