The VOR: Keeping Your Gaze Steady
- The VOR is a reflex that stabilizes your gaze during head movements.
- When you move your head, the VOR moves your eyes in the opposite direction to keep your eyes focused on a fixed point.
- This is important because the vestibular system (responsible for balance) is much faster than the visual system.
Why is the VOR Important?
- It allows you to see a clear image while your head is moving (e.g., reading on a train).
- The visual system is too slow to compensate for head movements on its own.
Modulating the VOR Gain
- The amount your eyes move with the VOR (gain) can be adjusted.
- When focusing on a near object, your eyes need to move more to maintain fixation compared to focusing on a distant object.
- The cerebellum (specifically the flocculus and nodulus) constantly adjusts the VOR gain to optimize gaze stability.
Turning Off the VOR
- In some situations, you don’t want the VOR to oppose head movements.
- For example, if you want to look far to the side, you need to move your head and keep your eyes focused within the head (not following the head movement).
- The cerebellum can turn off the VOR or adjust the gain to zero.
Clinical Applications
- Testing the VOR is a common way to assess brain function in unconscious patients.
- Dolls’ eyes: If the VOR gain is fixed at 1 (eyes always move opposite to head movement), it suggests cerebellar damage.
- No VOR: If the eyes move with the head, it suggests brain stem dysfunction.
Additional Points
- The cerebellum constantly adapts the VOR throughout the day.
- Changing glasses requires recalibrating the VOR, which is also controlled by the cerebellum.