W7

Question 1

What is the function of eye movements?

Answer 1

To move the eye across the visual scene + interesting parts of the image to land onto a high-resolution part of the retina: the FOVEA
To converge the eyes at different distances
Stabilise visual image on retina despite motion of eye or scene

Question 2

What is the fovea?

Answer 2

The part of the retina densely packed with photoreceptors (cones), giving high spatial and colour acuity. It has the highest resolution and color vision.

Question 3

What happens to the fovea in different light?

Answer 3

In daylight, the central fovea sees in fine detail + colour
At night, the peripheral retina (rods), sees in black and white with low resolution.

Question 4

What are gaze paths?

Answer 4

The spatial path of an eye as it moves across an image.
Our eyes jump from location to location (saccades) → allow a stable image to form on the retina
We skip predictable/common words, and focus maybe twice on longer words.
EYE MOVEMENT IS AUTOMATIC + CONTEXT DEPENDANT → controlled by our CENTRAL NERVOUS SYSTEM!!!!!!

Question 5

What are ocular muscles?

Answer 5

The muscles controlling the movement of the eyeball.

Question 6

What are the types of ocular muscles?

Answer 6

Intraocular muscles: control the iris and pupil size
Extraocular muscles: move the eyeball within the socket

Question 7

What do the 6 extraocular muscles consist of?

Answer 7

Superior + Inferior Rectus Muscle → move the eye up or down
Medial + Lateral Rectus Muscle → move the eye towards and away from midline
Superior + Inferior Oblique Muscle → apply torsional forces during movements

Question 8

How do extraocular muscles function?

Answer 8

Controlled by cranial nerves and rotate eyes → like opposing springs → naturally relaxed to forward gaze unless actively engaged for movement

Question 9

What is the classification of eye movement and direction? DVV

Answer 9

Duction: single-eye movements (adduction/abduction)
Version: both eyes move same direction
Vergence: eyes move in opposite directions

Question 10

What are the functional types of eye movement?

Answer 10

Stabilising: keep image steady (OKR, VOR)
Shifting: move gaze to new target (saccades, smooth pursuit, vergence)
Fixation: eyes are stationary between movements

Question 11

What is the Optokinetic Reflex (OKR)? Gaze stabilising mechanism…

Answer 11

Reflex to maintain gaze position. Assumes world is stationary.
This is achieved by reducing visual slip on the retina.
Eyes primarily rotate to track movement, but their limited rotation range causes a NYSTAGMUS pattern

Question 12

What is visual slip?

Answer 12

The brief, involuntary movement of the eyes off a moving target when smooth pursuit tracking fails to keep pace with the motion.

Question 13

What is nystagmus?

Answer 13

Alternating slow eye drift and rapid saccades.

Question 14

What is normal vs abnormal nystagmus?

Answer 14

Normal (OKR): Occurs when tracking moving visual fields (e.g., looking out a train window).
Abnormal: Caused by brainstem lesions (loss of positional eye control) or vestibular issues, resulting in inability to fixate on static objects and poor vision.

Question 15

What is a key limitation of the Optokinetic Reflex (OKR)?

Answer 15

The OKR is slow because it requires a multi-step visual processing pathway, slow negative feedback loop.

Question 16

What is the Vestibulo-Ocular Reflex (VOR)?

Answer 16

A reflex to maintain gaze position despite head movement.
14ms latency + 90% of head velocity counrteracted→ accuracy

Question 17

How does VOR work?

Answer 17

Head movement detection: Semicircular canals in the inner ear (vestibular system) detect head velocity.
Signal transmission: This movement signal travels to the vestibular nucleus.
Motor neuron activation: The signal crosses the midline and excites ocular-motor neurons, which control eye muscles.
Eye movement: This excitation causes the eyes to move in the opposite direction of the head movement, maintaining gaze on a fixed point.

Question 18

What is the role of the NPH (Nucleus Prepositus Hypoglossi)?

Answer 18

The PPH acts as a “memory” of head movement. It converts the short-lived (phasic) vestibular input into a sustained (tonic) signal through a self-exciting reverberating neural circuit.

Question 19

What does the PPH contribute?

Answer 19

Allows the eyes to maintain their position even after the head stops moving.
It stores a record of how far the eyes have rotated and continues to excite the ocular-motor neurons
This sustains the contraction of the eye muscles needed to hold the desired gaze.

Question 20

What happens if PPH is missing?

Answer 20

You lose the “memory” of eye position—gaze drifts back to center after head stops moving.

Question 21

What is vergence?

Answer 21

Vergence is the simultaneous movement of both eyes in opposite directions to maintain binocular vision. It helps in depth perception by adjusting eye position for near or far objects.

Question 22

What are the types of vergence?

Answer 22

Convergence – Both eyes move inward (toward the nose) when focusing on a near object.
Divergence – Both eyes move outward (away from the nose) when focusing on a distant object.

Question 23

What is smooth pursuit?

Answer 23

Slow, simultaneous movement of both eyes in same direction.

Question 24

What are smooth pursuit characteristics?

Answer 24

Suppresses the OKR
Limited to low velocities
Evolutionary new system to allow tracking of moving objects against stationary background
Slow visual feedback mechanism

Question 25

What are saccades?

Answer 25

Rapid, simultaneous eye movements of both eyes in the same direction.

Question 26

What are the Saccades characteristics?

Answer 26

Rapid gaze shift Constant velocity Reach 600 degree per second Duration related to amplitude (30-100 ms) Even moves during REM sleep 2-3 per second Feed-forward control: pre-programming the eye movement based on the initial target, without real-time sensory correction.

Question 27

What happens if a saccade misses the target?

Answer 27

A second, corrective saccade occurs, based on new visual feedback.

Question 28

What brain structure directly initiates the motor commands for saccades?

Answer 28

The Paramedian Pontine Reticular Formation (PPRF) has a direct connection to the ocular motor neurons, initiating saccade execution.

Question 29

How do Saccades work?

Answer 29

Light to Retina: Light from a target enters the eye and stimulates retinal photoreceptors. Signal to LGN: Retinal signals travel to the LGN. Fast Path to Superior Colliculus: A rapid signal goes from the LGN to the superior colliculus (SC). SC Activation Maps Target: The SC is activated according to the target's location on its retinotopic map. SC Signals Brainstem: The activated SC signals the brainstem's PPRF. PPRF Bursts OMNs: The PPRF generates a burst in ocular motorneurons (OMNs). Eye Muscles Move Rapidly: This OMN burst drives the eye muscles for the fast saccade. PPH Holds New Position: The brainstem's PPH provides a sustained signal to OMNs to maintain the new eye position. Cortex Selects Target (Voluntary): Cortical areas like FEF (voluntary) and LIP (selection) influence the target and initiation of the saccade

Question 30

What does the superior colliculus do?

Answer 30

Release central activity. Turn off omnipause neurons, disinhibiting the brainstem oculomotor system (PPRF). Release eyes from fixation. Drive the PPRF to generate a burst of activity, initiating a saccade. Facilitate the shifting of the stimulus's retinal location to the fovea as the saccade occurs.