Physical Defect Compensation
The optic nerve blind spot is located below the macula. As the macula is full of cones requiring brightness, that dimple becomes a 2nd blind spot in low light.
Full-picture night vision is autonomically created by constantly shifting the eyes 4° to 12° in saccades so that rods catch some photons.
With the intense processing required for moving image comprehension, the visual system cannot process information moving across the retina at more than a few degrees a second. For humans to see while moving, subconscious compensation for head motion is made by turning the eyes.
