Visual axis is
Axes of the eyes: 1. The optical axis is the line passing through the center of the cornea (P), the center of the lens (N) and meets the retina (R) on the nasal side of the fovea. 2. Visual axis is the line joining the fixation point (O), nodal point (N), and the fovea (F). 3. Fixation axis is the line joining the fixation point (O) and the center of rotation (C). simple definition of the visual axis is: " A straight line that passes through both the centre of the pupil and the centre of the fovea". There is also a stricter definition (in terms of nodal points) which is impoant for specialists in optics and related subjects Image : The Visual Axis of the eye Reference : Khurana comprehensive ophthalmology; 4th edition ; Page27
Center of cornea to retina
Object to fovea
Center of lens to cornea
Center of cornea to optic nerve
Optics and refraction