OKR and OKN describe different gaze-stabilizing mechanisms; which statement correctly differentiates them?

• A. OKR stabilizes image during head movements; OKN stabilizes image when the object moves with the head stationary.
• B. OKR stabilizes image during head movements; OKN stabilizes image when the head moves with the object stationary.
• C. OKR stabilizes image when the object moves; OKN stabilizes image during head movements.
• D. OKR and OKN describe the same mechanism.

Answer: (A)

Optokinetic responses are driven by motion of the visual field relative to the eye, and the two terms describe different driving conditions for gaze stabilization. The optokinetic response is what helps keep the image stable when you or your head are moving—the entire world appears to sweep across your retina, and your eyes smoothly follow that motion with a slow phase, then reset with a quick saccade. This mechanism is most evident when head or body movement causes the scene to move across your field of view.

Optokinetic nystagmus, on the other hand, is elicited when a moving visual stimulus travels across a stationary head—a moving object or scene sweeps across the retina while you aren’t turning your head. You still get the characteristic slow tracking in the direction of the motion and a rapid reset in the opposite direction, but the driving factor is the movement of the object or scene relative to a fixed head.

So, the best differentiation is that the optokinetic response stabilizes vision during head movements, whereas optokinetic nystagmus stabilizes vision when the object or scene moves across a stationary head.